Abstract. A research has been conducted to develop an 8MW electron cyclotron resonance heating and current drive (ECRH/ECCD) system on HL-2M tokamak. The ECRH system compromise eight 1MW gyrotrons, eight evacuated transmission lines and three launchers. The main purpose of the ECRH system was to suppress the neo-classical tearing modes and control the plasma profile. This paper presents an overview of the design and studies performed in this framework. Some primary test results of the critical components have been released in this paper, e.g. polarizers, power monitor and fast steering launchers.
Spontaneous emission of electromagnetic radiation in the ion cyclotron range of frequencies, usually referred to as ion cyclotron emission (ICE), is a frequently-observed property of tokamak plasmas containing suprathermal ion populations [1 – 4]. Links between such emissions and suprathermal ions have also been identified in the large helical device (LHD) stellarator  and in the Earth ’ s radiation belts [6 – 8], indi- cating that the phenomenon is not confined to one specific magnetic configuration. ICE measurements, in combination with appropriate modelling, can be used to obtain diagnostic information on the behaviour of confined fast ions, including charged fusion products, ions accelerated by waves in the ion cyclotron range of frequencies (ICRF), and, in some devices, beam-injected ions. It has been proposed that ICE could be used to study fusion α-particles in the burning plasma ITER device . Various types of ICE detector have been used , including detectors that are incorporated into ion cyclotron resonance heating (ICRH) antenna systems: this approach has been used successfully in the ASDEX Upgrade  and JET  tokamaks. With the use of suitable filters to suppress signals corresponding to the launched ICRH frequencies, ICE detection is possible in this case during radio-frequency heating, thereby making it possible to detect emission excited by ICRH fast ions. Another important advantage of this tech- nique is that it does not require the installation of any addi- tional hardware inside the vacuum vessel . Dedicated probes have also been used to detect ICE driven by ICRH fast ions in both ASDEX Upgrade  and JET .
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agrees with the results of full-wave numerical calculations. To conclude, we note that microwave reﬂection from the ECR heating region can contribute to the low- frequency modulation of the gyrotron power caused by the reﬂected wave. Since the reﬂection coeﬃcient depends strongly on the electron temperature, this eﬀect can, in principle, be used to estimate the electron temperature in the ECR region.
Abstract. For electron cyclotron resonance heating of the stellarator W7-X at IPP Greifswald, a 140 GHz/10 MW cw millimeter wave system has been built. Two out of 12 launchers will employ a remote-steering design. This paper describes the overall design of the two launchers, and design issues like input coupling structures, manufacturing of corrugated waveguides, optimization of the steering range, integration of vacuum windows, mitrebends and vacuum valves into the launchers, as well as low power tests of the finished waveguides.
On 10th December 2015 the first plasma was created in Wendelstein 7-X (W7-X). It is the world’s largest optimized stellarator (R = 5.5 m, a = 0.5 m) with 3-D shaped superconducting modular coils and a five-fold symmetry. W7-X aims to achieve reactor relevant plasma parameters in quasi steady state operation . For this reason, the device will be equipped with a 10 MW electron cyclotron resonance heating (ECRH) system allowing at least 30 minutes continuous operation. The design frequency of the 10 gyrotrons already installed is 140 GHz corresponding to second harmonic heating at the magnetic axis with a local magnetic field of 2.5 T . As a very versatile technique, ECRH can provide plasma start-up, bulk plasma heating, current drive as well as wall conditioning. Even though, the confinement of a stellarator is only given by the external field coils, electron cyclotron current drive (ECCD) can be used at W7-X to compensate a finite bootstrap current of up to tens of kilo-Ampéres in some magnetic field
perfectly harmonized. The ideal electric field should be a hyperbolic geometry distribution so that the potential yields a harmonic restoring force like a spring, and ions are oscillating back and forth at a reduced cyclotron frequency independent of the axial position. 60 However, the effective hyperbolic region in the conventional ICR cells, such as cubic, 186 simple cylindrical, 187 or Infinity cell 59 are only ideal near the centre of the cell, while ions are usually detected at ~50% of the cell radius for improved sensitivity. Due to the limited homogeneity region, the interior of the cell cannot be used effectively, and either the ions are confined to a smaller volume at the centre of the cell and are more likely to be influenced by space-charge effects, 126 or excited to a high orbit where the cell's electric field inhomogeneities will cause loss of coherence on ions’ motion and therefore decrease the resolving power and signal intensity. Furthermore, if ions are far away from the detecting plates, the sensitivity of the signal detection is also decreased. The above drawbacks limit the duration of the signal, and the effective transient signal recorded in the above cells are usually detectable for only a few seconds. The conventional cylindrical cell was modified by adding compensation rings which improved the electric field homogeneity over an orbit. 152, 188-189 Recently, Nikolaev and co-workers proposed the concept of a dynamically harmonized ICR cell, which creates a space-averaging potential distribution instead of a truly harmonic field. 46 The original data shows that the novel design extends the region of ideal electric field to almost the entire volume of the ICR cell, and the ion transient can last for minutes with minor decay in a 7 T instrument.
