From: Ramiro Debbe (debbe@sgs1.hirg.bnl.gov)
Date: Mon May 12 2003 - 13:34:47 EDT
If you are using the permanent Hall probe readouts without any further change you will not have the correct field value. The Hall probes are located right on the magnet poles and most on the time two to three gap heights into the magnet gap. At those locations they are sensing the saturation in the iron. That must be most of the deviation one can see in the plots. The value of By at high field deviates from a linear function of the current because of saturation and hopefully that is well described by the parametrisation in BRAT. The last measurements I did for all our magnets should give you the translation between permanent Hall probe readings and the value of the field in the middle of the gaps. For D4 I have two sets of measurements, one with the Hall probe in the old position, and a second one where the Hall probe was moved deeper into the magnet gap. (this last settings can be used for the dA and this last pp run and all future runs) Ramiro On Monday, May 12, 2003, at 12:21 PM, Claus O. E. Jorgensen wrote: > > Hi, > > I'm currently looking at the high field Au+Au runs and I'm having some > trouble at the edges of the acceptance - the data is not right on the > MC so I started looking at the magnetic field. Is it correct that we > still use the (2nd order) parametrization of the field? > > I've compared the field I get from BRAT and what has been measured (By) > with the Hall probe and there is a small discrepancy which I guess > would > effect the high field data the most. Have a look: > > www.nbi.dk/~ekman/fieldVsCurrent.gif > > Putting the numbers directly in BrMagnetVolume would be very easy, but > I > guess that's not good enough. Do we want to store this information in > the > DB? And what does it take? I think it's pretty important if we want to > make a good analysis of the high field data... > > Cheers, > > Claus > > +------------------------------------------------------------+ > | Claus E. Jørgensen Phone : (+45) 33 32 49 49 | > | Cand. Scient. (M. Sc.) Cell : (+45) 27 29 49 49 | > | Office : (+45) 35 32 54 04 | > | Niels Bohr Institute, Ta-2, Fax : (+45) 35 32 50 16 | > | Blegdamsvej 17, DK-2100, E-mail : ekman@nbi.dk | > | University of Copenhagen Home : www.nbi.dk/~ekman/ | > +------------------------------------------------------------+ >
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