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The measurement of accurate temperature profiles is critical for transport analysis and equilibrium reconstruction in the DIII-D tokamak. Recent refinements in the Michelson interferometer diagnostic have produced more precise electron temperature measurements from electron cyclotron emission and made them available for a wider range of discharge conditions. Replacement of a lens-relay with a low-loss corrugated waveguide transmission system resulted in an increase in throughput of 6 dB and a reduction of calibration error from 15% to 5%. The waveguide exhibits a small polarization scrambling fraction of 0.05 at the quarter-wavelength frequency and very stable transmission characteristics over time. Further reduction in error was realized through special signal processing of the calibration and plasma interferograms.

Inside launch (high field side) reflectometry is necessary for routine core access on DIII‐D and is a very attractive option for ITER and TPX. For high temperature reactor relevant plasmas, relativistic corrections for the left‐hand cutoff (inside launched) are relatively small, whereas these substantially affect the location of the normal right hand cutoff. On DIII‐D, core access using the right hand cutoff is restricted to low density plasmas, while O‐mode polarization is incompatible with flat H‐mode density profiles. Routine core access can, however, be obtained using the left‐hand cutoff and inside launch. On ITER and TPX, outside launch X‐mode systems need to operate at high frequency, ∼100–250 GHz, such that the left‐hand cutoff, which is at much lower frequency, ∼0–75 GHz, is an attractive option for high density operation. In addition, inside launch reflectometry can be used to investigate plasma asymmetries; on DIII‐D an inboard/outboard asymmetry in turbulence response is observed at the L‐H tr...

Divertor density profiles, asymmetries, turbulence, and MARFE diagnosis are extremely important and affect the divertor design process for ITER and other future devices. In addition, a functioning divertor density profile system will be essential for the operation of these machines. It is thus critical to prototype and demonstrate diagnostics capable of operating in a divertor environment. To meet these needs a divertor reflectometer system has been designed and installed on DIII-D. The design stresses flexibility, modularity, and simplicity. It consists of a circular, smoothwall, overmoded waveguide followed by a TE11⇒HE11 mode converter (the HE11 mode is a low loss Gaussian mode with a very symmetric radiation pattern, optimal for this use) thus allowing use of an arbitrary polarization (fpe,fLH,fRH). The design provides for testing of a variety of antennas/probing directions including: upward to probe the X-point region, including MARFEs, sideways to probe outboard/inboard divertor legs, and oppositely...

In order to improve the overall output characteristics of far‐infrared (FIR) lasers, recent development at UCLA has concentrated on the use of a metallic overmoded waveguide (smooth bore and corrugated) instead of a conventional smooth‐bore dielectric waveguide. The metallic waveguide has substantially lower propagation losses, especially at frequencies below 500 GHz, and also supports the desired HE11 mode. Laboratory results show a substantial increase in output power using a corrugated metallic waveguide, with 37 mW being obtained at 1.22 mm using 13CH3F (isotopic methyl fluoride) while maintaining the same mode quality and polarization. This represents an improvement of 100% over a smooth‐bore dielectric waveguide. Comparison of far‐infrared output using the three types of waveguide will be made.

Inside launch (high field side) reflectometry is necessary for routine core access on DIII‐D and is a very attractive option for ITER and TPX. For high temperature reactor relevant plasmas, relativistic corrections for the left‐hand cutoff (inside launched) are relatively small, whereas these substantially affect the location of the normal right hand cutoff. On DIII‐D, core access using the right hand cutoff is restricted to low density plasmas, while O‐mode polarization is incompatible with flat H‐mode density profiles. Routine core access can, however, be obtained using the left‐hand cutoff and inside launch. On ITER and TPX, outside launch X‐mode systems need to operate at high frequency, ∼100–250 GHz, such that the left‐hand cutoff, which is at much lower frequency, ∼0–75 GHz, is an attractive option for high density operation. In addition, inside launch reflectometry can be used to investigate plasma asymmetries; on DIII‐D an inboard/outboard asymmetry in turbulence response is observed at the L‐H tr...

A systematic procedure is developed for finding analytical solutions of certain ordinary linear differential equations of arbitrary order, describing reflection and conversion of waves in multiwave media having a concentrated region of nonuniformity. This procedure involves transformation to equations solvable by generalized hypergeometric functions which have the form of normal modes, exp(−ikz), in uniform regions. It is applicable when the variable coefficients in the original equation contain only linear combinations of one varying parameter, p(z), and in certain cases its derivatives or ratios thereof, if p(z) is proportional to tanhz. Arbitrary gradients and dissipation are allowed. The applicability of this procedure to solve for the reflection and conversion coefficients is indicated for second‐, fourth‐, and sixth‐order problems in magnetostatic, spin, and elastic‐wave conversion in magnetic insulators such as yttrium iron garnet, and for electromagnetic‐to‐electrostatic wave conversion in hot pla...

Most microwave scattering measurements in tokamaks are done with the polarization of the incident radiation approximately parallel to the toroidal field (ordinary mode) and at a frequency which is sufficiently above the plasma frequency ωpe that refraction effects are small. However, as confinement devices get hotter, drift wave turbulence is expected to occur at longer wavelengths. In order to observe density fluctuations associated with these phenomena with good spatial resolution, the ideal probe wavelength λi is near or beyond the ordinary cutoff at λi=2πc/ωpe. As a result, we have considered the propagation and scattering of the extraordinary (X) mode where the incident polarization is nearly perpendicular to the confining fields and where the cutoff density is significantly higher than in the ordinary mode. We have modeled the propagation of the X mode in a tokamak field geometry and shown that the polarization typically remains perpendicular to the local field along the ray path, simplifying the in...

Modified FM–CW radar techniques using swept millimeter–wave oscillators are useful for determining when a particular density has been reached in a plasma. Narrowband measurements on the Princeton Large Torus (PLT) demonstrate the suitability of these techniques for controlling high‐power auxiliary plasma heating systems. Broadband measurements using these same techniques are proposed, by which the density profile could be determined.

A 200‐kW, ∼60‐GHz gyrotron will be used on TFTR during D–T operation for collective Thomson scattering diagnostics of confined alpha‐particle velocity distribution and density. Scattering angles of up to 120° are under consideration using x‐mode propagation to increase the density cutoff limit. Useful signal‐to‐noise ratios will be possible in plasmas where ne≳5×1013 cm−3, nα≳2×1011 cm−3, and the background emission is ≲30 eV equivalent blackbody level.