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Electron Cyclotron (EC) Heating and Current Drive (H&CD), at 170 GHz, 20 MW, is one of the heating systems foreseen to assist and sustain the development of various ITER plasma scenarios starting with the very first plasma generated in ITER. This will be accomplished by launching the EC power via the Equatorial Launcher (EL), with the primary goal of heating and q profile tailoring in the central plasma region. The EL setup is made up of three mirror assemblies (TOP, MID, BOTTOM), with a steering mirror at the end of each assembly, located at the same major radial position R and three di ff erent z, with eight beams for each mirror . In the present design the toroidal injection angle β is varied in the range 20 ◦ ≤ |β| ≤ 45 ◦ while the poloidal angle α is kept fixed with the beams from MID mirror being injected horizontally (α = 0 ◦ ) and the beams from TOP and BOTTOM mirror poloidally tilted towards plasma center by α = ± 5 ◦ . Beams from the MID mirror are injected in the opposite toroidal direction with respect to the other mirrors to provide counter current drive.
Applying GNET code, we evaluated the velocity dis- tribution of δ f in the QHS configuration. Figures 3 (a) and 3 (b) show the velocity distribution at normalized mi- nor radius ρ ∼ 0.1 and 0.3 surface. The velocity distri- bution integrated over the volume, total δ f , is shown in Fig. 3 (c). They show deviation from the Maxwellian dis- tribution, where the red region means increasing and the blue region decreasing. Energetic electrons can be found in the outer regions apart from the heating point, which indicates that there is a radial electron flux, as shown in Fig. 4. Since we are not concerned about the local distri- bution, we integrate the velocity distribution over the flux surface and treat it in the term of a minor radius.
To reduce the induced loss of α-particles by RF waves, the configurations without the cyclotron resonance layer of the α-particles in plasma core were selected as candi- dates for ICRF heating in a helical reactor. The second har- monic resonance layer of tritium was located at the plasma core. The ICRF antenna for the helical reactor was not op- timized, but the large loading resistance of 10Ω and the high power injection of 20 MW from two antennas were found to be achievable in spite of the large distance of 500 mm between plasma and antennas. By the calculation of ray tracing, it was found that the wave number parallel to the magnetic field line was greatly up-shifted, especially in high-density IDB plasma, even if the initial wave num- ber was small, which enabled ELD/TTMP heating. The configuration of the second harmonic resonance layer on the magnetic axis shifted onto the saddle point makes the intense core heating possible.
have normal band structure. However, properties of such wells are not identical to those of normal-band-structure HgTe QWs with the same bandgap, namely wide HgCdTe QWs demonstrate indirect band structure, i.e., the side maximum in the valence band exceeds that in the center of the Brillouin zone. An informative method to probe the energy band structure both in bulk semiconductors and in QWs is the cyclotron resonance (CR) technique. How- ever, at the moment, there have been no systematic studies on CR in HgTe/CdTe QWs with diﬀerent band structures (cf. [6-9,13-19]). In this work, we present the ﬁrst results on CR measurements in a semimetallic sample with wide HgTe QW (inverted band structure) as well as in two sam- ples with normal band structures: narrow HgTe QW (for the ﬁrst time) and wide HgCdTe (about 15% of cadmium).
