• HV/signal grounds: Eugene pointed out that with this kind of PMT/base, it would be better to separate the high voltage ground from the anode ground. For this purpose, a 1 to 10 kohm resistor between both grounds would help (due to security reasons, it seems impossible to totally separate both grounds).

 
• HV cable setup: We now have all the power supplies at JLab. We have mainly discussed what kind of cables/connectors/transition panels would be used. We ended up with one setup in mind:

 

 
The remaining (and open) option is either to solder the cables on the circuit board, then have connectors on panel #1, or to put connectors on the base and solder the cables on panel #1. On one hand it's safer to handle bases with connectors since we won't have the cables hanging to them; on the other hand it's definitely trickier to put connectors on the base.
It seems we can control the high voltage power supplies through an ethernet port, Eugene will investigate this possibility.
 
• Signal cable setup: the main issue is how to get a sufficient (around 150 ns) delay for trigger purpose. It seems that we can build the trigger on a rack close to the detector. This rack would have the passive splitters and the basic OR circuit. Then, the 700 channels will go to the electronics hut using regular (5 ns/m) cables (about 50 m). On the other hand, the trigger (OR output) will go to the electronics hut using a fast (~4 ns/m, has to be checked) and shorter (about 25 m) cable. The timing difference (about 125 ns in this scheme) would be sufficient. Passive delay chips have been mentionned, but nobody seems to trust them (cross-talk between channels, ...). If we need the trigger to be formed at the electronics hut (radiation damage issues for instance), then the same scheme can be used, but with 50 fast cables (outputs of the splitters going to the main OR), which is still manageable.

 
• Phototube linearity: Hakob hasn't finished the linearity tests on the photomultipliers and the base prototype. A technical note will probably be available next week.

 
• Base circuit board prototype: We had several remarks about the base prototype that was shown at the meeting (add clamps for cables, add resistor to separate signal/HV grounds, new shape to make the board easier to cut by machine shop, ...). I'll try to produce the new version very soon. We will probably ask for 25 of this new prototype once Hakob has tested it. The prototype had thick (regular 5 ns/m) signal cables. We will switch right away to thin cables (Lemo style). We could use thiner HV cables (3 kV limit is enough): this will be investigated.

 
• Base (mechanical part) prototype: Tom was sick and couldn't show us the 1^st prototype. He will have it next week and will try to have the second discussed protype.

Franck Sabatie - 02/04/1999

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