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Measurements and simulations with the UEDGE code of radiated power, and ion saturation currents and power loads to the target plates have been compared for density scans in ohmic and low confinement mode plasmas in DIII-D, ASDEX Upgrade, and JET. Simulations including cross-field drifts and assuming elevated chemical sputtering yields of 3%–4% move the numerical solutions closer to many of the measurements compared to omitting the drifts and using the published Davis–Haasz yields. Adopting these assumptions the simulations reproduce the measured currents and powers, and their functional dependence on upstream density to within a factor of 2, with the exception of the ion currents to the low field side target in ASDEX Upgrade and the high field side target in JET. The applicability of using enhanced sputtering yields is discussed by comparing measured and simulated emission from low charge state carbon in the divertor regions.

This contribution examines the impact on plasma radiation and on power load to the divertor (i) of large type I ELMs with energies 0.25–1.3 MJ in high current H-mode JET discharges and (ii) of disruptions. (i) The ELMs provoke strong radiation losses, mostly confined to the inner divertor region. Large type I ELMs with ΔWELM ⩾ 0.72 MJ show enhanced radiation losses which are associated with the ablation of carbon layers in the inner divertor. Such large ELMs are usually followed by a phase of type III ELMs with an increased radiation in the plasma core. (ii) The unmitigated disruptions exhibit small radiation fractions with strong poloidal radiation asymmetry during the thermal quench, which could cause Be melting by radiation in ITER. In dedicated experiments on massive gas injection, about 60% of the thermal energy and a significant part of the magnetic energy was converted in radiation and spread uniformly over the first walls.

Detailed modelling of the plasma edge of ASDEX Upgrade in Ohmic and H-mode discharges was performed with the SOLPS (B2-EIRENE) code. A tendency of the code solutions to underestimate the divertor T e and overestimate the plasma density (thus, predicting cooler and denser divertor than in the experiment) has been reliably established. A possible cause of the observed discrepancies is the presence of a significant population of supra-thermal ions and electrons in the SOL and divertor, which cannot be modelled by the fluid plasma code B2.

In ASDEX Upgrade, a fast reciprocating probe positioned in the lower divertor, capable of accessing the low-field side (LFS) and high-field side (HFS) scrape-off layer (SOL) just below the x-point, as well as the private flux region, was equipped with a Mach head and used to investigate fast flow fluctuations and in–out divertor flow asymmetries during ELMs. We compare the flow behaviour during ELMs in the three separate regions. Flow enhancement is observed in the HFS SOL, with Mach number values reaching or exceeding M = 2, flow reversal in the LFS SOL, and complex fluctuating behaviour in the private flux region (which includes flow reversal). We discuss the possible mechanisms that could drive these observations.

Heat deposition onto plasma facing components outside the divertor by ELMs and fast particles has been investigated in ASDEX Upgrade. Heat fluxes up to tens of megawatts per square meter are found during ELMs on limiters and a few megawatts per square meter in between. The total deposited power on non-divertor structures can be up to 10% of the heating power and has to be considered for high power next step experiments. The mechanisms behind the observed heat load patterns are qualitatively understood. The main contributions come from fast ions created by neutral beam injection (and ion cyclotron minority) heating, and from ELMy energy bursts from the plasma edge.

An integrated exhaust scenario has been developed in ASDEX Upgrade providing simultaneous control of particle exhaust, time averaged divertor power flux and ELM power via pace-making of the ELM frequency. Feedback quantities are the divertor neutral flux (actuator: deuterium gas puff) and the divertor temperature as measured by thermoelectric currents (actuator: argon gas puff). The ELM frequency is stabilised to a level high enough for moderate ELM power load with repetitive injection of small pellets from the high field side. The scenario is fully compatible with the present tungsten wall coating, which constitutes about 65% of the area of the plasma facing components. It is intended for application in a future full-tungsten ASDEX Upgrade with strongly reduced intrinsic carbon radiation in order to simulate a possible full-tungsten stage of ITER.

