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).

L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

RFQ, IH1, IH2 UNILAC at GSI: Overview Alvarez DTL

Transfer to Synchrotron MEVVA MUCIS 1 ≤ A/q ≤ 65 RFQ IH1 IH2 HLI: (ECR,RFQ,IH) 1 ≤ A/q ≤ 9.5

Alvarez DTL PIG Gas Stripper

2.2 keV/u β = 0.0022

120 keV/u β = 0.016

1.4 MeV/u β = 0.054

11.4 MeV/u β = 0.16

L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

The UNILAC Alvarez DTL

Tank : E [MeV/u] : 1.4

A1 3.6

A2a A2b 4.8

54 m 5.9

A3 8.6

A4 • 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°) 11.4

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Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Section in Front of DTL

Gas Stripper 36 MHz 108 MHz L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Experimental Set-up & Procedure

rms-bunch length measurement • set beam current to 7.1 mA of 40 Ar 10+ (equiv. to FAIR design of 15 mA of 238 U 28+ ) • 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 L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Measurement

Data Reduction

Simulations • projection of 6-dim to 2-dim plane • matrix of pixels • pixel size 0.8 mm / 0.5 mrad • evaluation based on pixel contents • full 6-dim information available to compare measurement and simulation adequately, the evaluation procedures must be identical L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Data Reduction

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

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

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 L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Re-Construction of initial rms-Parameters for Simulations

horizontal vertical Start of Simulations check (β  ε) l Buncher 36 MHz rms-tracking backwards → (α, β, ε) xy Buncher 108 MHz DTL meas. (α, β, ε) xy guessed (α, β, ε) l 1. Selfconsistent backtracking finding ( α,β,ε) l that fit to measured bunch length 2. Varification wether applied machine settings would give full DTL transmission L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

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 0.25

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hor., Gauss_2s hor., Gauss_4s hor., Input for Sim.

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Number of Particles [% ]

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Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

90 100

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 L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

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 4 σ assumed L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Beam Transmission through DTL

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Transverse Phase Advance (zero current) [deg]

90 All codes reproduce measured full transmission. LORASR is lower by few percent L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

σ o = 35 °

Shapes of Final Horizontal Distributions

σ o = 60 ° σ o = 90 °

Int / Int_max [%]

0 – 5 5 – 10 10 – 20 20 – 40 40 -100 • agreement for intermediate σ o • disagreement for low/high σ o • high σ o : attached wings (islands) L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

σ o = 35 °

Shapes of Final Vertical Distributions

σ o = 60 ° σ o = 90 °

Int / Int_max [%]

0 – 5 5 – 10 10 – 20 20 – 40 40 -100 • differences even at intermediate σ o • high σ o : no attached wings L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Evolution of Simulated rms-Emittances (100%)

• growth occurs mainly along first two tanks (agrees to previous measurements*) *www-dapnia.cea.fr/Phocea/file.php?class=std&&file=Doc/Care/care-report-07-030.pdf

• LORASR predicts strongest growth • lowest growth at intermediate phase advances L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Final 95%-rms Emittances as Function of Phase Advance

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ver., DYNAMION ver., PARMILA ver., PARTRAN ver., LORASR 40 50 60 70 80

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Transverse Phase Advance (zero current) [deg]

90 • three codes underestimate growth • LORASR predicts more growth • codes predict peak at σ o =70 ° • three codes fit to meas. (except σ o ≤ 45°) • LORASR predicts more growth • codes predict peak at σ o =70 ° (but LORASR) results do not depend on initial long. emittance within 0.1

∙ ε l,o and 2∙ ε l,o L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Final 95%-rms Emittances as Function of Phase Advance

(horizontal + vertical) / 2 0.8

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Transverse Phase Advance (zero current) [deg]

90 • codes and measurements reveal minimum growth at σ o ≈ 60° • LORASR predicts strongest growth • DYNAMION, PARMILA, PARTRAN fit well at σ o ≥ 60°, LORASR fits well at σ o ≤ 60° • codes predict peak at σ o =70 ° (but LORASR) L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Mismatch to Periodic DTL Envelopes

rms-tracking algorithm for re-construction of initial distribution was used to estimate mismatch to DTL 1.0

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Rf Linear Accelerators

, p. 217 0.6

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90 L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

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) 1.0

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Transverse Phase Advance (zero current) [deg]

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

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

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) L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Outlook

• Using improved rms-matching measurements to be extended towards σ o ≈ 130° • Emittances to be measured after first DTL tank to avoid inter-tank-mismatch • Simulations predict a space charge driven 4 th order resonance (talk by D. Jeon) • Attempt for experimental verfication at UNILAC scheduled for Dec. 2008 0.4

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125 L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

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Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Gesellschaft für SchwerIonenforschung GSI

Synchrotron, Bδ = 18 Tm p: 4 GeV Ne: 2 GeV U: 1 GeV 3 sources Fragment Separator Stor. Ring, Bδ = 10 Tm UNILAC, p – U : 3 – 12 MeV/u ion species vary from pulse to pulse: simultaneous experiments using different ions High Energy Physics L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Construction of initial rms-Parameters for Simulations

initial bunch length & transv. emittances measured at different locations !!

"A" 15° 30° Buncher 36 MHz 15° Quadrupoles Buncher 108 MHz transv. emitt. meas. "t" Alvarez 1 st Tank bunch length meas. "l" starting point of simulations "s" • 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 -> 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 L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Re-construction of initial rms-Parameters for Simulations

"A" 15° 30° Buncher 36 MHz 15° Quadrupoles Buncher 108 MHz transv. emitt. meas. "t" 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 x&y-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": -> ok • if not: -> 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: -> ok, rms-parameters of distribution re-constructed • no agreement: -> do different guess on long. Twiss parameters at "t" L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

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) some halo strong halo 0 100 fraction of particles [%] L. Groening ,

Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Phase Advances

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Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

Dependence on Initial Long. rms-Emittance Value

(using Gaussians cut at 2 σ in each plane) 0.5

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Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL