Damping Of Ion Acoustic Waves Research Articles

Anisotropic Propagation and Damping of Ion Acoustic Waves in a Current-Carrying Plasma

Anisotropic Propagation and Damping of Ion Acoustic Waves in a Current-Carrying Plasma

Amortissement landau non lineaire d'une onde ionique pseudosonore

A non-linear damping of ion-acoustic waves is observed in a cesium plasma.

Controlled Landau Damping of Ion-Acoustic Waves

Controlled Landau Damping of Ion-Acoustic Waves

Effect of Collisions upon Plasma Ion Oscillations

The coupling between ion oscillations and electric currents introduced by collisional effects was studied. A growth of ion acoustic waves is found which extrapolates to the Vlasov gas value as the collision mean free path and wavelength become comparable. The damping of ion acoustic waves is calculated from the fluid equations. For a plasma confined by a strong magnetic field, convective oscillations can be excited by an electron drift along the magnetic field lines. The growth rate and frequency of these oscillations is compared to stellarator experiments.

Landau Damping of Ion Acoustic Waves in Highly Ionized Plasmas

Ion acoustic waves with frequencies between 5 and 100 kc/sec have been excited in highly ionized cesium and potassium plasmas by modulating the potential of a tungsten grid immersed in the plasma. The waves were detected by another grid, which could be moved along the plasma column. Because the plasma is produced at one end of the column, there is a net flow of plasma between the grids. Phase velocities of 1.3\ifmmode\times\else\texttimes\fi{}${10}^{5}$ cm/sec and 0.9\ifmmode\times\else\texttimes\fi{}${10}^{5}$ cm/sec along and against this drift were measured for cesium and 2.5\ifmmode\times\else\texttimes\fi{}${10}^{5}$ cm/sec and 1.3\ifmmode\times\else\texttimes\fi{}${10}^{5}$ cm/sec for potassium. The damping distance of the waves was found to be independent of ion density in the range between 2\ifmmode\times\else\texttimes\fi{}${10}^{10}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and 3\ifmmode\times\else\texttimes\fi{}${10}^{11}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and equal to 0.55 and 0.25 wavelength along and against the flow in cesium and 0.65 and 0.14 in potassium. A comparison between the results and the collisionless theory shows agreement within about 10%. In particular, it is shown how the present experiment provides a quantitative measurement of the Landau damping of ion acoustic waves.

Cesium and potassium plasma experiments

We review experiments performed on cesium and potassium thermal plasmas produced by thermal ionization of neutral atoms on tungsten and tantalum surfaces. A brief description of typical cesium or potassium thermal-plasma devices is given in section 2 of the paper. Section 3 deals with actual experiments, and the material is divided as follows:a. Experiments on plasma diffusion across a magnetic field. In these experiments it is found that when no current is passed through the plasma, diffusion proceeds according to the predictions of the “classical” theory (D⊥ ≈ 1/B2). The magnitudes of the diffusion coefficients are also in agreement with the results of classical theory based on ion-electron collisions.b. Excitation and propagation of low-frequency waves. Three different experiments are described. The first deals with ion waves excited by passage of a small current along the magnetic lines over a very small part of the plasma cross section. The frequency of the oscillations is generally slightly in excess of the ion cyclotron frequency, and the waves are electrostatic ion waves propagating almost at a right angle to the magnetic lines. The second experiment deals with ion waves propagating in the azimuthal direction across the magnetic lines and the radial density gradients of the plasma column. The phase velocity of these waves has the same magnitude as the ion macroscopic velocity of the zero-order motion. The third experiment deals with excitation, propagation along the magnetic lines and damping of ion acoustic waves. The phase velocity and the damping of the waves have been measured. In particular, the wave attenuation appears to be explainable only in terms of collisionless (Landau) damping.c. Spectroscopy experiments. We give a brief description of a spectroscopic determination of the recombination coefficient in cesium.d. Beam-plasma interaction. We discuss the effect of this interaction on the amplification of a microwave signal applied as a modulation to an electron beam that passes through a 2.2-cm length of cesium plasma.Section 4 contains a few considerations about experiments that appear feasible with alkali-metal plasma devices, some of which are under way. In particular, the production of a cesium plasma in a stellarator geometry is considered.

Propagation and Damping of Ion Acoustic Waves in Highly Ionized Plasmas

Propagation and Damping of Ion Acoustic Waves in Highly Ionized Plasmas