In order to limit the risk of stray light and in order to limit the required cut-outs in the DSM, the design solution has been to use waveguide rather than quasi- optical transmission via mirrors through the DSM. The chosen inner diameter of the circular corrugated waveguide is 88.9 mm. Transmitting a 1 MW probe beam through this waveguide and passing the fundamental resonance at an uncontrolled ambient pressure constitutes a genuine risk for creating a plasma breakdown inside the waveguide. This would hamper the diagnostic capability and in the worst case lead to partial or full absorption of the 1 MW beam in the waveguide. For this reason, mitigation mechanisms have to be implemented. Several mitigation actions have been considered. Presently, the most developed mitigation action is adapting a split biased waveguide. This solution has previously been used at DITE and DIII-D. In short, the launcher waveguide is split along its axis into two halves. They are isolated from each other (and the surroundings), and one half is grounded, while the other is connected to a bias voltage of +1 kV. In case the gyrotron probe beam ionises a neutral atom or accelerates a free electron, the sweep time (time from waveguide center to the biased wall) is much shorter than the gyration time. In this way, the risk of a breakdown should be mitigated. As a side effect, the biased waveguide will act as a diagnostic for such electron sweeping events; as such an event will generate a current.
The principle schematic of the generator is shown in Fig. 1, and an outline of typical waveforms is depicted in Fig. 2. The circuitry is similar to those used in resonant switching power supply units. The crucial difference between our de- sign and commercial power supply units is our higher avail- able operating frequency. The radio-frequency output voltage of the generator is generated by the transformer TR1. The transformer is driven by a symmetrical push–pull power stage consisting of two power metal–oxide–semiconductor field effect transistors 共 MOSFETs 兲 T1 and T2. The supply voltage for the power stage 共 +V 兲 is provided by an external power supply unit 共 PSU 兲 . The control signals for switching the power stage are derived from two monostable flip-flop circuits 共 monoflops 兲 and two drivers from output signals of an externally synchronized oscillator. The width of the con- trol pulses together with the magnitude of the supply voltage determines the amount of energy that is accumulated in the output transformer during each half cycle of the output sig- nal, thereby influencing the amplitude of the generator’s out- put voltage. The synchronization of the oscillator by the out- put voltage ensures that the device operates at approximately the resonance frequency of the output resonance circuit con- sisting of the inductance L and the capacity of the connected trap. When the resonance frequency shifts, for instance due to changes in temperature, the generator follows these changes and still operates with optimal efficiency. The output voltage can be shifted by applying an auxiliary dc voltage Vo via an inductance Lo that is connected to the center of the resonant circuit and which acts as a low pass filter.
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Whistler waves can be ducted in an L-shell of the magne- tosphere to continuously interact with the energetic electrons trapped in the same L-shell. The motions of energetic elec- trons are adversely affected by the wave fields which scatter some of them into loss cones (Helliwell et al., 1973). In- duced electron precipitation (Voss et al., 1984; Arnoldy and Kintner, 1989; Imhof et al., 1994; Pradipta et al., 2007) by whistler waves has been observed. The Doppler shifted elec- tron cyclotron resonance interaction (Kennel and Petschek, 1966; Villalon and Burke, 1991; Albert, 2000) has been sug- gested to be a likely electron precipitation mechanism. The numerical results show that the electron cyclotron resonance interaction can diffuse energetic electrons, with their initial pitch angles close to the loss cone angle, into the loss cone, via small angle scattering process (Albert, 2000). However, the number of electrons resonant with the wave at a given frequency is small. Moreover, the resonance condition is anisotropic, which makes it difficult to explain the observa- tion of precipitation events occurring simultaneously at ge- omagnetic conjugate regions due to a single lightning flash (Burgess and Inan, 1990).
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Experiments in KSTAR H-mode plasmas with 0.6 MA of plasma current, 2.8 T of central toroidal magnetic field and 4 MW of NBI power were performed to investigate the effect of ECH on the Ar impurity transport. Two plasmas with an ECH power of 600 and 800 kW (Shot #10649 and Shot #10640, respectively) are compared to a reference plasma without ECH (Shot #10647). For both ECH plasmas, the heating is focused on Z = 0 (mid-plane) and R = 1.68 m (which corresponds to 𝑟/𝑎 = 0.3) with 170 GHz ECH. The exact heating position and the shape of plasma are shown in figure 1. Figure 2 depicts the temporal behaviour of the following plasma parameters for the non-ECH and 800 kW ECH cases: the plasma current, the line-integrated electron density, the core channel of the electron cyclotron emission diagnostics for the electron temperature, and the Ar 15+ line-integrated emission.
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The discrepancy that was observed at TFTR and JET is characterized by ECE measurements of electron temperature that are systematically higher than the TS measurements at high temperatures. The discrepancy increases linearly with increasing temperature, but there is good agreement between the two measurements at low temperatures [3, 6, 8]. Differences between TS and ECE measurements are often observed in tokamak plasmas with strong Electron Cyclotron Resonance Heating (ECRH), Electron Cyclotron Current Drive (ECCD) and Lower Hybrid Current Drive (LHCD). In these cases, the presence of non-thermal electrons can enhance the EC emission above thermal levels. Such differences are reasonably well understood [9,10], in contrast to the JET and TFTR “discrepancy”.
