Energetic Electron Detector Research Articles

Comparison of Energetic Electron Fluxes Measured by GPS and THEMIS Spacecraft in the Inner Magnetosphere

AbstractKey elements of space weather models are energetic electron fluxes in the inner magnetosphere and the outer radiation belt. Flux depletion is driven by various loss processes: scattering into atmosphere, magnetopause shadowing. Flux enhancement is driven by various acceleration processes: local wave‐particle interactions, radial transport, plasma sheet injections. Many of these processes operate on ∼ hour timescales. Such mesoscale flux variations are not well traced by equatorial spacecraft with much longer orbits. Energetic electron detectors onboard the Global Positioning System (GPS) constellation provide a unique opportunity for probing such ∼ hour‐scale flux variations. Measurements from up to 23 identically instrumented GPS satellites cover a wide energy and L‐shell range with a subhour time resolution. However, their orbits are inclined and thus all measurements at L‐shell >4.3 are off‐equatorial. In this report, we present a comparison of equatorial THEMIS and nonequatorial GPS measurements of omnidirectional ≤600 keV electron fluxes. Such a comparison allows us to derive coefficients for using off‐equatorial GPS fluxes to infer the equatorial values. These coefficients depend on particle energy and L‐shell. We demonstrate a new data set derived from GPS measurements and discuss how it can be used to investigate mesoscale dynamics of energetic electron fluxes in the inner magnetosphere.

Calibration of the Falcon Solid‐state Energetic Electron Detector (SEED)

AbstractThe Falcon Solid‐state Energetic Electron Detector (FalconSEED) is an energetic charged particle sensor that has been developed and tested at the United States Air Force Academy in an effort to monitor electron flux across the energy range of 14 to 145 keV in geosynchronous orbit. This sensor has been developed to complement ongoing efforts by the Air Force Research Laboratory to advance a comprehensive space environment sensor suite, Compact Environmental Anomaly Sensor (CEASE3), for anomaly resolution. In addition, FalconSEED is intended to demonstrate the ability to operate a radiation sensor based on predominantly commercial off the shelf components in the geosynchronous environment. This paper describes the design, development, and calibration of FalconSEED. The electron energy spectrum of interest for the FalconSEED sensor is 14 to 145 keV, and is intended to supplement data acquired from the CEASE3 instrument for anomaly resolution. The calibrations at the Space Atmospheric Research Center at the United States Air Force Academy and Kirtland Air Force Base were used to first establish the conversion between histogram bin number and deposited energy in the sensor, and second have been used to determine the geometric factor as a function of energy. The FalconSEED will be integrated as a science payload on the Space Test Program Satellite‐6 which also includes the first flight of the CEASE3 instrument and is scheduled to launch in 2021.

The AEPEX mission: Imaging energetic particle precipitation in the atmosphere through its bremsstrahlung X-ray signatures

The Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) mission is a 6U CubeSat that will monitor energetic electron precipitation from the radiation belts into the upper atmosphere. The primary instrument will image energetic (50–300 keV) X-rays produced in the atmosphere by bremsstrahlung, providing a near-direct signature of electron precipitation. An energetic electron detector will measure the precipitating electron spectrum, while the X-ray observations will be used to determine the absolute flux. X-ray images will be produced with 10-s time resolution and 50–100 km spatial resolution. The 6U spacecraft uses flight heritage spacecraft bus subsystems, including the attitude determination and control, electrical power, and command & data handling systems. AEPEX is designed to be operated from low-Earth orbit at ~500 km altitude with a high inclination in order to cover the outer radiation belt. AEPEX will be the first spacecraft mission to measure X-rays in the 50–300 keV energy range emitted by Earth’s atmosphere in response to radiation belt precipitation, and the first to image that precipitation from above.

Global observations of energetic electrons around the time of a substorm on 27 August 2001

The magnetospheric substorm that occurred shortly after 04:00 UT on 27 August 2001 has been a topic of detailed study (Baker et al., 2002; Li et al., 2003). These studies included analysis of data from energetic electron detectors aboard the Cluster and Polar spacecraft that were located in the magnetotail during the substorm. Serendipitously, Chandra, the X‐ray observatory, also carrying an energetic electron detector, was located in the magnetotail several hours earlier in local time. Examination of data from the three magnetotail positions revealed that enegetic electrons (>35 keV) appeared simultaneously at all three locations, and that the appearance was ten minutes after the injection into geostationary orbit (GEO) as determine by examination of drift dispersion at several local times in GEO orbit. In addition to the substorm‐associated electrons, time‐correlated electron bursts were observed by the magnetotail spacecraft for a few hours prior to the substorm.

