The first experiments utilizing high-power radio waves in the ion cyclotron range of frequencies to heat deuterium–tritium (D–T) plasmas have been completed on the Tokamak Fusion Test Reactor [Fusion Technol. 21, 13 (1992)]. Results from the initial series of experiments have demonstrated efficient core second harmonic tritium (2ΩT) heating in parameter regimes approaching those anticipated for the International Thermonuclear Experimental Reactor [D. E. Post, Plasma Physics and Controlled Nuclear Fusion Research, Proceedings of the 13th International Conference, Washington, DC, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239]. Observations are consistent with modeling predictions for these plasmas. Efficient electron heating via mode conversion of fast waves to ion Bernstein waves has been observed in D–T, deuterium-deuterium (D–D), and deuterium–helium-4 (D–4He) plasmas with high concentrations of minority helium-3 (3He) (n3He/ne≳10%). Mode conversion current drive in D–T plasmas was simulated with experiments conducted in D–3He–4He plasmas. Results show a directed propagation of the mode converted ion Bernstein waves, in correlation with the antenna phasing.
An expression for local power absorption for linear wave propagation in a nonuniform hot magnetoplasma is derived from fundamental principles. The power-absorption definition is used to obtain a local power-conservation relation for a one-dimensional configuration. The formalism is applied to wave propagation in the ion cyclotron range of frequencies where strong damping and mode-conversion processes are present.
Fast magnetosonic wave absorption by fast alpha particles at small concentrations during an approach to ignition in ITER-like fusion plasmas is examined for the fundamental deuterium heating scheme. Numerical results are obtained using a full-wave code which solves coupled second order differential equations for the wave fields in a slab geometry. The fast alpha particle velocity distribution is approximated by a Maxwellian, chosen so that its velocity space density of resonant particles equals that of a slowing down distribution when both are evaluated at the absorption peak. For the cases considered, the thermal gyroradius of the Maxwellian alpha distribution satisfies the condition (k⊥ραf)2/2 < 1. Significant absorption of the fast wave by the alphas can occur in a parameter window characteristic of startup conditions. This is because the Doppler broadened alpha particle resonance zone encompasses the deuterium-tritium hybrid resonance where the left hand circularly polarized component of the wave electric field peaks
The feasibility of using a photoionized, low-ionization potential organic seed gas to initiate a high pressure plasma discharge is examined and compared to radio frequency breakdown of high pressure argon alone. The seed gas, tetrakis͑dimethylamino͒ethylene, which has an ionization potential of 6.1 eV is ionized by an ultraviolet laser through 6.4 eV photon absorption, and forms a plasma column inside a vacuum chamber. The plasma absorbs additional power through inductive coupling of 13.56 MHz helical antenna radio frequency wave fields to the plasma through electron acceleration, ionization, and collisional damping. Laser initiation of 2-6 mTorr of the seed gas in 1-150 Torr of argon is accomplished and produces steady-state line-average plasma densities of n e Ϸ4ϫ10 12 cm Ϫ3 in a volume of 300 cm 3 . The two-body recombination coefficient of the organic seed gas and its optimum partial pressure when mixed with argon are experimentally determined and analyzed. Particle loss and power requirements for maintaining the discharge are evaluated by examining ionization, diffusion, and recombination processes.
The Tokamak Physics Experiment is designed to develop the scientific basis for a compact and continuously operating tokamak fusion reactor. It is based on an emerging class of tokamak operating modes, characterized by beta limits well in excess of the Troyon limit, confinement scaling well in excess of H-mode, and bootstrap current fractions approaching unity. Such modes are attainable through the use of advanced, steady state plasma controls including strong shaping, current profile control, and active particle recycling control. Key design features of the TPX are superconducting toroidal and poloidal field coils; actively-cooled plasma-facing components; a flexible heating and current drive system; and a spacious divertor for flexibility. Substantial deuterium plasma operation is made possible with an in-vessel remote maintenance system, a lowactivation titanium vacuum vessel, and shielding of ex-vessel components. The facility will be constructed as a national project with substantial participation by U.S. industry. Operation will begin with first plasma in the year 2000.
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