Diego González-Díaz (GSI-Darmstadt)

A. Berezutskiy (SPSPU-Saint Petersburg), G. Kornakov (USC-Santiago de Compostela), M. Ciobanu (GSI-Darmstadt), Y. Wang (Tsinghua U.-Beijing), J. Wang (Tsinghua U.-Beijing)

Darmstadt, November 24th, 2009

one year ago

Diego González-Díaz (GSI, TU Darmstadt, Tsinghua University)

Y. Wang (Tsinghua U.-Beijing), J. Wang (Tsinghua U.-Beijing),

C. Huangshan (Tsinghua U.-Beijing), P. Kowina (GSI), P. C. Huangshan (Tsinghua U.-Beijing), P. Kowina (GSI), P.

Moritz(GSI)Moritz(GSI)

and the NeuLand-R3B groupand the NeuLand-R3B groupDarmstadt, February 10th, 2011

now

what has happened since?

X workshop on Resistive Plate Chambers and related detectors Darmstadt, February 9-12, 2010.Sponsored by HIC4FAIR.

1. RPC HADES-TOF wall cosmic ray test performance, A. Blanco.

2. FOPI MMRPC ToF barrel. M. Kis.

3. A multipurpose Trigger Readout board. M. Palka.

4. The Slow Control System of the HADES RPC wall. A. Gil.

5. High Resolution TDC ASIC for CBM-TOF, H. Flemming.

contributions directly connected to GSI

1. Progress of R&D and production of timing RPCs in Tsinghua University, Yi Wang.

2. A prototype of high rate MRPC for CBM-TOF, J. Wang.

3. Ceramics high rate MRPC for CBM-TOF, L. Naumann

4. Towards a high granularity, high counting rate, differential read-out RPC. M. Petris.

5. The CBM Time-of-Flight wall. I. Deppner.

6. Progress in the simulation of Resistive Plate Chambers with multi-strip readout.

D.Gonzalez-Diaz.

7. NeuLand: MRPC-based time-of-flight detector for 1 GeV neutrons. D. Bemmerer.

8. Development of MMRPC prototypes for R3B, FAIR. U. Datta Pramanik.

9. Some results of the R&D of a ToF-wall to identify relativistic ions. E. Casarejos.

10.Design and construction of iToF: a ToF-wall detector to identify relativistic ions in

R3B, FAIR, E. Casarejos.

11.A closed-circuit gas-recirculation system for RPC detectors. D. Rossi.

12.NeuLand MRPC-based detector prototypes tested with fast neutrons. C. Caesar.

13.Testing timing RPCs at ELBE/Dresden using 32MeV single-electron bunches with

picosecond time resolution. D. Stach.

14.NeuLAND MRPC prototypes tested at ELBE/Dresden. D. Yakorev.

contributions directly connected to FAIR

->28% of the workshop contributions were connected to GSI/FAIR.

->70% of the workshop contributions related to time-of-flight

((and)multigap, (and)multistrip) RPCS were connected to GSI/FAIR.

R3B/itof (SIS100)

GSI-FAIR in a nutshell (as of today)

R3B/neuLand (SIS100)

CBM (SIS100/SIS300)

FOPI (SIS18)

FOPI (SIS18/SIS100)

progress on the simulation and understanding of the counters

The simulation scheme in a nutshell

generation + induction

1transmission

2

FEE response

3

multi-strip

4

1. Dedicated measurements of transmission properties and benchmark of the electrostatic solver and modeling:

-Before: APLAC simulations(FDTD).-Now: MAXWELL-2D(FEM) + analytical solutions of lossy

telegrapher's equations.

2. Calculation of the induction profiles:-Before: analytical calculation (approximate).-Now: MAXWELL-2D(FEM). Analytical calculation used only for benchmarking the code.

3. Change of philosophy:-Before: work with induced charges (~slow amplifier).-Now: work with induced currents (broad-band amplifiers).

4. More realistic implementation of the Front End Electronics.

5. New parameters of the gas. MAGBOLTZ cross-sections re-obtained

to be consistent with 2009data for C2H2F4.

6. A simple parameterization of streamer formation introduced, based

on data.

7. Started porting the code MATLAB-based to C++ for usage in

FAIRroot both for R3B and CBM (~50% done).

What is new?

1. Upgrades in signal transmission

transmission

2

mg

mm

CC

C

L

L

0 mg

mm

CC

C

L

L

0mg

mm

CC

C

L

L

0

Experimental verification of electrostatic compensation

2m!

