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Diagnostics and commissioning on ERLP

This document details the diagnostics and commissioning efforts for the Enhanced Resolution Laser-driven Particle Injector (ERLP) project. Conducted from February 26-28, 2007, at Daresbury Laboratory, the review focuses on injector parameters, including a DC gun voltage of 350 kV, bunch charge from 0-80 pC, and advanced measurement methodologies. Key strategic goals include gun characterization, optimization at specific charge settings, understanding beam dynamics, and improving quantum efficiency. The report also addresses the challenges faced during commissioning phases, providing essential insights for future research and operational enhancements.

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Diagnostics and commissioning on ERLP

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  1. Diagnostics and commissioning on ERLP Yuri Saveliev ASTeC CONFORM Project: EMMA Design Review Workshop 26-28 February 2007, Daresbury Laboratory

  2. ERLP Injector parameters DC gun voltage 350kV Bunch charge 0-80pC Bunch repetition frequency 81.25Mhz Train length 0-100 ms Train PRF 1-20Hz Average current in train 6.5mA ( @ 80pC) Laser pulse duration ~6ps (~25ps with pulse stretcher) Laser pulse energy 0-40nJ Laser spot position on cathode variable Laser beam diameter on cathode 2-6mm FWHM (variable) Buncher input RF power ~2kW (~70kV peak voltage) RF kicker power ~200W

  3. ERLP diagnostic beamline

  4. ERLP Diagnostic beamline schematic NOTES: 1) Section “B” position coincides with the position of the 1st cell of booster 2) Everything downstream SOL-02 will be replaced by the booster

  5. Diagnostic beamline: what we can measure Bunch charge (Faraday cup) Electron energy (HV PSU voltage] Laser beam position/size on cathode (direct viewing, virtual cathode) Cathode QE (QE scanner, FC) Beam steering (YAGs, BPM) Transverse beam size and profile (YAGs) Transverse emittance (V & H slits, pepper pot, YAGs, FC) [both X and Y; transverse phase space] Energy spread / spectrum (dipole, YAG, slit, FC-02) [with buncher – correlated and uncorrelated energy spread] Bunch length / longitudinal profile (RF transverse kicker, YAG) [longitudinal phase space]

  6. Diagnostic beamline: what we need to do Strategic goals: - gun characterisation at various bunch charges Q; - gun optimisation at Q=80pC (or the highest Q available) needed for: (i) matching computer simulations and experiment; (ii) projecting the injector behaviour to nominal bunch charge Beam related tasks … - HV gun electrodes conditioning proper (done; 450kV) - laser pulse stretcher (done; ~25ps) - good laser transverse shape without the pinhole - QE >1% (done; =1.2%) - cathode lifetime - BPM, buncher and RF kicker characterisation (started) - ………

  7. Diagnostic beamline: what we need to do Beam studies - beam steering/focusing at high Q - beam halo (if any) - solenoid scans (var Q) - transverse emittance at buncher and 1st booster cell (var Q) - energy spread (correlated/uncorrelated) (var Q) - bunch length and longitudinal profile (var Q) - optimal settings for Q=80pC (or the highest available) Also … - keep an eye on QE and the cathode lifetime - effect of buncher operation on QE - optimisation of laser beam size (time permitted; unlikely though …)

  8. Commissioning problems Period 1 (21 July – 5 October, 2006) - conditioning resistor failure - gun not conditioned properly for 350kV operation - gun instability in 260-310kV range of voltages - low and rapidly deteriorating QE (~0.5% max and ~0.1% most of the time) - gun vacuum/current leakage problems after one of the cathode activations beam studies: ~1 week at 250keV and ~1 week at 350keV Period 2 (7 January – 3 February, 2007) - strong field emission from the cathode (due to new wafer ?) - rapidly deteriorating QE (although high initially >1%) - highly non-uniform QE map (due to wafer heating problems) - mechanical failure inside the cathode ball (flap) beam studies: <2 weeks at <350keV

  9. Quantum efficiency, bunch charge, lifetime • Quantum efficiency: - maximum registered (machine): QE=1.2% - on a stand-alone test system, QE=3.5% has been achieved • Bunch charge: - maximum registered: Q=9pC (with pinhole) • Cathode lifetime: -no solid data yet, but the lifetime is not good enough anyway (field emission)

  10. Dipole calibration Calibration made at 250keV because of Voltage instability at nominal 350keV Sensitivity with YAG-03 (Section D): 1.13mm/keV Scaling to other energies: Scaled to 350keV, the sensitivity is: 0.85mm/keV (Note: theory gives 0.86mm/keV)

  11. Beam steering • Beam steering is far from intuitive because of solenoids Solenoids: - Strong correctors :f=24cm at 300G => ~40mrad kick (!) at ~10mm offset - Rotate the beam by ~45o (at ~300G field)

  12. Transverse emittance • 350keV; Slit HSLT-01 (“B”) and screen “C” laser spot diameter = 5.2mm (approximately ±2σ) • Q=0.16pC ε = 0.9 mm.mrad (normalised) • Q=0.06pC ε = 0.8 mm.mrad (normalised) But: both are overestimated due to image saturation !!!

  13. Energy spread Only first rough estimates yet … At 300keV; Q<3pC : sE <0.5keV

  14. Bunch length “Non-conventional” technique (use of dipole and buncher) Bunch length estimated to be ~23ps (full bunch length) at low bunch charges

  15. ERLP diagnostics schematic

  16. ERLP diagnostics: Gun to Booster Slit Vertical

  17. ERLP diagnostics: Booster to Linac Energy spread/spectrum Absolute energy Buncher gradient / phase(?) setting Bunch charge Twiss parameters Energy spread Slit here ? Setting achromatic condition (Q01-Q05) Setting achromatic condition (Q10, Q12) Twiss parameters Emittance

  18. ERLP diagnostics: Linac to Arc 1 Twiss parameters Emittance Dispersion correction Slit here ? Bunch charge (?) Energy spread/spectrum Absolute energy

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