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

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 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. RF Amplitude Start Schottky measurement 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. 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 TsTs

Sensitivity of the sideband heights to the injection offset… 238 U MeV/u Gap amplitude 1kV Self-fields negligible Injection offset 0 MeV

Injection offset MeV …

Injection offset 0.01 MeV …

Quadrupolar Dipolar oscillation Injection offset 0.03 MeV …

ESR measurement on a 40 Ar 18+ DC-beam at 250MeV/u kinetic energy. Longitudinal Schottky band at m=30 used as test data for the fitting program. I ions =1mA. Electron current from the cooler was I e =1A [Original measurement: Schaaf, Fitting program: Ziemann, Svedberg Laboratory] 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

ESME simulation of 40 Ar 10+. 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. DC current traformer measurement: Beam loss profile of 40 Ar 10+ during the RF-capture. SimulationExperiment Beam losses during RF capture

Tune resonance diagram, showing 2 nd and 3 rd 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. Ions 40 Ar 10+ Intensity5x10 10.g.g2 BfBf 0.31 Kinetic energy11.39 MeV/u dp/p (2 x RMS)3.39x10 -3 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

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

Tomography applied to the Ar-Experiment Persistent tail!

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

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

40 Ar 10+ -Experiment Stage in machine cycle Growth Total Capture & acceleration (0-100ms)  40% Rest of acceleration ( ms) 18%  65.2%

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= N 7+ -Experiment with RF digital synchronization

Ar 18+ Experiment

40 Ar 18+ Experiment Intensity 2x10 9 Max. ramp rate 2.3T/s ‘Rounding’ time 32ms Kirk, Schütt, Redelbach. October 2004 Trig. for Spectrum Analyzer Gap signal

Emittance growth from DC-beam energy spreads October 2004 Damerau et al., November Ar 18+ 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 the initial conditions for the simulation. Schottky after debunching for a severly mismatched injection 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.