Transcript Status report about the e-m identifier F. Huveneers, Gh. Grégoire, M.

Status report about the e-m identifier
F. Huveneers, Gh. Grégoire, M. Cyamukungu
September 10, 2003
Study of shielding against the stray magnetic field at the downstream end of
the spectrometer
• The photomultipliers of the Cerenkov detector have to be
shielded.
• Shielding is made of a large and thick iron slab provided with a central
hole (diam. 50 cm) located around the beam axis.
• The z-position of (the upstream face of) this slab is presently
located 20 cm downstream of the last correction coil of the
spectrometer.
The present study estimates the residual field at the off-axis position of the
photomultipliers.
Active magnetic elements
From R. Palmer,Version 5
r
z
Current densities
Compute stray field in r-z space after the last correction coil with/without
an iron shielding of variable thickness
3D view of spectrometer with magnetic shielding
Correction coils
Focus
Matching
Soft iron shielding
Coupling
Solenoid
Computations
Field equations in the presence of ferromagnetic materials
are solved with Poisson/Superfish
http://laacg1.lanl.gov/laacg/services/possup.html
Field lines without shielding
z (cm)
;CAS 0 : pas de blindage
100
100
diam. 50 cm
Beam axis
80
80
60
60
40
40
20
20
r (cm)
0
0
O
-20
-20
0
Correction coil
20
40
60
80
100
120
140
C:\PUBLIC\FH_STAGE\LANL\ESSAIS\MICE\CAS0.AM
End of solenoid
160
8-18-2003
180
14:04:20
With a 5 cm thick shielding
5 cm thick soft iron
z (cm)
;CAS 3 : blindage 3
100
100
diam. 50 cm
Particle
flight path
80
80
60
60
40
40
20
20
0
0
20 cm
O
r (cm)
-20
-20
0
20
40
60
80
100
120
140
160
C:\PUBLIC\FH_STAGE\LANL\ESSAIS\MICE\CAS3.AM 8-18-2003 14:21:24
180
With 15 cm thick iron shield
10 cm thick soft iron
z (cm)
;CAS 1 : blindage 1
Particle
flight path
100
100
80
80
60
60
diam. 50 cm
40
40
20
20
r (cm)
20 cm
0
0
O
-20
-20
0
20
40
60
80
100
120
140
160
180
C:\PUBLIC\FH_STAGE\LANL\ESSAIS\MICE\CAS1\CAS1.AM 9-08-2003 10:20:30
Field along beam axis
End of correction coil
Field inside solenoid
45000
Bz along beam axis (r = 0)
30000
Bz [Gauss]
No shield
Shield 15 cm thick
10 cm
5 cm
15000
0
-80
-60
-40
-20
0
20
40
60
80
100
z [cm]
Location of the e-m identifier –
Look at next transparency for
detailed view
Stray field downstream along beam axis
8000
Bz along beam axis (r = 0)
Bz [Gauss]
6000
No shield
Shield 15 cm thick
10 cm iron
5 cm iron
4000
2000
1 kGauss limit
0
35
Approximate z-position
of photomultiplier axis
45
55
65
z [cm]
75
85
95
Influence of the shielding
Bz (with shield) - Bz (without shield) [Gauss]
2500
2000
1500
Shield 15 cm thick
1000
10 cm
500
5 cm
0
-80
-60
-40
-20
0
20
40
60
80
-500
-1000
-1500
-2000
-2500
Z [cm]
Shown here: modifications of Bz along beam axis (r=0)
100
Conclusions
A soft iron shield ~15 cm thick with a central hole of ~50 cm diameter is
needed to reduce to 1 kGauss the stray field at the PM positions.
- For thinner shields, the saturation of iron is reached around the central hole.
- The residual field is further reduced by a specific mumetal shield
around the photomultipliers
The subsequent field modifications affect:
-
the magnetic field configuration of the solenoid
the tracking of particles and the simulations both upstream and
downstream
- the construction of the containment vessel for the
correction coil and the solenoid.
They should be hopefully taken into account in close
cooperation with the relevant MICE experts.
Work underway
1.
Optimization of the shielding parameters
(thickness, central opening, shield saturation …)
2. Generation of a C++ program to evaluate field components at
any point downstream the last correction coil and the shielding
3. Implementation in Geant 4 + for downstream tracking
We are waiting for comments and suggestions from the experts …
( [email protected] )