Tests in magnetic field of conventional Hamamatsu R4998

MICE Collaboration
MICE-NOTE-DET-201
9 February 2008
Tests in magnetic field of conventional
Hamamatsu R4998 PMTs
R.Bertoni a, M.Bonesini a, Y.Kharadzov a,1, M.Rayner a,2 and
S. Terzo a
a Sezione
INFN Milano Bicocca, Dipartimento di Fisica G. Occhialini,
Piazza Scienza 3, Milano, Italy
This paper reports the measurements done at Milano Bicocca to study
the behaviour of conventional Hamamatsu R4998 PMTs with local massive iron box shieldings inside magnetic fields up to 600 G. A dedicated
solenoid was built for this purpose and extensive measurements done in
2007. As a conclusion, a local PMT shielding with 1 mm µ-metal + a
6 × 6 cm2 transverse area ARMCO pure iron box shielding was found
sufficient to shield TOF2 PMTs and gives a valuable alternative to more
complicate and expensive global shieldings.
1
2
permanent address Dept. of Physics, University of Sofia,Bulgaria
permanent address Dept. of Physics, University of Oxford, UK
Contents
1 Introduction
1
2 The chosen Hamamatsu R4998 PMT
1
3 PMT’s shielding: local versus global solution
2
3.1 Global shielding solution
4
3.2 Local shielding solution a la D0
4
4 Tests on Hamamatsu R4998 PMTs
5
4.1 PMTs test setup
5
4.2 Tests results for Hamamatsu R4998 PMTs.
8
5 Conclusions
12
References
17
2
1
Introduction
In the MICE experiment, precision timing measurements are required to relate the
time of the incoming beam muons to the phase of the accelerating field in each RF
cavity and simultaneously for particle identification (PID) by a time-of-flight (TOF)
method. Three time-of-flight detectors (TOF0, TOF1, TOF2) are foreseen [1], [2].
The last two (TOF1/TOF2) are at the entrance and the exit of the MICE cooling
channel; the first one (TOF0) instead is placed ∼ 10 m upstream of its entrance.
The first TOF0 station will work in the fringe field of the Q6 quadrupole magnet.
Estimations of the B field from [3] give a value well below 50 Gauss. The other two
TOF stations (TOF1/TOF2) will work instead in the stray fields of the measuring
solenoids with a magnetic field up to 0.09-0.1 T.
2
The chosen Hamamatsu R4998 PMT
Due to the low residual magnetic field, in the fringe field of the Q6 quadrupole where
the TOF0 detector will be placed, conventional PMTs with an elongated µ-metal
shielding (extending 30 mm beyond the photocathode surface) may be used. The
same apply for PMTs for TOF1/TOF2 provided an additional local or a global
shielding is built.
To obtain a good timing resolution, PMTs with a small transit time spread (TTS)
must be used. An additional requirement is a good rate capability, up to 0.5 MHz for
each counter. This has led, as a natural choice, to 1” R4998 PMTs from Hamamatsu
Photonics 1 . Table 1 displays their main characteristics.
R4998 PMTs have been delivered by Hamamatsu in assemblies (H6533MOD) that
include the PMT tube, the voltage divider chain and a 1 mm µ−metal shielding
(see figure 1 for details). To increase the countrate stability of PMTs, instead of a
conventional resistive divider type, active dividers or a booster on the last dynodes
were requested. In this way the theoretical rate capability is increased by a factor
∼ 8 (from ∼ 260 KHz to ≥ 1 MHz). After some tests, the performances of PMTs
equipped with a booster or an active divider were found equivalent and thus the
active divider option was chosen for its easier use. The distribution of gains at B=0
Gauss at a nominal -2250 V H.V., as deduced from Hamamatsu data sheets, is
shown in figure 2 for the sample of R4998 PMTs to be used on TOF0. In the same
figure the distribution of the anode dark current (in nA) is also shown. Variation in
gain up to a factor 5 are evident, even after the PMTs selection. This points to an
accurate matching of PMTs for the left-right side of each TOF scintillator bar.
