Re: Muon-On-Request

[Michael Barnes <barnes@triumf.ca>]

Dear Peter,

Further to my email of earlier today, I have had a chance to further 
think about the problem. I am now fairly well convinced that item "2" 
and item "3" in my earlier email canNOT result in what you are seeing. 
For example, for my item 3 a false signal back from the overcurrent 
protection would result in the appropriate LED on the TTL splitter being 
lit and the appropriate (pull-up or pull-down) stack would be turned 
continuously: however this cannot result in the HV power supply seeing 
an overcurrent unless there is a short circuit, e.g. on the output of 
the stacks. A similar argument applies to my item "2", a faulty 
interlock can trip the system and cause either the pull-up or pull-down 
stack to be turned on; however, again, this cannot result in the HV 
power supply seeing an overcurrent unless there is a short, e.g. on the 
output of the stacks
Hence I am sure that there must be a breakdown problem  (or short 
circuit) associated with HV1 cabinet (e.g. deflector plates, feed-thru, 
output of stacks ....).
When you tried starting up the kicker last night, at voltages of say 1kV 
on both HV power supplies were the currents drawn from the 2 HV supplies 
more or less identical or was HV1 higher current than HV2?t. What were 
the operating conditions (polarity of HV1 & MV1, approximate frequency 
and pulse duration).

Cheers,
Mike

>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
>


Winter Peter wrote:

> 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
>