Design and implementation of a multichannel millimeter wave interferometer for the Compact Toroidal Hybrid experiment

M. C. Miller; J. D. Hanson; G. J. Hartwell; S. F. Knowlton; D. A. Maurer; B. A. Stevenson

doi:10.1063/1.4732056

Design and implementation of a multichannel millimeter wave interferometer for the Compact Toroidal Hybrid experiment

M. C. Miller, J. D. Hanson, G. J. Hartwell, S. F. Knowlton, D. A. Maurer, B. A. Stevenson

Research output: Contribution to journal › Article › peer-review

4 Scopus citations

Abstract

A three-channel 1mm wave interferometer has been designed, assembled, and installed on the Compact Toroidal Hybrid torsatron (CTH). The interferometer design makes novel use of a subharmonic mixer for detection, which simplifies alignment. It employs a single electronically tunable source that is repetitively chirped using a sawtooth waveform of frequency up to 1MHz. The 15.25GHz drive oscillator is multiplied in two stages to 122GHz before a final doubler stage brings it to 244GHz. Local oscillator (LO) power at 122GHz is directed through waveguide to the LO input of the subharmonic mixer of each viewing chord, simplifying alignment. Phase detection is performed by directly digitizing the amplified mixer outputs at 50MHz and processing them with a software algorithm. Initial measurements made with the central chord of the new interferometer agree with those from the existing 4mm system at low densities. The 1mm system performs well in current-driven discharges reaching densities over 10 ¹⁹ m ^-3, whereas the lower frequency interferometer is found to be less reliable due to loss of fringes. This is a critical improvement for experiments studying the onset, avoidance, and vacuum magnetic transform dependence of disruptions in the CTH device.

Original language	English
Article number	10E332
Journal	Review of Scientific Instruments
Volume	83
Issue number	10
DOIs	https://doi.org/10.1063/1.4732056
State	Published - Oct 2012
Externally published	Yes

Funding

Work supported by (U.S.) Department of Energy (DOE) Grant No. DE-FG02-00ER54610. The authors thank W. Peebles and D. Brower of UCLA for advice in interferometer design and also J.-T. Chen for his contributions.

Funders	Funder number
U.S. Department of Energy	DE-FG02-00ER54610

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title = "Design and implementation of a multichannel millimeter wave interferometer for the Compact Toroidal Hybrid experiment",

abstract = "A three-channel 1mm wave interferometer has been designed, assembled, and installed on the Compact Toroidal Hybrid torsatron (CTH). The interferometer design makes novel use of a subharmonic mixer for detection, which simplifies alignment. It employs a single electronically tunable source that is repetitively chirped using a sawtooth waveform of frequency up to 1MHz. The 15.25GHz drive oscillator is multiplied in two stages to 122GHz before a final doubler stage brings it to 244GHz. Local oscillator (LO) power at 122GHz is directed through waveguide to the LO input of the subharmonic mixer of each viewing chord, simplifying alignment. Phase detection is performed by directly digitizing the amplified mixer outputs at 50MHz and processing them with a software algorithm. Initial measurements made with the central chord of the new interferometer agree with those from the existing 4mm system at low densities. The 1mm system performs well in current-driven discharges reaching densities over 10 19 m -3, whereas the lower frequency interferometer is found to be less reliable due to loss of fringes. This is a critical improvement for experiments studying the onset, avoidance, and vacuum magnetic transform dependence of disruptions in the CTH device.",

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Design and implementation of a multichannel millimeter wave interferometer for the Compact Toroidal Hybrid experiment

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