[Halld-physics] Solenoid - field and physics

[Eugene Chudakov]

I agree with Elton that the current repair plan should go ahead
independent on the results of the resolution studies.

Elton wrote:
> 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

Indeed, the full force on the coil 2 changes from -2 klb/column at 1000A to 
+2 klb/column at 1500A. However, the reinforcement of the coil is motivated by the force
on the tip of the downstream subcoil, which simply grows with the current
(SuperFish calculations):

1500A: -280 kN
1250A: -200 kN
1000A: -133 kN

Still, we should proceed with the reinforcement, since a) 200kN instead of 280kN
is still uncomfortable, while 1000A is most likely way too low; b) there is a
chance that the magnet will work at higher currents, which will improve
the physics potential.

I got an impression from the review discussions that we should be able
to TRY higher currents (at least up to 1500A), without a danger of a serious
damage.

Eugene


On Wed, 18 Nov 2009, Elton Smith wrote:

>
> 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/ 
>> 
>
>