Folie 1

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Simulation of Experiments on Transverse
rms-Emittance Growth Along an Alvarez DTL
L. Groening, W. Barth, W. Bayer, G. Clemente, L.
Dahl, P. Forck, P. Gerhard, I. Hofmann, G. Riehl,
S. Yaramyshev, GSI, Germany D. Jeon, ORNL,
U.S.A. D. Uriot, CEA/Saclay, France R. Tiede,
University of Frankfurt, Germany

• Introduction and set-up
• Data reduction
• Reconstruction of initial distribution
• Results of experiment and simulations
• Emittance growth reduction by rms-matching
• Summary outlook

We acknowledge the support of the European
Community Research Infrastructure Activity
under the FP6 "Structuring the European Research
Area" program (CARE, contract number
RII3-CT-2003-506395).
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UNILAC at GSI Overview
RFQ, IH1, IH2
Alvarez DTL
Transfer to Synchrotron
HLI (ECR,RFQ,IH)
MEVVA MUCIS
1 A/q 9.5
1 A/q 65
Alvarez DTL
RFQ IH1 IH2
PIG
Gas Stripper
11.4 MeV/u ß 0.16
2.2 keV/u ß 0.0022
120 keV/u ß 0.016
1.4 MeV/u ß 0.054
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The UNILAC Alvarez DTL
A1
Tank
A2a
A3
A4
A2b
E MeV/u
1.4
3.6
4.8
5.9
8.6
11.4
54 m

• 5 independent rf-tanks
• 108 MHz, 192 rf-cells
• DTL based on F-D-D-F focusing
• DC-quads grouped to 13 families
• Inter-tank focusing F-D-F
• Synchr. rf-phases -(30,30,30,25,25)

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Section in Front of DTL
Gas Stripper
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Experimental Set-up Procedure
rms-bunch length measurement

• set beam current to 7.1 mA of 40Ar10 (equiv. to
  FAIR design of 15 mA of 238U28)
• measure hor., ver., emittance and long.
  rms-bunch length at DTL entrance
• set DTL transverse phase advance to values from
  35 to 90
• tune depression varied from 21 (90) to 43
  (35)
• measure transmission, hor., and ver.
  rms-emittance at DTL exit

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Data Reduction

• Measurement
• projection of 6-dim to 2-dim plane
• matrix of pixels
• pixel size 0.8 mm / 0.5 mrad
• evaluation based on pixel contents

• Simulations
• full 6-dim information available

to compare measurement and simulation adequately,
the evaluation procedures must be identical
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Data Reduction

• particle coordinates from simulations are
  projected onto virtual meas. device
• projection is evaluated as a measurement

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Definition of Fractional rms-Emittance

• rms-emittance from a fraction of p of the total
  intensity
• calculate sum ?100 of all pixel contents
• sort pixels from top by their contents
• sum them up until the fraction p from ?100 is
  reached
• use the pixels included in this sum for
  rms-emittance evaluation

benchmarking used p 95 of the intensity
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Re-Construction of initial rms-Parameters for
Simulations
horizontal
vertical
Start of Simulations
DTL
Buncher 36 MHz
Buncher 108 MHz
? (a, ß, e)xy
check (ß?e)l
rms-tracking backwards
meas. (a, ß, e)xy
bunch length measurement
guessed (a, ß, e)l

• Selfconsistent backtracking finding (a,ß,e)l that
  fit to measured bunch length
• Varification wether applied machine settings
  would give full DTL transmission

10
Re-construction of initial type of Distribution
measured in front of DTL
horizontal
vertical
measured initial distribution inhabits different
amount of halo horizontally and vertically
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Re-construction of initial type of Distribution

• Gauss, Lorentz, Waterbag distributions do not
  fit the measured amount of halo
• Several functions tried in order to fit halo in
  both planes
• function found as

applying different powers for different planes
the amount of halo can be reproduced
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Initial Distribution and Codes
initial distribution
Simulations with four different codes as used by
the participating labs DYNAMION (GSI) PARMILA
(SNS) PARTRAN (CEA/Saclay) LORASR (Univ. of
Frankfurt)
Gaussian cut at 4s assumed
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Beam Transmission through DTL
All codes reproduce measured full transmission.
LORASR is lower by few percent
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Shapes of Final Horizontal Distributions

• agreement for intermediate so
• disagreement for low/high so
• high so attached wings (islands)

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Shapes of Final Vertical Distributions

• differences even at intermediate so
• high so no attached wings

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Evolution of Simulated rms-Emittances (100)

• growth occurs mainly along first two tanks
  (agrees to previous measurements)
• LORASR predicts strongest growth
• lowest growth at intermediate phase advances

www-dapnia.cea.fr/Phocea/file.php?classstdfile
Doc/Care/care-report-07-030.pdf
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Final 95-rms Emittances as Function of Phase
Advance
vertical
horizontal

• three codes underestimate growth
• LORASR predicts more growth
• codes predict peak at so70

