Minutes of HERA Meeting
25.11.2003
Radiation Safety (B.Racky)
- The neutron dosimeters were read out a few days after the proton beam
loss on 04.11.2003. Neutron doses of up to 2mSv were measured in the
North hall, up to 1mSv in the West hall. There was no high radiation
in the East and South halls.
- During the design of HERA doses of 0.5 to 2mSv were estimated for an
accidental proton loss. This was accepted by the authorities for
an event occurring with a very low probability.
- The radiation dose limit for the general public is 1mSv/y. It used
to be 5mSv/y.
- The following measures are being taken:
- The proton current is limited to 20mA. (The proton current before the
beam loss on 04.11.2003 was 60mA.)
- Repair of the proton quadrupole power supplies.
- Reduce the response time of the proton beam dump system to prevent
accidental beam losses.
- Establish controlled areas in the HERA halls, to be defined
individually for each hall.
- Before controlled areas can be established: No entry into the HERA
halls for visitors, persons under the age of 18, pregnant or
nursing women. No entry in HERA halls (detector level) for members
of contract companies, except ABB employees who have a special
permission.
- Later the normal DESY rules for controlled areas apply.
- Photon and neutron dosimeters are required for entry to the
controlled areas of the halls.
Neutron dosimeters were ordered. First delivery is expected
end of this week.
- The new rules will be translated into English.
- F.Willeke said that the BPM information will be implemented in the
proton beam abort this week, i.e. the beam will be dumped in case
of large orbit offsets. The BPM alarm was successfully tested a few
weeks ago. Work on a beam abort signal based on the current measurement
is in progress. The time estimate is about 6 weeks.
HERA
M.Bieler summarized HERA operation of last week.
- HERA delivered several luminosity fills with relatively low currents.
The proton current was limited to 20mA, the positron current to about 15mA
because of high temperatures of the proton beam pipe at absorber 4
SR11. The integrated luminosity was about 50nb-1/fill.
- The high temperatures of the proton beam pipe of absorber 4 SR11 are not
yet understood. The position of the temperatures sensors was changed
several times. An additional sensor was installed without contact to
the vacuum chamber. The suspicion was that it was heated up by
absorbed synchrotron radiation. Thermo-paper was installed and showed
similar temperatures as the sensors. The present beam dump limit of
65deg C was already reached at 12mA.
- Two sensors at the absorber NR11 were loose and mounted again with
steel band. The cable ties which had been used showed clear signs of
radiation damage. 2 sharp black line, about 1mm thick.
- This morning the GM magnet SR was moved by 0.5mm. The idea was protect
the proton beam pipe by changing the angle of the absorber.
- Tests performed in the lab, trying to create a leak by asymmetric heating
of the proton pipe flange, were discussed in the background task force
meeting on Friday. The design of the new absorber will be modified
to protect the beam pipe from synchrotron radiation.
- The maximum polarization achieved so far is 38%. Studies will continue.
H1
- After the regeneration of NEG pumps last week, the pressure in the
straight section decreased by a factor of 2. The pressure at the
IP has not improved significantly.
Last night the background conditions (chamber current) at Ie=12,Ip=20mA
was similar to the conditions before the leak.
The pressure NR11 is increasing slowly, could be an indication for a
small leak.
ZEUS
- Last night the background conditions (chamber current) were 40% better
than before. The maximum beam currents which can be tolerated are now
close to the design currents.
HERMES
- Took data at low positron currents. Sunday evening the background was
quite poor, both synchrotron radiation and particle background. It took
a couple of hours to improve the conditions.
Schedule
- Continue luminosity operation with 120 bunches. Try Ie=20mA.
- Check whether the temperature increase SR11 is less after moving the
GM magnet. The temperature limit will be set to 80deg C.
- Continue polarization tuning.
H1 is the coordinating experiment.
Uwe Schneekloth