George F. Renda

Gas puff imaging of edge turbulence (invited)

The gas puff imaging (GPI) diagnostic can be used to study the turbulence present at the edge of magnetically confined plasmas. In this diagnostic the instantaneous two-dimensional (2D) radial vs poloidal structure of the turbulence is measured using fast-gated cameras and discrete fast chords. By imaging a controlled neutral gas puff, of typically helium or deuterium, the brightness and contrast of the turbulent emission fluctuations are increased and the structure can be measured independently of natural gas recycling. In addition, recent advances in ultrafast framing cameras allow the turbulence to be followed in time. The gas puff itself does not perturb the edge turbulence and the neutral gas does not introduce fluctuations in the emission that could possibly arise from a nonsmooth (turbulent) neutral gas puff. Results from neutral transport and atomic physics simulations using the DEGAS 2 code are discussed showing that the observed line emission is sensitive to modulations in both the electron density and the electron temperature. The GPI diagnostic implementation in the National Spherical Torus Experiment (NSTX) and Alcator C-Mod tokamak is presented together with example results from these two experiments.

Initial operation of the national spherical torus experiment fast tangential soft x-ray camera

Fast, two-dimensional, soft x-ray imaging is a powerful technique for the study of magnetohydrodynamic instabilities in tokamak plasmas. We have constructed an ultra-fast frame rate soft x-ray camera for the national spherical torus experiment (NSTX). It is based on a recently developed 64×64 pixel charge-coupled device (CCD) camera capable of capturing 300 frames at up to 500 000 frames per second. A pinhole aperture images the plasma soft x-ray emission (0.2–10 keV) onto a P47 scintillator deposited on a fiber-optic faceplate; the scintillator visible light output is detected and amplified by a demagnifying image intensifier and lens-coupled to the CCD chip. A selection of beryllium foils provides discrimination of low-energy emission. The system is installed on NSTX with a wide-angle tangential view of the plasma. Initial plasma data and an assessment of the system performance are presented.

Thermal Management of a Fast UV Slitless Spectrometer for a Meteor Research Experiment

This paper presents the proposed thermal management design for an ultra-violet slitless spectrometer to be flown on either the Space Shuttle or on the International Space Station as a scientific experiment to capture the ultraviolet spectrum of meteors as they are heated by the Earth’s atmosphere. The proposed telescope was initially planned as a Hitchhiker experiment for the Space Shuttle. The Space Station environment is thermally more critical than the Hitchhiker application. The final thermal design is essentially passive; however, heaters will be used to maintain the component temperatures at acceptable levels during telescope nonoperating conditions. The major difference between the Space Station design and the Hitchhiker design is the use of external multi-layer insulation and thermal strapping on the former application. This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.Copyright

Ultrahigh-frame CCD imagers

This paper describes the architecture, process technology, and performance of a family of high burst rate CCDs. These imagers employ high speed, low lag photo-detectors with local storage at each photo-detector to achieve image capture at rates greater than 106 frames per second. One imager has a 64 x 64 pixel array with 12 frames of storage. A second imager has a 80 x 160 array with 28 frames of storage, and the third imager has a 64 x 64 pixel array with 300 frames of storage. Application areas include capture of rapid mechanical motion, optical wavefront sensing, fluid cavitation research, combustion studies, plasma research and wind-tunnel-based gas dynamics research.

Initial Operation of the NSTX Fast Tangential Soft X-Ray Camera

Fast, two-dimensional, soft x-ray imaging is a powerful technique for the study of MHD instabilities in tokamak plasmas. We have constructed an ultra-fast frame rate soft x-ray camera for the National Spherical Torus Experiment. It is based on a recently developed 64 x 64 pixel CCD camera capable of capturing 300 frames at up to 500,000 frames per second. A pinhole aperture images the plasma soft x-ray emission (0.2-10 keV) onto a P47 scintillator deposited on a fiber-optic faceplate; the scintillator visible light output is detected and amplified by a demagnifying image intensifier and lens-coupled to the CCD chip. A selection of beryllium foils provides discrimination of low-energy emission. The system is installed on NSTX with a wide-angle tangential view of the plasma. Initial plasma data and an assessment of the system performance are presented.

High Speed Imaging of Edge Turbulence in NSTX

The two-dimensional radial versus poloidal structure and motion of edge turbulence in NSTX (National Spherical Torus Experiment) were measured by using high-speed imaging of the visible light emission from a localized neutral gas puff. Edge turbulence images are shown and analyzed for Ohmic, L-mode (low-confinement mode) and H-mode (high-confinement mode) plasma conditions. Typical edge turbulence poloidal correlation lengths as measured using this technique are = 4 {+-} 1 cm and autocorrelation times are 40 {+-} 20 {micro}sec in all three regimes. The relative fluctuation level is typically smaller in H-mode than in L-mode, and transitions from H- to L-mode and can occur remarkably quickly (=30 {micro}sec). The two-dimensional images often show localized regions of strong light emission which move both poloidally and radially through the observed region at a typical speed of =10{sup 5} cm/sec, and sometimes show spatially coherent modes.

Fast tangential soft x-ray camera for NSTX

X-ray imaging is an important diagnostic technique for studying magnetohydrodynamic (MHD) instabilities in tokamak plasmas. A tangential view brings two advantages: (a) it naturally leads to two-dimensional imaging and (b) simulations [ 13 have shown that tangential measurements can lead to better resolution and localization of the imaging if the lines of sight are arranged to be more parallel to the magnetic field lines in the plasma. A first tangential camera was built for the TEXTOR tokamak [2] and has been used on the LHD stellarator. [3] At the moment we are constructing a Fast Tangential Soft X-ray Camera (FTSXC) €OT the National Spherical Torus Experiment (NSTX) in Princeton. This paper provides a detailed description of the Princeton FTSXC.

Advanced laser sensing receiver concepts based on FPA technology

The ultimate performance of any remote sensor is ideally governed by the hardware signal-to-noise capability and allowed signal-averaging time. In real-world scenarios, this may not be realizable and the limiting factors may suggest the need for more advanced capabilities. Moving from passive to active remote sensors offers the advantage of control over the illumination source, the laser. Added capabilities may include polarization discrimination, instantaneous imaging, range resolution, simultaneous multi-spectral measurement, or coherent detection. However, most advanced detection technology has been engineered heavily towards the straightforward passive sensor requirements, measuring an integrated photon flux. The need for focal plane array technology designed specifically for laser sensing has been recognized for some time, but advances have only recently made the engineering possible. This paper will present a few concepts for laser sensing receiver architectures, the driving specifications behind those concepts, and test/modeling results of such designs.