Summary of the Wire Chamber Working Group meeting on May 30 2000

(compiled by Burkhard)

1. Chamber Parameters:

The subject was introduced by a presentation of Werner with simulation results based on Heed, Magboltz, Garfield and Maxwell. He assumed a peaking time of 15ns, a wire diameter of 30um and an Ar/CO_2/CF_4 mixture. His results are summarized in a note, which can be found under /afs/cern.ch/user/r/riegler/public/MWPC/note.ps

a) Staggering In order to judge on the relevance of staggering, one has to consider it as function of the number of electrons required in order to be above the threshold, which is in our case close to 5 electrons. For tracks perpendicular to the wires in a 2 gap chamber one can see an improvement of the time RMS from 4ns (not staggered) to 2.6 ns (staggered). However, particles cross the chambers with angles up to 300 mrad, while staggering corresponds only to about 37 mrad. Therefore, staggering is not important in order to insure full efficiency, if we assume a wirespacing of 1.5mm.

b) Number of gaps Simulation results confirmed that in order to get the required time resolution and efficiency within 20 ns 2 gaps are neccessary. However, 2 single gaps, read out independently, would not yield the required redundancy. Three FE-layers per station would become too expensive (~600kCHF/FE-layer, including links). Moreover, construction wise, an even number of gaps is preferable. => Therefore we decided to have 2x2gaps with two FE-layers/station.

c) Gap Size Since only the first electrons are used to provide the signal, the gap size could in principle be reduced to 4mm, which would have the advantage to reduce the HV by 10%. However, the flatness of the surface would have to be better (by 20%). The general feeling was that we have not to decide on this now, and define only a range: Gap size will be 4-5mm.

d) Wire spacing An increase in wire spacing has only a minor impact on the reduction in HV. It would increase however the cluster size in the inner part of M2+M3 and deteriorate the time resolution. => We decided to have a wire spacing of 1.5mm. => For the inner part of M2+M3 more work is required in order to reach a conclusion on the optimal wire spacing.

e) Wire diameter We reviewed again the issue of wire diameter, concidering the various arguments as given in our meeting on May 11 for a 30um or 50um wire. => As for the gap size, we agreeed on a range between 30 and 50um and prefered to take a final decision only later, as no tests have been done so far by the muon group with a 50um wire. => In order to stay with the HV below 4kV it was felt, however, that if we would increase the wire diamter to 50 um, we should at the same time reduce the gap size to 4mm.

f) Chamber height We discussed in detail the issue of chamber height. An increase by a factor two from 20cm to 40cm in M1 (and projective chambers in the other stations, thus 31cm (62cm) in M5) would have the consequence that we have cathode-pad instead of anode-wire readout in R4. Against the advantage to have less chambers and less passive material stand the arguments that chambers with anode readout are better understood by the group, have signals which are a factor two larger and allow therfore the use of larger electrodes (less FE-channels), have less cross-talk and are more simple to construct. => As region 4 is covers a large surface, it was decided to stick to the chamber height of 20cm in M1.

2. Design Issues

The CERN, INFN and PNPI groups presented there first ideas on chamber design. We agreed that the wire should NOT be continuous in the 2 gaps (thus broken after wiring, glueing and soldering), to allow the use of the second gap in case of problems with one of the gaps, and to avoid problems with pick-up noise etc. The amount of work from point of view of soldering seems rather similar.

Further design work should aim at the reduction of the amount of passive material beyond the sensitive area, as we need the space between the chambers to bring out the cables. Details about the wire fixation and gap bars will be discussed in the meeting on June 9 with the aim to come to a conclusion for the prototypes to be build in the summer by the various groups.

In the inner part of the muon system, particularly in stations 2 and 3, four gap chambers are considered. The size of the logical units we agreed upon do not allow any elegant shifting of the two layers as considered for regions 3+4. Moreover, a four gap chamber of a total thicknes of ~6cm reduces the distance between the layers, and therefore the cluster size resulting from the OR between the layers.

We had a lively discussion about the issue of having also in regions 3+4 one four gap chamber or two double gap chambers. A four gap chamber would be more complicated, but would have the advantage of having less chambers. Moreover, the realiztion of the OR of the two gaps would be simpler, as no shift would occur between the chambers. The forming of the OR between the 2 layers could even be realized of the FE-board, although a much more detailed study would be required before concluding on this. On the other hand, a fourfold overlap instead of a two-fold overlap would be required with four gap chambers, which would imply that the chambers have to be much thinner. We haven't reached any conclusion on this and the issue needs more discussion.

3. Planning

We agreed that at least three wire chamber prototypes should be build this summer.

a) The PNPI group would build a full size prototype for region 4 with anode wire readout, preferably for M3.
b) The Frascati and Ferrara groups would build a chamber with cathode pad readout, either for region 3 in M1-M3 or for region 2 in M4 or M5.
c) The CERN and Rio groups would build a prototype for the inner part of station 2, where a combined anode-cathode-readout is foreseen and the highest granularity is required. In particular for this area more simulation studies are required before the design of the prototype can be finalized.

Besides Potenza also Ferrara is trying to get in contact with companies who could provide panels. As we need to have some panels rather soon in order to build the prototypes it was felt that a broader base to start with is useful.

The next meeting will be on June 9 at CERN.