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The Workshop on Polarized Sources,Targets, and Polarimetry has been a tradition for more than 20 years, moving between Europe, USA, and Asia. The 18th International Workshop on Polarized Sources, Targets, and Polarimetry (PSTP 2019) will take place at Knoxville, Tennessee. The workshop addresses technical challenges and accomplishments related to polarized gas/solid targets, polarized electron/positron/ion/neutron sources, polarimetry, and applications of polarized techniques.
Due to the extraordinary circumstances that many are experiencing, we will be accepting late submissions. If you would like to submit a contribution, but do not believe that you will be able to complete it before the end of March, please inform the chairperson.
A dynamically polarized target of protons and deuterons in irradiated NH3 and ND3 will be employed with the CLAS12 detector system to explore the spin structure of the nucleon in Hall B at Jefferson Lab. This target will feature a versatile horizontal 1 K refrigerator that has been constructed by a collaboration composed of Christopher Newport University, Old Dominion University, the University of Virginia, and the JLab Target Group. A description of the challenges involved with designing the target for the CLAS12 experiments and the collaboration’s solutions to them will be presented. These include a modular and compact design of the 1 K refrigerator and its ancillary equipment, as well as a novel mechanism for loading the target samples. Initial test results of the system will also be included.
Upcoming spin structure experiments in Hall B at Jefferson Lab will employ a new dynamically polarized target inside the CLAS12 detector system. Protons and deuterons in irradiated NH3 and ND3 will be polarized at 1 K using the 5 T field of the CLAS12 solenoidal magnet. For optimum polarization, the field uniformity requirements are around 100 ppm over the volume of the 12 cm3 target sample. I will present field map results for the solenoid, and discuss methods to improve the uniformity utilizing thin superconducting shim coils integrated within the 1 K refrigerator. I will also demonstrate that this method to adjust the 5 T field also enables the simultaneous opposite polarization of two adjacent target cells.
Solid polarized targets rely on continuous-wave Nuclear Magnetic Resonance techniques to provide measurements of the enhanced polarization provided under Dynamic Nuclear Polarization. Upcoming polarized target experiments in Jefferson Lab's Hall B present challenging conditions which would benefit from improvements to traditional NMR techniques. For decades, JLab has relied upon Liverpool Q-meters for NMR measurements, but these are aging and no longer produced. The polarized target group at Bochum has successfully produced replacement Q-meters with modern components, and we are following their example, exploring new designs for Q-meter systems. We are currently testing a prototype of our own Q-meter system, which hews closely to the designs of the Liverpool and Bochum systems with a few incremental improvements. At the same time, we are pursuing the possibility of an all-digital Q-meter system, eschewing an analog mixer for fast digitization and FPGA analysis. We will discuss the challenges presented by the new Hall B target, lay out our changes to the traditional Q-meter, and show results of initial tests of our designs.
In the $^{139}$La(n,$\gamma$)$^{140}$La reaction, a T-violating asymmetry is expected to be enhanced by about 6 orders of magnitude[1]. NOPTREX (Neutron Optics for Parity and Time Reversal EXperiment) collaboration is planning to search for the T-violation in this reaction, where a polarized target of $^{139}$La nuclear spin is indispensable. Basically, we are keeping two choices, Brute Force (BF) and Dynamic Nuclear Polarization (DNP) for realizing the polarized target, but each of them has some difficulties.
The BF method needs an advanced and complex cryogenic system. Achieving the 50% polarization in $^{139}$La, for example, requires the high magnetic field of 17 T and the low temperature of 10 mK.
The DNP do not need such hard cryogenic system, but strongly depends on characteristics of the target materials. The single crystal of Nd3+:LaAlO3 is promising target material because the crystal structure enables us to suppress the quadrupole relaxation and to give a sufficiently narrow linewidth in an ESR spectrum, which are essential for performing the DNP [2].
Since 2018, we have started to study the physical properties of LaAlO$_3$ crystal in Tohoku University and to prepare cryogenetic system for DNP study in RCNP.
In this presentation, we will report the current status of $^{139}$La polarized target study for the T-violation search.
References
[1] T. Okudaira, et. al., Phys. Rev. C 97, 034622 (2018).
[2] Y. Takahashi, H.M. Shimizu, and T. Yabuzaki, Nucl. Instrum. Methods Phys. Res. A Vol. 336 Issue 3, p.p. 583-586 (1993).
The Electric Dipole Moment (EDM) of elementary particles, including hadrons, is considered as one of the most powerful tools to study CP-violation beyond the Standard Model. Such CP-violating mechanisms are searched for to explain the dominance of matter over anti-matter in our universe.
Up to now EDM experiments concentrated on neutral systems, namely neutron, atoms and molecules. Storage rings offer the possibility to measure EDMs of charged particles by observing the influence of the EDM on the spin motion. A dedicated program is underway at the COSY storage ring to develop the required experimental and technical tools.
A step-wise approach starting with a proof-of-principle experiment at the existing storage ring Cooler Synchrotron COSY at Forschungszentrum Jülich, followed by an electrostatic prototype ring allowing for a simultaneous operation of counter circulating beams in order to cancel systematic effects, to the design of a dedicated 500 m circumference storage ring will be presented.
A new method has been demonstrated using the storage ring COSY to search for an axion-like particle by scanning for a resonance in the horizontal-plane rotation of the deuteron beam polarization. If an electric dipole moment (EDM) is present on the nucleus, the radial electric field that exists in the particle frame will create a rotation of the polarization out of the horizontal plane and into the vertical direction. If that EDM oscillates due to the presence of an axion-like field in synchronization with the rotation of the polarization, then the vertical rotation will accumulate near the resonance, producing a measurable vertical polarization component. In the spring of 2019, we used a 0.97-GeV/c vector-polarized deuteron beam to successfully demonstrate the procedure for the search. The phase of the oscillating EDM with respect to the rotation of the polarized beam in unknown. In order to be sensitive to both cosine and sine components of the oscillation, we prepared four bunches for the ring with different polarization directions. Starting with vertical polarization following injection into the ring, an RF solenoid operating on the $(1 + G\gamma )$ harmonic of the beam revolution frequency was used to rotate the polarization into the horizontal plane. This yielded a polarization pattern in which two of the bunches had polarizations that were nearly orthogonal. By looking separately for signals on both bunches, a signal would be found for any value of the axion phase. Beam polarizations were measured using the WASA Forward Detector. In order to improve the horizontal polarization lifetime, the beam was electron cooled as well as bunched. Once the orbit was established with minimal steering corrections, the ring sextupole magnets were adjusted to maximize the horizontal polarization lifetime. All scans were made with lifetimes in excess of 500 s. The sensitivity to an axion was tested and calibrated using the magnetic field of a horizontally mounted RF Wien filter to create vertical polarization jumps during a frequency scan of COSY. In a series of scans spanning a 1.5% change in the neighborhood of 120 kHz, no signals were seen that did not fit the statistical distribution that arises from event counting data collection. In this case, the sensitivity to an oscillating EDM approached 10$^{−22}$ e$\cdot$cm.
