The oscillating voltage on the longitudinal holding field supply appears
to be a readout problem. Measured at the supply the voltage and current
are quite steady. This was verified by AC and RJA
- TZ
Karen Dow wrote:
>
> DAQ and Trigger (Karen) --
>
> Missing ep and en coincidence events from yesterday (including
> empty target runs) was solved. Right sector paired TOFs were always
> TRUE going into MLU. In diagnosing this, had to disconnect a number
> of cables. After reconnecting everything, the problem was gone
> (although all the cables had appeared properly seated to begin with).
>
> A logic error was introduced into the trigger settings on 2/25/04
> by Karen, when attempting to remove the logic that said "electron is
> TOF AND Cerenkov or TOF AND neutron". Instead, since then a sector
> hit has been "TOF AND Cerenkov AND maybe neutron" OR "TOF AND no
> Cerenkov and no neutron". This is a problem anywhere we have neutron
> detectors behind the TOFs (most of the right sector, and the back left
> sector). Effectively we have been discriminating against pions in
> those regions, also against higher energy protons or deuterons that
> don't get stopped in the TOFs. For electrons, we have essentially
> been requiring the Cerenkov in the trigger except where the TOF and
> neutron bar acceptances don't match. This explains the high R
> Cerenkov efficiencies seen after adding L shielding on 2/24. It also
> might explain the low electron cross section at forward angles in the
> Right sector, if the RC0 efficiency is low. The error should not
> cause any asymmetries. Karen will fix it today.
>
> Vitaliy notes many events in the upstream end of the Ohio walls
> for the en trigger. Suspect this end is not covered by the TOF, so
> you can't use the TOF as a veto there in the hardware trigger.
>
> Our deadtime comes from several sources. It takes 800usec to read
> out an event. We do NOT use the buffering feature in the ADCs and
> TDCs, so we have a deadtime that is linear with event rate. There is
> also a non-linear part as the rate increases, and the probability of
> getting a second event in that 800usec goes up. We could experiment
> with buffering during the spring shutdown; you want to be careful that
> your event fragments match up. Finally, there is the wall we hit due
> to the Ethernet bandwidth (at about 340 events/sec). That wall can be
> moved to higher rates by introducing ADC readout thresholds, or by
> buying new PowerPC readout controllers.
>
>
> ABS (Genya) --
>
> On 3/22, found that the top half of the transverse holding field
> coil was shorted out. This explains the measured tensor asymmetries
> over the past 10 days. The measured transverse and longitudinal
> fields aren't balanced now, but the probe isn't in the ideal location.
>
> Genya is away 3/26-3/29. Vitaliy is the target expert for that
> period.
>
> The intensity is down 20% since the nozzle warmup. It has been
> taking longer after each warmup to regain intensity. This is a sign
> the nozzle should be replaced; will happen 3/30 when we're open to
> fill the solenoids. At least a full day job.
>
> The tensor elastic asymmetry from overnight is nearly consistent
> with zero (-2 +-4 and 6+-4, should be +12 and +30%). Vector qe looks
> fine. Could the tensor - state really be vector? Some checks will be
> made today. We may try pure longitudinal spin again.
>
> Quasielastic tensor statistics are still limited, can't say
> anything about the asymmetry there (Vitaliy).
>
> Neutron Bars (Michael via email) --
>
> The time calibration macros are almost final, also the macros to
> find the TDC offsets. Eugene, Sebastian, Vitaliy and Michael are
> working on this. All timing parameters are collected in blast.sc_cal,
> to be used when crunching.
>
> The timing walk has been measured on all LADS except the 15cm
> "right" wall. Ohio also still needs to be done. The technique varies
> the flasher input to the splitter boxes, and Ohio&L15R are in the top
> box with the photodiode. Varying the input means the photodiode
> doesn't fire the trigger. Will work on that next Tuesday during the
> regular hall access.
>
> Also next Tuesday, will try the RC circuit to get rid of the
> ringing in the phototube pulse that makes the time walk correction
> discontinuous.
>
>
> Cerenkov (Baris) --
>
> RC0 ADC looks narrow, seems to be a lower than expected number of
> photoelectrons in that box.
>
> One possibly bad tube (LC1 top?) to diagnose and replace next
> Tuesday.
>
>
> Beam (Shannon, Townsend) --
>
> Tried a lower injection rate last night for the fill (2Hz). Fills
> slower (10 seconds more) but better injection efficiency (by a factor
> of 2). No effect on detector rates, but may be better for wire
> chambers since more beam gets into the ring instead of being splashed
> around.
>
> If the beam tune didn't have to satisfy the Compton, BQM rates
> could be a factor of 3 lower with the slits out. When we are done
> changing the transverse holding field, Ops needs 1 day to tune best beam.
>
> Longitudinal holding field voltage is oscillating +-10% since
> yesterday. Townsend will investigate.
>
> Compton (Bill) --
>
> Circular light polarization correction is bigger than though
> (Pockels Cell is damaged). Electron polarization is a few % bigger
> than reported, closer to agreement with the transmission polarimeter
> at the front end (75% yesterday). Adjusted transmission of laser
> light yesterday so that only central part sees the electron beam,
> polarization is 99+%. During shutdown, will replace the Pockels Cell.
>
> The beam tune to satisfy Compton and BLAST makes compromises in
> the vertical steering (compensation for the transverse holding
> field). Perhaps adding steering coils will help; Townsend and Shannon
> will look into that.
>
>
> General --
>
> Collaboration meeting 4/2.
>
> Analysis meeting 4/1? Some outstanding analysis issues:
>
> 1) Tosca for Cerenkov shielding (Vitaliy)
> 2) Beam energy reconstruction -- do we get the beam energy? Same in L
> and R?
> 3) Resolution?
>
>
>
>
> Karen
>
>
>
>
This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:30 EST