1
A lower cost alternative based on 1” PET PMTs (R9800 from Hamamatsu), with a TTS
∼ 250 ps, a risetime ∼ 1 ns and a nominal gain G ∼ 1 × 10 6 , was available only after this
choice was made
1
R4998
Structure
Linear Focussed
Tube diameter
1”
Active area diameter
20 mm
No. stages
10
Q.E. at peak
.20
Gain (B=0 T) typ.
5.7 × 106
Risetime (ns)
0.7
Transit time (ns)
10
TTS (ns)
0.16
max hIa i (mA)
Table 1
Main properties of Hamamatsu R4998 PMTs.
0.16
Fig. 1. H6533MOD assemblies, with active divider, as delivered by Hamamatsu.
3
PMT’s shielding: local versus global solution
TOF1 and TOF2 will work inside the high residual magnetic field not fully shielded
by the 10 cm iron shield (“the Virostek plate”) either side of the measuring solenoids.
Figure 3 from [4] shows the longitudinal Bk and orthogonal B⊥ components of the
magnetic field at the position of TOF2, computed with a 2D Tosca [5] calculation
(z = 664 cm). 3D Tosca calculations were redone in reference [6] and results were
found compatible.
Orthogonal components (up to 0.1 T) and longitudinal components (up to 0.025 T)
of the fringe magnetic fields have to be shielded. Local or global shielding may be
2
Events
ID
Entries
Mean
RMS
7
6
100
40
3.875
1.950
5
4
3
2
1
Events
0
0
2.5
5
7.5
10
12.5
15
17.5
20 22.5 -6
25
G(B=0 T) x 10
ID
Entries
Mean
RMS
10
101
40
7.975
11.02
8
6
4
2
0
0
10
20
30
40
50
60
70
80
90
100
Idark (nA)
Fig. 2. Absolute gain G distribution at -2250 V (top) and anode dark current in nA
(bottom) for the sample of R4998 PMTs, to be used in the experiment on TOF0.
devised.
Fig. 3. Magnetic field components, after the “Virostek” plate at the position of TOF2 [4].
For conventional PMTs the most difficult component to be shielded is the one along
the PMT’s axis. Orthogonal components are more easily shielded. This report addresses mainly the first item.
3
3.1 Global shielding solution
In the global shielding solution, a magnetic cage bolted to the “Virostek plate” fully
embraces the TOF1 or TOF2 detector reducing the residual B field to a maneageable
value of the order of a few Gauss. The solution, albeit elegant, is quite expensive and
puts severe problems for access to the TOF detector PMTs inside. Figure 4 shows
it for the TOFI detector. The extraction mechanics of TOFI is quite complicate, as
16
15
14
13
12
L
11
10
ITEM QTY
PART NUMBER
1
1 Hindge Setup
2
1 Top Bracket & Support
3
2 Side Restraint Bracket
4
1 Bottom Support Bracket
5
1 Bottom Split Ring
6
1 Side Split Ring
7
1 Top Split Ring
8
1 Front Cage Shield
9
1 Virostek Shield
10
2 Stopper
11
2 Guide rail
12
2 Rail Spacer
13
2 Locking Pin
14
2 Stopper 1 spacer
15
2 Slide in Stopper 1
16
1 TOF CORE
K
Parts List
DRAWING NUMBER
MC-TOFS-SA01
MC-TOFS-SA02
MC-TOFS-SA03
MC-TOFS-SA04
MC-TOFS-SA05
MC-TOFS-SA06
MC-TOFS-SA07
MC-TOFS-SA08
MC-TOFS-SA09
MC-TOFS-SA10
MC-TOFS-SA11
MC-TOFS-SA12
MC-TOFS-SA13
MC-TOFS-SA14
MC-TOFS-SA15
Supplyed by MICE
9
8
7
6
5
4
3
2
1
L
DESCRIPTION
K
J
J
I
I
H
H
2
A ( 1:6 )
G
G
10
14
15
8
7
3
11
F
F
13
E
E
6
A
D
D
1
C
C
9
16
5
12
4
B
B
SCALE
UNIVERSITY OF OXFORD
DEPARTMENT OF PHYSICS
KEBLE ROAD
OXFORD, OX1 3RH
TEL. +44 (0)1865 273333
FAX. +44 (0)1865 273475
DRAWN BY
1:6
J.Tacon
CREATION DATE:
22/08/2007
LATEST DATE:
28/08/2007
PROJECT/ORIGINATOR
X.X
0.05
0.005
SOURCE FILE :
CHECKED
0.1
X.XX
X.XXX
TITLE
TOF Shielding
MICE
GENERAL TOLERANCES
UNLESS STATED
MATERIAL
COMPONENT WEIGHT
FINISH
NUMBER OFF
1
JOB NO. / EST. TIME
USED ON :
TOF Shielding RM.iam
DRAWN ACCORDING TO BS308
A
3rd ANGLE PROJECTION
ALL DIMENSIONS ARE IN MM
UNLESS OTHERWISE STATED
16
15
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13
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9
8
7
6
5
4
SIZE
A0
THIS DRAWING MAY NOT BE USED FOR COMMERCIAL USE
3
2
DRAWING NUMBER
A
MC-TOFS-MA
SHEET 1 OF 1
1
Fig. 4. Global shielding for TOFI, as designed in [7].
