sPHENIX discussion of the superconducting solenoid

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

Dear Glenn,

 

• How long did it take to recool after the 'quench' from full current, where you say the temperature went to 35K

 

I go to our LogView and plot the temperatures that I’ve been plotting (see recovery.gif).   It seems that those thermal sensors went back to their nominal

temperatures within about an hour or so.

 

• Is there any noticeable change in helium consumption when ramping at the faster rate, 1.0 vs 0.5 A/s ?
• I am hoping the lead temperature at the vapor cooled leads stays within good limits then?

 

We haven’t done 1A/s so far and we’ll try to do it today.   Yesterday, we did see the gas-cooled voltage rising from 2 mV to > 20mV.   But as I mentioned in the email,

the Cryo was reading wrong current etc. and they were trying to make changes yesterday.   They will try to optimize today.

 

• Is there anywhere an NMR probe to measure field, or an installed Hall probe in the bore?

 

John Haggerty and Frank Toldo placed a hall probe on a shaft attached to the EMCAL.  This is what he told me:

 

“BTW, my Hall probe showed 1.25 T at 4620 A, and the map at that location

gives 1.39 T, so I see a field that's 10% low, although we have not calibrated the probe. “

 

{ Power Supply needs to give 4620 A in order to produce 4596 A in the DCCT/Magnet.  Some current went to the dump resistor …}

 

Kin

 

From: Glenn Young <glennyoung82251 AT gmail.com>
Sent: Monday, October 24, 2022 10:48 PM
To: Yip, Kin <kinyip AT bnl.gov>
Subject: Re: FW: Magnet reached top current (4596 A) ... Tiny magnetic field at the top platform ... He-Gas-flow needs to be adjusted

 

Dear Kin,

Ah, this is very exciting.

How long did it take to recool after the 'quench' from full current, where you say the temperature went to 35K

 

Is there any noticeable change in helium consumption when ramping at the faster rate, 1.0 vs 0.5 A/s ?

I am hoping the lead temperature at the vapor cooled leads stays within good limits then?

 

Is there anywhere an NMR probe to measure field, or an installed Hall probe in the bore?

Thanks, Glenn

 

On Mon, Oct 24, 2022 at 6:57 PM Yip, Kin <kinyip AT bnl.gov> wrote:

 

 

From: sPHENIX-magnet-l <sphenix-magnet-l-bounces AT lists.bnl.gov> On Behalf Of Yip, Kin
Sent: Monday, October 24, 2022 6:46 PM
To: sphenix-magnet-l AT lists.bnl.gov
Cc: Michnoff, Robert J <michnoff AT bnl.gov>; Sandberg, Jon N <jsandberg AT bnl.gov>; Albanese, Marianna <malbanese AT bnl.gov>
Subject: [Sphenix-magnet-l] Magnet reached top current (4596 A) ... Tiny magnetic field at the top platform ... He-Gas-flow needs to be adjusted

 

Hi,

 

1. We have reached our operation current at 4596 A this afternoon around 5 pm.   Carl Schultheiss said that we should trust the voltage measured

in the DCCT (which measures 0 to 10 V for current of 0 to 6000 A).   We’ve found that we needed to set the “targetCurrentS” at 4620 A in order to

get 4596 A in DCCT.  I show the current plot in “current.gif”.

                Today, we have been ramping at 0.5 A/s.   Tomorrow, we’ll try 1 A/s.

2. Earlier this morning, we intentionally initiated a quench-back at ~300 A and at the 4596 A, we also initiated another quench-back by setting quench threshold to 0 at the quench detector.   
   Tim Costanzo, Ed O’Brien, Chris O’Shea and I were in the 1008 and we heard the big bang/noise.   But there was no smoke in the IR !

• The Roberto Than’s/Paul Orfin’s design works (i.e., the He gas was dumped outside 1008 on the berm between 1008 and 1008B 😊

 

The thermal sensor for the magnet went from 4.8 K to >35 K due to the quench😊

 

3. Before the quench, Chris O’Shea and I went to measure the fringe field.  At our so-called “5G” line (where the shielding block is/will be that I artificially set), it’s actually only

about 0.17 G and if you walked across it a few steps, it could be about 0.32 G.

At the 4 corners (gaps around the pole-tip doors), we measured ~11.5 G .   At the top platform, we measured magnetic field from 0.77 to 1.5 Gauss.   So, I think we can say
that there is no real danger of magnetic field while working at the platform.

4. The “scariest” or near-quenching moment (today) was just before 4 pm when we were sitting at 4000 A.  Carl has been monitoring the two gas-cooled-lead voltage all day.  Just before 4 pm, we
   saw that it almost went away to above 40 mV --- 50 mV is our quench threshold.  You may see this in the plot of “gas-cooled-lead.gif”.
   
   So, Carl immediately set the current down to 3500 A and called “Cryo”.   ( This is the “dip” in “current.gif” after 4 pm. )
   
   “Cryo” has had wrong current reading from DCCT today.  When we read 4000 A, they might be reading between 1700 or 1800 A or so.  They have tried to adjust the flow rate
   and at times, they thought it’s too high ---- I took a picture of the Current Leads (“20221024_170849.jpg”) during the magnetic field measurement and you can see a lot frost ---
   they tried to adjust it lower … Too high gas flow is no good because it might block or damage the gas pipe.   The wrong reading may be due to the fact that it should be voltage reading
   instead of current reading as it’s assumed and they may need to change a wire or two.
   
   After “Cryo” told us that they temporarily fixed the problem (for now) and got steady, we stopped the down-ramping and went back to 4000 A and  …. then 4596 A.   Tomorrow, Carl will

work the Cryo Group (Roberto and Brian) so that the Cryo group can optimize at each step (1000 A, 2000 A, …. ).

 

 

Overall, it’s a successful day and we ramped to the top without any uninitiated quench.    Pablo doesn’t seem to make any “compensation” adjustment as the parameters used in 2018 seem

good enough.

 

Kin

 

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Attachment: GC-voltages.gif
Description: GC-voltages.gif