Generation and Characterization of Magnetized Bunched Electron Beam
Generation and Characterization of Magnetized Bunched Electron Beam from DC High Voltage Photogun for JLEIC Cooler R. Suleiman and M. Poelker September 19, 2017 Motivation Jefferson Lab Electron Ion Collider (JLEIC) bunched magnetized electron cooler is part of Collider Ring and aims to counteract emittance degradation induced by intra-beam scattering, to maintain ion beam emittance during collisions and extend luminosity lifetime Magnetized Cooling Ion beam cooling in presence of magnetic field is much more efficient than cooling in a drift (no magnetic field): Ø Electron beam helical motion in strong magnetic field increases electron-ion interaction time, thereby significantly improving cooling efficiency Ø Electron-ion collisions that occur over many cyclotron oscillations and at distances larger than cyclotron radius are insensitive to electrons transverse velocity Ø Cooling rates are determined by electron longitudinal energy spread rather than electron beam transverse emittance as transverse motion of electrons is quenched by magnetic field Ø Magnetic field suppresses electron-ion recombination Photocathode Preparation Chamber Gun Solenoid Upon exit of Cathode Solenoid Electrons born in strong uniform Bz Upon entering Cooling Solenoid re= 0. 7 mm Bcool = 1 T Beam Dump Shield Tube Bunch length 60 ps (2 cm) Repetition rate 43. 3 MHz Bunch charge 3. 2 n. C Average current 140 m. A Transverse normalized emittance <19 microns Slit Viewer Screen Ø Use slit and viewscreens to measure mechanical angular momentum: 3. 14 mm 500 G Magnetization Measurements 0, 4 Magnetic Field at 400 A 1511 G at photocathode 0, 2 σ (V 1), mm σ (V 2), mm σ (V 3), mm 6 4 2 0 0, 1 0 200 Beam Size at Viewer 1 0, 0 z, m 1, 5 2, 0 • Using spare CEBAF Dogleg magnet power supply (500 A, 80 V) • Learned that gun solenoid can influence field emission • First trials with gun at high voltage and solenoid ON resulted in new field emission and vacuum activity • Procedure to energize solenoid without exciting new field emitters 3, 0 2, 5 2, 0 1, 5 1, 0 0, 5 0, 0 200 400 600 800 1000 Bz at Cathode, G 1200 600 800 1000 B@cathode, Gauss 1200 1400 1600 Slit 1 -V 2 40 Slit 1 -V 3 Slit 2 -V 3 25 10 -5 -20 -35 -50 0 400 Rotation Angle (measured) Viewer 1 Measured Size Rotation Angle, degree 1, 0 Beam Size (rms), mm 0, 5 ASTRA Simulation Summary & Plans Mag Beam Size (rms) 8 Beam Size (rms), mm Beamlet observed on downstream viewer 0 G at photocathode Bz, T Viewer Screens = 36 µm Gun Solenoid 0, 0 Gun HV Chamber Beamline Solenoid field at cathode (Bz) 0, 3 Experimental Overview Electron beam suffers an azimuthal kick at entrance of cooling solenoid. But this kick can be cancelled by an earlier kick at exit of photogun. That is purpose of cathode solenoid 0 200 400 600 800 1000 B@cathode, Gauss • Measured beam sizes and rotation angles • Rotation angles are influenced by Larmor oscillation in gun solenoid • Making good progress in modeling our apparatus and beam magnetization Acknowledgement: This work is supported by the Department of Energy, Laboratory Directed Research and Development funding, under contract DE-AC 05 -06 OR 23177 • K 2 Cs. Sb Photocathode Preparation Chamber, Gun HV Chamber, Gun Solenoid and Beamline are all operational • Photogun operates reliably at 300 k. V • Cathode solenoid can trigger field emission but we have learned how to prevent this • Have successfully magnetized electron beam and measured rotation angle • Delivered 1. 5 m. A DC magnetized beam • Preparing to install a mode-locked drive laser, to generate m. A magnetized beam with RF structure • Build and install TE 011 cavity to measure beam magnetization • Switch to 32 m. A 225 k. V HV power supply Thanks to: P. Adderley, J. Benesch, B. Bullard, J. Grames, J. Guo, F. Hannon, J. Hansknecht, C. Hernandez-Garcia, R. Kazimi, G. Krafft, M. A. Mamun, Y. Wang, S. Wijiethunga, J. Yoskovitz, S. Zhang
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