it includes brackets to allow access to the internal part of the cage.
3.2 Local shielding solution a la D0
In media, the magnetic field is defined by H=B- 4 π M where B is the magnetic
flux density and M the moment density of the media. The magnetic permeability µ
is defined by B= µ H for non-ferromagnetic materials or ferromagnets at low fields.
For ferromagnetic materials in large fields B = F(H) and depends on the media
history (hysteresis), but at least initially one may assume B ' µ H. For the ideal
case of a spherical shell of permeability µ the field inside the shield is reduced by a
factor µ−1 .
Magnetic shielding materials are chosen for their characteristics in respect to permeability and saturation. As permeability increase in magnetic shielding materials,
their saturation level decrease. Therefore, the highest permeability alloys (such as
µ−metal) have the lowest saturation values. As a saturated shield is a poor attenuator, for a given field a proper material must be chosen. Table 2 reports some
commercially available materials with their permeabilities. Up to fields ∼ 50−100 G
µ-metal shieldings are enough. For higher field values, such a shield saturate and
becomes ineffective. It must be surrounded by a supplementary shield, usually of
4
soft iron. The usual choice is a low carbon content iron (less than 0.01%, such as
ARMCO), that has relatively high permeability (compared to other steel) and excellent saturation characteristics.
As shielding is a mass effect, box-shaped soft iron shieldings are more effective than
cylindrical ones. This idea pioneered in the D0 experiment [8] has been tested in
the case of MICE using different geometrical configuration for the iron shielding
boxes and different iron materials: Fe360, ARMCO, ... The problem is usually the
longitudinal component Bk of the magnetic field, while the orthogonal component
B⊥ may be more easily shielded.
As an example, from reference [9] a simple mild-steel shield of inner diameter 32 mm
and thickness 4 mm (rin /rext = .80) in a field B⊥ = 1000 G gives an attenuation
∼ 100. An additional inner µ−metal shield with an inner diameter 29 mm and 1-mm
thickness (rin /rext = .936) gives an additional attenuation of about 500, leaving a
residual magnetic field of ≤ 1 Gauss. This shows that the soft iron box configurations
studied are more than enough for the shielding of B⊥ fields up to 1000 G. The only
remaining problem is the magnetic shielding of Bk fields.
material
% of C
µmax
r
Fe360 iron
0.25%
5000
ARMCO iron
≤ 0.01%
180000
21500
800000
8000
Super-permalloy
saturation (G)
µ−metal (80 % Nickel)
100000
Table 2
Properties of some commercially available shielding materials.
4
6500
Tests on Hamamatsu R4998 PMTs
4.1 PMTs test setup
Systematic studies have been done, using a built on purpose solenoid of 23 cm inner
diameter, 40 cm length shown in figure 5 2 . The magnetic field is created by five
windings in series, giving five solenoids in series on the same spool and crossed by
the same current I. Being a resistive magnet a special care was put into the thermal
resistance of the assembly (up to 100 C 0 ), using special insulating paints. For part
of the tests a Digimess 3040 laboratory power supply (0-32 V, 0-40 A) was used. At
higher fields an Eutron power supply (0-32 V, 0-100 A) on loan was used. The main
limit was the heating of the windings that limited the maximum circulating current
to about 55 A, due to the increase of conductor resistance giving higher voltage
2
built by TBM srl, Uboldo (VA), Italy
5
Fig. 5. The used resistive solenoid test magnet at INFN Milano Bicocca. A PMT under
test is shown inside.
drops (up to the maximum allowed value of ∼ 30V ). The big open bore allows tests
of the H6553 assembly both with field lines orthogonal or parallel to the PMT axis.
