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.

https://iopscience.iop.org/article/10.1088/0741-3335/39/11/001/pdf

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

In this review of plasma polarimetry, first the theory is discussed in general, then exact analytic solutions of the evolution equation for polarization are presented, as well as approximate analytic solutions. Numerical integration of the evolution equation is also discussed. The design of experiments is then considered taking into account the maximum amount of information which can be obtained from polarimetric measurements. Special attention is devoted to the techniques of polarization modulation (including both progressive and alternating modulation). Different alternative configurations are described which are of special interest because they can be realized in the far infrared and because they allow a measurement of phases rather than amplitudes. The effects of refraction are then briefly considered. Finally, the combination of polarimetry and interferometry on the same instrument is discussed, including the effects of polarization modulation.

http://iopscience.iop.org/article/10.1088/0741-3335/41/2/001/pdf

A review of plasma polarimetry—theory and methods

One of the systems envisaged for measuring the current density profile in the ITER is a 118 μm poloidal polarimeter system. The proposed system has two independent views: one fan of chords observes the plasma via an equatorial port and a second fan views down from an upper port. This article will present the status of the on-going work and will address issues as sensitivity and accuracy, refraction, Gaussian beam ray-tracing, alignment, and calibration as well as some specific design details.

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Poloidal polarimeter for current density measurements in ITER

Problems related to the development of diagnostics for steady state fusion plasma experiments are discussed. The paper concentrates on those necessities already appearing in current non-burning plasma fusion experiments when extending pulse lengths beyond 10 s, i.e. thermal load, erosion, deposition and long-time signal integration in magnetic diagnostics. Problems arising from high power ECRH under conditions of incomplete absorption are outlined. Individual standard diagnostic systems are discussed to identify their specific problems as well as the opportunities connected with long pulse operation. Burning plasma experiments characterized by intense n- and γ-radiation are briefly reviewed for reasons of completeness, dealing with radiation induced processes in windows, fibres, cables and mirrors. Methods of data handling, real time monitoring and plasma control are outlined.

/pdf/diagnostics-for-steady-state-plasmas-3yh19dtxc0.pdf

Diagnostics for steady state plasmas

Polarimetry, a powerful diagnostic tool, can provide information on the density and magnetic field, utilizing the Faraday and the Cotton–Mouton effects in a magnetized plasma. Both effects contribute to the change of the polarization of an electromagnetic wave traversing a magnetized plasma such that, unless both effects are small, the measurable output polarization does not provide the 'pure' effects in terms of Faraday rotation angle and Cotton–Mouton phase shift angle, which are directly related to simple line-of-sight integrals of the electron density times certain components of the magnetic field. In view of the importance of the latter, a new formalism has been developed, which delivers narrow limits to these quantities in terms of analytic formulae that contain nothing but the input and output polarization parameters. The approach is valid for vertical lines of sight in toroidal devices whose toroidal field dominates over other field components perpendicular to the line of sight. Examples relating to measurements at JET demonstrate the capabilities of the method.

Approximate method to extract the pure Faraday and Cotton?Mouton effects from polarimetry measurements in a tokamak

A formalism is presented for treating plasma polarimetry when both the Cotton–Mouton and the Faraday effects are large. For this general case it is shown that, for each measuring chord, up to nine parameters related to the plasma can be determined, instead of the usual single Faraday rotation. These parameters can be measured by a convenient modulation of the polarization state of the input radiation, and they can be used in the reconstruction of the magnetohydrodynamic equilibrium. Thus, the potential of the polarimetric diagnostic can be significantly increased, and the range of plasma conditions where the latter can be used, is extended. The importance of refraction is discussed.

S. E. Segre

Papers

Plasma polarimetry for large Cotton–Mouton and Faraday effects