Axions are CP-odd scalar particles appearing in many extensions of the Standard Model. In particular, the Peccei-Quinn axion can explain the smallness of the neutron electric dipole moment and is also a promising Dark Matter candidate. Axions also generate macroscopic P-odd and T-odd spin-dependent interactions which can be sought in sensitive laboratory experiments. As the axion's coupling to ordinary matter is extraordinarily weak, most searches for its effect have looked very carefully for the direct evidence of cosmologicial axions. This talk will instead introduce a set of experiments that aim to measure fresh, locally sourced Axions by using a periodically modulated mass to drive precession in a hyperpolarized gas sample.
The Axion Resonant InterAction DetectioN Experiment (ARIADNE) is designed to search for axion-mediated spin-dependent interactions between nuclei at sub-millimeter ranges. The experiment involves a rotating tungsten mass to generate the axion field, and a dense ensemble of laser-polarized \textsuperscript{3}He nuclei surrounded by a superconducting shield layer to detect the axion field by NMR. This novel technique will allow measurement of axions in the $100\,\mu\mathrm{eV}$ to $10\,\mathrm{meV}$ mass range, filling the remaining gaps in the traditional ``axion window.''
A preliminary version of the experiment with less sensitivity but zero cryogenics is being developed for the magnetically shielded room in Physikalisch--Technische Bundesanstalt (PTB) in Berlin. Like ARIADNE, this apparatus will use a mass rotating at the sample's Larmour frequency in an attempt to observe Axions via a resonant enhancement.
In this talk, I will first introduce the measurement technique before discussing the ongoing development of these experiments.
Macroscopic forces of nature beyond gravity and electromagnetism arise in many frameworks attempting to unify General Relativity and the Standard Model. We describe an experimental search for spin-dependent fifth forces in the sub-millimeter range. The experiment uses planar mechanical oscillators as test masses, which have been augmented with polarized rare earth iron garnets. These materials exhibit orbital compensation of the magnetism associated with the electron spins, substantially reducing the magnetic backgrounds. We describe the essential properties of the test masses and the progress of the apparatus developed to make optimal use of them, including a radiative cooling system, and discuss the experimental sensitivity.
Momentum measurements in the forward direction at collider experiments are inherently difficult as the deflection of charged particles to be observed requires a magnetic field component that is perpendicular to the propagation direction of those particles. This, in turn, would jeopardize the quality of the colliding beam particles. To overcome this difficulty we propose a magnetic cloak that is passively shielding the beam particles from any transverse magnetic field component and furthermore, maintain the character of the magnetic field. This would allow introducing dipole magnets in the forward region of any experiment at a collider, for instance, the Electron-Ion Collider.
We present a possible setup and show the design parameters, fabrication, and limitations of a magnetic field cloak
An experiment investigating quantum spin correlations of relativistic electrons will be presented. The project aims at the first measurement of the quantum spin correlation function (and the corresponding probabilities) for a pair of relativistic particles with mass. Theoretical studies revealed unexpected properties of entangled systems in the relativistic energy range, but in all of the correlation experiments performed until now the energy of the particles was insufficient to observe relativistic effects. This measurement will be the first attempt to verify the predictions of relativistic quantum mechanics in the domain of spin correlations.
The measurement will be carried out on a pair of electrons in the final state of Møller scattering (electron pairs under study will originate from polarized electron beam scattering off atomic electrons of an unpolarized target). The measurement regards correlations of spin projections on chosen directions for the final state pair. The detector consists of two Mott polarimeters, in which the spins of both Møller electrons are measured simultaneously.
Results and conclusions from the test measurements at Mainzer Mikrotron will be discussed. For testing purposes measurements were carried out with half of the setup, which can be used as a single polarimeter, allowing to measure the polarization of the beam, as well as the mean polarization of Møller electrons.
The PREFER (Polarization REsearch for Fusion Experiments and Reactors) collaboration aims to address the know-hows in different fields and techniques to the challenging bet on fusion with polarized fuel.
The efforts are focused on a variaty of duties and purposes, which are under the responsability of different institutes and research groups (presented here by the representative of the research center in the author list).
Starting from still open questions in the fusion reaction physics, as an example the study of d-d spin dependent cross sections - Vasilyev, till the production of polarized ion acceleration by laser - Büscher, there are many connections between the research groups involved. The collaboration is facing also the production of nuclear polarized molecules, recombined by polarized atomic beam - Engels, and its condensation and transport - G. Ciullo/ M. Statera.
Other chances of production are investigated: spin separation of molecules, in pMBS (polarized Molecule Beam Sources ) - Toporkov) and from photodissociation - Rakitizis.
The status of the different fields under investigation and the connections between the topics and the different research groups will be provided.
Photocathodes based on GaAs can be used in photo-electron sources to supply spin-polarized, high-current electron beams for various applications. An activation, adding a thin surface layer, is needed to achieve negative electron affinity (NEA) for such cathodes. Typically, Cs is used in combination with an oxidant. Previous studies have suggested that the addition of Li to this process can increase the quantum efficiency (QE) of the cathode as well as the lifetime of the cathode surface layer, both crucial parameters for photo-electron source operation.
Recently, first lifetime studies of bulk GaAs photocathodes activated with Cs, NF3, and Li have been conducted using the photo-electron gun of the Upgraded Injector Test Facility (UITF) at the Thomas Jefferson National Accelerator Facility (JLab), extracting beam currents of up to 100 µA. We will present the results of these measurements as well as planned measurements at the Institut für Kernphysik of Technische Universität Darmstadt.
*Work supported by DFG (GRK 2128 “AccelencE”), BMBF (05H18RDRB1), and through the Helmholtz Graduate School for Hadron and Ion Research for FAIR.
GaAs-based DC high voltage photo-guns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed high average current facilities that must operate at tens of milliamperes or more. Specifically, the operating lifetime is dominated by ion back-bombardment of the photocathode from ionized residual gas. While numerous experiments have been performed to characterize the operating lifetime under various conditions [1], detailed simulations of the ion back-bombardment mechanism that explains these experiments are lacking.
Recently, a new user routine was implemented using the code General Particle Tracer (GPT) to simulate electron impact ionization of residual beamline gas and simultaneously track the incident electron, secondary electron, and the newly formed ion. This new routine was benchmarked against analytical calculations and then applied to experiments performed at the CEBAF injector at the Thomas Jefferson National Accelerator Facility. These simulations were performed using detailed 3D field maps produced with CST Microwave Studio describing the photo-gun electrostatics.
In the first experiment, the electrically isolated anode of the CEBAF photo-gun was attached to a positive voltage power supply and biased to different voltages to study the effectiveness of limiting ions from entering the cathode-anode gap. In the second experiment, the size of the drive laser was varied in order to distribute the deleterious ions over a larger area of the photocathode (experimental results reported at PSTP17 in Daejeon, South Korea [2]). Discussion of these experiments and the application of this new GPT routine to model the experiments will be reported at the workshop.
