Observation of divertor and core radiation in JT-60U by means of bolometric imaging

Peterson, B. J.*; Konoshima, Shigeru; Parchamy, H.*; Kaneko, Masashi*; Omori, Toshimichi*; Seo, D. C.*; Ashikawa, Naoko*; Sukegawa, Atsuhiko; JT-60 Team

Journal of Nuclear Materials, 363-365, p.412 - 415, 2007/06

https://doi.org/10.1016/j.jnucmat.2007.01.090

Diagnosis of the radiation from both the divertor and core plasma regions is a key issue for the study of impurities resulting from plasma-surface interaction in existing magnetic plasma confinement experiments and future fusion reactors. An infrared imaging video bolometer has been designed, fabricated and installed on the JT-60U tokamak. This diagnostic utilizes an IR camera to image the temperature change of a thin foil which is exposed to plasma radiation through an aperture resulting in an image of the incident plasma radiation absorbed by the foil. In the 2004-2005 experimental campaign intitial data was taken which was limited to 8-bit analog video data from ohmic and hydrogen neutral beam discharges due to inadequate shielding. The semitangential, wide-angle view of the plasma covers the entire poloidal cross-section and the divertor extending over 90 degrees toroidally. This preliminary data showed a strong radiation zone from the divertor that moved up into the core plasma as the discharge terminated in agreement with the data from the resistive bolometer arrays. For the current campaign we have upgraded the system by improving the shielding against neutrons, and magnetic field. This has enabled operation of the camera during high magnetic field and some high power deuterium neutral beam discharges. We also improved the triggering and data transmission system to acquire 14-bit digital data. This will allow processing of the IR camera data to produce images of the radiation brightness at the foil which can be viewed as a movie with a frame rate of 30 fps. This data is used to study the toroidal uniformity of the radiation from the divertor in JT-60U.

Imaging bolometer development for application to fusion reactor diagnostics

Peterson, B. J.*; Alekseyev, A. G.*; Konoshima, Shigeru; Ashikawa, Naoko*; Parchamy, H.*; Sasao, Mamiko*; Miura, Yukitoshi

no journal, , 

The imaging bolometer concept is based on a thin foil which absorbs the broad-band radiation and/or energetic particles from the plasma. The resulting temperature change in the foil is measured by an infrared camera located outside the vacuum vessel. Development of imaging bolometers is being carried out for application in bolometry and lost alpha diagnosis for fusion reactors. In the case of an imaging bolometer, placing the foil behind a pinhole camera provides a two-dimensional image of the plasma radiation. In the case of a lost alpha diagnostic the foil is placed behind multiple layers of thin foils with one dimension being used for energy discrimination and the other layer being used for pitch angle discrimination. The work described includes the operation of imaging bolometers on the Large Helical Device and the JT-60U Tokamak, calibration experiments, testing prototype lost alpha diagnostic detectors on an ion beam facility and the design of an imaging bolometer and a lost alpha diagnostic for ITER.

Observation of radiation behavior by using an IR imaging bolometer in the JT-60U tokamak

Parchamy, H.*; Peterson, B. J.*; Konoshima, Shigeru; Ashikawa, Naoko*

no journal, , 

Foil bolometers are standard magnetic fusion plasma diagnostics, by which the energy lost from the plasma can be detected through the heating of a thin metal foil. Imaging bolometers have been used in experiments to make time traces of radiation, in neutral beam injection heated discharges. In our case, the radiation is observed by a semi-tangentially viewing IR imaging bolometer in the JT-60U Tokamak, where a graphite-coated gold foil with a thickness of 2.5microns and an effective area of 9cm7cm is used. The frame rate of this IR camera is 30Hz. Future calibration of the infrared imaging video bolometer will compensates for nonuniformities in the foil. We also improve the diagnostic by enabling the acquisition of 14bit digital data (compared with 8bit video data in the last campaign) and additional shielding for the IR camera against the magnetic field, neutrons and particles. The maximum brightness of the radiation from the plasma core during a disruption has been visible. The distribution of the radiation intensity in two dimensions (2D) could be inferred from the IR camera. These measurements yield a wealth of information on radiation behavior. The figure shows the intensity distribution of the black body radiation from the foil heated by the plasma radiation. Waveforms of the radiated power signal, shown in the bottom box, are processed with 0.1 second low pass filter for comparison with the imaging bolometer. This work was partly supported by Grants-in-Aid for Scientific Research of the JSPS, Nos.16560729/16082207.

Design of an imaging bolometer upgrade for JT-60U

Peterson, B. J.*; Konoshima, Shigeru; Kostryukov, A. Y.*; Kawashima, Hisato; Seo, D. C.*; Miroshnikov, I. V.*; Ashikawa, Naoko*; Parchamy, H.*; Liu, Y.*; JT-60 Team

no journal, ,