Temporal Evolution of the Light Emitted by a Thin, Laser-ionized Plasma Source

TL;DR

This study combines experiments and simulations to analyze the temporal evolution of light emitted by a laser-ionized helium plasma, providing a model that correlates plasma conditions with emitted light, aiding plasma diagnostics in accelerators.

Contribution

The paper introduces an integrated experimental and simulation framework to model and measure the time-resolved light emission from laser-ionized plasma sources, with a novel statistical measurement method.

Findings

Collisional excitation dominates plasma light emission.

The analytic model accurately predicts emission scaling with plasma parameters.

A cost-effective, nanosecond-resolving measurement technique was developed.

Abstract

We present an experimental and simulation-based investigation of the temporal evolution of light emission from a thin, laser-ionized Helium plasma source. We demonstrate an analytic model to calculate the approximate scaling of the time-integrated, on-axis light emission with the initial plasma density and temperature, supported by the experiment, which enhances the understanding of plasma light measurement for plasma wakefield accelerator (PWFA) plasma sources. Our model simulates the plasma density and temperature using a split-step Fourier code and a particle-in-cell (PIC) code. A fluid simulation is then used to model the plasma and neutral density, and the electron temperature as a function of time and position. We then show the numerical results of the space-and-time-resolved light emission and that collisional excitation is the dominant source of light emission. We validate our model by measuring the light emitted by a laser-ionized plasma using a novel statistical method capable of resolving the nanosecond-scale temporal dynamics of the plasma light using a cost-effective camera with microsecond-scale timing jitter. This method is ideal for deployment in the high radiation environment of a particle accelerator that precludes the use of expensive nanosecond-gated cameras. Our results show that our models can effectively simulate the dynamics of a thin, laser-ionized plasma source and this work is useful to understand the plasma light measurement, which plays an important role in the PWFA.