On Measurement of Plasma Current Profile by Neutral Beam Probe

A neutral beam probing method is proposed for measurement of plasma current profile in a tokamak. An emulsion plate is used to detect the secondary ions. This method is compared with the ion beam probing in which the primary particles are heavy ions. It has been concluded that a neutral beam is superior to an ion beam for the purpose of determining plasma current profile. From numerical orbit calculations, it has been found that this method is applicable to the tokamak NOVA II, with moderate requirements on the neutral beam source

Plasma Diagnostics Using Two-Component Neutral Beam

A method is proposed for simultaneously determining the electron temperature and the density of a plasma by using a two-component neutral beam of argon and hydrogen. The feasibility of this method has been demonstrated on the tokamak NOVA II, using an argon and a hydrogen beam separately. The electron temperature was determined from the attenuation of an argon beam. In the central electron temperature from 100 to 250 eV, the results obtained are in good agreement with the line-averaged values of the electron temperature estimated from the temperature and density profiles which have been measured by the Thomson scattering. The ion density was determined with a hydrogen beam, and was found to be consistent with the electron density measured by microwave inter-ferometry. This method of a two-component neutral beam probing can be applied to the diagnostics of the scrape-off layer plasmas in large devices

Electron Temperature Measurement by Thomson Scattering in Tokamak NOVA II

The Thomson scattering method was applied to determine the temperature and density profiles of plasma electrons in the NOVA II tokamak. To minimize the intensity of stray light, use was made of a viewing damp, which was an array of blue-glass knife edges. The radial profile of electron density has been found to be approximately parabolic, while the temperature profile appeared more peaky and can be represented by the square of the parabolic expression. The electron energy confinement time determined by this method is in good agreement with that predicted by the Alcator scaling law

Extension of the operational regime of the LHD towards a deuterium experiment

As the finalization of a hydrogen experiment towards the deuterium phase, the exploration of the best performance of hydrogen plasma was intensively performed in the large helical device. High ion and electron temperatures, Ti and Te, of more than 6 keV were simultaneously achieved by superimposing high-power electron cyclotron resonance heating onneutral beam injection (NBI) heated plasma. Although flattening of the ion temperature profile in the core region was observed during the discharges, one could avoid degradation by increasing the electron density. Another key parameter to present plasma performance is an averaged beta value $\left\langle \beta \right\rangle$ . The high $\left\langle \beta \right\rangle$ regime around 4% was extended to an order of magnitude lower than the earlier collisional regime. Impurity behaviour in hydrogen discharges with NBI heating was also classified with a wide range of edge plasma parameters. The existence of a no impurity accumulation regime, where the high performance plasma is maintained with high power heating  >10 MW, was identified. Wide parameter scan experiments suggest that the toroidal rotation and the turbulence are the candidates for expelling impurities from the core region

Reconstruction of the Eddy Current Distribution on the Vacuum Vessel in a Reversed Field Pinch Device based on the External Magnetic Sensor Signals

For the MHD equilibrium reconstruction of a reverse field pinch device, it is a big issue to identify accurately the strong eddy current flow on the shell. In the present work, boundary integrals of the eddy current along the shell are added to the conventional Cauchy-condition surface method formulation. The eddy current profile is unknown in advance but straightforwardly identified using only the signals from magnetic sensors located outside the plasma. Two ideas are introduced to overcome the numerical difficulties encountered in the problem. One is an accurate boundary integral scheme to damp out the near singularity occurring at the sensor position very close to the shell. The other is the modified truncated singular value decomposition technique to solve an ill-conditioned matrix equation when a large number of nodal points exist on the shell. The capability of the new method is demonstrated for a test problem modeling the RELAX device

A Data-Assimilation Based Method for Equilibrium Reconstruction of Magnetic Fusion Plasma: Solution by Adjoint Method

Accurately determining the magnetohydrodynamic (MHD) equilibrium is fundamentally important in controlling and stabilizing fusion plasmas. Development of reliable methods for equilibrium reconstruction is therefore crucial to advancing the fusion plasma research. However, since the dynamics of plasma phenomena are highly nonlinear and highly complicated dynamics, it is difficult to develop their rigorous mathematical model. We already proposed a method of equilibrium reconstruction for fusion plasmas based on data assimilation. In the method the problem is formulated as a parameter optimization and a solution by the sensitivity equation method is proposed. In this paper, we propose a solution of equilibrium reconstruction for fusion plasmas by the adjoint method for the purpose of reducing computation time. In order to ensure the applicability of the adjoint method to a wide class of fusion plasmas, the problem formulation and derivation of the reconstruction algorithm based on the adjoint method are performed in generic form. Furthermore, we implement the proposed method as equilibrium reconstruction algorithms applicable to axisymmetric toroidal plasmas, typical examples of which are tokamaks and reversed field pinches (RFPs). Finally, the proposed method is applied to a real RFP experiment, and it is shown that the proposed method has the capability of reconstructing the equilibrium with sufficient accuracy and dramatic reduction of computation time compared with the existing methods