Charge exchange measurements with an x-ray calorimeter at an electron beam ion trap

Abstract

We present K-shell x-ray spectra of highly ionized Mg acquired with the EBIT calorimeter spectrometer at a resolution of 4.5 eV in charge exchange recombination experiments using the LLNL EBIT-I electron beam ion trap. We measured the Doppler width of Mg11+ Lyα in the same experiments using a high resolution crystal spectrometer, giving an estimate of the ion temperature. We find hardness ratios for Mg11+ ranging from 0.6 to 1.6, depending on the neutral gas target. In most of the experiments, the ion temperature was ∼ 10–15 eV amu−1, indicating that the variations in hardness ratio are intrinsic to the choice of neutral target gas, and are not simply a consequence of variations in the collision velocity resulting from evaporative cooling of the trapped ions. The spectral variations show that high resolution x-ray spectroscopy is highly diagnostic of charge exchange reactions, but requires well-developed theory to interpret.