Experimental study of drift wave turbulence and anomalous transport

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Cavity diagnostics on fluctuating discharges

SIGLEAvailable from TIB Hannover: RO 9159(10-A4-91) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Study of lower-hybrid wave propagation in the presence of low-frequency fluctuations

SIGLEAvailable from TIB Hannover: RO 9159(1992,17) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Enhanced microwave pulse backscattering off externally excited lower-hybrid waves

In small tokamak and laboratory plasmas, the pulse (RADAR) modification of the enhanced scattering diagnostic permits observation of small-scale density fluctuations with high spatial and wavenumber resolutions. The method is experimentally studied on an r.f. generated linear discharge at which externally excited lower-hybrid waves are diagnosed. (orig.)Available from TIB Hannover: RO 9159(36)+a+b / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Anomalous transport and anomalous heating due to lower hybrid wave fields

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Evaluation of probe characteristics by non-linear fitting procedures

An automatic procedure to evaluate the current-voltage-characteristics measured by both plane and cylindrical probes is studied. The investigations are performed on a magnetised plasma column produced by extraction from a magnetic box. Accounting for the existence of an electron beam which thermalises along the column, different models for the EVDF are appropriate for plane and cylindrical probes, respectively. For the measurements with plane probes, we use Maxwellian at rest superposed by a thermal beam distribution. In the case of cylindrical probes, the electrons are described by a single or a bi-Maxwellian distribution function. Here, the proper description of the ion current is important since the electron current perpendicular to the magnetic field is strongly lowered. To treat the ion current, we use the orbital as well as the radial motion theory. The minimisation algorithm of Levenberg and Marquardt is applied to evaluate the probe characteristics. The plasma parameters, in particular the electron density, the electron temperature, and the plasma potential, are treated as free parameters of non-linear model functions that are fitted to the entire probe characteristic. The proposed evaluation procedure yields statistical errors of the fitted values as well as estimates of those systematical errors arising from incorrect probe models. By comparing these errors, one can decide whether or not the model used can be accepted. (orig.)Available from TIB Hannover: RO 9159(32)+a+b / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Study of lower-hybrid wave propagation by CO_2-scattering and RF probe diagnostics

SIGLEAvailable from TIB Hannover: RO 9159(13) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Propagation and damping of m =+1 and m =-1 helicon modes in an inhomogeneous plasma column

The effect of the density gradient on the dispersion of the m=+1 and m=-1 helicon modes is investigated both theoretically as well as numerically. In particular, attention is focussed on the helicon wave damping that is closely related to the rf power absorption and the Poynting flux. It is shown that the propagation characteristics of the m=-1 mode changes drastically when the density gradient is sufficiently strong: This mode exhibits a cut-off that depends on the gradient scale length and the plasma parameters. In the regime where both helicon modes propagate, the excitation of the m=-1 mode is unlikely as it is strongly damped. The results give evidence that the density gradient effect is decisive for the formation of helicon discharges which are predominantly sustained by the m=+1 mode. (orig.)SIGLEAvailable from TIB Hannover: RO 9159(66)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Study of radar enhanced scattering on a magnetized rf discharge

RADAR enhanced scattering (RES) is a sensitive diagnostic for measuring the wavenumber spectra of small-scale density fluctuations. It makes use of the small group velocity of the extraordinary wave near the upper-hybrid resonance (UHR). Microwave pulses irradiating a magnetized plasma (E, k_0 perpendicular to B_0) are back-scattered off density fluctuations with a measurable time delay which is proportional to the fluctuation wavenumber. In the present investigation, we study the RES diagnostic on a rf-generated linear discharge. Using externally excited lower-hybrid waves as test fluctuations, reasonable results are achieved. The features of the RES diagnostic are discussed. (orig.)Available from TIB Hannover: RO 9159(47)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Effect of the plasma inhomogeneity on the wave excitation and the rf power deposition in helicon discharges

The rf power deposition in helicon discharges generated through helical antennas depends sensitively on the radial density profile. The results obtained on two distinct devices give evidence that the density gradient is decisive for the formation of helicon discharges which are predominantly sustained by the helicon modes with azimuthal mode numbers m>0. The width of the density profile determines the degree of axial asymmetry of the discharge caused by the different propagation behaviours of m>0 and m<0 helicon modes. Furthermore, the total rf power absorption is significantly affected by the edge density. Our computational results show, in particular, that the Trivelpiece-Gould mode carries a considerable fraction of the rf power which is most likely rapidly lost at the plasma edge. With respect to plasma applications, the rf power coupling via m=+2 helical antennas may be very attractive because large-volume plasmas can be generated. (orig.)SIGLEAvailable from TIB Hannover: RO 9159(72)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman