[en] A lower hybrid system is under development for current drive and heating on the tokamak de Varennes. Near steady-state RF current drive and/or transformer recharge should allow long pulse operation of a diverted plasma for up to 30 sec at nearly full machine parameters (I_p ∼ 250 kA, n_e ∼3 x 10¹⁹ m^-3). The system design is for 1 MW of RF power at a relatively high N (variable around 3.1) in a narrow spectrum (0.4 FWHM) at 3.7 GHz. Design considerations and technical solutions are presented. (author). 5 refs., 5 figs

[en] The Lower Hybrid Simulation Code (LSC) is a computational model of lower hybrid current drive in the presence of an electric field. Details of geometry, plasma profiles, and circuit equations are treated. Two-dimensional velocity space effects are approximated in a one-dimensional Fokker-Planck treatment. The LSC was originally written to be a module for lower hybrid current drive called by the Tokamak Simulation Code (TSC), which is a numerical model of an axisymmetric tokamak plasma and the associated control systems. The TSC simulates the time evolution of a free boundary plasma by solving the MHD equations on a rectangular computational grid. The MHD equations are coupled to the external circuits (representing poloidal field coils) through the boundary conditions. The code includes provisions for modeling the control system, external heating, and fusion heating. The LSC module can also be called by the TRANSP code. TRANSP represents the plasma with an axisymmetric, fixed-boundary model and focuses on calculation of plasma transport to determine transport coefficients from data on power inputs and parameters reached. This manual covers the basic material needed to use the LSC. If run in conjunction with TSC, the ''TSC Users Manual'' should be consulted. If run in conjunction with TRANSP, on-line documentation will be helpful. A theoretical background of the governing equations and numerical methods is given. Information on obtaining, compiling, and running the code is also provided

[en] Kinetic theory is used to obtain a nonlinear equation, cubic in the lower-hybrid (LH) fields, which is appropriate for describing both the effects of strong turbulence (the modulational instability, soliton-like solutions, etc.) and those of weak turbulence (decays, scattering). A study is made of the modulational instability of LH waves propagating at an angle θ₀ with respect to the external magnetic field over a wide range of possible values of θ₀: 1 >> cosθ₀ ≥ (m/M)_1/2, where m/M is the electron-to-ion mass ratio. It is shown that even when the energy density of the pump wave is quite small it is possible for the modulational instability to dominate the effects of induced scattering right from the start. For pump waves of low intensity the condition on the wave vectors is found such that the open-quotes short-wavelengthclose quotes modulational instability (| Δk | >> | k₀ |, where Δk and k₀ are the wave vectors of the density modulation and pump wave, respectively) differs substantially from the behavior of the parametric instability (| k₀ | = 0). The effect of the modulational instability of a LH wave on the production of entrainment currents is treated. 23 refs

[en] The manifestations of the induced scattering effects in the generation process of current driven by lower-hybrid (LH) waves are studied taking into account the radiative-resonant interactions. The influence extent of the LH wave modulational instability on current drive is estimated. It is shown that the induced scattering of LH waves on plasma particles leads to a change of the LH waves spectrum and through this leads to an essential influence on fast electrons generation rate and the steady-state current drive. The modulational instability of LH waves can provide a 'spectral gap' filling in the case of sufficiently strong LH wave pumping. (orig.)

[en] The feasibility of a 1 MW low hybrid current drive (LHCD) microwave synthesized by two 500 kW high power klystrons is analyzed, and the scheme is designed. Through the MW level power synthesizer combining with the phase feedback technique to synthesize four channels 250 kW microwave of two tubes, the MW level LHCD source is obtained on the HL-2A LHCD experimental platform. The feasibility analysis shows that the synthesis efficiency decreases by about 1.8% due to the phase deviation of 15° and 0.1% when the amplitude deviation is 10%. Therefore, the specific implementation scheme of two-klystron power synthesis technology is obtained. (authors)

[en] A new method is proposed for investigating the current carrying superthermal tail using the electron cyclotron O-mode at downshifted frequency. The Letter discusses emission and transmission of radiation for propagation normal to or nearly normal to the magnetic field, with the emitting and receiving horns both located on an external side port in the equatorial plane, which requires a reflector for the O-mode radiation. A perfectly reflecting mirror is provided by the O-mode cut-off layer. Several applications are considered, and it is shown that the system permits local measurements of the tail properties. (author). Letter-to-the-editor. 9 refs

[en] The JET Lower Hybrid Current Drive Generator (LHCD) will consist of 24 Klystrons. The system is expected to be fully operational in 1990. It will be composed of six of four klystrons each and of two klystrons for the LHCD component. Two klystrons modules will be ready for operation with the JET machine in early 1989. In order to protect the klystrons in case of arching or overvoltage, crowbars near the klystrons are foreseen. For this purpose ignitrons as opposed to thyristors were chosen. The design of the crowbar for the LHCD takes into account the past experience obtained from operation of the Neutral Beam protection crowbars and follows a different approach for the ignitron triggering and the anode/cathode temperature control. (author). 5 refs.; 4 figs

[en] Reliability, Availability, Maintainability and Inspectability (RAMI) concepts and techniques, that acquired great importance during the first manned space missions, have been progressively extended to industrial, scientific and consumer equipments to assure them satisfactory performances and lifetimes. In the design of experimental facilities, like tokamaks, mainly aimed at demonstrating validity and feasibility of scientific theories, RAMI analysis has been often left aside. DEMO, the future prototype fusion reactors, will be instead designed for steadily delivering electrical energy to commercial grids, so that the RAMI aspects will assume an absolute relevance since their initial design phases. A preliminary RAMI analysis of the LHCD system for the conceptual EU DEMO reactor is given in the paper

[en] A multijunction launcher was designed and constructed to improve the directivity of launched waves with a narrow wave number spectrum by dividing each main waveguide into three secondary waveguides. The coupling characteristics agree fairly well with theory, and a power of up to 2 MW was obtained after a few days of conditioning. The dependence of the current drive efficiency η_CD (= n_eI_RFR/P_LH) on the wave spectrum was studied by changing the phase difference between the adjacent main waveguides. It was found that high current drive efficiency is obtained by waves interacting with fast electrons as far into the plasma as the waves travel. A maximum current drive efficiency of 2.8 x 10¹⁹ A·W^-1·m^-2 was achieved with this launcher at a plasma current of 1 MA. The efficiency of the multijunction launcher was higher by 40% than that of the previous conventional launcher on JT-60. (author). Letter-to-the-editor. 27 refs, 5 figs

[en] The instantaneous α-particle losses are found in the presence of an hf field. The kinetic equation for the α-particle distribution function is found when there is a loss region in velocity space, and the α-particle fluxes leaving the plasma are calculated as a function of the plasma parameters and the input hf power. The results are analyzed from the standpoint of achieving current drive in a tokamak reactor by means of lower-hybrid waves. 7 refs., 4 figs