Aging, High Rate

and Shielding

L. Lopes

Lip-Coimbra

Outline

Aging of Glass Timing RPCs

Results and latest updates

Development of high rate Timing RPCs

Resistive material, electric properties

Detector assembling

Experimental results

Shielded RPCs

Current status of the HADES final prototype.

Aging (2002-2003) humid, cold

After accumulating 800mC/cm2 (equiv. 8.5 years of normal operation) we don't observe any systematic long-term increase of dark current with time.

made some changes on the experimental setup.

• Room temperature

• “Standard” timing

RPCs gas

85%C2H2F4+10%SF6

+5% iso-C4H10, with

10% relative humidity

• Primary charges

were created by an

UV lamp

Aging (2004) dry, warm

T= const = 30 ºC

T= const = 55 ºC

Water-free gas mixture

•After 60 days

we begin to

observe a

systematic

increase of

dark current

with time.

• It was not

observed any

ionization

current

increase.

Why ?...Accumulated 100 mC cm-2

Aging (2004)

1 Anode Glass

2 Cathode Aluminium

1 Cathode Glass

2 Anode Aluminium

1

2

1

2

•Face to face marks in

one chamber electrodes.

•The effect seems more

severe in the cathodes.

•In glass cathode the

surface is mechanical

damaged.

Aging (New Setup) • So, we return to the initial gas mixture with 10% relative humidity.

• Change the irradiation source. Substituted the UV lamp by a 60Co source.

• Keep working at 55 ºC, to reach a resistivity decrease of one order of magnitude.

•Six single gap chambers, with

an effective area of 9 cm2.

•Three with glass cathode

and the others with aluminium

cathode.

•3 kV applied to all chambers

•Average operating current of

30 nA cm-2 in all chambers.

60Co

Aluminium cathode

Glass cathode

Aging (2005) humid, warm

• After more than 80 days we don’t observe any increase of the dark current.

• Which seems to stabilize.

• In chambers that operate at more than 2 kHz cm-2.

• Accumulated 200 mC cm-2

High Rate

High Rate

Resistive material Controlled resistivity alumina, Al940CD, from Wesgo® Ceramics.

Supplier volume resistivity, 1109 cm at room temperature.

Good surface finish.

Easily produced in large amounts (fully commercial)

Resistive material, our measurements Volume resistivity, between 1109 and 2109 cm at room

temperature, in very good agreement with the supplier.

Good surface finish.

Electronic-like conductor. We don’t observe any increase of the

resistivity with time, when we applied an external electric field.

- HV10 M

1 nF

1 nF

1 M

10 M

Gas filters

Metallic cathode

Alumina anode

Shielding box

300 m gap

High Rate

The detector Assembling under clean conditions.

Both electrodes require good surface finish.

Spacerless construction.

High Rate

Benchtop test setup

22Na

Reference Chamber(identical)

Test Chamber10 cm2

(CBM granularity)

X-ray Generator

Photon conversion on RPC yields an exponential pulse-charge distribution Less favourable than the reasonable peak found in a charged beam.

High Rate

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35

X-Ray Anode Current (mA)

Co

un

tin

g r

ate

(kH

z cm

-2)

2500 2600 2700 Linear (2700)

Counting rate

The counting rate was tested using a X-Ray generator, emitting 20 keV photons.

We can see that the chamber doesn’t lose efficiency at least until 100 kHz cm -2.

Threshold = 10 mVCounting rate vs.

“incident rate”. For

applied voltages

lower than 2.7 kV, at

high counting rates

the chamber lose

some efficiency

since we have a

gain reduction.

High Rate

0

50

100

150

200

250

300

2000 2200 2400 2600 2800 3000

Applied Voltage (V)

Cu

rren

t (n

A c

m-2

)

22Na X-Ray 5 mA

X-Ray 10 mA X-Ray 15 mA

X-Ray 20 mA X-Ray 24 mA

0

50

100

150

200

250

300

0 5 10 15 20 25 30 35X-Ray Anode Current (mA)

Cu

rre

nt

(nA

cm

-2)

2500 2600 2700

0

20

40

60

80

100

120

2000 2200 2400 2600 2800 3000Applied Voltage (V)

Co

un

tin

g r

ate

(kH

z cm

-2)

22Na X-Ray 5 mA

X-Ray 10 mA X-Ray 15 mA

X-Ray 20 mA X-Ray 24 mA

…as a result of the Ohmic drop in the

electrode. So depending on the

counting rate we should correct the

applied voltage.

High Rate

0

50

100

150

200

250

0 10 20 30 40 50 60

Counting rate (kHz/cm2)

Tim

ing

res

olu

tio

n (

ps)

Sigma from fitFWHM/2.362700-2900 V2500-2600 V

RandomCoincid.

Signal

But background of random coincidences fit with gaussian + symmetric exponentialHow does it affect the measurement of the real sigma? visit Rosendorf…

CBM goalwell in reach

Shielded RPCs

50

70

90

110

130

150

170

-600 -400 -200 0 200 400 600

Position (ps)

Tim

e r

es

olu

tio

n (

ps

)

Uncorrected Charge-corrected

Shielded timing RPCs

Actual parts, industrially produced.

Uniformity tests with 22Na (positron) source

Crosstalk for avalanches is below the noise level

49500

49550

49600

49650

49700

49750

49800

-600 -400 -200 0 200 400 600

Position (ps)

Me

an

Tim

e (

ps

)

Beam test in November

Final prototype of the HADES RPC-TOF wall

Designed to run warm (up to 60ºC)

Distributed temperature control system in development

Test bench with 25 elements

20 W heater

Hardware temperature limiter

1-WIRE® interface + power

Thermometer

Heating and sensing element

~1ºC accuracy

Conclusions Aging

No aging was observed operating at humid, cold conditions, during a time equivalent to 8 years at

normal conditions.

We observe severe aging in dry, warm conditions.

At the moment we are testing the effect in humid, warm conditions. No problem so far.

Water might be a useful gas mixture compound.

High rate We keep efficiency up more than 100 kHz cm-2.

50 kHz cm-2 with ~100 ps time resolution, possibly limited by statistical effects.

With a commercial material.

To be tested with 60Co, and then in beam at Rosendorf.

Shielded RPCs Final HADES prototype being now assembled for the November beam test.

Industrial production of the mechanical parts.

First tests satisfactory.

Design to run warm.