Heterodyne methods in millimetre wave plasma diagnostics with applications to ECE, interferometry and reflectometry

Abstract

Basic principles of heterodyne techniques are introduced and the various components of a heterodyne system are summarized. Special applications in ECE, interferometry and reflectometry are discussed after introducing the diagnostic principles. Realized systems as described in the literature are briefly outlined. Ordering principles are radiometer types in the case of ECE, mixing scheme and generation and stabilization of local oscillator and intermediate frequency signals in the case of interferometry and reflectometry. Special techniques and their impact on the performance of the diagnostic instruments are discussed. Contents Introduction 1694 Components of the heterodyne receiver 1695 2.1 Heterodyne detection scheme 1696 2.1.1 Mixers 1697 2.1.2 Local oscillators 1705 2.1.3 IF chain 1706 2.2 Sensitivity 1707 2.3 Antennas and waveguides 1709 Radiometry of electron cyclotron emission 1711 3.1 Principles of ECE diagnostics 1711 3.1.1 Frequency and intensity of the emission 1711 3.

Development and testing of a fast Fourier transform high dynamic-range spectral diagnostics for millimeter wave characterization

“…21 The process of mixing is mathematically equivalent to multiplying two harmonics yielding up-and downconverted frequency difference components. In this case, the f rf range is between 136 and 140 GHz.…”

“…The ͑equivalent͒ noise temperature of a system ͑T s ͒ can be calculated using the cascade noise equation of Friis, [21][22][23] …”

Waveguide Bandpass Filters for Millimeter-Wave Radiometers

“…This filter could be used in systems where harmonic-producing components such as mixers and multipliers are built-in. Another field of application is in receivers sensitive to radiation coming from fusion plasmas, the so called total-power radiometers [1][2][3][4][5]. These receivers are often sensitive in the range from 50 GHz (V-band) to 170 GHz (F-band).…”

“…It is therefore important that bandpass filters installed in this system have a high rejection up to at least 140 GHz [6,7]. Another type of diagnostic that uses bandpass filters with large fractional bandwidth is ECE spectroscopy where the objective is to determine the evolution of the electron temperature profile as a function of time covering the spectral range from 60 to about 800 GHz [3,12,13]. For example, the ECE diagnostics at ASDEX Upgrade detects radiation in a bandwidth of 20 GHz centered at 140 GHz [14].…”

ECE for NTM control on ITER

“…To the thermal ECE calculated using the perturbed temperature profile, thermal noise is added, determined by the video bandwidth B v and the intermediate frequency bandwidth B IF of the simulated multichannel radiometer used for detection. [12] The simulated ECE signals serve as input for the detection algorithm by Berrino et al [8] This algorithm detects the island position in terms of a detected frequency f det , which can be compared with the actual island frequency f isl , found from noise-free simulations. With averaging of temperature, temperature fluctuation amplitude and normalized temperature fluctuation correlation over 40, 80 and 400 measurement points and a threshold for the second derivative of 0.6 for NTM detection, only NTMs are detected.…”