In ECE Imaging, the approach taken is to collect broad bandwidth radiation on each element of an imaging antenna array, which is subsequently separated by frequency band. This, in essence, attaches a broadband multifrequency heterodyne radiometer electronics to each element of the one dimensional ECEI array.

The broadband ECEI detection electronics can be split into the following stages:

• Broadband millimeter-wave radiation is collected by imaging antenna, mixed with a fixed frequency local oscillator (LO) signal, and downconverted to microwave frequencies. In the case of TEXTOR, this LO frequency can be tuned between 97 and 125 GHz.
• A broad bandwidth microwave balun is employed to convert the balanced signals at the mixer into an unbalanced (i.e. signal and ground) form for propagation on connectorized microwave cables.
• The downconverted microwave signals are amplified (typically 40-60 dB) with low noise preamplifiers.
• The amplified signals are divided into 8 equal parts, each of which is mixed with a separate LO signal. On TEXTOR, these LO frequencies are 3.3, 3.8, 4.3, 4.8, 5.3, 5.8, 6.3 and 6.8 GHz.
• The result of this second downconversion operation are bandpass filtered (5-150 MHz passband), and then rectified with RF detector ICs.
• Finally, the detector output signals are video amplified and digitized.

In the following are photographs of some of the IF electronics modules that make up the 2-D ECE Imaging system on TEXTOR. Shown first is one of the 8 LO source modules that provide the 8 LO frequencies to each of the 16 IF detector modules, in this case the 4.3 GHz source module.

Next can be seen one of the 16 IF detector modules. LO signals from each of the 8 LO source modules are input via SMA connectors from the left, while the input microwave signal enters from the top. The output video signals, corresponding to the detected signals at each of 8 frequency bands, are available on LEMO connectors on the right.

The full 2-D 16x8 ECE Imaging electronics is formed by connecting the 16 outputs from each of the 8 LO source modules to each of the 8 LO inputs on each of the 16 IF detector modules via 16x8=128 microwave cables as shown below.

The unique features of the ECE Imaging diagnostics derive much from the use of wideband, low cost Schottky diode mixer arrays, coupled with quasi-optic notch filters for protection against high frequency plasma heating sources. Follow the links below to learn more about both the technology employed in ECE Imaging.

Imaging array design and fabrication
Quasi-Optical Notch Filters

UC Davis has fabricated and installed multichannel ECE Imaging systems on a number of 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 TEXTOR tokamak in Germany
ECE Imaging on the KSTAR tokamak in Korea
ECE Imaging on the RTP tokamak in the Netherlands (Reference Only)
ECE Imaging on the TEXT-U tokamak in the U.S.A. (Reference Only)

 Comments to: Calvin Domier