Interpretive Modeling of plasma evolution during fueling experiments at CMFX

TL;DR

This paper presents a time-dependent interpretive modeling framework for plasma evolution in CMFX, using limited diagnostics to infer plasma parameters and optimize fueling strategies, achieving higher voltages and neutron yields.

Contribution

The work introduces a novel interpretive analysis method combining a physics model and experimental data to infer plasma conditions in a sparse diagnostic environment.

Findings

Achieved deuterium neutron yields of up to 1.5×10^7 n/s

Inferred ion temperature reaching 950 eV

Identified improved fueling strategies for better plasma performance

Abstract

The Centrifugal Mirror Fusion Experiment (CMFX) is an axisymmetric magnetic mirror with a central cathode which generates an azimuthal, radially sheared, supersonic \( E \times B \) flow. The induced rotation stabilizes, confines, and heats the plasma. The diagnostic set on CMFX is sparse, giving limited insight to the state of the plasma. In this work, we developed a time-dependent interpretive analysis framework that uses applied voltage, input power, and measured neutron yield rate to infer evolving plasma conditions throughout a discharge. The 0D MCTrans++ code serves as the core physics model, incorporating centrifugal effects, viscous heating, and angular momentum confinement to infer plasma parameters from operating conditions and experimental observables. An iterative Newton's method was implemented to solve for the plasma state evolution consistent with experimental measurements averaged over successive time intervals. The interpretive analysis was applied to experiments comparing different fueling strategies, revealing a path to improved performance via several short puffs of fuel spread across the discharge. This insight led to operations at voltages up 70 kV. Deuterium neutron yields up to \(1.5 \times 10^7\) n/s were measured, and ion temperature was inferred to reach 950 eV. Until CMFX gains a more complete diagnostic set, this interpretive analysis framework provides useful insight into the evolution of centrifugal mirror plasmas.