A new second harmonic heterodyne ECE system, which is suitable for the future W7-X stellarator, has been developed and tested at W7-AS. It completes the older W7-AS system. The design was aimed at using less components and improving the system noise compared to the older system. A technical description and first measurements are presented.

Plasma discharges at W7-AS in the ‘electron root’ regime show highly peaked electron temperature- and pressure profiles. A switch-off of the ECRH leads to a fast temperature drop with time constants of less than 1 ms and a corresponding change of the Shafranov shift in the center of the plasma. For a temporally resolved comparison between calculated and measured temperature profiles, a fast method of gaining the mapping of the magnetic field to the radius along the ECE sightline is presented. Using these mappings to compare measured ECE signals with modeled temperatures (assuming plausible profiles of the radial electrical field), the time constant for the decay of the electric field after a ECRH power switch-off was found to be 0.6 ms.

The CERES/NA45 experiment at the CERN-SPS is dedicated to study the production of e + e − -pairs in ultrarelativistic heavy ion collisions. Compared to extrapolations from results obtained in proton-induced reactions, it has previously observed an enhanced production in S-Au [1] and Pb-Au [2] collisions. To verify this enhancement and to study its properties, higher statistics were accumulated during a runtime in 1996. We report here, for the first time, on the results of this analysis (for details see ref. [3]).

The behaviour of carbon in the divertor of ASDEX-Upgrade is investigated by means of optical spectroscopy, bolometry and thermography. Apparent chemical erosion yields, derived from CH molecular band emission and H β spectroscopy are shown to exhibit a pronounced flux dependence and isotope effect, Y chem m H x Γ -0.7 , while no dependence on surface temperature (T surf < 100°C) and impact energy is seen. The flux and isotope dependences also show up in the CII, CIII and total carbon radiation. The weak correlation between the carbon yields in the divertor and the core plasma carbon concentration supports the assumption that main chamber sources are important for the core plasma carbon content under the low temperature, high recycling conditions of this study.

A new divertor was installed in ASDEX Upgrade and went into operation in spring of 1997. The divertor was designed to handle heat fluxes relevant to ITER-like scenarios. For this, the tiles expected to receive the maximum load (strike point modules) are hardened by the use of carbon fibre composites covering about 20% of the total divertor area. The maximum heat flux detected by thermography in a H-mode discharge is only 4 MW/m 2 or below for a total input power of 20 MW without radiating mantle, except some ELMs showing a moderately higher heat flux. A broad distribution of the power load found in the measured poloidal distribution of the heat flux as well as the energy distribution, shows that less than half of the power flowing into the divertor is received by the strike point modules. The remaining power is loaded to other tiles of the divertor, particularly the transition module and parts of the roof baffle near to the strike point modules. The reconstructed radiation pattern reveals that the fraction of power radiated outside the divertor is comparable for both geometries. But the radiated fraction inside the divertor is increased by 10-15% in the Lyra shaped divertor.

Hadronic spectra from interactions of Pb on Au at 158 AGeV/c have been measured by the CERES experiment at the CERN SPS. We report on preliminary results on transverse mass spectra of identified pions and negative hadrons as well as spectra of the positive charge excess obtained by subtracting the negative particle distribution from that of positive tracks. We have also performed a study of the event azimuthal anisotropies which give evidence for directed and elliptic flow in non-central collisions.

The CERES/NA45 collaboration measured, at the CERN SPS, low-mass electron pair production in Pb Au collisions at 158 A GeV/c incident momentum. In this paper we present an analysis of the data taken during the SPS Pb-beam period in the fall of 1995. The results confirm previous findings of CERES showing that the pair production in the mass range 0.2 ee 2 , when scaled to the ion case with the event multiplicity, is enhanced over the expected yield from the known hadronic sources in pp collisions. A comparison of the results for different multiplicity bins indicates that the excess increases faster than linearly with charged-particle multiplicity. We also present the transverse-momentum distributions of the observed pairs.

