Scaled Models: Space-Charge Dominated Electron Storage Rings

Transcription

1 Scaled Models: Space-Charge Dominated Electron Storage Rings Rami A. Kishek Institute for Research in Electronics & Applied Physics University of Maryland, College Park, MD Research sponsored by US DOE & DoD ONR 1

2 Institute for Research in Electronics & Applied Physics University of Maryland (near Washington, DC) Research Focus: Interdisciplinary research in engineering and the physical sciences with emphasis on large and complex experiments. Faculty and students from Electrical & Computer Engineering, Physics and Materials Science. Specialties: Chaos and Nonlinear Dynamics Nanoscience and Engineering Beam Physics Microwaves and Electronics Space & Fusion Plasmas Materials Processing (using microwaves, plasmas, ion beams) 2

3 The Charged Particle Beam Group University of Maryland Electron Ring (UMER) Team: Patrick O Shea Martin Reiser Rami Kishek Irving Haber Renee Feldman Don Feldman Ralph Fiorito Henry Freund Terry F. Godlove Kevin Jensen Junior Scientists: Santiago Bernal Mark Walter Bryan Quinn Graduate: Gang Bai Kai Tian C Papadopoulos Diktys Stratakis Charles Tobin A. Shkvarunets Mike Holloway Dave Gillingham David Demske Nathan Moody Former: Yun Zou Jonathan Neumann Yupeng Cui Hui Li Yijie Huo John Harris 3

4 Maryland CPB Group: Projects Underway High-brightness, durable, photocathode development Advanced diagnostic development Self-consistent modeling and simulation Scaled experimental studies of collisionality and energy spread evolution for Heavy Ion Inertial Fusion Multi-disciplinary studies of breakdown and multipactoring in high-gradient metal and dielectric structures UMER: The University of Maryland Electron Ring 4

5 UMER: a testbed for space charge dynamics 1. Bright electron beams and space charge effects 2. The University of Maryland Electron Ring 3. Status update 4. Sample results and experiments 5. Conclusion 5

6 Ultra short wavelength Linac Coherent Light Source (Stanford) Interstate-280 Sand Hill Rd Goal: 1Å with pulses of a few fs 6

7 Requirements of an FEL beam 1. Bright electron beam intense space charge at the source 2. In ERLs the injection energy is lost, so injection at lower energies preferable space charge 3. Coherence for short wavelengths requires small emittance (ε n < γλ/4π) e.g. for LCLS, turns out ε n < 2 μm for λ = 1 nm 7

8 Dimensionless Space Charge Intensity Intensity Parameter: K χ = ka 2 2 o space charge force external focusing force 0 χ 1 2a Beam external focusing K a k 0 2 a ε + a 2 3 Space charge + emittance 8

9 Intensity Scalings Relativistic E-Beams Emittance Dominated λ D >> a Space-charge Dominated λ D << a Plasma Oscillations Curve ω P ω = 0 2χ Intensity Parameter (χ) Betatron Oscillations Curve ω 1 ω = χ 0 Beam Sources 9

10 Realistic pulse shapes are not clean Rectangular Pulse (thermionic) 100 ns Photoemission Drive Laser Pulse Parabolic Pulse (thermionic) 50 ns 2 ns 10

11 An X-Ray FEL is a complex Machine = Many possibilities for emittance growth! 1 km 7 MeV σ z 0.83 mm σ δ 0.2 % rf gun 150 MeV 250 MeV σ z 0.83 mm σ z 0.19 mm σ δ 0.10 % σ δ 1.8 % Linac-X L =0.6 m 4.54 GeV σ z mm σ δ 0.76 % GeV σ z mm σ δ 0.02 % Linac-0 L =6 m new new Linac-1 L =9 m Linac-2 L =330 m Linac-3 L =550 m...existing linac DL-1 L =12 m 21-1b 1b 21-1d 1d X BC-1 L =6 m 21-3b 24-6d BC-2 L =22 m 25-1a 30-8c undulator L =120 m DL-2 L =66 m SLAC linac tunnel FEL Hall P.Emma SLAC Two stages of chirped pulse bunch compression 11

12 Space Charge Raises Many Issues What is the ideal bunch shape? rectangular? ellipsoidal? How to model the source accurately? How will perturbations evolve? Can they be controlled? What is the time scale for irreversible mixing in beams? How soon do we have to perform emittance compensation? How to maintain a low emittance and prevent halo formation? 12

