Cryomodule Refurbishment and the Maximum Energy Available from CEBAF

A substantial fraction of the highest-priority, currently-approved experiments using CEBAF need beam energies near 6 GeV. Unfortunately, the maximum energy capability of CEBAF has been degraded due to a combination of the effects of the hurricane Isabel “warm-up” and the loss of gradient due to leakage of radiation-damaged valve seals. In response to this problem, the laboratory has developed a detailed plan to support the demand for higher energy beams from CEBAF as quickly as possible. It will involve both the refurbishment of the lowest-performing installed cryomodules and the installation of a new, high-performance 7-cell cryomodule. We share the plan with you here to insure you of our commitment to deliver these high energy beams as quickly as possible within the limitations of our financial constraints and to establish expectations for progress that everyone can follow.

The graph below shows the projected energy capability of the cryomodules installed in the CEBAF accelerator during the next 5 years (Note, however, that the maximum available beam energy prior to the 12 GeV Upgrade modifications will be 6.0 GeV, a limit due to the present recirculation system). Our primary goal is to refurbish cryomodules in order to increase the 5 pass energy to 5.75 GeV with modest (less than 15/hour) trip rates in the shortest possible time. The second goal is to maintain the 5 pass energy at 5.75 GeV or higher while increasing the energy capability to somewhat above 6 GeV in order to reduce the trip rate for 6 GeV beam delivery and to “harden” the accelerator for improved reliability.

There are a number of assumptions that have gone into these projections:

1. No cryomodule in the Linacs suffers a catastrophic failure.

2. The energy degradation per year stays at the present level.

3. The accelerator operations schedule will be planned to permit 3 day breaks in machine operations to allow the installation of a refurbished module and possibly to remove a module for refurbishment.

4. There will be no shuffling of cryomodules between NL and SL for energy optimization.

If you have questions or comments about this plan, please feel free to contact either of us.

Swapan Chattopadhyay

Larry Cardman