"Archana.Sharma@cern.ch" advertizes an adaptation of Garfield which is useful for GEM detectors. Archana claims that once you have a 3-D Electric field, you can import it into Garfield and let it do the tracking for you. We have a 3-D field map using ANSYS (Archana used MAXWELL). Now we need to find the time to learn how to implement it into Garfield. I asked Archana for his program but it seems that the last 5 years have not been kind to his file backup system.
2.) GEM Trigger
Finally had some cantact with R. Bellazzini, (NIM A478, 2002 pg
13-15), who triggers his ionization chamber using the GEM foils.
Their trigger circuit is built using AMPTEK's
A203
pre-amp and pulse shaper which is fed into AMPTEK's
A206 voltage
amplifier and low level discriminator. It will cost less
than $1k just for the parts and prefab board. We are going to
ask more questions to be sure this solution is what we want. I
see rise time of 50 ns for the A203 and 20 ns for the A206 are
reported in the spec sheet. The
GEM drift time is about 14 ns/mm. So the drift time to the
charge collector would be at most 28ns if I used the last GEM
foil stage and at most 82 ns using the 1st GEM foil stage. The
Helix integration time can be 100 ns (10 MHz clock) down to at
least 20 ns. I would like to clock the Helix chip at 20 MHz
(Moller rates are less than 12 MHz at 10nA). The pulsed X-ray
tube will be used to verify timing.
3.) Readout:
No real progress. Wire bonding trainees having trouble threading
wedge bonder.
4.) Detector Design: Yasuhiro Sakemi from the Research Center for Nuclear Physics in Osaka Japan has recently advertized a GEM based detector with Helix boards which is very similar to our design. His detector has a 200 micron pitch which requires using 4 Helix boards while ours only needs 2 Helix boards given that COMPASS was able to achieve a 70 micron tracking resolution using 400 micron pitch GEM charge collectors. Based on the COMPASS technical reports, we should be able to meet our spec of a 100 micron tracking resolution with a 400 micron pitch ( x-strips are 80 microns wide and the y-strips are 340 microns wide in order to have equal charge sharing). I plan to align the 80 micron wide strips in the "theta" direction.
5.) Test Apparatus : X-ray test lab being set up. Measured 2mrad X-ray rate using Tungsten target. (Tungsten needs about 80 kV before you see the X-ray peak, I only have a 10kV supply). This tube is only a loaner though, the final tube will be copper-moly with peaks at about 7 kev and 20 kev.
