Beam loss and longitudinal emittance growth in SIS

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Beam loss and longitudinal emittance growth in SIS

• M. Kirk
• I. Hofmann, O. Boine-Frankenheim, P. Spiller,
• H. Klingbeil, M. Kumm, P. Hülsmann, P. Moritz

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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

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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
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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.
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Coherent bunch oscillations a possible way to
optimize the cavity frequency at injection
Ts
Fig. 1. Waterfall plot of a single bunch pickup
?-signal (h4) 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
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Sensitivity of the sideband heights to the
injection offset
238U73 11.4 MeV/u Gap amplitude 1kV Self-fields
negligible
Injection offset 0 MeV
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Injection offset 0.002 MeV
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Injection offset 0.01 MeV
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Dipolar oscillation
Quadrupolar
Injection offset 0.03 MeV
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Schottky spectrum under high phasespace density
ESR measurement on a 40Ar18 DC-beam at 250MeV/u
kinetic energy. Longitudinal Schottky band at
m30 used as test data for the fitting program.
Iions1mA. Electron current from the cooler was
Ie1A Original measurement Schaaf, 1990.
Fitting program Ziemann, Svedberg Laboratory
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• 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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Beam losses during RF capture
Simulation
Experiment
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.
DC current traformer measurement Beam loss
profile of 40Ar10 during the RF-capture.
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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.
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• 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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Tomographical reconstruction
The ESME tracking code (FermiLab) was used to
benchmark Tomo (version 2, CERN) under conditions
of high phasespace densities.
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Tomography applied to the Ar-Experiment
Persistent tail!
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Tails are caused by the bandwidth of the pickups
Beam spectrum
Pickup response
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• 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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Simulation of Ar-experiment with ESME
RF-gap voltage amplitude
Phasespace of beam derived from tomographical
reconstuction at t100ms
RF-Gap voltage frequency
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40Ar10-Experiment
Stage in machine cycle
Growth Total Capture acceleration
(0-100ms) ?40 Rest of acceleration
(100-640ms) 18 ?65.2
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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.
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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
level2000
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Ar18 Experiment
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40Ar18 Experiment
Kirk, Schütt, Redelbach. October 2004
Intensity 2x109 Max. ramp rate 2.3T/s Rounding
time 32ms
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Emittance growth from DC-beam energy spreads
40Ar18 Simulated losses lt 0.2 Emittance growth
measured for RPOSI0.1mm ? 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.
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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. The final
  emittances aggreed reasonably well with
  simulation.
• The new digital synchronisation control of the 2
  RF cavities will help reduce losses, which at
  present occur near start of RF capture.