Static ECE Tomography

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Important physics issues of the nuclear fusion research are magnetohydrodynamic (MHD) instabilities and diffusion mechanism.Electron cyclotron emission (ECE) has advantage that the intensity is proportional to the electron temperature and the frequency is proportional to the magnetic field.Since the local electron temperature can be continuously measured with ECE, ECE is the strong tool to study the above issues.Especially, the pressure driven MHD instabilities become more important in the high temperature and the high density fusion plasma.These are often localized.The ballooning mode is the typical example.Ideal tool for the localized MHD instability is the two dimensional ECE imaging like a camera or the three dimensional ECE imaging (camera+frequency).A two dimensional microwave detector like TV camera is necessary for this purpose.In this research we have developed an element of the plane type microwave detector.A two dimensional imaging array of the element is a two dimensional microwave detector.This detector is a GaAs chip including a bow-tie antenna, a Shottky barrier diode (SBD) mixer and a heterojunction bipolar transistor (HBT) IF amplifier.This device is made using the monolithic microwave integrated circuit (MMIC) technology on GaAs substrate.This device has a flat response about the intermediate frequency of more than 10 GHz.The ECE from the plasma in the compact helical system (CHS) is successfully measured with this detector.ECE is focused using a polyethylene lens from the front side of the detector and the local wave (LO), which is generated by the 90GHz, 200mW IMPATT oscillator is focused from the back side.The intermediate frequency is amplified using 3-stage amplifier (total 96dB) and is divided to 4 band-pass-filters (1, 2, 34GHz) with band width of 0.3GHz.The DC level is 800mV while the signal level is 5mV in the case of T_e=600eV and n_e=2x10^<13>/cc.This result is the most important step in the development of the ECE imaging diagnostics.