This paper presents the results of JET experiments aimed at studying the operational space of plasmas with a Type III ELMy edge, in terms of both local and global plasma parameters. In JET, the Type III ELMy regime has a wide operational space in the pedestal n e-T e diagram, and Type III ELMs are observed in standard ELMy H-modes as well as in plasmas with an internal transport barrier (ITB). The transition from an H-mode with Type III ELMs to a steady state Type I ELMy H-mode requires a minimum loss power, P TypeI. P TypeI decreases with increasing plasma triangularity. In the pedestal n e-T e diagram, the critical pedestal temperature for the transition to Type I ELMs is found to be inversely proportional to the pedestal density (T crit ∝ 1/n) at a low density. In contrast, at a high density, T crit , does not depend strongly on density. In the density range where T crit ∝ 1/n, the critical power required for the transition to Type I ELMs decreases with increasing density. Experimental results are presented suggesting a common mechanism for Type III ELMs at low and high collisionality. A single model for the critical temperature for the transition from Type III to Type I ELMs, based on the resistive interchange instability with magnetic flutter, fits well the density and toroidal field dependence of the JET experimental data. On the other hand, this model fails to describe the variation of the Type III n e-T e operational space with isotopic mass and q 95. Other results are instead suggestive of a different physics for Type III ELMs. At low collisionality, plasma current ramp

ABSTRACT.Reactor relevant ICRH scenarios have been assessed during D-T experiments on the JET tokamak using H-mode divertor discharges with ITER-like shapes and safety factors. Deuterium minority heating in tritium plasmas was demonstrated for the first time. For 9% deuterium, an ICRH power of 6 MW gave 1.66 MW of fusion power from reactions between suprathermal deuterons and thermal tritons. The Q-value of the steady state discharge reached 0.22 for the length of the RF flat top (2.7 s), corresponding to three plasma energy replacement times. The Doppler broadened neutron spectrum showed a deuteron energy of 125 keV which was optimum for fusion and close to the critical energy. Thus strong bulk ion heating was obtained at the same time as high fusion efficiency. Deuterium fractions around 20% produced the strongest ion heating together with a strong reduction of the suprathermal deuteron tail. The edge localised modes (ELMs) had low amplitude and high frequency and each ELM transported less plasma energy content

Fourteen university, government, and industrial laboratories prepared a total of twenty pairs of single-layer titanium dioxide films. Several laboratories analyzed the coatings to determine their optical properties, thickness, surface roughness, absorption, wetting contact angle, and crystalline structure. Wide variations were found in the optical and physical properties of the films, even among films produced by nominally the same deposition techniques.

Results from recent experiments to study the effects of divertor geometry and increased plasma shaping on the L-H transition threshold on JET are reported. Equivalent septum configurations run with the new septum replacement plate (SRP) in the MkII Gas Box divertor have shown that the presence of the septum lowers the L-H transition power threshold, P th , by 20%. For X-point to virtual septum top distances of less than 6 cm, the SRP plasmas also demonstrate a significant decrease of the L-H P th and pedestal electron temperature, T e with reduced X-point height. Although, the SRP plasma's P th remains above that with the septum, there is no difference in the pedestal T e at the L-H transition. The influence of plasma shaping on the L-H transition has also been investigated for the first time on JET in a series of density scans at I p /B t of 2.5 MA/2.7 T. While keeping the lower triangularity, δ lower , and divertor geometry constant, the upper triangularity, δ upper , has been increased from 0.23 to 0.34 with no effect on P th or the pedestal T e or T i . In a separate edge n e scan, two configurations with different δ upper /δ lower values of 0.23/0.23 and 0.43/0.33 have been compared. A large difference in the transition threshold is observed at values of edge n e above 1.8 × 10 19 m −3 , with the higher δ plasmas characterized by P th of up to 25% lower at the highest densities scanned. This is thought to be the result of lowered X-point and outer strike point heights with increased δ.