[en] The transition n = 1 to n = 2 has the most simple structure of all hydrogen transitions and the corresponding spectralline Ly-α is therefore very appropriate to reveal discrepancies between theory and experiment. In this work mainly the Ly-α spectral line of neutral hydrogen has been studied. The electron density of the Z-pinch amounts to 1.5 x 10²⁴ m^-3 with an electron temperature of about 1.2 x 10⁵ K. In this parameter range the plasma can still be studied with spectroscopic methods in the visible spectral region. Based on a space and time resolved measurement of the continuous emission spectra the plasma parameters can be determined independent of line broadening. (orig./HT)

No abstract available

[en] The dense plasma phase of a dynamic z-pinch working at a high filling pressure is studied. By using the Schlieren-technique it is found that the compressed plasma column, though macroscopically stable for times less than 1 μs develops quickly from a homogeneous state to a turbulent one with a perturbation scale length of typically some millimeters. Quantitative measurements of light deflection give electron densities of typically 10¹⁹ cm^-3 at 0.25 torr He filling. (orig.)

[en] The plasma density and temperature of a dense z-pinch have been deduced from the continuum radiation of the plasma between 200 and 1000 nm, from the optical thickness of the plasma column, and from holographically obtained interferograms. At the time of maximum compression, the temperature is typically between 5 and 10 eV and the electron density between 5 x 10¹⁷ and 5 x 10¹⁹cm^-3, depending on the choice of filling gas and pressure. Both hydrogen and helium were used. The radial continuum radiation of the optically thick plasmas by applying Bartel's theory. (author)

[en] At TEXTOR, an X-ray spectrometer in a Johann mount is utilized to measure the X-ray spectra of He-like elements with intermediate Z. Up to now, the spectra of He-like argon have been investigated. The spectra have been modeled with the most recent atomic data using physically relevant parameters only. Good agreement has been found both in modeling the experimental spectra and in the determination of the plasma parameters, such as ion temperature and plasma motion and electron temperature. The deviations between the theoretical and experimental spectra are below 7% for all lines; the precision of the plasma parameters obtained by X-ray spectroscopy agrees with the accuracy of the standard diagnostics at TEXTOR.In addition, the abundance of Li-/He-like ions, as well as the H-/He-like ions, has been measured. For the higher densities, the abundance approaches the coronal expectation. Larger deviations to the coronal limit have been found with neutral beam injection. The system is now being upgraded for spatial resolution

[en] Important synergetic effects are observed when combining NBI-co and ICRH. These include (i) increase of incremental confinement time when each heating method is applied to a plasma preheated by the other one; (ii) enhancement of the current drive efficiency resulting in a 50% increase by the addition of an equal amount of RF power; (iii) enhancement of the density domain where sawtooth stabilization (of the monster type) is achieved; and (iv) significant enhancement of the neutron yield due to beam-target interaction. These effects generally need for their interpretation the assumption of a direct beam acceleration by the RF waves as is indeed observed by the NPA spectra. A synergetic effect is also seen in the combination NBI-co + NBI-counter leading, as for NBI-co + ICRH, to an improved confinement with respect to the Kaye-Goldston or Goldston L-mode scaling. (author). 13 refs, 3 figs

[en] The main results obtained during the first six months of experimental work on TEXTOR with ohmically heated plasmas are reported. The machine (R = 175 cm; a = 45-50 cm) was operated at wall temperatures up to 300⁰C with hydrogen gas, a toroidal field of 2 T and a maximum plasma current of 500 kA, yielding central electron temperatures of 1.2 keV, maximum line-averaged densities of 4 x 10¹³ cm^-3 and discharge durations of up to 2.7 sec (for Isub(p) <= 340 kA). Besides providing long-lasting reproducible plasmas for forthcoming plasma-wall interaction research, the following tasks were accomplished: (1) control of low Z impurities by effective wall cleaning and conditioning; (2) accurate plasma positioning for extended pulse durations; (3) determination of the current density distribution by way of Faraday rotation measurements; (4) investigation of plasma limiter interaction including spectroscopic determination of released neutral particle fluxes and measurement of the power density distribution in the scrape-off layer by infrared-thermography. (author)

[en] Line radiation from impurities in the boundary of a tokamak plasma is the main means for distributing the power flux uniformly onto the wall. Thereby, critical power loads to the limiter edge or the divertor plate can be avoided. The objective is to find the appropriate impurity species, which allow to radiate on a high power level and at the same time fulfill the principal requirements for radiation cooling in a fusion plasma: a) restriction of the radiation to the boundary zone, b) impurity concentration in the centre below a critical value (fuel dilution, bremsstrahlung) and c) thermal stability. The study of plasmas with various levels of radiation (γ=P_rad/P_heat) is a subject of ongoing research on TEXTOR. In particular, emphasis has been put on investigating the properties of plasmas with a cold radiative edge close to the density limit (detached plasma). These studies have first been concentrated on the case of pure ohmic heating, but recently have been extended to discharges with strong auxiliary heating. A quasi-stationary high radiation level (γ close to 100%) has been achieved by injecting Ne into the plasma. In the present paper we summarize these results, discuss the radiation characteristics and check the data with respect to the requirements for radiation cooling in a fusion plasma. (author) 9 refs., 5 figs

[en] The TEXTOR plasma serves as a test bed for plasma/wall interaction studies and ICRH experiments. Reproducible and long-lasting discharges with soft termination were generated in the internal disruptive mode. The operational regime for Ohmic heating is shown in a 1/q versus n-barsub(e)R/Bsub(T) diagram. A comparison of electrical conductivity derived from current density measurements with calculated values favours neoclassical theory. A pump limiter installed on TEXTOR demonstrated a particle removal rate of 6x10²⁰ particles per second out of the boundary layer. It could decrease the central electron density by 50%. The pump limiter was used to control fuelling and recycling characteristics of stable discharges. First experiments with additional ICRH showed a strong influence on the plasma boundary and scrape-off layer. The interaction of the radiofrequency with the boundary layer at present limits the power input to the plasma. Plasma boundary parameters have been measured by optical methods combined with neutral particle beams. (author)

[en] The TEXTOR research programme focusses on the systematic analysis of plasma wall interaction, the development of a suitable wall system and the production of quasi-stationary long-pulse high-temperature plasmas with tolerable impurity concentrations, with well-defined boundary layer and with relevant particle and power fluxes through the boundary. The method of wall carbonization developed in Julich and some characteristic features of the TEXTOR plasma obtained with this method for both, metal limiters and graphite limiters are described. The effect of ICRH heating (2MW, 1 sec) on plasma parameters and on the boundary layer is discussed, together with the application of the single head pump limiter ALT-I and of the localized set of magnetic perturbation coils for boundary 'ergodization'. (author)