The correlation between drift velocities in TPM2 as measured with tracks and fibers and the values read with DVMs was done by JH. I am a promoter of the use of the DVMs and I'm trying to fill the database with as much information as possible but my ignorance of our software tools makes me very slow. We stored the values obtained from the especial DVM runs in the ConditonsDVM table of the runs database. What I'm trying to do is to analyse the data from trigger 7 events included in all data runs. I have a macro to run within bratroot but I have to learn how to access the data stored in HPSS. When I look at the differential pressure across C1 windows I see a correlation with the drift velocity. It is not a one to one correlation but the big features do track. In a simple formulation of how electrons drift in a gas, atmopheric pressure does affect the average velocity of electrons thru their mean free path or mean time between collitions (the density of targets changes with pressure). At this moment the DVMs are not measuring the absolute value of the velocity because we use nominal values for the separation of the slits. There may be other parameters that are not well understood, in particular, DVM3 (T1) reads a value way below the other detectors. I did not have enough time to debug it when I replaced the counter. During the shut down I plan to look at these detectors more closely. Again, as JH showed, the DVM do measure the changes in drift velocity as a function of time. Their information is already in the database just waiting to be used. Ramiro On Fri, 14 Dec 2001, it was written: > Let me add a comment to this. > > Ramiro has very recently shown there is a correlation between the Vdrift > and the TPM1/2 best values (as also indicated in the mail below). Since he > has also shown the that output > DVM for ALL 4 tpcs correlate it is a safe bet to assume that Vdrift also > varies for T1 and T2. It would be > very good to get a confirmation of this from the FS data analysis > > ------------------------------------------------------ > Flemming Videbaek > Physics Department > Brookhaven National Laboratory > > tlf: 631-344-4106 > fax 631-344-1334 > > the physics runs since there is a vertical focusing effect due to the > > magnetic > > field. But one of the possibilities is that we use TPM2 Fiber information > > in > > zero-field runs, and comapare the measured positions of TPM1 tracks in the > > Fibers with the DVM values to get a scale factor (hopefully it's a > > constant). > > Then it's just drift velocity = DVM value*scale factor. > > Here is a y distribution of the TPM1 tracks projected to the Fibers on the > > front of TPM2 for the run 5823 (D5=0). The measured distances (integrated > > over x) between two Fibers are consistent with the physical separations > (2 > > cm) > > for this run, > > > > Fiber2-Fiber3 = 2.305-0.315 = 1.99 cm > > Fiber3-Fiber4 = 0.315+1.73 = 2.045 cm > > Fiber4-Fiber5 = -1.73+3.74 = 2.01 cm, > > > > which means that the TPM1 drift velocity we used (1.7) is correct for this > > particular run. I'm looking at some more Fiber data from zero-field > > runs, which we don't have much, with DVM values to see if we can > > just scale them with a constant factor. > > > > JH > > >
This archive was generated by hypermail 2b30 : Sat Dec 15 2001 - 10:32:57 EST