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Design Options for the New Light Source ESLS XVI, 28 th Nov 2008, Cockcroft Institute

Design Options for the New Light Source ESLS XVI, 28 th Nov 2008, Cockcroft Institute. Peter Williams ASTeC, STFC Daresbury Laboratory & Cockcroft Institute (on behalf of the NLS design team). New Light Source Project.

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Design Options for the New Light Source ESLS XVI, 28 th Nov 2008, Cockcroft Institute

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  1. Design Options for the New Light SourceESLS XVI,28th Nov 2008, Cockcroft Institute Peter Williams ASTeC, STFC Daresbury Laboratory & Cockcroft Institute (on behalf of the NLS design team)

  2. New Light Source Project • STFC-led project to examine and propose a 4th Generation synchrotron user facility for the UK with unique and world leading capabilities (NLS is a working title) • Three stages: • Science Case • Technical Design Study • Funding and Location • Science Case presented to STFC - PALS on 15rd Oct (www.newlightsource.org). From executive summary… • IMAGING NANOSCALE STRUCTURES: Instantaneous images of nanoscale objects can be recorded at any desired instant allowing, for example, nanometer scale resolution of sub-cellular structures in living systems. • CAPTURING FLUCTUATING AND RAPIDLY EVOLVING SYSTEMS: Rapid intrinsic evolution and fluctuations in the positions of the constituents within matter can be characterized. • STRUCTURAL DYNAMICS UNDERLYING PHYSICAL AND CHEMICAL CHANGES: The structural dynamics governing physical, chemical and biochemical processes can be followed by using laser pump- X-ray probe techniques. • ULTRA-FAST DYNAMICS IN MULTI-ELECTRON SYSTEMS: New approaches to measuring the multi-electron quantum dynamics, that are present in all complex matter, will become possible. • Outcome: Phase 2 Technical Design Study to go ahead 

  3. New Light Source Design Team • STFC-led collaboration involving (pretty much) all players in the UK (named persons contributed directly to this talk) • S. Appleton, P. McIntosh, J. McKenzie, B. Militsyn N. Thompson • R. Bartolini, Jang-Hui Han, R. Walker • H. Owen • B. McNeil

  4. NLS Technical Design Study • NLS is likely to be a coupled set of facilities including conventional lasers (high field/ultra-short pulse), long wavelength sources and at its core a short wavelength (<100nm) free electron laser • Facility requirements presented in Science Case • Photon energies tuneable over the range from THz/IR through to soft X-ray • Two-colours (i.e. UV/Vis or IR/THz synchronised with soft X-ray pulses) • Ultra-fast pulses with duration down to sub-femtosecond range • High temporal and transverse coherence • Decision last week to propose a high rep. rate machine ( >1kHz) based upon a Superconducting Linac – high rep rate pushed by users.

  5. Transverse Brightness  Not a Storage Ring! TME 6-cell (100 m) TME 12-cell (200 m) TME 24-cell (400 m) Linac: 1 mm-mrad (state of the art @ 1 nC charge) TME 48-cell (800 m) Storage Ring Horizontal Emittances Storage Ring Vertical Emittances (0.1% Coupling) TME (theoretical minimum emittance) is the smallest emittance possible in a ring, based on minimising Courtesy Hywel Owen

  6. Short Pulses  Strong Bunch Compression • A method to compress the length of electron bunches to small values, e.g. less than 1 ps • Chirp + Compression, similar to CPA in lasers • The chirp is conveniently carried out at the same time as the bunch is accelerated – in a series of radiofrequency cavities in a linear accelerator • The compression may be performed in a 4-dipole chicane Courtesy Hywel Owen

  7. Main RF 3rd Harmonic Cavity Final Linearised Chirp lh=l0/h 0 h= p Compression Scheme Design Non-Trivial BC1 BC2 L1 3H/4H L2 L3 Resistive wall wakes Collimator wakes Longitudinal cavity wake E.g. Trade off large CSR in transporting short bunch with jitter caused by large R56 Courtesy Hywel Owen

