sPHENIX discussion of the superconducting solenoid

[EdwardOBrien <eobrien AT bnl.gov>]

        John and Dave,
         I am not sure that it is standard practice for
        an experiment to reverse the polarity on a
        large superconducting solenoid. My intuition tells me that
        it exposes the coil leads to unnecessary stress. Before
        we add this to the plan we need to check whether Babar
        ever did this, and if so how often.

        Ed


On 7/10/2015 10:05 AM, John Haggerty wrote:
> Dave,
>
>   From the experiment's point of view, if we could reverse the field, we
> would only do so once or twice during a long RHIC run, as we do in
> PHENIX.  To me, it has always been an unproved assertion that there is
> all that much benefit from reversing the field in order to understand
> the systematic errors in the tracking, because after you do it, you have
> to recalibrate everything, but whenever you change the conditions of an
> experiment in a controlled way, there is the potential to learn something.
>
> I didn't reply earlier because it's not clear at all to me whether
> reversing the polarity is feasible from the point of view of mechanical
> stress and strain and the effects on the magnet in the case of a quench.
>    After thinking about it, I'd have to defer that to experts who could
> calculate it.
>
> But it seems to me that we would not need to reverse the polarity any
> more than PHENIX or STAR does now, and it takes a while to ramp up and
> ramp down anyway, so going to the trouble and expense of having a
> reversing switch does not seem necessary.
>
> I suppose we might want to start with the field "the same direction" as
> in BaBar... if we can figure out what that was.
>
> On 7/9/15 1:34 PM, Phillips, David B wrote:
> > The power supply/dump resistor from SLAC does not have a  reversing switch.
> >
> > Do we want/need one for sPHENIX?
> >
> > David Phillips
> >
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