meanwhile, us ODU guys (Rustam and myself) have also finished
remeasuring all wire tensions in Region 2 that are still accessible
(these are special sense type wires that are strung in lieu of the
pretension wires, i.e. they are located between the superlayers and
cover pretty much the whole length of our chambers). Here are the
results:
1) We found 1 bad connection (in Sector 3, but not in the region
where we know we have broken wires, so I assume it's a bad cable
leading from the wire to the outside).
2) We found a consistent increase in most wire tensions since the
last time we measured them (of about 20% average, which really means
most changed by 10 - 15 % and some by a lot more), EXCEPT for the
wires we've measured before with the CLAS field (sectors 6 and 1)!
I believe a similar result was found in Region 1, with most tensions
coming "back to normal" once you used a different magnet (?!?). This
seems to indicate that although the "2nd harmonic" method of measuring
tensions with the CLAS field works nicely in principle, it may give
too short periods (even after accounting for the factor of 2), or,
equivalently, too high tensions. My suspicion is that the stiffness
of the wires, plus the way they are not quite anchored at their end,
will give a somewhat unharmonic results which yields a 2nd "harmonic"
at a higher than expected frequency. This means: the wires "really"
didn't change in tension at all. This is indeed what we observe in
Sector 1 and 6, which we measured with the CLAS field before:
here, the changes are typically less than 5% and only 2% on
average (since February). Also, the shortest wires show consistently
the biggest change (up to 90% more tension!!!), which again argues
for an anharmonic effect (these poor guys have a really hard time
oscillating with TWO antinodes!).
3) Once I take this effect into account, it seems like no wire has
a tension that's off by more than 30% from its nominal value, except
in some cases the frontmost (short) wires look as if they've lost
up to 1/2 of their tension. This is, however, not reliable, since
both the measurement results and my "correction" are very doubtful
for these wires.
In summary: I believe that we have shown that the springs are doing
their job and the wires are overall in good shape tensionwise.
The systematic increase in measured tensions can most likely be
attributed to non-harmonic behaviour. The BAD news: this leaves us
at a loss to explain why we have broken wires - it's most likely
NOT due to overtension (so we can't take proactive steps by
lowering the tension). The GOOD news: maybe the rate of wires
breaking WILL eventually decline.
Respectfully -
--
- Sebastian
-----------------------
Phone: (757) 683-5804
FAX: (757) 683-5809
Email: kuhn@jlab.org
WWW: http://macsek.physics.odu.edu/