-some recent happenings-
Dave Tedeschi discovered that some Region 1 cables were
about 30 feet longer than the standard. This undoubtedly accounts for the
time shift seen for wires from STB 2 and 3 in Region 1 sector 6, which, by the
way, was present in early and late runs during the Feb. run. We can (and
will, automatically) correct for this difference in software as soon as
we analyse some pulse calibration data. Francois Roudot is working on
this analysis.
George Jacobs has discovered that the present MKS flow controllers which
we are presently using for mixing Argon and CO2 (into the high pressure
(140 psi) buffer) do not work if the differential pressure across them is
greater than 15 psi. He will buy 3 new mixing units which can take 140 psi
differential pressure. The two old units will be used to mix in a small
fraction of ethane or methane if we decide we need to. He is close to
having all gas flow from the gas shed to the chambers and back (no
recirculation yet).
Dan Carman has enlisted the help of "dedicated and caring" drift chamber
types and thanks to their efforts we have almost completed the cabling of
all of the drift chambers from STB to ADB to TDC. Thanks to all who
participated in the grungy but satisfying job. A few problems were uncovered:
- Region 1 is missing four signal cables (for sector 4)
- Reinhard Schumacher and our tech Christiana Martin discovered that the
Region 1 low voltage cable from the supply to the patch panel had connectors
which did not match the wire placement of those on the patch panel (they will
be remade in the next few days)
- despite efforts at strain-relieving cables, it is easy for cables to come
unplugged from the ADB input or from the TDC input as these are 96-channel
boards without locking connectors.
Francois Roudot and Richard Thompson are working on time-based tracking.
Here we give credit to Stepan Stepanyan who wrote the SimpleEventBuilder(SEB)
code which takes the track-layer bank (TRKL) information on track position
and track length as it passes through the outer detector layers. SEB then
returns track status (which track is an electron) and the event start time
(the time when the electron left the target). This allows us to calculate
the drift time and then the drift distance and so on to time-based tracking.
Francois and Richard are also implementing a bad wire list which can be used
by the track finding and fitting routines.
Liming Qin and Gail Dodge have been leading the effort to re-condition
the drift chambers as well as searching for bad HV connections and shorted
wires. Unfortunately, they have found some shorted (presumably broken) wires:
Reg.2 Sec.6 has 1 broken wire as does Reg. 2 Sec.3. They have also
found one broken wire in Reg.3 Sec. 3 (the only Reg. 3 sector which they have
checked so far). Bad news, but they're doing a good job in the checkout.
Liming and I made some progress in diagnosing and "fixing" the
"super hot wire" problem observed in Region 3 and Region 2. We found
that when we entered the "hot state" that we could turn the condition off
by actually RAISING the potential of one of the field wire busses.
This lowers the surface E field on field wires on the other bus. The
hyposthesis is that we have a massive cathode emission from one of the
field wires and that by lowering the surface electric field we turn this
emission off. We were able to turn some of the previously disconnected
sense wire busses back ON by disconnecting one of the field wire busses.
In several cases we have recovered sense wires. Note however, that their
field contours and isochrones will no longer be six-fold symmetric. We
will have to adjust the drift velocity function accordingly to reestablish
optimum resolution.
Amrit Yegneswaran and Peter Bonneau have been testing the CAEN HV crates
and boards. They have run a full gamut of tests including long-term
operability, tests of trip times, accuracy of output. With minor exceptions,
the system is performing very well. They are planning for installation
between May 26 and June 4.
Stan Majewski and the detector group will perform aging tests using some
small prototype chambers which Steve Christo built some time before for
this purpose.
that's some of the news from here,
regards, Mac