F/RCAL High Voltage History
1992-2000
Introduction
Whenever the shell script save_hvfrcal is executed by the CAL shift crew, the nominal high voltage values for F/RCAL are written to the directory /data/calhv/hvnominal/frcal_old. I have collected all these files and written a program to put the data in an ntuple. The archived data used for analysis consist of 63 files dating from 23 July 1992 to 9 August 2000 (2939 days). High voltage settings from all phototubes are included, regardless of whether the channel was considered "bad" or not. Two paw macros have been developed: 1) HV versus day, and 2) cumulative gain change estimate.
High Voltage versus Time
The macro hvtower.kumac creates a postscript file exhibiting the history of the high voltage settings for each of the 12 (6) phototubes in the user-chosen FCAL (RCAL) tower. Examples of such plots are fcal12_tower11.ps and rcal12_tower11.ps . An index of the plots for all towers is available here . Postscript files containing the plots for all FCAL (21 Mb) and RCAL (11 Mb) towers are also available.
The two types of tubes (XP1911 for FEMC and R580 for all the rest) show strikingly different long-term behavior. The XP1911 high voltage settings actually decreased for about four years, hitting a broad minimum at about the time I first performed such a study, which was in June, 1996. (For historical interest, this news message can be seen here.) Since 1996 they have begun rising again, reaching levels in 2000 comparable to the settings in 1992. In contrast, the high voltage settings for the R580 phototubes show a steady rise of somewhat less than 10 volts per year over the entire period 1992-2000.
Cumulative Gain Changes
By making an approximation to the relationship between voltage and gain similar to the one used to trim the voltage settings, one can make a rough estimate of the gain changes over the period under study. The approximation used for these plots is dG/G = 7.5 dV/V. The status of such plots in November, 1996, when it appeared that the FEMC gains had actually increased by about 10%, can be seen here. One can conclude that today the FEMC gains are similar to their 1992 values and that the R580 tubes have decreased by about 40% of their 1992 values in general.
BCAL High Voltages
The BCAL high voltage settings are also saved, but the format is different (and unknown to me). I have included these archived files in the distribution, but no analysis exists for them yet.
The Distribution TAR File
The archived files, fortran program creating the ntuples, the ntuples, and the paw macros are available in a gzipped tar file. To use it, simply download the file (14 Mb) to a directory of your choice, then perform gunzip dist080101.tar.gz and tar xvf dist080101.tar . Two subdirectories will be created, named hvhistory (fortran code, makefile, paw macros, ntuples) and hvnominal (archived high voltage settings).
e-mail: James.Crittenden@desy.de J.A. Crittenden
8 January 2001