The ORNL/ASDEX upgrade RF breakdown tester: Results and plans

Baity, F. W.; Barber, G. C.; Goulding, R. H.; Swain, D. W.; Bobkov, V.; Noterdaeme, J.‐M.

doi:10.1063/1.1424242

Cited by 5 publications

(3 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…After a preliminary study which demonstrated the potential of the method for this particular application, in 2011 an experimental campaign was conducted in the Manipulator eXPeriment (MXP) testbed [2,3] installed at IPP, Garching, Germany . In this experiment, the modulated signal (carrier frequency = 25MHz) was up-shifted to 400 MHz and then injected into the IC line through a commercial directional coupler.…”

Section: Previous Experiencementioning

confidence: 99%

Guided radar system for arc detection: Initial results at DIIID

Salvador

Maggiora

Goulding

et al. 2014

AIP Conference Proceedings

View full text Add to dashboard Cite

A guided radar arc detection and localization system has been designed, fabricated, installed in the feed line to one of the resonant loops on the 285/300 FW antenna, and successfully tested during vacuum conditioning. The system injects a train of binary phase-modulated pulses at a carrier frequency of 25 MHz up-shifted to around 450MHz into the main high power transmission line connected to the antenna through a septate coupler and a circulator. The pulses are reflected by arcs, and the time delay provides the distance to the arc. The reflected signals are analyzed in real time, with a time response sufficient to provide active arc detection as well as localization. RF pulses have been injected into the antenna at a power level of up to 650kW. The arc location was varied by either puffing gas into the vacuum vessel, in which case arcs always occurred in the antenna, or injecting RF without a gas puff, in which case the arcs almost always occurred in the transmission line feeding the antenna. The localization obtained during these initial tests had a relatively low resolution of about 2 m, but arcs occurring inside or outside the antenna could clearly be differentiated and corresponded with the expected location. The septate coupler proved fully compatible with the antenna feed and matching network and improved performance significantly in comparison to the use of directional couplers.

show abstract

Section: Previous Experiencementioning

confidence: 99%

Guided radar system for arc detection: Initial results at DIIID

Salvador

Maggiora

Goulding

et al. 2014

AIP Conference Proceedings

View full text Add to dashboard Cite

show abstract

“…In practice, antennas can often withstand 50 kV in vacuum conditions, but reductions of 30% to 50% are common when exposed to plasmas and magnetic fields during machine operations. [1,2] RF breakdown has been studied in the past on RF test stands under high voltage conditions [3,4] and multipactor conditions [5]. Breakdown can be initiated by electrons emitted from the antenna surfaces and from the formation of a plasma in the gap between surfaces.…”

Section: Introductionmentioning

confidence: 99%

Study of RF Breakdown Mechanisms Relevant to an ICH Antenna Environment

Caughman

Giraldo

Aghazarian

et al. 2007

AIP Conference Proceedings

Self Cite

View full text Add to dashboard Cite

The mechanisms that contribute to RF breakdown/arcing in an antenna environment are being studied. RF breakdown/arcing is a major power-limiting factor in antenna systems used for RF heating and current drive in fusion experiments. The factors that contribute to breakdown include gas pressure, gas type, magnetic field, materials, ultraviolet light, and local plasma density. The effects of these factors on RF breakdown are being studied in a resonant 1/4-wavelength section of vacuum transmission line terminated with an open circuit electrode structure. The electrode structure is designed to determine the role of the RF electric field strength and magnetic field orientation on the breakdown process. Changes in the electrical parameters, such as input impedance and the voltage at the electrodes, are being monitored to detect the breakdown events. Measurements of the light emission prior to and during an arc are also being made. For high vacuum conditions using copper electrodes, bright spots appear on the electrode surfaces prior to a breakdown event. An increase in the RF field results in an arc and a flash of light corresponding to copper line emission (578.2 or 521.8 nm). Analysis of the electrode surfaces show large areas of melting and formation of micron-sized rounded protrusions, especially along the sharp edges of small scratches. An increase in the chamber pressure results in a decrease in the maximum RF electric field that can be sustained without breakdown as the pressure approaches a few mTorr. The breakdown event leads to formation of a plasma in the structure, with light emission corresponding to the particular gas being used. The addition of an external magnetic field causes the formation of a plasma at lower pressures, thus limiting the amount of coupled RF power. The presence of UV light has been found to initiate multipactor under some operating conditions.

show abstract

“…By operating the two new antennas [5] at 80 MHz, and the older antenna [6] at 60 MHz, these spectra peak at certain fixed phase velocities suitable for matching on the average to the desired fast magnetosonic wave phase velocities in present DIII-D plasma. However, higher frequencies or arbitrary phase tunability will be needed to match to future higher temperature plasmas.…”

Section: Introductionmentioning

confidence: 99%