The magnetic field was measured via a gaussmeter 3 , with a better than 1% accuracy. The B field calibration curve is shown in figure 6 at the center of the solenoid
and at different z positions shifted along its longitudinal axis. From simulations
using a finite length solenoid approximation and performed measurements, a field
uniformity better than 3% may be assumed at the center of the test solenoid in a
volume of about 5 × 5 × 10 cm3 .
A fast light pulse 4 was sent to the PMT’s photocathode via a 3 m long multimode
3M TECS FT-110-LMT optical fiber (with a measured dispersion of ≤ 15 ps/m, see
[10]). At the end of the fiber a small Plexiglas prism, inserted in a black plastic cover
in front of the PMT window, allowed illumination at the center of the photocathode.
The laser spot was focused into the optical fiber (aligned by a micrometric x-y-z
flexure system 5 by a 10x Newport microscope objective, after removable absorptive
neutral density filters, to give light signals of different intensities. A broadband
beamsplitter (BS) divided the laser beam to give 50% of light on the fiber injection
system and 50% on a monitoring detector. A fast Thorlabs DET210 photodiode
(risetime ∼ 1 ns) was used in most measurements, to monitor the laser intensity.
Tests were done usually with a signal corresponding to about 150-300 photoelectrons:
a typical value for a minimum ionizing particle (MIP) crossing a scintillator 1”-2”
thick. The optical power was periodically monitored with an OPHIR NOVA laser
powermeter. The number of photoelectrons (Npe ) was estimated via absolute gain
measurement. This number was cross-checked with the powermeter measurements.
3
Hirst GM04 model, with axial Hall probe
a home-made system based on a Nichia NDHV310APC violet laser diode and an AvtechPulse fast pulser (type AVO-9A-C laser diode driver, with ∼ 200 ps risetime and AVX-S1
output module) was used. This system gave laser pulses at ∼ 409 nm, with a FWHM
between ∼ 120 ps and ∼ 3 ns (as measured with a 6 GHz 6604B Tek scope) and a max
repetition rate of 1 MHz
5 Thorlabs MBT613/M with 4 mm excursion and a resolution of ∼ 0.5 µm
4
6
Fig. 6. Upper panel: (left) calibration of the longitudinal field at the geometrical center
of the test solenoid, as function of the applied current; (right) variation of the calibration
slope as function of the axial displacement respect to the solenoid center. Lower panel:
difference of the magnitude of the B field as respect to z = 0 as a function of the circulating
current.
For gain measurements the PMT signal was acquired in average mode by a Tektronix
TDS 754C digital scope (500 MHz bandwidth, 2 Gs/s sampling rate) triggered by
the laser output sync., that had a maximum jitter of 15 ps as respect to the delivered
optical pulse. In part of the measurements the signal was sent after a passive 50%
T divider to a Canberra 2005 preamplifier, followed by an EG-G Ortec 570 shaper
(shaping time ∼ 1 µs, gain ∼ 200) followed by a Silena 8950 MCA analyzer, using as
external trigger the sync out signal of the laser. For timing measurements, the same
MCA chain was used with a Silena 7422 QVT (see figure 7 for details). The STOP
signal (tST OP ) was given by the PMT anode signal after a leading edge PLS 707
discriminator, while the START signal (tST ART ) was given by the sync out of the
pulser after a suitable delay and an ORTEC pulse inverter. In timing measurements
what is actually measured is the time difference ∆t = tST ART − tST OP , that accounts
for delay in cables and electronics and jitter in the transit time in the tested PMTs. A
lack of variation in this quantity or no deterioration in the FWHM of its distribution,
after increasing the magnetic field intensity, demonstrates the effectiveness of the
adopted shielding. The used TDC range (up to 0.1 µs) with the MCA resolution
(2K) allowed a resolution of 50 ps/count. Taking into account the TTS of the used
PMTs (160 ps at B=0 G), their transit time (∼ 10 ns) and risetime (tR ∼ 700 ps),
this resolution is well matched to possible incoming relevant effects.
