1. Setup optimization toward accurate ageing studies of gas filled detectors
Alhussain Abuhozaa,b, S. Biswasb, U. Frankenfeldb, J. Hehnerb, C. J. Schmidtb, H.R. Schmidtc
aKing Abdulaziz City for Science and Technology(KACST), Riyadh, Saudi Arabia
bGSI Helmholtzzentrum fur Schwerionenforschung GmbH, Darmstadt, Germany
cUniversity of Tubingen, Germany
The degradation of the performance or "ageing" of gas detectors under irradiation has been observed since the start of their use in particle physics experiments. High luminosity experiments like the Compressed Baryonic Matter (CBM) at FAIR, Germany will employ several types of gaseous detectors, since long term (~10 years) stable operation at high rates is essential. In general, the observed damage depends on the amount of radiation seen by the detector. In addition many other factors like construction materials, gas composition, gas quality, gas flow rate, particle rate, and particle type play an extremely important role
Motivations
The expected accumulated charge
~ 7.5 C/cm2 after 10 year operation.
~ 0.4 C/cm after 10 year operation.
The desired high accuracy coming from:
The necessity of performing the ageing test in the laboratory in comparable conditions with those in the real experiment.
The short period of the test comparing with the actual lifetime of the detector in the experiment.
Several improvements of the setup have been implemented to obtain the mandatory precision:
1- Modification in detector design
Two additional outer windows have been added to act as gas tightening windows whilst the two inner foils function as more stable cathodes.
2- Temperature dependence of Gas Flow Rate
The effect of temperature variations on the behavior of the MFCs has been investigated.
3- Premixed gas bottle
The stability of the normalized gain has been improved to a value better than 0.6% peak-to-peak variation.
Toward accurate ageing studies
Stability developments
0.2%
Outer windows
Inner windows
Gain Variation ~ 8% peak-to-peak
Without outer windows
Gain Variation ~ 1%
peak-to-peak
With outer windows
Ageing test of the influence of clean fiberglass - Vetronit G11 produced by VonRoll Holding Ltd.- has been performed. Other ageing test has been of contaminated G11 with sawing liquid –Micro 3000 produced by Microjet GmbH- which consists of alcohol and synthetic aster.
Ageing test of Vetronit G11
16nA/cm
11 nA/cm
Current density no
Ageing
140 hours
262 hours
Time
8 mC/cm
10.2 mC/cm
Accumulated charge
Vetronit G11 contaminated with
micro- 3000
Vetronit G11
This study has been performed with an apparatus consisting of two identical standard MWPCs, a clean gas system, an outgasing box, a Copper X-ray generator and an 55Fe X-ray source. In this setup the MWPC is continuously flushed by gas through an outgasing box at a given flow rate, where the box contains the construction materials under investigation, such as glues, frames etc.
Experimental setup
Studies of the ageing phenomena of gas filled detectors are necessary
A dedicated ageing test setup is operational in GSI DetLab
The ambient parameters (e.g. temperature, pressure etc.) should be kept constant during the test as much as possible and the residual should be corrected with the reference chamber
Many optimization tests have been performed to achieve high accuracy ageing test
Ageing tests are performed on clean and contaminated Vetronit G11.
Up to 10.3 mC/cm accumulated charge, no ageing effect has been observed from clean G11.
Up to 8mC/cm accumulated charge, no ageing effect has been observed from contaminated G11.
Summary
Ageing test approach
For periods of 12 mins, the ageing chamber is being irradiated 10 mins by copper X-ray generator, subsequently the mean position of pulse height of 55Fe X-ray source is being registered during 1 min each chamber. The reference chamber is being used for accurate normalization and to distinguish the deterioration of the gain due to ageing (if any) from the variation due to the ambient parameters (e.g. pressure, temperature, gas composition),. Therefore, the data (gain, counting rate, current, resolution, and the ambient parameters ) of both chambers are continuously recorded.