Outline of the proposed JLAMP VUV/soft X-ray FEL and the challenges for the photon beamlines and optics

Transcription

1 Outline of the proposed JLAMP VUV/soft X-ray FEL and the challenges for the photon beamlines and optics J. Michael Klopf Jefferson Lab - Free Electron Laser Division Workshop on Future Light Sources SLAC National Accelerator Laboratory March 1-5, 2010

2 Outline Layout and parameters of the existing IR and UV FEL at JLab Proposed machine design and parameters for the JLAMP VUV/soft X-ray FEL Requirements on the photon beamlines and optics for the users and for FEL R&D Challenges for the optical beamline design damage threshold due to extremely high peak and average brightness trade-offs between the pulsewidth and bandwidth of the photon pulses need for and requirements on the monochromator systems separation and delay control for coaxial high energy and low energy photon sources (e.g. pump-probe experiments) Preliminary conceptual beamline design Questions and comments

3 Jefferson Lab Jefferson Lab Newport News, VA

4 Existing Jefferson Lab FEL and THz Source 150 MeV, 135 pc, 75 MHz ERL driving IR or UV FEL oscillator IR: 950 nm 7 µm UV: 4 ev (fundamental) 12 ev (3 rd harmonic) THz (CSR) DC Gun UV FEL IR FEL high power THz (CSR) collected from final bunching chicane dipole primarily an ONR development project limited user ops Dump very high average power 14 kw IR FEL 100 W (40 W lab) THz ultrashort pulses (100 fs FWHM)

5 Proposed JLAMP VUV/soft X-ray FEL Planned design to Operates from 7 ev table-top laser energy to 500 ev with harmonics 3 to 6 orders greater average brightness than FLASH Scientific case focused on DOE-BES Grand Challenges from world-class committee materials science ARPES (angle resolved photoelectron spectroscopy) AMO (Atomic, Molecular, Optical Science) imaging Secondary goals address BES R&D priorities (injector, srf, collective effects, seed lasers) for next generation hard X-ray photon facility < $100M and fast schedule since it builds on existing FEL infrastructure

6 JLAMP in the Light Source Landscape JLAMP Ultimate LS JLAMP FLASH LCLS JLAMP harmonics JLAMP harmonics LCLS JLAMP delivers important parameter space un-addressed in hard X-ray proposals, with chemical selectivity to measure atomic structure at the nanoscale, measurement of dynamics on the femto to attosecond timescale of electron motion, and imaging

7 Proposed JLAMP Upgrade Concept Upgrade three cryomodules to new C100 design with >100 MeV/module Add two recirculations up in energy and two down in energy recovery Maintain IR/UV FEL capabilities

8 Proposed JLAMP Upgrade Concept 600 MeV, 2 pass acceleration 200 pc, 1 mm mrad injector Up to 4.68 MHz CW repetition rate Recirculation and energy recovery 10 nm fundamental output, 10 nm/n harmonic 50 fs-1000 fs near transform-limited pulses Baseline: seeded amplifier oper ation using HHG HGHG amplifier + oscillator capability THz Wiggler for synchronized pump/probe

9 Technical Specs for JLAMP and other Light Sources NGLS Photon Wavelengt Energy h (nm) (kev) Pulse duration (FWHM) (fs) FEL beamline Items in blue are estimates not from official project sources Items in italics are measured on operational facilities Average Brightness (CW) Average Brightness (bunch trains) Photons per pulse coherent Bandwidth repetition Peak rate (Hz) Brightness LCLS x x x x x x x x x10-3 JLAMP x x FLASH x x x x XFEL ~10-3 SPring ~10-3 XFEL ~ ~10-4 NLS SwissFEL ~

10 Competing Light Source Requirements Some users want ultrashort pulses (time resolved) Some users want minimum bandwidth (spectroscopy) Some experiments require high repetition rate (pump-probe, spectroscopy) Some experiments require low repetition rate or single-shot (extreme conditions, phase changes, microscopy, holography) Some users want what they cannot have ( E t < ħ/2) Also want to test scalability/feasibility for multipass ERL driven FEL Need to provide large range of achievable FEL parameters

11 Challenges for Photon Beamlines and Optics Damage threshold average power (thermal management) peak power (ablation) Focusing optics must accommodate variable source point (variable curvature) Control and delivery of required time-bandwidth product ( E t) to the user endstation Monochromator must operate over very wide spectral band must be characterized for all polarizations double-mono necessary for low photon energy Must preserve coherence of pulses to endstation Separation of VUV/X-ray and FIR beams (FLASH design)

