1. RF System for HESR Status report, January 2006 F. Etzkorn / A. Schnase, with help from S. An, K. Bongardt

2. Description of HESR RF System (1) High Resolution (HR) mode: N~10 10 Particles 3 GeV Injection of 200m RESR pulse into HESR Bunch rotation (BR) for reducing energy spread by dual harmonic RF system with (h=1, 2) Stochastic pre-cooling of DC beam 10% time gap is obtained by Barrier Bucket (h=1,…>5) system Capture with (h=1, 2); ac-/de-celeration with (h=1) sinusoidal waveform Bunch rotation (BR) for reducing energy spread Experiments with DC beam, electron/stochastic cooling counteracts target heating 10 % time gap is obtained by Barrier Bucket (h=1,…>5) system Energy change to 3 GeV: new RESR pulse

3. Description of HESR RF System (2) High Luminosity (HL) mode: N~10 11 Particles 3 GeV Injection of 200m RESR pulse, N<3.5*10 10 into HESR Bunch rotation (BR) for reducing energy spread by dual harmonic RF system with (h=1, 2) Stochastic pre-cooling of DC beam 10 % time gap is obtained by Barrier Bucket, (h=1,…>5) system Capture & ac-/de-celeration with (h=1, 2) sinusoidal waveform energy spread after pre-cooling is larger for N~10 11 Bunch rotation (BR) for reducing energy spread Experiments with DC beam, electron/stochastic cooling counteracts target heating 10 % time gap is obtained by barrier bucket (h=1,…>5) system Energy change to 3 GeV: particles are remaining in HESR

4. Description of HESR RF System (3) Phase compression of remaining particles to 200m length Bunch rotation by dual harmonic RF system with (h=1, 2) New RESR pulse is injected into empty half of HESR Bunch Rotation for new RESR bunch, matching for remaining particles synthetic waveform with (h=1,…5) leads to almost identical energy spread debunching => DC beam for stochastic pre-cooling : cycle continues Parameter limits for HESR RF system synthetic waveform, (h=1,…5) : < 3 kV for about 1 sec Energy change < 200 eV/ turn : (h=1): < 1 kV, (h=2): < 0.3 kV for maximal 300 sec Barrier Bucket, (h=1,…>5) for storage mode: > 1 V for >3000 sec

5. Material Tests At COSY an experiment was performed to study the signal synthesis for Barrier Buckets. At first, 3 different waveforms of possible Barrier Bucket Signals (B l = 0.9 / 2µs) were generated and applied to the multi-harmonic COSY Cavity, filled with VitroPerm. With the results at the gap, the transfer function of the RF system was calculated. With that transfer function, a pre-distorted function was calculated and applied to the cavity. The response resulted in exactly that pulse that could be expected with the available bandwidth of the COSY cavity system including the amplifier chain. A nearly clean pulse shape was obtained

6. The 3 tested waveforms Rectangle, sinusoidal and sinusoidal with DC offset Track 1: Input to amplifier (dark blue) Track 2: Response at gap (light blue) sinusoidal with DC offset (proposed by CERN) brings no usable result with our system. rectanglesinusoidal sinusoidal with DC offset

7. Pre-distorted waveforms Waveforms calculated with 16 harmonics Track 1: Pre-distorted Input to amplifier Track 2: Response at gap B l =0.9 Period=2µs Result of rectangle and sinusoidal waveforms are nearly equal Sinusoidal waveform looks a little better For nearly rectangular waveform much more harmonics and bandwidth are needed (up to h=50) We will continue with further tests as soon we have a working prototype system rectangle sinusoidal

8. Number of harmonics => wave form RF waveform for B l = 0.8 with different harmonics: voltage ripple leads to islands of stability Fourier decomposition with 5 harmonics Amplitude/AV1V1 V2V2 V3V3 V4V4 V5V5 B l =0.80.08-0.140.19-0.210.20

9. Status of cavity design It is foreseen to install 2 different sets of cavities. The first cavity will consist of 2 tanks with an acceleration gap in the centre. It will be driven by a push-pull tube amplifier up to 3kV. It will be broad band to allow multi-harmonic bunch manipulation. It will be used for injection, acceleration and deceleration. Because of the Ripple and noise of the tube amplifier, it’s not useable for small voltages below about 100V. The material will be probably FineMet. For voltages in the range from 1V to about 100V, a second, single tank cavity, loaded with VitroPerm is foreseen, directly driven by a transistor amplifier. The tanks will be build inside FZJ similar to the COSY cavity. A 1 kW transistor amplifier designed by CERN and improved by KEK for J-PARC will be ordered. An existing tube amplifier of COSY will be modified for broad band use to be able to drive the 2 tank cavity. Necessary supplies of COSY can be used for the prototype phase.