Advantage of tunnel installation:
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1. Lower latency in feedback loop --> higher gain = better regulation/robustness
(not really needed if LLRF in service building
meets 0.01 deg. short term spec., good chance)
Note: Only if klystron is also in the tunnel
2. Less phase drifts from cables --> better long term phase stability
(could be corrected with calibration scheme for LLRF in
service building, anyway also recommended for tunnel
solution).
3. Potential problem with radiation levels due to beam loss in collimators and bunch compressor.
4. People cannot touch hardware thereby causing problems.
Advantage of installation in service building:
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1. Continuous development and improvements supported. Will be required to achieve
requirements for field regulation and availability. Easy to upgrade.
2. Guarantees high availability due to easy access for maintenance and repair. Very high
availability if redundant system is used.
3. System will be available earlier (in 2010) then tunnel system for commissioning of the
injector rf. This is possible since configuration is flexible and components can be added
easily.
4. Supports continuously evolving commissioning needs.
5. Allows to study new control concepts with very little impact on commissioning and operation.
6. Simplifies trouble shooting if control problems occur. Problems after maintenance day can be easily fixed.
Conclusion:
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It will be absolutely necessary to have the 2 system in parallel (better 3 with 2 redundant systems in the service building as development and spare). This way, the system in the service building will provide high and early availability (with required or slightly reduced performance) and allow for the development of the high performance tunnel system while the system in the tunnel will provide the best field control when available.
