The time has come again for us to take action on resetting gains on
the phototubes in MACRO. Although we anticipate fewer tank-end
interventions than when this action was taken a year ago, there are
many tank ends where the gains on the two tubes in the end have
drifted too far apart for consistent slow monopole sensitivity. This
will require us to set gains for each tube separately in at least 30%
of tank ends and perhaps more. This will make the job take a bit
longer than just addressing tube pairs. Fortunately, we do have a
solid technical team to undertake this task.
I anticipate that the entire job will take on the order of 3 weeks
to complete (about 1 week per supermodule pair). As usual, frontend
electronic thresholds will likely need some adjustment following the
gain resetting. We propose to start the work shortly after the
Frascati collaboration meeting. We anticipate that only 2 supermodules
will be affected at a time. It may be of interest to combine some
other maintenance tasks on those supermodules at the same time. Please
let me and/or Erik and/or Alessandra know if you have other work that
should be coordinated during this period and whether there is any
particular problem with beginning this work in the time period which
we are suggesting.
Given the wide range of sensitivities which we attempt in MACRO, it is
important to keep the PMT gains within a fairly narrow range. Our
experience suggests that in order to do this, an intervention like we
propose is probably necessary about once every year.
Doug