Transmission characteristics in time-domain (I)

mg

mm

CC

C

L

L

0 mg

mm

CC

C

L

L

0 mg

mm

CC

C

L

L

0

Transmission characteristics in time-domain (II)

mg

mm

CC

C

L

L

0 mg

mm

CC

C

L

L

0 mg

mm

CC

C

L

L

0

figures of merit for typical signals

transmission characteristics in frequency-domain

transmission

near-end cross-talk

far-end cross-talk

transmission (single-strip)

possibly the most important figure of merit

the cross-talk to the over-next neighbor is the relevant figure of merit!

The CBM-TOF wall. Design requirements

compensation for N-strips requires of the following conditions:

00 L

L

C

C mm 12 m

m

C

C

Diego Gonzalez-Diaz, Chen Huangshan, Yi Wang, arXiv.1102.1389

generally satisfied generally not satisfied

then all the system velocities become equal! (no modal dispersion)

details and proof in:

induction

1

2. Upgrades on signal induction and charge profiles

'Weighting field' technique for calculating induction profiles

analytic calculation MAXWELL-2D calculation

The analytical calculation usually fails in between strips

induction

1

3. Upgrades on avalanche modeling

this part is still considerably behind the 'state of the art' simulations (the practical importance of a better modelization is not clear)

Determination of C2H2F4 cross-sections from most recent data. MAGBOLTZ accuracy improved down to 1%. (S.

Biagi)

before

now

Avalanche model constrained by world-wide survey

efficiency charge distribution

+ streamer parameterized in a crude way (when avalanche reaches a certain charge it 'explodes' into a streamer)

Diego Gonzalez-Diaz, doi:10.1016/j.nima.2010.09.067

FEE response

3

3. Upgrades on FEE modeling

Upgrades on FEE modeling (based on APLAC)

Modeling this is the weakest part so far. Requires hands-on work. Can not be modeled without detailed measurements. The main parameters of the electronics (threshold, gain) are now fixed to describe data

simplified sketch of the FEE developed by the RICE University (STAR)

how does it look like?

~centerof

strip

~regionbetween

strips

representation•gain=1•Vth equivalentat input

modestly fast~100evts/s

some results

multi-strip prototypes for CBM

two selected chambers

24cm-long, 5x2(0.25gap)

1m-long, 6x2(0.22gap)

charge distributionsTriggered events24cm-long, 5x2(0.25gap)

Triggered eventscharge distributions

1m-long, 6x2(0.22gap)

Triggered eventsand RPC firedcharge distributions

1m-long, 6x2(0.22gap)

efficiency and cross-talk resolution

Global response

efficiency profiles

efficiency profiles (with ideal position information)

multi-strip prototypes for R3B. Transmission.

D. Yakorev et al.submited to NIM A

Global response. Electrons at ELBE (~mips).

Outlook

●A MATLAB toolbox for fast RPC characterization is close to be finished. A fast scheme to simulate these counters has been implemented.

● With a larger scope, a software package is being created and integrated in FAIRroot. Results have not been presented here (see my talks at the last CBM collaboration meeting). The amount of work done, as compared to the MATLAB toolbox is ~50%. Speed is comparable, at present.

●Measurements on transmission and FEE characterization have to be done at least once, anyhow. Simulations are too much detail-sensitive. Simulations of this type will hardly replace measurements.

Appendix

-V

+V 1m

1m

the inocent problem

-V

+V 1m

1m

I) a signal is induced due to the movement of the avalanche charges.The influenced area is very localized.

II) the signal must travel till the end of the structure

III) the signal must be measured at the end of the structure

Cg

CmLo

Lm

RR

?

-V

+V 1m

1m

the signal starts moving

due to the mutual inductance a current of magnetic origin with opposite sign couples to the neighbor strip (Lenz law)

Cg

CmLo

Lm

RR

a signal is electrically coupled through the mutual capacitance, with equal strength for both ends

xLxCxct mmIII ,,,

dt

dV

Z

LCI

c

mmxct

2,

dt

dVC

L

L

C

CI mm

xct 000

,

cmmxct Zdt

dIL

dt

dVCI

1,

2,

1

cmmxct Zdt

dVL

dt

dVCI

dt

dI

vL

L

C

CI mm

xct

1

00,

-V

+V 1m

1m

Cg

CmLo

Lm

RRx

after a series of 'minor' reasonable assumptions... (~usually termed 'low coupling')cIZV

00

1

CLv

0

0

C

LZc

summing up the contributionsof infinite C/L elements along the line

dt

dI

v

x

L

L

C

CI mmct

00

dt

dI

v

x

L

L

C

CI mmct

00

increases with the unbalance between capacitive and inductivecoupling. It can change sign!

increases with the propagation distance

increases with the signal slope/rise-time

can we make this zero?

