Application Of Electron Cyclotron Resonance Heating Research Articles

Overview of ECR plasma heating experiment in the GDT magnetic mirror

This paper summarizes the results of experiments on electron cyclotron resonance heating (ECRH) of plasma obtained at the axially symmetric magnetic mirror device gas dynamic trap (GDT) (Budker Institute, Novosibirsk). The main achievement is the demonstration of plasma discharges with extremely high temperatures of bulk electrons. According to the Thomson scattering measurements, the on-axis electron temperature averaged over several sequential shots is 660 ± 50 eV with peak values exceeding 900 eV in a few shots. This corresponds to an at least threefold increase as compared to previous experiments both at the GDT and at other comparable machines, thus demonstrating the maximum quasi-stationary (∼0.6 ms) electron temperature achieved in open traps. The breakthrough is made possible with the successful implementation of a sophisticated ECRH scheme in addition to standard heating by neutral beams (NBs). Another important result is the demonstration of the significantly increased lifetime of NB-driven fast particles with the application of ECRH, leading to a 30% higher plasma energy content at the end of the discharge. All available data including the previously demonstrated possibility of plasma confinement with β as high as 60%, allows us to consider fusion applications of axially symmetric magnetic mirror machines on a realistic basis.

Electron particle transport and turbulence studies in the T-10 tokamak

The goals of this paper are to compare the results of electron particle transport measurements in ohmic (OH) plasmas by means of a small perturbation technique, high-level gas puff and gas switch off, investigate the phenomenon of ‘density pump out’ during electron cyclotron resonance heating (ECRH) and to correlate density behaviour with turbulence. Two approaches for plasma particle transport studies were compared: the low perturbation technique of periodic puff (δn/ne = 0.3%) and strong density variations (δn/ne < 50%), including density ramp-up by gas puff and ramp-down with gas switch off. The model with constant in time diffusion coefficients and pinch velocities could describe the core density perturbations but failed at the edge. In the case of strong puff three stages were distinguished. Degraded energy confinement and, respectively, low turbulence frequencies were observed during density ramp-up and ramp-down, while enhanced confinement and higher turbulence frequencies were typical for the intermediate stage. Density profile variation during this intermediate phase could be described in the framework of the transport model with constant in time coefficients. The application of ECRH at the density ramp-up phase provided the possibility of postponing the ‘density pump out’. The increase in the low-frequency modes in turbulence spectra was observed at the ‘density pump out’ phase during central ECRH. Although the high- and low-frequency bands of turbulence spectra behaved as trapped electron mode and ion temperature gradient, respectively, they both rotated at the same angular velocity as a rigid body together with magnetohydrodynamic mode m/n = 2/1 and [E × B] plasma rotation.

Summary of EC-17: the 17th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating (Deurne, The Netherlands, 7–10 May 2012)

An overview is given of the papers presented at the 17th Joint Workshop on Electron Cyclotron Emission (ECE) and Electron Cyclotron Resonance Heating (ECRH). The meeting covered all aspects of the research field ranging from theory to enabling technologies. From the workshop, advanced control by electron cyclotron heating and current drive is emerging as probably the main application of ECRH in fusion devices. Large progress is reported from various experiments on real-time control applications. At the same time ECE is developing into a multi-dimensional plasma diagnostic taking advantage of new technological developments. The resulting multi-dimensional ECE data reveal exciting new details of the complicated plasma dynamics in fusion devices.

Electron velocity distributions measured with soft x-ray PHA at RTP

A soft x-ray pulse height analysis (PHA) system is begin used at the Rijhuizen Tokamak Project to study the electron velocity distribution. A liquid nitrogen cooled Si(Li) detector is used to view the plasma along a tangential line of sight. A gas cell in combination with Al foils is used for filtering. The data-acquisition system is set up in such a way that 16 subsequent spectra, of 1ms–1 s duration and in the energy range 4–30 keV, can be measured during a single tokamak discharge. The PHA system has been used extensively for measuring the electron temperature, the effective charge number Zeff, and the species and concentrations of high-Z impurities in the plasma. Special attention was devoted to study the effect on the electron velocity distribution of electron cyclotron resonance heating (ECRH) power (60 GHz, up to 180 kW) launched in the ordinary mode from the low-field side. During application of ECRH the temperature deduced from PHA always exceeds the value from Thomson scattering. This deviation can be explained by the presence of nonthermal components in the electron velocity distribution. Finally, the effect of boronization of the vacuum vessel on the impurity concentration was studied.