[Halld-physics] Solenoid - field and physics

Wed Nov 18 23:32:21 EST 2009

Hi All,

We should certainly be prepared to answer the question about the impact of 
running the magnet at lower than 1500 A. However, I do not think this 
possibility would change any of the repairs or testing that are planned. 
The only repair/refurbishment that might be affected by the restriction of 
operation to lower field is the repair of coil 2 to reinforce the 
slipage of the unsupported coil windings. However, the calculations show 
that the maximum stresses already occur at this lower field. So unless we 
are willing to run at 1000 amps or less, the testing and repair plan is 
essentially independent of whether we can accept running at 80-90% of full 
field.

Unless my argument is incorrect (I may be missing something), we should 
not get too side tracked  by trying to specify a hard limit for the 
minimum current for magnet operation.

My two cents. Elton.

Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton at jlab.org
(757) 269-7625
(757) 269-6331 fax

On Wed, 18 Nov 2009, Curtis A. Meyer wrote:

> Hi Everyone -
>
>    first a couple of clarifications. At one point in the last year, we 
> thought that the magnet
> would be able to run at 2.5T. I recall that this was the design value, but 
> that value had never
> been reached. The 2.2 number is what I was sure LASS ran at back at SLAC. 
> Certainly,
> at Los Alamos for MEGA, that  field was not reached (they also left one of 
> the coils out).
> So, are we talking 80-90% of the 2.5T number or 80-90% of the 2.2 number 
> (where I thought
> LASS ran)?
>
>     In support of the 2.2 number, I enclose a copy of the Cassel report from 
> 1999. There is
> a table at the end which was compiled by Bill Dunwoodie, one of the main 
> physicists on
> LASS. In that table, Bill clearly lists the LASS field as 2.24T. Thus, at 
> some point in the
> past the magnet did run with sufficient current to reach 2.24 T. I also went 
> back through the material that had been compiled in 2002 or so on the magnet. 
> There it is listed that a current
> of 1800A was used in LASS. Thus,  I am fairly confused on what is going on 
> here.
>
>   Unfortunately, from home I cannot access LASS papers to see what field 
> they published,
> but I have no reason to doubt Bill's statement that it was 2.24T. I was also 
> under the
> impression that the actual design field for the solenoid was 2.5 T, and that 
> it indeed never
> reached that value.
>    My question now is what has changed that causes us to think that LASS did 
> not run
> at 2.24T  If there is some reason to now think that maximum LASS current ( 
> 1250A ??)
> no longer produces the LASS field of 2.24T, then we certainly need to be 
> concerned.
>
>  Perhaps a good starting point is to address this.
>
>
>   As per the PWA, I think that all the work that we have done recently has 
> been with the
> all-neutral final states. Sadly, we could have done this in 2000 with 
> software that parametrized
> the detector, but that stopped working a long time ago and can't really be 
> resurrected. Presumably, we could take our parametrized Monte Carlo and 
> degrade the charged particle
> momentum resolutions the scaled field. We could then look at the impact of 
> this resolution
> on reconstructing complete final states and at least quantify how much 
> leakage from background
> we get with reduced resolutions.
>
> A classic case where we know that there is a hole in the detector are the 
> recations like
>
> gamma p -> n pi+ pi+ pi-
>
> gamma p -> Delta-0 pi+ pi+ pi-    Delta0 -> n pi0 
> some fraction of the latter throw the pi0 into the backwards hole, so simply 
> quantifying
> the leakage in the two filed cases would tell us. The level of this latter 
> leakage would at
> least set some limit on how small signals could be.
>
> I think that this topic should be put on the Monday Physics meeting agenda.
>
>
>   curtis
>
> Eugene Chudakov wrote:
>> Hi,
>> 
>> today we ran through a review of the solenoid project, see:
>> 
>> http://www.jlab.org/Hall-D/reviews/Solenoid_Magnet_Internal_Review_Nov09/
>> 
>> They gave a recommendation to show the physics impact of
>> running at 80-90% of the planned field (2.2T at 1500A).
>> 
>> The point is that the magnet may not reach 1500A. Before,
>> it ran at not more than 1250A. Also, it turns out that the full axial force 
>> on coil 2 changes sign at 1350A, which might become a problem.
>> This magnet is not expected to quench, but still, if a piece of conductor 
>> moves it may generate a voltage which would look
>> like quenching to the control system, which would power the magnet down. 
>> Other problems may occur.
>> 
>> Before the review we discussed this question with Curtis. It seems
>> that no hard numbers have been collected in one place to be used
>> in such occasions.
>> 
>> We must provide this info before the next Lehman review
>> (February?). We should assume the detector design finished
>> and not adapted to a lower field. Here I list several possible impacts to 
>> consider:
>> 
>> a) Higher EM background close to the beam. Result - running
>>     at lower luminosity, losses of small angles.
>> 
>> b) Missing mass resolution. Let us take 3-4 reactions and estimate
>>     the contamination from reactions with an additional pion (unseen).
>> 
>> c) Particle identification (pi/K/p) from TOF and kinematic fitting.
>>     BG for events with charged kaons and no missing particles.
>> 
>> d) The ultimate parameter is the sensitivity to an exotic wave
>>     at a certain confidence level, at least for one "gold" reaction.
>> 
>> While a)-c) are simple, c) is complex, but quite important, since similar 
>> questions will be asked in future.
>> 
>> Any numbers or suggestions? Who would work on this?
>> 
>> Eugene
>> ------------------------------------------------------
>> Eugene Chudakov
>> http://www.jlab.org/~gen
>> phone (757) 269 6959  fax (757) 269 6331
>> Thomas Jefferson National Accelerator Facility
>> 12000 Jefferson Ave,
>> Newport News, VA 23606 USA
>> _______________________________________________
>> Halld-physics mailing list
>> Halld-physics at jlab.org
>> https://mailman.jlab.org/mailman/listinfo/halld-physics
>>
>> 
>
>
> -- 
> Prof. Curtis A. Meyer		Department of Physics
> Phone:	(412) 268-2745		Carnegie Mellon University
> Fax:	(412) 681-0648		Pittsburgh PA 15213-3890 
> cmeyer at ernest.phys.cmu.edu	http://www.curtismeyer.com/ 
>
>