Rocket-borne Langmuir probe for plasma density irregularities

Abstract

Ionospheric plasma density exhibits very large spatial and temporal variations known as ionosphere irregularities. These irregularities are generated by a number of processes related to plasma as well as neutral dynamics. The rocket-or satellite-borne Langmuir probe (LP) is very simple and yet a very powerful tool to measure spatial variation of plasma density enabling one to study ionosphere irregularities. This article describes how a rocket-borne LP can be used to study ionosphere irregularities. It begins with the basic principle of the LP, the ionospheric regions where it can be used, various sizes and shapes of the LP sensors, the effect of geomagnetic field and vehicle wake on LP measurements. Mechanical and electronic details of typical LP instrument are given next. Strengths, weaknesses and specifications of LP instrument are also given. Rocket-borne LP has been used by a large number of scientists in the world to study ionospheric irregularities produced through plasma instabilities in the equatorial electrojet region, in spread F and those produced by neutral turbulence. Highlights of such irregularity measurements are presented to give the reader a flavor of the type of studies which can be undertaken using a rocket-borne LP. The present capability of rocket-borne LP is to detect vertical scale sizes of ionospheric irregularities from a few km down to about 10 cm with percentage amplitudes as small as 0.001%. Finally, a few suggestions are given for the improvement the LP instrumentation for future use. Key words: Langmuir probe, plasma density irregularities, in situ measurement. Rocket-borne Langmuir Probe for Plasma IrregularitiesThe Langmuir probe (LP) is used on rockets to determine the amplitude and spectra of electron density irregularities over a large vertical scale-size range, typically lying between a few km down to about 10 cm. Plasma irregularities have been studied at all latitudes, especially so around geomagnetic equator, due to special geometry of geomagnetic field lines which are horizontal. Horizontal magnetic field along with vertically upward (downward) Hall polarization electric field during the day (night), is the major destabilizing forcing for the excitation of a range of plasma instabilities at altitudes higher than about 85 km. Neutral turbulence produces fluctuations in neutral density, at altitudes below about 100 km, which can be transferred to electron density, due to high neutral-ion collision frequencies at such altitudes and the charge neutrality of plasma. Although gross features of various plasma instabilities and neutral forcings producing these irregularities are understood, there are many aspects which still defy a suitable explanation, such as why equatorial spread F irregularities are present on some nights and absent on other nights. It is, therefore, essential that the parameters of irregularities such as amplitudes, scale sizes and spectrum be measured along with other complementary parameters such as electric fields, electric currents, composition, neutral...

Generation of Post Sunset E Region Electron Density Stratifications at the Magnetic Equator: An Analysis Using In Situ Measurements and Theoretical Estimations

“…The simple principle of the Langmuir probe is to expose a conducting surface biased to a potential with respect to the undisturbed plasma and to measure the collected current. The theory of Langmuir probe is well discussed in several papers (Chen, 2003;Conde, 2011;Mott-Smith and Langmuir, 1926;Sinha, 2013). Normally a Langmuir probe is subjected to a sweep voltage and the current due to the incoming plasma species is measured.…”

On the In Situ Observations of Irregularities During Rocket Flights From Thumba for Different Geophysical Conditions and the Associated Causative Mechanisms

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