浅村 和史

In some types of mass spectrometers, such as time-of-flight mass spectrometers (TOF-MSs), it is necessary to control pulsed beams of ions. This can be easily accomplished by applying a pulsed voltage to the pusher electrode while the ionizer is continuously flowing ions. This method is preferred for its simplicity, although the ion utilization efficiency is not optimized. Here we employed another pulse-control method with a higher ion utilization rate, which is to bunch ions and kick them out instead of letting them stream. The benefit of this method is that higher sensitivity can be achieved; since the start of new ions cannot be allowed during TOF separation, it is highly advantageous to bunch ions that would otherwise be unusable. In this study, we used analytical and numerical methods to design a new bunching ionizer with reduced resources, adopting the principle of the electrostatic ion beam trap. The test model experimentally demonstrated the bunching performance with respect to the sample gas density and ion bunching time using gas samples and electron impact ionization. We also conducted an experiment connecting the newly developed bunching ionizer with a miniature TOF-MS. As a result, the sensitivity was improved by an order of magnitude compared to the case using a nonbunching ionizer. Since the device is capable of bunching ions with low voltage and power consumption, it will be possible to find applications in portable mass spectrometers with reduced resources.

Abstract We report a statistical result of electrons inside the loss cone with energies of 67 eV–88 keV using electron measurements obtained in situ by the Arase satellite in the inner magnetosphere around the magnetic equator for 60 months. Loss cone electrons are found with a high occurrence probability from the nightside to the dawnside at approximately L = 6. For 641 eV–88 keV electrons, the high‐occurrence region shifts toward later magnetic local times (MLTs) with increasing loss cone electron energy. The spatial distribution of the occurrence probability around MLT = 22–3 at L = 5–6 is consistent with the calculated average resonance energy distribution of whistler mode chorus waves near the magnetic equator. These results suggest that pitch angle scattering driven by chorus waves plays the main role in electron precipitation in this region.

Abstract Strong Thermal Emission Velocity Enhancement (STEVE) is a latitudinally narrow, purple‐band emission observed at subauroral latitudes. Stable Auroral Red (SAR) arcs characterized by major red emission, and red/green arcs with both red and green emissions also occur at subauroral latitudes. Characteristics of magnetospheric source plasma and electromagnetic fields of these three types of arcs have not been fully understood because of the limited conjugate observations between magnetosphere and the ground. In this study, we report 11 conjugate observations (2 STEVEs, 7 SAR arcs, and 2 red/green arcs), using all‐sky images obtained at seven ground stations over more than four years from January 2017 to April 2021 and magnetospheric satellites (Arase and Van Allen Probes). We found that, in the inner magnetosphere, the source region of STEVEs and red/green arcs were located outside the plasmasphere, and that of the SAR arc was in the region of spatial overlap between the plasmasphere and ring current region. Electromagnetic waves at frequencies below 1 Hz were observed for STEVEs and red/green arcs. SuperDARN radar data showed a strong westward plasma flow in the ionosphere, especially during STEVE events, whereas the plasma flows associated with SAR arcs and red/green arcs were generally weaker and variable. The STEVE and SAR arc can appear simultaneously at slightly different latitudes and STEVEs and red/green arcs can transform into SAR arcs. These first comprehensive ground‐satellite measurements of three types of subauroral‐latitude auroras increase our understanding on similarlity, differences, and coupling of these auroras in the ionosphere and the magnetosphere.

Abstract We estimated the altitude of aurora by combining data from all‐sky cameras at multiple places which were obtained during the LAMP sounding rocket experiment in Alaska on 5 March 2022. During the launch window of the rocket, three high‐speed all‐sky cameras were operative at three stations immediately below the trajectory of the rocket: Poker Flat, Venetie and Fort Yukon. The all‐sky cameras captured all‐sky images with a temporal resolution of 100 Hz (80 Hz for the Fort Yukon case). The method of altitude determination is based on analyses of time‐series of the optical intensity obtained from the all‐sky cameras in Venetie and Poker Flat covering the downrange area of the rocket trajectory. The estimated altitude of pulsating aurora during the rocket experiment was found to be consistent with that derived from the in‐situ observation of precipitating electrons with a model of optical emission, which confirms the feasibility of deriving the emission altitude through correlation analyses using time‐series. The estimated altitude of aurora decreased after the expansion onset of the substorm and stayed slightly below 100 km during the interval of pulsating aurora in the recovery phase. In particular, prompt and brief lowering of the auroral emission, well down to around 90 km, was detected during a transition of auroral form from discrete to diffuse which occurred ∼10 min after the onset. This result implies an existence of a process causing harder electron precipitation operative soon after the start of the expansion phase of auroral substorm.