1. 22/03/1999A.Blas1 Hollow bunches A. Blas, S. Hancock, S. Koscielniak, M. Lindroos, F. Pedersen, H. Schonauer  Why: to improve space charge related problems.  How: Increase the I mean / I peak = BF value by creating a hollow distribution in the longitudinal phase space

2. 22/03/1999A.Blas2 Hollow bunches (history)  F. Pedersen (PSB 1978): h = 5 bucket deposit in a 50 MeV coasting beam and acceleration with h = 5 and 7.10 10 p (no fast FB!).  K. Schindl (PSB 1978): Use of dual harmonic debuncher in the Linac transfer line  Results: loss of hollowness when closing any loop. Abandoned because of the success of dual harmonic (h5 + h10) operation.  R. Garoby, S. Hancock (PS 1992): Phase shaking at ~ 0.94 f S and homogenization with 200 MHz cavity. Very successful from 1GeV to 26 GeV trough transition.  S. Hancock (PSB 1997): same method as above, but h=16 frequency control too poor at that time to get proper results.

3. 22/03/1999A.Blas3 Pre-requisite  BTFM: longitudinal beam transfer function measurement (H. Schonauer, M. Sjöström)

4. 22/03/1999A.Blas4 Bucket deposition

5. 22/03/1999A.Blas5 Bucket deposition

6. 22/03/1999A.Blas6 Bucket deposition

7. 22/03/1999A.Blas7 Bucket deposition (rf set-up)  An “empty” bucket is brought into the injected beam before capture C16 cavity for “hole- generation” C02 cavity for acceleration (h=1) C04 cavity for bunch shaping Time (s) Voltage (kV) 310 315320325330335 Time (s) Frequency (kHz) 310 315320325330 Frequency of the “synchronous” particle C16 frequency Sweep time 40 kHz 4 8 C16 C02 C04 injection

8. 22/03/1999A.Blas8 1. Single Harmonic 1.2 1D Line density 1D Line density

9. 22/03/1999A.Blas9 1. Single Harmonic  C02=8 kV  C16=6 kV Red: 8 ms sweep Black: 1 ms sweep  Energy = 50 MeV  3 turns injected (?) 2D density profiles Synchrotron frequency 2D density profiles

10. 22/03/1999A.Blas10 2. Dual Harmonic 2.4 Line density 2D density profile1D line density

11. 22/03/1999A.Blas11 2. Dual harmonic 2.1 Amplitude distribution  C02=8 kV  C04=4 kV  C16 red: 0 kV and no sweep green: 3 kV and 0.5 ms sweep blue: 3 kV and 8 ms sweep lilac: 6 kV and 8 ms sweep  Energy: 50 MeV  3 turns injected 2D Density Profile Synchrotron frequency

12. 22/03/1999A.Blas12 2. Dual Harmonic 2.2 Emittance 2D density profiles

13. 22/03/1999A.Blas13 2. Dual harmonic 2.3 Phase space images

14. 22/03/1999A.Blas14 3. Dual harmonic instability 3.1 Time development  C02=8 kV  C04=4 kV  Energy: 212 MeV at instability (green) 2D density profiles Synchrotron frequency Before instability During instability After instability 129 MeV212 MeV655 MeV

15. 22/03/1999A.Blas15 3. Dual harmonic instability 3.2 “Phase space” before, during and after

16. 22/03/1999A.Blas16 3. Dual harmonic instability 3.3 Instability frequency Basic repetitions rate: 4184.3 Hz If octupolar: f = 4184.3 / 4  1046 Hz f synch. =1046 Hz

17. 22/03/1999A.Blas17 Conclusion  Bunching factor is increased 0.28 to 0.38 in the single harmonic case 0.45 to 0.55 in the dual harmonic case (values at 100 MeV)  Single harmonic acceleration was successful...but loss of hollowness after 390 ms  Dual harmonic operation unstable...from 50 ms to 250 ms