Re: Beam termination and possible effects on tagger

[Elton Smith <elton@jlab.org>]

HI Pavel,

Thanks for the comments, and the suggestion of tying the bend string and
the tagger together is a useful one.

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, Pavel Degtiarenko wrote:

> Hi Elton,
>
> Highly focused 3 uA beam is capable to produce local damage in materials
> at the point of impact, especially if thermal conductivity of the
> material is low. So I think we should not let the beam hit the concrete
> wall directly, even if it is a rare event. Better to have an iron block
> at the place of possible impact at the wall.
>
> Same considerations are valid for the magnet and the vacuum chamber
> walls. Beam excursions during fast shutdowns, or due to the tagger
> trips, generally may lead to short beam hits there. The materials should
> be capable to withstand corresponding local thermal stresses. (They most
> probably are).
>
> In this respect, may be it's worthwhile to consider an option to join
> consecutively the power supplies of the tagger and of the magnet couple
> that elevates the beam in the tunnel. If they trip simultaneously, the
> beam remnants in the machine will hit the tunnel stub upstream, instead
> of a place in the tagger area.
>
> Regards,
> Pavel
>
> Elton Smith wrote:
> > 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
> >>
> >>
> >>
>
>