BEAM DYNAMICS TOOLS FOR THE LINAC 4 COMMISSIONING
BEAM DYNAMICS TOOLS FOR THE LINAC 4 COMMISSIONING Veliko Dimov 5 August 2016
http: //cds. cern. ch/record/1626566? ln=en Few words on The new Linac • First step of the LIU - LHC Injectors Upgrade Project • Higher energy: 160 Me. V. • Accelerates H • Charge exchange injection to the PSB. • Will increase the performance of the LHC injectors. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 2
Basic architecture of Linac 4 45 ke. V H- ion source Low Energy Beam Transport 3 Me. V Radio Frequency Quadrupole Medium Energy Beam Transport (3 RF cavity) 50 Me. V Drift Tube Linac (3 Tanks) 102 Me. V Cell-Couple Drift Tube Linac (7 Modules) 160 Me. V Pi-Mode Structure (12 Tanks) http: //linac 4 -project. web. cern. ch/linac 4 -project/ • • 26 independent RF cavities! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 3
L 4 commissioning stages • 45 ke. V • 3 Me. V: • After the RFQ • After the MEBT • • 12 Me. V: after the first DTL tank 50 Me. V: after the DTL 107 Me. V: after the first PIMS tank 160 Me. V: whole linac (will start in few weeks) During the commissioning period it is possible to use more complex beam diagnostics all along the linac!!! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 4
WHY do we need beam commissioning? • Set/find the operational voltage and phase of the cavities. • Set/check the magnet (quadrupole/ solenoid) settings for optimal operation. • Check if the machine works as designed. • Measure the beam parameters. • Learn as much as possible with the extra diagnostics. • Benchmark the model of the machine in the simulation codes. • Check the accuracy of the simulation codes. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 5
Tracking codes ATION SIMUL UREM E MEAS Life makes more sense when the measurements agree with the simulations!!! NT What did you expect? What did you get? • PATH Manager (the main code for Linac 4): multi-particle • Trace. Win : multi-particle • Trace-3 D : envelope • Parmteq : multiparticle (only for the RFQ) V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 6
V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 7
Low energy beam transport (LEBT) Measurement Set-up Measurements both with proton and H- beam. Only the measurements after December 2012 will be presented here!!! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 8
Measured Transverse Phase spaces proton beam V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 9
Measured Transverse Phase spaces proton beam Generate a multi particle beams for tracking!!! Backtrack and check if they are the same!!! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 10
Few words on backtracking • S: state of a system • T: time reversal operator • TS: time-reversed state Position Velocity Charge density Current density The motion of classical charged particles in electromagnetic fields is time reversal invariant! (when retarded fields and radiation is ignored) Electric field Magnetic field Tested for different energies and beam currents. More on backtracking: Ph. D. Thesis: CERN Linac 4 Beam Dynamics Studies and Commissioning up to 12 Me. V V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 11
Space-charge compensation in LEBT • Ionization of the residual gas decreases the space charge effects in the LEBT. https: //cds. cern. ch/record/1965917/plots “Effective beam current” is decreased. More on space-charge compensation: Ph. D. Thesis: Space charge compensation on the low energy beam transport of Linac 4 V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 12
Backtracking by varying the effective beam current Measure of how different the 3 backtracked beams are! Measured (at Faraday Cup) I_beam=15 m. A. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 13
Backtracked beams 100% compensation! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 14
the H- Beam measurements Measured (at Faraday Cup) I_beam=14 m. A. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 15
The backtracked H- Beams ~80% compensation! This is what was expected theoretically: V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 http: //cds. cern. ch/record/1975939? ln=en 16
V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 17
First beam through the RFQ: March 2013 The very first beam at 3 Me. V measured with a beam current transformer after the RFQ. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 18
First beam through the RFQ https: //cds. cern. ch/record/1528228 V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 19
RFQ transmission for different LEBT Pressure The measured emittance in LEBT was bigger than the RFQ acceptance. RFQ transmission with nominal beam > 90 % V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 20
V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 21
Medium energy beam transport Linac 4 MEBT V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 22
Emittance measurements and confirmation of transverse beam dynamics Vary the last 4 quads Measure the transverse phase spaces! Backtrack to RFQ exit V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 23
Expected from the RFQ simulations vs. measured beam Blue: from PARMTEQ simulations Red: backtracked V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 24
