UC Davis PDG:ECE Imaging on TEXTOR - Specifications

TEXTOR is a relatively large tokamak, with a major radius R=1.75 m, and a minor radius a=46 cm. The TEXTOR ECE Imaging system looks at the plasma through a large viewing window (45 cm high by 30 cm wide) made of BK-7. The 16 imaging channels are spaced 13 to 15 mm apart, and cover approximately 21 cm of the plasma centered on the plasma midplane. The antennas in the ECE imaging array are arranged in a staggered pattern of 16 vertically spaced elements arranged in two parallel (horizontally displaced) rows. Here, even and odd channels are toroidally displaced by 32 mm.

In TEXTOR, there is a 500 kW, 110 GHz ECRH system in which the RF power is coupled to the tokamak plasma by mirrors through the air. Hence, large levels of stray 110 GHz radiation around the tokamak hall exist which can affect not only system performance but could endanger the Schottky diode mixer array itself. All the optical components mounted on the tower are enclosed by a shielding box built to reject stray ECRH power at 110 GHz, leaving only the front surface of lens G open to collect second harmonic plasma radiation.

Any stray ECRH radiation received by lens G is rejected by the dichroic filter. To ensure mixer array safety, a dichroic plate attached to the array box functions as a high pass filter, the performance of which is shown to the right. In Ohmic discharges (discharges without additional ECRH heating), this filter can be removed to extend the operation frequency to below 110 GHz. The system performance is well characterized both with and without the dichroic filter and the difference is found to be small.

The unique features of the ECE Imaging diagnostics derive from the use of wideband, low cost Schottky diode mixer arrays coupled with innovative, low cost electronics. Follow the links below to learn more about the technology employed in ECE Imaging.

Imaging array design and fabrication
2-D ECE Imaging electronics
Quasi-optical notch filters

UC Davis has fabricated and installed multichannel ECE Imaging systems on other fusion plasma tokamaks across the world. Follow the links below for a description of the systems involved, and to sample data collected with these systems.

ECE Imaging on the KSTAR tokamak in Korea
ECE Imaging on the TEXT-U tokamak in the U.S.A. (reference only)
ECE Imaging on the RTP tokamak in the Netherlands (reference only)

Comments to: Calvin Domier