Joseph Grames
A5028184113- Photocathodes and Microchannel Plates
- Particle Accelerators and Free-Electron Lasers
- Particle accelerators and beam dynamics
- Particle Detector Development and Performance
- Particle physics theoretical and experimental studies
- Electron and X-Ray Spectroscopy Techniques
- Muon and positron interactions and applications
- Radiation Therapy and Dosimetry
- Superconducting Materials and Applications
- Gyrotron and Vacuum Electronics Research
- Quantum Chromodynamics and Particle Interactions
- Plasma Diagnostics and Applications
- Radiation Detection and Scintillator Technologies
- Nuclear Physics and Applications
- Dark Matter and Cosmic Phenomena
- Atomic and Molecular Physics
- Advanced Optical Sensing Technologies
- Nuclear physics research studies
- X-ray Spectroscopy and Fluorescence Analysis
- Advancements in Photolithography Techniques
- International Science and Diplomacy
- Medical Imaging Techniques and Applications
- Electrostatic Discharge in Electronics
- Atomic and Subatomic Physics Research
- Laser Design and Applications
Thomas Jefferson National Accelerator Facility
2015-2024
Laboratoire de Physique des 2 Infinis Irène Joliot-Curie
2023
Oak Ridge National Laboratory
2023
Universidad de Guanajuato
2023
Autonomous University of Sinaloa
2023
Old Dominion University
2020-2021
Brookhaven National Laboratory
2021
Fermi National Accelerator Laboratory
2021
Cornell University
2018
George Washington University
2013
We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < or =Q2 =1.0 GeV2. These asymmetries, arising from interference electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions currents proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer detect recoiling protons liquid hydrogen target. results indicate nonzero, Q2 dependent, provide new information...
We have measured parity-violating asymmetries in elastic electron-proton and quasielastic electron-deuteron scattering at ${Q}^{2}=0.22$ $0.63\text{ }\text{ }{\mathrm{GeV}}^{2}$. They are sensitive to strange quark contributions currents the nucleon axial-vector current. The results indicate of $\ensuremath{\lesssim}10%$ charge magnetic form factors these four-momentum transfers. also present first measurement anapole moment effects current
The Polarized Electrons for Positrons experiment at the injector of Continuous Electron Beam Accelerator Facility has demonstrated first time efficient transfer polarization from electrons to positrons produced by polarized bremsstrahlung radiation induced a electron beam in high-Z target. Positron up 82% have been measured an initial momentum 8.19 MeV/c, limited only polarization. This technique extends positron capabilities GeV MeV beams, and opens access physics wide community.
We report the most precise measurement to date of a parity-violating asymmetry in elastic electron-proton scattering. The was carried out with beam energy 3.03 GeV and scattering angle =6 degrees, result A_PV = -1.14 +/- 0.24 (stat) 0.06 (syst) parts per million. From this we extract, at Q^2 0.099 GeV^2, strange form factor combination G_E^s + 0.080 G_M^s 0.030 0.025 0.006 0.012 (FF) where first two errors are experimental last error is due uncertainty neutron electromagnetic factor. This...
We have measured the beam-normal single-spin asymmetry $A_n$ in elastic scattering of 1-3 GeV transversely polarized electrons from $^1$H and for first time $^4$He, $^{12}$C, $^{208}$Pb. For $^1$H, $^4$He measurements are agreement with calculations that relate to imaginary part two-photon exchange amplitude including inelastic intermediate states. Surprisingly, $^{208}$Pb result is significantly smaller than corresponding prediction using same formalism. These results suggest a systematic...
GaAs-based dc high voltage photoguns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed average current facilities that operate tens of milliamperes or more. This paper describes techniques to maintain good vacuum while delivering beam, and minimize the ill effects ion bombardment, dominant mechanism reduces yield photogun. Experimental results presented here demonstrate...
This review paper describes the energy-upgraded Continuous Electron Beam Accelerator Facility (CEBAF) accelerator. superconducting linac has achieved 12 GeV beam energy by adding 11 new high-performance cryomodules containing 88 cavities that have operated cw at an average accelerating gradient of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mn>20</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mi>MV</a:mi><a:mo>/</a:mo><a:mi...
Two ${\mathrm{K}}_{2}\mathrm{CsSb}$ photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferson within a compact vacuum apparatus pressure $\ensuremath{\sim}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{Torr}$. These evaluated using dc high voltage photogun biased voltages up 200 kV, illuminated with laser light wavelengths 440 or 532 nm, generate electron beams currents 20 mA. Some conditions produced exceptionally large photocathode charge lifetimes, without...