Acknowledgment
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.
References
[1] J. Grames, R. Suleiman, P. A. Adderley, J. Clark, J. Hansknecht, D. Machie, M. Poelker, and M. L. Stutzman, “Charge and fluence lifetime measurements of a dc high voltage GaAs photogun at high average current” Phys. Rev. ST Accel. Beams 14, 043501 (2011).
[2] J. Grames, P. Adderley, J. Hansknecht, R. Kazimi, M. Poelker, D. Moser, M. Stutzman, R. Suleiman, S. Zhang "Milliampere beam studies using high polarization photocathodes at the CEBAF Photoinjector", in Proc. of 2017 International Workshop on Polarized Sources, Targets and Polarimeters (PSTP17), Oct 15 - 20, 2017, Daejeon, South Korea.
GaAs photocathodes provide a source of highly polarized electron beams. To ensure reliable operation for high current applications it is necessary to increase charge lifetime. To improve the local vacuum condition around the cathode the use of a cryogenic sub-volume is proposed. It is expected that the cryogenic adsorption of reactive residual-gas molecules yield an enhanced lifetime of the negative-electron-affinity surface of the cathode. Additional cooling of the cathode itself allows a higher laser power to be deposited in the material, resulting in higher possible beam currents. Implementation and first measurements are planned to be conducted at the TU-Darmstadt Photo-CATCH test set-up to investigate the operational parameters of the new source. Supported in parts by BMBF (05H18RDRB1) and by DFG (RTG 2128 “Accelence”).
In order to facilitate Real Compton scattering studies off of nucleons a novel, high intensity, compact photon source (CPS) was developed for Halls A and/or C at Jefferson Lab. This source will provide a factor of 30 figure of merit improvement over existing technology. While developed for use in nuclear/particle physics experiments, the CPS design can be adapted to other fields. The source design as well as the main technical challenges associated with it will be discussed.
In this talk I will give an overview of the Hall A Moller Polarimeter at Jefferson Lab and I will present recent results on the beam polarization measurements taken during the PREX II experiment.
The recently developed Jefferson Lab Hall-A moller polarimeter Geant4-based simulation [MolPol] is a vital tool in understanding the analyzing power of the polarimeter for parity experiments ranging from PREX-II at 1 GeV to future 11 GeV experiments. I'll discuss the application's role in the development of optics solutions, understanding of e- transportation through the polarimeter and the calculation of the analyzing power of a given optics tune; additionally, MolPol application development, issues and future challenges will be touched upon. Results against recently taken data at 2.137 GeV and 0.95 GeV show that data is qualitatively consistent with MolPol expectations.
The international JEDI (Jülich Electric Dipole moment Investigation) collaboration is preparing a first-ever direct measurement of the deuteron Electric Dipole Moment (EDM), using the COSY storage ring at Forschungszentrum Jülich (Germany).
A new polarimeter is required to detect the very slow and minuscule polarization change with time: starting in 2016, we have designed, built and commissioned a new modular type storage ring EDM polarimeter based on LYSO inorganic scintillator crystals. The polarimeter concept exploits LYSO modules (3x3x8 cm3), individually coupled to modern large area SiPM arrays which are operating at low voltage.
The detector system and its vacuum system have radial symmetry and a thin exit window, making the polarimeter very efficient for online up-down and left-right asymmetry measurements.
After several tests at the external COSY beam, we have recently installed the complete system in the COSY ring for use with internal beams. We are planning to commission the detector at various polarized beam conditions together with the WASA polarimeter. After that, it will be employed as the polarimeter for JEDI and possibly other users.
In this talk, I will summarize the achievements of our group and discuss the latest results.
In this presentation, the design of the polarized target to be used in the SPINQUEST experiment at FermiLab will be discussed. The polarized target, consisting of either NH3 or ND3, is centered in a 5T magnet field and polarized by 140 GHz microwaves. A new NMR system will measure the degree of polarization. The evaporation of the helium surrounding the target, caused by the intense beam of protons necessary for the experiment, is accommodated by a 14,000 m3/hr Roots pumping system. NH3 polarizations above 90% have been achieved, comparable to what has been achieved in other systems.
The Liverpool Q-meters were developed in the late 70s and became a de facto industry standard for NMR-based polarization measurements of polarized solid targets. However, it is becoming increasingly more difficult to produce the required number of q-meter channels as the components have become obsolete. The Los Alamos National Laboratory (LANL) group has developed a new NMR-based polarization measuring system following the basic Liverpool design. The new Q-meter will have multiple improvements, such as remote tuning and compact design. These improvements present opportunities for achieving a higher figure of merit for experiments exploiting polarized solid targets by potentially increasing the accuracy of the polarization measurements. The new LANL Q-meter is intended to be used in Fermilab SpinQuest/E1039 experiment which is part of the continuing world-wide effort to shed light on the nucleon spin composition puzzle. The current status of this work will be presented.
The UVA-LANL polarized target system consists of a 5T, split-coil, superconducting magnet and uses a 140 GHz microwave source to provide highly polarized protons and deuterons via dynamic nuclear polarization (DNP). The DNP process leverages the large discrepancy between the electron and proton magnetic moments, along with Zeeman splitting in the magnetic field, and spin-spin coupling to pump protons (deuterons) into a highly polarized state. For my presentation, I will give a brief overview of the the UVA-LANL target system with a focus on the microwave system, its role in the DNP process, and the challenges of providing consistently high average polarization in an experimental setting.
The SpinQuest experiment at Fermilab aims to measure the Sivers asymmetry for the $\bar{u}$ and $\bar{d}$ sea quarks in the nucleon using the Drell-Yan process. The experiment will use a 5 T magnet, a $^4$He evaporation fridge with a large pumping system and 140 GHz microwaves to produce transversely polarized NH$_3$ and ND$_3$ targets. The proposed beam intensity is 1.5 $\times$ 10$^{12}$ of 120 GeV proton/sec. A quench simulation in the superconducting magnet is performed to determine the maximum intensity of the proton beam before the magnet transition to the resistive state. In this presentation a GEANT based simulation used to calculate the heat deposited in the magnet is discussed and the subsequent cooling processes which are modeled using the COMSOL Multiphysics are presented.
Spherical Neutron Polarimetry (SNP) analyzes complex magnetic structures through distinguishing contributions from nuclear-magnetic interference and chiral structure in addition to nuclear magnetic scattering separation. This analysis is achieved through determining all components in the polarization transfer process. Currently, wide-angle SNP is being realized at Oak Ridge National Laboratory (ORNL) for multiple beamlines including: the polarized triple-axis spectrometer (HB-1) and general-purpose small angle neutron scattering instrument (CG-2) at the High Flux Isotope Reactor (HFIR), as well as the hybrid spectrometer (HYSPEC) at the Spallation Neutron Source (SNS). The SNP device consists of three units: incoming/outgoing neutron polarization control, sample environment and a zero-field chamber. The incoming/outgoing neutron polarization regions use high-T_c superconducting YBCO films and mu-metal to achieve full control of neutron polarization. The device was transported and tested at the University of Missouri research reactor (MURR). We report the test results and provide a new method for placing the device on a time-of-flight beamline.
