sPHENIX discussion of the superconducting solenoid

[Kin Yip <kinyip AT bnl.gov>]

Hi,

Today, we tried twice to ramp (2.5 A/s to 1000 A once and 2A/s in general ... and then in 200 A step from 2000 A onwards). 
The first time, the quench signal dropped to create fast discharge after 2801 A  and the second time the quench signal dropped
at ~4128 A.   Especially for the 2nd time, Pablo could see Helium smoke ~15 feet and all the bang noise. 

[  The highest field today we saw was like 1.1113 T.

It's close to our target of 4600 A (but no cigar).

In the plot of VT20A_VT10_VT9.gif, you can see that Inner_Mag_Coil_Neg (VT9-VT10) --- Black and Neg_Magnet_Lead (VT10-VT20A)  --- Read, both increased
to 300 mV before the quench signal was triggered --- Blue, during the quench of 2801 A.

In the picture 300mV.gif, you can see that the 300 mV were still there after the quench ended for some time (half an hour).  But at the end, they both dropped to 0.
To prove that it was a open leads, Carl went up to the lower platform and manually detach the wires and he saw the 300 mV, ~ 11:15 am that you can see in the plot.

The quench detection system needs the threshold to be violated > 36 times (net) before the quench is triggered.

At the 2nd time (2nd_time.gif), similar things happened (though not so obvious as it's ramping with big voltages due to dI/dt).

So, it seems that VT10 was the unreliable voltage tap (after we took out VT11 earlier).   Too bad.    We are thinking of reconfiguring using VT9 - VT20A (instead of
VT10 - VT20A) and then we have to change the inner coil to VT9 to VT20A   and also the outer  VT7 to VT19A.   A little bit of headache there ........

We'll discuss again (probably including some experts like Piyush and Joe ....) and decide whether we run on Tuesday or not.

Kin

PS:  I include the PDF file if you want to know where voltage taps are located.

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Attachment: VT20A_VT10_VT9.gif
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Attachment: sPHENIX Voltage-Tap layout.pdf
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