[en] The transport inside the scrape-off layer (SOL) of a tokamak is analysed. In particular, poloidal asymmetries in electron density profiles measured in the presence of a toroidal limiter are compared with results obtained from a numerical two-dimensional code (SOLXY). The relevance of poloidal and radial drifts for these asymmetries is demonstrated by a reversal of the main magnetic field. The results are important for the validation of the theoretical model SOLXY. (author). Letter-to-the-editor. 13 refs, 3 figs

[en] Erosion of POCO graphite by helium in PISCES-A was measured by carbon spectroscopy at temperatures from 550deg-2000deg C, energies of 30-250 eV and fluxes of 1-2x10²² m^-2 s^-1, Yields at low energies were higher than predicted in current models. The effect of redeposition is discussed. (orig.)

[en] Newly developed bulk-boronized graphites and boronized C-C composites with a total boron concentration ranging from 1 wt% to 30 wt% have been evaluated as plasma-facing component materials for the International Thermonuclear Experimental Reactor (ITER). Bulk-boronized graphites have been bombarded with high-flux deuterium plasmas at temperatures between 200 and 1600deg C. Plasma interaction induced erosion of bulk-boronized graphites is observed to be a factor of 2-3 smaller than that of pyrolytic graphite, in regimes of physical sputtering, chemical sputtering and radiation enhanced sublimation. Postbombardment thermal desorption spectroscopy indicates that bulk-boronized graphites enhance recombinative desorption of deuterium, which leads to a suppression of the formation of deuterocarbon due to chemical sputtering. The tritium inventory in graphite has been found to decrease by an order or magnitude due to 10 wt% bulk-boronization at temperatures above 1000deg C. The critical heat flux to induce cracking for bulk-boronized graphites has been found to be essentially the same as that for non-boronized graphites. Also, 10 wt% bulk-boronization of graphite hinders air oxidation nearly completely at 800deg C and reduces the steam oxidation rate by a factor of 2-3 at around 1100 and 1350deg C. (orig.)

[en] Plasma-facing components for experimental and commercial fusion reactor studies may include cladding or coatings of refractory metals like tungsten on metallic structural substrates such as copper, vanadium alloys and austenitic stainless steel. Issues of safety and fuel economy include the potential for inventory buildup and permeation of tritium implanted into the plasma-facing surface. This paper reports on laboratory-scale studies with 3 keV D₃⁺ ion beams to investigate the hydrogen transport behavior in tungsten coatings on substrates of copper. These experiments entailed measurements of the deuterium re-emission and permeation rates of tungsten, copper, and tungsten-coated copper specimens at temperatures ranging from 638 to 825 K and implanting particle fluxes of approximately 5x10¹⁹ D/m² s. Diffusion constants and surface recombination coefficients with enhancement factors due to sputtering were obtained from these measurements. These data may be used in calculations to estimate permeation rates and inventory buildups for proposed diverter designs. (orig.)

[en] In the toroidal magnetic field coils of the critical plasma testing device JT-60, the outline of coil insulation was already reported. As the insulation structure, it is the extension of the insulation techniques for the stator coils of large rotary machines, but consideration is given so as to sufficiently withstand the repeated loading of large mechanical force and the X-ray irradiation at the time of escaped electron discharge from plasma. The toroidal magnetic field coils for JT-60 are outlined. The layer insulation material is epoxy resin pre-impregnated aromatic polyamide paper sheet, lined with glass non-woven fabrics on both sides, and the sheets are inserted between coil conductors. The ground main insulators are epoxy resin impregnated mica paper tapes lined with glass cloths. The breakdown voltage, tensile strength and adhesion strength of these materials were evaluated. After the irradiation, the tensile strength and breakdown voltage hardly decreased, but the tensile rupture elongation lowered. As to the materials for insulation bushes, packings and spacers, the bending and compressive strength were tested. Also the fatigue test on the insulating materials was carried out, but the deterioration due to the irradiation was scarcely observed. (Kako, I.)

[en] A failure cause analysis method to be used in a failure diagnosis system for large tokamak fusion machines is proposed. The diagnosis system is designed to identify causes of the abnormal states indicated by alarm annunciators in the machine. The proposed method is based on a cause consequence tree (CCT) model. The analysis comprises two steps; (1) selection of several possible causes from all causes in the CCT, (2) search for the most probable cause from among them. Simulation tests on the circulation system for cooling of a tokamak machine show that this method correctly selects causes in rate of more than 90%. Average computation time for cause determination is within 17 seconds. (author)

[en] This patent describes a fusion device wherein atomic nuclei react to generate reaction products with kinetic energies convertible to useful energy. It comprises: wall means defining and confining a reaction chamber, means for generating a substantially constant unidirectional magnetic field of predetermined strength in at least a portion of the reaction chamber, first and second source means for providing respective first and second positive hot ions at temperatures in a range where the first and second positive hot ions have substantially optimum cross sections for their mutual fusion reaction to generate the reaction products, first and second means for accelerating the first and second positive hot ions, respectively, to predetermined velocities, means for neutralizing the accelerated positive hot first and second positive ions by electrons, means for directing the first and second positive hot ions neutralized by electrons into the portion of the reaction chamber substantially orthogonally of the magnetic field utilizing self-polarization, and means for draining the polarization of the neutralized and polarized first and second positive hot ions to separate the neutralizing electrons

[en] Vacuum conditioning in the HL-1 tokamak is summarised. The gaseous impurities were reduced from 5.3 x 10^-5 Pa in 1984 to 1.1 x 10^-5 Pa in 1987. Only when the ultimate pressure is less than 1.3 x 10^-5 Pa, and the percent concentration of H₂O components less than 5%, it is suitable for initial wall conditioning of tokamak discharges. By using the GH₃₉ SS limiter, G₃ graphite limiter or sublimating Ti, the average density of C + O in HL-1 was respectively 6.1 x 10¹¹, 1.4 x 10¹² or 1.1 x 10¹² cm^-3. After sublimating Ti, O decreased nearly 24% and C nearly 16%

[en] Activation calculations, taking irradiation conditions derived from a first wall position in the DEMO design, have been performed for all stable elements with Z numbers between 3 and 83, with the aid of a recently upgraded database. Activity and surface gamma dose rate are used as indices to compare the activation properties of elements. Comparisons with previous results have been made, and improvements to the database discussed. The activation properties of several candidate first wall compositions, including 2 vanadium alloys have been considered. (author). 12 refs.; 4 figs

[en] LCL (LE CARBONE LORRAINE) is involved in the fusion programmes since 1976. The earlier studies in collaboration with CEA Saclay led to the definition of the properties of the materials for TOKAMAK inner protection (low Z, high purity, thermal shock resistance, heat sink). The relevant grades of graphite were selected and thus the grade 5890 PT has been chosen by a number of machines TFR, JET, ASDEX, TORE SUPRA, RFX, VARENNES, TJL. This paper discusses briefly the neutron irradiation resistance of polygranular graphites, the resistance to thermal shock of the AO5 carbon/carbon composite, and the development of two types of high heat transfer assemblies. (H.W.). 6 figs.; 2 tabs