[lcdds 127] Re: [bds 177] question on field outside the detector

["T.Tauchi" <toshiaki.tauchi@xxxxxx>]

Dear Andrei and colleagues;

We can estimate the calculation error of the GLD leakage field from
experiences of the BELLE detector.

The BELLE group had the very similar problem at the first excitation test in
1997, for reduction of leakage field along the beam line.  The group has
been able to reduce the field by filling 8cm gap between barrel and endcap
return yoke with iron plates as shown in the presentation by H.Yamaoka,
whose file can be downloaded from webpage of
http://acfahep.kek.jp/subg/ir/bds/mdi/answers/Q1(B)/Leakage-Belle.pdf and
http://acfahep.kek.jp/subg/ir/bds/mdi/answers/Q1(B)/Leakage-Belle.ppt.
Also, the group compared measurements with calculations before and after the
reduction.

The BELLE solenoid has a coil of 3.6m diameter and 3.91m length. The central
magnetic field is Bz=1.5 Tesla.  The degree of saturation is 1.4% at the
current of I=4100A, which shows deviation from the linear function of
current at Bz=1.5T .

Before the reduction, the results of 4 measurements are consistent in each
other. They are compared with calculations of OPERA(2d-RZ=20m, 3d-XYZ=50m)
and ANSYS, where the 2d-RZ=20m and 3d-XYZ=50m are 2 and 3 dimensional ones
with boundary conditions of Bz=0 at R,Z=20m and X,Y,Z=50m, respectively, and
ANSYS is 2 dimensional calculation with axial symmetry. The calculations
deviate from the measured ones at z>4.5m; i.e. +25% at Z=6m.

After the reduction; i.e. with 8cm Fe plate, measurements are compared with
calculations of OPERA-3d,XYZ=50m and ANSYS.  The OPERA reproduces the
measured ones very well.  ANSYS has a systematic deviation, while the
difference of field strength is less than 3 Gauss.  The difference was
understood to be due to effects from magnets at the beam line, since the
OPERA included these effects.

Therefore, we conclude that the GLD calculation must have similar accuracy,
which is good enough.

To: Andrei,
Could you provide us tolerable strength of the leakage field ?  If
necessary, we could reduce the field by increasing iron structure.

Best regards,
Hiroshi Yamaoka / Toshiaki Tauchi , GLD group.





 


> From: "Seryi, Andrei" <seryi@xxxxxxxxxxxxxxxxx>
> Reply-To: <bds@xxxxxxxxxxxxxx>
> Date: Fri, 30 Sep 2005 12:02:09 -0700
> To: "Angal-Kalinin, D (Deepa)" <d.angal-kalinin@xxxxxxxx>, "Appleby, RB
> (Robert)" <r.b.appleby@xxxxxxxx>, Grahame Blair <blair@xxxxxxxxxxxxx>, I
> Agapov <ilya.agapov@xxxxxxxxxx>, Phil Burrows <p.burrows@xxxxxxxxxx>, "Woods,
> Michael B." <mwoods@xxxxxxxxxxxxxxxxx>, "Markiewicz, Thomas Walter"
> <twmark@xxxxxxxxxxxxxxxxx>, Olivier Napoly <Napoly@xxxxxxxxxxxxx>, "T.Tauchi"
> <toshiaki.tauchi@xxxxxx>, Olivier Dadoun <dadoun@xxxxxxxxxxxx>, "Spencer,
> Cherrill M." <cherrill@xxxxxxxxxxxxxxxxx>, <witold@xxxxxxxxxxxxxxxxx>,
> DELFERRIERE Olivier DAPNIA <olivier.delferriere@xxxxxx>, Francois Richard
> <richard@xxxxxxxxxxxx>, David Miller <djm@xxxxxxxxxxxxx>, Ties Behnke
> <ties.behnke@xxxxxxx>, Philip Bambade <bambade@xxxxxxxxxxxx>,
> <karsten.buesser@xxxxxxx>, "Maruyama, Takashi" <tvm@xxxxxxxxxxxxxxxxx>, Carter
> John <john.carter@xxxxxxxxxx>, <torrence@xxxxxxxxxxxxxxxxxxx>, "Seryi, Andrei"
> <seryi@xxxxxxxxxxxxxxxxx>
> Cc: <lcdds@xxxxxxxxxxxxxx>, <bds@xxxxxxxxxxxxxx>
> Subject: [bds 177] question on field outside the detector
> 
> 
> Dear Colleagues, 
> 
> This question is addressed to colleagues who design the detector solenoids
> for LDC, GLD and SiD.
> 
> In the 2005 field maps the solenoid field tail at 10m from IP is large,
> it reach 1 kilogauss for LDC (for SiD and GLD somewhat smaller).
> 
> If this field is real, there are consequences for beam optics, safety,
> and it also could mean that detector iron is saturated too much,
> as discussed in the attached file.
> 
> Hopefully, this field is not real, and is due to computational error, simply
> because 
> the region outside the detector was not considered important and people
> did not pay attention.   If so, we ask you to update the field maps,
> also providing an estimation for inaccuracy of the calculated field.
> 
>  Best regards, 
>   Andrei Seryi for WG4
>