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Linac Coherent Light Source Update

Linac Coherent Light Source Update. John N. Galayda LCLS Project Manager Basic Energy Sciences Advisory Committee Meeting 2-3 August 2001. R&D progress Gun Bunch compression Undulator X-ray optics FEL experiments Near-term R&D goals Determine baseline gun performance

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Linac Coherent Light Source Update

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  1. Linac Coherent Light Source Update John N. Galayda LCLS Project Manager Basic Energy Sciences Advisory Committee Meeting 2-3 August 2001

  2. R&D progress • Gun • Bunch compression • Undulator • X-ray optics • FEL experiments • Near-term R&D goals • Determine baseline gun performance • Improve understanding of coherent synchrotron radiation effects • Sub-Picosecond Photon Source (SPPS)

  3. 1977-1990 National Synchrotron Light Source, Brookhaven National Lab 1990-2001 Advanced Photon Source, Argonne National Lab

  4. LINAC COHERENT LIGHT SOURCE I-280 Sand Hill Rd

  5. Performance Characteristics of the LCLS Peak and time averaged brightness of the LCLS and other facilities operating or under construction ~ TESLA Performance

  6. Self-Amplified Spontaneous Emission Electrons are bunched under the influence of the light that they radiate. The bunch dimensions are characteristic of the wavelength of the light. Excerpted from the TESLA Technical Design Report, released March 2001

  7. At entrance to the undulator Exponential gain regime Saturation(maximum bunching) Excerpted from the TESLA Technical Design Report, released March 2001

  8. R&D progress – Gun • BNL Accelerator Test Facility • Measurement of 0.8 mm-mrad emittance with 0.5 nC of charge • Such high performance could make shorter LCLS pulses possible • Details to be published in NIM-A, 2001 FEL Conference Proceedings

  9. R&D progress – Gun • SLAC gun test facility • Comparison of computed and measured emittances • Agreement is good for configurations tested thus far • Facility upgrades planned to study configurations with lower emittance ge, mm-mrad LCLS Specification Charge, picocoulombs

  10. Producing short bunches At low energy, space charge repulsion degrades the beam properties Accelerate the bunch, then compress it. 250 MeV z  0.19 mm   1.8 % 4.54 GeV z  0.022 mm   0.76 % 14.35 GeV z  0.022 mm   0.02 % 7 MeV z  0.83 mm   0.2 % 150 MeV z  0.83 mm   0.10 % Linac-X L0.6 m rf=180 RF gun Linac-1 L9 m rf -38° Linac-2 L330 m rf -43° Linac-3 L550 m rf -10° new Linac-0 L6 m undulator L120 m 21-1b 21-1d 21-3b 24-6d 25-1a 30-8c X ...existing linac BC-1 L6 m R56 -36 mm BC-2 L24 m R56 -22 mm DL-1 L12 m R56 0 DL-2 L66 m R56 = 0 SLAC linac tunnel undulator hall

  11. DE/E DE/E DE/E Over-compression Under-compression 2sz0 z z z 2sz V = V0sin(wt) Dz = R56DE/E RF Accelerating Voltage Path Length-Energy Dependent Beamline

  12. Coherent Synchrotron Radiation (CSR) sz Coherent radiation for: lr >> sz lr A |AB| B e– R <<1 ...from Derbenev, et. al. Free space radiation from bunch tail at pointAovertakes bunch head, a distancesahead of the source, at the pointBwhich satisfies... s = arc(AB) – |AB| = R– 2Rsin(/2)  R 3/24 and fors = sz(rms bunch length) the overtaking distance is... L0  |AB|  (24szR2)1/3, (LCLS: L0 ~ 1 m)

  13. CSR Effects  Bunch Energy Gradient Charge distribution sz TAIL DE/E HEAD (mean loss) ~CSR wakefield z

  14. CSR Effects  Emittance Growth Energy loss in bends causes transverse position spread after bends x-emittance growth Radiation in bends s DE/E = 0 DE/E < 0

  15. minimum compression Elegant model • R&D Progress – Coherent Synchrotron Radiation • CSR sets a lower limit on LCLS as a laser • LCLS could produce ~50 fsec pulses of spontaneous radiation • New ANL model fits latest data – is the model accurate? • LCLS bunch compression can be retuned to accommodate energy spread [%] rms bunch length [ps] emittance [mm-mrad] Q 0.3 nC M. Borland, PRST-AB v.4, 074201(2001) Borland, Braun, Doebert, Groening, & Kabel, CERN/PS 2001-027(AE) Courtesy M. Borland, J. Lewellen, ANL

  16. R&D Progress – Prototype Undulator • Titanium strongback mounted in eccentric cam movers • Magnet material 100% delivered • Poles >90% delivered • Assembly underway

  17. Helmholtz Coil – magnet block measurement Translation stages for undulator segment Poletip alignment fixture Magnet block clamping fixtures

  18. Planned beam diagnostics in undulator include pop-in C(111) screen To extract and observe x-ray beam, and its superposition on e-beam

