LBNL%20Interests%20in%20the%20PS2

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LBNL Interests in the PS2
US LHC Accelerator Research Program
bnl - fnal- lbnl - slac

• Miguel A. Furman
• LBNL
• mafurman_at_lbl.gov
• LARP CM11
• FNAL, 27-28 October 2008

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Items

• Laser stripping of H
• Laser systems
• Integration with beam optics
• Space-charge effects
• Halo formation, particle losses
• Space-charge compensation
• Conventional collective effects
• Impedances and instabilities
• Multibunch broadband feedback
• Electron-cloud effects
• EC build-up and mitigation
• Effects of EC on beam

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H Stripping for the PS2

• Benefits from the ongoing SNS developments
• Encouraging results in RD tests
• Based upon a three-step approach
• Magnetic stripping of outer electron
• Laser excitation of inner electron
• Magnetic stripping of excited inner electron
• Key goal is 100 stripping
• Needs powerful laser
• LBNL is well equipped for the task (strong
  experience w/ lasers)
• CERN requested a study (deliver a White Paper)
• Potential synergies with Project X

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Optical cavity and H stripping setup
transport optics
from laser
H beam
20cm
Beam travels perpendicular to page
waist, 40 mm
evacuated tube
transmitted power
active alignment
reflected power
piezoelectric positioner, controller (cavity tune)
Four-mirror cavity Round-trip time relatively
independent of focal spot size Cavity length is
actively tuned to stay on optical resonance Pulse
length is long enough to not require
stabilization of laser offset frequency Transport
system needs evacuated tube, active alignment for
stable cavity injection
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Stripping laser source concept and timing
double- passed NdYVO amp
pulsed power supply
2 Hz trigger
l1.064 mm
352 MHz machine timing
50 ps
modelocked NdYAG laser
synch- ronizer
optical switch
NdYVO preamp
1.2 ms burst 352 MHz, 50 ps 200 W during
2 Hz trigger
1.2 ms pulse generator
high voltage pulser
isolator
to transport optics and buildup cavity
Peak output laser power is 10 kW in 50 ps Average
power during 1.2 ms pulse is 200 W Assumes 100x
buildup cavity All components are commercially
available Lasers are diode-pumped for stability,
reliability
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Laser stripping status and plans

• Assessed early feasibility
• Optical parameters for the buildup cavity have
  been calculated to provide required focal spot
  size and roundtrip time
• SNS personnel (S. Danilov) has confidence of
  achieving 100 efficiency with this design
• We have identified vendors for all the laser
  components and cavity optics
• Plans
• Complete feasibility study
• Specify major components
• commercial parts selection and pricing
• Integrate with design of injection optics and
  hardware
• laser system consistent with complete system
  conceptual design
• include specifications of magnets and transfer
  lines
• beam pipe and windows
• Include possible beam diagnostics

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Space-charge effects

• Space charge is a serious intensity limitation in
  the PS and PS Booster
• Effects of space-charge on dynamic aperture and
  beam quality (eg., haloes)
• Combine impedance with space charge on
  single-bunch effects
• Investigate possible space-charge compensation
  schemes
• eg., octupoles, electron lens or neutralization
• Support the effort of collimator designers
• build tools to enable work flow between
  space-charge simulations and collimator design
• Use existing IMPACT and MaryLie/IMPACT codes
• We will add time-dependent B-fields
• Determine required simulation parameters for
  acceptable numerical accuracy
• eg., order of transfer maps, number of
  space-charge kicks, etc.
• Perform long-term simulations with realistic
  lattice
• Include fully 3D space-charge effects
• This will be a collaborative effort with other
  LARP labs
• FNAL benchmark with SYNERGIA code (P.
  Spentzouris)

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Example of long-term simulationspace-charge-driv
en dynamic emittance exchange

• Sample result
• MARYLIE/IMPACT code (3D parallel)
• 1 GeV protons, sp.-ch. tune shift 0.10.3
• Ramp longitudinal tune from below to above
  resonance
• Propagate beam through a linac
• 1 linac period 35o phase adv.
• constant focusing lattice approx.
• Goal check scaling law (I. Hofmann and G.
  Franchetti, PAC07)
• this is the first 3D numerical check
• Part of a longstanding collaboration with GSI on
  space-charge simulations
• 106 macroparticles, 643 grid
• 1.3x106 space-charge kicks (5 kicks/cell)
• 32 hrs on 64 processors (IBM/SP5)

emittances vs. time
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Conventional collective effects

• PS2 will be high-current machine (I2.5 A,
  Ipk12-25 A)
• Need impedance reduction relative to PS
• Estimate single-bunch instabilities in PS2
• Based on best guesses for impedances and vacuum
  chamber geometry
• Develop impedance model and revisit single-bunch
  instabilities
• Contribution of components like bellows etc.
• Include RF system impedances
• based on FNAL booster cavity or a better model if
  available
• Analyze LLRF feedback
• Include 2nd-harmonic RF impedance model
• Revisit instability growth rates for single- and
  multi-bunch cases
• Design a multi-bunch broadband feedback system
• Estimate feedback parameters
• Develop concepts for kickers
• Work will be a SLAC-LBNL-FNAL collaboration

