Detectors for Heavy
Fragments : Design
[1]
Overview
Position
detectors
Beam is momentum-tagged by measureing the
position at the momentum dispersive focal plane (F5). Beam phase space is measured by a set of position detectors
befort the target. From the required
momentum resolution and the bending power of the magnet, tracking detectors are
designed to have an angular resolution of about 
, assuming
that the beam positions are measured by extrapolating the beam trajectory, and
that positions and angles are measured downstream of the magnet. In addition, another chamber is installed
between the target and the magnet to measure the scatteering angle. In addition, This requires a low-mass
chamber, much less than 
, with a good
position resolution.
Detectors
for Particle Identification
Particle identification
of heavy fragments requires velocity measurement or total-energy measurement in
addition to the rigidity and the charge measurement. In order to have 5s separation (
) at A=100,
velocity resolution of 
or total energy resolution of 
is necessary. When the TOF method is used for velocity measurement, necessary
time resolution is 
for 10 meters of flight path. Considering the necessity of a thin start
detector for TOF, this method seems to be marginal.
We have considered two techniques for
velocity and total-energy measurements: a Cherenkov detector operated at the
total internal reflection (TIRC) for velocity measurement and pure CsI detector
for total-energy measurement.
Design
policy
Since all the detailed design of these
detectors (i.e. all the contracts) had to be made in FY2008 due to the nature of the construction budget, design of
these detectors are , more or less, conventional.
Detector
Summary
There are four kinds of detector groups for
heavy ion measurements.
*
Position measurement
* Beam Proportional Chamber
(BPC): beam rigidity tagging at F5
* Beam Drift Chamber
1, 2 (BDC1,BDC2) : beam
phase space
* Forward Drift Chamber
1 (FDC1)
: scattering angle of
fragments
* Forward Drift Chamber
2 (FDC2)
: rigidity analysis for fragments
* Proton Drift Chamber
1,2 (PDC1,2) : momentum
analysis for protons
*
Charge measurement
* Ion Chamber for Beam
(ICB)
: beam charge
* Ion Chamber for Fragments
(ICF)
: fragment charge
*
Velocity (& charge) measurement
* Hodoscope for Fragment ( HODF) : velocity & charge for
fragments
* Hodoscope for Protons (HODP) : velocity & charge for
protons
* Total Internal Reflection
Cherenkov (TIRC) : velocity
for fragments
*
Total energy measurement
* Total Energy Detector
(TED)
: total energy
*
Readout electronics for position detectors
As a readout circuits of position detectors,
anode signals are converted into LVDS logic signals using Amp-Shaper-Discriminator
boards (ASD, 16ch/board, gnd, GNA210) mounted directly on the detectors. ASD Power Supply modules are used to supply
±3V, threshold voltage, and test pulses : one ASD PS handles 10 ASD boards. Logic signals are further processed by multihit
TDC’s (AMSC, 64ch AMT-VME TDC module) with 0.8 nsec/ch precision.
*
Gas mixture for position detectors
When detectors are operated at 1 atm,
He+60%CH4 is used. This
mixture comes from the compromise among multiple scattering, position resolution
and running cost. At low pressure, BPC,
BDC, and FDC1 are operated using pure i-C4H10.
[2] Beam Proportional Chamber
(BPC)
*
Design
BPC is used to tag the rigidity of
secondary beams at the momentum dispersive focal plane F5 by measuring the horizontal
position. It is a 4mm-spacing multiwire
proportional chamber with 2 anode planes.
It is housed in detector box, which is placed in the F5 vacuum chamber. Since the momentum dispersion at F5 is
~33mm/%, 4mm-spacing provides momentum resolution of less than 0.1% (rms).
BPC
is shown in Fig. 1 and summarized in the table.