We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely polarized 3 GeV electrons from unpolarized protons at Q2=0.15, 0.25 (GeV/c)2. The results are inconsistent with calculations solely using nucleon intermediate state and generally agree significant inelastic hadronic contributions. A(n) provides a direct probe imaginary component 2gamma exchange amplitude, complete description which is important interpretation data precision electron-scattering experiments.
We have measured the beam-normal single-spin asymmetries in elastic scattering of transversely polarized electrons from proton, and performed first measurement quasielastic on deuteron, at backward angles (lab angle 108°) for Q² = 0.22 GeV²/c² 0.63 beam energies 362 687 MeV, respectively. The asymmetry arises due to imaginary part interference two-photon exchange amplitude with that single-photon exchange. Results proton are consistent a model calculation which includes inelastic...
Polarized electron beams have played an important role in scattering experiments at moderate to high beam energies. Historically, these been primarily targeted studying hadronic structure — from the quark contribution spin of protons and neutrons, nucleon elastic form factors, as well contributions factors (strange) sea quarks. Other aimed place constraints on new physics beyond Standard Model. For most experiments, knowledge magnitude polarization has not a limiting systematic uncertainty,...
This contribution describes the latest milestones of a multiyear program to build and operate compact $\ensuremath{-}300\text{ }\text{ }\mathrm{kV}$ dc high voltage photogun with inverted insulator geometry alkali-antimonide photocathodes. Photocathode thermal emittance measurements quantum efficiency charge lifetime at average current up 4.5 mA are presented, as well an innovative implementation ion generation tracking simulations explain benefits biased anode repel beam line ions from...
We report on the design and performance of a Mott polarimeter optimized for nominal 5-MeV electron beam from Continuous Electron Beam Accelerator Facility (CEBAF) injector. The rf time structure this allows use flight in scattered detection, making it possible to cleanly isolate those detected electrons that originate scattering foil, resulting measured asymmetries which are exceptionally stable over broad range conditions, currents, foil thicknesses. In two separate series measurements...
The Thomas Jefferson National Accelerator Facility (Jefferson Lab) in Newport News, Virginia, USA, is one of ten national laboratories under the aegis Office Science U.S. Department Energy (DOE). lab managed and operated by Associates (JSA). primary facility at Lab Continuous Electron Beam (CEBAF). was created 1984 as CEBAF started operations for physics 1995. accelerator uses superconducting radio-frequency (srf) techniques to generate high-quality electron beams with high-intensity...
We present a capture concept for the continuous wave (CW) polarized positron injector Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (Ce+BAF). This two-step is based on (1) generation of bremsstrahlung radiation by longitudinally electron beam 1 mA, 120 MeV, 90% polarization), passing through tungsten target, and (2) production e+e--pairs these photons in same target. To provide highly-polarized beams (>60% polarization) or high-current (>1 µA) with low polarization...
GaAs photocathodes in dc high-voltage photoguns are highly susceptible to ion back-bombardment, which reduces the photocathode quantum efficiency and limits useful operating lifetime for producing polarized electron beams. This paper demonstrates that applying a small positive bias photogun anode can significantly suppress back-bombardment increase charge lifetime. technique was studied extensively using Continuous Electron Beam Accelerator Facility photogun, where beams created...
The parity-violating (PV) asymmetry of inclusive π- production in electron scattering from a liquid deuterium target was measured at backward angles. measurement conducted as part the G0 experiment, beam energy 360 MeV. physics process dominating pion for these kinematics is quasifree photoproduction off neutron via Δ0 resonance. In context heavy-baryon chiral perturbation theory, this related to low-energy constant d(Δ)- that characterizes γNΔ coupling. Zhu et al. calculated model...
A beam-normal single-spin asymmetry generated in the scattering of transversely polarized electrons from unpolarized nucleons is an observable related to imaginary part two-photon exchange process. We report a 2% precision measurement elastic electron-proton with mean angle θ_{lab}=7.9° and energy 1.149 GeV. The result B_{n}=-5.194±0.067(stat)±0.082 (syst) ppm. This most precise this quantity available date therefore provides stringent test models at far-forward angles (θ_{lab}→0) where they...
Parity-violating electron-scattering experiments represent an important focus of the nuclear physics experimental program at Continuous Electron Beam Accelerator Facility (CEBAF) Jefferson Lab. These pose significant challenges because scattering asymmetries can be very small, order parts-per-million and smaller. To succeed, properties electron beam such as current, position, size energy, must nearly identical in two electron-polarization spin states (parallel anti-parallel relative to...