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Longitudinal beam loss mechanisms for LIU and LAGUNA beams. E. Shaposhnikova w ith input from T. Argyropoulos , T. Bohl , J. E. Muller, C. Lazaridis, H. Timko LIU-SPS collimation review CERN 21.11.2013. SPS Beam Performance. - PowerPoint PPT Presentation
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Longitudinal beam loss mechanisms for LIU and LAGUNA beams
E. Shaposhnikovawith input from T. Argyropoulos, T. Bohl, J. E. Muller, C. Lazaridis,
H. Timko
LIU-SPS collimation review CERN 21.11.2013
SPS Beam Performance
*Feasibility including operational viability (especially in the PS) remains to be demonstrated
11/21/2013 LIU-SPS collimation review 2
Operation SPS record After LIU (2020)
Beam type: LHC CNGS LHC CNGS LHC post-CNGS
SPS beam energy [GeV] 450 400 450 400 450 400bunch spacing [ns] 50 5 25 5 25 5bunch intensity/1011 1.6 0.105 1.3 0.13 2.2 0.17number of bunches 144 4200 288 4200 288 4200SPS beam intensity/1013 2.3 4.4 3.75 5.3 6.35 7.0*PS beam intensity/1013 0.6 2.3 1.0 3.0 1.75 4.0*PS momentum [GeV/c] 26 14 26 14 26 14PS cycle length [s] 3.6 1.2 3.6 1.2 3.6 1.2*SPS cycle length [s] 21.6 6.0 21.6 6.0 21.6 6.0SPS average current [μA] 0.17 1.17 0.28 1.4 0.47 1.9
SPS power [kW] 77 470 125 565 211 747
LIU-SPS collimation review 3
LHC beam
11/21/2013
LIU-SPS collimation review 4
Distribution of losses in LHC cycle
• Very large losses in the past, reduced with time (machine tuning, e-cloud scrubbing?)
• Can be a serious limitation in future for very high intensity required by LIU for HL-LHC
• Relative losses increase with intensity N, absolute ~ N2?• Losses occur
– at capture (bunch shape)– on flat bottom (full bucket due to injected bunch shape)– during ramp above 120 GeV/c due to multi-bunch instabilities
or/and controlled longitudinal emittance blow-up (1-2%)
11/21/2013
LIU-SPS collimation review 5
Capture loss due to PS bunch shape(after rotation in longitudinal phase space)
Shape can be improved by higher PS voltage: => tails are less populated but losses are there!
11/21/2013
H. Timko et al.,ESME simulationsof realistic bunchdistribution from PS tomography(no intensity effects included)
bestresults:2.5% loss
operation:5% loss
LIU-SPS collimation review 6
Capture losses: uncaptured beam after injection(200 MHz signal )
Injection at 26 GeV/c A few seconds later
11/21/2013
Uncaptured beam is always moving to the left.Energy loss (dp/p < 0) due to resistive impedance?
Uncaptured beam
Transmission of 25 ns beamin MDs with Q20 optics (2012)
11/21/2013 LIU-SPS collimation review 7
J. Esteban Muller et al.
=> Large losses and also increase with intensity
LIU-SPS collimation review 8
Losses Transmission (from BCT and Larger) ~ 85-89 % for single batch 90-92 % for 3 or 4 batches continuous losses along flat bottom
larger inj. emittance with similar intensitiesÞ scrapping
on FB
T. Argyropoulos et al.
Single batch
11/21/2013
LIU-SPS collimation review 9
Voltage programs for Q20 (MDs) 200 MHz voltage program settings:
I. 2.5 to 4.5 MV - 4 dips at injections II. 4.5 MV constantIII. 3.5 to 4.5 MV – 1st injection and 2.5 to 4.5 MV – for the restIV. As in III + 500 kV at acceleration and flat top (avoid losses for
higher intensities)V. As in IV but no first dip
optimal
T. Argyropoulos et al.
Þ Voltage increase during ramp required for higher intensities
Þ Voltage close to the limit
Þ For higher intensitiesÞ particle lossesorÞ increase length of the
cycleÞ longer LHC filling time
11/21/2013
Acceleration: voltage and power for nominal intensity in Q20 and Q26
Voltage Power
11/21/2013 LIU-SPS collimation review 10
=> Power will be at the limit also during acceleration above nominal intensity!