Amp-shaper-discriminators (ASD) are mounted
directly on the detector box in the F5 vacuum chamber. LVDS signals are timed , through the vacuum
feed through, by TDC’s. Isobutane gas
is used at about 20 torr for Kr, and about 200 torr for protons.
|
Anode |
20μmφ Au-W/Re |
|
Anode
spacing |
2mm
(2 wires are or-ed for readout) |
|
Anode
– cathode gap |
5mm
(5mm-thick G10) |
|
Cathode,
window |
12μm-thick Al-Mylar |
|
Effective
area |
240mm
(H) x 150mm (V) |
|
Anode
configuration |
x1
- x2 |
|
#readout
channels |
64
anodes /plane x 2 planes = 128anodes |
|
Window
of detector box |
80μm-thick Kapton x2 |
|
Operation
gas |
i-C4H10
at 20 to 200 torr |
|
HV |
cathode |
|
Readout |
ASD
x8, ASD PS x1, TDC x2 |
Fig. 1 : BPC assembly
[3] Beam Drift Chambers
(BDC1, BDC2)
*
Design
Two sets of BDC’s are used to measure the
phase space of the incident secondary beams on the reaction target. It is a Walenta-type drift chamber with
2.5mm drift distance for high beam rates.
BDC is shown in Fig. 2, and summarized in the table.
|
Anode
wire |
16μmφ Au-W/Re |
|
Potential
wire |
80μmφ Au-Al |
|
anode
– potential (drift) distance |
2.5mm |
|
anode
– cathode gap |
2.5mm
(combination of 2.4mm & 2.6mm-thick G10) |
|
cathode |
8μm-thick Al-Kapton, x 9 |
|
gas
window |
4μm-thick Aramid, x2 |
|
effective
area |
80mm
x 80mm |
|
anode
configuration |
xx’yy’xx’yy’ |
|
#anode
/ plane x #planes |
16
wires/plane x 8 planes = 128 wires/detector |
|
Operation
gas |
He+60%CH4
at 1 atm, i-C4H10 below 200 torr |
|
HV |
cathode,
potential |
|
Readout
/ 2sets |
ASD
x16, ASD PS x2, TDC x4 |
Fig. 2 : BDC assembly
[4] Forward
Drift Chamber 1 (FDC1)
*
Design
FDC1 is placed between the target and
SAMURAL magnet in order to measure the emission angle of the projectile
fragments. It also has wide opening in
order not to interfere with projectile-rapidity neutrons at zero degrees. It is a Walenta-type drift chamber with 5mm
drift distance in order to handle relatively high beam intensity right after
the target.
|
anode
wire |
20μmφ Au-W/Re |
|
potential
wire |
80μmφ Au-Al |
|
anode
– potential (drift) distance |
5mm |
|
anode
– cathode gap |
5mm
(5mm-thick G10) |
|
cathode |
8μm-thick Al-Kapton, x
15 |
|
gas
window |
8μm-thick Al-Kapton, x2 |
|
effective
area |
315mmφ |
|
open
area for neutrons |
620mm
x 340mm |
|
anode
configuration |
xx’uu’vv’xx’uu’vv’xx’,
(±30° for u/v) |
|
#anode
/ plane x #planes |
32
wires/plane x 14 planes = 448 wires |
|
operation
gas |
He+60%CH4
at 1 atm, i-C4H10 at low pressure |
|
HV |
cathode,
potential |
|
Readout |
ASD
x28, ASD PS x3, TDC x7 1 VME crate (with
BDC1,2) |
Fig. 3 : FDC1 assembly
[5] Forward
Drift Chamber 2 (FDC2)
*
Design
FDC2 is placed after SAMURAI magnet for rigidity
analysis of projectile fragments. The
cell structure is hexagonal with 10mm drift length. Two staggered planes named super layer, such as xx’, are
separated by 100mm pitch with shield planes in between.
Fig 4 : FDC2 cell
structure
Although it was originally planned to put
FDC2 in the detector box for low-pressure operation, FDC2 will be operated at 1
atom for the time being due to technical difficulties.
|
Anode
wire |
40μmφ Au-W/Re, 20mm pitch |
|
Field
& shield wire |
80μmφ Au-Al, 20mm pitch |
|
Cell
structure |
hexagonal,
10mm drift length |
|
Configuration |
s-xx’-s-uu’-s-vv’-s-xx’-s-uu’-s-vv’-s-xx’-s (±30°for u/v) |
|
window |
2296mm
x 836mm |
|
#anode
wires (dummy) |
224(4)
anodes/super layer x 7 super layer = 1568 (28) anodes |
|
#field
/ shield wires |
4788
(field), 328 (shield) |
|
Operating
gas |
He+60%CH4
at 1 atm ( i-C4H10 below 100 torr) |
|
HV |
field
wires, shield wires |
|
Readout |
ASD
x98, ASD PS x11, TDC x25, 2 VME crates |
Fig. 5 : FDC2 Assembly
[6] Proton Drift Chamber 1,
2 (PDC1, PDC2)
*
Design
PDC1 and PDC2 are placed downstream of
SAMURAI magnet, and used to measure the momentum of projectile-rapidity
protons. Since counting rate is
expected to be low and in order to reduce number of planes, position
information is obtained using the cathode readout method. For the anode plane, Walenta-type drift
chamber, with 8mm drift length, is adopted in order to reduce the number of
anode wires. Three kinds of cathode
orientation are used to detect multi particles.
