sPHENIX discussion of the superconducting solenoid

["Yip, Kin" <kinyip AT bnl.gov>]

Hi,

It took us sometime to gather all the equipment this morning --- including a 
baroscope that I borrowed from our ATF colleagues
last Friday.

(0) Last Thursday, we set the threshold at 10 micro-amp and let the voltage 
ramp continuously and Lead A(+) failed but Lead B(-) succeeded.

(1)  Carl always has a suspicion of humidity.   ( Today is dryer than last 
Thursday ? )

(2) This morning, when we poking around and Carl didn't like a piece of 
Aluminium tape near the end chimney (at the bottom).  Though it's
attached and outside a Kapton, Carl said that Kapton can have holes ?! ....   
This is probably not the reason but I'd just like to write it down here.
I took a picture of the Aluminium tape that we took off from the end of 
chimney.   I took a picture.

We also tried to keep a bit of distance of those wires from the ends of the 
leads near the end of chimney.

(3)  As I suspected in my last email (below) was that, today when we did the 
hipot with Carl's "Stanford" meter/power-supply, he just
keyed in the voltage like 50 V, 75 V, 100 V, 150 V ... until 520 V.   Each 
time when the voltage increases, you saw some instantaneous
jump at the current for a split of a second such as 10 micro-amp or 50 
micro-amp but then it became "0" amp.      At DC, we always 
saw "0" micro-amp.   That meter can see only 0.01 mA (10 micro-amp).    The 
maximum threshold was the default 5 mA.

So, at DC, even at 520 V (our hipot voltage), the leakage current is still 0 
A (as far as the meter sensitivity goes).

We did this for Lead A first and succeeded.  Later on, we did it for Lead B 
(and we realized that the threshold was 5 mA and we set it to 1 mA)
and Lead B succeded as well.


=>>  So,

(1) Carl has advised that we should use Kapton tape as much as possible.

(2) We'll do this hipot whenever there is major change.   So, this afternoon, 
at 1:30 pm or so, Ken Riker would use Kapton to re-tape the
ceramic break.    We'll do another hipot.   And then if it's OK, we'll tape 
another ceramic break and do another hipot.

(3) I left a "logbook" there.  I recorded what we did this morning.   I asked 
the Cryo group (Ken Riker, Paul Orfin ...) to please write down
anything that they did.   So that we may keep track ....  I attach the 
picture of the first page of the "logbook".

Kin

-----Original Message-----
From: Yip, Kin 
Sent: Monday, April 4, 2022 4:44 PM
To: Schultheiss, Carl <carls AT bnl.gov>
Subject: Manual/slow hipot ...

Hi Carl,

I just chatted with Don Bruno and I remember the hipot test that we did 
in early 2018 for the high-field test.

When SMD techs did the hipot test, the voltage ramped continuously at 
first at 3V/second and was later changed to probably 1.5V/second or so.


But when I talked with Don, Don told me that you guys usually ramp it up 
slowly by hand, and you'd stop at each step to allow the leak current to 
be steady before you ramp up again.   I think it was like that too when 
we did the hipot test in 2018.

But this was not the case when we did the hipot test last Thursday.  
Because their "automatic" program just kept rising constantly (at 3V/s 
or 1.5V/s without waiting for a steady leak current) until it failed and 
went beyond 10 micro-Amp or suffered an "arc failure".  [ In any case, 
-Lead is better than +Lead. ]

Maybe, if we do the hipot more slowly, the hipot could succeed. Don told 
me that it should be "DC", not "AC".  { During nominal ramping for the 
sPHENIX Magnet, the voltage is low, like 10-20 V or something like that. }


This "slow" scheme could result in the same failure but may be not ?! 
It's worthwhile trying.

You are the expert :-)   It's just a thought ...

Kin

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