Effect Of Electron Cyclotron Resonance Heating Research Articles

The influence of electron cyclotron resonance heating on ion-driven fishbone instability

The effect of electron cyclotron resonance heating (ECRH) on fishbone instability is studied based on the generalized energy principle. Off-axis ECRH plays a stabilizing role in fishbone instability, while on-axis ECRH does not distinctly change the growth rate. The frequency of fishbone instability increases (decreases) for off-axis (on-axis) ECRH. The effect of ECRH is greatest when power is deposited near the rational surface. More concentrated power deposition has a better stabilizing effect. Furthermore, the non-resonance effect of trapped energetic electrons is the main factor behind the stabilization effect in the off-axis case, while it has a weak effect in the on-axis case. The frequency of fishbone instability is changed mainly by the Shafranov shift effect on trapped energetic ions since it can change the precessional drift frequency. The Shafranov shift effect can also affect the growth rate because the onset threshold of energetic ion beta is related to the frequency. The effects of magnetic Reynolds number and slowing-down critical energy are weak and can be neglected. This provides the possibility of using off-axis ECRH targeted to the rational surface to control fishbone instability.

Refined Multiphysics Analysis of W7-X Cryopumps

Ten identical cryopumps (CVPs) are to be installed in corresponding divertor volumes of Wendelstein 7-X (W7-X) stellarator before commencing the steady-state phase of operation (OP 2). Each CVP is typically made of two units connected by a transfer line and is fed through a dedicated vacuum vessel feed through. The units consist of water baffle, liquid nitrogen (LN2) baffle, helium panel, and LN2-cooled housing. All components are expected to be well cooled with the available cooling capacity during long-pulse plasma operation in order to maintain the helium panel at about 4 K and hence ensure the desired absorption rate. The LN2-cooled housing has to minimize both the effect of electron-cyclotron resonance heating (ECRH) and the thermal radiation from backside of in-vessel components on the 80-K CVP shield elements. Moreover, the ECRH is unevenly distributed in W7-X, which requires analyses of several cases and sophisticated cooling scheme as described. This paper presents the thermal behavior of CVP components and is followed by the discussion of several important issues for assessment. In addition, eddy current and electromagnetic (EM) forces on CVP copper components are analyzed for the events of fast discharge (FD) of main superconducting coils, plasma current decay, alternating current in control coils, and FD of trim coils. Moreover, sharing of eddy currents between plasma vessel shell and attached CVP is estimated. Structural analysis taking temperature gradients and EM forces into account indicates that the mechanical performance is acceptable.

Effect of ECRH and resonant magnetic fields on formation of magnetic islands in the T-10 tokamak plasma

Experiments in the T-10 tokamak demonstrated possibility of controlling the plasma current during disruption instability using the electron cyclotron resonance heating (ECRH) and the controlled operation of the ohmic current-holding system. Quasistable plasma discharge with repeating sawtooth oscillations can be restored after energy quench using auxiliary ECRH power when PEC / POH > 2–5. The external magnetic field generation system consisted of eight saddle coils that were arranged symmetrically relative to the equatorial plane of the torus outside of the vacuum vessel of the T-10 tokamak to study the possible resonant magnetic field effects on the rotation frequency of magnetic islands. The saddle coils power supply system is based on four thyristor converters with a total power of 300 kW. The power supply control system is based on Siemens S7 controllers. As shown by preliminary experiments, the interaction efficiency of external magnetic fields with plasma depends on the plasma magnetic configuration. Optimal conditions for slowing the rotation of magnetic islands were determined. Additionally, the direction of the error magnetic field in the T-10 tokamak was determined, and the threshold value of the external magnetic field was determined.

Simulations of peeling-ballooning modes with electron cyclotron resonance heating

The effects of the deposited power and deposited position of Electron Cyclotron Resonance Heating (ECRH) on Peeling-Ballooning (P-B) modes are simulated using BOUT++ code in this paper. The simulation results show that as the deposited position moves from the top to the bottom of the pedestal, the edge localized mode (ELM) size decreases first and then increases, finally decreases again. For ECRH with different deposited power, the effects on P-B modes are similar if they have the same peak value of the power deposition profile. These results show that the effects of ECRH on P-B modes are primarily determined by the change in pressure profile caused by ECRH. As long as ECRH can lead to large enough change in pressure profile, ECRH can efficiently affect the dynamics of P-B modes.

Investigation of impurity transport using laser blow-off technique in the HL-2A Ohmic and ECRH plasmas

Impurity transports in two neighboring discharges with and without electron cyclotron resonance heating (ECRH) are studied in the HL-2A tokamak by laser blow-off (LBO) technique. The progression of aluminium ions as the trace impurity is monitored by soft x-ray (SXR) and bolometer detector arrays with good temporal and spatial resolutions. Obvious difference in the time trace of the signal between the Ohmic and ECRH L-mode discharges is observed. Based on the numerical simulation with one-dimensional (1D) impurity transport code STRAHL, the radial profiles of impurity diffusion coefficient D and convective velocity V are obtained for each shot. The result shows that the diffusion coefficient D significantly increases throughout the plasma minor radius for the ECRH case with respect to the Ohmic case, and that the convection velocity V changes from negative (inward) for the Ohmic case to partially positive (outward) for the ECRH case. The result on HL-2A confirms the pump out effect of ECRH on impurity profile as reported on various other devices.

