sPHENIX discussion of the superconducting solenoid

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

Hi,

 

When we ramp up, we can control but not when we ramp down.

 

At the t=0, the di/dt is the highest.   I’ve calculated using :

https://www.c-ad.bnl.gov/kinyip/sPHENIX_Ramp_Down.html  (which tracks the high field quite accurately if you put in the right values),

 

if I put in 1.25 mOhm and 2.57 H ( BaBar’s value from their liternature),

 

it’s about  -2.51 A/s at the instant of ramping down (t=0).

 

With L=2.33 H --- that’s the new inductance for Wuzheng’s new model that I have just computed (and he confirmed),

 

it’s  -2.77 A/s at that instant of t=0.    di/dt drops quite slowly.  

 

From the BaBar’s document, ramping up >  ~2.7 A/s or so, would quench.   People  told me that it’s in principle the

same when  you ramp down.

 

We couldn’t ramp up at 2 A/s all the way to 4600 A without quench  during our limited trials of high-field test.

 

So, in order to get the ramp down rate at t=0 to  -2.51 A/s, with L=2.33, I’d need to have 1.12 mOhm, which is about the highest

the resistance is.

 

If your total resistance can be down to 1 mOhm, it’s even better.   It’ll be -2.27 A/s  with 1 mOhm.   This gives us extra margin

as the Magnet may have “deteriorated” ☹

 

The time to ramp down from 4600 A to 1000 A (when we can do the fast discharge) is  40.5 minutes at 1.12 mOhm and it’s

44.2 minutes at 1 mOhm.    We can add a few minutes for extra safety/tolerance 😊

 

Kin

 

 

From: Phillips, David B
Sent: Tuesday, March 26, 2019 9:05 AM
To: Yip, Kin <kinyip AT bnl.gov>
Subject: RE: the difference is due to inductance

 

So what ramp rate do we want?

 

From: Yip, Kin
Sent: Monday, March 25, 2019 2:40 PM
To: Phillips, David B <phillips AT bnl.gov>
Subject: the difference is due to inductance

 

Hi,

What I was saying in my email in July 2018 (below),  was that,  if I plugged in our inductance ~2.4 H, instead of 2.5x in BaBar, it leads to an average ramp
rate of 1.7 A/s  vs 1.6 A/s in BaBar.  Here 1.25 mOhm is assumed in both 1.6 or 1.7 A/s.

Kin

On 3/25/19 10:45 AM, Phillips, David B wrote:

 

 

From: Yip, Kin
Sent: Tuesday, July 17, 2018 12:47 PM
To: sphenix-magnet-l AT lists.bnl.gov; Phillips, David B <phillips AT bnl.gov>
Subject: ～1 milli-Ohm

 

Hi Dave,

From  \\bnl.gov\c-adnas\babar\BaBar P.S. Manual\Babar P.S. Section1.pdf, p.11 (PDF page),

you can see that the cable resistor in BaBar is 1.25 milli-Ohm.   In our high-field test, we've 0.666 milli-Ohm (measured by Carl).

Putting 1.25 mOhm and our inductance ~ 2.4 H (Wuzheng's old sPHENIX model --- which he may update in near future),
into my calculator webpage :  https://www.c-ad.bnl.gov/kinyip/sPHENIX_Ramp_Down.html

it'd take about ~1959 s (more than half an hour) to go from 4600 A to 1300 A.   This is (4600-1300)/1959 ~ 1.7 A/s on average (faster a the beginning than at the end).

Our inductance is slightly less than BaBar's => 1.7 A/s =>  slightly faster than BaBar's 1.6 A/s on average.

So, I'd think that you should make the total cable resistor not more than 1.25 mOhm.   1 mOhm may be even better.   I guess we won't worry about
a few more minutes in "slow discharge"/ramp-down   but it's  good not to ramp down too fast.

Kin