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
Jan 20, 2016
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
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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]
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2
)(
)(2
))()((1
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1)(
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zEwzzwiiGF
zEwBeAP C
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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
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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)
200 Per. Gleitender Durchschnitt (Dual cavity 12kV each)
200 Per. Gleitender Durchschnitt (Single cavity at 12kV)
Ar18+ Experiment
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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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Radial position at injection RPOSI [mm]
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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.