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

ERLP Injector parameters DC gun voltage 350kV Bunch charge 0-80pC Bunch repetition frequency81.25Mhz Train length  s Train PRF1-20Hz Average current in train 6.5mA 80pC) Laser pulse duration ~6ps (~25ps with pulse stretcher) Laser pulse energy 0-40nJ Laser spot position on cathodevariable Laser beam diameter on cathode 2-6mm FWHM (variable) Buncher input RF power ~2kW (~70kV peak voltage) RF kicker power ~200W

ERLP diagnostic beamline

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

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]

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) - ………

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 1 st 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 …)

Commissioning problems Period 1 (21 July – 5 October, 2006) - conditioning resistor failure - gun not conditioned properly for 350kV operation - gun instability in kV 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

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)

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)

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 ~45 o (at ~300G field)

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 !!!

Energy spread Only first rough estimates yet … At 300keV; Q<3pC :  E <0.5keV

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

ERLP diagnostics schematic

ERLP diagnostics: Gun to Booster Slit Vertical

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

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