[b1_ana] Follow up on Re: Fwd: Re: A_PV with Deuteron Target

[O. A. Rondon]

Hi Don,

The +/- 50 deg. is only for the downstream cone, not the upstream side.
So the entrance beam directions are much more limited, which is
understandable for a magnet installed in CLAS.

In any case, since the plan is to take data with the HMS and SHMS on
opposite sides of the beam, it's only possible to point the field along
one of the q vectors, which would be very bad for the other spectrometer.

Cheers,

Oscar

Donald G. Crabb wrote:
> Hi Oscar,
> 
>  The angular openings for the Hall B magnet are the same as for the late lamented Hall C magnet, ie +/- 17 degrees in transverse and +/- 50 degrees longitudinal. Surely the target group must have drawings. I have a folder of the early draft drawings but not the as-built ones.
> 
>    Don
> 
> 
> 
> 
> 
> 
> 
> 
> On Mon, 20 May 2013 14:32:00 -0400
>  "O. A. Rondon" <or at virginia.edu> wrote:
>> One more thought: since the plan is to use the Hall B coils, the option
>> of suppressing A_V^d by aligning the field along q is very restricted.
>>
>> I don't know very well the geometry of those coils, but I found a hand
>> sketch on the JLab Target Group pages (there must be something more
>> professional somewhere). From the numbers there I get that the coils
>> could be rotated to a maximum theta_q < ~ arctan(8/(19+4) = 19 deg,
>> keeping a 1 cm upstream clearance for the slow raster's 1.1 cm radius
>> envelope.
>>
>> Given the uncertainties in surveys, and beam wandering, especially with
>> a chicane (needed to correct the beam deflection for rotated coils,) 1
>> cm is the minimum clearance I would advocate.
>>
>> The dimension along the beam to the target center 19cm + 4 cm comes from
>> taking 1/2 the coils' 8 cm split, per NIM paper on the CLAS target. If
>> one sticks to the numbers on the sketch, the target center is at 19cm +
>> 9cm (per note on the right), so theta_q < 15.9 deg.
>>
>> The above consideration indicates that it's most likely that my 19 deg.
>> estimate is way over optimistic, and since our two high x points have
>> theta_q > 19 deg., trying to align the field along q to suppress the
>> target-only A_V^d does not compensate for the trouble of setting up the
>> beam line.
>>
>> The rough sketch of the Hall B coil dimensions is here
>> https://userweb.jlab.org/~ckeith/EG1/Autopsy/banjo_dim.jpg
>>
>> Again, I encourage everyone to review the above points carefully.
>>
>> Cheers,
>>
>> Oscar
>>
>>
>>
>>
>>
> 
> -------------------------------------------------------------
> D. G. Crabb
> Research Professor of Physics
> University of Virginia
> 382 McCormick Rd.
> Charlottesville
> VA 22903
> USA
> Phone: 434-924-6790
> Fax:    434-924-4576
>