A polarimeter was constructed to measure the longitudinal polarization of a spin-polarized electron beam at 5 and 7 MeV. The polarimeter takes advantage of Compton scattering between circularly polarized bremsstrahlung photons produced by a longitudinally polarized electron beam striking a copper radiator and the spin-polarized electrons orbiting the iron atoms of an analyzing magnet. This so-called Compton transmission polarimeter is compact and relatively inexpensive compared to Mott-scattering polarimeters because no spin manipulator is required. This work presents the design of the radiator, analyzing magnet, photon detector assembly, and data acquisition system of the Compton transmission polarimeter as well as beam commissioning results performed at the Upgraded Injector Test Facility at Jefferson Lab.

The addition of spin-polarized, continuous-wave (c.w.) positron beams to the 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) would provide a significant capability to the experimental nuclear physics program at Jefferson Lab. Based on bremsstrahlung and pair-production in a high-Z target, the positron source requires a 120 MeV spin-polarized c.w. electron beam of several milliamperes. While the beam dynamics of the high-current electron beam are tenable, sustaining this current for weeks of user operations requires an unprecedented charge lifetime from a high-polarization GaAs-based photocathode. A promising approach to exceed the kilocoulomb charge lifetime barrier is reducing the ion back-bombardment fluence at the photocathode. By increasing the laser size and managing the emittance growth with an adequate cathode/anode design, significantly enhanced charge lifetime may be achieved. Based upon a new simulation model that qualitatively explains the lifetime data previously measured at different spot sizes, we describe the practical implications on the parameter space available for a kilocoulomb-lifetime polarized photogun design.

This review paper describes the energy-upgraded CEBAF accelerator. This superconducting linac has achieved 12 GeV beam energy by adding 11 new high-performance cryomodules containing eighty-eight superconducting cavities that have operated CW at an average accelerating gradient of 20 MV/m. After reviewing the attributes and performance of the previous 6 GeV CEBAF accelerator, we discuss the upgraded CEBAF accelerator system in detail with particular attention paid to the new beam acceleration systems. In addition to doubling the acceleration in each linac, the upgrade included improving the beam recirculation magnets, adding more helium cooling capacity to allow the newly installed modules to run cold, adding a new experimental hall, and improving numerous other accelerator components. We review several of the techniques deployed to operate and analyze the accelerator performance, and document system operating experience and performance. In the final portion of the document, we present much of the current planning regarding projects to improve accelerator performance and enhance operating margins, and our plans for ensuring CEBAF operates reliably into the future. For the benefit of potential users of CEBAF, the performance and quality measures for beam delivered to each of the experimental halls is summarized in the appendix.

We present a scheme for the generation of a high polarization positron beam with continous wave (CW) bunch structure for the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Laboratory (JLab). The positrons are created in a high average power conversion target and collected by a CW capture linac and DC solenoid.

Nuclear physics experiments requiring spin polarized positron beams are being proposed at the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Laboratory. This workshop proceedings describes the framework for implementing polarized positron beams at CEBAF and highlights some of the main technical challenges. Specifically, a new polarized positron injector is needed, where the positron beam polarization is created from the bremsstrahlung of an intense continuous-wave (CW) spin polarized electron beam.

Since the early 1990s, the injector of the CEBAF accelerator at Jefferson Lab has relied on a normal-conducting RF graded-beta capture section to boost the kinetic energy of the electron beam from 100 / 130 keV to 600 keV for subsequent acceleration using a cryomodule housing two super-conducting 5-cell cavities similar to those used throughout the accelerator. To simplify the injector design and improve the beam quality, the normal-conducting RF capture section and the cryomodule will be replaced with a new single booster cryomodule employing a superconducting, 𝛽 = 0.6 , 2-cell-cavity capture section and a single, 𝛽 = 0.97 , 7-cell cavity. The Upgraded Injector Test Facility at Jefferson Lab is currently hosting the new cryomodule to evaluate its performance with beam before installation at CEBAF. While demonstrating satisfactory performance of the booster and good agreement with simulations, our beam test results also speak to limitations of accelerator operations in a noisy, thermally unregulated environment.

