An Experimental Platform for Creating White Dwarf Photospheres in the Laboratory

TL;DR

This paper introduces a novel experimental platform at Sandia National Laboratories that creates white dwarf-like plasmas in the laboratory to measure hydrogen line profiles, aiding in the calibration of astrophysical models.

Contribution

It presents a radiation-driven plasma platform that isolates heating from the plasma, enabling precise measurement of hydrogen Balmer lines under white dwarf conditions for the first time.

Findings

First laboratory measurement of hydrogen Balmer lines at WD conditions

Platform decouples radiation heating from plasma state

Potential to study non-LTE and other plasma species

Abstract

We present an experimental platform for measuring hydrogen Balmer emission and absorption line profiles for plasmas with white dwarf (WD) photospheric conditions (T_e ~ 1 eV, n_e ~ 10^17 cm^-3). These profiles will be used to benchmark WD atmosphere models, which, used with the spectroscopic method, are responsible for determining fundamental parameters (e.g., effective temperature, mass) for tens of thousands of WDs. Our experiment, performed at the Z Pulsed Power Facility at Sandia National Laboratories, uses the large amount of x-rays generated from a z-pinch dynamic hohlraum to drive plasma formation in a gas cell. The platform is unique compared to past hydrogen line profile experiments in that the plasma is radiation-driven. This decouples the heating source from the plasma to be studied in the sense that the radiation temperature causing the photoionization is independent of the initial conditions of the gas. For the first time we measure hydrogen Balmer lines in absorption at these conditions in the laboratory for the purpose of benchmarking Stark-broadened line shapes. The platform can be used to study other plasma species and to explore non-LTE, time-dependent collisional-radiative atomic kinetics.