Beyond Zeeman spectroscopy: Magnetic-field diagnostics with Stark-dominated line shapes

Abstract

A recently suggested spectroscopic approach for magnetic-field determination in plasma is employed to measure magnetic fields in an expanding laser-produced plasma plume in an externally applied magnetic field. The approach enables the field determination in a diagnostically difficult regime for which the Zeeman-split patterns are not resolvable, as is often encountered under the conditions characteristic of high-energy-density plasmas. Here, such conditions occur in the high-density plasma near the laser target, due to the dominance of Stark broadening. A pulsedpower system is used to generate magnetic fields with a peak magnitude of 25 T at the innerelectrode surface in a coaxial configuration. An aluminum target attached to the inner electrode surface is then irradiated by a laser beam to produce the expanding plasma that interacts with the applied azimuthal magnetic field. A line-shape analysis of the Al III 4s-4p doublet (5696 and 5722 Å ) enables the simultaneous determination of the magnetic field and the electron density. The measured magnetic fields are generally found to agree with those expected in a vacuum based on the pulsed-power system current. Examples of other transitions that can be used to diagnose a wide range of plasma and magnetic field parameters are presented.

Fraunhofer-type absorption line splitting and polarization in confocal double-pulse laser induced plasma

“…Nevertheless, this self-generated magnetic field, estimated by the authors to be of 26 kG (2.6 T) at 1 Torr ambient pressure and 265 mJ of plasma excited laser pulse energy, is too small to explain such a high degree of polarization. The results presented by Tessarin et al [30], show that an even much higher external magnetic field causes very small changes in shape of the Al III line at 569.66 nm in LIP. Thus the results from [27][28][29] need further discussion.…”

Magnetic Field Measurements in Plasmas: Beyond the Traditional Zeeman Spectroscopy

“…To illustrate the impact of this uncertainty, we use again the example of plasma diagnosed by the Al III 4s -4p doublet. Let us assume first line-widths and width-difference corresponding to n e = 10 18 cm -3 and B = 15 T (typical values in the experiment in [3]). The same parameters of line-widths and width-difference, but assuming Doppler-broadened line-shapes instead of Stark (i.e., we assume a Gaussian instead of a Lorentzian), yield T i ~ 16 keV and B ~ 19.5 T. Therefore, in the worst-case scenario, when no information can be obtained on the line-shape (i.e., only the line-widths and width-difference can be extracted), and a Voigt profile with similar Gaussian and Lorentzian contributions is considered for each component, an error of less than ± 15% is incurred.…”

“…By doing so, not only the magnetic field is determined with a high accuracy, but also it is possible to quantitatively analyze the plasma electron density distribution. In a recent experiment aimed at testing the method under a wide range of plasma densities and magnetic-field magnitudes (details will be given in a future report [3]), the spatial resolution was varied to record spectra emitted from different plasma regions with different densities. The modeling of these spectra infers the mean magnetic field, and in addition, reveals unambiguously the presence of at least two distinct plasma regions with significantly different electron densities [3].…”

Shielding of the azimuthal magnetic field by the anode plasma in a relativistic self-magnetic-pinch diode

“…For the conditions of the SMP diode, Zeeman splitting cannot always be resolved due to the large Stark broadening in the high-density plasma formed over the anode surface. For these cases, detailed line-shape analysis, [11][12][13] considering the Stark and Doppler broadenings, the instrumental response, and the Zeeman-effect contribution, is made for obtaining the information on the magnetic field and plasma density. Due to this rather complex line-shape processing, the data from the inner radii mainly allowed for determining an upper limit for the magnetic fields.…”