V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 25
https: //cds. cern. ch/record/2056633/files/ 12 Me. V commissioning stage after DTL-1 Permanent magnet quadrupoles inside drift tubes. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 26
L 4 up to 12 Me. V with the measurement bench V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 27
Estimate the RF phase with transmission measurements MEBT bunchers off MEBT bunchers on beam vs. acceptance V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 Transmission through 28 DTL-1
Time of Flight measurements for different RF amplitudes of DTL tank-1 VT: Operational tank voltage Dots: measurement Lines: simulation V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 29
Direct Emittance measurements at 12 Me. V The comparison of the space plots of the measured (red) and simulated (blue) beams after DTL tank 1. Permanent magnet focusing channel works as designed!!! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 30
important step!!! Requires Linac 4 team to have another celebration ! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 31
V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 32
50 Me. V commissioning stage RFQ DTL Tank-1 DTL Tank-2 DTL Tank-3 V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 Measurement Bench 33
It was not always boring ? ? ? 20 m. A Tank-1 Tank-2 5 m. A Tank-3 Measurement Bench 20 m. A before the DTL When we started the 50 Me. V stage, we had up to 5 m. A at the measurement bench. 25% transmission! Not really what we expected (should be 100%)! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 34
Where is the problem? Tank-1 Tank-2 Measurement Bench Tank-3 High losses measured by Radiation Protection Group Permanent magnet quads Q 22 Q 31 Q 21 Tank-2 Tank-3 Q 33 Measurement Bench Suspicion on inverted quads. We had to be sure before any intervention. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 35
Trouble shooting with the help of simulations Study different scenarios with simulation codes and identify the problem! Permanent magnet quads Q 22 Q 31 Q 21 Tank-2 Q 33 Tank-3 Measurement Bench Simulation: When Both Q 22 and Q 31 are inverted (z= 0 DTL start) Transmission and measured beam sizes on the bench agreed well with this scenario. The intertank between the DTL Tank 2 -Tank 3 was opened. It was confirmed that the two quads on the covers (end of tank 2 beginning of tank 3) were inverted. After the polarity of the quads were corrected, expected transmission was recovered. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 36
Life is back to normal • Transmission was recovered. • After setting the phase and amplitude of the DTL cavities we started beam measurements. Tank-1 Tank-2 Tank-3 Measurement Bench Above 12 Me. V: Indirect measurement of transverse emittance using measured beam profiles at three secondary electron emission (SEM) grids. Indirect measurement of longitudinal emittance using measured beam profiles at bunch shape monitor (BSM). Space-charge must to be taken into account! Used during the beam commissioning at 50 and 100 Me. V. 37
indirect emittance measurement, 3 Monitor method Rms ellipse Beam profile V. A. Dimov HB 2016, Malmö, Sweden 6 July 2016 38
indirect emittance measurement, 3 monitor method Rms ellipse ? Beam profile V. A. Dimov HB 2016, Malmö, Sweden 6 July 2016 39
3 Monitor method, space-charge effects are ignored ? Transfer matrix from well known beam line Information we get from the measured rms beam size!!! V. A. Dimov HB 2016, Malmö, Sweden 6 July 2016 40
3 monitor method, space-charge effects are ignored ? Transfer matrix from well known beam line Information we get from the measured rms beam size!!! Where do they come from in the initial phase space? V. A. Dimov HB 2016, Malmö, Sweden 6 July 2016 41
3 monitor method, space-charge effects are ignored Linear mapping of the measured rms beam size onto the initial phase space. Initial phase space V. A. Dimov HB 2016, Malmö, Sweden 6 July 2016 42
3 monitor method, space-charge effects are ignored Linear mapping of the measured rms beam size onto the initial phase space. Initial phase space V. A. Dimov HB 2016, Malmö, Sweden 6 July 2016 43
3 monitor method, space-charge effects are ignored Linear mapping of the measured rms beam size onto the initial phase space. Initial phase space V. A. Dimov HB 2016, Malmö, Sweden 6 July 2016 44
Rm se m itt an ce ell ip s e 3 monitor method, space-charge effects are ignored Linear mapping of the measured rms beam size onto the initial phase space. Initial phase space V. A. Dimov HB 2016, Malmö, Sweden 6 July 2016 45
Phase space tomography, spacecharge effects are ignored One can linearly map the measured profiles onto the initial phase space and use tomography to reconstruct the distribution of particle density in a phase space. Linear mapping of the measured profiles onto the initial phase space. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 46
What about space charge? From the entrance of the bench Transverse to SEM-3 no space-charge From the entrance of the bench Transverse to SEM-3 with space-charge In the transverse planes, in case of space-charge, linear mapping is not possible! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 47
