14 May 1997, PSB MD Report

PS/RF/Note 97-13 (MD)

12 August 1997

14 May 1997, PSB RF MD Report; h = 1 + 2 with Protons

Participants : J. Bento, A. Blas (reporter), A.Findlay, M. Haase, M. Paoluzzi

Experiment limitations

1 GeV maximum energy

(main power supply ready for 1.4 GeV in 3/98 and septa in 3/99)

B field programmed for a h = 5 constant bucket area

(will be modified for h = 1 by M. Lindroos and R. Steerenberg for the 22/5/97)

Target

Extraction and synchronisation of 8 E12 protons at 1 GeV with a  1.2 [eV.s] longitudinal emittance per bunch, and a bunch length of 217 ns.

Results

710 E10 particles accelerated and synchronised with C02 and C04 at 80 % level (-2 dB).

700 E10 with C04 at 50 %. Bunch length = 200 ns (276 ns with 180o phase shift)

Results obtained using only three servo-loops in the beam control. (main phase loop, 2nd harmonic loop and synchronisation phase loop)

Figure 1: Beam measurement for C04 = 80 % of C02 and 15 turns

Figure 2: Beam measurement for C04 = 80 % of C02 and 13 turns

Figure 3: Beam measurement without C04 and 13 turns

1. INJECTION-CAPTURE

Figure 4: Capture losses with respect to cavity voltage rise

(13 turns injected and C02 on its own)

Top traces: Beam current (4 E12 p/V)

Bottom traces: C02 cavity voltage (log scale: 10 dB/V, 0 V  100 Vp.)

Start Phase loop at injection + 150 s

Start Frequency increase @ injection + 180 s

The losses starting at the end of the cavity voltage rise are supposed to be driven by the Laslett Q detuning related to the bunching factor (mean-to-peak line charge density).

Cures:

1) Increase the bunching factor by increasing the second harmonic voltage up to the fundamental voltage.

2) Fill the obtained bucket by increasing Linac p/p or by dropping the rf voltage for a given p/p.

Figure 5 : Beam current (4 E12 p/V) with 13 turns at injection

Bottom trace: without rf

Middle trace: with C02 only

Top trace: With both C02 and C04 cavities

Figure 6 : Scanning of the beam from injection (bottom) to the next 5 ms (top).

One scan each 166 s. C02 cavity on its own at 8 kV and 13 turns injected.

Figure 7 : Scanning of the beam from injection (bottom) to the next 5 ms (top).

One scan each 166 s. C02 cavity with C04 at 50% voltage and 13 turns injected.

Figure 8 : Scanning of the beam from injection (bottom) to the next 5 ms (top). One scan each 166 s. C02 cavity with C04 at 80% (-2dB) voltage and 13 turns injected.

Figure 9 : Scanning of the beam from injection (bottom) to the next 5 ms (top). One scan each 166 s. C02 cavity with C04 at 112 % voltage (+1dB) and 13 turns injected.

2. ACCELERATION

Figure 10 : Scanning of the beam 100 ms after injection (bottom) during 5 ms.

One scan each 100 Revolution. C02 cavity with C04 at 50 % voltage (-6dB) and

13 turns injected.

Figure 11 : Scanning of the beam 100 ms after injection (bottom) during 5 ms.

One scan each 100 Revolution. C02 cavity with C04 at 80 % voltage (-2dB) and

13 turns injected.

Figure 12 : Scanning of the beam 100 ms after injection (bottom) during 5 ms.

One scan each 100 Revolution. C02 cavity with C04 at 112 % voltage (+1dB) and

13 turns injected.

Figure 13 : Beam currents (4 E12 p/V) (top) and C02 Voltage (log scale) (bottom).

Measured with C04 at 80 % voltage level and 13 turns injected.

Figure 14 : Beam currents (4 E12 p/V) (top) and B dot (bottom).

Measured with C04 at 80 % voltage level and 13 turns injected without the voltage bump at 200 ms.

Losses occur without voltage bump at 200 ms after injection.

Cure: The new B field function should avoid this.

Figure 15 : Scanning of the beam 430 ms after injection (bottom) during 5 ms.

One scan each 300 Revolution. C02 cavity with C04 at 50 % voltage (-6dB) and

13 turns injected.

Figure 16 : Scanning of the beam 430 ms after injection (bottom) during 5 ms.

One scan each 300 Revolution. C02 cavity with C04 at 80 % voltage (-2dB) and

13 turns injected.

Figure 17 : Scanning of the beam 430 ms after injection (bottom) during 5 ms.

One scan each 300 Revolution. C02 cavity with C04 at 112 % voltage (+1dB) and

13 turns injected.

Figure 18 : Scanning of the beam 430 ms after injection (bottom) during 5 ms.

One scan each 300 Revolution. C02 cavity with C04 at 50 % voltage (-6dB) and

13 turns injected.

To be tested:

First we shall introduce the new B field program to avoid the voltage increase where the B dot is maximum, but we shall have to concentrate all our effort on the first five milliseconds:

There we expect some efficiency gain with an increase of the Linac energy dispersion, so to make use of the improved Bucket height ( 730 keV instead of 430 keV with h=5).

In the same time we shall also try to smoothen the frequency evolution during the capture process (steps for each Gauss) so as to reach the theoretical longitudinal acceptance.

For a given Linac p/p we shall choose the lowest rf voltage in order to increase the bunching factor and thus improve the capture efficiency (less transverse losses due to Laslett detuning).