7
Laser driver
xyz flexure
Sync out
optical fiber
Laser Head
BS
Delay
Filters
Magnet
Powermeter/
Photodetector
B
Inverter
SHAPER
ext Vin
trigger
MCA
PVC
CAP
HV
PMT
In
Out
QVT
Splitter
OUT
TEK 754C
READOUT
Fig. 7. Layout of the test setup for PMTs measurements (not in scale). In some measurements the readout section (MCA) was replaced by a TEK 754C scope.
4.2 Tests results for Hamamatsu R4998 PMTs.
4.2.1 Absolute gain measurements
− 9210
Pulser Lecroy
variable
attenuator
Test in
Preamp
Camberra
2005
OUT
IN
ORTEC
570
V in
MCA
Fig. 8. Layout of the test setup for absolute Gain measurement.
The absolute gain G and PMT linearity as a function of HV supply was measured
for some R4998 PMTs at B=0 Gauss, by using the test setup outlined in figure
8. A continuous train of pulses was delivered by a Lecroy 9210 pulser, through an
attenuator, to the test input of a Canberra 2005 preamplifier. The signal was shaped
to 2µs by an Ortec 570 shaping unit and then fed into a Silena MCA. In this way the
MCA scale was calibrated in pC/channel. Then the preamp was connected to the
PMT output, with an illumination corresponding to a SER peak condition. From
the MCA peak position, it was thus possible to determine the output charge Q in
pC as a function of HV and thus the absolute gain G, shown for a typical R4998
PMT in figure 9.
8
G (x 10|6)
1 inch conv PMT/active divider - gain
8
7
6
5
4
3
2
1
2000
2100
2200
2300
2400
2500
HV (V)
Fig. 9. Absolute gain G for a typical R4998 PMT, with active divider.
4.2.2 Behavior in magnetic field
The PMTs were inserted in the central region of the test solenoid, where the field
had a uniformity better than ∼ 3%, using a support to incline them to 00 or 900
as respect to the field lines in the magnet (Bk or B⊥ ). Environment light was
accurately masked, to reduce noise. Measures were done to see gain reduction and
possible deterioration in timing resolution as a function of the magnetic field (B)
and the relative orientation angle (θ), between the PMT axis and the magnetic
field B. The tested shielded solutions were the mu-metal shielding only option (as
given by the H6553MOD standard assembly) and various options with shielding
with additional soft iron in box shapes. As the magnetic shielding is mainly a “mass
effect” we may expect box shieldings to be more effective than cylindrical ones,
having more shielding mass. The tests have been done with different configurations:
– only µ-metal shielding (1 mm thick, 15 cm long: extending 3 cm beyond the
photocathode area)
– a 15 cm long iron box of transverse area 5 × 5 cm2 or 6 × 6 cm2 with a central
hole of 3.2 cm diameter (to accomodate inside the PMT assembly with a 1 mm
µ−metal shielding) made of different iron types: Fe360, Armco, ...
– the same recessing the PMT assembly 1, 2 or 3 cm inside the edge of the iron
shielding
Results are shown for the signal reduction and timing versus the B field value in
Figures 10 to 17, starting from a simple 1 mm µ-metal shielding and going to a
composite shielding that includes also an iron box. Figure 17 shows a comparison
for the different shieldings (signal reduction and timing versus the magnetic field
intensity B) for the average and rms of a sample of ten PMTs.
As a general conclusion, we see that:
9
Fig. 10. Signal ratio at field B and B=0 G, with only the mu-metal shielding of 1 mm, as
function of the magnetic field B. Plots are for individual PMTs. Top panel: longitudinal
field along the PMT axis, bottom panel: orthogonal field.
– very low carbon content iron (Armco) is more effective than standard Fe360, even
if this is quite good up to 500 G fields
– as expected, bigger shielding (from 5 × 5 cm2 to 6 × 6 cm2 transverse area shieldings) are better
– extending the iron shielding beyond the µ-metal shielding improves the situation
As long as the signal has a sizeable pulse-height no deterioration in timing is seen
6
.
