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Lee Jones Accelerator Physics Group ASTeC STFC Daresbury Laboratory
ALICE Energy Recovery Linac Prototype: Current Status and Commissioning Successes Lee Jones Accelerator Physics Group ASTeC STFC Daresbury Laboratory
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ALICE ERL Prototype status update: Content
Introduction Project status Ongoing work Photon science on the ALICE (formerly known as ERLP) The EMMA NS-FFAG project Injector commissioning results Future plans
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ALICE ERL Prototype: Technical priorities
Primary Goals: Foremost: Demonstrate energy recovery Produce and maintain bright electron bunches from a photoinjector Operate a superconducting Linac Produce short electron bunches from a compressor Further Development Goals: Demonstrate energy recovery during FEL operation (with an insertion device that significantly disrupts the electron beam) Develop a FEL activity programme which is suitable to investigate the expected synchronisation challenges and demands of 4GLS/NLS Produce simultaneous photon pulses from a laser and an ERL photon source which are synchronised at or below the 1 ps level
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ALICE ERL Prototype: Location
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ALICE ERL Prototype: Layout
Nominal gun energy 350 keV Injector energy MeV Circulating beam energy 35 MeV Linac RF frequency 1.3 GHz Bunch repetition rate MHz Max bunch charge 80 pC Bunch train 100 ms Maximum average current 13 µA All the components of an advance energy recovery machine High brightness photoinjector Super-conducting cavities TBA arc Magnetic chicane for bunch compression FEL Return arc Recovery and Dump
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Construction status
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Construction status Photoinjector laser system operating since April 2006 Gun installed and commissioned into a dedicated diagnostic beamline over a period of several months during three commissioning phases Accel superconducting modules undergoing commissioning Cryogenic system installed by Linde and DeMaco, and used to cool accelerating modules down to 1.8 K All of the electron beam transport system has been installed and is under vacuum Installation work proceeding for various photon beam transport systems
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Drive laser: Summary Diode-pumped Nd:YVO4
Wavelength: 1064 nm, doubled to 532 nm Pulse repetition rate: MHz Pulse duration: 7, 13, 28 ps FWHM Pulse energy: up to 45 nJ (at cathode) Macrobunch duration: Hz Duty cycle: 0.2% (maximum) Timing jitter: < 1 ps (specified) < 650 fs (measured) Spatial profile: Circular top-hat on photocathode Laser system commissioned at Rutherford Lab in 2005, then moved to Daresbury in 2006 L.B. Jones, Status of the ERLP Photoinjector driver laser, ERL ’07 proceedings
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Gun Assembly JLab design Cs:GaAs cathode 500 kV DC supply Cathode ball
Single bulk-doped ceramic, manufactured by WESGO Cathode ball Cathode Ceramic SF6 Vessel removed Electrons Laser XHV Support Stem Power supply commissioned 2005 Ceramic delivery March 2006 Spare ceramic delivered Nov 2006 Anode Plate
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Gun Commissioning Status
Electron gun operated Jul-Aug ‘06, Jan-Apr ‘07 & Oct-Nov ‘07 Problems experienced with cathode activation. Q.E. poor First beam from the gun recorded at 01:08 on Wednesday 16th August 2006, with the gun operating at 250 kV Operating at 350 kV soon afterwards Routinely conditioning gun to 450 kV Steady improvement in both Q.E. & lifetime Problems encountered with beam halo, field emission and high voltage breakdown Improved bakeout º Better vacuum Repeated failure of ceramic, now using Stanford spare
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Design criteria demonstrated so far ……
Beam energy: 350 keV ü Bunch charge: > 80 pC ü Quantum Efficiency (Q.E.): % with 1/e lifetime of ~100 hours ü Bunch train length: Single 7 ps pulse to 100 µs ü Train repetition rate: Operated up to 20 Hz ü
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Cryosystem & accelerating modules
2006 Apr – 1st Accelerating module delivered May - 4 K cryo commissioning carried out Jul – 2nd Accelerating module delivered Oct - Linac cooled to 2 K Nov – Booster cooled to 2 K Dec - Modules cooled together Simulated a dynamic resistive heat load of ~ 112 W in both modules Achieved a pressure stability of ± 0.03 mbar at full (simulated) dynamic load in both of the modules at 2 K Achieved ± 0.10 mbar at 1.8 K
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ScRF Accelerating modules
2 × Stanford/Rossendorf cryomodules, one configured as the Booster and the other as the Main Linac, also using the JLab HOM coupler 2 × 9 - Cell 1.3 GHz cavities per module Booster module: 4 MV/m gradient 52 kW RF power Main Linac module: 13.5 MV/m gradient 16 kW RF power Quality factor, Q0 ~ 5 × 109 Total cryogenic load: ~ 180 W at 2 K
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ScRF Accelerating modules
