requirements and layout of the CBM ToF wall
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Transcript of requirements and layout of the CBM ToF wall
Diego González-Díaz (GSI-Darmstadt)
A. Berezutskiy (SPSPU-Saint Petersburg), G. Kornakov (USC-Santiago de Compostela), M. Ciobanu (GSI-Darmstadt), J. Wang (Tsinghua U.-Beijing)
Some references used in this talk
[1a] H. Alvarez Pol et al., 'A large area timing RPC prototype for ion collisions in the HADES spectrometer', NIM A, 535(2004)277.[2a] A. Akindinov et al., 'RPC with low-resistive phosphate glass electrodes as a candidate for CBM TOF', NIM A, 572(2007)676.[3a] J. Wang et al., paper in preparation.[4a] L. Lopes et al., 'Ceramic high-rate RPCs', Nuclear Physics B (Proc. Suppl.), 158(2006)66.[5a] D. Gonzalez-Diaz et al., 'The effect of temperature on the rate capability of glass timing RPCs', NIM A, 555(2005)72.[6a] A. Ammosov et al., talk at XIII CBM collaboration meeting, Darmstadt, Germany.[7a] L. Nauman et al., talk at XIV CBM collaboration meeting, Split, Croatia.[1] A. Mangiarotti et al., 'On the deterministic and stochastic solution of Space-Charge models and their impact in high resolution timing' talk at RPC Workshop Seoul, 2005.[2] G. Chiodini et al., 'Characterization with a Nitrogen laser of a small size RPC', NIM A 572(2007)173.
[3] A. Colucci et al., 'Measurement of drift velocity and amplification coefficient in C2H2F4-isobutane mixtures for avalanche-operated
resistive-plate counters', NIM A, 425(1999)84. [4] W. Riegler et al., 'Detector physics and simulations of resistive plate chambers', 500(2003)144 .[5] E. Basurto et al., 'Time-resolved measurement of electron swarm coefficients in tetrafluoretane (R134a)', Proc. to 28th ICPIG, Prague, 2007.[6] P. Fonte, V. Peskov, 'High resolution TOF with RPCs', NIM A, 477(2002)17.[7] P. Fonte et al., 'High-resolution RPCs for large TOF systems', NIM A, 449(2000)295.[8] A. Akindinov et al. 'Latest results on the performance of the multigap resistive plate chamber used for the ALICE TOF', NIM A 533(2004)74.[9] G. Aielli et al., 'Performance of a large-size RPC equipped with the final front-end electronics at X5-GIF irradiation facility', NIM A
456(2000)77. [10] S. An et al., 'A 20 ps timing device—A Multigap Resistive Plate Chamber with 24 gas gaps', NIM A 594(2008)39. [11] A. Blanco et al., 'In-beam measurements of the HADES-TOF RPC wall', NIM A 602(2009)691.[12] W. Riegler, D. Burgarth, 'Signal propagation, termination, crosstalk and losses in resistive plate chambers', NIM A 481(2002)130.[13] T. Heubrandtner et al., NIM A 489(2002)439.
Talk layout
• CBM at FAIR-Darmstadt.• RPC working principle.• Rate capability of various prototypes.• Avalanche simulation.• Induction simulation.• Cross-talk and FEE simulation.• Comparison with data.
FAIR (Facility for Antiproton and Ion Research)
L.V. Bravina et al., Phys. Rev. C60 (1999) 044905
Au+Au collisions up to 11 AGeV: exploring properties of dense hadronic (resonance) matter in the vicinity of the phase transition
E. Bratkovskaya, W. Cassing
The CBM physics goal at SIS-100
This T-μB phase-space region has been measured before (AGS, SPS). Idea: take advantage of the new technologies and focus on rare observables (open charm, di-leptons, hyper-nuclei, multi-strange hyperons, J/Ψ, Ψ')
Dipolemagnet
The Compressed Baryonic Matter Experiment
Ring ImagingCherenkovDetector
Transition Radiation Detectors
ResistivePlate Chambers(TOF)
Electro-magneticCalorimeter
SiliconTrackingStations
Tracking Detector
Muondetection System
Projectile SpectatorDetector(Calorimeter)
VertexDetector
The CBM-TOF wall. Design requirements
● Overall time resolution (including start time) σT = 80 ps.
● Occupancy < 5 % for Au-Au central collisions at E=25 GeV/A.
● Space resolution ≤ 5 mm x 5 mm.
● Efficiency > 95 %.
● Pile-up < 5%.
● Rate capability = 20 kHz/cm2.
● Multi-hit capability (low cross-talk).
● Compact and low consuming electronics (~65.000 electronic
channels).
