RE: Muon-On-Request

[Michael Barnes <barnes@triumf.ca>]

Dear Peter,

There sounds as thought there is a problem with an electrical breakdown in
one of the NEG cabinets: the 'NEG 1' LED identifies an over current fault.
However I cannot recall which cabinet 'NEG 1' is (i.e. HV1 or MV1,
although I think it is probably HV1) -- it depends on how the fiber optic
cables have been connected back to the TRIUMF splitter box. NEG indicates
the bottom stack in the cabinet. What polarity is HV1 supply (negative I
assume)?.

2kV is probably the lowest voltage that the over current circuit can
indicate a fault (approx. 8A of current = 2kV/((19R*9)+17R)). But this
fault current must be flowing to ground through only the one stack.

I agree with Gary that this cannot be caused by a problem with a single
card. Instead there is either:
1) a conductor (e.g. wire or grounding rod) or a real fault/breakdown near
the output to the deflector plates;
2) a problem with an interlock (which, depending on the interlock, would
cause the controls to switch on all the cards to short the stacks to
ground) -- but I doubt this as the fault current must be flowing though
only one stack for the fault to be indicated at only 2kV;
3) A problem with the fiber optic signal from the over current circuit in
the lower stack.

I will have to give some thought to the best way of diagnosing this -- so
I will email you again later. In the meantime please let me know the
polarity of HV1 and have a look for any obvious clearance problems.

Good luck,
Mike

> Dear Mike,
>
> this evening we were trying to start the kicker again after it wasn
> running on HV the last days. While trying to ramp the HV up, we had a
> current regulation on the HV1 side. We could go up until 2kV and then
> suddenly the current went to 112mA and the voltage dropped to 0.41kV.
> There was a red LED on the small black box at the 'NEG 1'. We reset the
> kicker and went up with the HV on the HV2 side without problems. Then we
> tried slowly to ramp the HV1 side again and at 1.4kV we could see the red
> LEDs being on. The current was ~75mA and therefore still below 112mA but
> higher than usual. We then noticed that on the lower stack of the cards in
> HV1 the card DOWN-13 didn show a red LED.
> With the online help of Francoise we took out this card and checked the
> resistance. It showed 1.6MOhm in one direction (similar to one of the
> spare cards). Then we put it back and bypassed the door interlock in order
> to measure the voltage on the resistor C13. That measurement gave 15.1 V
> while the two neighbouring cards had 14.9 and 15.06 V for this resistor.
> According to what I learned from Francoise, this card might not be a
> problem.
> Now we don want to switch on this half of the kicker before we have some
> advice what to do next. Do you have any suggestions / ideas for the high
> current? In principle we could exchange the card with a spare one and test
> the kicker again but we rather wait for your answer.
> Looking forward for any suggestions,
> best greetings
> Peter
>