[en] An ion heating by excited low hybrid waves has been observed in a coaxial type double plasma device. The lower hybrid resonance heating is examined on the two components of the kinetic energy perpendicular and parallel to the magnetic field. (Auth.)

[en] We have observed repetitive, parallel electric-field wave packets with extremely large amplitude (>80 kV/cm) in the current limiting phase of a high-voltage linear plasma discharge. The power spectral density of the whole span of the wave packets shows the peak frequency, 60 MHz in the vicinity of the lower hybrid frequency. Corresponding to these repetitive electric-field bursts, the 70 GHz microwave interferometer recorded an electron density modulation, δn_e/n_e that is estimated as large as a few x10%. The cross-correlation measurement of the electric-fields indicates the excitation of lower hybrid modes by electron beams produced in the onset phase of a linear plasma discharge. (author)

[en] Using a coaxial double plasma device the authors excited the lower hybrid wave in an argon plasma in mirror magnetic fields. When the lower hybrid wave was excited the perpendicular ion energy E(transverse) and the plasma density n were increased. A relation between the relative changes of the average energy ΔE(transverse)(mean)/E(transverse)(mean) and the density Δn/n agrees very well with a relation expected from loss-cone considerations. (Auth.)

[en] Low frequency wide-band noises below 5 MHz spontaneously excited around plasma boundaries near a line cusp are suppressed by the positive bias to a mesh inserted at the cusp with a result of marked reduction of leak width to a value of the order of the hybrid diameter. (author)

[en] An optically-isolated transmission system used in conjunction with a floating double electric probe was developed to measure directly fluctuating large amplitude electric fields and to isolate the measuring system from high common-mode voltages generated in the high-voltage straight discharge in a longitudinal magnetic field. A train of repetitive pulses of the axial electric field, frequently with the negative polarity where the electric field is directed axially from the cathode-side toward the anode-side, and with amplitude 10 kV/cm (although considerably underestimated value) was observed in close correlation with the enhanced current limitation. Moreover an intense E-field pulse, identified as a moving double layer, with amplitude typically 15 kV/cm and 30 nsec in half width was observed at the instant of abrupt current limitation. (Auth.)

[en] Density fluctuations in the outer edge of the plasma, behind the limiter, have been investigated in the TEXTOR tokamak by a new technique using a probing beam of thermal neutral lithium. With this method, radial profiles of the electron density and its fluctuations are obtained and thus also the relationship between turbulence and plasma parameters, especially the density gradient scale lengths. The turbulences are found to consist of coherent fluctuations in the frequency range of sawtooth oscillations (<100 Hz) and fluctuations having a broadband spectrum of frequencies up to ∼1 MHz. The frequency spectra vary, depending on radial position and the density gradient scale length. It is also shown that the fluctuation level is well correlated with the density gradient scale length. (author). Letter-to-the-editor. 17 refs, 9 figs

[en] Since the pioneer work on nonlinear phenomena of Langmuir waves done by Zakharov, considerable progress has been made in this area. There have been growing interests in nonlinear evolution of high frequency modes in an unstable plasma. The dispersion properties of unstable waves there are quite different from those in a stable plasma. We have experimentally investigated nonlinear wave phenomena of unstable electron beam waves and briefly reported the formation of a localized structure. In this paper, we will present experimental results on one dimensional nonlinear evolution of initial disturbance and generation of a soliton-like excitation, and discuss these with the theory developed by Yajima and Tanaka. (author) 8 refs., 5 figs

No abstract available

[en] The propagation and spatial evolution of a potential hump generated explosively near the cathode were observed in the current-limiting phase of high-voltage straight discharge with a preexisting hydrogen plasma. Potential profiles along the axis numerically calculated from the real time E field data demonstrate the evolution of a potential hump into a strong double layer (asymmetric electron hole) with an inverse potential jump (ephi/sub D//kT/sub e/ < or approx. =10³) as moving toward the center of the device with a mean velocity 1.2--1.8 x 10⁸ cm/sec

[en] Floating double electric probes in conjunction with optoisolators have been applied to detect strong local electric fields (approx. 1.5 kV mm^-1) in a moving double layer generated by a high-voltage straight plasma discharge. The probe current estimated from the electric signal picked up and the input impedance is found to be very much larger than the ion saturation current (convection current). The result can be explained if one supposes that these probes collect the polarisation current induced by the passage of a highly polarised space-charge layer. (author)