Effects of the space plasma density oscillation on the inter-spacecraft laser ranging for TianQin gravitational wave observatory

TL;DR

This study models how plasma density oscillations in space can induce phase noise in laser signals for the TianQin gravitational wave observatory, affecting measurement precision.

Contribution

It provides a realistic simulation of plasma-induced phase deviations and analyzes their impact on TianQin's laser interferometry accuracy.

Findings

Plasma oscillations can cause phase deviations up to 2×10^-6 rad/Hz^1/2.

Phase spectrum separation increases during magnetic storms.

Phase deviations depend on the orbital radius.

Abstract

The TianQin space Gravitational Waves (GW) observatory will contain 3 geocentric and circularly orbiting spacecraft with an orbital radius of 10^5 km, to detect the GW in the milli-hertz frequency band. Each spacecraft pair will establish a 1.7*10^5 km-long laser interferometer immersed in the solar wind and the magnetospheric plasmas to measure the phase deviations induced by the GW. GW detection requires a high-precision measurement of the laser phase. The cumulative effects of the long distance and the periodic oscillations of the plasma density may induce an additional phase noise. This paper aims to model the plasma induced phase deviation of the inter-spacecraft laser signals, using a realistic orbit simulator and the Space Weather Modeling Framework (SWMF) model. Preliminary results show that the plasma density oscillation can induce the phase deviations close to 2*10^-6 rad/Hz^1/2 or 0.3pm/Hz^1/2 in the milli-hertz frequency band and it is within the error budget assigned to the displacement noise of the interferometry. The amplitude spectrum density of phases along three arms become more separated when the orbital plane is parallel to the Sun-Earth line or during a magnetic storm. Finally, the dependence of the phase deviations on the orbital radius is examined.