MNX Research Program


MNX experiments were first aimed at forming supersonic neutral jets from low-temperature, moderate-density magnetized helium plasma. The phase transition from magnetized plasma to neutral gas, via recombination of plasma electrons with ions, is of fundamental interest, probing normal modes and irreversible processes of the system. Experiments showed plasma recombination to occur at high neutral gas pressures and high plasma density (Forming supersonic neutral jets from low-temperature, moderate-density a magnetized helium plasma: movie).

The transformation of plasma to a jet of neutral atoms is essential to several applications. For example, plasma detachment from magnetic field lines is necessary for spacecraft propulsion. Without detachment, the exhausted plasma would return to the spacecraft along magnetic field lines, reducing the thrust. Several processes, including recombination, charge exchange, or loss of magnetization, may bring about detachment of supersonic ions. Our studies of rapid plasma expansion by a nozzle did not show plasma cooling expected from a fluid picture of the plasmas, confirming a nonlocal kinetic plasma model (Figure 1).


Experimental investigations then looked for acceleration of the plasma effected by a variety of nozzles. This effort was rewarded by the discovery of a double layer near the nozzle throat, producing lif_measurementssupersonic velocities in a distance of a few mms. Laser-induced fluorescence (LIF) measurements, obtained with a West Virginia University (WVU) diagnostic (Figure 2), showed argon ion energies over 70 eV, sufficient for spacecraft propulsion applications. Double layers also have special prominence in the fields of planetary plasmas and astrophysics.

Research now focuses on methods to accelerate the plasma to even higher speeds and to promote detachment via a de-magnetization mechanism. Modeling the expanding plasma, to understand the mechanism responsible for the formation of the double layer, is an important element in this program (Figure 3).


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Professor Samuel A. Cohen
Princeton Plasma Physics Laboratory
P.O. Box 451 (Mail Stop 17)
Princeton, NJ 08543-0451

PPPL is funded by the USDOE Office of Science
and is managed by Princeton University.

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