● Multi-strip design in the outer region, due to the very
low occupancies. Why? -> Why not?. If electrically
possible it is mechanically much more easy.
In order to accommodate the different granularities as a function of the polar angle, five different regions were defined:
➔Pad region (1): 2.0 x 2.0 cm2 ( 27072 channels,
~10 m2) ➔Strip region (2): 2.0 x 12.5 cm2 ( 3840 x 2 channels, ~10
m2)➔Strip region (3): 2.0 x 25.0 cm2 ( 5568 x 2 channels, ~30
m2)➔Strip region (4): 2.0 x 50.0 cm2 ( 6150 x 2 channels, ~60
m2 )➔Strip region (5): 2.0 x 100.0 cm2 ( 2900 x 2 channels, ~60
m2 )
TOTAL ( ~65000 channels, ~170 m2)
RPC geometry in simulation (I)
A multi-gap RPC in general. Here a differential RPC ('a la' STAR), just for the sake of 'electrical elegance'
Rin
standard PCBwith read-outstrips on oneside
HV insulatorwith Vbreak>10-15 kV
HV coating withR~100 MΩ/□
+V
-V
differential pre-amplifier
at least 4 gas gaps (~0.3 mm thick)
float glass
particle
*parameters not from STAR
More electrical schemes are (un)fortunately possible
ALICE-LHC
V
-V
-V
STAR-RHIC
V
-V
V
HADES-SIS
-V
-V
FOPI-SIS
-V
V
all these schemes are equivalent regarding the underlying avalanche dynamics... but the RPC is also a strip-line, and this is manifested after the avalanche current has been induced. And all these strip-lines have a completely different electrical behavior.
-V
V
V
-V
V
S. An et al., NIM A 594(2008)39 [10]
!
HV filtering scheme is omitted
prompt (e-) component
Slow (ion) component
g/ve ~ 1 ns g/vi ~1 μs
E=ΔV/g
ev
D
/1
p
particle
e--I+
How (we believe) is the avalanche produced?
vtwo eEqti )(
ith
space-chargelimitation
Eav~E
avalanche growth
decreases!
τg ~ 1 s (glass relaxation time)
see [4],for instance
A parentheses: rate capability of various CBM prototypes
for small fluxes and in a simple DC-model
gappergapper dqg
EE1
)(
see for instance: D. Gonzalez-Diaz et al. Nucl. Phys. B (Proc. Suppl.) 158(2006)111
dqAoTT ,)(
dqBo )(
A parentheses: rate capability and DC-model systematics
In first order, it fits! dqAoTT ,)(
dqBo )(
Back to the avalanche. How to create a simple avalanche model
• The stochastic solution of the avalanche equation is given by a simple Furry law (non-equilibrium effects are not included).
• Avalanche evolution under strong space-charge regime is characterized by no effective multiplication. The growth stops when the avalanche reaches a certain
number of carriers called here ne,sat.
• The amplifier is assumed to be slow enough to be sensitive to the signal charge and not to its amplitude. We work, for convenience, with a threshold in charge
units Qth.
log 1
0 n e
lect
rons
~7
to t
space-charge regime
exponential-growthregime
~7.5
tmeas
avalanche Furry-typefluctuations
~2
Raether limit 8.7
exponential-fluctuationregime
threshold
0
simplifying assumptions
continuous line: data from Basurto et al.
in pure Freon [5]
α extrapolated to mixture by using Freon's partial pressure:
αmixture = αFreon(E/fFreon) fFreon
vd directly taken from Freon (inspired on microscopic codes)
vd,mixture = vd,Freon
Parameters of the gas used for input: α* (effective Townsend coefficient), vd (drift velocity), no (ionization
density)
HEED(from Lippmann[4])
n o [m
m-1]
little dependencewith mixture!
*purely phenomenological!
Induction and weighting field Ez
(t)nedzvEti )( t=2.5 mm
w=22 mm HV
read-out
wide-pad limit t << w
gap
totz C
C
gE
1
additionally when g<<t (typicalsituation) Ez does not depend on the position –z- along the gap
g=0.3 mm
ws-s ~0 mm
T. Heubrandtner et al. NIM A 489(2002)439
We use formulas from: problem: under-estimation of Ez
for large inter-strip separations
MC results. Efficiency and resolution for 'wide-pad' type detectors
qinduced, prompt [pC]
qinduced, total [pC]
1-gap 0.3 mm RPC standard mixture
simulated
measured
Eff = 74%
Eff = 60%
Eff = 38%
measured
simulated
ne,sat= 4.0 107 (for E=100 kV/cm)
qinduced, prompt [pC]
assuming space-charge saturation at
4-gap 0.3 mm RPC standard mixture
data from Fonte, [6,7]
MC results. Prompt charge distributions for 'wide-pad' type
detectors
multi-strip detectors
First of all... what is a strip?
