sPHENIX discussion of the superconducting solenoid

[Kin Yip <kinyip AT bnl.gov>]

Hi, Pasquale,

Thanks a lot !  I checked with Wes Craddock and from my probing, it also seems to me that BaBar didn't really do the kind of hysteresis that we talked about.  ( Wes sent me a BaBar paper, NIM A 432 (1999) 24-47, that they did demagnetization cycle for 200 A or something like that to try to minimize the fringe field to < 5 G or even 1 G. )

Kin

On 8/16/22 15:28, pasquale.fabbricatore wrote:

Kin,

I got the answer from CMS colleagues. Practically they do not make special magnetization cycle. 

Here the answer:

"For CMS we don’t perform magnetization cycles. The magnetic cycles mentioned for CMS are simply the ramps from zero to nominal field, and back to zero when the magnet is stopped (ramp down at fixed di/dt or resistive discharge). The ramp rate is defined according to the electrical characteristics of the circuit.

 

The yoke was first magnetized during the first magnet ramp in 2006, and we don’t expect to have any change in time (this is construction steel, so quite stable). The magnetic field mapping was also done in 2006, after the first ramp up-down cycle, and it is a reference input into the calculated CMS fieldmap model used for particle identifications.

 

We don’ want or plan to change the polarity or do any hysteresis  cycling over [-B;+B], with decreasing B to have demagnetization, despite it shall not affect the central field in the tracker region, but it may on the yoke end cap noses and in the rest of  the yoke (barrel and end cap) with the muon detectors"

That is all. In your case you could make magnetization cycle only after a long stop (months).

Pasquale 

Inviato dal mio Galaxy

-------- Messaggio originale --------

Da: "Yip, Kin" <kinyip AT bnl.gov>

Data: 12/08/22 15:42 (GMT+01:00)

A: "pasquale.fabbricatore" <pasquale.fabbricatore AT ge.infn.it>

Oggetto: RE: hysteresis

Thanks 😊  I can wait of course.  Any information will be useful.   ( We’ll try to figure it out ourselves during the mapping but

if you can share CMS information with us, it’ll be great ! )

 

Kin

 

From: pasquale.fabbricatore <pasquale.fabbricatore AT ge.infn.it>
Sent: Friday, August 12, 2022 9:21 AM
To: Yip, Kin <kinyip AT bnl.gov>
Subject: RE: hysteresis

 

Done! I will be waiting for an answer. Consider that in Europe this is a vacation time and the answer could come not soon.

 

Pasquale 

 

 

 

Inviato dal mio Galaxy

 

 

-------- Messaggio originale --------

Da: "Yip, Kin" <kinyip AT bnl.gov>

Data: 12/08/22 15:13 (GMT+01:00)

A: "pasquale.fabbricatore" <pasquale.fabbricatore AT ge.infn.it>

Oggetto: RE: hysteresis

 

Hi,

 

• Unfortunately I am not aware of the process used for Babar excitation. I could ask to some colleagues of CMS.

 

Thanks a lot !   Yes, if you can find out anything from CMS (about hysteresis or not), can you please let me know ??

 

Kin

 

From: pasquale.fabbricatore <pasquale.fabbricatore AT ge.infn.it>
Sent: Friday, August 12, 2022 9:09 AM
To: Yip, Kin <kinyip AT bnl.gov>
Subject: RE: hysteresis

 

Kin,

I think than you do not need to redo the hysteresis run after few hours or even a day at zero current. I image the iron keeps the residual magnetization for long time ( but I am not able to quantify). Unfortunately I am not aware of the process used for Babar excitation. I could ask to some colleagues of CMS.

 

Pasquale 

 

 

 

Inviato dal mio Galaxy

 

 

-------- Messaggio originale --------

Da: "Yip, Kin" <kinyip AT bnl.gov>

Data: 12/08/22 12:38 (GMT+01:00)

A: "pasquale.fabbricatore" <pasquale.fabbricatore AT ge.infn.it>

Oggetto: RE: hysteresis

 

Hi,

 

We will certainly ramp the magnet (up and down) more than once before we start mapping.

 

My question is whether we will need to do this hysteresis run (0 A to 4596 A and then 0 and then to 4596 A) EVERY time we ramp down the magnet to 0 A and rest for a few hours or a day (at 0 A) ?

 

Do you know whether BaBar did that or not (hysteresis) all the time ?  Or just at the beginning (in 1998) ?

 

Kin

 

 

 

-------- Original message --------

From: "pasquale.fabbricatore" <pasquale.fabbricatore AT ge.infn.it>

Date: 8/12/22 6:22 AM (GMT-05:00)

To: "Yip, Kin" <kinyip AT bnl.gov>

Subject: RE: hysteresis

 

Hi Kin.

 

I cannot remember we discussed about magnetic hysteresis. However, in general for yoked magnets it is good practice to make a first  magnetic field cycle before putting the magnet in operating conditions.

Have you planned magnetic measurements in the detector zone?

 

Cheers

Pasquale 

 

 

 

Inviato dal mio Galaxy

 

 

-------- Messaggio originale --------

Da: "Yip, Kin" <kinyip AT bnl.gov>

Data: 11/08/22 15:37 (GMT+01:00)

A: "Pasquale.Fabbricatore AT ge.infn.it" <pasquale.fabbricatore AT ge.infn.it>

Oggetto: RE: hysteresis

 

Hi,

 

When I said “hysteresis”, I meant “hysteresis loop”, i.e., running the magnet from 0 A to operating current (maybe a tiny bit higher) ,

going down to 0 A and then back to the operating current again.  People are worried that if you don’t do so, it may not be at its optimal

field ?!

 

Not sure whether it matters, we probably will ramp at ~1 A/s .

 

Kin

 

From: Yip, Kin
Sent: Thursday, August 11, 2022 9:22 AM
To: Pasquale.Fabbricatore AT ge.infn.it
Subject: hysteresis

 

Hi Pasquale,

 

I remember (but I couldn’t find any evidence) that you told us some years ago that this Magnet (BaBar -> sPHENIX) probably doesn’t require hysteresis.   Or does it ?

 

Can you please explain why you think this doesn’t require hysteresis (while other magnets do) ??

 

Kin