The uncertainties in these studies came mainly from the following areas:
(i)
(ii)
(iii)
(iv)
uniformity of the magnetic field
stability of the laser pulses
error in positioning of PMTs inside the magnetic field
statical errors in the measure
6
only with the 1 mm µ-metal shielding or the 1 mm µ − metal shielding + 5 × 5 cm 2
Fe360 box shielding some effect was evident in timing (∆t or its FWHM) when the signal
amplitude experienced a reduction of a factor ∼ 10 in one case or two in the other
10
Fig. 11. Timing difference, measured as ∆t = t ST ART − tST OP with only the mu-metal
shielding of 1 mm, as function of the magnetic field B. Plots are for individual PMTs. Top
panel: longitudinal field along the PMT axis, bottom panel: orthogonal field.
As regards the first item, the uniformity of the magnetic field was estimated at
better than 3% in the region of measurement and cross-checked with gaussmeter
measurements. The stability of the laser pulses (second item) was monitored by
beam-splitting the laser light and monitoring it with a PIN photodiode 7 . The
overall stability of the system was within 5%, with maximum excursion in some bad
runs up to 10%. The simple mechanics of the system allowed us a reproducibility of
the positioning of the different PMTs’ at the level of some mm. From all the previous
sources of errors, we may conservatively estimate a measurement error below 10%.
Every single measurement referred to about 500 events, giving a negligible statistical
error as compared to systematics.
No study was done to assess eventual azimuthal angle effects on the PMTs and
hysteresis effects in the shielding.
As expected PMTs behave well for orientation of the B field orthogonal to the PMT
axis (900 ), where the shielding effect is maximal, while along the PMT axis (00 ) the
gain reduction may be more marked. The local shielding with 6×6 cm2 ARMCO iron
in addition to the 1-mm µ−metal case seems more than adequate for TOF2 PMTs.
7
DET210 from Thorlabs
11
only muMetal, B field orthogonal
1.4
V PMT(B)/VPMT(0)
V PMT(B)/V
PMT
(0)
only muMetal, B field parallel
1.2
1
1.4
1.2
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0
0
0.2
10
20
30
40
50
60
70
80
90
Bsolenoid [Gauss]
3
2.5
40
60
80
100
120
140
160 180
200
Bsolenoid [Gauss]
2
100
120
140
160 180
200
Bsolenoid [Gauss]
4
3.5
3
2.5
2
1.5
1.5
1
1
0.5
0
0
20
only muMetal, B field orthogonal
3.5
FWHM(B)/FWHM(0)
FWHM(B)/FWHM(0)
only muMetal, B field parallel
0
0
0.5
10
20
30
40
50
60
0
0
70
80
90
Bsolenoid [Gauss]
20
40
60
80
Fig. 12. Signal ratio at field B and B=0 G and FWHM ratio at field B and B=0 G for the
timing difference, measured as ∆t = t ST ART − tST OP with only the mu-metal shielding
of 1 mm. Left panel: longitudinal field, right panel: orthogonal field. The plots show the
average and rms for a sample of ten R4998 PMTs.
In addition the PMTs individual shields will be magnetically connected between
them and to the “Virostek” plate, giving extra mass effect and so more effective
shielding. In this way, our tests on single local PMTs represents a situation worse
than the real one. Figure 18 shows how the local shielding is foreseen for TOF2,
using a single bar for all PMTs of one side, instead of single boxes for individual
PMTs. This is a preliminary design that can be clearly optimized with suitable
computations, some of which have been proposed [6].
5
Conclusions
Measurements have been done up to longitudinal fields of 600 G for a sample of
R4998 PMTs, with different shielding options. While a simple 1-mm µ-metal shielding is enough up to 60 (150) G for a longitudinal (orthogonal) B field, an additional
ARMCO (6 × 6 cm2 ) shield is enough for longitudinal fields up to 600 G. As a
final remark, a local shielding with 6 × 6 cm2 ARMCO shielding surrounding a 1
mm µ-metal works well to shield TOF2 PMTs, avoiding a much more expensive
global shielding (“cage”). In this way TOF2 and KL may be put in a much nearer
configuration, avoiding dead spaces.
