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Longitudinal matching by sawtooth

Longitudinal matching by sawtooth. H.Horii Kyoto University. FFAG ’ 07 Workshop. Purpose of this study Fast capture with sawtooth High efficiency for capture and acceleration Instrument Booster Broad band cavity Simulation phase rotation (sin , sawtooth , adiabatic )

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Longitudinal matching by sawtooth

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  1. Longitudinal matching by sawtooth H.Horii Kyoto University FFAG’07 Workshop

  2. Purpose of this study Fast capture with sawtooth High efficiency for capture and acceleration • Instrument Booster Broad band cavity • Simulation phase rotation (sin , sawtooth , adiabatic ) Capture voltage and accelerating voltage • Experiment Recent study of Booster • Summary

  3. FFAG complex @KURRI

  4. Details of Booster E_inj : 1.5[MeV] Magnet type : DFD E_ex : 11.5[MeV] R_min : 0.965[m] k : 2.5 R_max : 2.145[m] F_inj : 1.962[MHz] phase slip factor(injection) : 0.711

  5. These data are from Mitubishi Electric RF Cavity of Booster Acceleration 1.962 <= f_rf < 4.1[MHz] (1.5 MeV to 11.5 MeV) Impedance[Ohm] Sawtooth 1.962 <= h*f_s < 8.0[MHz] (Up to h=4) Frequency[MHz] V_rf < 1.4[kV] Gap voltage[kV] Our operating point Amp output[kW]

  6. Sawtooth f_s: frequency of synchronous particle harmonic : 4 harmonic : 10

  7. Phase rotation (Sawtooth & Adiabatic capture) Initial(dp/p=0.3[%]) Sawtooth(h=4) 90turn(45μs) 250turn 1000turn 20000turn(1ms) Adiabatic capture V_max : 1.0[kV],uptime : 1[ms] Vertial : -delta U/omega_s[eV*s] Horizontal:phi[rad]

  8. From capture to acceleration(phi_s:10[degree],phi_jump:10[degree]) Number of initial particles : 10000 20000turn(1ms),1kV(max) Survived : 8379 90turn(45μs),1kV Survived : 9622 Sawtooth Adiabatic If working frequency is 100[Hz], 1ms is 10[%] of available time

  9. Contour of survived particle’s ratio These graphs show each states just after 1/4 synchrotron oscillation Ratio = (number of Survived)/(number of initial) In case of sawtooth (harmonic : 4) (dp/p=0.3[%])

  10. Contours for various dp/p and phase-jumps dp/p=0.3[%] dp/p=0.5[%]

  11. Figure1: Low level 2007/08/29 Phi_s:25[degree] Phi_jump:25.4[degree] V_saw / V_acc : 0.5 Saw tooth capture Sin wave acceleration There is no data of real output voltage yet!

  12. Figure2 : signals of pickup monitor @BSTRby saw tooth capture 2007/08/29 accelerating time of BSTR is about 8ms

  13. Figure3 : Detail of the injection to BSTR Capture time is about 36[μs] This dip is caused by bump magnet’s decay ramp

  14. Result of experiment Efficiency of acceleration reached almost 100% !! beam current before injection is about 10[nA] beam current before extraction is about 1.0[nA] bump decay time is around 8[μs] (this is about 10[%] of injection pulse widths ) Beam current using this saw tooth RF pattern is twice more than one using usual sin wave capture (no adiabatic capture) Stability of Booster became better than before

  15. Summary To make fast acceleration of FFAG as stable sale’s point, Sawtooth capture is very good method. (there is no possibility to choose adiabatic capture) When sawtooth capture is used, It is most important to match bunch’s height as accelerating bucket’s height

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