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Re: Beam termination and possible effects on tagger




Hi Bob,

I am copying this message to the halld-tagger group in case anyone has
additional comments.

My assumption has been that beam operation would be interlocked with the
tagger power supply, and in the (infrequent) event that beam was lost due
to the loss of power and or other circumstances in the beamline that the
detectors would be able to handle the instantaneous exposure until the
fast shutdown turned the beam off. However, it is probably true that a
full analysis of the effect on the detectors has not been carried out.

The permanent magnet is in place to prevent the electron beam from being
transmitted down the photon line for any reason. In case of the tagger
magnet supply failure, the beam would be dumped below the photon beam and
into the berm which again we assume can handle an instantaneous dump of
the electron beam.

If you want to discuss this further, just let me know.

Cheers, Elton.



Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625

On Tue, 8 May 2007, may wrote:

> Elton,
>
> Pavel and I were talking about the accidental beam loss situation where
> electron beam transport to the point of the permanent magnet results in
> beam offset to the tagger area east wall and what, if anything, should
> be placed to intercept the beam. We were also wondering about what the
> effects would be on the tagger (detectors, pmts, etc.) if a high power
> beam loss occurs at some point in the tagger.
>
> As beam is terminated by the fast shutdown system, it seems to "wander".
> For example, we often see a spike in ion chambers in a hall associated
> with a fast shutdown event somewhere in the CEBAF accelerator. Whatever
> is occurring at the moment of fast shutdown, the result seems to be beam
> offset, an increase in energy spread perhaps, or a combination of this
> and other things. I don't know if there has been any discussion about
> how this might affect tagger detector hardware if momentary beam offset
> from a fast shutdown event result in some beam loss in the tagger. Do
> you think we should meet to talk about this?
>
> Bob
>
>