Quasi-optical Mirrors Research Articles

Detection system operating at up to 7THz using quasioptics and Schottky barrier diodes

We have developed a wide-bandwidth, high-sensitivity, continual terahertz-wave sensor that utilizes a quasioptical parabolic mirror and a Schottky barrier diode and successfully applied it at up to 7THz range. This sensor utilizes a parabolic cylindrical mirror, a long-wire antenna, and a Schottky barrier diode. The antenna, placed at the focal point of the parabolic mirror, quasioptically collects the terahertz signal. This configuration eliminates the need for frequency-dependent reception readjustments of the antenna and the mirror positions, greatly improving operability.

High-Efficient Mode Converter for ITER Gyrotron

A high-efficiency mode converter of the ITER gyrotron operating mode into the Gaussian wave beam has been developed. It includes an irradiating waveguide with shallow deformation and profiled quasi-optical mirrors to increase the Gaussian content. Low-power tests were carried out with a TE25.10 mode exciter and a mode converter. A prototype of the short-pulsed 170 GHz gymtmn with the new converter was manufactured and tested. Diffraction losses measured inside the tube were less then 2% at the 1 MW power level. A high Gaussian mode content in the output beam has been also demonstrated.

Fast ion millimeter wave collective Thomson scattering diagnostics on TEXTOR and ASDEX upgrades

Collective Thomson scattering (CTS) diagnostic systems for measuring fast ions in TEXTOR and ASDEX Upgrade are described in this article. Both systems use millimeter waves generated by gyrotrons as probing radiation and the scattered radiation is detected with heterodyne receivers having 40 spectral channels at TEXTOR and 50 spectral channels at ASDEX Upgrade. The antenna patterns of probe and receiver, both steerable, determine size and location of the measuring volume, and the direction of the resolved fast ion velocity. With overmoded transmission lines, consisting of waveguides and quasioptical mirrors, the antenna patterns depend on the alignment of the entire transmission line. Alignment is aided by visible laser beams relayed by small optical mirrors, inserted in the quasioptical mirrors.

Production of an Intense, Well-Collimated Submillimeter Wave Beam and Its Application to Plasma Scattering Measurements

Intense submillimeter wavelength radiation (f=354 GHz, P=110 W) from Gyrotron FU II is converted into a well-collimated, linearly-polarized beam by a quasi-optical transmission line consisting of a quasi-optical antenna and several mirrors. The observed focusing of the beam agrees with calculations based on the Huygens equation. We have used this intense beam to study low frequency density fluctuations by plasma scattering in Compact Helical System (CHS) plasmas at the National Institute for Fusion Science.

Improvements of mode converters for low-power excitation of gyrotron-type modes

To test quasi-optical mode converters for gyrotrons, efficient low-power generators for rotating high-order modes of high purity are necessary. Based on previous designs consisting of a coaxial cavity with a perforated wall and a quasi-optical mirror, the paper shows a more rigorous synthesis and analysis procedure, leading to an efficiency enhancement (in some cases from 2% to 22%) and to a significantly higher mode purity. Designs of 140GHz generators for the TE22,6 and TE76,2 modes are presented. Experimental results on the TE22,6 mode exciter are discussed.

Mirror synthesis for gyrotron quasi-optical mode converters

A new approach for the design of a quasi-optical gyrotron mode converter is proposed. It is based on the synthesis of quasi-optical mirrors using diffraction (Helmholtz-Kirchhoff) integrals. First application of such a method we already described in [1, 2]. Now a more powerful technic is used to provide optimal distributions of the wave beam field. It is shown that by means of specially shaped mirrors parameters of the main converter are enhanced strongly. In this paper we review the search for the optimal scheme of the converter, present and compare results of calculations and measurements of the gyrotron wave beam.

Application of quasi-optical approach to construct RF power supply for TeV linear colliders

An idea to use a quasi-optical approach for constructing an RF power supply for TeV linear e +e − colliders is developed. The RF source of the proposed scheme is composed of a large number of low-power RF amplifiers commutated by quasi-optical elements. The RF power of this source is transmitted to the accelerating structure of the collider by means of quasi-optical waveguides and mirrors. Such an approach enables one not only to decrease the required peak RF power by several orders of magnitude with respect to the traditional approach based on standard klystron technique, but also to achieve the required level of reliability, as it is based on well-developed technology of serial microwave devices. To illustrate the proposed scheme, a conceptual project of 2 × 500 GeV X-band collider is considered. Accelerating structure of the collider is of the standard travelling wave type and the RF source is assumed to be composed of 0.7 MW klystrons. All equipment of such a collider is placed in a tunnel of 12 × 6 m 2 cross section. It is shown that such a collider may be constructed at the present level of accelerator technique.

Quasi-optical mirrors made by a conventional milling machine

A modified method for machining off-axis mirrors has been described. By a careful choice of machine parameters, revolution surface can be generated with a sufficient accuracy for λ>15 μm. A large set of spherical, paraboloidal and ellipsoidal mirrors, whose focal lengths are comprised between 50 mm and 900 mm, have been machined using the method. Focal ratio improving the uppest limit expected by ERICKSON have been manufactured. These optical devices have essentially been used in the development of our far-infrared heterodyne spectrometer. Due to the rather low source power achievable in these kind of intruments the greatest care has to be taken in the design of optical lines. The whole system will be described in a separate paper. It will be seen that powers losses in beam propagation have reached very low absolute levels, rarely exceeding 1 or 2%.