A rigorous derivation of the expression for Ict starting from the telegrapher's equations provides the same result in the low-coupling limit

problem: inductances are not very intuitive for most of people

dt

dI

v

x

C

C

C

CI mmct

00

0

0

solution: a well known theorem relates the inductance with the capacitance matrixes of the structure in empty space (more intuitive, although not directly measurable)

when is this zero?. When the field lines couple through a single dielectric material.When it is zero we will say that the system is 'electrostatic compensated'.

r

000

0

CC

CC

r

mrm

the basic questions:

is it possible to reasonably compensate an inhomogeneous structure?

2,r

3,r1,r

?4,r

even if we manage, can we compensate if we have more than 2 strips?

2,r

3,r1,r

?4,r

(for most RPCs, yes)

(for some RPCs, yes)

even if we manage, what happens if the system is lossy (R,G) ?

2,r

3,r1,r

?4,r

(quite ok, but be careful)R G

G

?000

0

0

C

C

C

C mm

?000

0

0

C

C

C

C mm

?000

0

0

C

C

C

C mm

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

Avalanche generation. 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

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 adapted to multi-gap the formulas from: problem: under-estimation of Ez

for large inter-strip separations

Cross-talk in a 2-strip RPC modeled as a loss-less transmission-line (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

)(]9ln22)(

[)(2 v

ztI

tv

z

v

v

RZ

RZtI o

rise

o

inc

inmtc

for exponential signals

)(4

)(2,1v

ztItI o

tc

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 dispersion

zo = position along the strip where the signal is induced

see also [12]

the 2 modes are fullydecoupled

Cross-talk in a 2-strip RPC modeled as a loss-less transmission-line (II). Limits.

in

mg

mm

c

m

mgc

mg

mm

mg

RZ

Z

CC

C

L

L

Z

Z

CC

LZ

CC

C

L

L

v

v

CCLv

det

det

0

0

0

1

0

2

2

1

)(

History revisited: 1.6m-long 2-strip RPC (P. Fonte et al., 2002)

width = 5cm

strip separation = 1mm

glass = 3mm

gap = 0.3mm

length= 1.6m

Cross-talk in Fonte multi-strip RPC

Cg=521 pF/m

Cm=88 pF/m

Fct=50% !

BW=1.5 GHzRin=50 Ω

very dispersive!

experimental conditions:Π, E=3.5 GeV, low rates, trigger width = 2 cm

Fct=40%

'fine-tunning'

80%-90% measured cross-talk levels reproduced

Zc~13 Ω

transverse scan

Cross-talk in Fonte multi-strip RPC

HV=5.7 kV

x10

->increase stripseparation

Cg

Cm

Δv/v

trise

Minimizing cross-talk (I)

x6 /2.5

/6

->increase strip/widthseparation->reduce glass thicknessCg

Cm

Δv/v

trise

Minimizing cross-talk (II)

x6 /2.5

/6

BW/10

->increase strip/widthseparation->reduce glass thickness->reduce band-width

Cg

Cm

Δv/v

trise

low couplinglow dispersion

Minimizing cross-talk (III)

guard strip

->put guard strip

Cg

Cm

Δv/v

trise

Minimizing cross-talk (IV)

not mirrored

->use only two electrodes

Cg

Cm

Δv/v

trise

(it flips!)

Minimizing cross-talk (V)

not mirrored

coupling to PCB

->use only two electrodes->couple locally to groundCg

Cm

Δv/v

trise

low couplingNO dispersion

Minimizing cross-talk (VI)

Minimizing cross-talk + detector response (I)

x10

Minimizing cross-talk + detector response (II)

x6 /2.5

/6

Minimizing cross-talk + detector response (III)

x6 /2.5

/6

BW/10

Minimizing cross-talk + detector response (IV)

not mirrored

coupling to PCB

Minimizing cross-talk + detector response (V)

Ideal case: no cross-talk + perfect tracking

'some' of the new CBM prototypes(preliminary short compilation)

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

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

1-m long counter, 6-strip RPC, 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.

No simulations available yet

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

No simulations available yet

1-m long counter, 12-gap, mirrored and shielded

conclusions and outlook

• Multi-strip design of timing RPCs 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%).

• For making a multi-strip fully robust against streamer-crosstalk there is still a long way to go (maybe impossible).

-> Detailed optimization based on physics performance soon to follow. Then we will know if cross-talk is 'high' or not.

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 )(

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

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

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 )(

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

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 (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 (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

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).

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