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Jeff Dooling Presented at The Ninth

Second Harmonic capture in the IPNS RCS: Transition from SH to fundamental rf operation during the acceleration cycle using CAPTURE_SPC. Jeff Dooling Presented at The Ninth Second Harmonic RF/Low Output-Impedance Amplifier Collaboration Meeting Argonne National Laboratory, June 14-15, 2004.

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Jeff Dooling Presented at The Ninth

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  1. Second Harmonic capture in the IPNS RCS: Transition from SH to fundamental rf operation during the acceleration cycle using CAPTURE_SPC Jeff Dooling Presented at The Ninth Second Harmonic RF/Low Output-Impedance Amplifier Collaboration Meeting Argonne National Laboratory, June 14-15, 2004

  2. Motivation • Currently, we believe our ferrite will not allow second harmonic (SH) rf operation up to the maximum acceleration frequency— 5.15 MHz x 2 = 10. 3 MHz • Most loss occurs at injection • Can we run SH early in cycle using the new 3rd cavity, switching to fundamental later and still realize a net increase in current?

  3. Guide field, b, and Vrf

  4. Frequency and energy vs. time

  5. Bucket Area in the RCS

  6. Fundamental and SH voltage and current profiles from Hofmann-Pedersen elliptical distributions

  7. Maximum bucket area vs. maximum bunching factor

  8. Capture Efficiency and Fundamental-SH phase angle, q

  9. Goal: Full SH rf for the full acceleration cycle(the following animation includes the phase ramp)

  10. Potential benefit

  11. Modify CAPTURE to include d(t) * CALL CPfield( tn, evol, fnuS, omegaS, & flagrf, Nrfpoints, rf_time, rf_evol, & rf_sh_phase, Imax, secHarmPhase ) * * CALL CPfield( tn, evol, fnuS, omegaS, & flagrf, Nrfpoints, rf_time, rf_evol, & rf_sh_phase, rf_sh_ampl, Imax, & secHarmPhase, secHarmFactor ) *

  12. CASE 1: Run SH at d=0.55 for the first 4 ms Ramp SH to 0 between 4 and 5 ms Leave Vrf unchanged CASE 2: Run SH at d=0.55 for the first 4 ms Ramp SH to 0 between 4 and 5 ms Ramp Vrf to 1.55*Vrf between 5 and 6 ms Two cases

  13. Ramping Vrf up after 5 ms

  14. Second Harmonic rf early, d=0.55ramping off between 4 and 5 ms

  15. Second Harmonic rf early, d=0.55; ramping off between 4 and 5 ms; ramping back on in the fundamental between 5 and 6 ms (to 1.55*Vrf)

  16. Transmission efficiency and loss rate

  17. Observations • Transmission efficiency improves with SH rf even when no further rf is applied • Ramping back on Vrf shuts off the loss by increasing the bucket size • Timing is important—implied in these simulations is the fact that the third cavity is being made to go from full SH voltage to full fundamental voltage in 2 ms. • May not need to go to full 1.55*Vrf in the fundamental to gain efficiency

  18. According to Chao, the limiting tune shift is, One way to look at this is to say that SH effectively moves injection to higher energy --A . W. Chao, Physics of Collective Beam Instabilities in High Energy Accelerators, Wiley, New York, 1993, p. 14. Why does SH early improve capture efficiency when no additional rf is applied

  19. Conclusions Third cavity, even with limited SH capability, will allow for important capture studies. Also, the 3rd cavity may provide a modest improvement in RCS beam current limit.

  20. Acknowledgement This work would not be possible without the dedication and hard work of the IPNS Accelerator Operations Group.

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