Robert L. Miller

The Spherical Tokamak Path to Fusion Power

AbstractThe low-aspect-ratio tokamak or spherical torus (ST) approach offers the two key elements needed to enable magnetic confinement fusion to make the transition from a government-funded research program to the commercial marketplace: a low-cost, low-power, small-size market entry vehicle and a strong economy of scale in larger devices. Within the ST concept, a very small device (A = 1.4, major radius ~1 m, similar size to the DIII-D tokamak) could be built that would produce ~800 MW(thermal), 200 MW(net electric) and would have a gain, defined as QPLANT = (gross electric power/recirculating power), of ~2. Such a device would have all the operating systems and features of a power plant and would therefore be acceptable as a pilot plant, even though the cost of electricity would not be competitive. The ratio of fusion power to copper toroidal field (TF) coil dissipation rises quickly with device size (like R3 to R4, depending on what is held constant) and can lead to 4-GW(thermal) power plants with QPL...

Low‐frequency current drive and helicity injection

For ω≪Ωi, where Ωi is the ion cyclotron frequency, circularly polarized waves can drive current far exceeding the current resulting from linearly polarized waves. Further, the efficiency can be independent of plasma density. In some cases, this circular polarization may be interpreted in terms of helicity injection. For tokamak applications, where the wavenumber in the toroidal direction is a real quantity, wave helicity is injected only with finite Ez waves, where z is the direction of the static magnetic field. The Alfven waves are possible current drive candidates but, in the cylindrical model considered, the compressional wave is weakly damped because Ez =0, while the shear Alfven wave is totally absorbed at the surface because of finite Ez. A mixture of the two modes is shown to drive an oscillatory surface current even though the efficiency is high and independent of density. A more promising current drive candidate is a fast wave that propagates to the plasma interior and is damped by the minority ...

Archimedes Plasma Mass Filter

Some 60,000 and 46,000 MT of sodium rich nuclear waste are now in storage in the US at Hanford a nd SR S facilities, respectively. We have de veloped a technology that uses the high sodium content to advantage: aqueous slurry wastes are first calcined into sodium hydroxide ( NaOH) melt slurries, then vaporized an d injected into a pl asma. The Archimedes Filter separates plasma ions into light and hea vy mass groups. For the first time, it is feasible to economically separate large amounts of material in a single-pass plasma device. Such a s eparation would s ubstantially decontaminate H igh Level Waste since most radionuclides partition to the h eavy fraction. The p lasma process is based o n setting up fast ExB rotation of a cylindrical plasma. At a certain critical rotational velocity E > B/2 ions are not confined by axial magnetic field and are lost radially. Because the critical rotational velocity depends on magnetic field the plasma and machine parameters can be set u p to separate heavy radionuclides from majority of the light elements in the plasma and, thus, accomplish waste cl ean up. The paper discusses the F ilter process, describes a de monstration device t hat has been constructed i n San Diego, USA, and presents the first experimental results.

Current drive by wave helicity injection

It is shown that a steady‐state current can be sustained by the injection of wave helicity. In generalizing to waves of arbitrary polarizations and damping directions, the wave helicity has to include both a magnetic and a kinetic component. A physical picture is presented describing competing effects on current generation, and a generalized helicity conservation equation is derived that encompasses all the results discovered.

Response to Schalit and Bellan

The ac helicity effect discussed by Schalit and Bellan does not impact the current drive efficiency obtained by Ohkawa.