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Beam loss and longitudinal emittance growth in SIS

Beam loss and longitudinal emittance growth in SIS. M. Kirk I. Hofmann, O. Boine-Frankenheim, P. Spiller, P. H ü lsmann, G. Franchetti, H. Damerau, H. G ünter König, H. Klingbeil, M. Kumm, P. Sch ütt, A. Redelbach. Outline of talk. Optimisation of injection into SIS

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Beam loss and longitudinal emittance growth in SIS

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  1. 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

  2. Outline of talk • 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

  3. Schottky at injection for UNILAC and SIS setup Longitudinal Schottky measurements on the beam shortly after multi-turn injection into SIS. 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

  4. RF Amplitude Start Schottky measurement Time Momentum spread of debunched beam for optimisation 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.

  5. Coherent bunch oscillations: a possible way to optimize the cavity frequency at injection Ts 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. 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]

  6. Sensitivity of the sideband heights to the injection offset… 238U73+ 11.4 MeV/u Gap amplitude 1kV Self-fields negligible Injection offset 0 MeV

  7. … Injection offset 0.002 MeV

  8. … Injection offset 0.01 MeV

  9. … Dipolar oscillation Quadrupolar Injection offset 0.03 MeV

  10. Schottky spectrum under high phasespace density 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]

  11. 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

  12. Beam losses during RF capture Simulation Experiment ESME simulation of 40Ar10+. Beam loss profileduringtheRF-capture (withoutspace charge). The transverse acceptancewas 200mm (beampipe diameter). Momentum spread of DC beam taken from Schottky spectrum data. DC current traformer measurement: Beam loss profileof 40Ar10+ duringtheRF-capture.

  13. Ions 40Ar10+ Intensity 5x1010 .g 2 Bf 0.31 Kinetic energy 11.39 MeV/u dp/p (2 x RMS) 3.39x10-3 Losses from space charge tune shift? Emittances required: x 128 mm mrad y 32 mm mrad to reach the resonance indicated by the arrow in fig. A1 Transverse acceptance: x, max = 200 mm mrad y, max = 50 mm mrad Working point Resonance concerned 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. Franchetti et al.

  14. 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

  15. Tomo: Phasespace reconstruction Produced by ESME Projected reconstruction and original profile (black) Tomographical reconstruction The ESME tracking code (FermiLab) was used to benchmark Tomo (version 2, CERN) under conditions of high phasespace densities.

  16. Tomography applied to the Ar-Experiment Persistent tail!

  17. Deconvoluted Original Tails are caused by the bandwidth of the pickups Beam spectrum Pickup response

  18. 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

  19. Simulation of Ar-experiment with ESME RF-gap voltage amplitude Phasespace of beam derived from tomographical reconstuction at t=100ms RF-Gap voltage frequency

  20. 40Ar10+-Experiment Stage in machine cycleGrowthTotal Capture & acceleration (0-100ms) 40% Rest of acceleration (100-640ms) 18%65.2%

  21. 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) Klingbeil et al.

  22. 14N7+-Experiment with RF digital synchronization 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

  23. Ar18+ Experiment

  24. Trig. for Spectrum Analyzer Gap signal Kirk, Schütt, Redelbach. October 2004 40Ar18+ Experiment Intensity 2x109 Max. ramp rate 2.3T/s ‘Rounding’ time 32ms

  25. Damerau et al., November 2002 Emittance growth from DC-beam energy spreads 40Ar18+ Simulated losses < 0.2% Emittance growth measured for RPOSI=0.1mm :  Factor growth 3.7 from 1.7 to 6.3 eVs October 2004 (0.1mm  53Hz offset in cavity RF) Schottky after debunching for a severly mismatched injection energy. Simulation: Factor 1.5 from 1.7 to 2.62 eVs  Schottky at injection used as the initial conditions for the simulation.

  26. 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.

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