Review of in-space plasma diagnostics for studying the Earth’s ionosphere

Abstract

This review details the state of the art in in-space plasma diagnostics for characterizing the Earth’s ionosphere. The review provides a historical perspective, focusing on the last 20 years and on eight of the most commonly used plasma sensors—most of them for in situ probing, many of them with completed/in-progress space missions: (a) Langmuir probes, (b) retarding potential analysers, (c) ion drift meters, (d) Faraday cups, (e) integrated miniaturized electrostatic analysers, (f) multipole resonance probes, (g) Fourier transform infrared spectrometers, and (h) ultraviolet absorption spectrometers. For each sensor, the review covers (a) a succinct description of its principle of operation, (b) highlights of the reported hardware flown/planned to fly in a satellite or that could be put in a CubeSat given that is miniaturized, and (c) a brief description of the space missions that have utilized such sensor and their findings. Finally, the review suggests tentative directions for future research.

Autonomous, Additively Manufactured, Multi-Langmuir Probe for CubeSat Plasma Diagnostics

“…LPs attract free-floating charged particles that are registered as current through the electrodes; the current is measured and used to estimate plasma properties. In the case of the single LP configuration, a range of bias voltages is swept (a ±100 V voltage range is typically employed for LPs intended for electric propulsion diagnostics [8], while a ±10 V voltage range is typically used in LPs for ionospheric studies [6]), varying from negative to positive relative to a common reference point such as the vacuum chamber (on-ground operation) or the spacecraft frame (in-space operation). The measured currents (which can range from µA level or less to mA level or more, depending on the plasma and the dimensions of the exposed tip of the LP) can be plotted against the applied bias voltage to produce an I-V characteristic that is analyzed to extract various plasma properties (Fig.…”

“…An important parameter that strongly influences the behavior of the LP is the Debye length, 𝜆 > . The Debye length is the distance that an electrostatic field penetrates a plasma and is specific to a given plasma [6]. The Debye length is given by…”

“…Previous experiments with the laboratory plasma used to characterize the MLP showed the plasma generated by the helicon source had associated Debye lengths as large as 100 μm [13], i.e., the MLP electrodes needed to be at least 200 µm apart to avoid interference. In contrast, plasmas in the ionosphere have much larger Debye lengths, approximately 1 mm [6]. Therefore, two housing tops were developed: a top with an electrode spacing of 300 µm that pushed the lower bound of separation and fabrication precision available for the MLP study (Fig.…”

“…Langmuir probes (LPs) are plasma sensors known for their simplicity, versatility, and minimal maintenance requirements, which makes them an excellent choice as plasma instrumentation onboard CubeSats [6]. Moreover, the utilization of rapid prototyping techniques enables their swift and cost-effective manufacturing, with minimal waste, even in space.…”

Determining sheath edge electric field around cylindrical pins of a DC-biased hairpin resonator probe

“…The interaction of sheathaccelerated, unidirectional positive ions determines the anisotropic etching on silicon substrates [2]. The charging of satellites in zero-gravity conditions [7], plasma thrusters [8,9], surface creation of negative ions in neutral beam sources [10], plasma diagnostics [11][12][13][14][15], plasma confinement [16], and dust particle interaction [17,18] are other examples where sheath physics finds relevance. As a result, a number of theoretical [19][20][21][22][23][24][25][26][27][28] and experimental investigations [29][30][31][32][33] have been carried out to understand the nature of the sheath regions that are typically formed in low-temperature laboratory plasmas.…”