  8. 4th Generation Machines Worldwide Blue – single-stage Red – multi-stage (inc. harmonic correction) Yellow – ERL (various methods) Bold – they have measured that bunch length NLS SC Design NLS NC Design • Users want 1kHz rep. rate, 20fs pulses, 3 GeV ideally • Our initial interpretation, a ~1 GeV SC linac, upgradable to 3 GeV • Other approach, a 3 GeV NC linac (R. Bartolini) • Recirculating option being developed

  9. Similar Schemes to a SC NLS WiFEL Both about 2 GeV Both about 600 m (facility) LBNL

  10. An NLS SC Design (Hywel Owen and Peter Williams) • 735 MeV chosen as it corresponds to 1 nm, the limit for HHG seeding i.e. this is a possible extraction energy where we want short bunches • Compression scheme must be carefully designed – linearisation, cavity wakefield compensation, CSR, LSC • 200 pC bunch charge chosen, based injector on XFEL • EPAC08: MOPC034, MOPC035 available at www.jacow.org • PR-STAB in preparation

  11. Elegant Projected CSRtrack Projected CSRtrack 3D An NLS SC Simulation – The Upright Bunch Peak currents (for FEL lasing) After first compressor 11.8 kA 11.4 kA Numerical LSC microbunching CSR e-spread 16.6 kA After second compressor

  12. NLS Future Work: Questions For Upright Bunch • How does the current spike survive misalignments? (probably not well) • What about timing jitter? Keep BC2 R56 low, but still… • How does microbunching limit an upright bunch? After all, the microbunching is now ‘sideways’. • 200 pC was used in these simulations – what is the best charge to use? It seems that there is a weak scaling of peak current with total bunch charge. • What is the best way of managing wakefields when compressing? • Might it be sensible to consider a multi-frequency design, to benefit from higher gradients at higher frequency? (e.g a C-band or X-band light source). Not favoured at present

  13. undulators Gun X01 S06 S02 S03 S04 S05 S01 S07 S09 S10 S12 S08 S11 DL BC1 BC2 Astra genesis elegant An NLS NC Simulation – R. Bartolini (DLS) • 3 GeV NC S-Band linac with 2 stage compression, 200 pC bunches chosen • NC RF S-band gun, 0.21 mm mrad at injector exit – more later • CSR – yes, LSC – no. Bin width ~1 fs Long. PS Energy Spread Emittance Current

  14. undulators Gun X01 S06 S01 S03 S04 S05 S02 S07 S09 S11 S08 S12 S10 DL BC1 BC2 Astra genesis elegant An NLS NC Simulation – R. Bartolini (DLS) • On varying BC2 R56 through fully compressed configuration • CSR spoils your emittance at full compression • Working point is BC2 R56 = 19.8mm – slight over-compression – just like ours! Bunch Length (RMS) Peak Current Projected Emittance

  15. Initial NLS Options Study • Riccardo’s emittance and energy spread are better than ours! • But we used CSRTrack 3-D in compressors (slice emittance increased ~30%) • Also Longitudinal space charge • We need to optimise injector – include an SRF gun emittance from 1 to 0.4 mm mrad • Operate further off crest (bigger energy spread) because want to keep BC2 R56 down (jitter)

  16. NLS Current Work: Recirculation • Users want high rep. rate ( > 1 kHz)  superconducting machine  capital expense • Mitigation strategy – Recirculation • Example: Build a 1 GeV SC linac as a first stage, recirculate to 2 (3) GeV. • Possible issues: • Compression Scheme (no ~10 fs bunches at high energy – do we need this) • Emittance Degradation (CSR, ISR, LSC) due to arcs • Beam Break Up • High Energy Diagnostics • Linearisation • Jitter due extra transport • Investigation of these underway based on 4GLS-XUV arcs

  17. NLS Current Work: Recirculation • Regular FODO channel – eventually rejected for 4GLS-XUV (size, non-zero R56) • Went to a zero R56 compact QBA design • GA optimisation algorithm by James Jones, Daresbury