In this talk:
A strip is a read-out structure that must be described (due to the phenomena under study) like a transmission-line. In the simplest single-strip description, it is something characterized by 2 magnitudes: a transmission coefficient and a propagation velocity.
This is a definition based on the electrical properties of the structure.
In standard language:
- strip: something read-out in two ends/something 'quite rectangular'- pad: something read-out in one end/something 'quite squared'
Induction + transmission + FEE. Sketch (I)
induction
1transmission
2
FEE response
3
multi-strip
4
Induction + transmission + FEE. Sketch (II)
Five stages in order to get a predictive result
• Avalanche generation with the previous code.
[->Comparison with eff vs V and fine-tune, if needed, of threshold value. This approach seems to be flexible enough.]
• Induction, based on analytical formulas from [13], extrapolated to multiple-gaps by using the effective series permittivity of the corresponding group of layers.
• Propagation based on HF simulator APLAC (http://web.awrcorp.com/Usa/Products/APLAC/).
[-> Validation of APLAC for the structure of interest with a pulse generator (nowadays we do not need this step anymore)]
• Termination and other circuit elements are included, together with FEE, simulated also with APLAC.
A 2-strip RPC as a loss-less transmission-line. Example (I)
om
mo
CC
CCC
om
mo
LL
LLL
om
moc ZZ
ZZZ
1ˆ TvTLZc
112 ˆ)ˆ(ˆ TLCTv
momo LLCC
20
02
vv
vv
v
cc
o
m
co
mc
c
ZZC
C
ZC
CZ
Z
roo
cCLv
1
)(3moom LCLCvv
cCC
LZ r
oo
oc
1
two different modes in the transmission line!. This causes 'modal dispersion' unless:
o
o
m
m
L
C
L
C true for
homogeneous transmission lines!
a 4-gap RPC seen as a transmission-line
om
mo
RR
RRR
dominated by skin-effect:small for typical dimensionsand rise-times
om
mo
GG
GGG
very small, due to the presence of gas and glass
)(ˆ CC
for typical materials (glass)
loss-less line!
W. Riegler, D. Burgarth, NIMA 481(2002)130 [12]see
if
1)
2) 0, mm LC
)(]9ln4[)(
)(v
ztI
tv
z
v
v
R
RZ
C
C
RZ
RZtI o
rise
o
in
inc
ground
m
inc
inctc
for exponential signals
)(][)(
)(2v
ztI
R
RZ
C
C
RZ
RZtI o
in
inc
ground
m
inc
inctc
mo
mo
LL
CC
low-frequency /small distance/ non-dispersivelimit
high-frequency /large distance/ dispersivelimit
1
rise
o
tv
z
v
v
1
rise
o
tv
z
v
v
small dispersion
very large dispersionin general
A 2-strip RPC as a loss-less transmission-line. Example (II)
zo = position along the strip where the signal is induced
see also [12]
the 2 modes are fullydecoupled
A 2-strip RPC as a loss-less transmission-line. Example (III)
2-strip geometry and signal taken from [12]
injected signal cross-talk signal
non-dispersive limit(zo=0)
dispersive limit (zo->∞)
->Continuous line is the exact analytical solution from [12].->Dashed and dotted lines are the numerical solution from APLAC used later in this work.
Measurements of cross-talk with RPC mockup
cathode 150 anode 1
50
50
50
cathode 250 anode 2
50
50
50
cathode 350 anode 3
50
50
50
cathode 4anode 4 50
50
cathode 550 anode 5
50
50
50
Cross-talk in an un-terminated line
signal from BC420scintillator (used as current generator)
cathode 150 anode 1
50
50
50
cathode 250 anode 2
50
50
50
cathode 350 anode 3
50
50
50
cathode 450 anode 4
50
50
50
cathode 550 anode 5
50
50
50
Cross-talk in a terminated line
Cross-talk and signal shape
cross-talkconstant, very independent from the signal shape
low dispersion counter, typical working conditions, BW=260 MHz
Take as a typical shape the one of an avalanche produced at the cathode
Even for dispersive counters it is reasonable since most of the charge is coming from that region
Typical plots where to look at
• Transverse profile of the efficiency, with and w/o valid charge.
• Cross-talk probability. Integral and as a function of the charge in the main strip.
• Resolution when a second hit is present in the module.
• Cluster sizes (not shown here).
• Dependence with HV of the above observables (not shown here).
data
old 'reference' data
1.6 m long wide-strip (P. Fonte et al., 2002)
Cg=514 pF/m
Cm=88 pF/m
Cm/Cg =17%
Fct=50% !
