title: Technical overview of the millimeter-wave imaging reflectometer on the DIII-D tokamak (invited).
abstract: The two-dimensional mm-wave imaging reflectometer (MIR) on DIII-D is a multi-faceted device for diagnosing electron density fluctuations in fusion plasmas. Its multi-channel, multi-frequency capabilities and high sensitivity permit visualization and quantitative diagnosis of density perturbations, including correlation length, wavenumber, mode propagation velocity, and dispersion. The two-dimensional capabilities of MIR are made possible with 12 vertically separated sightlines and four-frequency operation (corresponding to four radial channels). The 48-channel DIII-D MIR system has a tunable source that can be stepped in 500 μs increments over a range of 56 to 74 GHz. An innovative optical design keeps both on-axis and off-axis channels focused at the cutoff surface, permitting imaging over an extended poloidal region. The integrity of the MIR optical design is confirmed by comparing Gaussian beam calculations to laboratory measurements of the transmitter beam pattern and receiver antenna patterns. Measurements are presented during the density ramp of a plasma discharge to demonstrate unfocused and focused MIR signals.
authors.affiliation: Department of Electrical and Computer Engineering, University of California Davis, 347 Memorial Un, Davis, California 95616, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Muscatello
authors.affiliation: Department of Electrical and Computer Engineering, University of California Davis, 347 Memorial Un, Davis, California 95616, USA.
authors.forename: C W
authors.initials: CW
authors.lastname: Domier
authors.affiliation: Department of Electrical and Computer Engineering, University of California Davis, 347 Memorial Un, Davis, California 95616, USA.
authors.forename: X
authors.initials: X
authors.lastname: Hu
authors.affiliation: Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.
authors.forename: G J
authors.initials: GJ
authors.lastname: Kramer
authors.affiliation: Department of Electrical and Computer Engineering, University of California Davis, 347 Memorial Un, Davis, California 95616, USA.
authors.forename: N C
authors.initials: NC
authors.lastname: Luhmann
authors.affiliation: Department of Electrical and Computer Engineering, University of California Davis, 347 Memorial Un, Davis, California 95616, USA.
authors.forename: X
authors.initials: X
authors.lastname: Ren
authors.affiliation: Department of Electrical and Computer Engineering, University of California Davis, 347 Memorial Un, Davis, California 95616, USA.
authors.forename: P
authors.initials: P
authors.lastname: Riemenschneider
authors.affiliation: Department of Electrical and Computer Engineering, University of California Davis, 347 Memorial Un, Davis, California 95616, USA.
authors.forename: A
authors.initials: A
authors.lastname: Spear
authors.affiliation: Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Tobias
authors.affiliation: Department of Electrical and Computer Engineering, University of California Davis, 347 Memorial Un, Davis, California 95616, USA.
authors.forename: E
authors.initials: E
authors.lastname: Valeo
authors.affiliation: Department of Electrical and Computer Engineering, University of California Davis, 347 Memorial Un, Davis, California 95616, USA.
authors.forename: L
authors.initials: L
authors.lastname: Yu