Frontend electronics

ePC1 (ePC2) have 384(640) and 512(1024) cathode and anode channels, respectively. In total we have 1024 cathodes channels and 1536 anode channels. To keep the expenses for the readout manageable we plan the following readout scheme:

Anodes.

The original anode electronics is not available any more. Fortunately, we are able to obtain 2700 channels of frontend electronics from the recently finished E871 experiment at FermiLab (21,000 wire chamber channels total). The readout chain consists of a preamps/discriminators card and a gated latch card. The preamp/discriminator cards are mounted on the end rings of the E871 chamber. We will construct a similar mounting for the ePC chambers or power the cards in crates, which are connected to the anode connectors on the end rings by short coax cables (as done originally).

Cathodes.

The cathode signals are connected by existing 70 coax cables to the Aachen preampliers PRA1. Four crates of 20 modules are needed to operate 4x20x16=1280 cathode channels. One position per crate is used for an additonal module which distributes a test signal via the backplane. The differential outputs of the preamps can be connected by twisted pair cables to postamplifier modules, which have a gain of unity and convert the differential signals to single ended ones. Presently we plan to connect these analog signals to discriminator cards, probably modified E871 discriminators. A simple one discriminator readout is expected to give a center of gravity within one cathode strip resolution. According to our Monte Carlo studies, this is sufficient, compared to the multiple scattering resolution. Nevertheless, we plan to study more sophisticated center of gravity methods based on two threshold readout or fast analog methods.

TDC's

The total number of ePC readout channels 1024+1536=2560 exceeds the planned number of CAEN TDC channels 6x128=786 by roughly a factor of 4 (allowing some tdc channels for the eSC). We will reduce the number of channels by 4 to 1 multiplexers. The output of the multiplexer will connect to the TDC, so that 4 groups of wires can be strobed to the input of one TPC channel in 25 ns intervals. The resulting effective time resolution of each channel will then be 100ns, which is acceptable compared to the intrinsic time resolution of these chambers of around 30ns. Note that the important time difference used in the final histogram is that between electron hodoscope and muon entrance counter. The MWPCs are only used for spacial reconstruction. The multiplexer will be realized based on the E871 latch card or by custom boards.

Table 6:

PRA1	characteristics
R	70 , ac
voltage gain	1400
sensitivity	4.8 V/pc
noise	15000e/80ns equivalent
bandwidth	8MHz, 3dB
rise time	13 ns
fall time	50 ns
width	75 ns
linearity
R	2x50 , ac
output full swing	2x1.1 V, 50 load
power consumption	100mW per channel

Up to now, initial tests have been performed with ePC1 (Sindrum chamber 3) at PSI to verify its basic performance. These tests will be continued in March. Afterwards the chamber will be shipped to UIUC, where its instrumentation and readout will be developed and the overall system will be thoroughly tested. Once this is underway, the second chamber will be tested at PSI and eventually instrumented with identical electronics.