Including the effects of Space charge We can extend the classical methods by combining them with multi-particle tracking including space-charge effects. For the indirect emittance measurements in the presence of space charge, two methods were developed, tested and applied during the Linac 4 commissioning ØThe “Forward Method” Ø Takes measured rms beam sizes as input. Ø Estimates rms emittance, alpha and beta. Ø Simpler but still very powerful. ØHybrid phase space tomography Ø Takes measured beam profiles as input. Ø More sophisticated, estimates phase space density. Both methods use multi-particle tracking including space-charge! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 48
The forward method Matching the input beam to the measured beam sizes. 3 horizontal beam size from 3 monitors 3 vertical beam size from 3 monitors J-B. Lallement, A. M. Lombardi and P. A. Posocco, “Linac 4 beam commissioning strategy”, in Proc. HB’ 12, Beijing, China, Sept. 2012, 283 -285. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 49
Hybrid phase space tomography • Hybrid phase-space tomography combines multiparticle tracking (including space-charge) and tomography. • PATH is used for the multi-particle tracking. • PATH can give initial coordinates of any selected particles along the beam line. Simplifies mapping even in the case of nonlinear mapping. From the entrance of the bench Transverse to SEM-3 with space-charge V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 50
Hybrid phase space tomography Binned measurement data from 3 monitors Simulate with spacecharge • Simulate the initial test beam by including space-charge. • Find which particles fall on which wires. • Deduce the new distribution of density in the phase space. • Generate a new beam distribution and use it for the next iteration. More on tomographic reconstruction: https: //hb 2016. esss. se/prepress/talks/wepm 1 y 01_talk. pdf https: //hb 2016. esss. se/prepress/papers/wepm 1 y 01. pdf V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 51
BACK to Linac 4 50 Me. V measurements Transverse Comparison of phase space plots of the expected beam (grayscale) and measured at 50 Me. V (colour scale) after the DTL. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 52
Application to the longitudinal plane TY I V A RF C Both forward method and hybrid phase space tomography can be applied to the longitudinal phase space reconstruction where the phase and/or amplitude of an RF cavity is varied and the phase or momentum profile is measured downstream. In the case of Linac 4, phase spread was measured by a BSM. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 53
50 Me. V commissioning Longitudinal 30 Me. V Before DTL Tank 3 Comparison of the phase space plots of the measured (grayscale) and expected (colour scale) beams at the entrance of the DTL tank 3 at 30 Me. V. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 54
V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 55
100 Me. V stage DTL Tank-3 CCDTL Mod-1 CCDTL Mod-2 CCDTL Mod-3 CCDTL Mod-4 CCDTL Mod-5 CCDTL Mod-6 CCDTL Mod-7 PIMS 1 Diagnostic Bench Cell-Coupled Drift Tube Linac Module. Pi-Mode Structure tank V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 56
Setting cavities one by one Dots: measurement Lines: simulation CCDTL Module 2 CCDTL Module-7 V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 CCDTL Module-4 PIMS Tank-1 57
First 107 Me. V beam V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 58
100 Me. V commissioning Beam at 50 Me. V DTL Tank-3 CCDTL Mod-1 CCDTL Mod-2 CCDTL Mod-3 CCDTL Mod-4 CCDTL Mod-5 CCDTL Mod-6 CCDTL Mod-7 PIMS 1 Diagnostic Bench Comparison of the phase space plots of the expected (grayscale) and measured (colour scale) beams at 50 Me. V. Measurements with hybrid phase space tomography. Expected beam: previously measured in MEBT then simulated. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 59
100 Me. V commissioning Beam at 80 Me. V DTL Tank-3 CCDTL Mod-1 CCDTL Mod-2 CCDTL Mod-3 CCDTL Mod-4 CCDTL Mod-5 CCDTL Mod-6 CCDTL Mod-7 PIMS 1 Diagnostic Bench Comparison of the phase space plots of the expected (grayscale) and measured (colour scale) beams at 80 Me. V. Measurements with hybrid phase space tomography. Expected beam: previously measured in MEBT then simulated. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 60
100 Me. V commissioning Beam at 107 Me. V DTL Tank-3 CCDTL Mod-1 CCDTL Mod-2 CCDTL Mod-3 CCDTL Mod-4 CCDTL Mod-5 CCDTL Mod-6 CCDTL Mod-7 PIMS 1 Diagnostic Bench Comparison of the phase space plots of the expected (colour scale) and measured (grayscale) beams at 107 Me. V. Measurements with hybrid phase space tomography. Expected beam: previously measured in MEBT then simulated. V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 61
Coming soon V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 62
ATION SIMUL MEAS UREM E NT Conclusion Successful Beam Commissioning t. Hank you! V. A. Dimov - Beam dynamics tools for the Linac 4 commissioning - 5 August 2016 63
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