LIU-SPS collimation review 11
High intensity LHC beam• High intensity: Np = 1.36x1011 p/b at FT
• TWC 200 MHz voltage program: case III
Controlled emittance blow-up is difficult to optimise for high intensity beam
11/21/2013
LIU-SPS collimation review 12
High intensity FT (LBNO) beam
11/21/2013
LIU-SPS collimation review 13
Main intensity limitations in the SPSfor CNGS-type beam (LBNO)
• Equipment heating (MKE, HOM couplers, beam instrumentation…)
• Beam losses• Transverse damper (40 MHz bandwidth)• RF voltage and power, beam control:
• Beam stability and bucket area for (un)controlled emittance blow-up
• Maximum available voltage in the 200 MHz RF system: – 7.5 (8) MV
• Maximum available RF power in one 200 MHz TW cavity:– 700 kW for full SPS ring (CNGS-type beam)
11/21/2013
LIU-SPS collimation review
LHC and CNGS-type beams in the SPS
• FT/CNGS beam from PS: – practically debunched beam– 5-turn extraction– no bunch-to-bucket transfer– injection below transition
14
Nominal parameters of two main types of proton beam in the SPS
11/21/2013
high intensity run
LIU-SPS collimation review 15
Particle losses during cycle
• Capture– Beam structure from the PS: de-bunched beam with 200
MHz density modulation => no bunch-to-bucket transfer
• Ramp– Uncontrolled emittance blow-up due to instabilities
during transition crossing and at higher energies (Nth ~ 1/E)
– Limited RF bucket area due to beam loading with RF power limited to 750 kW
11/21/2013
LIU-SPS collimation review 16
Loss distribution during high intensity run (2004)
• Injection losses - 5%• Losses on flat bottom ~ 2%• Particles in the kicker gap - losses
at extraction ( 2%) => cleaning by trans. damper
• Capture loss 3-4%• Beam losses at transition: 4%• Continuous losses after transition:
5% - 2% => early beam dump - main intensity limitation for the 2004 record of 5.3x1013
11/21/2013
Critical losses
LIU-SPS collimation review 17
Bunch length along the batch during cycle for high intensity beam (5.6x1013 injected, 15% losses)
(AB-Note-2005-034 RF, T. Bohl et al.)
t=1.315 s
t=3.286 s
t=1.534 sγ>γt
t=4.163 s
11/21/2013
LIU-SPS collimation review 18
FT/CNGS acceleration cycle:voltage and power
Þ at the moment maximum available voltage is used due to uncontrolled emittance blow–up during transition crossing - any voltage reduction leads to beam losses
11/21/2013
Christos Lazaridis (CERN)
MD with CNGS Beam in 2012
● Goals of 2012 measurements :● Study beam stability● Verify present intensity limitations
MD data analysis was done by C. Lazaridis
200MHz RF Voltage Program
Beam momentum
Obtained profiles
~3600 bunches
2 PS batches after 2nd injection in SPS
11/21/2013 LIU-SPS collimation review 19
CNGS Cycle
Christos Lazaridis (CERN)
Nominal CNGS Cycle
• Injected beam is practically debunched
• Bunches not well defined after injection
• transition
• instability at the end of the cycle
Bunch Length
Batch 1Average and min-max
for each frame
Beam structure after injection
Batch 2
11/21/2013 LIU-SPS collimation review 20
a.u.