Bremsstrahlung effects in energetic particle detectors

The energetic charged particles of the Earth's magnetosphere are routinely detected by solid‐state satellite instruments. Quantitative data are increasingly required for engineering dose calculations and for space weather science. However, the design of some energetic particle detectors can be severely constrained. Background effects must be accurately modeled in such cases to extract quantitative information. In particular, bremsstrahlung radiation from electrons impacting the detector and the satellite often dominates the background noise. Numerical tools are presented here to calculate total bremsstrahlung effects in energetic electron detectors. The calculations are illustrated for the low‐energy particle detector of current Global Positioning System satellites.

A new numerical technique to design satellite energetic electron detectors

Energetic charged particles trapped in the magnetosphere are routinely detected by satellite instruments. However, it is generally difficult to extract quantitative energy and angular information from such measurements because the interaction of energetic electrons with matter is rather complex. Beam calibrations and Monte-Carlo (MC) simulations are often used to evaluate a flight instrument once it is built. However, rules of thumb and past experience are common tools to design the instrument in the first place. Hence, we have developed a simple numerical procedure, based on analytical probabilities, suitable for instrumental design and evaluation. In addition to the geometrical response, the contributions of surface backscattering, edge penetration, and bremsstrahlung radiation are estimated. The new results are benchmarked against MC calculations for a simple test case. Complicated effects, such as the contribution of the satellite to the instrumental response, can be estimated with the new formalism.

Wave‐particle interactions induced by SEPAC on Spacelab 1: Wave observations

Space experiments with particle accelerators (SEPAC) flew on Spacelab 1 in November and December 1983. SEPAC included an accelerator which emitted electrons into the ionospheric plasma with energies up to 5 keV and currents up to 300 mA. The SEPAC equipment also included an energetic plasma generator, a neutral gas generator, and an extensive array of diagnostics. The diagnostics included plasma wave detectors, an energetic electron analyzer, a photometer, a high sensitivity television camera, a Langmuir probe and a pressure gauge. Twenty‐eight experiments were performed during the mission to investigate beam‐plasma interactions, electron beam dynamics, plasma beam propagation, and vehicle charging. The wave‐particle interactions were monitored by the plasma wave instrumentation, by the energetic electron detector and by the optical detectors. All show evidence of wave‐particle interactions, which will be described in this paper.

Nighttime auroral energy deposition in the middle atmosphere

From 1976 through 1982, eight distinct nighttime auroral events have been probed with rocket payloads in a series of high latitude studies at Poker Flat Research Range, Alaska, and Andøya, Norway. The instrument packages have contained X ray and energetic electron detectors, permitting a measure of these energy forms and their absorption in the middle atmosphere. Although the specifics of each event show a wide range of values for energy flux and spectral hardness, certain general characteristics persist in all cases. The primary energy sources for the middle atmosphere under the active conditions examined here are mainly relativistic electrons and bremsstrahlung X rays. Each of these sources is found to dominate ionization in a separate altitude region, with the electrons usually controlling ionization in the upper heights above 55–60 km and the X rays below to about 40 km, where cosmic rays take over. The relativistic electron ionizing radiation source has not usually been considered in modeling studies for the ion chemistry of the lower mesosphere (55–70 km), yet this radiation is capable of increasing ion concentration and electrical conductivity in excess of a factor of 10. Moreover, the persistence of relativistic electrons as an important source in all events studied here strongly suggests that this deficiency be corrected.

A technique for rocket-borne detection of electron bunching at megahertz frequencies

Energetic electrons precipitating in the auroral ionosphere may be bunched at frequencies up to several megahertz as a result of local wave-particle interactions. A technique is described whereby this megahertz bunching can be observed using conventional rocket-borne energetic electron detectors counting at rates below 10 5 cps. Electron arrival time information is pre-processed on board the rocket and any bunching present can be realized by subsequent computer processing on the ground using only a modest data transmission rate from the rocket. Results of a pilot rocket experiment prove the value of the technique and lead on to formulating the design of a future experiment where the maximum amount of data processing is performed on the rocket. The technique should perform an important diagnostic role, helping us to understand the complex wave-particle interactions occuring in the auroral ionosphere.

High-latitude troughs and the polar cap boundary

OGO 6 observations of troughs in the thermal plasma densities in the topside ionosphere are discussed. Ion mass spectrometer measurements were correlated with energetic electron detector and electric field measurements. It is shown that the variation of ion composition at high latitudes is complex and frequently characterized by mid-latitude and high-latitude density depression. Prominent high-latitude troughs in the atomic ion (H, He, O) distributions were seen to lie frequently near the polar cap boundary. This indicates that these troughs are unrelated to the plasmapause which is found on closed magnetic field lines away from the trapping boundary. The production of the high-latitude troughs is shown to be related to enhancements in the soft electron flux and/or to the convection electric field.