Elliptical Spectrometer for the Study of X-Pinch Physics through Absorption Spectroscopy

Adam Cahill, Cornell University

We discuss the use of the x-pinch X-ray source together with an elliptical crystal spectrometer for determining plasma conditions in high energy density plasmas. The use of absorption spectroscopic techniques for the study of plasma conditions often is restricted to diagnosing non-radiating plasma samples. This is done to avoid radiation emitted by the samples from being recorded along with the probing radiation. This can easily obscure or conceal the features of the absorption spectrum and introduce substantial error in inferred conditions.
We propose that this limitation may be overcome by adopting an experimental geometry differing from the traditional arrangement of the source, sample, crystal, and film. We place the dispersive element between the source and the sample so as to separate the probing radiation into its individual wavelengths before interacting with the sample. This eliminates sample spectral features in the data at the expense of decreased signal-to-noise ratio, which is mitigated by an aluminum filter that passes only magnesium absorption lines to the film.
The proposed arrangement is realized by placing both the source and sample at an ellipseā€™s foci while the dispersive crystal forms the surface of the ellipse. The wavelength band to be used for the study is selected by adjusting the eccentricity of the ellipse. The probing radiation in such a setup converges onto the sample radially with each wavelength entering at a different azimuth. Thus we require that the sample possess azimuthal symmetry to facilitate analysis of the data.

We present the concept for this new spectrometer along with the design compromises made during construction of a test device. A finalized spectrometer design for the study of magnesium-doped aluminum x-pinches using continuum radiation is shown along with preliminary data used for characterization and validation of the design.

Abstract Author(s): A. D. CahillC. L. HoytT. A. ShelkovenkoS. A. PikuzD. A. Hammer