hera_minutes_050616.html

F.Willeke reported on the experience with mirror tunes (transparencies )

HERA switched to mirror tunes May 25. After some machine studies luminosity operation with mirror tunes and polarization tune-up started June 2.
The specific luminosity is about 10% lower than for operation with regular tunes. Last week the average specific luminosity was 1.6 10 ^30 cm-2 s-1 mA-2 compared to 1.8 10^30 in May. High specific luminosity and large polarization seems to be anti-correlated. The strong decay during a fill can be reduced by going to extreme tunes.
The maximum polarization achieved so far is 43%. The specific luminosity was however low (1.0 10^30 cm-2 s-1 mA-2). Polarization tuning is still in progress.
There are no indications for increased background conditions for operation with mirror tunes.
The most recent experience is encouraging. Good polarization (40%) was obtained a few days ago with high horizontal and low vertical tunes. The present fill has 36% polarization with reasonable specific luminosity (1.6 10^30).
Optimization of polarization and luminosity is not yet completed. F.Willeke proposed to continue operation with mirror tunes until the August maintenance day and to switch back to nominal tunes if polarization is not significantly larger with high luminosity.

Additional information on the polarization studies was provided by M.Vogt, see transparencies (not shown in the meeting).

R.Carlin estimated the polarization weighted integrated luminosity (transparencies)

The integrated luminosity was estimated making some reasonable assumptions on the beam parameters with and without mirror tunes. The result is a 20% reduction of integrated luminosity for the present situation.
Using the same model the luminosity averaged polarization increases from 25 to 43%.
A 10% loss of luminosity would be acceptable if the average polarization is 40 instead of 25%.

A fast rise and high polarization is important for HERMES. Part of the physics program cannot be done with 30% polarization.
HERA should continue operation with mirror tunes.

D.Pitzl transparencies ( 1, 2)

Specific luminosities of 2.0 10^30 cm-2 s-1 mA-2 were routinely optained in May. Presently, the specific luminosity is lower and shows a faster decay during the fill. The run averaged specific luminosity is reduced by 17% (21% for the last 5 days).
The priority for H1 is high luminosity. HERA should now return to the nominal working point, unless the luminosity can be increased soon.

The luminosity weighted polarization is important for the experiments, i.e. a fast rise is as important as the final polarization. HERA should demonstrate that large polarization can be achieved early in the fill with good specific luminosity and acceptable background conditions.
A 10% loss of integrated luminosity would probably be acceptable for the collider experiments if the luminosity weighted polarization is significantly increased.

Continue operation with mirror tunes until the July maintenance day.
Continue optimization of polarization and specific luminosity. In particular, try to obtain high polarization at the beginning of a fill.
Re-discuss the situation in early July.

Uwe Schneekloth