1. Aging, High Rate and Shielding L. Lopes Lip-Coimbra

2. 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.

3. Aging (2002-2003) humid, cold After accumulating 800mC/cm 2 (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%C 2 H 2 F 4 +10%SF 6 +5% iso-C 4 H 10, with 10% relative humidity Primary charges were created by an UV lamp

4. 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

5. 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.

6. 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 60 Co 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 cm 2. 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. 60 Co Aluminium cathode Glass cathode

7. 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

8. High Rate

9. Resistive material  Controlled resistivity alumina, Al940CD, from Wesgo ® Ceramics.  Supplier volume resistivity, 1  10 9  cm at room temperature.  Good surface finish.  Easily produced in large amounts (fully commercial) Resistive material, our measurements  Volume resistivity, between 1  10 9 and 2  10 9  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.

10. 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.

11. High Rate Benchtop test setup   22 Na Reference Chamber (identical) Test Chamber 10 cm 2 (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.

12. High Rate 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 mV Counting 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.

13. High Rate …as a result of the Ohmic drop in the electrode. So depending on the counting rate we should correct the applied voltage.

14. High Rate Random Coincid. Signal But background of random coincidences  fit with gaussian + symmetric exponential How does it affect the measurement of the real sigma?  visit Rosendorf… CBM goal well in reach

15. Shielded RPCs

16. Shielded timing RPCs Actual parts, industrially produced. Uniformity tests with 22 Na (positron  ) source Crosstalk for avalanches is below the noise level Beam test in November Final prototype of the HADES RPC-TOF wall Designed to run warm (up to 60ºC)

17. 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

18. 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 60 Co, 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.