Abstract
The development of diplexers for ECRH has been pursued at a number of institutes because of their attractive variety of applications: Power combination, non-mechanical, electrically controlled switching (of combined beams) between launchers with tens of kHz, and discrimination of low-power ECE signals from high-power ECRH is feasible. In a first part, this paper reports on plasma experiments with a ring resonator (Mk IIa) at ASDEX Upgrade. Commissioning experiments on fast switching between two launchers for synchronous stabilization of neoclassical tearing modes, as well as in-line ECE measurements have been performed, and experimental issues and first results are discussed. A clear influence of the switching phase on the amplitude of the 3/2 NTM mode was measured, complete stabilization could, however, not be demonstrated yet mainly due to imperfect resonator control. Concepts for improved tracking of the diplexers to the gyrotron frequency are presented. In a second part, the design of diplexers with ring resonators matched to HE11 fields is briefly discussed; these devices can be connected to corrugated waveguides without any mode converters. A compact version (MQ IV) is under investigation, which is compatible with the ITER ECRH system (170 GHz, 63.5 mm waveguide, vacuum tight casing), with the final goal of high-power tests at the 170 GHz gyrotron facility at JAEA in Naka, Japan. First low-power test results are presented.
Highlights
In the past years, high-power diplexers have become of growing interest for applications in ECRH systems
The example of the 170 GHz/24 MW ITER ECRH system [3], where the power can be switched between the equatorial launcher (EL) and the upper launchers (UL) by waveguide switches, illustrates the many options
If the mechanical switches were replaced by four-port resonant diplexers, the power could be (i) arbitrarily distributed between the launchers according to the physics needs by tuning the resonance frequency, while the gyrotrons run continuously
Summary
High-power diplexers have become of growing interest for applications in ECRH systems. If the mechanical switches were replaced by four-port resonant diplexers, the power could be (i) arbitrarily distributed between the launchers according to the physics needs by tuning the resonance frequency, while the gyrotrons run continuously. For synchronous NTM stabilization [4], a gyrotron voltage modulation synchronous to the rotation frequency of the islands together with a proper tuning of the diplexer would (ii) strongly amplify the amplitude modulation in the UL and yield high stabilization efficiency. In this context, the mode purification characteristics of the resonator could (iii) improve the focussing and reduce the possible beam squint of the UL. More compact diplexers have been built; in chapter 4, first tests are presented for the version MQ IV, which is compatible with the ITER ECRH
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