2 × Stanford/Rossendorf cryomodules, one configured as the Booster and the other as the Main Linac, also using the JLab HOM coupler 2 × 9 - Cell 1.3 GHz cavities per module Booster module: 4 MV/m gradient 52 kW RF power Main Linac module: 13.5 MV/m gradient 16 kW RF power Quality factor, Q0 ~ 5 × 109 Total cryogenic load: ~ 180 W at 2 K Booster Linac Cavity 1 Cavity 2 Vertical tests at DESY, July - December 2005 Eacc (MV/m) 18.9 20.8 17.1 20.4 Qo 5 × 109 Acceptance tests at Daresbury Laboratory, May - September 2007 Max Eacc (MV/m) 10.8 13.5 16.4 12.8 Measured Qo 3.5 × 8.2 MV/m 1.3 × 11 MV/m 1.9 × 14.8 MV/m 7.0 × 9.8 MV/m Limitation FE Quench RF Power
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Electron beam transport system
Dipole Magnet Quadrupole Magnet OTR Girder All modules now installed and under vacuum. Ready for beam ! Corrector Coil and EBPM Assembly Ion Pump
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Current / ongoing work Preparing for 4th phase of gun commissioning 1st phase of beam comissioning RF Conditioning of accelerating modules Optimising of the cryogenic system with RF present Commissioning of high-power RF & PLC control systems Commissioning of electron BTS sub-systems: Controls / Diagnostics Beam Loss Monitor Machine Protection System Installation of the photon BTS for THz, FEL, EO & CBS
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ALICE ERLp Photon science:
North West Science Fund award of £3m over 3 years ALICE ERLp Photon science: X-rays: Time resolved X-ray diffraction studies probing shock compression of matter on sub-picosecond timescales. 90º focus mirror X-rays Probe Pump IR 180º focus mirror CBS Interaction Point THz THz: Ultrahigh intensity, broadband THz radiation to be utilised for the study of live tissues. 25TW Laser Started Dec 2005 Laser-SR synergy: Pump-probe expts with table-top laser and SR
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Accelerator Hall Laser Room Diagnostics Room 2.2 mJ, 35 fs
at 1 kHz for EO 800 mJ, 100 fs at 10 Hz for CBS Diagnostics Room Courtesy G. Priebe, DL
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Compton Back-Scattering Þ X-rays
8 TW in 100 fs Hz Side-on Collision Peak Energy ≈ 15 keV X-ray Flux 8 × 106 phs-1 Pulse Duration ~ Laser Pulse Length Source Size 10 μm × 20 μm 8 TW in 100 fs Hz Head-on Collision Peak Energy ≈ 30 keV X-ray Flux 15 × 106 phs-1 Pulse Duration ~ Electron Bunch Length Source Size 50 μm × 20 μm Courtesy J. Boyce, JLab Courtesy DL Engineering Office
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High Harmonic Generation Þ UV
Courtesy G. Priebe, DL Current [A] energy [eV]
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Longitudinal diagnostics:
Electro-Optic concept Longitudinal diagnostics: encoding (bunch profile into optical pulse) probe laser bunch to laser diagnostic decoding (optical pulse into profile measurement) Courtesy S. Jamison, DL
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Tunable Free-Electron Laser
Encoders JLab Wiggler (on loan) FEL Tunability by varying: electron energy (24-35 MeV range) undulator gap (12-20 mm range) l = mm
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The EMMA Project EMMA
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Awarded £6.9m over 3½ years to design and build EMMA
BASROC : British Accelerator Science and Radiation Oncology Consortium EMMA The long-term aim of BASROC is to build a complete hadron therapy facility using Non-Scaling Fixed-Field Alternating Gradient accelerator technology (NS-FFAG), combining the best features of cyclotron and synchrotron accelerators An FFAG combines the intensity and ease-of-use of cyclotrons coupled with the benefits of synchrotrons, specifically beam control and the ability to accelerate proton and heavy ion beams to various energies EMMA: The Electron Model of Many Applications will use ALICE as an injector at 10 MeV, accelerating electrons to 20 MeV. The goal is to learn how to design NS-FFAGs for various applications, including hadron therapy PAMELA: The Particle Accelerator for MEdicaL Applications will be a MeV proton NS-FFAG, itself a prototype to demonstrate the potential use of NS-FFAGs in hadron therapy, thus strengthening the case for hadron therapy Leading to a complete facility for the treatment of patients using hadron beams Awarded £6.9m over 3½ years to design and build EMMA
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EMMA on the ALICE ERL Parameter Design Value Energy range 10 to 20 MeV
Number of cells 42 Lattice Doublet Cell length 393 mm Circumference m Height from ground 1.4 m Repetition rate 1 Hz Orbit swing 3 cm
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ALICE Gun diagnostic beamline
transverse RMS emittance measured by double-slit scans at positions ‘A’ and ‘B’ bunch length with slit ‘A’ and kicker cavity Courtesy Y. Saveliev, DL
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RMS Geometric emittance (function of bunch charge)
RMS geometric emittance as a function of bunch charge: - Horizontal ( ) - Vertical ( ) ALICE ERLp target was specified as 1·p mm-mrad by ASTRA for Q = 80 pC Some factors are missing from the ASTRA model 1,2 1 I.V. Bazarov et al., Proceedings of PAC’07, Albuquerque, 2007, pp 2 F. Zhou et al., Phys. Rev. ST - AB 5, , 2003.
