Status of the new multi-frequency ECRH system for ASDEX Upgrade

Abstract

Currently, a new multi-frequency ECRH system is under construction at the ASDEX Upgrade tokamak experiment. This system employs, for the first time in a fusion device, multi-frequency gyrotrons, step-tunable in the range 105–140 GHz. The first two gyrotrons, working at 105 and 140 GHz, were installed and tested. The matching optics unit includes a set of phase correcting mirrors for each frequency as well as a pair of broadband polarizer mirrors. The transmission line consists of non-evacuated corrugated HE11 waveguides with an inner diameter (ID) of 87 mm and has a total length of about 70 m. Transmission losses were deducted from calorimetric measurements both at the beginning and at the end of the transmission line at both frequencies and are in reasonable agreement with theory. Two transmission lines are completed so far and first plasma experiments with the new system have started. The first gyrotron Odissey-1 is currently being equipped with a broadband chemical vapour deposition (CVD) diamond Brewster output window and will become a step-tunable gyrotron with the additional frequencies 117 and 127 GHz. A tunable double-disc CVD-diamond window will be mounted at the torus. The system includes fast steerable launchers at the front end that will allow very localized feedback controlled power deposition in the plasma.

Resolving the bulk ion region of millimeter-wave collective Thomson scattering spectra at ASDEX Upgrade

“…On AUG the probing radiation is delivered by a dual frequency gyrotron normally used for electron cyclotron resonance heating (ECRH) at 140 GHz. The probing gyrotron is part of the ECRH-2 system on AUG [44][45][46] , which is comprised of four gyrotrons referred to here as gyrotrons 5-8 (gyrotrons 1-4 comprise the ECRH-1 system on AUG). The gyrotrons have separate transmission lines and launching antennae, which are mounted in close proximity above and below the equatorial midplane on the low-field side on the tokamak as illustrated in Fig.…”

“…The calibration curve is then adjusted numerically to the relevant setting of the variable attenuator using the measured attenuation levels. Similarly, the effects of the diamond window between the ECRH waveguides and the vacuum vessel are also included numerically in the calibration based on a theoretical calculation of the small amount of reflection caused by this window 44 . Effects of absorption in the high-power ECRH waveguides are not expected to change the spectral shape significantly across the narrow frequency range monitored here and are neglected.…”

Development of a dual frequency (110/138 GHz) gyrotron for JT-60SA and its extension to an oscillation at 82 GHz

“…In the early 2000s from the late 1990s, high-power (~ 1 MW) oscillations at the millimetre wave frequencies above 100 GHz were realized by some individually developed gyrotrons in Japan, EU, Russia and US [1]. These gyrotrons were used in some tokamak devices such as JT-60U [2], DIII-D [3] and ASDEX-U [4]. Recently, long-pulse oscillations of several hundreds of seconds at an output power of 1 MW have been demonstrated at the frequencies of 140 GHz for W7-X [5] and 170 GHz for ITER [6,7].…”

“…In addition to developments for realizing higher power and longer pulse, developments for realizing multi-frequency oscillations are in progress since an application of multifrequency gyrotron gives a flexibility of the ECH/ECCD system for wider experimental conditions without significant increase in a construction cost. In ASDEX-U, a dual-frequency gyrotron was installed and operated for various experiments with the maximum gyrotron output power of 0.95 MW at 140 GHz and 0.85 MW at 105 GHz for 10 s [1,4].…”

Bragg reflection band stop filter for ECE on WEGA

“…Sensitive millimeter-wave diagnostic systems need to be protected against ECRH stray radiation [1]. In addition, a specific problem concerning notch filters is the frequency drift of high power gyrotrons specifically at the beginning of the pulse [2]. This frequency drift also varies for different gyrotrons from several tens up to hundreds of MHz.…”