The Jefferson Lab KL experiment [1] will run at the Continuous Electron Beam Accelerator Facility with a much lower bunch repetition rate (7.80 MHz or 15.59 MHz) than nominally used (249.5 MHz or 499 MHz). While the proposed average current of 2.5 5.0 μA is relatively low compared to the maximum CEBAF current of approximately 180 μA, the corresponding bunch charge is atypically high for CEBAF injector operation. In this work, we investigated the evolution and transmission of low-rep-rate, high-bunchcharge (0.32 to 0.64 pC) beams through the CEBAF injector. Using the commercial software General Particle Tracer, we have simulated and analyzed the beam characteristics for both values of bunch charge. We performed these simulations with the existing injector using a 130 kV gun voltage. We have calculated and measured the transmission as a function of the photocathode laser spot size and pulse length. We report on the findings of these simulations and optimum parameters for operating the experiment. INTRODUCTION The KL experiment (a new nuclear physics experiment) at Jefferson Lab in Hall D requires time-of-flight measurements which in turn requires substantially lower bunch repetition rates in Continuous Electron Beam Accelerator Facility (CEBAF) than the nominal 249.5 MHz or 499 MHz. The momenta of KL particles will be measured using the time-of-flight between RF signal of CEBAF accelerator and start counters surrounding LH2 target. A schematic view of beamline is presented in Fig. 1. At 12 GeV an average current of 2.5 5.0 μA corresponds to 30 60 kW of beam power, which will converted by the CPS to illuminate the Be target. Table 1 summarizes the individual bunch charges corresponding to these beam requirements for the KL experiment. We are developing new operating parameters of the CEBAF injector for the KL experiment. This experiment requires relatively low rep rate but the bunch charge at the high end of what CEBAF delivers to achieve its goals. This paper describes the evolution and transmission of low-reprate, high-bunch-charge (0.32 to 0.64 pC) beams through the CEBAF injector. Using the computational software packages, we will describe designed beam size, the initial electron beam distribution, and analyze the beam characteristics for ∗ Work supported by U.S. DOE, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 † spokh003@odu.edu Figure 1: Schematic view of Hall D beamline on the way e → γ → KL. Electrons first hit the copper radiator inside the Compact Photon Source (CPS). Then photons illuminate the Be target, and finally, neutral kaons hit the LH2/LD2 cryogenic target. Beam goes from left to right [1]. Table 1: CEBAF Injector bunch currents and repetition rates for KL experiment [1]. Current Repetition SubharBunch Equivalent Rate monic of Charge 249.5 MHz (A) (MHz) 499 MHz (pC) current (A) 2.5 15.59 32nd 0.16 40 2.5 7.80 64th 0.32 80 5.0 15.59 32nd 0.32 80 5.0 7.80 64th 0.64 160 both values of bunch charge for 130 kV gun voltage. We characterize the transmission as a function of the photocathode laser spot size and pulse length. Finally, we describe measurement for two injector laser drive frequency modes : one with 500 MHz, and another with 250 MHz. BEAMLINE SETUP AND SIMULATION DETAILS Figure 2 shows the general layout of the CEBAF injector, showing the elements related to bunching, timing and focusing the beam. Our injector model for KL beam conditions focuses on the beam line between the gun and the captured solenoid S6 (MFA0I03) upstream of the Chopper 1 RF cavity and retains the pre-upgraded injector beam line downstream from S6 (MFA0I03) onward [2]. The beam originates on a 130 keV photocathode. Then the beam transits through the elements of a 30 m beamline which consist of 1 pre-buncher cavity, 1 buncher cavity, 5-cell capture section, 1/4 cryomodule booster (2 Cornell-style 5-cell cavities), focusing solenoids, and quadrupoles. We performed the simulations using the commercial software General Particle Tracer (GPT) [3]. For the particle distribution at cathode in simulation, the beam is assumed to have a Gaussian distribution in t, x, y 13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW Publishing ISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOTK052 MOPOTK052 C on te nt fr om th is w or k m ay be us ed un de rt he te rm s of th e C C B Y 4. 0 lic en ce (© 20 22 ). A ny di st ri bu tio n of th is w or k m us tm ai nt ai n at tr ib ut io n to th e au th or (s ), tit le of th e w or k, pu bl is he r, an d D O I 580 MC5: Beam Dynamics and EM Fields D01: Beam Optics Lattices, Correction Schemes, Transport North LJNAC East ARC Compact Photon Source \ Tagger Area Pair Speclrometer

