Transcript MICE MAGNETIC FIELDS & SHIELDS J. H. Cobb & H. Witte Oxford University Magnet fields for MICE (VI) calculated including magnetic shield discs at.

MICE MAGNETIC FIELDS & SHIELDS
J. H. Cobb & H. Witte
Oxford University
Magnet fields for MICE (VI) calculated including magnetic shield discs
at request of software people
Minor adjustments to end-coil currents to get uniform field in spectrometers
Recalculate fields at positions of PID detectors with shields
 All documented in MICE Note 119, q.v. for details 
Some comments on possibility of lighter shield
Some minor amendments/additions for PID meeting 7/9/05
PID PC 7th Sept 2005
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Shield:
100 mm soft iron
400 mm from end coil
Spectrometer
solenoid
PID PC 7th Sept 2005
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Calculations made with FemLab after comparison with OPERA
B in solenoid – no visible difference
between FemLab & OPERA
PID PC 7th Sept 2005
Used OPERA default B – H
curve for soft iron
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OUTSIDE
Z
r
INSIDE SOLENOID
Field in iron
Average ~ 1.5 T – not saturated
Hot Spot is artefact of FEA calc.
PID PC 7th Sept 2005
Bz in channel, r = 0
Minimal difference iron/no iron
except at ends
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Shield
External B (obviously) less with iron
Beam less confined
Problem ?? TBD (software folk)
PID PC 7th Sept 2005
Adjust end-coil current only by ~2.5%
to give dB / B < 1% in solenoid
i.e. like no iron
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Shielding efficiency – summary table follows
|B|
TOF
Ckov
r
Black = No Iron
Red = with Iron
EMCal
Residual B @ EMCAL ~2x higher
than shown in TDR ~ 38mT
PID PC 7th Sept 2005
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• Fields  with currents adjusted for the iron  are
calculated & available as z – r map
• Fields at positions of TOF, Ckov & EMCAL calculated
•  S/W & PID people must see if they are OK
• This Shield does little for EMCAL
• NOTE No allowance for ‘Tunnel’ (shielding around hall)
• Investigate if it’s possible to reduce amount of iron for
same shielding efficiency by subdividing shield....
PID PC 7th Sept 2005
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Subdivide Iron Shield -- Summary (plots follow)
Fields in mTesla
Discs
0
1
1
2
2
2
2
2
10
10
(TDR w.Tun- w/o Tun)
-----------------------------------------------------------------------------T1
0
100 165 50
50
50
50
25
5|
6.35| 100mm
T2
0
50
25
25
10
25
-x10
-x10
Gap
0
50
50
10
25
25
5|
6.35|
-----------------------------------------------------------------------------Tot Fe
0
100 165 100
75
75
60
50
50
63.5
100mm
==============================================================================
TOF
246
105 92 90
98 110 117 124 118
102
80 --100
-----------------------------------------------------------------------------Ch
96
68
66
66
67
67
69
48 -- 60
Cal
46
36
39
.... all ~35
38
22 -- 28 Now/TDR~1.8
------------------------------------------------------------------------------TOF @ r = 25cm
Chkov
@ r = 38cm
Cal @ r = 35cm
Total Fe(mm)
0 50
60 64 75 100 165
----|-------------------------------|
Total Gap 0| 246
105 92 |
(mm) 10|
110
|
25|
124 117
[105] [97]
|
50|
118 *109
98
90
|
57|
102
|
|-------------------------------|
PID PC 7th Sept 2005
Including more from
HW 23 Aug, i.e.
since VC.
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|B| at TOF for 8 configurations of Iron Discs & Gap
PID PC 7th Sept 2005
With 165mm of Fe (23 Aug 2005)
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A LOOK AT SCRAPING IN SHIELD
RMS beam radius can be
calculated assuming:
Gaussian Beam
Beta function and
Gaussian beam,
Fields without iron
Emittance
Choose 200 MeV/c SFOFO
‘beta = 42cm’ and emittance
that scrapes (at some level)
in absorbers (r=15cm)
scale by sqrt(beta)  Shield
sigma(x) = sqrt {beta*(m/p)*epsilon-N}
PID PC 7th Sept 2005
Reduction of Bz due to iron does
not matter since ~ in drift region
outside tracker solenoid (see
10
page 5)
Summary
• Field maps exist; scraping probably not problem for
25cm hole
• Need response from PID group on residual fluxes
– Is 105 mT OK?
– Safety Margin?
– Further reduction  more iron and/or space
• Shield does a lot for TOF, some for Chkov, little for
EMCAL
• Possible ‘Shield Lite’ solution using 10 x 1/4” plates
(though is it worth the extra effort?)
PID PC 7th Sept 2005
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Subdivide Iron Shield -- Summary (plots follow)
Fields in mTesla
Discs
0
1
2
2
2
2
2
10
10
(TDR w. Tun-- w/o Tun)
-----------------------------------------------------------------------------T1
0
100
50
50
50
50
25
5|
6.35| 100mm
T2
0
50
25
25
10
25
-x10
-x10
Gap
0
50
50
10
25
25
5|
6.35|
-----------------------------------------------------------------------------Tot Fe
0
100 100
75
75
60
50
50
63.5
100mm
==============================================================================
TOF
246
105
90
98 110 117 124 118
102
80 -- 100
-----------------------------------------------------------------------------Ch
96
68
66
66
67
67
69
48 -- 60
Cal
46
36
39
.... all ~35
38
22 -- 28 Now/TDR~1.8**
------------------------------------------------------------------------------TOF @ r = 25cm
Chkov
@ r = 38cm
Cal @ r = 35cm
Total Fe(mm)
0 50
60 64 75 100
----|---------------------------|
Total
0| 246
105 |
Gap (mm) 10|
110
|
25|
124 117
[105] [97]|
50|
118 *109
98
90 |
57|
102
|
|---------------------------|
PID PC 7th Sept 2005
• B @ TOF most sensitive to shield
configuration
• Shield does ~0 for EMCAL !!
• Subdivision gives equal shielding
with less iron but more total length
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|B| at TOF for 7 configurations of Iron Discs & Gap
 10 x 6.35mm (0.25”) plates + 9 x 6.35mm gaps  |B| = 102 mT
c.f. 105 mT for single 100mm plate
Total length = 121mm; saves ~35% of the mass of the iron for extra 21mm
PID PC 7th Sept 2005
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