12 Damage Threshold for Beamline Optics Numbers to Watch 300 ev 900 ev energy/pulse: 60 µj 42 µj σ : 7.9 µrad 3.5 µrad area: 0.98 mm mm 2 fluence: 0.06 mj/mm mj/mm 2 power density: 61 W/mm W/mm 2 * LN 2 cooling may be needed * We have experience with cryo-cooled mirrors which enabled the 14 kw operation of the JLab IR FEL numbers from WIFEL proposal courtesy of Ruben Reininger (BNL)

13 Damage Threshold for Beamline Optics Ablation: fluence/pulse damage to Au film from a single pulse of the FLASH FEL (λ = 98 nm, 40 fs) Peak power density ~ 100 TW/cm 2 Material Threshold Fluence Carbon: 0.6 mj/mm 2 Silicon: 0.3 mj/mm 2 Gold: 0.4 mj/mm 2 *sample threshold also critical* courtesy of Ruben Reininger (BNL) and FLASH

14 Focusing Optics The source point moves along the length of the wiggler as a function of e - beam energy and the γ wavelength variable curvature variable focal length KB mirror pair simple, control curvature in each plane separately Is the wavefront preserved? critical for minimum pulsewidth could be important in extreme pressure experiments Other mirror designs (Pros/Cons) Toroidal Ellipsoidal

15 Control of Bandwidth/Pulsewidth Need to have control of the bandwidth delivered to endstation (monochromator) Reducing bandwidth increases pulsewidth (transform limit) Users need to understand bandwidth pulsewidth constraints Need to have photon diagnostics to characterize bandwidth and pulsewidth parameters * Will photon diagnostics be supported??? *

16 FEL bandwidth will often be greater than the experimental requirements Monochromators are the primary means for controlling bandwidth For high γ energy: σ and λ are small small k short pulse For low γ energy: photon beam needs to be cleaned of spontaneous and background emission double mono can clean beam and preserve pulsewidth Monochromators for FELs σ RMS source limited resolution: RMS illuminated lines: Each line delays λ/c: Diffraction limit: σ r k = l/mm σ λ = sinα r k λ E σ hc E = = sinα 2 λ r k λ σ ' r k N = sinα λ σ ' r k λ t = N = c sinα c σ σ ' E t = h λ λ σ σ ' = E t = 4π 2 courtesy of Ruben Reininger (BNL) α

17 Double Monochromator Design G : grating M : mirror Double mono functions like a prism pair in a mode-locked ultrashort pulse laser Bandwidth controlled by slit width

18 JLAMP Conceptual Beamline Design source point K-B mirror pair diffraction gratings mirror variable slit focusing mirror sample focus

19 Other Beamline Challenges Will full coherence be preserved to the sample through all of the beamline optics? JLAMP to also include FIR undulator downstream of VUV/soft X-ray wiggler (pump-probe studies) coaxial beams to be separated using a mirror with a hole to pass low divergence high energy beam and reflect low energy FIR beam (FLASH) FIR and X-ray pulse delay scheme at JLAMP to utilize e - bunch pairs (FIR pulses lead X-ray pulses) and FIR delay line (unlike FLASH) WHAT HAVE I MISSED???

20 Conclusions FELs can enable time-resolved measurements on a femtosecond or better time scale combined with X-ray measurement techniques The laws of Physics still hold: E t < ħ/2 Monochromators will need to operate over a very wide spectral range, and must provide a range of spectral bandwidth Double monochromator is likely necessary for low γ energy to clean the beam and preserve the pulsewidth Average and peak power density must be kept well below damage threshold for beamline optics and sample!!! (gas attenuator) Will photon diagnostics be supported??? WHAT HAVE I MISSED???

21 Acknowledgements Ruben Reininger (BNL) Peter Johnson (BNL) Hongbo Yang (BNL) Jonathan Rameau (BNL) Michael Gensch (FLASH/DESY) Kevin Morris (CAMD) FEL Team (JLab) This work supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the Air Force Research Laboratory, The US Army Night Vision Lab, and by DOE under contract DE-AC05-060R23177.

22 The Jefferson Lab FEL Team April 24, 2009 This work supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the DOE Air Force Research Laboratory, The US Army Night Vision Lab, and by DOE under contract DE-AC05-060R23177.