Good beam and data taking, then vacuum problems, then blast power
supply trips.
_ Got beam at 19.40, injection ca. 100 mA
_ Quick rate check, bckg rates nicely consistent with previous shifts. No
marked improvement due to added polyethillene neutron shield
_ Running a more open trigger: tof#10-15 in coinc with 0-5 of opposite
sector
_ Took out all delays of 4518 LTOFdel,RTOFdel, made all 1 ns (doesn't
affect the trigger timing since the TS is strobed)
_ Rates (with slits on, no field) ca 1.25 Hz/mA on empty. Rate w/ 1 SCCM
of H2 is 5-6 Hz/mA !!
_ Took plenty of data, also with any_coincs trigger (tof 0-15)
_ Have to settle to 80 mA injection current
_ Coda running well up to 300 KB/s and 600 Hz of triggers. Max limit
from ROC network interface is 1 MB/s. Coda would still occasionally
sleep but kicks back in. Never a need to reboot crates.
_ Investigated this issue, maybe related to "ROC has not reported status"
warning message. The Jlab code appears buggy so this monitoring useless
buggy (thanks Taylan). Tried to suppress it from run_control but probably
did not help
_ Field on at 5000 A, rates on empty target ca. 0.7 Hz/mA (consistent!)
However injection current is poor (35 mA) at best
_ Take empty runs with field on
_ Start gas flow 1 SCCM, VACUMM TRIP... Again the exhaust to the
IT roughing pumps were clogged. Wait for tech in. Vacuum ok at 00.30
_ Get beam with field on, first fill is 90 mA (!). Ligit baseline pressure
is 1x10-8. Background rate on empty is 0.3 Hz/mA, lifetime is 7.2 m at
70 mA with slits in
_ Only noticeable difference is that the beam stacks quite slowly.
_ Taking coinc data with field on, target 1 sccm, rate with gas is 0.6
Hz/mA, lifetime is 5.8 m at 50 mA with slits in. Switched trigger to
any coinc, rate goes up a factor of 3 (2.0 Hz/mA). Injection with
gas and field on, 60 mA and very slow
_ Note that with same gas (but bad chamber vacuum) and field off the
any_coinc trigger rate was up to 40 Hz/mA from 6 (restricted trigger)
_ Got about 20,000 good events in run 1136. Then the blast power supply
TRIPS and the night is over. Effect of trip on beam is none, however
rates went up high
regards,
tancredi
________________________________________________________________________________
Tancredi Botto, phone: +1-617-253-9204 fax: +1-617-253-9599
research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
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