Parameters for the cathode readout are as
follows.
|
anode
wire |
30μmφ Au-W/Re, 16mm pitch
(8mm drift length) |
|
potential
wire |
80μmφ Au-Al, 16mm pitch |
|
anode
– cathode gap |
8mm |
|
cathode
wire |
80μmφ Au-Al, 3mm pitch |
|
cathode
strip width |
12mm
(4 cathode wires are or-ed for one strip) |
Present design of PDC is as follows. Anode wires are or-ed and positive HV is
applied. Anode wires are not
readout. Slight negative HV is applied
to potential wires. Cathode strips are
directly connected to the readout without decoupling capacitors.
Present design of the PDC is shown in Fig 6.
|
configuration |
cathode(U)-Anode(V)-cathode(X)-anode(U)-cathode(V) |
|
wire
angle |
X(0°), U(+45°), V(-45°) |
|
Effective
area |
1700mm
x 800mm |
|
anode
wire (U,V) |
106
anodes/plane x 2cplanes = 212 anodes |
|
potential
wire (U,V) |
107
potentials/plane x 2 planes = 214 potentials |
|
cathode
wire (U,V,X) |
544
wires/plane, 136 cathode strips (4
wires are or-ed)/plane |
|
HV |
Anode(+),
potential(-) |
|
Operating
gas |
Ar+25%
i-C4H10 or Ar+50%C2H6 |
Fig 6 : PDC assembly
*Readout
(status)
We have tested the charge division readout
for cathode signals in order to reduce the readout channel. Cathode strips are daisy-chained by
resistors, and cathode charges are read out via charge sensitive pre amp in
every 8 strips. Using a prototype
detector (600mm x 480mm effective area) with roughly the same geometry,
position resolution of 1mm (rms) were obtained for x-rays. With this method, about 110ch of charge
sensitive preamp, shaping amp, and peak sensitive ADC’s are necessary to read 2
PDC’s.
Since 2 proton events can not be handled
properly by this method, we are developing a new readout circuit: every cathode
signals are connected to charge sensitive preamp, shaper, sample & hold,
and digitized in the front-end board (FEB, 16ch/board), and digital data are
sent to the VME memory. This method
also improve the position resolution by ~factor of 5. About 810 ch of circuits
(8-9 FEB’s/plane x 6 planes) are necessary.
[7] Ion Chamber for Beam
(ICB)
*
Design
ICB is a multi-layer ion chamber, and
placed upstream of the target. It is
used to measure the charge of incident
secondary beams.
|
electrodes |
12μm-thick Al-Mylar , 10
anode & 11 cathode planes |
|
Anode-cathode
gap |
21mm |
|
window |
16μm-thick Aramid |
|
effective
area |
140mm
x 140mm x 420mm (deep) |
|
gas |
P10
@1atm |
|
HV |
anode(+) |
|
readout |
10ch,
preamp ( Mesytec-MPR16 with 10μs decay time), shaping amp (MSCF-16LE, active
BLR, unipolar output, 0.25μs
shaping time), & peak sensitive ADC (MADC32) |
Fig 7 : ICB assembly
[8] Ion
Chamber for Fragment
(ICF)
*
Design
ICF is a multi layer ion chamber, and
placed after the SAMURAI magnet. It is
used to measure the charge of projectile fragments.