A hybrid electron cyclotron resonance metal ion source with integrated sputter magnetron for the production of an intense Al⁺ ion beam.

A metal ion source prototype has been developed: a combination of magnetron sputter technology with 2.45 GHz electron cyclotron resonance (ECR) ion source technology-a so called magnetron ECR ion source (MECRIS). An integrated ring-shaped sputter magnetron with an Al target is acting as a powerful metal atom supply in order to produce an intense current of singly charged metal ions. Preliminary experiments show that an Al(+) ion current with a density of 167 μA/cm(2) is extracted from the source at an acceleration voltage of 27 kV. Spatially resolved double Langmuir probe measurements and optical emission spectroscopy were used to study the plasma states of the ion source: sputter magnetron, ECR, and MECRIS plasma. Electron density and temperature as well as Al atom density were determined as a function of microwave and sputter magnetron power. The effect of ECR heating is strongly pronounced in the center of the source. There the electron density is increased by one order of magnitude from 6 × 10(9) cm(-3) to 6 × 10(10) cm(-3) and the electron temperature is enhanced from about 5 eV to 12 eV, when the ECR plasma is ignited to the magnetron plasma. Operating the magnetron at constant power, it was observed that its discharge current is raised from 1.8 A to 4.8 A, when the ECR discharge was superimposed with a microwave power of 2 kW. At the same time, the discharge voltage decreased from about 560 V to 210 V, clearly indicating a higher plasma density of the MECRIS mode. The optical emission spectrum of the MECRIS plasma is dominated by lines of excited Al atoms and shows a significant contribution of lines arising from singly ionized Al. Plasma emission photography with a CCD camera was used to prove probe measurements and to identify separated plasma emission zones originating from the ECR and magnetron discharge.

The effect of ECRH on the electron velocity distribution function

Electron cyclotron resonance heating (ECRH) is a mature technology that has progressed constantly over a period of forty years, particularly as a tool in magnetic confinement fusion. As with other heating methods, this technique has seen a steady increase in the sophistication of its applications, from bulk heating through profile tailoring and finally to distribution function engineering. By comparison with other techniques, ECRH presents the significant advantages of good coupling, localized power deposition, easy launching and precise directionality. This paper reviews some recent applications related to third harmonic ECRH and highlights the role of the relaxation dynamics of suprathermal electrons, both in real space and in velocity space, in regulating the overall effect of ECRH on fusion plasmas. A technique for direct visualization of these relaxation phenomena, using modulated ECRH, is described and demonstrated.

The effect of ECRH on the stability of the radiation induced m = 2 mode and on the current quench of a major disruption

The results of a series of experiments done in RTP which had the purpose to avoid or ameliorate radiative density-limit disruptions, will be reported. Avoidance of disruptions was achieved by stabilizing the m = 2 radiation induced tearing mode (RTM) with electron cyclotron resonance heating (ECRH). Both continuous and modulated power deposition was studied. It was found that stabilization with modulated ECRH in phase with the O-point was less efficient than continuous ECRH, contrary to theoretical expectations. Detailed scans of the EC power deposition and of the power intensity were in agreement with the assumption that radiative heat loss is the driving mechanism of this m = 2 mode. Amelioration of disruptions was achieved, in a pilot experiment, by applying ECRH at the end of the energy quench. In this way, the current decay that follows a major density-limit disruption could be reversed.

Sawtooth stabilization by localized electron cyclotron heating in the WT-3 tokamak

The effect on sawtooth oscillations (STO) by localized electron-cyclotron-resonance heating (ECH) on the WT-3 tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 1, p. 563] is studied. STO are strongly modified or stabilized by ECH near the q=1 surface, where q refers to the safety factor. The effect of ECH is much stronger when it is applied on the high-field side as compared to the low-field side. Further, even when ECH is applied outside the q=1 surface, the amplitude of STO decreases and STO stabilizes. In the very high qL discharge, the excitation of STO can be obtained by applying ECH.

Sawtooth stabilization by electron cyclotron heating at the q=1 surface in the WT-3 tokamak

Sawtooth oscillations (STO) in the Ohmically heated (OH) WT-3 tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1988 (IAEA, Vienna, 1989), Vol. 1, p. 563] are strongly modified or suppressed by localized electron cyclotron resonance heating (ECH) near the q=1 surface, where q refers to the safety factor. The effect of ECH is much stronger when it is applied on the high-field side, as compared to the low-field side. Complete suppression of the STO is achieved for the duration of the ECH when it is applied on the high-field side, in a low-density plasma, provided the ECH power exceeds a threshold value. This threshold decreases with the increasing safety factor at the limiter qL and the complete stabilization of STO can be obtained even when ECH is applied on the low-field side in the high-qL region. It is noticeable that these complete stabilizations can be obtained only by the localized ECH with the elliptic antenna. The STO stabilization is attributed to a modification of the current density profile by high-energy electrons generated by ECH, which reduces the shear in the q=1 region.