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Linac4 commissioning strategies (part I, up to 12MeV)

Linac4 commissioning strategies (part I, up to 12MeV). G Bellodi (BE-ABP-HSL) , Jim Stovall & L4 beam dynamics group. Timeline. not many handles to play with (V vs T). RFQ MEBT TANK1 TANK2 + TANK3. 01/2011 04/2011 07/2012 01/2013?.

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Linac4 commissioning strategies (part I, up to 12MeV)

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  1. Linac4 commissioning strategies (part I, up to 12MeV) G Bellodi (BE-ABP-HSL) , Jim Stovall & L4 beam dynamics group

  2. Timeline not many handles to play with (V vs T) RFQ MEBT TANK1 TANK2 + TANK3 01/2011 04/2011 07/2012 01/2013? Linac4 test stand area very important to achieve beam quality : non periodical lattice, larger beam modulations, important space charge effects, ‘new’ technology not quite fully established Linac4 tunnel all PMQs for transverse planes, find correct matching between tanks and longitudinal RF set points

  3. Permanent diagnostics: MEBT Wire scanners Transformers clamp-on steerers

  4. Temporary diagnostics : movable test bench Emittance meter, spectrometer, 2-3 PUs, 2-3 BCTs, Feschenko, halo monitor for machine commissioning & to calibrate permanent diagnostics (to be used in operation)

  5. Beams ..& procedures: • 1) Transverse plane: • Steering/orbit correction • Quad tuning • Transverse beam matching • 2) Longitudinal plane: • RF amplitude/phase scans • longitudinal matching

  6. MEBT commissioning path 0 – beam transport, orbit correction, preliminary quad setting 1 – longitudinal plane characterisation, set RF f/A points for buncher cavities 2 – transverse beam matching , quad tuning, halo studies 3 – chopper functionality (time integrated) 4 – chopper functionality (time resolved)

  7. phase 0 – transport & steering SETUP: low current & pencil beam, chopper plates OFF AIM: ensure beam transport through MEBT and test bench, measure beam offsets and perform orbit correction, preliminary quad setting PROCEDURE: Observe beam profiles on wire scanners, beam position signals on BPMs and measure (differential current) transmission at the BCTs. Measure quadrupole response matrix, beam offsets and perform orbit correction. Relative readings of BCTs 1, 2 (MEBT) 3,4 (test stand) for several input currents [bunchers off- no retuning]

  8. Response matrix at WS Measure beam position at WS while scanning quadrupole field gradients and derive beam offsets inside quads . Correct the orbit with steerers.

  9. AIM: characterisebuncher cavities, set RF phase and amplitude points, measure beam average energy/ energy spread phase 1: longitudinal PROCEDURE: On the spectrometer line (pencil beam, chopper plates OFF) : Find RF phase point: set max voltage on cavity and spectrometer Bfieldfor 3 MeV (NMR probe). Measure beam displacement on SEM while scanning over phase: beam centered for f=±90o Find RF amplitude point: set phase to 0deg and measure beam displacement on SEM while scanning over voltage values. f=±90deg  no energy gain f=0, 180deg  max energy deviation STEPS: Calibrate buncher1 – bunchers 2, 3 off Calibrate buncher2 – buncher1 at nominal, buncher3 off Calibrate buncher3 – bunchers 1, 2 at nominal

  10. Sensitivity: 0.5mm per deg offset, 0.2mm for 1kV offset/ ok for SEM grid resolution

  11. TOF measurement Crosscheck with TOF measurement of average beam energy  BPMs phase calibration PUs at s=4318, 5148, 6275 mm (from start of chopper line) Case1 : df=2deg, dL=0 Case2 : df=1deg dL=0.3mm Sensitivity: ~ok for case2 and 1‰ sensitivity requirement

  12. Beam debunchingvs current

  13. AIM: characterise longitudinal plane, find matching point to DTL (full current beam, chopper plates OFF )  Feshenko monitor calibration (bkgnd subtraction of detached e-) Longitudinal matching with Feshenko PROCEDURE: Measure bunch profiles with Feschenko monitor while varying buncher settings. 3-points emittance measurement with low intensity beam? 1 deg phase resolution Gaussian fitted RMS spread vsbuncher settings s=35,30,26 deg

