Development of High Brightness Electron Photoinjectors at ASTeC B.L. Militsyn Accelerator Science and Technology Centre Science & Technology Facility Council, Daresbury, UK JAI Fest, 10 December 2015, Oxford, UK 10 December 2015B.L. Militsyn, JAI Fest,Oxford, UK

Outline Requirements to the modern High Brightness Electron Injectors Electron sources – photocathodes –Semiconductor photocathodes –Metal photocathodes DC electron photoinjectors for ERL applications –ALICE photoinjector NCRF electron photoinjectors for FEL –VELA photoinjector –CLARA High Repetition Rate photocathode Gun (HRRG) Next steps – CLARA project 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

Compact Linear Accelerator for Research and Applications CLARA The existing VELA RF Photoinjector Test Facility ELECTRONS GENERATED HERE ELECTRONS ACCELERATED AND MANIPULATED INTERACTIONS WITH LASER BEAMS FEL OUTPUT GENERATED FEL OUTPUT STUDIED Notes: 1. CLARA uses European RF frequencies 2. X-band cavity is used for phase space linearisation

General requirements to electron injectors Beam energy – 100’s keV – GeV’s Bunch peak current – Amps – kA’s –Bunch charge – fC’s – nC’s –Bunch duration – fs’s – ns’s Beam average current – nA’s – 100 mA’s –Bunch charge – fC’s - –Bunch repetition rate – Hz – 100’s MHz Beam energy spread – 0.1 %’s –Correlated –Non-correlated Beam emittance – sub µm’s 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

Very general concept of the electron injectors Electron emission –Thermionic cathodes –Field emission cathodes –Photocathodes (laser system required) Electron acceleration –DC high voltage –Pulsed high voltage –Radiofrequency acceleration Normal conductive acceleration Superconductive acceleration Post acceleration beam processing –Compression Velocity bunching Magnetic compression –Heating/Cooling 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

Photocathode Materials 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK Photons (Laser) Electrons Photocathode ClassMaterialQEWavelengthGunApplication Normally conducting metals Cu, Mg UVNC-RFLow rep rate FELs (VELA, CLARA) Super conducting metals Nb,Pb UVSC-RFHigh rep rate FELs Positive e - affinity semiconductor CsTe, CsSb, etc Visible - UVNC-RF, DC FELs, ERLs Negative e - affinity semiconductor GaAs, etc IR- VisibleDC (XHV) Polarized sources, ERLs (ALICE)

Daresbury Energy Recovery Linac ALICE 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

Nominal gun energy350 keV Injector energy8.35 MeV Circulating beam energy35 MeV Linac RF frequency1.3 GHz Bunch repetition rate81.25 MHz Maximum bunch charge80 pC Macropulse train lengthup to 100 ms Macropulse repetition rate1 – 20 Hz Maximum average current13 µA ALICE ERL. General Layout 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

High average current GaAs photocathodes 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

ALICE photocathode gun 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

GaAs photocathode preparation facility K.J. Middleman et al., PESP2010 Kovar cathode holder Inconel spring Titanium base plate Molybdenum mount 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

New ALICE gun RGA Dedicated pumping port for bakeout NEG pumping Transfer arm for winding cathode forward Viewing ports Ceramic Electrons 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

ALICE photocathode gun upgrade Photocathode gun 500 kV power supply Photocathode preparation facility Upgrade of the gun allows to  Reduce the down time required for activation of the photocathode and allows ALICE for operation with higher bunch charge.  Remove activation/caesiation procedure out of the gun  Improve vacuum in the gun  Reduce contamination of the high voltage electrodes with Cs and other products of photocathode preparation  Make photocathode activation more controllable  Allows for experiments with different types of photocathodes 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

VELA Injector Area 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

VELA Photoinjector Module Gun Solenoid Lightbox YAG, H & V Slit Collimators 4 x Ion Pump Transverse Deflecting Cavity YAG, V & H Slit Quadrupole magnets Synthetic Granite Girder WCM Support Pedestal YAG, V Slit 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

VELA photocathode gun VELA gun specificationVELA photocathode gun TechnologyNC RF Operation frequency, MHz Cavity design2.5 cell Maximum cathode field, MV/m70 Maximum beam momentum, MeV/c 5.0 Maximum RF pulsed power, MW10 RF pulse duration, µs3 RF pulse repetition rate, Hz10 Photocathode technologyMetal copper Maximum bunch charge, pC250 Photocathode is integrated into the gun as back wall of the cavity. Qe estimated as December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

VELA laser system Specification of the VELA/CLARA drive laser Technology Mode locked triple frequency Ti:Sapphire Laser wavelength, nm266 Pulse energy in IR, mJ12 Pulse energy in UV, mJ1 Pulse repetition rate, Hz400 RMS pulse duration, fs76 RMS arrival time jitter, fs December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

HRRG requirements 100 Hz400 Hz PulsedTrain pulsed Gun field MV/m /80 Beam energy, MeV664 Bunch charge, pC pC25250 pC Field amplitude stability, % Field phase stability, degree0.1 1 Average 1.5 cell gun RF power, kW /4.35 Micropulse separation, ns-100- Cavity temperature stability,  C Photocathode Metal interchangeable Cs 2 Te interchangeable Metal interchangeable RF feedbackRequired - LLRF feed-forward phase correction-Required- 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

HRRG Design overview H shape coupler Cathode plug and spring retaining plate. Gun Cavity RF probe* Cooling channels 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

Metal photocathode research Photocathode design is based on INFN/DESY design with reduced 10 mm tip Baseline – metal photocathodes R&D on photocathode infrastructure Research facility with extensive analytical instrumentation Preparation facility Photocathode transport system compatible with other laboratories Developed photocathode preparation procedure – O 3 plasma cleaning plus annealing 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

Nearest and Future plans Installation of CLARA Phase 1 –Installation of the ALPHA-X gun at VELA beam line and demonstration of the Phase 1 operation –Installation and commissioning of the HRRG at VELA beam line –Investigation of different type of metal photocathode at HRRG while it is in VELA Installation of HRRG at CLARA beam line Development of a ultra-high brightness photoinjector for ongoing projects 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

~5 MeV ~50MeV Phase 1 parameters: Max Energy~50 MeV Max Charge250 pC Norm. Emitt.<1 mm mrad Min Bunch Length 50fs (rms), (10 MeV) Max Peak Current2kA Bunches/RF pulse1 Pulse Rep Rate10 Hz (400Hz later) ~50MeV VELA + CLARA Phase 1 (2015) 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

Thank you for your attention! 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

Emittance of electron photoinjectors Field strength Technology0.01 nC0.1 nC1.0 nC 10 MV/mDC gun MV/mVHF gun MV/mL-band gun MV/mS-band gun December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

ALICE photoinjector 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

2.5-cell S-band VELA gun 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

Versatile Electron Linear Accelerator - VELA 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

VELA. Artists view 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

First VELA Beam 5 th April 2013 Successfully conditioned the photocathode Gun up to 4.9 MW RF power, that corresponds to the field of 70 MV/m with a 2 μ s pulse length With appropriate RF and laser parameters an electron beam with bunch charge ~170 pC was produced along module 1 This was monitored on a YAG screen and Faraday Cup Image of the beam on YAG-01 Signal on the temporary FC 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK

H-shape Coupler Phase adjustment screw Waveguide flanges copper coated inside. Waveguide split/pumping 10 December 2015 B.L. Militsyn, JAI Fest,Oxford, UK