Speaker
Kirk Davis
(Jefferson Lab)
Description
Transient microphonic and Ponderomotive effects have been observed and measured
under a number of different operating conditions. Microphonic effects are those
sources that are external to the cryomodule, or by devices such as piezo tuners and
mechanical tuners. Ponderomotive effects are changes in frequency due to changes
in
rf field through the Lorentz force. This talk will give a brief summary of some of
these effects. Of particular interest is recovery from an arc in the region of the
cold window on a 5-cell CEBAF structure. Closed loop gradient control was employed
during arc recovery experiments conducted in the CEBAF accelerator at Jefferson
Lab.
During this test, instabilities were observed in the cavity forward power signal,
which were determined to be ponderomotive in nature. These ponderomotive effects
were quantified using a cavity resonance monitor and a VCO_PLL RF system. Two
types
of ponderomotive effects were observed depending on the type of arc event. If the
arc occurred in the vacuum space between the warm and cold windows, the transient
frequency shift was about 75 Hz peak-to-peak. If the arc occurred on the cavity
side
of the cold window the transient frequency shift was about 400 Hz peak-to-peak.
The
background microphonics level for the tested cavity was approximately 30 Hz peak-to-
peak. Other data relating to dynamic Lorentz force and piezo tuner transient
effects will also be presented. Experimental results, analysis of the resultant
klystron power transients, the decay time of the transients, and the implications
with respect to fast reset algorithms will be presented.
Author
Mr
Tom Powers
(Jefferson Lab)
Co-author
Kirk Davis
(Jefferson Lab)
