Linac Low Level RF System

Page contents:

1. Block diagram of the ALS Linac

2. Linac Timing Diagram

3. Block diagram of the phase loop

4. Block diagram of the trigger module

5. Photograph of the trigger module

6. Video detector location diagram

7. Block diagram of the video detector

8. Photograph of the video detector

linaclowrf.jpg (31241 bytes)

Linac low level RF Rack

Paper on this system:

C.C. Lo, B. Taylor and H. Lancaster, Low Power RF System for the ALS Linac, Proceedings of 1991 IEEE PAC, Vol. 2, pp.807-809, LBL 29909

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ALS Linac RF System Bolck Diagram

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ALS Linac Timing Diagram

Notes:

The master trigger comes from the main ALS Timing System that starts the sequence of event as described by the timing diagram. The Gun pre-trigger gate also comes from the main timing system. This signal inhibits the phase error sampling while the gun pulse is still present.

The heart of the time delay generator is the AD9500 programmable delay generator. The 8 bit switch is accessable from the front panel behind a removeable cover. UNLESS you are sure what you are doing, do not adjust these settings to 'try things out'.

All timing modules are powered by OEM open frame power supplies. Most of these power supplies have built in crowbar protection. Power interruptions may cause this circuit to activate. Resetting is achieved by turning the power off and then on again.

The phase correction loops are not not in use at this time.

The fast phase pulse is used for beam loading compensation. Since the klystrons are operating in the saturation mode, an up shift in output power is not applicable to compensate for RF power loss due to beam loading due to the first few bunches. However ;by shifting the phase (or timing in time domain terms) of the RF it is the same as shifting the RF power as as the beam is concerned. The phase shifting is achieved by modulating the phase via the phase shifter in the solid state driver amplifier. The present system may need up grading in terms of control and timing accuracy.

phaseloop.jpg (84415 bytes)

Note: module not in used at this time

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Linac timing and trigger module chassis

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Video detector monitoring points in the ALS Linac

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ALS Linac video detector