Minutes of Meeting on Background and Radiation Monitoring 13.11.2000
____________________________________________________________________
Present: J.Stewart, J.Steijger, E.C.Aschenauer, G.v.d.Steenhoven, C.Niebuhr,
D.Pitzl, K.Ehret, J.Spengler, U.Koetz, W.Zeuner, U.Holm, D.Dannheim,
R.Carlin, T.Carli, W.Wierba, M.Bieler, F.Willeke, U.Schneekloth
Agenda
- Review of 2000 running - background and accumulated dose
- Short description of radiation monitor after HERA upgrade
- Beam abort trigger from experiments
- Status of HERA e beam abort system
- How can we prevent accidents during HERA re-start?
- AoB
- Date of next meeting
Presentations
ZEUS
Radiation Background, U.Holm ps file
Figures: FCAL gamma dose ps file , RCAL gamma dose ps file ,
FCAL neutron dose ps file , RCAL neutron dose ps file
MVD Radiation Monitor, R.Carlin ps file
HERMES
Beam loss monitor, J.Steijger ps file
H1
Dosimetry and Radiation Monitoring in H1 1996-2000, D.Pitzl
RPL and TLD type glass dosimeters were mounted on the central and backward
silicon strip detectors of H1, 4 positions in azimuth, integrating over
one running period:
CST BST BST
R=7cm R=6cm R=12cm
z=+25cm z=-38cm z=-38cm
1996 e+ 30- 40 Gy
1997 e+ 26- 57 Gy 24- 36 Gy
98/99 e- 120-245 Gy 100-400 Gy
99/00 e+ 23- 38 Gy 30- 50 Gy 6-7 Gy
CST CMOS chips at R=6 and 11cm will be replaced by rad.hard DMILL chips.
BST chips are at 12cm, non-rad hard, lifetime 500-1000 Gy.
The H1 silicon radiation monitor consists of 12 Si PIN diodes (3x3mm^2)
with charge sensitive preamps and line drivers mounted on BST and CST.
The DAQ is independent of the H1 central DAQ.
Pulses above threshold are counted, dynamic range is 0.1 Hz - 0.6 MHz, the
upper limit due to 1 us shaping time. Typical rates during lumi are 50 Hz
per diode, with several 100 Hz during injection and lumi tuning. Each
e-beam dump caused a short spike of several 10 kHz. Due to noise the
thresholds had to be set such that charged particles where seen (100 keV
deposit) but not X-rays from SynRad (peaking at 10-20 keV).
Beam dump alarm was given by the H1 shift to HERA after 2 minutes of 10
kHz summed rate. There were 5 dumps each in 1997 and 1998, 3 of them
fake due to noise, 2 real dumps in 1999 and none in 2000.
The high doses from e- running in 98/99 where not seen as high rates in
the Si diodes, which could be explained by soft X-rays below threshold.
Damage was seen in the inner layer of the CST but not in the outer and not
in the BST. The increase in leakage current in the Si sensors was small at
10% or less.
The Si RadMon will be used after the upgrade, with improved shielding and
cabling. The SynRad spectrum will be harder, peaking at 100 keV, where Si
is transparent. We intend to use 2 diodes of GaAs, which require 400V bias
instead of 25-40V for Si.
HERA B
Radiation dose in 2000, J.Spengler
During the running period 2000, the HERA-B target was operational 94% of
the available lumi-time (84 % in 1999). The integrated interaction rate
was 4.7*10**7 MHz s, which corresponds to about 12 % of the original
design luminosity which was 40 MHz for 10**7 sec. The corresponding number
for the year 1999 is 6.5*10**7 or 16.3 %.
At the exit window of the vertex vessel a dose of 206 Gy was measured
during the year 2000 at a distance of 35 mm from the proton beam axis.
This has to be compared to the expected rate of 80 kGy at a distance of 10
mm when operating the Silicon detectors at design rates. Taking into
account that the Si detectors saw about 10% of the design lumi, the
measured dose corresponds to 206 Gy * 10 * (35/10)**2 = 25 kGy, which is
in reasonable agreement with the expectations.
HERA
Status of the HERA Electron Beam Dump System, M.Bieler ps file
For the Hera electron beam dump three kicker magnets and one beam
absorber will be installed in the straight section west left.
The kicker magnets and the absorber are ready for installation,
the vacuum chambers will be brazed next week. The supports are
to be delivered this week. The pulsers for the kicker magnets are
available.
The trigger units (one in each HERA hall) are available, the software
is under way. A system test is planned in January 2001.
Beam dump trigger sources will be
-temperature sensors at S.R. absorbers and collimators
-electron rf trips
-one trigger signal from each experiment
-quench protection for GG and GO magnets
-a manual beam dump switch in the BKR
-the electron beam stopper (interlock system)
-the fast vacuum valve
-S.R. monitors
-trips of main magnets
-sudden drops in beam current
The beam dump system will be available for the startup of HERA.
HERA Startup, F.Willeke
HERA will startup with small beam currents, probably just 1 bunch with
10% of the nominal intensity. The plan is to check out the new optics,
new hardware components, including the new beam position and synchrotron
radiation monitors.
Colliding beams will start with 10 bunches, also at small intensities.
A bake out of the electron vacuum is foreseen. This will start with small
currents.
The hardware of the new electron beam dump will be ready at startup of the
machine.
HERMES is going to startup without the Si vertex detector. It will be installed
during a 3 day access.
The H1 FPS will not be equipped with fibers for the startup. Fibers will
be installed during the Christmas break.
The next meeting is planned before the restart of HERA.
Uwe Schneekloth