Hall-B Meeting : July 17, 2006 Mac Mestayer Problems in the CLAS Drift Chambers We’ve had a couple of problems: ~60 severe* / year 16 broken wires adb per yr. better now? ~ 10 lv per yr. worse now? * severe problems/ breakthroughs in elog

Hall-B Meeting : July 17, 2006 Mac Mestayer Broken Wires: CLAS Drift Chambers region sector r3: sec’s 2,3 worst

Hall-B Meeting : July 17, 2006 Mac Mestayer ADB Problems: CLAS Drift Chambers ADB problems power supplies outright failure voltage sagging  pulse shortening loss of hits

Hall-B Meeting : July 17, 2006 Mac Mestayer LV Problems: CLAS Drift Chambers After years: problems appeared on the STB boards fuses began shorting corrosion on the boards and on the SIP’s  doubled cables  replace SIP’S

Hall-B Meeting : July 17, 2006 Mac Mestayer New Kind of Wire Chamber Aging “ Those who do not learn from history are condemned to repeat it.” - Santayana “ -- and those who do learn from history will find new ways to screw up.” - Anonymous CLAS drift chambers –hexagonal wire layout; 90:10 Argon:CO 2 ; low gain ~ 2 X 10 4 Unusual aging observed: –no loss of gain –no extra noise hits but -- high voltage currents increase and stay high when beam is off High current episodes seem to be “ignited” high radiation H 2 O in gas catalyst? trapped species? episode

Hall-B Meeting : July 17, 2006 Mac Mestayer what we know : not a “Malter effect” –adding H 2 O hurts not a surface current: proportional to (Vs-Vf); not Vs, Vf alone current draw is “quiet” –not hits, no avalanche –negative ions are not electrons –~ linear current vs. voltage 5  A water vapor current

Hall-B Meeting : July 17, 2006 Mac Mestayer which molecules are reacting? H2OH2O O2O2 Ar N2N2 CO 2 H 2 O + CO 2  H 2 CO 3 ? + electric field  metal-carbonate + hydrogen gas?

Hall-B Meeting : July 17, 2006 Mac Mestayer Manpower to fix DC’s - Repair periods shown in yellow

Hall-B Meeting : July 17, 2006 Mac Mestayer Drift Chamber Calibrations track resolution –dc3 program: (t0, tmax, slope parms.)  caldb cook  trk_mon  dc3  caldb  re-cook  etc. semi-automated but still complex –further study: effect of wire sag, better functional forms –alignment: user_align, aligndc minimize “space” residuals from a set of tracks vary position, angle of one (R3) chamber new event selection cuts allows it to work for photon runs doesn’t always converge to “sensible” answer change to body-centered rotations?

Hall-B Meeting : July 17, 2006 Mac Mestayer r3sec2 - alignment history 1 mm  x vs. time  z vs. time

Hall-B Meeting : July 17, 2006 Mac Mestayer Drift Chamber Calibrations, cont. track efficiency –dead wire list - used in gpp improved to “sick wire” list further improved to correlated inefficiencies –further study: widespread use of correlated inefficiencies comprehensive track efficiency (without req. tof!)

Hall-B Meeting : July 17, 2006 Mac Mestayer CLAS Drift Chamber Operations large, complex systems on-call maintenance, repair, calibration good teams –on-call: Jacobs, Gram, McMullen, Insley, inst. group –DC “experts”: Bellis, (Lawrence, Qin, Klein, Carman, Mueller) –post-doc/students: Asavapibhop, Feuerbach, Morrow, Klimenko, many others steep learning curve  longer tenures for students/post-docs  sharing between run-groups ?