sPHENIX discussion of the superconducting solenoid

["Makdisi, Yousef I" <makdisi AT bnl.gov>]

Kin et al.,

Congratulations to all on the wonderful accomplishment and a job well done. 

A 100 Amps is the beginning and a good start. 

Regards,

     Yousef

 

On Mar 22, 2016, at 5:32 PM, Yip, Kin <kinyip AT bnl.gov> wrote:

We’ll have our regular sPHENIX weekly meeting tomorrow at 1:30 pm at 902 conference room :

 

Agenda (https://indico.bnl.gov/conferenceDisplay.py?confId=1854)

<image001.png>      Low field Test

<image002.gif>      Piyush will do quench detection on Thur. ?

<image001.png>      Force variations at various currents

<image002.gif>      After Wuzheng leaves, we’ve got Holger Witte/Nick Tsoupas in C-AD as well as Walter Sondheim to help us with “Opera”

<image001.png>      Working towards High-Field Test

<image001.png>      AOB

 

 

 

I check that the Solenoid Magnet arrived at BNL on Feb. 5, 2015 (very late almost midnight).   We started cool-down on Feb. 25, 2016 and today (Mar. 22, 2016), we’ve finally done our 100 A test.   You can call it a failure or completely incompetent (taken so much time …) if you’re somebody like D. Trump of the opposite party (that he could do it in a few days)  OR you can simply call it a success J    … Somebody a couple doors from my office just told me not to get too excited as it is “just 100 A”.

 

At the end, it’s more of a cool-down exercise as it seems to have taken the Cryo group quite a bit of effort to make all the connections and then

cool it down to 4.5 K.    ( Not all the coil thermometers show 4.5 K.  MT01 was probably the ones that did show temperature < 4.5 K for many hours. )

Thanks to the Cryo group for all the works and efforts.  

 

Earlier on, we ramped the coil to 10 A, you already saw ~26 G, ~65 G at 25 A, and ~130.5 G at 50 A.   At the end, at 100 A (actually 99.8 +/- 0.05 A), it showed almost 260 G ( I attach a picture “Magnetic Field Measurements.jpg” shows the total magnetic field to be ~259.48 G at that instant).  Wuzheng’s

magnetic field calculation in Opera said ~ 270 G [  Wuzheng hasn’t bothered to use the final BaBar turn nos., a couple % lower … I’m not sure whether the probe of 1.5 inches away from the center mattered or not. ]  I guess it’s close enough.

 

At the beginning, we ramped it at 0.1 A/s, then 1 A/s and then later 2.5 A/s most of the time.   “Current_in_Coil.jpg” showed you the ramp to 100 A,

staying there for some time and ramping down.   When ramping down, it couldn’t go as fast as we wanted because the reverse voltage triggered the

diode (at the right reverse biase) and it discharged exponentially.

 

Most of the time, we were playing with the quench detection system.    We artificially shut it off a few times or set the quench threshold very close to “0” in order to trip it.   At one point, we stayed at ~100 A for  half an hour.

 

At the very end, we became “braver”, we set the ramp to 3 A/s.   You may see the voltage in the plot “3A_per_s.jpg”.

At the first time, we didn’t increase the threshold voltage (during ramp) for the entire coil and it did trip.   But after we increased the threshold

a bit, it ramped at 3A/s to the top.  ( BaBar operated ~2.5 A/s or something like that. )

 

When ramping up and down, there is voltage induction = LdI/dt.   L is 1.1-1.2 H per coil (inner/outer).  From  “3A_per_s.jpg”, you can see that

the induced voltage during ramp goes above 3 V which is LdI/dt .

 

In the morning, when John Haggerty asked us (after we ramped to 100 A) how we knew it’s superconducting.  We spent a few seconds arguing

whether the non-superconducting Al (stabilizer) could hold 100 A; but then a smarter guy (~engineer) pointed out that the voltage across the coil

of 100 A   is ~0 !!!  You can see this in “3A_per_s.jpg”.   Which is the proof for superconductivity J   [  I bet Donald Trump would need less than

1 ps to point this out.  ]

 

Before we finished, Ray and Sonny have reset the linear potentiometer so hopefully, we’ll see the entire range to the warm-up temperature.

 

We left 1 A in the magnet coil and the data acquisition running so that when the temperature reached 10 K, we could have a resistance value

and by measuring the resistance again at room temperature, we’ll have a measurement of RRR.

 

<3A_per_s.jpg><Current_in_Coil.jpg><Magnetic Field Measurements.jpg><2016-3-22 17-03.JPG>_______________________________________________
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