Fields In Dense Plasmas Research Articles

Specific features of electromagnetic waves in degenerate two stream electron-ion plasma: self-induced magnetic field

Abstract Generation and amplification of magnetic fields is a subject of interest to both laboratory and astrophysical plasmas. The counter-streaming instability or Weibel instability is a mechanism responsible for self-generating magnetic fields in plasmas. In this paper, we investigate that the non-stationary ponderomotive force of a large amplitude electromagnetic wave (EMWs) propagating through dense two stream quantum electron ion plasma, may lead to the generation of d.c. magnetic fields. It is shown that degeneracy parameters, specifically the exchange correlation potential and Fermi pressure can reduce/control the self-induced magnetic field. Next the linear propagation of EMWs through plasma under consideration has also been considered in the presence of exchange correlation potential along with other quantum effects. Linear dispersion relation, the instability conditions and growth rate have been derived. It is found that the degeneracy parameters stabilize the propagation of instability and lead to reduction of the exponentially growing magnetic field. Threshold scale length of EMWs is also obtained for the stable propagation. The present result may be account helpful to understand the seed magnetic fields in dense plasmas.

Nonlinear saturation of the Weibel instability in a dense Fermi plasma

AbstractWe present an investigation for the generation of intense magnetic fields in dense plasmas with an anisotropic electron Fermi–Dirac distribution. For this purpose, we use a new linear dispersion relation for transverse waves in the Wigner–Maxwell dense quantum plasma system. Numerical analysis of the dispersion relation reveals the scaling of the growth rate as a function of the Fermi energy and the temperature anisotropy. The nonlinear saturation level of the magnetic fields is found through fully kinetic simulations, which indicates that the final amplitudes of the magnetic fields are proportional to the linear growth rate of the instability. The present results are important for understanding the origin of intense magnetic fields in dense Fermionic plasmas, such as those in the next-generation intense laser–solid density plasma experiments.

New method for polarization measurements of magnetic fields in dense plasmas

Measurements of magnetic fields based on observations of the Zeeman splitting /spl omega//sub B/ of spectral lines is a virtually impossible task in dense plasmas of powerful Z-pinches where the Stark splitting in the ion microfields /spl omega//sub F/ is much greater than /spl omega//sub B/. In this situation, much better diagnostics of magnetic fields can be achieved through polarization difference contours obtained by subtracting profiles of the same spectral line observed in two orthogonal linear polarizations. In this way the obscuring role of the Stark effect is significantly diminished. In the present paper it is shown that the most sensitive and accurate measurements of the magnitude and the direction of the magnetic field in a dense plasma can be conducted employing central Stark components of hydrogen or hydrogen-like spectral lines. The polarization contour of a central Stark component turned out to be much more sensitive to the magnetic field than the polarization contour of a lateral component of the same line, namely by a factor of (/spl omega//sub F///spl omega//sub B/)/sup 3//spl Gt/1. This constitutes a drastic enhancement of the previously suggested method that had used the polarization contour of a lateral Stark component because in dense plasmas a typical value of the above factor is (/spl omega//sub F///spl omega//sub B/)/sup 3//spl ges/10/sup 3/. The new method can also be used for laser fusion plasmas and for some astrophysical objects such as magnetic white dwarfs.

High-Order Harmonic Generation in Dense Plasmas with a High Intensity Light Field

High-order harmonic generation by an oscillating current due to intense laser electric fields in dense plasmas is investigated. In solid target plasmas produced by an intense ultra-short pulse laser, the intense laser radiation directly interacts with overdense plasmas. In such a case, plasma screening effects are important in the plasma response to the laser field. For such plasmas, the higher harmonics are evaluated by using a dynamical form factor for plasma electrons and ions. There is a peak in the harmonic spectrum at twice the plasma frequency.

Induced electrostatic fields in dense plasmas with an intense ultrashort pulse laser.

The electrostatic fields induced by an intense laser field around an ion in a solid density plasma are investigated. In a plasma produced by irradiating an intense ultrashort pulse laser on a solid target, the electron and ion temperatures are not in thermal equilibrium, and the electron temperature is higher than the ion temperature. For such a plasma, the dynamical form factor of a plasma electron is derived. By using the dynamical form factor, the screened potential and the induced oscillating electrostatic field around an ion are obtained. As a result, the plasma screening effects on the direct ionization by the laser are clarified.

Broadening of Lyman lines of hydrogen and hydrogenic ions by low-frequency fields in dense plasmas

A previously developed extension of the quasistatic approximation which allows for the broadening of hydrogen lines by low-frequency fields is applied to the first four Lyman lines of hydrogen, ionized helium, C VI, and Ar XVIII. It is demonstrated numerically that the low-frequency Stark broadening is Gaussian in the case of relatively small dynamical corrections. Extrapolation of this Gaussian approximation to cases with large corrections leads to good agreement with measurements of the Lyman-..cap alpha.., -..beta.., and -..gamma.. lines of hydrogen and allows the prediction that the Lyman-delta should retain its central dip.

Broadening of the Lyman-αline of hydrogen by low-frequency electric fields in dense plasmas

Using the quasistatic approximation as basis for the description of broadening by ion-produced fields and the impact approximation for electron-produced high-frequency fields, an analytic approximation procedure is developed and applied which allows for slow variations of the total field acting on a radiating atom. This low-frequency Stark broadening depends on the radiator velocity and is therefore correlated with the thermal Doppler broadening. The theory is extended to Lyman-$\ensuremath{\alpha}$ lines of hydrogenic ions.