D. A. Hammer

Heating of Counterstreaming Ion Beams in an External Magnetic Field

Ion heating by a strong ion‐ion two‐stream instability perpendicular to a magnetic field in the presence of a relatively cold electron background (Te≪miVd2) is considered. The magnetic field strength is such that the ion trajectories are straight, whereas the electrons are bound to the field lines (krLe≪1≪krLi). Theory is presented for both quasilinear and nonlinear stages of the evolution of the system for the case that the instability is electrostatic [(B2/8π) (1+β) >nmiVd2/8] and is compared with a series of computer simulation experiments. It is found that the quasilinear theory gives a fairly accurate description of spatially averaged plasma properties until the ion beams have been sufficiently modulated for ions to be trapped by the waves. In the subsequent nonlinear stage, stabilization occurs when the ion trapping period is equal to the reciprocal growth rate associated with the instability. The directed ion beam energy is mainly converted into random ion energy. The possible role of this instabil...

NONEQUILIBRIUM ENERGY CONSTANTS ASSOCIATED WITH LARGE-AMPLITUDE ELECTRON WHISTLERS.

Two independent energy constants are derived for arbitrary‐amplitude electron whistler distrubances propagating parallel to a uniform magnetic field B0. These constants exhibit precisely how energy is partitioned between the fields and the components of plasma kinetic energy perpendicular and parallel to B0.

Reversed‐field configuration generated by a rotating relativistic electron beam

A reversed‐field plasma confinement geometry has been produced by plasma currents induced by a rotating relativistic electron beam injected into 85 mTorr neutral hydrogen. The resulting belt‐pinch‐like configuration has a rectangular cross section, with length‐to‐width ratio of 20, and midplane β=0.5. An equilibrium model, fitted to measurements of the excluded flux and induced axial (ΔBz) and azimuthal (Bϑ) magnetic fields, is in agreement with the annular plasma observed with radial Thomson scattering scans, CO2 interferometry, and end‐on streak photographs. After beam passage, ΔBz remains constant for 5 μsec until Bϑ becomes small, at which time the plasma collapses radially. The observed decay times of 4 μsec and concurrent increase in Te (from 5 to 10 eV) are consistent with classical dissipation of the induced currents.

Intense relativistic electron beam interaction with a cool theta pinch plasma

Experimental results are presented for the heating of a 4 m long plasma confined by a uniform magnetic field of 4–5 kG by an intense relativistic electron beam. Beam parameters were 0.5–1 MeV, 25–80 kA, 60–70 nsec pulse duration, and electron density of 2–5×1011/cm3. The initial plasma density ranged from 5×1013/cm3 to 4×1015/cm3 and the electron temperature was 1–3 eV. The lower density cases were partially ionized with Te≫Ti, and the higher density cases were highly ionized with Te≈Ti. In all cases, the energy coupled from the beam to the plasma was greater than can be explained by binary collisions between beam electrons and the plasma particles. Beam energy transferred to the plasma ranged from 2–7%/m, and was uniform over the 4 m length of the plasma. Over most of the density range tested, 5×1013/cm3 to 1.5×1015/cm3, the plasma heating cannot be explained by classical processes. These results are found to be explained quantitatively by the use of a full nonlinear treatment of the electron‐electron tw...

ENERGY CONSTANTS ASSOCIATED WITH THE NONLINEAR THEORY OF ELECTROMAGNETIC INSTABILITIES.

For configurations relevant to transverse electromagnetic instabilities, two independent energy constants are derived within the framework of the fully nonlinear Vlasov‐Maxwell equations. It is assumed that the spatial variation in equilibrium and perturbed quantities is perpendicular to a uniform external magnetic field B0. The case B0 = 0 is not excluded, and the spatial variations may be one‐or two‐dimensional. The energy constants, which are applicable in both the stable and unstable regimes, exhibit precisely how the energy is partitioned between the fields and the individual components of plasma kinetic energy perpendicular and parallel to the propagation direction. The corresponding constants at the quasilinear level of description are also examined.

Transverse Electromagnetic Instabilities in Collisionless Plasmas.

Abstract Computer simulation experiments are reported which verify the energy constants associated with the nonlinear theory of transverse electromagnetic instabilities.

Formation of closed magnetic field line plasma systems using intense relativistic electron beams

Abstract Closed magnetic field plasma confinement geometries produced by plasma currents induced by rotating intense relativistic electron beams are discussed conceptually. Experimental evidence for the formation of such layers is presented.

Localized measurements during intense relativistic electron beam interaction with a cool theta-pinch plasma

A 1‐MeV 40–80‐kA 60‐nsec 40‐cm2 electron beam was injected into a 3‐eV 2×1015‐cm−3‐density plasma. Plasma density and temperature within the beam channel were measured by Thomson scattering, and local time‐dependent magnetic probe measurements were made across a plasma diameter. The observed plasma heating rate was an order of magnitude larger than can be explained on the basis of classical collisional processes.

Magnetic probe for use in intense electron beam environment

A quartz housed, liquid dielectric insulated, magnetic probe capable of withstanding electron beam current densities exceeding 3.5 kA/cm2 is described as it is employed on the ’’Triton’’ electron beam–plasma interaction experiment.