  18. NLS Current Work: Recirculation • Do some simple-minded 1-d longitudinal phase space transformations… an example… • Assume a transport rather than dog-bone to start with. Should we minimise CSR in arc by keeping bunch as long as possible in the first pass by putting first compression after all arcs? • Answer is no! Cannot linearise. However microbunching MAY require BC1 @ > 250 MeV • Why? See Yujong Kim’s talk at microbunching instability II workshop “Solutions against COTR in LCLS and design concepts of XFEL driving Linacs” • Also 1st pass = 1 GeV, but 2nd pass = 1.7 GeV

  19. NLS Current Work: Recirculation

  20. NLS Current Work: Recirculation

  21. NLS Current Work: Recirculation • Do some simple-minded 1-d longitudinal phase space transformations… an example… • Assume a transport rather than dog-bone to start with. Should we minimise CSR in arc by keeping bunch as long as possible in the first pass by putting first compression after all arcs? • Answer is no! Cannot linearise. However microbunching MAY require BC1 @ > 250 MeV • Why? See Yujong Kim’s talk at microbunching instability II workshop “Solutions against COTR in LCLS and design concepts of XFEL driving Linacs” • Also 1st pass = 1 GeV, but 2nd pass = 1.7 GeV

  22. NLS Current Work: Recirculation

  23. NLS High Rep. Rate (to GHz) Photoinjector Options • HV DC gun: Status - operational in user facilities. Experience with technology at DL. Lower emittance due to lower field strength (10MV/m) at cathode. Need XHV vacuum and have HV issues ie ceramic insulator. Can use GaAs photocathodes + others. • VHF NC RF gun: Status - design studies (LBNL). ~100MHz gun, similar beam transport/dynamics to DC gun but due to higher field strength (20MV/m) at cathode have lower emittance. NC-RF technology is well established. Cannot use GaAs so use multi-alkali photocathodes such as K2CsSb. • SRF gun: Status - under commissioning (ELBE). Don’t require a buncher/booster. Therefore less timing jitter but less tuneability. Perfomance limit is the amount of power you can couple in. Up to 50MV/m should be possible giving very low emittance beam. Cannot use GaAs, probably use Cs2Te Linac 2008 TUP042: Boris Militsyn, Carl Beard, Julian McKenzie – Daresbury

  24. NLS Low Rep. Rate (to kHz) Photoinjector Options • NC RF gun at L-Band well proven at PITZ. Up to 50MV/m, upgradable to 1kHz. Transverse emittance: 0.68 mm mrad @ 1 nC and 0.33 mm mrad @ 0.2 nC • NC RF gun at S-Band scaled down from DESY L-band gun. Cooling-water channel redesigned  400 Hz rep. rate. Up to 120MV/m field strength at cathode. Transverse emittance: 0.42 mm mrad @ 1 nC and 0.21 mm mrad @ 0.2 nC. • SCSS style thermionic gun with CeB6 cathode. Only 60Hz at present. Thanks to Jang-Hui Han, Diamond

  25. NLS Linac Module Options • SC cryomodule options: CEBAF, XFEL, BESSY-FEL, ALICE / ELBE, • Daresbury International Cryomodule (Daresbury, Stanford, Cornell, LBNL, Rossendorf) • NC options: SLAC-type 3 GHz studied Thanks to Pete McIntosh, Daresbury

  26. NLS FEL Options : Resonance Condition Approximate minimum beam energy required for a given FEL wavelength, for 10mm and 5mm undulator gap. Also shown are data from current and proposed FEL projects Thanks to Neil Thompson, Daresbury & Brian McNeil, U. Strathclyde

  27. NLS FEL Options: Seeded + Exotic Wavelength coverage for the generic FEL types: Self-Amplified Spontaneous Emission, High Harmonic Generation gas seeded / Harmonic Optical Klystron, High Gain Harmonic Generation (modulator + radiator) (laser seeded) Oscillator FEL e.g. 4GLS-VUV Regenerative Amplifier

  28. Summary • NLS project now in technical design phase • Wide range of options for major systems being studied (injectors, linac, FELs, layout) • Technology selections will be made in next few months  Detailed proposal by October 2009

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