Development of high-rate timing RPCs

L. Lopes1,2, R. Ferreira Marques1,2, P. Fonte1,3,

A. Pereira1, V. Peskov4, A. Policarpo1,2

1 - Laboratório de Instrumentação e Física Experimental de Partículas (LIP), Portugal.

2 - Departamento de Física, Universidade de Coimbra,Portugal.

3 - Instituto Superior de Engenharia de Coimbra, Portugal.

4 - Royal Institute of Technology, Stockholm, Sweden.

P.Fonte CBM collaboration meeting GSI 13.4.04 2

Rate capability – Standard RPCs

0

500

1000

1500

2000

2500

3000

3500

1.0E+09 1.0E+10 1.0E+11 1.0E+12 1.0E+13

Resistivity ( cm)

Max

Co

un

tin

g R

ate

(Hz/

cm2)

LHCbCERN+BolognaWarsawCERN+RioATLASCMS-forwardCMS-barrelALICE-TOFBeijingALICE-muon

"Multigap"RPC

Streamer mode

uniformand

continuous illumination Timing RPCs

P.Fonte CBM collaboration meeting GSI 13.4.04 3

Rate capability – Special RPCs

PPAC

microRPC

Si plate =104 cm-HV

0.1-0.5 mm Drift gap

Amplification gap

Resistive anode on a metal base= 107 cm

Wire meshes (50 m wires at 0.5 mm pitch)

15 mm

3.5 mm

Protected PPAC

microRPC

1.0E+04

1.0E+05

1.0E+06

1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06

Counting rate (Hz/mm2)

Eff

ectiv

e ga

in

N0 = 200 e-

=

Metallic (PPC) limit

Ava

lanc

he C

harg

e (e

lect

rons

) 1.0E+08

1.0E+06

1.0E+07What about timing

RPC?Gain is huge (G0~1012)

Must be tested.

[Fon

te e

t al.,

199

9]

[Car

lson

et a

l, N

SS

2001

]

P.Fonte CBM collaboration meeting GSI 13.4.04 4

Construction technique

No spacers

Resistive electrode

ENSITAL® SD (polimer)

~ 4109 cm

Good surface finish

Commercial material

Gas system

Gas filters used to prevent discharges due to gas impurities

Gas Mixture:

TFE (R-134a) / SF6 = 90% / 10%

Assembled under clean conditions

P.Fonte CBM collaboration meeting GSI 13.4.04 5

Test Setup

P.Fonte CBM collaboration meeting GSI 13.4.04 6

Event Generation

Compton scattering

Very low background counting rate during all the measurements. Less than 2 Hz/cm2 below the streamer threshold.

511 keV photons from the annihilation of positrons

662 keV

P.Fonte CBM collaboration meeting GSI 13.4.04 7

Acquisition System

P.Fonte CBM collaboration meeting GSI 13.4.04 8

Results - Current & Counting Rate

Tired chamber

Current saturation due to electrode resistivity around 2.8 kV

Linear due to space charge effect

(kH

z/cm

2 )

Counting plateau

P.Fonte CBM collaboration meeting GSI 13.4.04 10

Time Resolution

i0

beam ~ 50 ps

Wider initial current distribution

Kt

photons ~ 90 ps

Compton electrons

P.Fonte CBM collaboration meeting GSI 13.4.04 11

Results - Time Resolution 1

The time resolution remains essentially unchanged from

2 kHz/cm2 to 25 kHz/cm2 at a level around 90 ps .

Typical time spectrum

P.Fonte CBM collaboration meeting GSI 13.4.04 12

Results - Time Resolution 2

For a given

counting rate,

an increase of

the applied

voltage doesn't

considerably

improve the

time resolution

Counting Plateau

P.Fonte CBM collaboration meeting GSI 13.4.04 13

Problems – Chamber CurrentIf 0.95Ii at 1.55 mfrom source

If 0.90Ii at 0.85 mfrom source

Time elapsedbetween Ii

and If, 8 min on average

The counting rate presents a similar behaviour

P.Fonte CBM collaboration meeting GSI 13.4.04 14

Problems - Electrode resistivity

After 5 min

with V= 0 V

i+5= 1.15 i

on average.

After 20 min

with V= 0 V

i+20= 1.30 i

External Measurement

Short term behaviour

P.Fonte CBM collaboration meeting GSI 13.4.04 15

Problems - Electrode resistivityExternal Measurement

0 V 600 V100 V

i=185 nAi=122 nA

Full recoveryalso possible

Average value during beam test

2x1010

P.Fonte CBM collaboration meeting GSI 13.4.04 17

Results - Current & Counting Rate

(kH

z/cm

2 )

60Co (3000 Ci)

Initially, when the electrode presents its lower volume resistivity, it is possible to reach much higher currents and counting rates.

P.Fonte CBM collaboration meeting GSI 13.4.04 18

Conclusions

• Time resolution of 90 ps was demonstrated at 25 kHz/cm2.

• Commercial plastic material, ionic conductor must find

something else. Very active field within the ATOF/I3HP

project...

• Up to 50 kHz/cm2 with the lowest resistivity value (but no time

information).

• Strict clean conditions must be observed. Considerably more

difficult technology than low rate RPC.