Spherical neutron polarimetry (SNP) is a powerful neutron scattering technique that can unambiguously determine complex types of magnetic order in materials such as chiral antiferromagnets, multiferroics, superconductors, and magnetoelectrics. Currently, four polarimeter designs exist worldwide and several instruments operate year round that utilize them. Of the three existing SNP designs, two have been developed for wide-angle, single crystal diffraction and they are known as CRYOPAD and MuPAD. The most recent effort in SNP development has been in North America producing CryoCUP and SANPA geared for small-angle neutron scattering applications. As the number of SNP instruments grows, the demand for high precision SNP measurements increases with it. Recently a new strategy for precision calibration of and SNP apparatus has be proposed. Preliminary results published this year in the development of SANPA at the NIST Center for Neutron Research suggest that a new high precision calibration method will yield a deeper understanding of neutron polarization manipulation in the laboratory environment and provide an improved method for comparing different SNP instruments. Here we will discuss an international effort to begin pushing the precision limit with existing SNP designs.
Polarized neutron experiment probes magnetic structures and distinguish contribution from incoherent scattering, nuclear scattering and magnetic scattering1. While polarized neutron measurement are widely used among current neutron beamlines, the applications are usually limited to depolarization measurement among a single direction. More complexed polarimetry technique such as xyz polarimetry2 or spherical neutron polarimetry3 limit their application to single wavelength beamline. This limitation is caused by the neutron polarization manipulation process of polarimetry measurement, which involves controlled neutron precession. To expand the application of Neutron Polarimetry onto time-of-flight neutron, it is necessary to explore new experiment method and develop new magnetic field restraining equipment4. In this presentation, we introduce our research plan and effort to explore the combination of neutron polarimetry and time-of-flight neutron. The research is performed through designing new polarimetry instrument using high-Tc superconductor and developing new algorithm of polarimetry analysis through time-of-flight neutron.
1 M. Blume, Phys Rev 130 (5), 1670 (1963).
2 O. Scharpf and H. Capellmann, Phys Status Solidi A 135 (2), 359 (1993).
3 V. Hutanu, W. Luberstetter, E. Bourgeat-Lami, M. Meven, A. Sazonov, A. Steffen, G. Heger, G. Roth, and E. Lelievre-Berna, Rev Sci Instrum 87 (10) (2016).
4 T. Wang, S. R. Parnell, W. A. Hamilton, F. Li, A. L. Washington, D. V. Baxter, and R. Pynn, Rev Sci Instrum 87 (3) (2016).
The aCORN experiment measured the electron-antineutrino angular correlation coefficient (the ‘a’ coefficient) in free neutron decay on the NG-C neutron beam at the National Institute of Standards and Technology (NIST). Though the NIST neutron beams are expected to be unpolarized, an earlier run of the experiment found a small polarization on the NG-6 beamline. The aCORN measurement is quite sensitive to neutron polarization, and the beam polarization was used as a blind on the aCORN results. To unveil the blind, the beam polarization was measured using a 3He cell polarized by spin-exchange optical pumping (SEOP). After a brief overview of the aCORN experiment, the neutron polarimetry system will be discussed.
Understanding the interactions leading to magnetic quantum phenomena in a wide range of quantum materials is important for development of new quantum materials and future technologies. Quantifying these interactions and the resultant magnetic matter in quantum materials that exhibit exotic matter such as quantum spin liquids, topological insulators, and Weyl semimetals, is currently being limited by a range of challenges including the lack of sizable crystals, limited sample environment conditions, and the ability to disentangle the intrinsic quantum phenomena versus effects from defects and site-disorder. Polarized neutron diffraction could play an important role in exploring magnetic matter and interactions. We recently upgraded the HB-3A four-circle diffractometer by installing a large area position sensitive detector and integrated a set of extreme sample environment equipment for quantum material study purpose and renamed the HB-3A as DEMAND (Dimensional Extreme sample environment Magnetic Neutron Diffractometer). In this presentation, we will focus on the polarized neutron diffraction capabilities recently developed at DEMAND, which used both the S-bender supermirror and the He-3 polarizers that are still under development.
The research was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Early Career Research Program Award KC0402010, under Contract DE-AC05-00OR22725 and the U.S. DOE, Office of Science User Facility operated by the Oak Ridge National Laboratory.
Nuclear spin-polarized 3He is widely used in many scientific areas. One of the applications is used as a neutron spin filter to polarize neutrons. Among all the neutron polarizing techniques, nuclear-spin-polarized 3He neutron spin filters have shown great flexibility and versatility because of its highly spin-dependent neutron absorption cross section, large neutron acceptance angle and working over a broad neutron wavelength band. At the Oak Ridge National Laboratory, 3He is routinely polarized via spin-exchange optical pumping (SEOP). Over the last several years, various SEOP-based systems have been developed to suit the needs of different neutron instruments at the Spallation Neutron Source (SNS) and the High Flux Isotope Reactor (HFIR). Particularly, great efforts have been made in developing in situ systems to address the problem of 3He polarization decay in the drop-in cell setup. Because most instruments at SNS and HFIR have very limited space, the in situ system development has been focused on having a compact form factor design tailored to each individual beamline while still achieving high 3He polarization. We report the development and optimization of polarized 3He spin filters at ORNL and present the latest results.
3He has a strong spin-dependent neutron absorption cross section and polarized 3He gas by optical pumping can be employed to effectively polarize and spin-analyze large area, widely divergent, and broadband neutron beams. The adiabatic fast passage (AFP) nuclear magnetic resonance (NMR) technique allows to invert the 3He nuclear polarization, hence the neutron polarization. These unique features of a 3He neutron spin filter (NSF) together with the recent advancements in the 3He NSF technique have made many new polarized neutron measurement capabilities possible, including thermal triple axis spectrometry, small-angle neutron scattering, wide-angle polarization analysis, and diffuse reflectometry. I will present an overview of the recent development of the 3He NSF technique at the NIST Center for Neutron Research. I will discuss a substantial effort towards improving the 3He polarization close to the theoretical limit (~95%) set by the anisotropic spin exchange optical pumping (SEOP). I will show how one can achieve a nearly lossless 3He polarization inversion to address the need of inverting the polarization in an order of minutes. I will present a recent development of a large fully-reblown “horseshoe”-shaped SEOP cell necessary for a neutron spin analyzer of a wide-angle polarization analysis capability with a simultaneous scattering angle coverage of 240 degrees. I will discuss the development of compact magnetostatic cavity devices that provide a homogeneous magnetic field to maintain the 3He polarization with field gradients on the order of 10-4 cm-1 for a cell volume of 1000 cm3. The polarized neutron measurement capabilities developed have played an important role to uncover the nature of magnetism in complex materials in condensed matter physics and materials science. Examples of such scientific applications will be presented.