Electron cyclotron (EC) resonance heating and current drive (H&CD) will be one of the auxiliary sys- tems available in ITER , and it is particularly important to have the EC system ready and optimized since the first phases of operation, in order to support scenarios development. To this goal, fast and accurate modelling tools are needed, and as an answer to this need, many laboratories developed EC codes, able to describe EC waves behavior in realistic tokamak plasma scenarios.
Electron Bernstein Waves were shown to possess qualities highly desirable in electron cyclotron heating - they are strongly damped, even at higher harmonics, over a short distance implying the absorp- tion is highly localised. The EBWs’ absorption on high velocity particles would also make them highly suitable for driving non inductive current, but it is hoped that they might be able to drive current near the center of the plasma to supplement the bootstrap current. Unfortunately strong damping at higher harmonics also means that the wave will be wholly absorbed near the edge of the plasma, making it impossible to use EBWs to heat the plasma and drive currents in the interior of the plasma, the latter being one of the best uses the mode could be put to in a spherical tokamak power plant. If some scheme were to be devised that enabled us to use EBWs at the center of the plasma it would enable us to exploit the highly desirable qualities of the modes.
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It has been suggested (Axford and McKenzie, 1997) that magnetic reconnections occurring in the chromospheric net- work at small-scales may create high-frequency Alfv´en waves, and that these waves represent the main energy source for the heating of the solar corona. Following this idea, Tu and Marsch (1997) assumed a wave spectrum in the fre- quency range from 10 −4 to 200 Hz at the coronal base. The part of the energy spectrum that is swept by the proton fre- quency while the wind expands is assumed to be the ion thermal energy source in a two-fluid solar wind model. To produce high-speed wind, the spectrum needs be as high as 106 nT 2 Hz −1 at about 200 Hz (see their model 1). No physical mechanism or observation has yet been presented in support of this assumption. However, the model results are found to be consistent with the proton velocity and the ef- fective temperature observed by UVCS/SOHO (Kohl et al., 1998). Given that these waves exist, they should be ab- sorbed preferentially by the minor heavy ions with low gyro- frequencies, and thus, it is unclear whether there is actually enough wave energy left over in the extended corona for the heating and acceleration of the major solar wind ions, protons and alpha particles, after the multiple absorption by many heavy ions (Cranmer, 2000). Here some selected re- sults of a hybrid kinetic-fluid model (Tu and Marsch, 2001a, 2001b) for the heavy ions are discussed in the context of re- cent SOHO observations.
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lower-port antennas. The absorption rate for the diﬀer- ent types of resonance can be discriminated independently and eﬀectively by the stair-like injection. An obvious in- crease in the stored energy was observed during both the first and second ECH pulses, while there was no change in the density. Figure 2 shows the profiles of electron temper- ature measured by Thomson scattering and electron den- sity measured by a far-infrared laser (FIR) interferometer just before (t = 1.37 sec) and during (t = 1.57 sec) ECH power injection. The plasma center was heated eﬃciently, and the increment in the temperature reached 0.2-0.3 keV. The electron density profile was rather hollow both before and during the ECH pulse. Density pump-out is noticed around the center during ECH (t = 1.57 sec).
Electron cyclotron heating (ECRH) and electron cyclotron current drive (ECCD) has been proven to be one of the most effective and promising methods for plasma heating and current profile control for present and future nuclear fusion research [1-3] , also on HL-2A [4-5] . HL-2A is a medium size tokamak with major radius of 1.65m and minor radius of 0.4m. The toroidal magnetic field could be operated at 2.4T or 1.2T. As the main heating method, until 2010, 3MW/68GHz ECRH system has been developed and upgraded on HL-2A [6-7] , for which the maximum power 2.5MW is injected into plasma. The installed 3MW/68GHz HL-2A ECH/ECCD system has six 0.5MW gyrotrons, six non-evacuated 10m-long transmission lines  , and two types of launchers. Launcher A1 was fabricated for two wave beams and the injection angles could only be changed in the toroidal direction with 0°-20° by manual.  Launcher A2 has the function to inject four wave beams into plasma with the fixed mirrors.