From: Ian Bearden (bearden@nbi.dk)
Date: Mon May 19 2003 - 10:02:15 EDT
Do I remember correctly that the map measurements were made using data only up to roughly 1/2 the maximum field? If so, I guess we need to remap (in particular D4) the FS magnets for the high field. But maybe this has already been done well enough? I agree that we should discuss this 'face-to-face'...who will present what? We (where we probably is Claus?) can look into the data, but we do not have the maps, AFAIK. I think it might be nice to kill this issue once and for all (if that is possible). Cheers, Ian On mandag, maj 19, 2003, at 15:48 Europe/Copenhagen, Flemming Videbaek wrote: > Dear Claus, > > I will ask Ramiro to correct me if I am wrong,. My understanding of > this is > > a) The parametrization in Brat comes from a measurement of the > currents vs the central By ie. > on the mid-plane in the magnet. > b) The Hall probe field does NOT measure the central By, but only in a > fringe region which has a different > satuation effect. > c) The Brat parametrization comes from the current, and the final > values was worked out by Pawel as I recall. > > That there aresome effects at high field is certainly true, and the > saturation at edges indicates this. > The assumption in the reconstruction is of course that the effective > edge is good i.e. that the central > measured Bdl can be appiled for all (relevant) paths through the > magnet. This is probably not true, in particular for D4, > with the dispersed coils; The way to study these effects is as has at > least been mentioned a couple of times over the > years to , implement a realistic field map e.g. from the Tosca > calculations in BRAG and reconstruct with the effective > edge to see how important this is. > > I would object at this point to change the parametrization since the > By of the Hall probes is not the > proper central field. I suggest we have one discussion session at > krakow on this issue > - Pawel can (re) tell the story how the fits were done. > - we can have the field map's and data at hand, and talked how to > proceed. > > > > Flemming > > ------------------------------------------------------ > Flemming Videbaek > Physics Department > Brookhaven National Laboratory > > tlf: 631-344-4106 > fax 631-344-1334 > e-mail: videbaek@bnl.gov > > > | > | Hi Ramiro, > | > | After a busy week I've looked at the fields again, and I think the > | parametrization in BRAT is not right on the data. > | > | > 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 plots (www.nbi.dk/~ekman/fieldVsCurrent.gif) shows that the > measured > | By and the parametrization in BRAT (solid lines) differs sligthly at > the > | high fields. It's clear that a 2nd degree pol cannot reproduce the > | saturation effect that the Hall probes show, so the question is if > we want > | to put the numbers in the DB (I can see that Kris started this > project > | some time ago) or maybe we could just use a 3rd degree pol in BRAT? > | > | If there are no objections I would like to change the > parametrization, > | and then we can always put the numbers in the DB later. I just want > to be > | sure that the By values I got are the right ones. Could you please > send > | me tables with the latest and greatest measurements? > | > | Cheers, > | > | Claus > >
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