Simulation Study of the Magnetized Electron Beam Sajini

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Simulation Study of the Magnetized Electron Beam Sajini A. K. Wijethunga 1, J. R.

Simulation Study of the Magnetized Electron Beam Sajini A. K. Wijethunga 1, J. R. Delayen 1, G. A. Krafft 2, F. E. Hannon 2, R. Suleiman 2, M. Poelker 2, J. Benesch 2, M. A. Mamun 2 1 Department of Physics, Old Dominion University, Norfolk, Virginia 23529, USA 2 Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA Introduction Electron cooling of ion beam plays an important role in electron ion colliders to obtain the required high luminosity. This cooling can be enhanced using a magnetized electron beam, where the cooling process occurs inside a solenoid field. This presentation provides a comparison between the beambased magnetization measurements conducted from the magnetized electron beam generated from a DC high voltage photo-gun and simulations from ASTRA and GPT software, as a function of beam size and rotation angle variations along the beamline, for different solenoid currents and ASTRA simulation studies on the magnetic field map dependence on mismatch oscillations. Modelling Beam Line 1 D Electric and Magnetic Field maps Cathode Solenoid Diagnostic Cross 3 (YAG Screen) Diagnostic Cross 1 (Slit + YAG Screen) Cathode Green Anode Laser K 2 Cs. Sb Photocathode Diagnostic Cross 2 (Slit + YAG Screen) Injector Focusing Solenoid • Beam line is modeled using ASTRA (A Space Charge Tracking Algorithm) and GPT (General Particle Tracer) software separately. • ASTRA used 1 D electric field map and GPT used 2 D electric field map. • Magnetic field map is distorted by the steel covers of the focusing solenoids. • MATLAB is used to do the post-processing and calculate the beam sizes and rotation angles. 4 m Beam line is mainly consists of a K 2 Cs. Sb photocathode preparation chamber, DC highvoltage photo-gun operating at 300 k. V, cathode solenoid magnet with maximum 400 A, two YAG screen-slit combinations at 0. 5 m and 2. 0 m, a YAG-screen at 3. 75 m, three focusing solenoids, correctors, harp, vacuum pump and dump. Beam Profile Measurements: Beam at 0 A on 1 st Screen Max Bz at the cathode 0. 1511 T xy_rms, Gaussian 0. 301 mm t_rms, Uniform 24 ps Gun voltage 300 k. V x_off 0 mm y_off 0. 5 mm Emittance 0. 56 mm mrad/ mm ASTRA simulation results ASTRA: Beam rotation ASTRA: Beam at 0 A on 1 st Screen Mismatch Oscillations Rotation angle variation of a diverging beam- 180 A Slit 1 -Viewer 2 Slit 1 -Viewer 3 Slit 2 -Viewer 3 ASTRA: Energy profile • Magnetic field is not uniform in z. Rotation angle variation of a converging and diverging beam – 100 A • Thus, no transverse equilibrium occurs and unbalanced forces inside the magnetic field cause the mismatch oscillations. • Larmor frequency increases with the B field. Measurements vs Simulations (ASTRA & GPT) ASTRA σ (V 1) σ (V 2) σ (V 1)_Sim GPT Beam Size vs Gun Solenoid Current on Two Viewers Simulation results massively depend on the field maps. Beam Size vs Gun Solenoid Current on Two Viewers σ (V 1) σ (V 2)_Sim σ (V 2) σ (V 1)_Sim ASTRA simulation results cont’d σ (V 2)_Sim Magnetic field map without including metal shielding near solenoids 16 16 14 14 1. 2 12 0. 8 6 1. 2 1 0. 8 0. 6 0. 4 0. 2 0 0 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 0 0. 2 0. 3 0. 4 ASTRA 0 20 40 60 80 100 120 140 160 180 200 I (A) 220 240 260 280 300 320 340 360 380 0. 5 0. 6 0. 7 0. 8 0. 9 -0. 5 0 0. 5 Slit 1 -v 2 _Sim Slit 1 -v 2 ASTRA Measured values 50 50 Rotation Angle (degrees) 60 40 30 20 10 0 0 50 100 150 200 -10 250 300 350 400 1. 5 1 I (A) • • • 400 500 Measured values 2 1. 5 1 0 0 0 100 200 300 400 500 0 100 200 300 I (A) Summary and Outlook 40 30 20 10 0 0 -20 2. 5 0. 5 Slit 1 -v 2 _Sim 50 100 150 200 250 -10 -20 2 2. 5 I (A) 60 1. 5 3 2 70 1 z (m) 300 k. V 0. 106 mm viewer 1 2. 5 400 Rotation Angle vs Gun Solenoid Current for slit 1 - viewer 2 combination Rotation Angle vs Gun Solenoid Current for slit 1 viewer 2 combination 70 0. 1 300 k. V 0. 106 mm viewer 1 I (A) Slit 1 -v 2 B (T) 0 6 2 40 0. 2 z (m) 4 20 0. 4 8 4 0 0. 6 x_rms (mm) 8 10 x_rms (mm) 10 σ_rms (mm) 12 Beam gets off axis quickly with the currents, should use correctors to bring it on axis. Magnetic field map including metal shielding near solenoids 1 Rotation Angle (degrees) • Simulation Parameters I (A) GPT and ASTRA shows same variations with the measurements. Gun solenoid magnetizes the beam but also focuses the beam. Rotation angle influenced by Larmor oscillations in the gun solenoid. Negative angles occurs due to the beam convergence. Other slit –viewer combinations showed the same pattern. 300 350 400 • Successfully simulated the magnetized beam using ASTRA and GPT software and they are in good agreement with the measurements. • Beam sizes and rotation angles oscillates rapidly due to the focusing and defocusing effects. • Mismatch oscillations occurred due to the non-uniform magnetic field map which results to unbalance the forces inside the magnetic field. • Convergence of the beam caused in negative rotation angle values. • Accuracy of the field maps greatly affect the simulation results. • 3 D field maps give more reliable results on simulations than 2 D or 1 D field maps. • Increase the bunch charge and continue simulations on space charge effect of the magnetized beam. • Simulate the emittance vs laser size for maximum gun solenoid current. Acknowledgement: This work is supported by the Department of Energy, Laboratory Directed Research and Development funding, under contract DE-AC 05 -06 OR 23177 [email protected] org