Optical emission spectroscopy as a noninvasive plasma diagnostic was employed to study mode transitions and hysteresis in an inductively coupled plasma in Ar and Ar/ N 2 mixtures. Using selected Ar lines, basic plasma parameters, relevant to the analysis of the mode transitions, were evaluated. Small changes of the electron energy distribution function in the vicinity of the mode transition were detected. The role of metastable Ar atoms in mode transitions and in a hysteresis was clarified. Enhanced production of metastables in the hysteresis region as well as faster transitions in plasmas with higher influence of metastables were observed.

Time-and-space resolved comparison of plasma expansion velocities in high-power diodes with velvet cathodes J. Appl. Phys. 113, 043307 (2013) Development of a diffuse air-argon plasma source using a dielectric-barrier discharge at atmospheric pressure Appl. Phys. Lett. 102, 033503 (2013) Nonmonotonic radial distribution of excited atoms in a positive column of pulsed direct currect discharges in helium Appl. Phys. Lett. 102, 034104 (2013) Iterative Boltzmann plot method for temperature and pressure determination in a xenon high pressure discharge lamp J. Appl. Phys. 113, 043303 (2013) Additional information on Rev. Sci. Instrum. Imaging bolometers utilize an infrared ͑IR͒ video camera to measure the change in temperature of a thin foil exposed to the plasma radiation, thereby avoiding the risks of conventional resistive bolometers related to electric cabling and vacuum feedthroughs in a reactor environment. A prototype of the IR imaging video bolometer ͑IRVB͒ has been installed and operated on the JT-60U tokamak demonstrating its applicability to a reactor environment and its ability to provide two-dimensional measurements of the radiation emissivity in a poloidal cross section. In this paper we review this development and present the first results of an upgraded version of this IRVB on JT-60U. This upgrade utilizes a state-of-the-art IR camera ͑FLIR/Indigo Phoenix-InSb͒ ͑3-5 m, 256ϫ 360 pixels, 345 Hz, 11 mK͒ mounted in a neutron/gamma/magnetic shield behind a 3.6 m IR periscope consisting of CaF 2 optics and an aluminum mirror. The IRVB foil is 7 cmϫ 9 cm ϫ 5 m tantalum. A noise equivalent power density of 300 W / cm 2 is achieved with 40ϫ 24 channels and a time response of 10 ms or 23 W / cm 2 for 16ϫ 12 channels and a time response of 33 ms, which is 30 times better than the previous version of the IRVB on JT-60U.

An overview of the research and development of imaging bolometers giving a perspective on the applicability of this diagnostic to a fusion reactor is presented. Traditionally the total power lost from a high temperature, magnetically confined plasma through radiation and neutral particles has been measured using one dimensional arrays of resistive bolometers. The large number of signal wires associated with these resistive bolometers poses hazards not only at the vacuum interface, but also in the loss of electrical contacts that has been observed in the presence of fusion reactor levels of neutron flux. Imaging bolometers, on the other hand, use the infrared radiation from the absorbing metal foil to transfer the signal through the vacuum interface and out from behind a neutron shield. Recently a prototype imaging bolometer known as the InfraRed imaging Video Bolometer has been deployed on the JT-60U tokamak which demonstrates the ability of this diagnostic to operate in a reactor environment. The application of computed tomography demonstrates the ability of one imaging bolometer with a semi-tangential view to produce images of the plasma emissivity. In addition, new detector foil development promises to strengthen the foil and increase the sensitivity by an order of magnitude.

No abstract

The object of the present paper is an infrared video bolometer with a bolometer foil consisting of two layers: the first layer is constructed of radiation absorbing blocks and the second layer is a thermal isolating base. The absorbing blocks made of a material with a high photon attenuation coefficient (gold) were spatially separated from each other while the base should be made of a material having high tensile strength and low thermal conductance (stainless steel). Such a foil has been manufactured in St. Petersburg and calibrated in NIFS using a vacuum test chamber and a laser beam as an incident power source. A finite element method (FEM) code was applied to simulate the thermal response of the foil. Simulation results are in good agreement with the experimental calibration data. The temperature response of the double layer foil is a factor of two higher than that of a single foil IR video bolometer using the same absorber material and thickness.