From: Pawel Staszel (ufstasze@if.uj.edu.pl)
Date: Thu May 29 2003 - 15:18:16 EDT
Hi All, 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's right, however I introduced parametrizations olny for D3 and D4. Currently I updated my local brat with new D2 parametrization (I got measurement from Ramiro during my last stay at BNL) and will test the effect on the D2 - D3/D4 momentum correlation. We need the same for D1. Ramiro, please re-sent me your excel file with the measurement, so I can retrieve the values for D1 as well. (for D2 there is 1-2% deviation between new and the old parametrization - new D2 momenta are suspected to be lower by 1-2% as compare to the old D2 momenta). Regards Pawel. >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 > > > >
This archive was generated by hypermail 2.1.5 : Thu May 29 2003 - 09:17:01 EDT