sPHENIX discussion of the superconducting solenoid

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

 

Hello,

 

1.      So, Paul Giannotti and Frank Toldo have finally completed the strain-gauge and linear pot connections.   Winston Pekrul is trying to read them out using the KeySight DIMM.  He’s read half of them.

We have got one puzzle this afternoon/evening and we realized what at the end.   At 10 mA, we don’t seem to have current output from the Precision source.   Randomly, or my trial and error, when I set the current at 1 mA … and actually up to 9 mA, we do measure voltage across the strain gauge etc.  But just not at 10 mA or larger.  We realized later that, Jon Hock’s 4 linear-pot which he added at the end, have very large resistor which would give us to ~24 V, 30 V, 24 V and 29 V è which is 107 V.  This eats up most of the voltage capability of the precision source ~110 V !

We can use 9 mA instead.  Or, Winston suggested that the Keysight DIMM can measure resistance by supplying current itself.  So, we think we just take out the 4 Hock’s linear pots out of the current loop and Winston just measures resistances directly.   The rest should work as before J   [   I’ll talk with Paul/Frank tomorrow … ]

I’ve  included Paul’s email and his spreadsheet can be found :
https://collab.external.bnl.gov/sites/sPHENIX-Magnet/Shared%20Documents/High%20Field%20Test/2017-12-28%20SG%20Channel%20Assignment.xlsx

2.      Roberto and the Cryo group tried to switch to a mode that could go faster to 100 K.  You can read his email below and it seems that they couldn’t do it in a controlled manner (delta < 40 K).  So, they decide to let it drop at the current rate ~0.5 K per hour to 100 K and then they can do the cooling without worrying the “delta < 40K” constraint.  { delta is the temperature difference between inlet and outlet temperature sensors. }

I attach the current Cryo graphic as usual and one can calculate that the temperature would reach 100 K in a few days.   They plan to do the switch on Jan. 2 (next Tuesday)

and if all work, we can possibly be ~4.x K on the day of Jan. 2^nd !

 

 

Kin

 

 

From: Giannotti, Paul
Sent: Thursday, December 28, 2017 4:57 PM
To: Pekrul, Winston <wpekrul AT bnl.gov>
Cc: Yip, Kin <kinyip AT bnl.gov>; Hock, Jonathan <jhock AT bnl.gov>
Subject: Displacement Pots Resistance

 

Hi Winston,

 

For channels 36, 37, 38, and 39 (linear displacement potentiometers LP1, LP2, LP3, and LP4 respectively) here are the baseline resistance readings before start of cool down:

 

LP1: 2,430 ohms

LP2: 3,000 ohms

LP3: 2,400 ohms

LP4: 2,900 ohms

 

With 10mA current through the pots, the corresponding voltages into the front end of the Keysight multiplexer are then, 24.3V, 30V, 24V, and 29V for channels 36, 37, 38, and 39 respectively.

 

I don’t think it matters for maximum input voltage, but all the other channels are seeing somewhere less than 4 volts each from the strain gages and Tie Rod temperature elements and magnet pots.

 

See my revised channel number chart showing final tested instruments. See defective channels. I did not change the multiplexer input wiring so the defective channels are bypassed in the wiring chain and therefore those channels will just read zero during each scan.

 

Thanks,

Paul

 

 

 

Tried. But we had an instability issue supplying from the storage dewar.

Pressure surge between the storage dewar and cold control valve 3613

Results of liquid vaporizing all of a sudden and expanding. When you operate below 2.2 bar: subcritical you will have 2 phase flow.

Supplying from storage dewar we are at below 1.8 atm.

 

Controlling the supply temperature was difficult to keep the 40K gradient.

So we will continue till we get to 100K.

Then no control is needed after that.

 

Roberto Than

Cryogenic Systems, Collider-Accelerator Department
Brookhaven National Laboratory
Building 1005S, MS 1005S, Room 212
Upton, NY 11973-5000
Telephone: (631) 344-7165
Cell 631-487-6842 
E-mail: ythan AT bnl.gov

 

 

 

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