[en] Species and impurity measurements on the DITE phase II neutral injectors are described. Measurements have been made of Doppler-shifted Hsub(α) line radiation, using a fast-scanning monochromator, and of the energy spectrum of charge-exchange neutrals resulting from the interaction of the beams with gas infill in the DITE torus using a tangentially viewing neutral particle energy analyser. Hydrogen-bearing impurities have been detected by both methods. Measurements have also been made with a normal incidence vacuum ultraviolet monochromator of lines from C IV and O VII ions in the plasma observed whilst neutral injection is in operation. The origin of the observed Dopper-shifted spectra from these highly ionised impurities is discussed. (author)

[en] In 1997, the JET device was operated for an extensive campaign with deuterium-tritium (D-T) plasmas (the 'DTE1' campaign). A comprehensive network of machine protection systems were necessary so that this experimental campaign could be executed safely without damage to the machine or release of activated material. This network had been developed over many years of JET deuterium plasma operation and therefore the modifications for D-T operation were not a significant problem. The DTE1 campaign was executed successfully and safely and the machine protection systems proved reliable and robust and, in the limited cases where they were required to act, functioned correctly. The machine protection systems at JET are described and their categorisation and development over time are summarised. The management, commissioning and operational experience during DTE1 are discussed and some examples of fault scenarios are described. The experience with protection systems at JET highlights the importance of correct design and philosophy decisions being taken at an early stage. It is shown that this experience will be invaluable data input to the safe operation of future large fusion machines. (author)

[en] The computerised control, safety and interlock system on the first JET Neutral Beam Injector is described

[en] Several Neutral Beam Injection (NBI) systems are now capable of injection of powers greater than 20 MW, some for pulse lengths in excess of 5 s. These high power NBI systems have demonstrated the flexibility and utility of neutral beam heating; coupling easily to many plasma configurations; providing heating, fuelling and current drive capability and allowing access to new, improved plasma confinement regimes. All the high power NBI systems have now achieved routinely high reliability and system availability (> or approx.80-90%). The current status of NBI systems is reviewed and successful solutions to the technological problems encountered in design of high power beams, ranging from high heat transfer elements to large area cryopumps, are discussed. The interface to tokamak operations such as the drift duct, stray field cancellation and fast interlock mechanisms are presented, emphasising the considerable progress in these areas. The upgrading of NBI systems for tritium injection on JET and TFTR is reviewed. The possible parameters for a 'Next Step' injector are presented, showing the choice of negative ion beams as an attractive option. With reference to the existing conceptual designs for ITER/NET it is shown that the main areas of uncertainty exist in the source and accelerator stack designs. The beamlines themselves should be able to take advantage of the properties of negative ions to lead to some marked simplifications. (orig.)

[en] Full text: The JET Trace Tritium Experimental (TTE) campaign used trace tritium (T) plasmas (nT/nD<5%) to investigate thermal fuel-ion transport, fast particle dynamics and heating and current drive physics. Precisely timed tritium gas puffs, and short pulse (<500 ms) Tritium Neutral Beam Injection (TNBI) were used. Transport coefficients were derived by fitting 14 MeV and 2.5 MeV neutron profiles' evolution. Rho*, nu*, beta and q95 were varied in pairs of sawtoothing ELMy H-Mode discharges, comparing fuel-particle and energy transport coefficient scalings. Particle transport data are consistent with gyro-Bohm scaling, similar to energy transport. Particle confinement increases with nu* and declines with beta, but energy confinement degrades weakly with nu* and is independent of beta. High edge diffusion during ELMs clearly affects the neutron emission. TTE experiments compared three fuelling methods in otherwise similar Internal Transport Barrier (ITB) plasmas: T gas-puffs; T wall-recycling; and TNBI. T gas-puff data showed reduced triton diffusion at all ITB locations. Thermalised TNBI ions deposited inside the ITB radius, demonstrated ITB effects on central particle confinement. In hybrid plasmas (qmin∼1, low positive shear, no sawteeth), T particle confinement time (τ_pT*) improved by ∼50% as triangularity was varied from 0.2-0.46 at constant energy confinement (HβN/q95² ∼ 0.42). At low delta, τ_pT * scaled with Ip. Fast-ion confinement in Current-Hole (CH) plasmas, with minimal central toroidal current density was tested by injection of TNBI into JET CH plasmas. Gamma-rays from nuclear reactions between fusion alphas (generated by TNBI) and beryllium impurities were measured in majority-deuterium plasmas after TNBI turn-off. Gamma-ray emission rate decay times measured the fast fusion-alpha population evolution. These decay times for JET plasmas are consistent with classical alpha slowing down times for high plasma currents (Ip >2MA) and monotonic q-profiles. In CH discharges the gamma-ray emission decay times are a factor 5 below classical values based on total Ip, indicating alpha confinement degrades due to orbit losses as predicted by a 3-D Fokker Planck numerical code. In TTE, ICRF at 23 MHz was coupled to T-minority ions, producing energetic tritons with tail temperatures 80-120keV, derived from neutron energy spectra. (author)

[en] The diode viewing array and its control electronics, which together form the Protection Plate Viewing System for the JET Neutral Injectors, are described

No abstract available

[en] An account is given of the high performance plasmas established by development of the H-mode regime in JET in the experimental campaigns up to 1992. High performance in this case is measured in terms of the confinement enhancement achieved over the L-mode scaling as measured using the plasma diamagnetism. Three JET H-mode regimes have achieved enhancement factors (H_G^DIA) over Goldston L-mode scaling of 2.5 < H_G^DIA < 4.0. These are the Pellet Enhanced Performance (PEP) H-mode, the high bootstrap fraction (high β_POL) H-mode and the Hot Ion (HI) H-mode. Common features between the high β_POL and HI regimes are identified which suggest that they are effectively two aspects of a unified Very High (VH) confinement regime. (author)

[en] The Neutral Injection Test-Bed (NITB) is a major experimental assembly in support of the Neutral Beam Heating Programme for JET. In addition to its prime function of testing the Neutral Injection hardware, the Test Bed serves as the prototype to test the computer control and data acquisition system, which is described in this paper. The software system has been written in a portable, data-driven manner with the aim to adapt it, with only minor modifications to the operation of the first. Neutral Injection Beamline on JET, which will involve operation both synchronous and asynchronous with that of the JET Tokamak

[en] The neutral beam injection (NBI) system of the Joint European Torus (JET) [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1985), Vol. 1, p. 11] has proved to be an extremely effective and flexible heating method capable of producing high performance plasmas and performing a wide range of related physics experiments. High fusion performance deuterium plasmas have been obtained in the hot-ion (HI) H-mode regime, using the central particle fueling and ion heating capabilities of the NBI system in low target density plasmas, and in the pellet enhanced plasma (PEP) H-mode regime, where the good central confinement properties of pellet fueled plasmas are exploited by additional heating and fueling as well as the transition to H mode. The HI H-mode configuration was used for the First Tritium Experiment (FTE) in JET in which NBI was used to heat the plasma using 14 D⁰ beams and, for the first time, to inject T⁰ using the two remaining beams. These plasmas had a peak fusion power of 1.7 MW from deuterium--tritium (D--T) fusion reactions. The capability for injection of a variety of beam species (H⁰, D⁰, ³He⁰, and ⁴He⁰) has allowed the study of confinement variation with atomic mass and the simulation of α-particle transport. Additionally, the use of the NBI system has permitted an investigation of the plasma behavior near the toroidal β limit over a wide range of toroidal field strengths