[Bteam] no joy again: delivering high current, parity quality beam to Hall C

[Geoffrey Krafft]

Hi All,

I talked to Alicia this morning, and the symptoms
remind me of some problems we had awhile ago.
Have we let the beam size in the first injector module
get out of hand (get too big!)? Are the spots out of the
unit proper? The deal is that if the beta isn't small at
the first cavity, the beam size becomes very sensitive to
RF phase changes.

What else could be changing?

Geoff

On 1/26/2011 11:44 PM, Todd Satogata wrote:
> The Hall C Qweak beam problem continues even after spending 12h today on
> injector configuration checks, 5s polling removal, and retuning with the
> PREx configuration from August. After work by Reza, Alicia, and Mike
> Spata, we were able to transport 165 uA to the injector dump, but were
> only able to transport 80-90 uA to Hall C. About an hour later these
> numbers were down to about 50-60 uA to the injector dump and 20-30 uA
> to Hall C, with trips in both the injector chicane and hall transport.
>
> This means that the "changing the configuration" card did not help, and we
> should be prepared tomorrow to take the next step, moving forward (or
> rather reverting) to the 130 kV gun voltage. It's important that we do
> whatever we can to put ourselves in the position of beam delivery to
> both halls over the upcoming weekend. We'll have another meeting tomorrow
> morning after the 8 AM to review further alternatives and review
> comparisons of injector viewers taken several times during the day on
> Wednesday.
>
> Some items of note:
>     - 5-pass pathlength looks reasonable
>     - Fopt out of the injector looks to have some vertical steps later
>       into the arcs, but injector match into NL looks okay
>     - Viewer profiles in Hall C have basically the same aspect ratios
>       as design, but harp scans show beam sizes 150% larger than "good"
>       values seen before.
>     - Prebuncher voltage/phase were reliable enough that Joe got good
>       prebuncher voltage calibration data earlier in the day, so
>       the prebuncher is likely stable.
>
>                                                   -Todd
>
> --------------+---------------------------+----------------+------------------
> Todd Satogata | CASA Group, Jefferson Lab | (757) 269-6281 | satogata at jlab.org
> --------------+---------------------------+----------------+------------------
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