Minutes of the HERA Meeting 6.9.2005

1.
p spikes and the GA magnet circuit in the North:

The HERA loogbook from week 29, 24.07_M has a long history (in German).
In short: since 7.7. the 6 magnets in the GA group North were operated
from 2 supplies:
Das alte Netzgeraet mit dem Namen 'GA08 N' betreibt nun die rechte Seite
(I_max = 500 A) und heisst 'GA08 NR', das neu hinzugekommene Netzgeraet
(I_max = 1500 A) die linke Seite im Norden und heisst 'GA08 N'.

This went well until the night of 17./18.7. when GA08 NR30 (with the
'old' supply) started to cause spikes again.

On Mon 18.7. the power supplies for GA NL and GA NR magnet groups were
exchanged. The spikes remained with the 'old' GA supply.

On Wed 20.7. the background spikes became intolerable for H1 and ZEUS.

MKK had found a spare GA power supply and it was decided to install it
starting Thu 21.7. It was ready by Fri evening, but showed large
irregularities even at 40 GeV, such that no p beam could be stored.
Adjustment of the new supply continued on Sat 23.7. without success.
On Mon 24.7. the new supply was operated with a test magnet (Doris
dipole) in Hall North 6th floor and showed irregularities.
We have 3 GA supplies (500 A, 1200 V):
Mk506A/11 = original North
Mk506A/12 = South, no problems
Mk506A/13 = spare, faulty

On Mon 24.7. the electronics from /11 was installed in /12 South, which
then operated Mon night without apparent problems.

Today the electronics from /12 South is being installed in /11 North,
which will then be used to operate 3 magnets at NL.

In parallel, since Mon, the 6 magnets in the GA North circuit are being
tested individually with a BZ56 chopper supply.

Cable connections were exchanged and copper connection bars at the magnets
were inspected.

The cause of the GA spikes has not been found yet. Systematic studies
continue.


2.
A superconducting e RF cavity developed a vacuum leak on Sat 23.7. at 7:01
during acceleration of 42.5 mA e-. The getter pump at that cavity had been
suspicious since 2 weeks, showing unrealistically low currents.

On Mon the cryostat was warmed up for a leak search. The leak turned out
to be large (the cavity was vented to atmospheric pressure) and glueing is
unlikely to be successful.
On Tue it was decided to dismount the cryostat (with 2 cavities out of
16), and install a warm beam pipe instead. This would limit the e-
current to less than 45 mA and the warm RF sections have to be operated at
slightly higher voltage. Special loads and absorbers have to be installed
in the RF circuit. The cavity will then be repaired in the lab.
It is hoped that the work including shielding in Hall West can be finished
by Thu morning.


3.
It was decided that the regular maintenance day on Wed, Aug 3 will be
cancelled.


4.
ZEUS is coordinating experiment.

Daniel Pitzl, 26.7.2005