Profiles of the Balmer lines D,(H,), Db(Hs) and D, (H,) have been measured in the scrape-off layer and within the edge of the TEXTOR (upgrade) plasma, under Ohmic conditions and with neutral-beam injection. Each line profile shows a strong Zeeman effect in the vicinity of line centre, and a marked central dip when mainly the ( I components are observed. The line core evidently originates from cold atoms in the edge plasma, excited in the course of molecular dissociation, while the broad pedestal on which the core rests is radiated by excited atoms produced through chargeexchange recombination of deuterons (protons), transported outwards from the much hotter plasma interior, and by atoms heated directly by collisions with the deuterons (protons). Core temperatures of about 0.5 eV and less are obtained from line profile analysis.

During runaway discharges in TEXTOR, intense infrared (IR) radiation is-emitted in the electron flow direction. This can only be explained by synchrotron radiation of fast electrons. The observed spectral dependence is consistent with electrons of 25-30 MeV energy; the intensity corresponds to about 1016 electrons or to an electrical current of 40 kA. From the spatial structure of the observed IR pattern, new insight into the spatial distribution of the runaway electrons and their perpendicular momentum can be gained. The runaway electrons populate a torus with a diameter of 0.5-0.6 m, which is slightly larger than the plasma radius; the perpendicular momentum is determined from the vertical extent of the IR pattern and amounts to about 5 m0c. The transformation rate of electrons to runaways can be estimated from the time delay of the IR signal as 2 × 10−4 s−1; this agrees with theoretical expectations derived from the ratio of the electrical field strength to the critical field strength. In TEXTOR, runaways are confined up to energies of 50 MeV, which is just below the limit where a phase should exist in which runaways radiate as much energy as they gain per turn.

Experimental results from TEXTOR are presented to provide strong evidence for the feasibility of the "cold radiative plasma mantle", a concept which might be a possible solution for the energy exhaust problem in a fusion reactor. The concept is compared with the high density divertor. The compatibility to other constraints, limitations and open problems are discussed, in particular the issues of stationarity (feed-back control, thermal instabilities, q=2), energy confinement. Heexhaust and fuel dilution.

The Doppler broadened profile of a C I line in the infrared (λ =909.5 nm, 3P2 to 3P20) has been measured with high spectral resolution (λ/Δλ > 105) in front of a graphite limiter in the TEXTOR tokamak. The line shows a strong Zeeman effect, but by selecting the pi component with a polarizer, the influence of the magnetic field of TEXTOR on the line shape can be practically eliminated, and the profile is determined only by the velocity distribution of the carbon atoms. By a comparison of shots with a 'detached plasma' and shots with injected gas (CO, CH4) it could be shown that the carbon flux from the limiter is mainly determined by chemical sputtering in a 'detached plasma'. In a plasma attached to the limiter, the energy of the released carbon atoms increases with the electron temperature (Te) at the limiter, the typical width of the line gradually increases from about 16 pm to 50 pm (corresponding to velocities of 5 × 105 to 1.5 × 106 cm/s or energies of 1.5 to 13.5 eV), indicating that physical sputtering dominates at high Te and that chemical sputtering then gives only a small contribution (<15%) to the impurity production at the limiter

Examples are presented of Doppler broadening measurements on singlet, doublet and triplet emission spectra from the following impurity ions found in the boundary layer of the TEXTOR tokamak: CII, CIII, CIV, Sin, and Sim. The shapes of these spectral lines are significantly influenced by the confining magnetic field of some 2T, in some cases exhibiting an appreciable Paschen-Back effect which complicates their appearance. It is shown that reliable values for the particular ion temperature can be obtained from the Doppler widths of the various Zeeman components, when the presence of the magnetic field is properly accounted for. Such temperatures derived from partially ionised impurity species should, however, be cautiously interpreted, as the ions in question probably do not exist for long enough in the particular ionisation stage to achieve thermal equilibrium with the background deuterons and protons. This interpretation of our results is supported by a simple one-dimensional model of ionisation and collisional heating processes in the plasma boundary.

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The first encouraging experiments demonstrating direct, explicit control of the He 2+ density in a tokamak plasma have been performed in the TEXTOR tokamak with the Advanced Limiter Test-II pump limiter. Helium is injected in a short gas puff from the outside of the plasma, is observed to reach the plasma core, and then is readily removed from the plasma. An exhaust efficiency of -8% is obtained. Active charge-exchange spectroscopy is used to study the exhaust and transport of He 2 * within the plasma, and the density evolution is modeled with a diffusive-convective transport code.PACS numbers: 52.25.Fi, 34.70.+e, 52.55.Fa, 52.70.Kz In future burning fusion devices, helium (He) ash must be continuously removed from the core to prevent dilution of the deuterium-tritium (D-T) fuel and concomitant quenching of the burn. Thus, He ash removal is fundamental to the operation of any fusion reactor, since the rate at which the a-particle by-products of the fusion reaction are purged from the core plasma will determine the pulse length available before the burn is quenched. For proposed steady-state tokamaks, such as the International Thermonuclear Experimental Reactor (ITER), continuous purging of the He ash is essential. Recent estimates 1 show that newly created He ions must be removed within 7 to 15 energy confinement times to maintain continuous reactor operation.The recycling of injected He from the wall and the lack of direct diagnostic capability to measure He concentrations have complicated previous efforts to determine the He removal rate. 2 " 4 Estimating this rate requires knowledge of the recycling coefficient, which can only be determined indirectly and depends on the wall conditioning status and history of the device. The experiments reported here are the first in which direct, explicit removal of injected He has been demonstrated. This is made possible by the Advanced Limiter Test-II (ALT-II) system, a toroidal belt limiter 5-7 that uses turbomolecular pumps (TMPs). Most existing particle exhaust schemes use gettering materials or cryopumping systems, which do not pump He. We simulate the presence of recycled He ash in a tokamak by puffing concentrations of 3%-5% He (relative to n e ) into the TEXTOR plasma just before or during neutral-beam injection (NBI). The transport of the He into the plasma core and its subsequent pump-out phase using the ALT-II system are followed with spectroscopic techniques by observing the He in three locations: the plasma core, the plasma edge at the ALT-II limiter, and the ALT-II pumping duct. By combining the results from these measurements, the exhaust efficiency for the He found in the plasma core is obtained during ALT-II pumping.In the plasma core, the He density is measured by charge-exchange excitation (CXE) spectroscopy, in combination with NBI. Measuring spatially and temporally resolved ion temperatures and absolute densities using CXE line intensities is a well-established technique on many tokamaks. 8 " 11 We use CXE spectroscopy to obtain the local He 2+ densi...