Thermonuclear physics

The physics of high-temperature, multi-keV, collisionless plasmas, usually immersed in a magnetic field of complex geometry, is dominated by the behavior of unique many-body systems in which collective phenomena dominate over rare two-body collisions. These plasmas are usually far from the thermodynamic equilibrium, due to sources of mode-excitation energy that owe their existence to factors including: electrodynamic forces with spatial inhomogeneties (this is the case in magnetic or inertial confinement systems with gradients of density, temperature, magnetic field, etc.); the presence of high-energy subgroups of particles (or beams); and large-amplitude electromagnetic waves that propagate in the plasma and transfer their energy, inducing strong nonlinear interactions among background collective modes and charged particles.

At MIT, pioneering investigations on the physical properties of high temperature plasmas at very high densities have been carried out for more than two decades by the Alcator experimental program. Alcator is an acronym for the Latin phrase Alto Campo Torus, meaning high field torus. The Alcator A and C tokamaks in the 1970’s and 1980’s operated at very high magnetic fields (up to 12 Tesla) and ultra high densities (ne = 2 x 1015cm­3), and surpassed the minimum required value of the plasma density times every confinement time for “fusion breakeven” (although at lower temperatures then necessary for true breakeven conditions). At lower densities, significant toroidal plasma currents were generated efficiently by high-power traveling electromagnetic waves with frequencies in the GHz range.

The Alcator confinement and the current drive experiments both received the “Excellence in Plasma Physics Research Award” of the American Physical Society. Following these successes, the Plasma Science and Fusion Center proceeded to build a new, state-of-the-art high magnetic field experiment, Alcator C-Mod, which has an advanced magnetic divertor and allows for optimal shaping of the plasma cross-section. PSFC scientists have achieved truly exciting results by being able to heat high density plasmas in C-Mod to 6 keV temperature by injecting multi-MW radio frequency power at the ion cyclotron frequency (80 MHz). The ultimate goal of these experiments is to find a path to achieve thermonuclear ignition in laboratory experiments. Thus, a considerable effort is being devoted to the Ignitor project, first proposed and studied at MIT; this program has begun the construction of prototype components in Italy for the first machine capable of achieving fusion burn conditions.

We should also mention here the MIT experimental program in Inertial Fusion. Researchers and graduate students carry out experiments off-site at the Nova laser facility at the Lawrence Livermore National Laboratory, as well as at the OMEGA facility at the University of Rochester. Their objective is to understand the physics of pellet implosion and fusion products during intense laser irradiation of targets.
Thermonuclear physics

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