Poloidal inhomogenity of the particle fluctuation induced fluxes near the LCFS at lower hybrid heating and improved confinement transition at the FT-2 tokamak

This paper deals with the new spectral and microturbulence experimental data and their analysis, which show that the radial electric field E _r generated at the lower hybrid heating (LHH) in the FT-2 is high enough to form the transport barriers. The ETB is formed when LHH is switched off. The radial fluctuation-induced E × B drift flux densities near LCFS in SOL are measured at two different poloidal angles. For this purpose two Langmuir probes located at low and high field sides of the torus are used. Registration of the poloidal and radial components of the electric field and density fluctuations at the same time during one discharge permits to measure the poloidal asymmetry of the transport reduction mechanism of the radial and poloidal particle fluxes in the SOL. The absolute fluctuation levels show dependence on the sign of E _r shear. The modification of the microscale turbulence by the poloidal E _r × B rotation shear _{E × B} at the L-H transition near LCFS is also studied by X-mode fluctuation reflectometry. The new data were obtained by spatial spectroscopic technique.Presented at the Workshop Electric Fields Structures and Relaxation in Edge Plasmas, Nice, France, October 26–27, 2004.     

Spectroscopic Diagnostic of the Peripheral Plasma in the Globus-M2 Tokamak with the Injection of Neutral Helium

JETP Letters - The diagnostic of the peripheral plasma parameters in terms of the relation of lines of neutral helium is included in the diagnostic complex of the tokamak Globus-M2. The first...     

Dynamics of the transport barrier formation on the FT-2 tokamak caused by lower hybrid heating

Experiments at the FT-2 tokamak had demonstrated effective plasma LH heating, which was accounted for by both direct absorption of RF power and plasma transport suppression. The improved core confinement accompanied by Internal Transport Barrier (ITB) formation was observed. The RF pulse switch off is followed by triggering of LH transition and the External Transport Barrier (ETB) formation near the last closed flux surface. The present paper is devoted to a much more detailed study of the radial electric fieldE _r behaviour in the region of ITB and ETB and its influence on the tokamak microturbulence in these regions. The new experimental data were obtained by spatial spectroscopic technique using additional pulse helium puffing in hydrogen plasma. Simultaneously microscale plasma oscillations in the frequency band (0.01–2) MHz are observed with local enhanced microwave scattering diagnostics and by x-mode fluctuation reflectometry. Experiments demonstrate that the improved confinement is associated with the modification of microturbulence by the shear of theE×B poloidal velocity. This conclusion is also confirmed by the data obtained by Langmuir probes in the edge plasma. Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreux, Switzerland, June 23–24, 2002”. The study was performed with the support of the Ministry of General and Professional Education of RF (TOO-7.4-2797), INTAS-01-2056 and the RFBR Grants 00-02-16927, 01-02-17926 and 02-02-17684.     

A Study of the Near-Wall Plasma of the Globus-M Tokamak Using an Array of Divertor Langmuir Probes

Technical Physics - An array of ten built-in divertor probes was installed on the lower dome of the Globus-M spherical tokamak. It was used to measure the profiles of the floating potential,...