L. Groening, 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 Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL 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 ).

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL UNILAC at GSI: Overview MEVVA MUCIS PIG RFQ IH1 IH2 Alvarez DTL HLI: (ECR,RFQ,IH) Transfer to Synchrotron 2.2 keV/u β = keV/u β = MeV/u β = 0.16 RFQ, IH1, IH2Alvarez DTL Gas Stripper 1.4 MeV/u β = ≤ A/q ≤ ≤ A/q ≤ 65

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL The UNILAC Alvarez DTL E [MeV/u] : Tank : A1 A2a A3 A4 A2b 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°) 54 m

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL Section in Front of DTL 36 MHz 108 MHz Gas Stripper

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL Experimental Set-up & Procedure 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 rms-bunch length measurement

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL 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

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 horizontal vertical → (α, β, ε) xy rms-tracking backwards meas. (α, β, ε) xy guessed (α, β, ε) l bunch length measurement check (β  ε) l Re-Construction of initial rms-Parameters for Simulations 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 DTL Buncher 108 MHz Buncher 36 MHz Start of Simulations

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

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL 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 Gaussian cut at 4σ assumed Simulations with four different codes as used by the participating labs: DYNAMION (GSI) PARMILA (SNS) PARTRAN (CEA/Saclay) LORASR (Univ. of Frankfurt)

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL Beam Transmission through DTL 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 Shapes of Final Horizontal Distributions σ o = 35°σ o = 60° Experiment σ o = 90° DYNAMION PARMILA PARTRAN LORASR agreement for intermediate σ o disagreement for low/high σ o high σ o : attached wings (islands) Int / Int_max [%] 0 – 5 5 – – –

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL σ o = 35°σ o = 60° Experiment σ o = 90° DYNAMION PARMILA PARTRAN LORASR Shapes of Final Vertical Distributions differences even at intermediate σ o high σ o : no attached wings Int / Int_max [%] 0 – 5 5 – – –

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*) LORASR predicts strongest growth lowest growth at intermediate phase advances *www-dapnia.cea.fr/Phocea/file.php?class=std&&file=Doc/Care/care-report pdf

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 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 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 T.P. Wangler, Rf Linear Accelerators, p. 217

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) 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

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL

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

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL Alvarez 1 st Tank transv. emitt. meas. "t" Buncher 36 MHz Buncher 108 MHz Quadrupoles bunch length meas. "l" 15° 30° starting point of simulations "s" Construction of initial rms-Parameters for Simulations 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 "A" initial bunch length & transv. emittances measured at different locations !!

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL transv. emitt. meas. "t" Buncher 36 MHz Buncher 108 MHz Quadrupoles bunch length meas. "l" 15° 30° Starting point of simulations "s" Re-construction of initial rms-Parameters for Simulations 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" "A"

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 fractional rms-emittance fraction of particles [%] 0100 no halo (KV) some halo strong halo

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL Phase Advances

L. Groening, Simulation of Experiments on Transverse rms-Emittance Growth Along an Alvarez DTL Dependence on Initial Long. rms-Emittance Value (using Gaussians cut at 2σ in each plane)