• three codes fit to meas. (except so 45)
• LORASR predicts more growth
• codes predict peak at so70 (but LORASR)

results do not depend on initial long. emittance
within 0.1el,o and 2el,o
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Final 95-rms Emittances as Function of Phase
Advance
(horizontal vertical) / 2

• codes and measurements reveal minimum growth at
  so 60
• LORASR predicts strongest growth
• DYNAMION, PARMILA, PARTRAN fit well at so 60,
  LORASR fits well at so 60
• codes predict peak at so70 (but LORASR)

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Mismatch to Periodic DTL Envelopes
rms-tracking algorithm for re-construction of
initial distribution was used to estimate
mismatch to DTL
T.P. Wangler, Rf Linear Accelerators, p. 217
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Reduction of Mismatch

• algorithm used to rms-match (incl. space charge)
  the initial distribution to periodic DTL
• test of matching by re-measuring emittance
  growth (one year later)

• significant reduction of emittance growth by
  rms-matching including space charge
• reduction demonstrates that algorithm to
  re-construct initial rms-values is valid

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Summary

• rms-emittance growth along a 5-tank DTL measured
  for 12 phase advances from ..35 to 90
• Measurements simulated using four codes
  (DYNAMION, PARMILA, PARTRAN, LORASR)
• Special emphasis put on re-construction of
  amount of halo within initial distribution
• Very good agreement found among DYNAMION,
  PARMILA, and PARTRAN
• LORASR predicts higher growth rates with respect
  to other three codes
• Codes describe well the behavior of measured sum
  of hor. and ver. emittances
• Considerable differences between meas. sim.
  growth within single planes
• For low and high phase advances orientations and
  shapes of final distributions ..depend on the
  code
• Systematic reduction of rms-mismatch to DTL
  under space charge conditions
• rms-mismatch reduction resulted in considerable
  emittance growth reduction
• (experimental reduction from 90 to 20 for
  space charge conditions equivalent to FAIR
  requirements)

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Outlook

• Using improved rms-matching measurements to be
  extended towards so 130
• Emittances to be measured after first DTL tank
  to avoid inter-tank-mismatch
• Simulations predict a space charge driven 4th
  order resonance (talk by D. Jeon)
• Attempt for experimental verfication at UNILAC
  scheduled for Dec. 2008

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Gesellschaft für SchwerIonenforschung GSI
Synchrotron, Bd 18 Tm p 4 GeV Ne 2
GeV U 1 GeV
3 sources
Fragment Separator
Stor. Ring, Bd 10 Tm
UNILAC, p U 3 12 MeV/u
High Energy Physics
ion species vary from pulse to pulse simultaneous
experiments using different ions
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Construction of initial rms-Parameters for
Simulations
initial bunch length transv. emittances
measured at different locations !!
Buncher 108 MHz
Buncher 36 MHz
Quadrupoles
15
15
"A"
30
Alvarez 1st Tank
transv. emitt. meas. "t"
starting point of simulations "s"
bunch length meas. "l"

• DTL transmission is very sensitive to buncher
  settings, i.e. long. mismatch
• applied buncher settings resulted in full DTL
  transmission and minimized low energy tails
• -gt useful in re-constructing the long. input
  distribution for simulations
• transv. and long. emittance were measured at
  different locations, i.e. at "t" "l"
• distances from "l" and "s" to point "A" differ
  by 0.4 m
• to merge transv. long. measurements together
  some approximations were used

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Re-construction of initial rms-Parameters for
Simulations
Buncher 108 MHz
Buncher 36 MHz
Quadrupoles
15
"A"
15
transv. emitt. meas. "t"
30
bunch length meas. "l"
Starting point of simulations "s"

• to merge measurements together some
  approximations were used
• "transport" from "l" to "s" approximated by
  drift of 0.4 m (with space charge)
• at "t" combine measured xy-rms-Twiss
  parameters with guessed long. rms-Twiss
  ..parameters
• rms-tracking with space charge from "t" to
  "s-0.4m", using applied machine settings
• if bunch length at "s-0.4m" agrees reasonably
  with measured one at "l" -gt ok
• if not -gt do different guess on long. Twiss
  parameters at "t"
• put "s"-rms-Twiss parameters (x,y,l) into
  rms-matching routine
• compare suggested buncher settings with those
  used during experiment
• agreement -gt ok, rms-parameters of distribution
  re-constructed
• no agreement -gt do different guess on long.
  Twiss parameters at "t"

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Re-construction of initial type of Distribution

• emittance growth is sensitive to type of initial
  distribution (i.e. amount of halo)
• amount of halo can be visualized by plotting the
  fractional emittance vs. fraction

no halo (KV)
fractional rms-emittance
some halo
strong halo
0
100
fraction of particles
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Phase Advances
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Dependence on Initial Long. rms-Emittance Value
(using Gaussians cut at 2s in each plane)