5 research outputs found
Plasma Cleaning of LCLS-II-HE verification cryomodule cavities
Plasma cleaning is a technique that can be applied in superconducting
radio-frequency (SRF) cavities in situ in cryomodules in order to decrease
their level of field emission. We developed the technique for the Linac
Coherent Light Source II (LCLS-II) cavities and we present in this paper the
full development and application of plasma processing to the LCLS-II High
Energy (HE) verification cryomodule (vCM). We validated our plasma processing
procedure on the vCM, fully processing four out of eight cavities of this CM,
demonstrating that cavities performance were preserved in terms of both
accelerating field and quality factor. Applying plasma processing to this
clean, record breaking cryomodule also showed that no contaminants were
introduced in the string, maintaining the vCM field emission-free up to the
maximum field reached by each cavity. We also found that plasma processing
eliminates multipacting (MP) induced quenches that are typically observed
frequently within the MP band field range. This suggests that plasma processing
could be employed in situ in CMs to mitigate both field emission and
multipacting, significantly decreasing the testing time of cryomodules, the
linac commissioning time and cost and increasing the accelerator reliability.Comment: 11 pages, 10 figure
A Photometric Survey for Variables and Transits in the Field of Praesepe with KELT
The Kilodegree Extremely Little Telescope (KELT) project is a small aperture,
wide-angle search for planetary transits of solar-type stars. In this paper, we
present the results of a commissioning campaign with the KELT telescope to
observe the open cluster Praesepe for 34 nights in early 2005. Lightcurves were
obtained for 69,337 stars, out of which we identify 58 long period variables
and 152 periodic variables. Sixteen of these are previously known as variable,
yielding 194 newly discovered variable stars for which we provide properties
and lightcurves. We also searched for planetary-like transits, finding four
transit candidates. Follow-up observations indicate that two of the candidates
are astrophysical false positives, with two candidates remaining as potential
planetary transits.Comment: 45 pages, 16 figures. Submitted to AJ. PDF version with full
resolution figures located at
http://www.astronomy.ohio-state.edu/~pepper/kelt.pd
A technique to actively reduce cryogenic pressure fluctuations
A device was designed and built to damp pressure fluctuations in a cryogenic system containing a superconducting radio frequency resonator cavity. The device uses an audio speaker to create pressure waves that travel into the system through an attached tube. The device was characterized in a few different configurations and many resulting trends were found. The device was operated in a range of 10 to 40 Hz and was able to create pressure fluctuations with amplitudes up to 2.09 Torr and resonant frequency shifts in the resonator cavity with a frequency oscillation amplitude of up to 30500 Hz depending on the configuration and settings used. The results indicated that the specific system and even the method of connection to a system had great effect on the frequency response of the device. The device was operated with a range of system pressure from 23.5 Torr to 1200 Torr, and the pressure was also shown to have an effect on the frequency response of the device