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Electron-cloud effects

• EC is a serious limitation in the SPS and
  possibly in the upgraded injectors
• PS2 EC build-up studies at LBNL started in 2006
• At the request of CERN personnel
• Results presented at LUMI2006, ECL2 and other
  venues
• Effect can be strong
• Sensitivity to the bunch spacing scenarios
• Sensitivity to the vacuum chamber radius
• may influence the RT vs. SC choice
• Simultaneously, we are assessing the EC for the
  FNAL MI upgrade
• At the request of FNAL personnel
• 15 papers since early 2006
• Experimental calibration of simulations at MI
  increases confidence in simulations

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PS2 and MI upgrade
PS2 MI upgrade
Circumference m 1256 3319
RF freq. MHz 40 53
Inj. kin. energy GeV 4 8
Extr. kin. energy GeV 50 (75) 120
Cycling time sec 3 2
Bunch spacing ns 25, 50, 75 19
Bunch popul. 1011 2, 5.4, 6.6 3
Chamber material St. St. (?) St. St.
Transition gamma (30-40)i 20

• In same ballpark vis-à-vis ecloud
• PS2 EC studies will benefit from simulations,
  measurements and code validation at MI

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Examples simulated ecloud density in
PS2()dipole bend, Eb50 GeV, peak SEY1.2, 1.3,
1.4
ecloud density vs. bunch intensity

• Estimated ecloud densities (a few) x 1011 m3
• gt mandatory to examine effect on the beam
• Gröbner (y) is a simple estimate of the
  vertical beam-induced multipacting condition.
• () PS2 parameters used as input to the
  simulation taken from psplusetcparameters.xls
  (F. Zimmermann, 2006). Bunch intensities from R.
  Garoby, BEAM07.

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Ecloud proposed tasks

• Refine assessments of electron-cloud build-up
• Sensitivity to physical and numerical parameters
• Assess the need to combine space charge with
  electron-cloud effects
• Explore parameter space, especially RT vs. SC
  choice
• Compare and understand differences of EC build-up
  at the PS2 vs. FNAL MI upgrade
• Assess electron-cloud mitigation mechanisms
• low-SEY coatings, grooved chambers, clearing
  electrodes
• Assess impact of EC on the PS2 beam
• start with quasistatic approximation
• then extend it to 3D self-consistent simulations,
  including effects from space-charge, gas
  desorption and its ionization
• If above indicates an SPS-style instability,
  design and propose a broadband feedback system
• Work in collaboration with SLAC

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Summary effort level and personnel(this is
LBNLs portion only)

• Laser stripping
• 1/2 FTE per year in FY09 and FY10, plus 20k/yr
  in travel to CERN and SNS
• J. Byrd, R. Wilcox, ???
• Space-charge studies
• For FY09 and beyond, total 1 FTE/per year plus
  30k/yr travel
• R. Ryne, J. Qiang, M. Venturini
• Conventional collective effects
• 1/2 FTE (FY09), 1/2 FTE (FY10)
• J. Byrd, S. de Santis, M. Furman
• Electron-cloud
• FY09 0.7 FTEs plus 30k/yr travel
• FY10 and FY11 0.6 FTEs/yr plus 30k/yr travel
• M. Furman, M. Venturini, J.-L. Vay, G. Penn

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Additional material
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Laser stripping plans

• Complete feasibility study
• Specify major components
• commercial parts selection and pricing
• Integrate with design of injection optics and
  hardware
• laser system consistent with complete system
  conceptual design
• include specifications of magnets and transfer
  lines
• beam pipe and windows
• Include possible beam diagnostics

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MI simulated ecloud build-up C3319.4 m, h588 ,
fRF53 MHz

• Present operation Nb6x1010, 548 bunches/fill
  (Ntot3.3x1013)
• But have reached Nb1x1011 for some fill patterns
• Upgrade goal Nb3x1011 (Ntot1.64x1014)

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Laser stripping technical approach

• High intensity is achieved in optically resonant
  buildup cavity
• Interaction point is some distance away from
  narrow focus, to utilize beam spread angle
• as Doppler frequency spread
• 352 MHz, 1.2 ms burst, 2 Hz repetition rate
• High peak power (in 50 ps) mode-locked laser (at
  352 MHz) is amplified in high average power amp
• Repetition rate and pulse timing is slaved to
  machine frequencies
• Laser beam is transported to optical buildup
  cavity via actively aligned transport optical
  system
• Cavity is actively tuned to maintain coherence
  with incoming pulses, obtain gt100x buildup
• Laser is diode-pumped for high stability and
  reliability

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Ecloud proposed tasks(combined LBNL-SLAC effort)

• Refine assessments of electron-cloud build-up (4
  person-months in FY09)
• Assess the need to combine space charge with
  electron-cloud effects in the simulation effort.
  Assess the feasibility of combining the
  corresponding simulation codes (2 PM in FY09).
• Explore parameter space, especially RT vs. SC
  choice (4 PM in FY09)
• Compare and understand differences of EC build-up
  at the PS2 vs. FNAL MI upgrade (3 PM in FY09)
• Assess electron-cloud mitigation mechanisms
• eg., low-SEY coatings, grooved chambers and
  clearing electrodes (4 PM).
• Assess impact of EC on the PS2 beam
• start with quasistatic approximation
• then extend it to 3D self-consistent simulations,
  including effects from space-charge, gas
  desorption and its ionization (12 PM in FY10).
• If above indicates a single-bunch instability,
  design and propose a broadband feedback system (4
  PM in FY10 or FY11)