Due to several technical difficulties
(available size of double-sides Al-Mylar foils, method to make double-sided
segmented anodes, etc.), effective area of the present ICF is much smaller than
that of FDC2. We should have used the
wire cathode as well to have larger
effective area.
|
electrodes |
12
anode & 13 cathode planes |
|
anode-cathode
gap |
20mm |
|
effective
area |
750mm
(H) x 400mm (V) x 480mm (deep) |
|
anode |
80μmφAu-Al, 5mm pitch, 18
wires are or-ed to make a 90mm-wide strip, 2
strips are or-ed for readout (4ch/plane) |
|
cathode,
window |
12μm-thick Al-Mylar |
|
Gas |
P10
@1atm |
|
HV |
cathode
(-), anode is at ground potential |
|
readout |
4ch/plane
x 12 planes = 48ch, preamp ( Mesytec-MPR16 x3 with 10μs decay time), shaping
amp (MSCF-16LE x3, active BLR, unipolar output, 0.25μs shaping time), &
peak sensitive ADC (MADC32 x2) |
Fig 8 : ICF assembly
[9] Hodoscope for Fragment/Proton
(HODF, HODP)
*
Design
HODF and HODP are conventional
scintillator hodoscopes. They are
placed after FDC2 and ICF to measure TOF and charge of particles.
|
plastic
scintillator |
BC408,
1200mm(V) x 100mm(H) x 10mm(T) |
|
slat |
Plastic
is coupled to HPK H7195 PMT (with a booster connector) via 100mm-long
fishtail light guide. |
|
Effective
area |
16
slats/hodoscope, 1600mm(H) x 1200mm(V) |
|
HV |
32ch/hodoscope
x 2 = 64ch, with additional HV’s for booster, CAEN
A1733N x6(+4) |
|
Readout |
16ch
CAMAC discriminator (Phillips 7106) x4, 500nsec
logic & analog cable delay x 64, CAEN
32ch ADC V792AC x2 CAEN
32ch TDC V775AC x2 |
Fig 9 : HODF/HODP
Assembly
[10] Total Internal Reflection
Cherenkov (TIRC)
*
Design
TIRC is a Cherenkov detector operated at
the total internal reflection (TIR) threshold.
Since photon numbers increase sharply at the TIR threshold, good
velocity resolution is expected.
Refractive index of the radiator chosen is n~1.9 so that the TIR
threshold is around 250 MeV/A.
|
radiator |
TAFD30(n~1.92), 65mm x 240mm x 2mmt (max. size available) |
|
PMT |
HPK
H6559 (3”φ) with
booster connector, radiator is viewed by 2 PMT’s. 10 PMT’s available |
|
effective
area |
632(317)mm
x 240mm(V), covered by 10(5) elements |
|
HV |
20(10)
ch, CAEN A1733N x2(1) |
|
readout |
20(10)
x 500nsec cable delay, CAEN 32ch ADC V792AC x1 |
Fig 10 : TIRC assembly
[11]
Total Energy Detector (TED)
*
Design
|
crystal |
Pure
CsI, 100mm x 100mm x 50mm-thick |
|
PMT |
HPK
– R6233HA(3”φ), with non-UV window, booster connector |
|
breeder |
tapered,
with high breeder current (3mA @1kV),
|
|
effective
area |
800mm(H)
x 400mm(V), with 8 x 4 (32) crystals |
|
HV |
32
ch, CAEN A1733N x3 |
|
readout |
32
x 500nsec cable delay, CAEN 32ch ADC V792AC x1 |
*
R&D for TED
As a total energy detector, we have
tested (1) NaI(Tl) coupled to PMT, (2)
HP-Ge crystal, (3) CsI(Tl) coupled to photodiode, using Ar & Kr &
secondary beams between 200 – 400 MeV/A.
Energy resolution of 0.3 – 0.4 % (rms) for total energy of 25 – 30 GeV was obtained only at low
counting rate (below 1kHz).
Since above detectors are relatively slow,
we have also tested pure CsI crystal coupled to PMT. It has smaller light output compared to CsI(Tl), but has faster
decay time and believed to be strong against the radiation damage. After high-current tapered breeder was
designed, energy resolution of 0.2 to 0.4% was observed for Kr beams at 400
MeV/A. By comparing the light output
between Ar and Kr beams, large saturation effect was observed. Since energy resolution between PMT with UV
window and with non-UV window has no noticeable difference, PMT with non-UV window
was selected. Light output was stable
for beam rates up to 10-20kHz. It was
also observed that the pulse shape for heavy ion is different from those for γ-rays, electrons, and
possibly protons.
Fig 14 : TED assembly
Kobayash
@lambda.phys.tohoku.ac.jp
Updated
2-Sep-2011