Plasma noise in TianQin time delay interferometry

TL;DR

This paper evaluates the impact of solar-wind plasma noise on TianQin's laser interferometry, demonstrating that TDI effectively suppresses plasma noise below secondary noise levels under normal solar conditions.

Contribution

It provides a comprehensive assessment of plasma noise in TianQin's TDI, including modeling, simulations, and analysis of noise suppression capabilities.

Findings

Plasma noise after TDI is below secondary noise requirements.

TDI moderately suppresses plasma noise below ~10^{-2} Hz.

Under normal conditions, plasma noise is manageable for TianQin.

Abstract

TianQin is a proposed geocentric space-based gravitational wave observatory mission, which requires time-delay interferometry (TDI) to cancel laser frequency noise. With high demands for precision, solar-wind plasma environment at $\sim 10^5$ km above the Earth may constitute a non-negligible noise source to laser interferometric measurements between satellites, as charged particles perturb the refractivity along light paths. In this paper, we first assess the plasma noises along single links from space-weather models and numerical orbits, and analyze the time and frequency domain characteristics. Particularly, to capture the plasma noise in the entire measurement band of $10^{-4} - 1$ Hz, we have performed additional space-weather magnetohydrodynamic simulations in finer spatial and temporal resolutions and utilized Kolmogorov spectra in high-frequency data generation. Then we evaluate the residual plasma noises of the first- and second-generation TDI combinations. Both analytical and numerical estimations have shown that under normal solar conditions the plasma noise after TDI is less than the secondary noise requirement. Moreover, TDI is shown to exhibit moderate suppression on the plasma noise below $\sim 10^{-2}$ Hz due to noise correlation between different arms, when compared with the secondary noise before and after TDI.