sPHENIX discussion of the superconducting solenoid

[Kin Yip <kinyip AT bnl.gov>]

Hi,

Feeling like a historian or a bit like fact-checker after a presidential debate, I've quickly skimmed through a BaBar conference paper that
I uploaded last year (May 15, 2015) :

https://collab.external.bnl.gov/sites/sPHENIX-Magnet/Shared%20Documents/BaBar%20Documents/Availability%20and%20Failure%20Modes%20of%20the%20BaBar%20Superconducting%20Solenoid.pdf

which was published in Oct. 2004, discussing about unplanned interruptions (63 times) to the BaBar Magnet.

In yesterday's meeting, some people seemed to think/say that when the magnet protection system 'acted', it'd be mostly/always ~
"fast discharge" (that you wouldn't have time to react).   It's NOT !   The above-mentioned "magnet protection" (hardware and software)
is more than just "quench protection".

In this paper, you can see that they did mention both "ramp down" and "fast discharge".  But as you may read yourself, it's mostly
"ramp down" due to reasons like power failure or even as "stupid" as "PC failure" (!) etc. :-)  The word "ramp" appears 17 times (15
of "ramp down" and 2 of "ramp down") in this paper whereas "discharge" only appears 4 times (actually only in general description).

From what I've learnt (from Bob/Piyush/Carl and elsewhere),

ramp down    --- slow discharge through the freewheeling diode => lower reistance => larger time constant => longer time reach ~0 current
fast discharge --- quick discharge through the dump resistor => higher reistance => smaller time constant => quick to reach ~0 current

If a fast discharge happens, the current and therefore heat generated would actually cause read quench to the Magnet/superconducting coil.
It's a bit of "chicken and egg" problem as Piyush has said.    "Ramp down" seems less damaging ...

On page 2, under "II. OBSERVED FAILURE MODES", it's said: "None of these can be shown to be the result of a spontaneous quench in the coil"
which is something that people like Pasquale has said (many times).

In this paper, they also reported what they have done to reduce the "unplanned interruptions" and I guess we'll learn and try to avoid what we can
prevent.


After finishing reading this and driving back to the Lab. this morning, I've suddenly realized :

even though what you have written might seem useless at the time of writing,  it may be useful to somebody (whom you may not know) in the future ...

Kin