BW=1.5 GHzRin=50 Ω
very dispersive!
experimental conditions:Π, E=3.5 GeV, low rates, trigger width = 2 cm
good agreement with MC avalanche
Fct=40%
'fine-tunning'
80%-90% measured cross-talk levels reproduced
Zc~13 Ω
transverse scan
new data
35-cm long wide-strip, mirrored and shielded
... ...
Zc~18 Ω
BW=260 MHzRin=100 Ω
Fct=11%little dispersive
experimental conditions:~mips from p-Pb reactions at 3.1 GeV, low rates, trigger width = 2 cm (< strip width)
Fct=19%
'fine-tunning'inter-strip regiondominated by trigger width
probability of pure cross-talk:1-3%
Analysis with high resolution tracking on-going.
transverse scan
Cg
Cm
50-cm long wide-strip, mirrored and not shielded
... ...
probability of pure cross-talk: 1-3%
similar cross-talk levels than in previous case
experimental conditions:~mips from p-Pb reactions at 3.1 GeV, low rates,
trigger width = 2 cm (< strip width)
BW=260 MHzRin=100 Ω
Zdet~20 Ω
Cm=18 pF/m
Cg=276 pF/m
dispersiveCm/Cg =6.5%
Fct=11.5%
30-cm long narrow strip, differential
... ...
Cm=20 pF/m
Cdiff=23 pF/m
Fct=9%
experimental conditions:~mips from p-Pb reactions at 3.1 GeV, low rates, high resolution (~0.1 mm) tracking
probability of pure cross-talk:1-3%
intrinsic strip profile is accessible!
Zdiff=80 Ω
dispersive
transverse scan
1-m long counter, 12-gap, mirrored and shielded
... ...
experimental conditions:~mips from p-Pb reactions at 3.1 GeV, low rates, trigger width = 2 cm (< strip width)long run. Very high statistics.
The last point: cross-talk influence in the timing of a coincident (double) hit. A simple derivation.
log[q(t)]
t
qth
variations in base-line due to cross-talk
variations in time at threshold due to cross-talk 2talkcrossrms
space-charge
exponential regime
Cross-talk influence in timing (simple derivation)
Assumptions: Within the same primary collision cross-talk extends up-to infinite time. It does not depend on position. Fluctuations in time of cross-talk signal are smaller than fluctuations coming from the avalanche charge distribution. Pick-up strips are separated by a typical distance bigger than the area of influence of the avalanche. Charge sharing during induction can be neglected!. Cross-talk is small, given by Fct.
Tctth
ctriseq
th
Fq
qF
t
q
rms
q
qrms
~
9lntalkcross
q
qF thct
cross-talk is expected to affect timing when
no double hitdouble-hit in any of 1st neighborsdouble-hit in any of 2nd neighborsdouble-hit in any of 3rd neighbors
1-m long counter, 12-gap, mirrored and shielded
1-m long counter, 12-gap, mirrored and shielded
conclusions and outlook
• Multi-strip design at 1-m scale with acceptable cross-talk, small cluster size and small deterioration of time resolution seems doable.
• Further optimized structures based on simulations are on the way (Fct~1%).
• Rate capability seems to be achievable. Stability tests already started.
-> Detailed optimization based on physics performance soon to follow. Then we will know if cross-talk is 'high' or not.
-> Comparisons between simulations and data will continue
Appendix
Multi-strip-MRPC (MMRPC)
1.1 mm
Glass: ε=7.5, strip width = 1.64 mm, strip gap = 0.9 mm, strip length = 900 mm
1.1 mm
0.5 mm
0.22 mm
copper (20 μm)
8 gaps
The FOPI counter
Induction. Example FOPI case.
n(t)dwvEtI )(
The FOPI counter (11th strip)
50 anode 0 50
50 anode 1 50
50 .......... 50
anode 11 50
50 anode 12 50
50
cathode
50 anode 13 50
50 anode 14 50
50 50anode 15
The FOPI counter (9th strip)
50 anode 0 50
50 anode 1 50
50 .......... 50
anode 9 50
50 anode 10 50
50
cathode
50 anode 11 50
50 anode 12 50
50 .......... 50
50-cm long, mirrored and not shielded
... ...
~1-m long, non-mirrored and shielded
... ...
several electrons (I)
•An ionizing particle at fixed energy creates an average number of ionizations no randomly distributed along the gap, with each cluster having a (1/ne in cluster)2 probability to produce more than 1 electron. This is very easy to generate. Then each cluster can be made to fluctuate according to Furry law.
HEEDcalculation