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Bunch length (function of bunch charge, at 10% level)
Bunch length at 10% of the peak value used due to non-uniformity of the longitudinal profile. Data were obtained with the RF transverse kicker (full circles), “energy mapping method” (square) and zero-crossing method (triangle). Open circles are the results from the ASTRA model.
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Total and tilt-compensated energy spread
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FWHM Beam size for Q = 54 pC First solenoid Second solenoid
B1 , G B2 , G First solenoid Second solenoid Comparison of predicted and measured beam sizes [mm] as a function of solenoid field strength [guass] for Q = 54 pC
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ASTRA Longitudinal phase space predictions
PI Gun driven by differing laser pulse durations Experiment ASTRA model 28 ps 7 ps flat top two pulse single ex, mm 1.95 1.91 0.56 0.80 0.49 ey, mm 1.43 1.47 Dz, mm 19.1 18.6 23.8 23.5 25.5 DEtot, keV 24.4 29.7 22.5 23 28 DEcomp, keV 5.1 2.8 6.0 7.2 1.3 DEtot/Dz, keV/mm 1.28 1.60 0.95 0.98 1.10 ASTRA Longitudinal phase space predictions
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Longitudinal drive laser profile
PI Gun driven by differing laser pulse durations Experiment ASTRA model 28 ps 7 ps flat top two pulse single ex, mm 1.95 1.91 0.56 0.80 0.49 ey, mm 1.43 1.47 Dz, mm 19.1 18.6 23.8 23.5 25.5 DEtot, keV 24.4 29.7 22.5 23 28 DEcomp, keV 5.1 2.8 6.0 7.2 1.3 DEtot/Dz, keV/mm 1.28 1.60 0.95 0.98 1.10 Longitudinal drive laser profile
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PI Gun driven by differing laser pulse durations
Experiment ASTRA model 28 ps 7 ps flat top two pulse single ex, mm 1.95 1.91 0.56 0.80 0.49 ey, mm 1.43 1.47 Dz, mm 19.1 18.6 23.8 23.5 25.5 DEtot, keV 24.4 29.7 22.5 23 28 DEcomp, keV 5.1 2.8 6.0 7.2 1.3 DEtot/Dz, keV/mm 1.28 1.60 0.95 0.98 1.10
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PI Gun driven by differing laser pulse durations
Experiment ASTRA model 28 ps 7 ps flat top two pulse single ex, mm 1.95 1.91 0.56 0.80 0.49 ey, mm 1.43 1.47 Dz, mm 19.1 18.6 23.8 23.5 25.5 DEtot, keV 24.4 29.7 22.5 23 28 DEcomp, keV 5.1 2.8 6.0 7.2 1.3 DEtot/Dz, keV/mm 1.28 1.60 0.95 0.98 1.10
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PI Gun driven by differing laser pulse durations
Experiment ASTRA model 28 ps 7 ps flat top two pulse single ex, mm 1.95 1.91 0.56 0.80 0.49 ey, mm 1.43 1.47 Dz, mm 19.1 18.6 23.8 23.5 25.5 DEtot, keV 24.4 29.7 22.5 23 28 DEcomp, keV 5.1 2.8 6.0 7.2 1.3 DEtot/Dz, keV/mm 1.28 1.60 0.95 0.98 1.10 Conclusion: Longer laser pulses do not confer significant benefits below ~ 20 pC when compared to short pulses in terms of bunch length & energy spectra.
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Immediate / future plans
Beam through the booster, main linac and arcs Demonstrate energy recovery Followed by: Fine tuning of the machine: tune injector for minimum emittance, optimisation of energy recovery at nominal beam parameters, extensive beam measurements Short pulse commissioning: longitudinal dynamics, EO diagnostics Energy recovery with FEL and first IR light from the FEL Simultaneously: THz & IR-FEL research programmes will start, as will CBS X-ray production using head-on electron-photon collisions Future: Load-lock gun upgrade and possible re-design for vertical ceramic Re-installation of gun diagnostic line Installation of an improved high-current cryomodule Current position on all 4GLS related activities 4GLS design ERLP lessons Have to keep strictly to time as there’s a bottle of alcoholic content resting on it isn’t there Trevor. Some of the overheads might well appear as subliminal messages…
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Questions ? Thank you for listening …… Acknowledgements:
EPAC ’08 Proceedings: Y.M. Saveliev et al., Results from ALICE (ERLP) DC photoinjector gun commissioning, MOPC062, pages Y.M. Saveliev et al., Characterisation of electron bunches from ALICE (ERLP) DC photoinjector gun at two different laser pulse lengths, MOPC063, pages Linac ’08 proceedings: D.J. Holder on behalf of the ALICE team, First results from the ERL prototype (ALICE) at Daresbury Acknowledgements: K.J. Middleman Y.M. Saveliev D.J. Holder S.P. Jamison S.L. Smith B.L. Militsyn B.D. Muratori G. Priebe N.R. Thompson J.W. McKenzie Questions ?
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