12
fe360, 5x5-2cm extension
1.4
0.8
PMT
1.4
1.2
0.6
0.2
0.4
100
200
300
400
0.6
0.4
0.2
0.2
500
600
Bsolenoid [Gauss]
0
0
100
200
300
400
1
0.8
0.4
0.2
0
0
1.4
1.2
1
200
300
400
600
Bsolenoid [Gauss]
400
500
600
Bsolenoid [Gauss]
300
400
500
600
Bsolenoid [Gauss]
1.2
1
0.6
0.4
0.4
0
0
500
300
1.4
0.6
0.2
0.2
100
200
0.8
0.8
0.6
100
fe360, 5x5-2cm extension
FWHM(B)/FWHM(0)
1.2
0
0
500
600
Bsolenoid [Gauss]
fe360, 5x5-1cm extension
FWHM(B)/FWHM(0)
FWHM(B)/FWHM(0)
fe360, 5x5 no extension
1.4
1.2
0.8
0.8
0.4
1.4
1
1
0.6
0
0
V PMT(B)/V
1
(0)
fe360, 5x5-1cm extension
1.2
V PMT(B)/VPMT(0)
V PMT(B)/VPMT(0)
fe360, 5x5 no extension
100
200
300
400
0
0
500
600
Bsolenoid [Gauss]
100
200
Fig. 13. Signal ratio at field B and B=0 G and FWHM ratio at field B and B=0 G for
the timing difference, measured as ∆t = t ST ART − tST OP with a Fe360 iron box shieldings
(transverse area 5×5 cm2 ) in addition to the the mu-metal one extending 0 cm (left panel),
1 cm (middle panel) and 2cm (right panel) beyond the end of the mu-metal shielding. The
B field is along the PMTs axis. The plots show the average and rms for a sample of ten
R4998 PMTs.
V PMT(B)/VPMT(0)
fe360, 6x6-2cm extension
fe360, 6x6-1cm extension
1.4
V PMT(B)/V PMT(0)
1.2
1
0.2
0
0
0.2
100
200
300
400
500
600
Bsolenoid [Gauss]
fe360, 6x6 no extension
0
0
100
200
300
400
500
600
Bsolenoid [Gauss]
fe360, 6x6-1cm extension
1.4
FWHM(B)/FWHM(0)
FWHM(B)/FWHM(0)
0.4
0.4
0.2
1.2
1
0.8
1.4
1.2
1
0.4
0.2
0.2
100
200
300
400
500
600
Bsolenoid [Gauss]
0
0
200
300
400
500
600
Bsolenoid [Gauss]
300
400
500
600
Bsolenoid [Gauss]
fe360, 6x6-2cm extension
1.4
1.2
1
0.6
0.6
0.4
100
0.8
0.8
0.6
0
0
0.6
0.6
0.4
0
0
1
0.8
0.8
0.6
1.2
1.2
1
0.8
1.4
1.4
FWHM(B)/FWHM(0)
V PMT(B)/VPMT(0)
fe360, 6x6 no extension
0.4
0.2
100
200
300
400
500
600
Bsolenoid [Gauss]
0
0
100
200
Fig. 14. Signal ratio at field B and B=0 G and FWHM ratio at field B and B=0 G for
the timing difference, measured as ∆t = t ST ART − tST OP with a Fe360 iron box shieldings
(transverse area 6×6 cm2 ) in addition to the the mu-metal one extending 0 cm (left panel),
1 cm (middle panel) and 2cm (right panel) beyond the end of the mu-metal shielding. The
B field is along the PMTs axis. The plots show the average and rms for a sample of ten
R4998 PMTs.
Acknowledgments
The essential help of Mr. F. Chignoli and R. Mazza of INFN Milano Bicocca for the
preparation of this report is acknowledged. We would like to thank Mr. M. Piselli
of University of Milano Bicocca for help and the generous loan of an Eutron power
13
Fig. 15. Signal ratio at field B and B=0 G and timing difference ∆t as a function of field B
and, measured with an ARMCO iron box shieldings (transverse area 6×6 cm 2 ) in addition
to the the mu-metal one extending 0 cm beyond the end of the mu-metal shielding. The
B field is along the PMTs axis. The plots are for a set of ten R4998 PMTs.
