Beam loss and longitudinal emittance growth in SIS

M. Kirk

I. Hofmann, O. Boine-Frankenheim, P. Spiller, P. Hülsmann,

G. Franchetti, H. Damerau, H. Günter König, H. Klingbeil,

M. Kumm, P. Schütt, A. Redelbach

• Optimisation of injection into SIS

• Beam loss measurement and its interpretation

• Method used to determine the emittance

• Emittance growth determined from theory and experiment

• Summary

Outline of talk

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dp/p FWHM=+/-5.2780E-4 [11:10:05]dp/p FWHM=+/-5.0654E-4 [11:11:15]dp/p FWHM=+/-5.1686E-4 [11:12:21]dp/p FWHM=+/-4.9103E-4 [11:13:30]dp/p FWHM=+/-9.2129E-4 [04:46:53]dp/p FWHM=+/-8.6965E-4 [02:27:58]dp/p FWHM=+/-8.7535E-4 [02:28:55]dp/p FWHM=+/-8.0942E-4 [02:29:23]dp/p FWHM=+/-7.6959E-4 [12:59:09]dp/p FWHM=+/-7.6672E-4 [01:00:43]dp/p FWHM=+/-7.9835E-4 [01:01:16]

Change in relative momentum spread from Unilac during the course of the experiment. Please note that the rightmost point corresponds to a momentum distribution that is asymmetric and thus non-Gaussian, with a low FWHM but the rms is still considerably bigger and the full width at 10% of the maximum is ±9.45x10-4

Longitudinal Schottky measurements on the beam shortly after multi-turn injection into SIS.

Schottky at injection for UNILAC and SIS setup

Momentum spread of debunched beam foroptimisation of the injection RF frequency

Optimizing dp/p of the debunched beam by varying radial injection offset; the RPOSI parameter. The chosen optimal setting is indicated by the dashed line.

RF Amplitude Start Schottkymeasurement

Time

Fig. 1. Waterfall plot of a single bunch pickup -signal (h=4) starting from ~3 ms before the RF amplitude flattop was reached. Bunch profiles lie horizontally.

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Frequency [kHz]

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Fig. 2 Log-Power-Frequency spectrum of the bunch signal in figure 1.

[Kirk et al., Experimental optimisation of the RF capture frequency at injection in SIS, GSI Annual Report, 2003]

Coherent bunch oscillations:a possible way to optimize the cavity frequency

at injection

Ts

Sensitivity of the sideband heights to the injection offset…

238U73+

11.4 MeV/uGap amplitude 1kVSelf-fields negligible Injection offset 0 MeV

Injection offset 0.002 MeV

…

Injection offset 0.01 MeV

…

Quadrupolar

Dipolar oscillation

Injection offset 0.03 MeV

…

ESR measurement on a 40Ar18+ DC-beam at 250MeV/u kinetic energy. Longitudinal Schottky band at m=30 used as test data for the fitting program. Iions=1mA. Electron current from the cooler was Ie=1A[Original measurement: Schaaf, 1990. Fitting program: Ziemann, Svedberg Laboratory]

2

2

)(

)(2

))()((1

)(2

1)(

2

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zEwzzwiiGF

zEwBeAP C

D

Schottky spectrum under high phasespace density

• Optimisation of injection into SIS

• Beam loss measurement and its interpretation

• Method used to determine the emittance

• Emittance growth determined from theory and experiment

• Summary

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Time [ms]

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ESME simulation of 40Ar10+. Beam loss profile during the RF-capture (without space charge). The transverse acceptance was 200mm (beampipe diameter). Momentum spread of DC beam taken from Schottky spectrum data.

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DC current traformer measurement: Beam loss profile of 40Ar10+ during the RF-capture.

Simulation Experiment

Beam losses during RF capture

Tune resonance diagram, showing 2nd and 3rd order resonances in the neighbourhood of the working point (4.275, 3.255). The crosses represent the experimentally detected resonance lines.

Losses from space charge tune shift?

Franchetti et al.

yxyf

incy B

g

ec

IRr

A

ZQ

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330max,

Ions 40Ar10+

Intensity 5x1010

.g 2

Bf 0.31

Kinetic energy 11.39 MeV/u

dp/p (2 x RMS) 3.39x10-3

Emittances required:x 128 mm mrady 32 mm mradto reach the resonance indicated by the arrow in fig. A1Transverse acceptance:x, max = 200 mm mrady, max = 50 mm mrad

Working point

Resonance concerned

• Optimisation of injection into SIS

• Beam loss measurement and its interpretation

• Method used to determine the emittance

• Emittance growth determined from theory and experiment

• Summary

Tomographical reconstructionThe ESME tracking code (FermiLab) was used to benchmark Tomo (version 2, CERN) under conditions of high phasespace densities.

Producedby ESME

Tomo: Phasespace reconstruction

Projected reconstructionand original profile (black)

Tomography applied to the Ar-Experiment

Persistent tail!

Beam spectrum

Pickup response

Tails are caused by the bandwidth of the pickupsDeconvolutedOriginal

PUPUB RCi

RcligIU

1))exp(1(

• Optimisation of injection into SIS

• Beam loss measurement and its interpretation

• Method used to determine the emittance

• Emittance growth determined from theory and experiment

• Summary

Phasespace of beam derived from tomographical reconstuction at t=100ms

RF-gap voltage amplitude

RF-Gap voltage frequency

Simulation of Ar-experiment with ESME

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Experiment Simulation

40Ar10+-Experiment

Stage in machine cycle Growth TotalCapture & acceleration (0-100ms) 40%Rest of acceleration (100-640ms) 18% 65.2%

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Klingbeil et al.

Digital system for dual RF cavity synchronization• Frequency response of low-level RF/driver/power amplifier/cavity chain different for both cavities• Cavity synchronization system compensates for these differences• Synchronism better than ±5 achieved• No difference observed between single and dual cavity operation• DSP system and additional H/W & S/W components flexible enough for beam phase control (future)

Bunching factor versus time from 20ms to 200ms after start of gap voltage ramp.DSP parameters of dual cavity phase control: Gain=-1000, Noise level=2000

14N7+-Experiment with RF digital synchronization

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Simulation (w ith direct space charge)

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Ar18+ Experiment

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Gap voltage amplitude

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DC Transformer

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Current [mA]Beam loss

40Ar18+ Experiment

Intensity 2x109

Max. ramp rate 2.3T/s‘Rounding’ time 32ms

Kirk, Schütt, Redelbach.October 2004

Trig. forSpectrum Analyzer

Gap signal

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Emittance growth from DC-beam energy spreads

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.T0)

[eV

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Simulation (ESME)

October 2004 Damerau et al.,November 2002

40Ar18+

Simulated losses < 0.2%Emittance growth measured for RPOSI=0.1mm : Factor growth 3.7 from 1.7 to 6.3 eVs

Schottky at injection used as theinitial conditions for the simulation.

Schottky after debunchingfor a severly mismatchedinjection energy.

(0.1mm 53Hz offset in cavity RF)

Simulation:Factor 1.5 from 1.7 to 2.62 eVs

Summary• Beam losses during capture may come from the

particle tunes crossing resonance lines due to space charge detuning.

• Emittance growth in longitudinal phasespace during acceleration ~18%.

• Debunched beam emittances show however a much larger growth of ca. 270% increase, whereas simulation shows ~50% increase.

• The new digital synchronisation control of the 2 RF cavities will help reduce losses, which at present occur near start of RF capture.