Christos Lazaridis (CERN)
RF Voltage optimization at injection
Nominal voltage1.99 MV0.6 MV
Nominal voltage
0.6 MV
Batch 1 - 0.6 MV/1.99 VAverage Bunch Length
ms
MV
SPS BCT
11/21/2013 LIU-SPS collimation review 21
Batch 2 - 0.6 MV/1.99 V
• RF voltage at injection was varied in range 0.6 - 2.0 MV leading to changes in emittance• Trying to reduce capture losses=> Nominal 0.9 MV close to optimal
Greater bunch spreadMore capture losses
s
ns
Transition crossing and after
Average Bunch Length
Relative Bunch Length
Batch 1/Batch 2
Reference : 1450 ms
Reference
11/21/2013 LIU-SPS collimation review 22
1457 msγ transition(1480 ms)1490 ms 1501 ms
• Bunch oscillations start immediately after transition (1480.2 ms)
Bunch number
End of cycle
Average Bunch Length
Relative Bunch Length
Batch 1/Batch 2
Reference : 1546 ms
Reference
11/21/2013 LIU-SPS collimation review 23
1932 ms 2760 ms 3588 ms4278 ms
• Beam is very unstable at the end of ramp
• Small losses observed
Bunch number
Christos Lazaridis (CERN)
Reducing beam losses• Losses due to instabilities around
2.8 s in the cycle• Maximum 200 MHz RF voltage
• Tried reducing voltage to improve stability• Constant bucket area• Increasing synchrotron frequency
spread inside the bunch
Nominal voltageModified
ms
Bucket AreaNominal voltage
Modified
Beam Intensity
11/21/2013 LIU-SPS collimation review 24
For intensities ~3.7x1013 losses are 3.5%=> 0.2% reduction in high-energy losses
Proposed changes applied to CNGS cycle
LIU-SPS collimation review 25
Possible future improvements for beam loss reduction
• 200 MHz power upgrade – limit will be still at 750 KW (due to full ring), but with 2 extra sections
• LLRF upgrade of 200 MHz RF– Separate capture of each PS batch in the SPS would allow
voltage capture modulation (e.g. 0.9 MV increased to 2.5 MV) – Variable gain of 1-turn-delay feedback – Upgrade of the frequency range of the feed-forward system
(below 26 GeV/c)• Use of the 800 MHz RF system during cycle• Impedance reduction• Q20 optics(?)
11/21/2013
LIU-SPS collimation review 26
The 200 MHz RF system
Presently both voltage and power are at the limit: 7.5 MV used after transition crossing (due to uncontrolled longitudinal emittance blow-up) Improvement after power upgrade with 6 cavities (18 sections)
4200 bunches spaced by 5 ns
N = 4.8x1013 (Irf = 0.73 A)-> V=7.5 MV
N = 7x1013 (Irf = 1.06 A) -> V = 9 MV
11/21/2013
Voltage available for acceleration with Pmax=0.7 MW
LIU-SPS collimation review 27
Voltage during FT/CNGS cycle for two optics
Q26 Q20
=> voltage above present limit of 7.5 MV even for 0.4 eVs
=> after transition crossing some bunches have emittance > 0.6 eVs
11/21/2013
limit
LIU-SPS collimation review 28
Can new optics help to reduce uncontrolled emittance blow-up?
Voltage program for 0.6 eVs Slip factor (~ beam stability)
11/21/2013
LIU-SPS collimation review 29
Summary• LHC beam
– Capture losses are determined by S-shape of injected bunches – Better stability for larger PS emittance, but more losses as well– Flat bottom losses are defined by full bucket– High energy losses come from beam instabilities and controlled emittance blow-
up in conjunction with limited RF voltage (power)• FT high intensity beam
– Absence of bunch-to-bucket transfer will be always a source of capture loss– Beam control during transition crossing is difficult - a source of losses– Only small increase in available voltage can be expected after the 200 MHz
power upgrade -> limited voltage (bucket) at high energies• Relative losses increase with intensity -> high absolute losses can be
expected during HL-LHC era (and LBNO) in the SPS at high energies unless beam instabilities are eliminated at source (impedance)
11/21/2013
LIU-SPS collimation review 30
LIU-SPS upgrades• Main difference between the two beams:
– injection at 14 GeV/c and transition crossing => different beam control (LLRF)– CNGS beam fills whole SPS ring and LHC beam – only half => different requirements for beam power (continuous and pulsed
regimes)– bunch spacing => multi-bunch effects (instabilities, heating)
• CNGS-type beam will profit from planned SPS upgrades: – impedance reduction (shielding of MKE kickers, …) – e-cloud mitigation– 200 MHz and 800 MHz RF upgrade– beam instrumentation – low γt (transition energy) optics?
11/21/2013