WG2 on ERL light sources CHESS & LEPP

Transcription

1 Charge: WG2 on ERL light sources Address and try to answer a list of critical questions for ERL light sources. Session leaders can approach each question by means of (a) (Very) short presentations (b) Open discussions (c) Panel discussions (d) Distribution of problems to be solved, etc. During the course of the workshop, the session leaders will formulate an answer to their question. This might require work and meetings of experts outside the workshop sessions. Furthermore extra discussion time can be scheduled at the end of the second day. Some questions might require computer simulations, and (windos/linux) access is available in the meeting room.

2 2 Question to be addressed (Tuesday) () Overview of critical ERL issues (2) Project overviews (a) (b) (c) (d) JLAB Cornell Daresbury KEK / JAEA (3) Particle transport (a) (b) (c) (d) Are there optimal schemes to minimize bunch length and energy spread? What is the optimal injector / linac merger design? What should start to end simulations include? What are beam abort strategies and beam loss tolerances? (4) What are diagnostic needs?

3 courtesy Lia Merminga 3 An existing ERL Promise: Reality: High average laser power (~ 00 kw) High overall system efficiency Reduced beam dump activation JLab 0kW IR FEL and kw UV FEL JAERI 2.3kW IR FEL Novosibirsk NRF 80MHz recuperator Superconducting rf linac Injector Beam dump IR wiggler UV wiggler

4 4 5GeV ERL ERL Upgrade Layout for CESR The split linac can be useful for bunch compression, bunch linearization, and bunch flattening in phase space.

5 5 Energy Recovery Linac Prototype Daresbury

6 6 Split Linac Bunch Flattening Nonlinear time of flight 2 nd order time of flight th order time of flight

7 7 Split Linac Bunch Linerizing Nonlinear time of flight 2 nd order time of flight Subsequent bunch compression is linearlized and relatively simple

8 8 Second Order Time of flight T566(m) 0 Δϕ = 5 RF 0.44% energy spread δ (0 3 ) Center of arc (5GeV) ρ(τ ) σ τ = 85μm Δτ 30μm FWHM = After ERL L(m) δ (0 3 ) τ (mm) τ (mm) τ (mm) The energy spread is too large

9 9 Undercompression Peak at 6 0 RF phase Overfocused peaks Such peaked distributions lead to strong CSR effects δ With second order optimization: 9 0 RF phase and undercompression Center of arc (5GeV) 3 3 (0 ) δ (0 ) 3 σ δ = σ τ = 27μm 0 Δϕ = 9 After ERL (0MeV) τ (mm) τ (mm) τ (mm)

10 0 CSR microbunching picosecond Micro-bunching: Longitudinal Bunch Profile Measurements at TTF

11 Emittance with CSR and nonlinear optics Horizontal emittance with coherent synchrotron radiation ε x = x.8 ε (0) Result: After suitable nonlinear bunch length manipulation, the emittance growth can be controlled in all undulators. m

12 2 Question to be addressed (Thursday) (5) What are vacuum and aperture needs for ERL light sources? (6) What are advantages and limits of multi-turn ERLs? (7) RF issues (a) (b) What is the maximum Q L possible, and what stabilization is needed? What are optimal cavity parameters? (8) What are good beam stabilization strategies and their limits? (9) What are undulator issues that are specific to ERLs? (0) What issues are critical for all proposed ERLs? Reports (drafts) for each question should be finished by Friday morning!

13 3 Ion accumulation in the beam potential Ion are quickly produced due to high beam density Ion accumulate in the beam potential. Since the beam is very narrow, ions produce an extremely steep potential they have to be eliminated. Conventional ion clearing techniques can most likely not be used: ) Long clearing gaps have transient RF effects in the ERL. 2) Short clearing gaps have transient effects in injector and gun. DC fields of about 50kV/m have to be applied to appropriate places of the along the accelerator, without disturbing the electron beam.

14 4 Current limit due to BBU Beam breakup instability (BBU) in one dimension (originally a major concern for current limit) Vertical Offset Horizontal HOM Horizontal Kick X/Y Coupling 320 identical cavities Current limited to 25mA Randomized frequencies with rms of 0MHz Current limited to 500mA Polarized Cavities and x to y coupling Current limited to 2000mA >> required 00mA Now the current limited by a technical choice: Cooling capacity of the HOM Dampers

15 5 cavity field field [arb. units] High loaded Q cavity control Lorentz-Force Add Microphonics detuning:! 3 Δf Hz = K E bandwidth 2 = many bandwidths! Frequency [GHz] 000 (Hz) frequency.3 [GHz].3 GHz [Hz] [Hz] 0 Run cavity at highest possible loaded Q for Energy recovery linac mode, i.e. without beam loading But: The higher the loaded Q, the maller the cavity field [MV/m] accelerating field [MV/m] phase [deg] phase [deg] Without σ A /A feedback: time [sec] time [sec] σ ϕ 0.02 deg Vibration time [sec] Mode

16 6 Stability issues (Rings)

17 7 Goals Short-Term Goals Long-Term Goals Modes: (A) Flux (B) High- Coherence (C) Short- Pulse (D) Ultra High- Coherence (E) Ultra Short- Pulse Units Energy GeV Current ma Bunch charge pc Repetition rate MHz Norm. emittance mm mrad Geom. emittance pm Rms bunch length fs Relative energy spread Beam power MW Beam loss < < < < < micro A

18 8 Non Light Source ERLs Electron Cooling for RHIC ions and protons CLIC-like drive beam ERL Electron Ion Collider A low emittance RF source Could save the electron damping ring in a LC