A simple analytic model of divertor radiation is used as a framework for identifying different routes to divertor detachment. Three means of achieving detachment are demonstrated experimentally including, increasing plasma density, purposely increasing the impurity level and increasing the scrape-off layer connection length. The resulting low electron temperatures in the divertor causes friction processes to dominate ionization in the recycling region, giving rise to plasma pressure loss along field lines. The pressure loss is in approximate agreement with simple analytic modelling.

Power exhaust is one of the critical questions to be solved for ITER, especially with the side condition of sufficient particle exhaust. Since the H-mode threshold might require a high power flux over the separatrix, only small power losses inside the bulk plasma might be permitted, and thus eventually a large fraction of the power must be removed in the scrape-off layer and divertor plasma. Neutral energy losses can only remove a small fraction of the power, and therefore most of the power flux has to be radiated, either by hydrogen isotopes, by the intrinsic impurities (mainly carbon) or by additionally seeded impurities. However, all these scenarios with reduced power flow to the divertor imply also a reduced particle flow into the divertor. This might be critical for particle exhaust, especially concerning the helium ash. Reduction of the power flow to the divertor by enhanced radiation losses has been investigated in the large divertox experiments like JET, DIII-D, ASDEX Upgrade, and JT-60U, and an experimental overview of the present status will be given in this paper, together with a discussion of impurity exhaust (mainly He and Ne) in these scenarios.

In this paper we describe impurity line emission measurements in the divertor of ASDEX Upgrade during high power neutral beam heated discharges. We focus on detached conditions where the dominating part of the radiation comes from the X-point region. Spatially resolved line emission in the VUV and visible spectral region of the intrinsic carbon and additionally puffed impurities (neon and nitrogen) is presented. A simple interpretation of the line emission profiles is given and they are also compared to the results of bolometry.

We report preliminary results of the first measurement of low-mass electron pairs in 160 GeV/nucleon PbAu collisions at central rapidities in a wide multiplicity range. This work is the continuation of our systematic studies on pair production in p-Be, p-Au and SAu interactions. The motivation for this effort derives from a new source of lowmass dileptons recently observed in SAu and S-W collisions by CERES and HELIOS/3, respectively. The results obtained in the analysis of the PbAu data confirm our previous finding that pair production in the mass range 0.2 < mee < 1.5 GeV/c2 is enhanced over the contributions from hadron decays while no significant excess could be observed for mee ≲ 2mπ. A comparison of the results for different multiplicity bins favours a non-linear dependence of the e+e−-yield on the accompanying charged particle densities.

We report on the performance of a doublet of 3 in. cylindrical silicon drift detectors installed as an upgrade of the CERES/NA45 electron pair spectrometer for the Pb-beam at the CERN SPS. The silicon detectors provide external particle tracking and background rejection of conversions and close Dalitz pairs. Results on vertex reconstruction and rejection from a Pb test-run in 1994 are presented.

CERES is an experiment dedicated to measure e+ e−-pairs in nucleus-nucleus collisions at the CERN SPS. Following the experiences gained with proton and sulfur beams the CERES spectrometer was upgraded to cope with the much larger charged particle densities produced in PbPb collisions. Major parts of the upgrade were completed in time for a 10 days test with a lead beam in November 1994. The results clearly demonstrate the feasibility of the experiment in the environment of central PbPb collisions.

Detailed experimental divertor data are presented on the profiles of density and temperature in the inner and outer divertor fans, the radiated power distribution, the gas pressure and the spectroscopically derived particle fluxes, all as a function of the discharge density. At low and medium density, the inner divertor is cold and dense compared to the outer divertor. At high density, strong X-point MARFE and separatrix radiation partially detaches the inner divertor. Probe measurements which penetrate into the X-point MARFE at the outer divertor are presented.

We have for the first time identified e + e − -pairs produced by strongly varying electromagnetic fields in distant SPt collisions at 200 GeV/u projectile energy at the CERN-SPS. The differential cross section for the mass range 10 MeV/ c 2 ≤ m ee ≤ 100 MeV/ c 2 and the polar angle range 141 mrad ≤ θ e ≤ 260 mrad agrees well with a lowest-order perturbation QED-calculation.