  19. R&D Progress – Undulator diagnostics • P. Krejcik, W. K. Lee, E. Gluskin • Exposure of diamond wafer to electron beam in FFTB- • Same electric fields as in LCLS • No mechanical damage to diamond • Tests of crystal structure planned Before After

  20. R&D Progress – X-ray optics • LLNL tests of damage to silicon crystal • Exposure to high- power laser with similar energy deposition • Threshold for melting 0.16 J/cm2, as predicted in model • Fabrication/test of refractive Fresnel lens • Made of aluminum instead of carbon • Machined with a diamond point • Measurements from SPEAR presently under analysis

  21. Warm Dense Matter Experiment 250 mm aperture Back-scatter x-ray spectrometer Incident Beam Monitors Laser FEL Beam Spectrometer 100 mm thick sample Outgoing Beam Monitor Focusing Optic 50-100 mm aperture Imaging detector Variable beam attenuator Sample Tank PPS beam stops Optics Tank WDM Shielded Room 13 m

  22. R&D Progress – FEL physics • More complete analysis of HGHG • A. Doyuran, et al. PRL vol. 86, Issue 26, pp. 5902-5905, June 25, 2001 • LEUTL experiments ongoing • Milton, et al. Science vol. 292, Issue 5524, 2037-2041, June 15, 2001 • VISA experiment saturation • To be published in proceedings of 2001 FEL conference Data from BNL/ANL High-Gain Harmonic Generation(HGHG) Experiment

  23. LEUTL Gain Curve @ 530 nm on March 10, 2001 107 106 105 104 Radiated Energy (a.u.) 103 October,2000 102 101 100 10 25 5 20 15 0 Distance Traversed in Undulator (m)

  24. 16 March 2001 Visible to Infrared SASE Amplifier BNL-LLNL-SLAC-UCLA VISA Pulse Energy vs. Position Wavelength 830 nm Onset of Saturation Data Points taken along VISA Undulator Wavelength 830nm RMS Bunch Length: 900 fs Average Charge: 170 pC Peak Current: ~200 A Measured Projected Emittance: 1.7 mm mrad Energy Spread: 7×10-4 Gain Length 18.5 cm Equivalent Spontaneous Energy: 5 pJ Peak SASE Energy: 10 mJ Total Gain: 2×106 Pop-In Diagnostics Enclosure for 4-m long VISA undulator Direction of Electron Beam Preliminary recent results (unpublished) from VISA showing large gain (2 106) in SASE FEL radiation and evidence of saturation at 830 nm.

  25. Near-term R&D goals • Gun R&D • Thorough investigation of gun operation at LCLS parameters • Laser upgrade • Linac energy upgrade • Experiment/model comparison at 1 mm-mrad emittance, 0.5-1 nC • Bunch compression, coherent synchrotron radiation • Install a bunch compressor in the SLAC linac • Continue start-to-end modeling

  26. Bunch compression studies with SLAC linac in 2003 • Compatible with PEP-II injection • Capable of producing 80 fsec electron bunches • Goal: first studies in 1/2003, 1 year of tests • pump/probe techniques • Accelerator physics opportunities to study wake fields • Of great importance to LCLS • Short bunches are ideal for advanced accelerator R&D; Strong SLAC support

  27. DE/E z LCLS – X-ray Laser Physics The “sixth” experiment – Produce < 230 fsec pulses of SASE radiation LCLS will be used to explore means of producing ultra short bunches (< 50 fs). Alternative techniques will be investigated: • Stronger compression of the electron bunch • No new hardware is required • Photon bunch compression or slicing • Principle:spread the electron and photon pulses in energy; recombine optically or select a slice in frequency • Seeding the FEL with a slice of the photon pulse • Principle: select slice in frequency, then use it to seed the FEL

  28. Two-Stage Chirped-Beam SASE-FEL for High Power Femtosecond X-Ray Pulse Generation C. Schroeder*, J. Arthur^, P. Emma^, S. Reiche*, and C. Pellegrini* ^ Stanford Linear Accelerator Center *UCLA Strong possibility for shorter-pulse operation

  29. DEFW/E = 1.0% Energy Energy 1.010-4 time time DtFW = 230 fsec DtFW < 10 fsec UCLA Si monochromator (T = 40%) x-ray pulse time time e- 30 m 52 m 43 m SASE gain (Psat/103) SASE Saturation (23 GW) Two-stage undulator for shorter pulse Mitigates e- energy jitter and undulator wakes Also a DESY scheme which emphasizes line-width reduction (B. Faatz)

  30. LCLS Construction • FY2003: $6M for project engineering and design, $3M for R&D • Prepare bid packages • FY2004: Start of Construction • Injector construction and installation • Bunch compressor construction • Start construction of near hall • Undulator procurement • FY2005: • Injector commissioning • Bunch compressor installation • Start construction of far hall • Undulator, experiment construction • FY2006: Installation • Linac commissioning • Undulator and experiment installation • LCLS commissioning

  31. LCLS research activities span the full range of challenges to be met in creating and exploiting an x-ray laser SLAC has supplemented its extraordinary capabilities with the expertise and resources at partner labs to make LCLS possible LCLS can be a reality by 2007

  32. End of Presentation

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