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Abstract: A polarized hydrogen/deuterium internal gas target has been constructed and operated at the internal target region of the South Hall Ring (SHR) of the MIT-Bates Linear Accelerator Center to carry out measurements of spin-dependent electron scattering at 850MeV. The target used an Atomic Beam Source (ABS) to inject a flux of highly polarized atoms into a thin-walled, coated storage cell. The polarization of the electron beam was determined using a Compton laser backscattering polarimeter. The target polarization was determined using well-known nuclear reactions. The ABS and storage cell were embedded in the Bates Large Acceptance Toroidal Spectrometer (BLAST), which was used to detect scattered particles from the electron–target interactions. The target has been designed to rapidly switch operation from hydrogen to deuterium. Further, this target was the first to be operated inside a magnetic spectrometer in the presence of a magnetic field exceeding 2kG. An ABS intensity and a high polarization inside the storage cell have been achieved. The details of the target design and construction are described here and the performance over an 18 month period is reported. [Copyright &y& Elsevier]

We propose a new measurement of the ratio of positron-proton to electron-proton elastic scattering at DESY. The purpose is to determine the contributions beyond single-photon exchange, which are essential for the Quantum Electrodynamic (QED) description of the most fundamental process in hadronic physics. By utilizing a 20 cm long liquid hydrogen target in conjunction with the extracted beam from the DESY synchrotron, we can achieve an average luminosity of 2.12 × 10 35 cm - 2 · s - 1 ( ≈ 200 times the luminosity achieved by OLYMPUS). The proposed two-photon exchange experiment (TPEX) entails a commissioning run at a beam energy of 2 GeV, followed by measurements at 3 GeV, thereby providing new data up to Q 2 = 4.6 (GeV/c) 2 (twice the range of current measurements). We present and discuss the proposed experimental setup, run plan, and expectations. [ABSTRACT FROM AUTHOR]

A proposed new high-luminosity electron–ion collider requires a polarized electron source of extremely high intensity. The MIT-Bates Laboratory, in collaboration with Brookhaven National Laboratory (BNL), has developed a new polarized electron gun that can be operated at currents in the mA range. This paper describes the design of the gun and beam line and also presents the results of the beam tests. [ABSTRACT FROM AUTHOR]

A windowless hydrogen gas target of nominal thickness 1 0 19 cm−2 is an essential component of the DarkLight experiment, which is designed to utilize the megawatt electron beam at an Energy Recovery Linac (ERL). The design of such a target is challenging because the pressure drops by many orders of magnitude between the central, high-density section of the target and the surrounding beamline, resulting in laminar, transitional, and finally molecular flow regimes. The target system was assembled and operated at Jefferson Lab's Low Energy Recirculator Facility (LERF) in 2016, and subsequently underwent several revisions and calibration tests at MIT Bates in 2017. The system at dynamic equilibrium was simulated in COMSOL to provide a better understanding of its optimal operation at other working points. We have determined that a windowless gas target with sufficiently high density for DarkLight's experimental needs is feasible in an ERL environment. [ABSTRACT FROM AUTHOR]

Abstract The design, construction, installation, and testing of a Faraday Cup intended to measure the current of a 3 MeV, 1 μ A electron beam is described. Built as a current monitor for a Møller scattering measurement at the MIT High Voltage Research Laboratory, the device combines a large angular acceptance with the capability to measure a continuous, low energy beam. Bench studies of its performance demonstrate current measurements accurate to the percent level at 1 μ A. The Faraday Cup was designed and constructed at MIT and has been in use at the HVRL since 2017, providing a significantly more detailed measurement of beam current than was previously available. [ABSTRACT FROM AUTHOR]

We have performed a novel comparison between electron-beam polarimeters based on Møller and Compton scattering. A sequence of electron-beam polarization measurements were performed at low beam currents ( < 5 μ A ) during the Q weak experiment in Hall-C at Jefferson Lab. These low current measurements were bracketed by the regular high current ( 180 μ A ) operation of the Compton polarimeter. All measurements were found to be consistent within experimental uncertainties of 1% or less, demonstrating that electron polarization does not depend significantly on the beam current. This result lends confidence to the common practice of applying Møller measurements made at low beam currents to physics experiments performed at higher beam currents. The agreement between two polarimetry techniques based on independent physical processes sets an important benchmark for future precision asymmetry measurements that require sub-1% precision in polarimetry. [ABSTRACT FROM AUTHOR]

Abstract: An internal hydrogen target system was developed for the OLYMPUS experiment at DESY, in Hamburg, Germany. The target consisted of a long, thin-walled, tubular cell within an aluminum scattering chamber. Hydrogen entered at the center of the cell and exited through the ends, where it was removed from the beamline by a multistage pumping system. A cryogenic coldhead cooled the target cell to counteract heating from the beam and increase the density of hydrogen in the target. A fixed collimator protected the cell from synchrotron radiation and the beam halo. A series of wakefield suppressors reduced heating from beam wakefields. The target system was installed within the DORIS storage ring and was successfully operated during the course of the OLYMPUS experiment in 2012. Information on the design, fabrication, and performance of the target system is reported. [Copyright &y& Elsevier]

Abstract: Tests were performed to pass a 100MeV, 430kWatt c.w. electron beam from the energy-recovery linac at the Jefferson Laboratory's FEL facility through a set of small apertures in a 127mm long aluminum block. Beam transmission losses of 3p.p.m. through a 2mm diameter aperture were maintained during a 7h continuous run. [Copyright &y& Elsevier]

Abstract: We report measurements of photon and neutron radiation levels observed while transmitting a 0.43MW electron beam through millimeter-sized apertures and during beam-off, but accelerating gradient RF-on, operation. These measurements were conducted at the Free-Electron Laser (FEL) facility of the Jefferson National Accelerator Laboratory (JLab) using a 100mev electron beam from an energy-recovery linear accelerator. The beam was directed successively through 6mm, 4mm, and 2mm diameter apertures of length 127mm in aluminum at a maximum current of 4.3mA (430kW beam power). This study was conducted to characterize radiation levels for experiments that need to operate in this environment, such as the proposed DarkLight Experiment. We find that sustained transmission of a 430kW continuous-wave (CW) beam through a 2mm aperture is feasible with manageable beam-related backgrounds. We also find that during beam-off, RF-on operation, multipactoring inside the niobium cavities of the accelerator cryomodules is the primary source of ambient radiation when the machine is tuned for 130mev operation. [Copyright &y& Elsevier]

High-power, relativistic electron beams from energy-recovering linacs have great potential to realize new experimental paradigms for pioneering innovation in fundamental and applied research. A major design consideration for this new generation of experimental capabilities is the understanding of the halo associated with these bright, intense beams. In this Letter, we report on measurements performed using the 100 MeV, 430 kW cw electron beam from the energy-recovering linac at the Jefferson Laboratory's Free Electron Laser facility as it traversed a set of small apertures in a 127 mm long aluminum block. Thermal measurements of the block together with neutron measurements near the beam-target interaction point yielded a consistent understanding of the beam losses. These were determined to be 3 ppm through a 2 mm diameter aperture and were maintained during a 7 h continuous run. [ABSTRACT FROM AUTHOR]

Abstract: The polarized electron source at MIT-Bates has been developed to provide beams for nuclear physics experiments with a very diverse set of requirements. The source has combined operation at high peak and average current with high polarization. Developments have included the pioneering of several techniques used in parity violating experiments to remove helicity correlations from beam properties. This paper describes the design of the source and its performance during beam operations. [Copyright &y& Elsevier]