13 UMER: a testbed for space charge physics in bright beams 13

14 UMER Parameters Energy Energy Spread Current Range rms Emittance Range 10 kev 20 ev ma μm Circulation time 200 ns Pulse length ns Zero-Current Tune 7.6 Depressed Tune

15 Present UMER Operating Points Relativistic E-Beams Emittance Dominated UMER Range Space-charge Dominated Plasma Oscillations Curve ω P ω = 0 2χ Beams Circulated ma 7.2 ma ma 85 ma Intensity Parameter (χ) Betatron Oscillations Curve ω 1 ω = χ 0 Beam Sources 15

16 UMER Schematic The University of Maryland Electron Ring Injection/ matching section 10 kv Gun Extraction/ diagnostic section Aug m 16

17 UMER Magnets & Lattice 72 Quads (~ 7.8 G/cm) 32 cm 36 Dipoles (~ 15 G) 17

18 Commencement of Multi-Turn Operation (Work in Progress) 6 Turns Oct First Current Pulse indicating Multiple Turns 5/5/2005 (courtesy M. Walter) 18

19 Example Results and Experiments 19

20 Generating Perturbations with Lasers Electron Beam Beam Current Heated Photocathode Thermionic only, 100ns pulse Drive Laser Photoemission + Thermionic 5ns pulse Photoemission only (Cool cathode) 20

21 Drive Laser Setup Laser Mask Telescope Mirrors /filters BBO KTP UV (355nm) Laser Photon energy: 3.5 ev Work function: 2.7 ev Nd:YAG Laser 21

22 Experiment: Propagation of Perturbed Beam 20 ma thermal-emission beam current 20 ma photo-emission beam current Beginning End Y. Huo 22

23 Experimental Study of Beam Energy Spread Energy Analyzer Design Collimating Cylinder kV Retarding Mesh V Collector Measured Longitudinal Phase Space kev am 3 rd Generation: Res. < 1 ev Grounded Housing Y. Zou and Y. Cui 23

24 Aside: Anomalous Growth of Energy Spread -3 log ΔE ΔE f o kev 4 kev 5 kev IL log Ia o 24

25 Space charge converts density perturbation to an energy perturbation Current/A time/ns Initial Current vs time 5040 mean energy (ev)5160 Experiment Simulation (WARP) 5000 K. Tian time/ns Energy vs time 2-m downstream 25

26 Direct Electron Beam Modulation at Cathode using a Ti:Sap driver laser RF Gun : 5 MeV RF Tanks: 75 MeV RF Tanks : Induce Δγ/γ for time diagnostics To Wigglers Experiment Magnetic Chicane Long Wavelength Diagnostics J. Neumann Time Diagnostics Laser Pulse Shaping on sub ps time scale 1 2 Electron Beam Dynamics Laser structure preserved through linac THz Radiation Measurements Production of Photoemission-Modulated Beams in a Thermionic Electron Gun,.J.G. Neumann, J.R. Harris, B. Quinn, and P.G. O'Shea, Review of 26 Scientific Instruments, 76, (2005).

27 Beam Control System Software Quadrupoles Control Central Control Platform network Hui Li Dipoles Control network BPMs Control network Steering Module Skew Correction Module Matching Module Tomography 27 Module

28 Low Energy (10 kv) Optical Transition Radiation Images Ideal for exploring the fast time structure of low energy beams in injector 8.5 nc 3.8nC 1.6 nc Fiorito & Feldman 0.12 nc 28

29 Self-Consistent Gun Simulations Current at iz = 12 Current at iz = ^ V Current vs. time for different grid voltages 2. 10^-4 (~ 0.6 mm from the cathode) -30V time (s) 10^-9 Current at iz = V time (s) 10^ All i Current at iz = ^ V 10^-4 1. WARP Simulations Irving Haber time (s) 10^ ^-9

30 Conclusion Brighter electron beams can result in smaller, less expensive FELs UMER is a unique, well-diagnosed and flexible testbed for experimenting with space charge-dominated beam dynamics at reasonable time scales UMER can produce benchmarks for space-charge codes Collaborations welcome! Website: Publications: 30

31 Virtual Cathode Movie 31