1. Study of Cross-talk on the MAPMT-to-Hybrid cable

2. Overview As HV is increased beyond ~600V, we start to see capacitive coupling between channels. Initial studies indicated it was due (mostly) to the flat cable connecting the baseboard to hybrid.

3. Possible Short-Term Solutions Use the same cable (~3) but with spacing between the wires. Use a very short cable of 0.5 (approximated a direct connection from baseboard to hybrid) Study each alternative cable as a function of HV and Threshold.

4. Schematics Optical fiber MAPMT LED

5. Plots Old cable (3) at 600V and threshold 117 New cable (3) at 600V and threshold 117 Old cable (3) at 700V and threshold 117 New cable (3) at 700V and threshold 117 Old cable (3) at 700V and threshold 105 New cable (3) at 700V and threshold 105

6. Plots Old cable (3) at 750V and threshold 105 New cable (3) at 750V and threshold 105 Old cable (3) at 750V and threshold 90 New cable (3) at 750V and threshold 90 Old cable (3) at 800V and threshold 90 New cable (3) at 800V and threshold 90

7. Plots Old cable (3) at 700V and threshold 105 Old cable (3) at 800V and threshold 90 New cable (3) at 700V and threshold 105 New cable (3) at 800V and threshold 90 Short cable (0.5) at 700V and threshold 105 Short cable (0.5) at 800V and threshold 90

8. Summary Both the split cable and short cable reduce the interwire coupling, but neither eliminates it. Possible other sources/tests. Make a cable with 2 wires only at positions 1 & 32 and check if coupling still persists. Connectors? Traces on hybrid, baseboard? Possibly try injecting charge directly into the pre- amp through a 10 pF cap (nominally, 62Ke-/mV)