Determination ofZ_effby integrating measurements from x-ray tomography and charge exchange recombination spectroscopy

Abstract

The effective ionic charge, Z eff , is determined through the integration of soft x-ray tomography and charge exchange recombination spectroscopy impurity density measurements in the Madison Symmetric Torus. Z eff is found is be 2.3 ± 0.1 in the core of high temperature, high current, improved confinement discharges, with a slightly hollow profile peaking near mid-radius. A Bayesian probability framework, developed as part of an ongoing effort in Integrated Data Analysis, was used to incorporate these two measurements. This framework provides a method to address different systematic and statistical uncertainties associated with each diagnostic and to test hypothetical contributions to Z eff against the existing data set. The combined analysis provides much higher confidence in the result than previous single-diagnostic attempts to characterize Z eff using near-infrared bremsstrahlung or x-ray spectroscopy.

Simulation, design, and first test of a multi-energy soft x-ray (SXR) pinhole camera in the Madison Symmetric Torus (MST)

“…The benefit to the MST program lies, therefore, in the ability of Note: Paper published as part of the Proceedings of the 22nd Topical Conference on High-Temperature Plasma Diagnostics, San Diego, California, April 2018. a) Electronic mail: ldelgado@pppl.gov the new detector to characterize the Al line-radiation present in MST which nicely complements the data obtained with the existent two-color diode array suite which uses conventional Be filters with 50% transmission at 4 and 5 keV. [3][4][5][6][7][8][9] The strong line-emission of Ar and Mo shown in Figs. 1(c) and 1(d)-characteristic of He-and H-like Ar as well as Ne-like Mo charge states [see Figs.…”

Validation metrics for turbulent plasma transport

“…Advances in UQ are needed on both the experimental and modeling sides, to better quantify and characterize the uncertainties in the equilibrium profiles and gradients, and then efficiently propagate these uncertainties through both power balance and turbulent transport models. On the experimental side, using techniques such as Gaussian process regression 119,120 or integrated data assessment [121][122][123][124] should be investigated more widely. For simulations, propagation of uncertainties requires a transition from single, deterministic simulations at a given point to ensembles of calculations as the default workflow.…”

“…It should also be noted that for some profiles, multiple independent diagnostics are often combined (such as Thomson scattering and electron cyclotron emission for measurements of T e profiles) to increase confidence in the final fit. In such cases, the use of integrated data assessment (IDA) techniques [121][122][123][124] can enable significantly improved estimates of profile and gradient uncertainties. Finally, in some experiments, it is possible to use small "jogs" or scans of the plasma through the diagnostic viewing locations to obtain more smoothly varying profile (and thus gradient) measurements; 125 similar results for diagnostics such as ECE can be obtained through small variations in toroidal field strength.…”

Using integrated data analysis to extend measurement capability (invited)

“…Specifically we allowed either argon, representing mid-Z impurities, or helium, representing low-Z impurities, to be present in the plasma. 39 It was found that argon may be present in trace amounts; however, the maximum possible density was sufficiently small that it had a minimal effect on the inference of Z eff . Similarly, while helium may be present in larger amounts than argon, the charge of helium is so low that it also has minimal effect on Z eff .…”

“…More details on the profile parameterizations for the hollow impurity density profiles can be found in Ref. 39.…”