As a neutron scatters from a target nucleus, there is a small but measurable effect caused by the interaction of the neutron's magnetic dipole moment with that of the partially screened electric field of the nucleus. This spin-orbit interaction is typically referred to as Schwinger scattering [1] and induces a small rotation of the neutron's spin on the order of 10$^{-4}$ rad for Bragg diffraction from silicon [2]. In our experiment, neutrons undergo greater than 100 successive Bragg reflections from the walls of a slotted, perfect-silicon crystal to amplify the total spin rotation. A magnetic field is employed to insure constructive addition as the neutron undergoes this series of reflections. The strength of the spin-orbit interaction, which is directly proportional to the electric field, was determined by measuring the rotation of the neutron's spin-polarization vector. Two approaches were employed for the polarizing and analyzing the monochromatic cold neutron beam: supermirrors [3] and remotely polarized $^3$He-based neutron spin filters [4]. Whereas better statistics were obtained with supermirrors, this approach presented a systematic effect associated with a small transverse polarization component due to the need for adiabatic rotation of the neutron spin. At the expense of statistics, this systematic effect was eliminated with spin filters. Our measurements show good agreement with the expected variation of this rotation with the applied magnetic field, whereas the magnitude of the rotation is $\approx$40\% larger than expected.
[1] J. Schwinger. Phys. Rev. 73, 407 (1948).
[2] C.G. Shull. Phys. Rev. Lett. 10, 297 (1963).
[3] F. Mezei, Commun. Phys. 1, 81–85 (1976).
[4] W.C. Chen et al, Journal of Physics: Conf. Series 294, 012003 (2011).
Despite the challenges, neutron resonance spin echo (NRSE) still holds the promise to improve upon neutron spin echo (NSE) for measurement of slow dynamics in materials. In particular, the modulated intensity with zero effort (MIEZE) configuration allows for the measurement of depolarizing samples and is naturally suited for combination with small angle neutron scattering (SANS) as a result of there being no spin manipulations performed after the sample. The application of NRSE and MIEZE require a radio frequency (RF) spin flipper with high efficiency, and for use in time-of-flight instruments an adiabatic spin flip is desirable. We present a bootstrap RF neutron spin flipper using high temperature superconducting (HTS) technology, with adiabatic spin flipping capability. A frequency of 2MHz has been achieved, which would produce an effective field integral of 0.35 Tm for a meter of separation in a NRSE spectrometer at the current device specifications. In bootstrap mode, the self-cancellation of Larmor phase aberrations can be achieved by the appropriate selection of the polarity of the gradient coils and has been observed.
Scattering length neutrons for cold protons remarkably depends on relative direction of their spins. Thus, scattering pattern of polarized neutrons varies as a function of proton-polarization (P$_H$) of samples. This technique called spin-contrast-variation (SCV) enables us to determine detailed structure of composite materials from the P$_H$-dependent multiple scatterings.
Since Stuhrmann et al. firstly demonstrated in 1989, the SCV technique has been applied to small-angle neutron scattering (SANS) measurements. We have also carried out SCV-SANS measurements of variety of samples in Japan Research Reactor (JRR-3) and Japan Proton Accelerator Research Complex (J-PARC). Recently, we newly applied the SCV technique to neutron reflectometry to study surface and interface structure of multi-layered thin-films. Now, we are developing SCV neutron powder diffractometry to determine polycrystalline structure.
The spin dependence of the neutron scattering cross section, especially for hydrogen, makes Dynamic Nuclear Polarization a powerful technique for improving neutron diffraction measurements, especially for biological and soft matter systems. Oak Ridge National Laboratory has demonstrated the application of this technique to Neutron Macromolecular Crystallography, with an eye towards DNP become a normal part of the user program for the Second Target Station that is being built at the SNS. The status of the current system will be discussed, as will the plans for future measurements using Small Angle Neutron Scattering, and the plans for DNP at the Second Target Station.
The A2-Collaboration at the Mainz Microtron MAMI measures photon absorption cross sections using circularly and linearly polarized 'Bremsstrahlung' photons up to an energy of ~1.5GeV. We use a 4 π detection system with the 'Crystal Ball' as central part.
We have developed a Frozen Spin Target in close collaboration with the polarized target group of the Joint Institute for Nuclear Research in Dubna, Russia. The 3/4Helium dilution refrigerator provides temperatures down to 25 mKelvin. Both longitudinally and transversely polarized protons and deuterons are possible with the help of superconducting holding coils.
In this talk our experimental program using Frozen Spin Targets will be described.
In 2018 the COMPASS experiment at CERN applied a transversely solid polarized proton target with a negative pion beam to measure the Sivers asymmetry using Drell-Yan process. The target system consists of a 50 mK dilution refrigerator, a 2.5 T solenoid magnet, two sets of 70 GHz microwave system. Solid NH$_3$ beads of the target material was contained in 2-target-cell of 55-55 cm long with a 4 cm diameter. The longitudinal polarization of the target is obtained by the DNP method. After polarizing for 1 day, the spin was oriented perpendicular to the beam direction by using a 0.6 T dipole magnet and the data was taken for 6 days.
I will present the results of the proton polarization, the relaxation time during the data taking and the radiation damage of the target material.
In 2021 the experiment will exchange the NH$_3$ target material for $^6$LiD as a polarized deuteron target in order to perform SIDIS program with muon beam.
I will also present the status of the preparation.
Bar Opens at 5:30
Dinner is at 6:00
Polarized neutron scattering is a powerful tool to study from materials to fundamental physics,and polarized $^3$He gas is now playing an important role at high flux neutron sources as neutron spin filters (NSF). At the spallation neutron source in J-PARC (Japan Proton Accelerator Research Complex), a polarized inelastic neutron spectrometer, POLANO, is now under commissioning, and an in-situ polarized $^3$He NSF is about to be installed in the instrument for the incident neutron beam polarization. The in-situ polarized $^3$He NSF has been originally designed and build for POLANO but it can be used in other instruments with minimal modification because of its compact size and versatility.
We will present some techniques developed for the in-situ polarized $^3$He NSF as well as other measurements carried out with $^3$He NSF at J-PARC.
Polarized neutron techniques have been widely developed and integrated into many instruments at major neutron sources around the world. At the China Spallation Neutron Source (CSNS), the polarized neutron and sample environment groups are developing a complete system to support the ongoing beamline design and construction efforts. In this presentation, we will introduce the current development of a polarized 3He system1,2 at the CSNS. The polarized 3He neutron spin filter system, both off-situ and in-situ, shall provide a reliable universal polarized neutron source to the current beamlines at CSNS, which include Small Angle Neutron Scattering (SANS), neutron reflectometry and powder diffraction. The spin filter will also aid in the advancement of future beamlines through testing and developing customized systems. We shall also give a brief introduction to the future plan of polarized neutron technologies developed based on the polarized 3He spin filter.
