maxiavalanche ageing tests

1
ALICE Dimuon Trigger meeting Aillon-le-jeune 3-4
November
maxi-avalanche ageing tests Francesca Poggio
2
highly-saturated avalanche operation
2 RD lines to fullfill the different requirement
3
maxi-avalanche beam test
preliminary test with cosmic rays in Clermont
Ferrand g Frédéric Yermia RD on RPC for the
Muon Trigger System for ALICE experiment in view
of p-p data taking IEEE - Nuclear Science
Symposium 2004 - Gaseous Detectors session
detailed results ALICE Dimuon Trigger meeting,
January 2004 - Frédéric Yermia
4
ageing test setup (CERN GIF)

• monitor the efficiency for the detection of
• cosmic ray under ?-induced counting rate

5
RAV1 ageing results

• after 225 Mhit/cm2 (34 mC/cm2)
• dark current 1 mA and dark rate lt1 Hz/cm2
• no efficiency loss without and with g
  irradiation (120 Hz/cm2)
• efficiency stable at 94
• m beam from SPS-X5 the mean efficiency over the
  whole surface
• at HV10900 V (working point) is 95

6
gas mixture modification

• we decrease the SF6 percentage to lower the
  working point
• beam test on 2 small prototypes (50x50 cm2) to
  check the performances with the gas mixtures
• 89.7 C2H2F4, 10 C4H10 0.3 SF6 RH50
• 89.7 C2H2F4, 10 C4H10 0.6 SF6 RH50
• to make a direct comparison with the gas mixture
  with 2 SF6
• performances
• cluster size 1.8 (1 cm strip)
• time resolution 1-2 ns
• efficiency in all position the efficiency
  plateau reaches 95-96
• no significant differences with respect to the
  gas mixture with 2 SF6
• see the document written by Franck Manso
• working HV10000-10100 V (800 V lower)
• streamer contamination lt20

7
RAV3 RAV4 efficiency plateaux
RAV3
RAV4

• in all position the plateau reaches 0.95-0.96 of
  efficiency
• the mean efficiency at HV10100 V (working point)
  is 0.94?0.01

• in all position the plateau reaches 0.95 of
  efficiency
• the mean efficiency at HV10100 V (working point)
  is 0.94?0.01

8
streamer contamination

• of streamer in the 25 tested
• positions at 3 different HVeff
• (10000 V, 10100 V and 10200 V)
• obtained with thresholds
• setting at 80 mV
• the distributions of these values
• are shown in next slide

effect of a low humidification? NOTE recent
measurement shows a factor 2
9
streamer contamination distribution
10
up to now
rate RAV3 g 50-100 Hz/cm2 RAV4 g 50-100 Hz/cm2
december
11
analysis

• specific analysis for each kind of trigger
• trigger CR (cosmic ray)
• efficiency
• cluster size, number of cluster e multiplicity
• single counts
• HV and current
• autotrigger
• 3D plot g irradiation uniformity, noise
  distribution
• precise estimation of the rate of each cell
• trigger PG (Pulse Generator)
• single counts check

12
trigger CR (cosmic rays), RAV3
histograms of major importance
13
trigger CR (cosmic rays), RAV3
14
trigger CR (cosmic rays), RAV3
15
trigger CR (cosmic rays), RAV3
16
trigger CR (cosmic rays), RAV3
17
trigger CR (cosmic rays), RAV4
histograms of major importance
18
trigger CR (cosmic rays), RAV4
19
trigger CR (cosmic rays), RAV4
20
trigger CR (cosmic rays), RAV4
21
trigger CR (cosmic rays), RAV4
22
autotrigger RAV3
23
autotrigger RAV4
24
trigger PG, single counts (Hz/cm2)
25
RAV3 results
26
RAV4 results
27
efficiency plateaux
after 310 Mhits/cm2 (47 mC/cm2)
after 255 Mhits/cm2 (34 mC/cm2)
RAV3 rate 60 Hz/cm2
RAV4 rate 50 Hz/cm2

• no plateau displacement without and with g
  irradiation (50-60 Hz/cm2)
• the efficiency over the whole surface of both
  RPCs has been recently measured g 93-95, 80-90
  in the corners (geometric problems)

28
conclusions

• the 2 tested prototypes work satisfactorily up
  to about
• 460-500 Mhit/cm2 fulfilling the requirement
• for 4.5-5 years of the p-p program for the most
  irradiated RPC
• for gt20 years of the p-p program for other RPCs
• the test is going on
• next
• alternation streamer/maxi-avalanche
• gas flow reduction (at the present moment 6
  vol/hour)
• efficiency radiography in the bench test for
  final RPC
• (Turin, 7 comuni) g efficiency on 2x2 cm2 cells

29
backup slides
30
p-p data taking
see Yermia PhD Thesis, ALICE-INT-2003-041
31
heavy-ion collisions
streamer gas mixture 50.5 Ar, 41.3 C4H10, 7.2
C2H2F4, 1 SF6 - RH50
32
preliminary studies with cosmic rays

• test on 50x50 cm2 RPC
• (Clermont-Ferrand laboratory)
• FEE thresholds set at 10 mV
• efficiency
• the shape of each signal is sampled each ns to
  study amplitude, timing and released charge
• streamer comtamination

33
beam test, setup - FEE
34
beam test results (I)

• the detector showed a stable behaviour with
• dark current (source off) ? 1 mA
• dark single rate (source off) ? 0.1 Hz/cm2
• current drawn with source-on ? 1/3 of the
  current drawn in streamer for the same
  irradiation conditions
• time resolution ? 1-2 ns
• efficiency close to 100, no plateau
  displacement due to the irradiation rate

• 4 efficiency calculation methods
• Coincidence Register
• tracking with DWC
• total
• core (higher beam irradiation rate)
• outer circle (lower beam irradiation rate)
• T/p correction
• HVeffHV0(T/T0)(p0/p)
• with T0293.15 K, p0970 mbar

35
beam test results (II)
36
beam test gas analysis

• during the test g analysis of the exhaust gas
  were performed both for streamer and
  maxi-avalanche operation of the RPC

positive message in view of ageing w.r.t.
streamer, maxi-avalanche operation gives a
smaller content of impurities and a spectacular
decrease of HF content
37
RAV1 efficiency map

• in all position the plateau reaches 0.95-0.97 of
  efficiency
• the mean efficiency at HV10900 V (working point)
  is 0.95?0.001

low efficiency due to geometrical problems
38
instability problem (I)

• hp local discharge
• g the temperature in correspondence of the
  discharge point should increase appreciably

RPC without external mechanics, with the ground
side fully covered by thermosensitive
adhesives
39
instability problem (II)
mean T ?25 C over the whole surface (measured
with an IR thermometer)
RPC
40
RAV3 efficiency map