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For both magnetic and inertial fusion, new capabilities have been developed. Sophisticated theory, diagnostics to measure fine details of plasma parameters, and experimental techniques to control and alter plasma parameters and the geometry in which they are imbedded have provided increased understanding and the ability to dramatically improve plasma performance over what was possible 10 or 20 years ago. Some examples are: control of the current profile changes the magnetic field produced by the current, and can produce reversed central shear in tokamaks - this has improved confinement to the theoretical limits, although still on a transient basis (Ishida, 1999; Watkins, 1999). The beta (plasma pressure normalized to the magnetic field pressure) of magnetically confined plasma has been increased to theoretical limits, and in some cases has broken through into a new second stability regime producing higher limits in tokamaks. Rayleigh-Taylor instability growth rates of planar targets have been measured as a function of small imperfections in the surface of the target or the laser uniformity, and have been found to agree with theory. Rayleigh-Taylor instabilities also limit the compression of thin spherical shells, but to a lesser degree than predicted by early theories: additional stabilizing effects that relax the Rayleigh-Taylor constraints have been predicted and experimentally verified.

Today, fusion energy is at a crossroads - the $10 billion price tag of the ITER has dismayed many supporters (Glanz and Lawler, 1998). A vigorous reevaluation of magnetic and inertial concepts is currently underway (Glanz, 1999). A consensus is growing for developing multiple concepts with low-level funding at the exploratory level. Those that appear attractive will be funded at the higher level proof-of-principle stage, and the best of those will reach the performance extension stage. Beyond that, one or two will enter the engineering test facility phase, and probably only one will enter the demonstration power plant phase, but only if the costs are much less than that of ITER. Most of the world's magnetic fusion programs are still studying tokamaks, but the emphasis is now on advanced modes of operation that improve the power plant potential of the tokamak. A few alternative concept experiments are just beginning operation, with more following.

The emerging new phase bears a cursory resemblance to the early days of fusion when a large zoo of magnetic configurations was studied experimentally, with only tenuous ties to theory. This apparent resemblance is misleading - with the theoretical and experimental tools that have been developed and honed, researchers are able to ask more subtle questions and obtain answers. Many of the techniques learned in studying tokamaks are applicable to other configurations.

Our view is that the ITER Project has demonstrated one route to a fusion power plant that would work - we now have an existence theorem for fusion energy in the form of engineering drawings for a device that would have a high probability of working as intended. This enables us to turn with renewed confidence to exploring other routes to fusion that will be more cost effective, and that will be better able to realize the potential of fusion energy. An innovative fusion energy research program, focused on the critical issues, will maximize the probability of achieving the full potential of fusion energy. The development of a virtually limitless energy source will provide a profound benefit to future humanity.

List of Abbreviations

COE

cost-of-electricity

DPSSL

diode-pumped solid-state laser

FIRE

Fusion Ignition Research Experiment

FRC

field reversed configuration

IFE

inertial fusion energy

ITER

International Thermonuclear Experimental Reactor

JET

Joint European Torus

JT-60(U)

Japan, largest Tokamak, slightly larger than JET

KrF

Krypton-fluoride laser

LMJ

laser megajoule

MFE

magnetic fusion energy

MTF

magnetized target fusion (or magnetically-insulated IFE)

NIF

National Ignition Facility

RFP

reversed field pinch

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