Commissioning of inline ECE system within waveguide based ECRH transmission systems on ASDEX upgrade
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Commissioning of inline ECE system within waveguide based ECRH transmission systems on ASDEX upgrade
W.A. Bongers 2
W. Kasparek 1
N. Doelman 0
R. van den Braber 0
H. van den Brand 2 6
F. Meo 5
M.R. de Baar 2 6
F.J. Amerongen 2
A.J.H. Donné 2 6
B.S.Q. Elzendoorn 2
V. Erckmann 4
A.P.H. Goede 2
L. Giannone 1
G. Grünwald 4
F. Hollman 4
G. Kaas 2
B. Krijger 2
G. Michel 4
L. Lubyako 3
F. Monaco 4
F. Noke 4
M. Petelin 3
B. Plaum 1
F. Purps 4
J.G.W ten Pierik 2
C. Schüller 2
J.W. Slob 2
J.K. Stober 4
H. Schütz 4
D. Wagner 4
E. Westerhof 2
D.M.S. Ronden 2
0 Department of OptoMechatronics, TNO Technical Sciences , NL-2600 AD, Delft , The Netherlands
1 Institut für Plasmaforschung, Universität Stuttgart , D-70569 Stuttgart , Germany
2 Dutch Institute For Fundamental Energy Research , NL-3439 BE Nieuwegein , The Netherlands
3 Inst. of Applied Physics, Russian Academy of Science , 603950 Nizhny Novgorod , Russia
4 Max-Planck-Institut für Plasmaphysik, EURATOM Association D-17491 Greifswald , and D-85748 Garching , Germany
5 Risø DTU National Laboratory for Sustainable Energy , DK-4000 Roskilde , Denmark
6 Eindhoven University of Technology , NL-5600 MB, Eindhoven , The Netherlands
A CW capable inline electron cyclotron emission (ECE) separation system for feedback control, featuring oversized corrugated waveguides, is commissioned on ASDEX upgrade (AUG). The system is based on a combination of a polarization independent, non-resonant, Mach-Zehnder diplexer equipped with dielectric plate beam splitters [2, 3] employed as corrugated oversized waveguide filter, and a resonant Fast Directional Switch, FADIS [4, 5, 6, 7] as ECE/ECCD separation system. This paper presents an overview of the system, the low power characterisation tests and first high power commissioning on AUG.
1 Introduction
For high performance tokamak plasmas, neoclassical tearing modes (NTMs) and sawteeth
instabilities need to be controlled by locally applied Electron Cyclotron Current Drive (ECCD).
Measuring electron temperature using Electron Cyclotron Emission (ECE) along the line of sight of
ECCD offers the advantage that temperature fluctuations, resulting from NTMs and sawteeth, are
measured relative to the deposition position. Such a system, in which ECE is measured in the EC
transmission line, provides signals for feedback control without making any assumptions on the
plasma equilibrium. These signals are insensitive to drifts in the absolute measurement or deposition
position, because ECE and ECCD have similar beam propagation and are affected equally by the
launcher. An inline ECE system was demonstrated to be effective on TEXTOR in a quasi-optical
configuration [
1
].
For ASDEX Upgrade (AUG) a high power configuration based on oversized corrugated waveguides
is required. In this paper, the design requirements for the inline ECE system on AUG are presented,
resulting in a total system configuration specification (chapter 2). The low power measurements on
individual parts, are described in chapter 3. Installation and Line-of-sight commissioning tests of the
system on AUG are presented in chapter 4. Chapter 5 concludes with the commissioning results of
the Line-of-sight system together with suggestions for further improvement.
2 Requirements inline ECE AUG
Unlike the quasi-optical TEXTOR system, AUG employs non-evacuated corrugated HE11
waveguides (of 87 mm inner diameter) to transport the mm-wave beam from the gyrotron sources to
the plasma [
8
]. A special feature of the AUG ECCD system is the fast directional switch (FADIS)
Mk II, a circular corrugated waveguide compatible version of FADIS designed by the IPF Stuttgart
[
4
]. The main purpose of FADIS is to improve the efficiency of ECCD stabilization of NTMs by
enabling the switching of the gyrotron power between two launchers positioned at the same toroidal
location but at different vertical positions, such that each launcher is targeting a different phase of
the NTM island. FADIS experiments performed on AUG are described in a separate paper [
6
]. Since
FADIS is installed on AUG it can also be employed as a frequency selective diplexer, placed in
lineof-sight ECE setup, to serve the purpose of separating the low-power ECE signal from the
highpower ECCD, see Fig. 1.
From
To Plasma
In
ECE
Out
ECE
Stray radiation or
isolation leakage FADIS
Fig. 1. Principle of FADIS for high power mm-wave application. The schematic on the left shows a
4mirror quasi-optical cavity with grating couplers for switching the high power gyrotron beam (top left) to
either Out 2 (lower right) or Out 1 (upper right) ports by shifting the gyrotron frequency from f1 to f2. If
the FADIS control system [
7
] tunes the resonant mode to the gyrotron frequency f2, by moving its upper
corrugated mirror, the system serves to isolate the low power ECE radiation entering at the lower right
plasma port Out 2 via the non-resonant channel coupled to the diagnostics port at the lower left (...truncated)