14:55 〜 15:10
[PEM10-16] Fast Langmuir Probe observations of thermal plasmas during “SS-520-3” sounding rocket campaign in the ionospheric cusp region
キーワード：観測ロケット、電離圏カスプ、ラングミュアプローブ、イオン上昇流、プラズマ温度
Sounding rocket “SS-520-3” campaign was conducted on November 4, 2021 in Svalbard, Norway. The main purpose of this rocket experiment is to elucidate the plasma acceleration/heating mechanism responsible for the ion upflow in the ionospheric cusp region using a combination of the high time resolution in-situ rocket measurements and the ground-based optical and radar observations. In this campaign, the rocket equipped with a suite of 9 science instruments was launched at 11:09:25 CET from the SvalRak launch facility at Ny-Ålesund after confirming that the rocket would traverse a region of the ion upflow. In this presentation, we will focus on observations of thermal plasmas by FLP (Fast Langmuir Probe) instrument onboard the rocket.
The stainless probe adopted to the FLP is a cylindrical shape with a length of 200 mm and a diameter of 3 mm and was deployed into a direction vertical to the rocket spin axis during the rocket flight. The probe is directly biased by a triangular voltage with amplitude of 4 V with respect to the rocket potential and a period of 100 msec so as to provide the current-voltage relationship. A current incident to the probe was sampled with a rate of 6400 Hz and amplified by two different gains (low and high) so that it can measure in a wide range of the plasma density. In order to measure the ion current as well as the electron current, the amplifier has an offset voltage of +0.5 V; a positive (> 0.5V) voltage means the electron current while a negative one does the ion current. The calibration signal is obtained by switching the input from the probe to the resistance once every 30 seconds. The electron temperature and number density can be derived from a relationship between the incident current versus voltage applied to the probe.
Initial results from the preliminary analysis of FLP data are summarized as follows: The FLP successfully made its measurement during both upleg and downleg of the rocket flight, which results in the estimation of the local electron temperature and density. The observed electron density is larger than the predicted value, which suggests a possible traverse of the rocket through a region of the electron precipitation. The probe current may contain information on electron density perturbation because a small-scale (< 10 msec) variation in the electron current was observed. It seems that the degree of negative charging of the rocket increased with altitude, which cannot be explained by plasma density variation alone. Both a ratio of electron to ion random currents and a floating potential of the rocket significantly changed with altitude, which may be attributed to a change in a ratio of electron to ion temperature. This will be further analyzed by connecting with the ion heating that would play an inherent role in the ion upflow.
In this presentation, we give a report on the preliminary analysis of the thermal plasma measurements by FLP in more detail.
The stainless probe adopted to the FLP is a cylindrical shape with a length of 200 mm and a diameter of 3 mm and was deployed into a direction vertical to the rocket spin axis during the rocket flight. The probe is directly biased by a triangular voltage with amplitude of 4 V with respect to the rocket potential and a period of 100 msec so as to provide the current-voltage relationship. A current incident to the probe was sampled with a rate of 6400 Hz and amplified by two different gains (low and high) so that it can measure in a wide range of the plasma density. In order to measure the ion current as well as the electron current, the amplifier has an offset voltage of +0.5 V; a positive (> 0.5V) voltage means the electron current while a negative one does the ion current. The calibration signal is obtained by switching the input from the probe to the resistance once every 30 seconds. The electron temperature and number density can be derived from a relationship between the incident current versus voltage applied to the probe.
Initial results from the preliminary analysis of FLP data are summarized as follows: The FLP successfully made its measurement during both upleg and downleg of the rocket flight, which results in the estimation of the local electron temperature and density. The observed electron density is larger than the predicted value, which suggests a possible traverse of the rocket through a region of the electron precipitation. The probe current may contain information on electron density perturbation because a small-scale (< 10 msec) variation in the electron current was observed. It seems that the degree of negative charging of the rocket increased with altitude, which cannot be explained by plasma density variation alone. Both a ratio of electron to ion random currents and a floating potential of the rocket significantly changed with altitude, which may be attributed to a change in a ratio of electron to ion temperature. This will be further analyzed by connecting with the ion heating that would play an inherent role in the ion upflow.
In this presentation, we give a report on the preliminary analysis of the thermal plasma measurements by FLP in more detail.