1 C. Y. Jiang, X. Tong, D. R. Brown, W. T. Lee, H. Ambaye, J. W. Craig, L. Crow, H. Culbertson, R. Goyette, M. K. Graves-Brook, M. E. Hagen, B. Kadron, V. Lauter, L. W. McCollum, J. L. Robertson, B. Winn, and A. E. Vandegrift, Physcs Proc 42, 191 (2013).
2 X. Tong, C. Y. Jiang, V. Lauter, H. Ambaye, D. Brown, L. Crow, T. R. Gentile, R. Goyette, W. T. Lee, A. Parizzi, and J. L. Robertson, Rev Sci Instrum 83 (7) (2012).
In-situ polarization can provide the highest performance over time for polarized $^3$He over time where $^3$He polarizations in excess of 80% can be maintained. The polarization rates and magnitude achieved are aided by using high performance $^3$He cells produced all in house and techniques such as hybrid spin-exchange optical pumping and chipped volume Bragg grating narrowed laser diode array bars. For the magnetic environments we normally use so called magic boxes which give very high 3He lifetime performance and good isolation from external magnetic fields due to their geometry that creates a magnetic field transverse to the beam propagation direction which also allows decoupling of the the optical pumping light path to the orthogonal neutron beam path. As an example, recently for a user experiment on the ROT effect in $^{235}$U one of our polarizers gave a $^3$He polarization in excess of 81% for over 20 days with a polarization build rate of 7 hours, this corresponded to a neutron polarization of 99.3% at 22% neutron transmission at 1.15 Å.
The Neutron OPtics Time Reversal Experiment (NOPTREX) collaboration is working towards a sensitive search for time reversal violation in polarized neutron transmission through polarized heavy nuclei. The experiment requires an intense, stable polarized neutron beam at the resonance energies of interest near 1 eV. We have recently constructed a $^3$He neutron spin filter at Indiana University which makes use of the very large spin dependent neutron absorption cross-section of $^3$He to polarize neutrons. We polarize $^3$He gas using spin-exchange optical pumping (SEOP). We have combined our laser optics and oven with a $\mu$-metal shielded solenoid and a $^3$He gas cell from ORNL to realize our polarizer. We also discuss a planned experiment to measure neutron pseudomagnetic precession in polarized xenon gas. $^{131}$Xe is one of the nuclei on interest for the NOPTREX test, and this measurement will help us determine a significant systematic error related to spin dependent components in polarized neutron-nucleus transmission and also measure the spin-dependent scattering amplitudes of both $^{129}$Xe and $^{131}$Xe for the first time. This experiment will use an Neutron Spin Echo spectrometer to measure pseudomagnetic precession and an existing SEOP system to polarize both $^{129}$Xe and $^{131}$Xe.
Since most of the $^{3}He$ spin is carried by the unpaired neutron, polarized $^{3}He$ targets have been widely used as a effective polarized neutron target in electron scattering experiments to study the spin structure of neutron. Over the past a couple of decades, polarized $^{3}He$ targets had been successfully utilized in thirteen electron scattering experiments during JLab 6 GeV era. At JLab, a technique called Spin-Exchange Optical Pumping (SEOP) is used to polarized the $^{3}He$ target. For the past decade, several developments including Rb-K hybrid alkali system and high power narrow line-width diode lasers were implemented to the polarized $^{3}He$ target in order to reach higher 3He polarization with world record luminosity. As JLab completed 12 GeV upgrade in 2017, there are seven upcoming approved polarized $^{3}He$ target experiments. Upgrade of the target with convection cell and Pulse Nulear Magnetic Resonance (PNMR) polarimetry were completed for the first upcoming 12 GeV era experiment $A_{1}^{n}$ (E12-06-110) with collaboration of $d_{2}^{n}$ (E12-06-121) in JLab Hall C. For typical $10^{22}/cm^{2}$ high-density target used in this collaboration experiment, the maximum polarization reached over 50% under $30 \mu A$ electron beam, thus the luminosity of $10^{36}/cm^{2}/s$ will be achieved.
We discuss the application of an open storage cell as gas target for a proposed LHC fixed-target experiment LHC-spin. The target provides a high areal density at minimum gas input, which may be polarized 1H, 2H, or 3He gas or heavy inert gases in a wide mass range. For the study of single-spin asymmetries in pp interaction, luminosities of nearly 10^33/cm^2 s can be produced with existing techniques.
One aim for the new electron accelerator MESA is to measure the weak mixing angle in electron proton scattering to a precision of 0.14 %. The beam polarization significantly contributes to this measurement. The Møller polarimeter proposed by V. Luppov and E. Chudakov opens the way to reach a sufficiently accurate determination of polarization. At the moment the polarized atomic hydrogen target is under construction. The current R&D status is presented.
The P2 Experiment at the new Mainz Energy-recovering Superconducting Accelerator (MESA)
aims at measuring the weak mixing angle sin² θ_W at low Q² with high precision. Therefore
the polarization of the incident electron beam has to be known with a very high accuracy (< 0.5%).
Conventional Mott polarimeters are limited by uncertainties in the extrapolation and theoretical
calculations required to determine S eff .
The Double Scattering (Mott-) Polarimeter (DSP) presented in this talk offers an alternative method
for the calibration of the target foils by using double Mott scattering, allowing a high precision in
the determination of the effective analyzing power of the scattering process by only relying on
asymmetry measurements on two target foils. First results that were achieved with 100 keV beam
energy, the injection energy of MESA, are presented.
The Compton polarimeter at Jefferson Lab's experimental Hall A provides a continuous, non-invasive measurement of electron beam polarization via electron-photon scattering. The electron beam passing through the polarimeter intercepts green laser light stored in a Fabry-Perot cavity. Scattered electrons are detected in an electron detector while back scattered photons are detected in a GSO crystal calorimeter. For an accurate beam polarization measurement, the laser polarization inside the Fabry-Perot cavity must be well known. We have performed studies to optimize the laser polarization inside the cavity and to know it precisely. I will discuss the methods and results from these investigations.
The Jefferson Lab Continuous Electron Beam Accelerator Facility’s experimental Hall A employs a Compton polarimeter to measure incoming beam polarization for parity violating electron scattering experiments. The polarimeter operates by amplifying green laser light in a Fabry-Perot cavity which then compton scatters off the incoming electron beam. The scattered photons are then passed through a scintillating GSO (Gadolinium Oxyorthosilicate) crystal which creates light which registers in a photomultiplier tube. The polarization measurement is conducted by taking advantage of the helicity-dependence of compton scattering. By measuring the integrated signal from photons scattered while the beam is in different helicity states, we generate a differential asymmetry between these states, which then yields information about the electron beam’s longitudinal polarization. Measuring the asymmetry requires a robust background subtraction of helicity-correlated asymmetry as well as identifying the compton edge from observing spectra. This measurement aids in minimizing a key source of systematic error in many parity-violating electron scattering experiments. This talk will be about the integrating photon detector analysis as well as the recent results from the PREX-II experiment.
