EMU CSC Aging Test
EMU CSC Aging Test
By Yu. Bonushkin
e-mail bonushki@physics.ucla.edu
The chamber production plan calls for start of panel cutting in '99. Before that we have a crucial test to perform, namely, to age our chamber and see if the current mass production version can withstand 10 years of LHC radiation environment. To accomplish that we plan to install a sector of a 20-degree chamber at GIF and have it fried there for 2 months with the source fully opened. A similar chamber will be kept outside the irradiation zone for a reference measurement. A number of 55Fe sources will be inserted in interesting points of the chamber plane to minotor dark current and 5.9keV peak position for an evidence of aging. After the irradiation the samples of wire and cathode surface will be studied with electronic microscope.
| Name | Institution | Responsibility |
| Giorgio Apollinari | Fermilab | chamber production coordination |
| Yuri Bonushkin | UC, Los Angeles | test coordination |
| David Chrisman | UC, Riverside | DAQ |
| Gennady Gavrilov | PNPI, Gatchina | tests at CERN, sample studies |
| Bill Gorn | UC, Riverside | DAQ |
| Lisa Gorn | UF, Gainesville | on-line monitoring, off-line |
| Andrei Korytov | UF, Gainesville | overall coordination |
| Sergei Kovalenko | PNPI, Gatchina | tests at CERN, DAQ software |
| Anatoli Krivshich | PNPI, Gatchina | coordination at PNPI |
| Sergei Medved' | Perdue Univ. | chamber testing at FNAL |
| Oleg Prokofiev | Fermilab | chamber production and testing at FNAL, shipping to CERN |
| Slava Razmyslovich | Fermilab | chamber design |
| Leonid Shipunov | PNPI, Gatchina | tests at CERN, sample studies |
| Bryan Smith | Carnegie Mellon Univ. | off-line |
At nominal gas gain in 10 LHC years a charge of 0.1 C/cm of wire is accumulated at an average hit rate of 200 Hz/cm^2 (1 kHz/cm^2 in the worst case). So, to accumulate the similar charge in 2 months of operation at GIF in Febuary-April, we will need to increase the hit rate by a factor of 60, which is 12(60)kHz/cm^2. The source is 1 GBq 137Cs (30 yrs half-life, beta-, 94% of electrons with endpoint energy 0.514MeV, followed by 0.662MeV gamma, or 6% 1.176Mev e's). Recalling that last summer P2 was counting (above 20 fC threshold) 400 Hz/cm^2 at 3.5 meters away from the source and assuming quadratic dependence of the fluence on the distance from the source, we will have to move the chamber as close as 0.6 meters from the source. And, if it is impossible, we will have to crank up the high voltage to adjust the gas gain to get the right amount of charge.
There will be 2 identical chambers in the setup: one with the full chamber volume "uniformely" irradiated, inside the GIF controlled access area, presumably 0.6 meters away from the fully opened source; and another one for reference measurements. The chambers are simply an slightly modified design of a bottom segment of an ME2/1 chamber, with addition of an extra guard strip in the middle of the sinsitive volume. The major modification allowed to apply negative high voltage to one of the 2 layers of the chamber, while the other layer remained as in a regular chamber - with positive HV applied to the anode wires. The modification was necessary to allow for precision measurement of the dark currnt from individual wires and wire groups, which would otherwise be impossible because of the blocking HV caps.
Both chambers have special source holes to allow 55Fe gammas inside the sensitive volume. The holes are not through the entire panel, - about 200-300 microns was left to keep the gas volume tight and do not allow alien materials and vapors inside the chamber. The location of the holes was discussed on numerous meetings and the final version is shown here (790k ps). We put them at every four wires adjacent to the guard strips both at the edge of the sensitive area and in the middle; in the middle of the chamber "regular structure", and near the anode bars. Those are the interesting points.
There was also a suggestion (B. Gorn) to attenuate the irradiation by a factor of 10 in a certain area of the chamber. In terms of learning about aging, it is very useful to decouple effects of the anode wire aging due to some "plasma chemistry" in the intense discharge from the uniform "poisoning" of the chamber by the gas carrying fragments of dissociated gas molecules all over the chamber volume. We will easily accomplish this by placing an iron plate in front of the chamber horizontal segment. Another idea we check this way is whether aging is faster at lower rates.
The test chamber will be located inside GIF and will be 50-60 cm away from the source. The reference chamber will be located outside GIF in the gas system area behind the beam line. It also makes sense to place electronics and DAQ there.
To be cont'd...