[Halld] Potential continuation of commissioning at 6 GeV endpoint

[Eugene Chudakov]

Dear colleagues,

As a result of the power outage on Mar 25 the accelerator has serious
problems. Most likely, it would be able to provide only a ~6GeV beam
for the rest of the Spring run.

There are two 2K helium liquifiers (CHLs) servicing two accelerator
linacs. The Northern CHL is tripping because of a differential
pressure increase at some element. The problem is attributed to ice
(some contamination frozen). They are going to warm it up to get rid
of the ice. It will be done by Friday. There is a good chance that the
CHL will be able to run at 2K after that. The Southern CHL
demonstrates a serious mechanical failure in one of the
compressors. If true, the repair may take weeks/months. One working
CHL can provide only a ~6GeV acceleration.

We expect that by Wednesday the Lab will decide on the path forward -
whether to run at 6 GeV and whether to extend the run beyond the
current cutoff at May 4.

The HPS experiment in Hall B uses a low energy and would probably
benefit from the 6 GeV run. The Hall A DVS experiment would probably
not. We have to decide if we would like to run and what the program
would be.

Certainly, a part of the Hall D commissioning can be done at 6 GeV, in
particular the wire chambers work, some calorimeter calibration and
some DAQ work. We need to prepare by Wednesday a preliminary
objectives for such a running and consider possible implications (say,
a larger relative noise in the trigger). We are planning to start such
discussion at 8:45 meeting on Wednesday.

Regards,
Eugene
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Eugene Chudakov
https://userweb.jlab.org/~gen/
phone (757) 269 6959  fax (757) 269 6331
Thomas Jefferson National Accelerator Facility
12000 Jefferson Ave, STE 4,
Newport News, VA 23606 USA