  14. phase 2 – transverse beam matching SETUP: full current beam, chopper plates OFF AIM: establish transverse matching conditions, find initial Twiss parameters, quad tuning PROCEDURE: Quadrupole gradients scan technique with measurement of beam profiles at WS, transmission on BCTs and emittances on scanner STEPS: RFQ to MEBT : 1st FODO (L4L.QDA3010, L4L.QFA3030,L4L.QDA3050,L4L.QFA3070) MEBT central quads MEBT to DTL : last FODO (L4L.QDD3170, L4L.QFD3180,L4L.QDA3200,L4L.QDA3220)

  15. RFQ to MEBT quad gradient scan (±20%) Beam measured on MEBT diagnostics: WS and BCT Fairly ideal simulation case, no mismatch, no errors; only one quad gradient varied at any one time (others assumed at nominal settings) Nice signature for quad2, not so clear for other quads Clear peak signature, can tune to few % level if we can resolve 1% in differential beam current with BCT

  16. Measurements on test bench installed after Tank1 Fairly ideal simulation case, no mismatch, no errors; only one quad gradient varied at any one time Good if already close to the solution… MEBT to DTL classic quad gradient scan (±20%) No clear signature with available diagnostics resolution [ 0.1mm mrad / 0.5mm]…

  17. MEBT to DTL random quad gradient scan (±20%) Beam measured on test bench installed after Tank1 no mismatch, no errors All quads randomly varied at the same time Apart from Q10, no clean single knob for tuning, but rather flat signal

  18. Multi-variables approach (offline/online?) Build a statistical database of cases. Cut in multivariable space to reduce data sample and plot data projections Example: eRMS (x,y) < 0.4 mm mrad & T> 95% Mean ≈1 , s≈10%

  19. Automated transverse beam matching? (a` la SNS/JPARC ) WS Bench/WS? WS • High level software application to: • •Compare measured and model predicted beam sizes in the MEBT for a variety of • MEBT magnet settings • •Solve for MEBT entrance Twissparameters to best match measured wire profiles under a variety of quad settings • •Uses solver + online model packages with live machine data input.

  20. phase 3 – chopper functionality (time ∫) SETUP: low current beam, chopper ON DC AIM: measure individual elements’effect on beam deflection PROCEDURE: measure beam centroid deflection on MEBT WS near dump & residual transmission on TRAFOs.

  21. X - Y Y-Y’ W/o optical deflection enhancement with optical deflection enhancement

  22. Not completely chopped bunch Transmitted bunch phase 4 – chopper functionality (time resolved) SETUP: MEBT+ test bench, full current beam, chopper ON AC AIM: test time resolved chopper functionality PROCEDURE: measure intensity of partially chopped beam with Masaki’s detector, chopping efficiency, rise/fall times with beam mm scale, <2ns resolution

  23. DTL commissioning Steerer P.U. EMQ Steerer P.U. Steerer , P.U. EMQ,BCT,Profile (SEM) • Transverse commissioning should be easier, if we get the initial conditions right! (all intertank PMQs) • Set RF point by scanning in phase/amplitude and looking for best match with simulated characteristic curves. Measure output average phase and energy DTL1 DTL2 DTL3 Permanent diagnostics

  24. DTL commissioning: RF curves

  25. DTL tank1 acceptance studies Input beam cut at 10.5MeV output energy Can be further developed to obtain alternative calculation of longitudinal profiles and/or emittance by measuring beam losses (BCTs, BLMs?) Tank2, Tank3  Jim’s talk

  26. Software applications desiderata • Service applications: • elogbook • logger • Device specific applications: • Wire scanner • Emittance meter • Beam losses • Feshenko, halo monitor • General purpose tools: • scope application • f(t) • histograms • (1-D,2-D?) scan application • correlator application • Online model: • automated longitudinal f/A scans and signature match • comparison of measured and model predicted beam sizes for a variety of settings, iterative optimisation match to solve for Twiss parameters • orbit correction through steering basic complex

  27. Reserve slides

  28. Phase spread at the exit of tank2 TOF for DTL tank2, tank3? Phase spread at the exit of tank3 Lengths DTL tanks:4.2m,7.6m,7.4m CCDTL: 2.6-3.3m PIMS modules: 1.3-1.5m (2modules at least for 1‰dE/E)

  29. 30keV resolution for at least 1.5m distance b/w PUs

  30. 50keV resolution for at least ~2m distance b/w PUs

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