The 2020 update of the European Strategy for Particle Physics emphasised the importance of an intensified and well-coordinated programme of accelerator R&D, supporting the design and delivery of future particle accelerators in a timely, affordable and sustainable way. This report sets out a roadmap for European accelerator R&D for the next five to ten years, covering five topical areas identified in the Strategy update. The R&D objectives include: improvement of the performance and cost-performance of magnet and radio-frequency acceleration systems; investigations of the potential of laser / plasma acceleration and energy-recovery linac techniques; and development of new concepts for muon beams and muon colliders. The goal of the roadmap is to document the collective view of the field on the next steps for the R&D programme, and to provide the evidence base to support subsequent decisions on prioritisation, resourcing and implementation.

In this work, we investigated the evolution in bunch length of beams through the CEBAF injector for 8?770 fC charge per bunch. Using the software General Particle Tracer (GPT), we have simulated beams through the beamline of the CEBAF injector to predict bunch lengths at the location of a beam chopper for comparison with measurements and to validate the model. We performed these simulations with the existing injector using a 130 kV gun voltage. The mea- surements have been done using chopper phase scanning technique for two injector laser drive frequencies 499 MHz and 249.5 MHz. Acknowledgement 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.

The effects of high beam currents and different types of electron sources on the emittance of the beam at the 3.5 MeV beamline of the Mainzer Microtron MAMI were observed. A thermionic BaO source and a GaAs-based photo-source that allows spin polarization were used. In order to measure the beam size, a new type of wire scanner was utilized. The results show maximum normalized emittance values in the order of a few hundred nm rad for both sources, which lies distinctly within the acceptance of the higher energy stages of the accelerator [1]. MAINZER MICROTRON The MAMI accelerator consists of four consecutive racetrack microtrons and is able to provide continuous electron beam currents up to 100 μA at 1.5 GeV. The beam current is limited by the available RF power of the third microtron (RTM3). Using pulsed beam modes with a low duty cycle of 10−4 can circumvent this principal limitation. A main purpose of our investigations was to measure a possible increase of the beam emittance since much higher currents are planned for the new MESA accelerator in Mainz [2]. All measurements were done at a kinetic energy of 3.5 MeV at which the beam is already relativistic and therefore has passed the regions where emittance blow-up due to space charge forces may have occurred.

Recent developments in the field of high intensity electron beams in the regime below 10 MeV, e.g. energy recovery linacs or magnetized high energy electron coolers, have led to special demands on the beam diagnostics. Since commonly used diagnostic tools like synchrotron radiation and scintillation screens are ineffective or not able to withstand the beam power without being damaged, new methods are needed. Hence, a beam profile measurement system based on beam induced fluorescence (BIF) was built. This quite simple system images the light generated by the interaction of the beam with the residual gas onto a PMT. A more elaborated system, the Thomson Laser Scanner (TLS) — the non-relativistic version of the Laser Wire Scanner — is proposed as a method for non-invasive measurement of all phase space components, especially in the injector and merger parts of an ERL. Both methods are implemented in a 100 keV photo gun.

One of the challenges in a relativistic electron cooler is the powering of high voltage exceeding 2 MV and the powering of HV-solenoids, which sit on different high potentials within a high voltage vessel and need a floating power supply. In this report we present the turbo generator “Green Energy Turbine” (GET), an assembly of a turbine and a generator, as a possible candidate for powering e.g. the HVsolenoids and give an overview over the future road map.