Synchrotron radiation plays an important role in the polarization dynamics of an electron beam in the energy range of Jefferson Lab Electron-Ion Collider (JLEIC). High polarization of the JLEIC electron beam is achieved using two design features. The first one is a continuous full-energy top-off of the stored electron beam by a highly-polarized beam from CEBAF. The second one is arrangement of vertical spin orientations alternatively parallel and anti-parallel to the dipole fields in the two arcs of the figure-8 collider ring to neutralize the radiative Sokolov-Ternov effect on the electron polarization and compensate the energy dependence of the spin tune. For hadrons, the JLEIC figure-8 ring design compensates the primary effect of the ring arcs on their spins, i.e. the ring is "transparent" to the spins. This allows for efficient preservation of the source polarization as well as maintenance, control and manipulation of the stored beam polarization of any hadrons including deuterons using only additionally introduced weak magnetic field integrals that do not perturb the beam dynamics. The criterion for polarization stability is that the spin rotation induced by the weak field integrals must be much greater than that caused by lattice imperfections and beam emittances. We present the results of theoretical and numerical studies of the electron and hadron polarization dynamics in JLEIC.
The electron-ion collider (EIC) eRHIC at BNL aims at a luminosity of 10^34 cm^-2 sec^-1 in collisions of polarized electron and polarized proton, deuteron, and 3He beams. We will present an overview of the proposed facility with an emphasis on generation and acceleration of the polarized beams and the expected polarization performance.
The capability of accelerating a high-intensity polarized $^{3}$He ion beam would provide an effective polarized neutron beam for new high-energy QCD studies of nucleon structure. This development is essential for the future Electron Ion Collider, which could use a polarized $^{3}$He ion beam to probe the spin structure of the neutron. The proposed polarized $^{3}$He ion source is based on the Electron Beam Ion Source (EBIS) currently in operation at Brookhaven National Laboratory. $^{3}$He gas would be polarized within the 5 T field of the EBIS solenoid via Metastability Exchange Optical Pumping (MEOP) and then pulsed into the EBIS vacuum and drift tube system where the $^{3}$He will be ionized by the 10 Amp electron beam. The goal of the polarized $^{3}$He ion source is to achieve $2.5 \times 10^{11}$ $^{3}$He$^{++}$/pulse at 70% polarization. An upgrade of the EBIS is currently underway. An absolute polarimeter and spin-rotator is being developed to measure the $^{3}$He ion polarization at 6 MeV after initial acceleration out of the EBIS. The source is being developed through collaboration between BNL and MIT.
Compton polarimetry is the prime candidate for electron polarization measurement since it is virtually ininvasive and can reach very good level of accuracy with best measurements at the 0.4 % level accuracy. It is especially suitable at high energy since the analyzing power grows with electron energy.
I will present the current Compton Polarimeters available at Jefferson Laboratory and also give a summary of the studies which were done for Compton Polarimetry in the context of the Electron Ion Collider.
The broad physics program at a future electron-ion collider is, in part, based on the availability of high electron and proton beam polarizations. Proton polarimetry will have to include an absolute normalization as well as fast measurements of the polarization of the bunched beam. The required high luminosities in combination with short bunch spacing represent specific challenges. Additionally, the polarization direction has to be determined at the experimental interaction point where spin rotators allow for a choice of transverse or longitudinal polarization. This talk will summarize methods that have been successfully employed to the high energy proton beams at RHIC and discuss possible improvements to meet the demands of an electron-ion collider. Also, other options will be discussed that can be helpful in a lepton-proton collider. For example, new tools may be based on recent experimental confirmation of spin dependent neutron production in ultra-peripheral proton-ion collisions.
In the eRHIC high-luminosity collider proposal the number of ion bunches will be increased and the bunch spacing will be reduced from current 107 ns (RHIC) to 34.8 ns at the first stage and finally to 8.7 ns. This beam timing structure will be a challenge for the elastic events identification in the RHIC CNI (Coulomb Nuclear Interference) polarimeters and an essential upgrade of the polarimeters is required. It this paper, we will discuss possible solutions of this problem.
Critical dressing, the simultaneous dressing of two spin species to the same effective Larmor frequency, is a technique that can, in principle, improve the sensitivity to small frequency shifts. The benefits of spin dressing and thus critical dressing are achieved at the expense of generating a large (relative to the holding field $B_{0}$,) homogeneous oscillating field. Due to inevitable imperfections of the fields generated and current supplied by the power supply, the benefits of spin dressing may be lost from the additional relaxation and noise generated by the dressing field imperfections. In this analysis the subject of relaxation, frequency shifts, and phase noise are approached with simulations and theory. Analytical predictions are made from a new quasi-quantum model that includes gradients in the holding field $B_{0}=\omega _{0}/\gamma $ and dressing field $B_{1}=\omega _{1}/\gamma $ where $B_{1}$ is oscillating at frequency $\omega $, as well as noise generated by the power supply. It is found that irreversible DC gradient relaxation can be canceled by an AC spin dressing gradient in the Redfield regime. Furthermore, it is shown that there is no linear in $E$ frequency shift generated by gradients in the dressing field. Critically dressed modulation techniques that extend the relaxation time by orders of magnitude are considered and application to tipping pulses are investigated.
The existence and size of a neutron electric dipole moment (nEDM) remains an important question in particle and cosmological physics. The SNS nEDM experiment proposes a new limit for nEDM search by using ultra-cold neutrons (UCN) in a bath of superfluid helium. The experiment uses polarized 8.9Å neutrons to create polarized UCN in situ in superfluid helium via superthermal downscattering. This process requires the 8.9Å neutrons to retain their polarization as they pass through the magnetic shielding and nEDM cryostat windows. This talk will describe a setup to measure the neutron polarization loss from the magnetic shielding and cryostat windows.
The Nab experiment at the Fundamental Neutron Physics Beamline (FnPB) at the Spallation Neutron Source (SNS) aims to make precision measurements of the electron-neutrino correlation and Fierz interference term, associated with the beta decay of free neutrons. Residual polarization of the incident beam presents a potential source of systematic error in this measurement. In order to understand and mitigate these effects we must measure the beam polarization and the efficiency of our newly designed Neutron Spin Flipper. If we use $^3$He polarizers to accomplish these measurements, it will require careful control of the magnetic environment along the beam line, in order to assure adiabatic spin transport of the neutrons, and prolong the polarization lifetime the $^3$He cells. However the space for incorporating the necessary components is limited, and requires careful magnet construction to obtain the requisite magnetic fields.
