X. Kong

Development of KSTAR ECE imaging system for measurement of temperature fluctuations and edge density fluctuations.

The ECE imaging (ECEI) diagnostic tested on the TEXTOR tokamak revealed the sawtooth reconnection physics in unprecedented detail, including the first observation of high-field-side crash and collective heat transport [H. K. Park, N. C. Luhmann, Jr., A. J. H. Donné et al., Phys. Rev. Lett. 96, 195003 (2006)]. An improved ECEI system capable of visualizing both high- and low-field sides simultaneously with considerably better spatial coverage has been developed for the KSTAR tokamak in order to capture the full picture of core MHD dynamics. Direct 2D imaging of other MHD phenomena such as tearing modes, edge localized modes, and even Alfvén eigenmodes is expected to be feasible. Use of ECE images of the optically thin edge region to recover 2D electron density changes during L/H mode transitions is also envisioned, providing powerful information about the underlying physics. The influence of density fluctuations on optically thin ECE is discussed.

Commissioning of electron cyclotron emission imaging instrument on the DIII-D tokamak and first data.

A new electron cyclotron emission imaging diagnostic has been commissioned on the DIII-D tokamak. Dual detector arrays provide simultaneous two-dimensional images of T(e) fluctuations over radially distinct and reconfigurable regions, each with both vertical and radial zoom capability. A total of 320 (20 vertical×16 radial) channels are available. First data from this diagnostic demonstrate the acquisition of coherent electron temperature fluctuations as low as 0.1% with excellent clarity and spatial resolution. Details of the diagnostic features and capabilities are presented.

The next generation of electron cyclotron emission imaging diagnostics (invited)

A 128 channel two-dimensional electron cyclotron emission imaging system collects time-resolved 16x8 images of T(e) profiles and fluctuations on the TEXTOR tokamak. Electron cyclotron emission imaging (ECEI) is undergoing significant changes which promise to revolutionize and extend its capabilities far beyond what has been achieved to date. These include the development of a minilens array configuration with increased sensitivity antennas, a new local oscillator pumping scheme, enhanced electron cyclotron resonance heating shielding, and a highly flexible optical design with vertical zoom capability. Horizontal zoom and spot size (rf bandwidth) capabilities are also being developed with new ECEI electronics. An interface module is under development to remotely control all key features of the new ECEI instrument, many of which can be changed during a plasma discharge for maximum flexibility.

Advancements in electron cyclotron emission imaging demonstrated by the TEXTOR ECEI diagnostic upgrade.

A new TEXTOR electron cyclotron emission imaging system has been developed and employed, providing a diagnostic with new features and enhanced capabilities when compared to the legacy system it replaces. Optical coupling to the plasma has been completely redesigned, making use of new minilens arrays for reduced optical aberration and providing the new feature of vertical zoom, whereby the vertical coverage is now remotely adjustable on a shot-by-shot basis from 20-35 cm. Other innovations, such as the implementation of stacked quasioptical planar notch filters, allow for the diagnostic to be operated without interruption or degradation in performance during electron cyclotron resonance heating. Successful commissioning of the new diagnostic and a demonstration of the improved capabilities are presented in this paper, along with a discussion of the new technologies employed.

Electron cyclotron emission imaging in tokamak plasmas

We discuss the recent history and latest developments of the electron cyclotron emission imaging diagnostic technique, wherein electron temperature is measured in magnetically confined plasmas with two-dimensional spatial resolution. The key enabling technologies for this technique are the large-aperture optical systems and the linear detector arrays sensitive to millimeter-wavelength radiation. We present the status and recent progress on existing instruments as well as new systems under development for future experiments. We also discuss data analysis techniques relevant to plasma imaging diagnostics and present recent temperature fluctuation results from the tokamak experiment for technology oriented research (TEXTOR).

Innovations in optical coupling of the KSTAR electron cyclotron emission imaging diagnostic

The installation of a new electron cyclotron emission imaging diagnostic for the Korea Superconducting Tokamak Advanced Research (KSTAR) is underway, making use of a unique optical port cassette design, which allows placement of refractive elements inside the cryostat region without adverse effects. The result is unprecedented window access for the implementation of a state of the art imaging diagnostic. A dual-array optical design has been developed, capable of simultaneously imaging the high and low field sides of the plasma with independent features of focal plane translation, vertical zoom, and radial channel spacing. The number of translating optics has been minimized by making use of a zoom lens triplet and parabolic plasma facing lens for maximum channel uniformity over a continuous vertical zoom range of 3:1. The simulated performance of this design is presented along with preliminary laboratory characterization data.

Miniature elliptical substrate lenses for millimeter-wave imaging

The use of an array of miniaturized elliptical substrate lenses or mini-lenses, combined with an array of printed antennas, is proposed for plasma imaging applications. Compared with its predecessor, the large hyper hemispherical lens, the new configuration demonstrates reduced sidelobe levels, minimal off-axis aberrations, increased RF bandwidth, and enhanced local oscillator coupling with substrate side LO illumination.

Recent advances in ECE imaging performance

ECE Imaging (ECEI) systems have been installed and are presently operating on the KSTAR, DIII-D, ASDEX-UG, and HT-7 tokamaks. All are inherently 2-D systems, collect-ing second harmonic ECE radiation to form temporally-resolved localized Te images. System resolutions range from 16 × 8 (HT-7 and ASDEX-UG) to 20 × 16 (DIII-D) to 24 × 16 (KSTAR), with a spatial resolution as low as 1.0 cm (vertical) by 0.9 cm (radial), and with video bandwidths up to 400 kHz. Noise and drift performance of ECEI systems installed on KSTAR and DIII-D were significantly improved in 2011 with new zero bias detectors. This higher level of performance has resulted in new physics advances as ECEI is employed to visualize high temperature plasmas from the plasma edge (pedestal region) through the plasma core, with examples presented herein. In addition to these systems, a new expanded view ECEI system has been developed for the EAST tokamak that produces 24 × 16 Te images from a single imaging array and which is currently being commissioned.

Antenna development for high field plasma imaging.

Electron cyclotron emission imaging (ECEI) and microwave imaging reflectometry (MIR) are two microwave nonperturbing plasma visualization techniques that employ millimeter-wave imaging arrays with lens-coupled planar antennas, yielding time-resolved images of temperature (via ECEI) and electron density (via MIR) fluctuations within high temperature magnetic fusion plasmas. A series of new planar antennas have been developed that extend this technology to frequencies as high as 220 GHz for use on high field plasma devices with toroidal fields in excess of 3 T. Antenna designs are presented together with theoretical calculations, simulations, and experimental measurements.

Dual array ECE imaging on the DIII-D tokamak

Advances in heterodyne receiver array technology coupled with a simplified optical design have resulted in significantly expanded plasma coverage and enhanced sensitivity, while simultaneously reducing the local oscillator power levels required to pump the imaging mixer arrays. Details of the next generation plasma imaging concept and its application on the DIII-D tokamak are discussed. Additionally, details of imaging technologies applied on the redesigned TEXTOR ECE imaging system are provided.