Minutes of HERA Meeting
18.01.2005
HERA
F.Willeke summarized HERA operation of last week.
- Proton background spikes were the biggest problem during operation
last week. Operation was interrupted to work on power supplies,
a thyristor unit and exchange of a chopper.
- A GN magnet (normal conducting proton quadrupole NL23)
developed a ground fault on Wednesday. Operating the GN with
modified ground was not successful. After disconnection GN NL23,
the other GN magnets were operated over night to make sure that there
was no other problem.
- Preparations for replacing the magnet started on Friday: removal of
shielding in the west hall and installation of the HERA tram.
Special tooling was built on the weekend to allow removal of the
lower half without breaking the vacuum. The adjacent GN magnet
was opened, checked and closed again. All 4 coils of the
defective GN were replaced. The magnet will be reconnected today.
The plan is to remove the tram and reinstall the shielding in the
evening shift today. If everything goes as planned, machine
operation can resume tonight.
- The short is probably related to the damage of the GN NL20 in
October/November. During re-commissioning in October the GN magnets in
the north were operated at 1638A for an extended period of time.
A small instability in the cooling may have caused overheating and
damage.
During luminosity operation the current is 1500A for positrons,
slightly lower for electrons. The manufacture said that 1600A
should still be possible.
- There was a discussion whether the risk for another GN failure can
be reduced.
- Additional temperature sensors were installed.
- The magnet current would not be reduced, if the beam size
at the IP is increased. Reducing the proton beam energy would
lower the magnet current.
- The peak currents during the magnet cycling
procedure were already reduced.
- In principle, separate cooling
with lower water temperature should be possible, but needs large
cooling capacity. This will be discussed with MKK.
- The last spare coils were used. The removed coils will be examined.
New coils will be ordered.
Schedule
- Hopefully resume operation tomorrow. Startup with small
number of bunches. Continue luminosity operation with 120 bunches.
HERMES is the coordinating experiment.
Uwe Schneekloth