The Neutron Spin Rotation (NSR) slow neutron polarimeter is an apparatus designed to measure and constrain fundamental interactions to high precision through the use of neutron optical techniques. This apparatus was initially constructed to search for parity-violating spin rotation of neutrons transmitted through liquid $^{4}\text{He}$. This experiment placed a limit on the rotation angle per unit length of $d\phi/dz =[+2.1 \pm 8.3 (\textit{stat.})\, ^ {+2.9} _{-0.2} (\textit{sys.})]\times10^{-7}$ rad/m. This data has been used to constrain light $Z'$ bosons, in-matter gravitational torsion, and nonmetricity. A second target system operated with the same polarimeter was designed to search for an axial coupling of neutrons $g_{A}^{2}$ to light $Z'$ bosons, placing limits on the rotation angle $\phi=[1.4\pm 2.3(\textit{stat.}) \pm 2.8(\textit{sys.})]\times10^{-5}$ rad, improving $g_{A}^{2}$ bounds. The polarimeter and targets are being upgraded for future measurements planned for the NG-C beam at NIST Center for Neutron Research. The precision should be sufficient to see the Standard Model contribution to n-$^{4}$He spin rotation and improve the limits on $g_{A}^{2}$ by about two orders of magnitude. An overview of the apparatus will be presented, along with details of both target systems design and performance. [1]
[1] W. M. Snow, et al., Rev. Sci. Inst. 86, 055101(2015)
Highly-polarized, frozen-spin targets of solid Hydrogen Deuteride (HDice) have been successfully used with photon beam for nuclear physics measurements for over a decade. With Jefferson Lab’s upgrade to 12 GeV, a new effort has begun to expand the physics reach using HDice targets with electron beam. Three “high impact” experiments, which plan to utilize transversely polarized HDice targets and electron beams to study nucleon structure, have been approved by the JLab PAC with “A” ratings. Testing HDice targets with electron beams (eHD) is scheduled to begin this fall at the JLab’s Upgraded Injection Test Facility (UITF). Preparations for these eHD tests are well underway. The experimental design and the status of major components will be reported, along with the anticipated schedule.
In this talk I will discuss the dilution refrigerator used in our lab for Polarized Target Physics. Originally constructed at CERN by Niinikoski in the mid 1970’s, modified by the Helmholtz Zentrum Geesthacht laboratory for neutron studies, and finally obtained us at UVA for use in the HIGS collaboration. I will discuss the changes that have been made after we started using it. In November 2017, we discovered a leak in the still between two separate vacuum spaces and had no choice but to build a new dilution unit. I will lay out the progress we have made so far, what is currently happening, and the next steps that need to be taken.
A new dynamic nuclear polarization (DNP) target system has recently come on-line at the University of New Hampshire. DNP is driven by a novel solid-state 140 GHz mm-wave source with quasi-optics transmission and low-loss (<0.1 dB/m) overmodal waveguide that is insensitive to magnetic fields. We have also developed a method to 3D print with Kel-F, which was used to produce target material cups and is being used to study quasi-optical properties of Kel-F lenses. Other off-the-shelf 3D printed materials have been found to survive multiple 1 K temperature cycling and are utilized in target stick construction. Polarization measurements are made and cross-compared on a Liverpool Q-meter, LANL Q-meter, and low-cost software-defined-radio based vector network analyzer. An overview of this system and current progress will be presented.
We have previously developed a concept for a polarized 3He ion source based on the existing Electron Beam Ionization Source (EBIS) at Brookhaven National Laboratory (BNL). Successful tests of polarizing 3He in a high magnetic field have led to the development of the Extended EBIS upgrade. The spin-rotator and 3He++ beam polarimetry development is also in progress in collaboration with MIT.
There is a unique opportunity for precision measurements of the absolute 3He++ polarization at beam energies 5.0-6.0 MeV after the EBIS Linac. It was shown in Ref. [1], that the analyzing power for the elastic scattering of spin-1/2 particles (3He) on spin-0 particles (4He) can reach the maximum theoretical value |P| = 1 at some point (Ebeam, θCM). Using the experimental data [2], several such points were established for 3He+ 4He elastic scattering including the P= +1 at beam E ≈ 5.3 MeV and θ (center of mass) ≈ 91°. Therefore, the main effort of this R@D will be development of precision absolute polarimeter for the measurements of the 3He++ beam polarization produced in the EBIS as a reference for the further polarization measurements (and possible polarization losses) along accelerator chain.
The polarimeter vacuum system is integrated in the spin-rotator transport line. The 3He++ ion beam will enter the scattering chamber through the thin window to minimize beam energy losses. The scattering chamber is filled with 4He gas at ~ 5 torr pressure. The silicon strip detectors will be used for energy and TOF measurements of the scattered 3He and recoil 4He nuclei (in coincidence) for the identification of the scattering kinematics with analyzing power AN ~ 1. Two sets of detectors will measure both nuclei and left-right asymmetry at the spin –flip.
The status of polarimeter development (vacuum system, scattering chamber, thin window, Si-strip detectors and WFD- based DAQ) will be presented.
[1] R. J. Spiger and T. A. Tombrello. Scattering of He3 by He4 and of He4 by Tritium".
In: Phys. Rev. 163 (4 1967), pp. 964{984.
[2] G.R. Plattner and A.D. Bacher. \Absolute calibration of spin 1/2 polarization"
Physics Letters Volume 36B, number 3 (1971), pp. 211-214
Polarized light ion beams are essential to the physics program for a future electron-ion collider (EIC), and polarized deuterons have been identified as essential tools to probe the sea quark and gluon distributions in studies of hadronization. Polarized deuterons form an especially unique system for study by providing a combination of quark and nuclear physics, and thus can yield new insights in the understanding of hadron structure that cannot be achieved with other polarized nuclei. Both the Jefferson Lab Electron-Ion Collider (JLEIC) and the electron-ion collider at Brookhaven National Lab (eRHIC) machine design concepts have integrated polarized deuteron transport into their designs, but there are currently no operational polarized deuteron beam sources in the United States. A new method for production of neutral polarized atomic deuterium beams is discussed. The method utilizes infrared stimulated Raman adiabatic passage (IR STIRAP) in the production of polarized deuterium halide molecules, from which polarized deuterium atoms can be accessed through photodissociation. The method has the potential to generate neutral polarized atomic deuterium beams with densities that are orders of magnitude greater than that in existing devices.
GaAs-based photocathodes are widely used to produce highly spin polarized electron beams at high currents. Spin polarized photoelectrons can escape into vacuum only when GaAs surface is activated to Negative Electron Affinity (NEA). The NEA surface is notorious for extreme vacuum sensitivity, and this results in rapid QE degradation. We activated GaAs samples by unconventional methods using Cs, Sb, and oxygen. We present successful NEA activation on GaAs surface and more than a order of magnitude improvement in charge extraction slifetime compared to the standard Cs-O2 activation without significant loss in spin polarization.