V PMT(B)/VPMT(0)
feARMCO, 6x6 no extension
V PMT(B)/V
PMT
(0)
feARMCO, 5x5 no extension
1.2
1.4
1
1.2
0.8
1
0.6
0.8
0.4
0.6
0.2
0.4
0
0
0.2
100
200
300
400
500
600
Bsolenoid [Gauss]
feARMCO, 5x5 no extension
1.4
1.2
1
200
300
400
500
600
Bsolenoid [Gauss]
300
400
500
600
Bsolenoid [Gauss]
1.4
1.2
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
0
100
feARMCO, 6x6 no extension
FWHM(B)/FWHM(0)
0
0
FWHM(B)/FWHM(0)
1.4
100
200
300
400
500
600
Bsolenoid [Gauss]
0
0
100
200
Fig. 16. Signal ratio at field B and B=0 G and FWHM ratio at field B and B=0 G for the
timing difference, measured as ∆t = t ST ART − tST OP with an ARMCO iron box shieldings
(transverse area 5 × 5 cm2 (left panel) or 6 × 6 cm2 (right panel)) in addition to the the
mu-metal one extending 0 cm (left panel) beyond the end of the mu-metal shielding. The
B field is along the PMTs axis. The plots show the average and rms for a sample of ten
R4998 PMTs.
suppy. We are indebted also to Dr. L. Confalonieri, Hamamatsu Italia, and Ing. L.
Vernocchi for help and many enlightining discussions.
14
V PMT(B)/VPMT(0)
Comparison Between Shields
1.4
1.2
1
0.8
0.6
Shield
fe360, 5x5 no extension
0.4
fe360, 6x6 no extension
feARMCO, 5x5 no extension
0.2
feARMCO, 6x6 no extension
00
100
200
300
400
500
600
Bsolenoid [Gauss]
300
400
500
600
Bsolenoid [Gauss]
FWHM(B)/FWHM(0)
Comparison Between Shields
1.4
1.2
1
0.8
0.6
Shield
0.4
0.2
0
0
fe360, 5x5 no extension
fe360, 6x6 no extension
feARMCO, 5x5 no extension
feARMCO, 6x6 no extension
100
200
Fig. 17. Signal ratio at field B and B=0 G and FWHM ratio at field B and B=0 G for the
timing difference, measured as ∆t = t ST ART − tST OP with different iron box shieldings in
addition to the the mu-metal one. The B field is along the PMTs axis. The plots show the
average and rms for a sample of ten R4998 PMTs.
15
Fig. 18. CAD drawing of TOF2 with local shieldings for PMTs, using a single bar of
ARMCO 6 cm thickness for each side [11].
16
References
[1] M.Bonesini, “The design of MICE TOF0 detector”, internal note MICE-NOTE-DET0145, 2006.
[2] M.Bonesini et al., “ Study of the MICE TOF prototypes performance at the BTF test
beam”, internal note MICE-NOTE-0163, 2006.
[3] K. Tilley, private communication, MICE Collaboration Meeting, RAL, October 2005.
[4] H. Witte,J. Cobb “The Magnetic Field in vicinity of TOF2”, MICE-NOTE-MAGNXXX in preparation.
[5] http://www.vectorfields.com
[6] G. Gregoire, “ Shielding update”, MICE presentation 7/11/2007.
[7] G. Gregoire, “ TOFI cage”, MICE presentation at CM18, 13/6/2007;
W.Lau, “Final discussion of drawings for TOFI shielding cage”, MICE presentation
31/7/2007.
[8] R. Stephens et al., D0 Note 2706, 1996 (brought to our attention by L. Tortora).
[9] S.O. Flyckt and C. Marmonier, “ Photomultiplier tubes: principles and applications”,
Photonis, Brive, 2002.
[10] M. Bonesini et al., IEEE Trans. Nucl. Sc. NS-50 (4) (2003) 1053.
[11] R. Mazza, Sezione INFN Milano Bicocca, private communication.
17