SAK-3 Experiment Description

The SKA-3 set of particle detectors installed onboard the AURORAL PROBE is aimed to measure distribution functions of electrons and ions. It consists of two energy-angle analyzers EA-2 and EA-3 for low energy particles, and two identical oppositely directed time-of-flight (TOF) analyzers EM-1-1 and EM-1-2 for high energies. The instruments are mounted outside the pressurized container on the back side of the satellite, opposite to sunward direction, with fields of view perpendicular to the satellite rotation axis (which is sunward directed). The satellite spinning thus scans the range of the pitch angles studied depending on the angle between the sunward direction and magnetic field. The spin period of the satellite is 120 s. Temporal resolution of observation modes varies from 0.8 s to 6.4 s, spatial resolution at apogee is about 110 km.

Analyzers of low energy charged particles (EA-2 and EA-3).
EA-2 and EA-3 are energy-angle spectrometers based on electrostatic toroidal analyzers. Analyzers differ in polarity of voltages applied to systems of electrostatic deflection and microchannel plates (MCP) circuitry. EA-2 measures energy-angle distributions of electrons, EA-3 measures ion distributions. During satellite rotation each window (of 22.5 width with a gap of 22.5 in between) scans all the phase angle range. The instruments allow to measure simultaneously in eight angular sectors evenly distributed in the angle 2 perpendicular to the satellite rotation axis, and sequentially in 7 energy intervals for each angular sector. The central energies of energy intervals are as follows: 30, 85, 240, 680, 1900, 5300, 15000 eV, the energy resolution E/E is about 10%. The particles are recorded by means of the MCP's with spaced anodes for eight angular directions. In order to improve the angular resolution of the detector, a mask is applied to the MCP's corresponding to location of anodes, and a special sectioned collimator is also attached to the entrance aperture. The calculated geometric factor is 0.06 cm2sr.
Analyzers of medium energy charged particles (EM-1-1 and EM-1-2).
The instruments EM-1-1 and EM-1-2 are identical time-of-flight energy-mass spectrometers. They allow to measure electrons deflected from the ion aperture by a magnet and ions with masses 1, 4 and 16 in 7 energy intervals in the energy range from 20 to 500 keV. The principle of functioning of these spectrometers is based on a combination of TOF device with a thick silicon semiconductor detector of full energy at the end. The fields of view of the two detectors are directed oppositely and perpendicular to the satellite rotation axis. Field of view of the spectrometers is a cone of full angle 8. Table 1 presents the ranges of energy intervals for each type of particles. Calculated geometric factor is 0.003 cm2sr.
Interval Energy ranges, keV
eM=1 M=4 M=16
1 20-40 30-50 35-55 55-90
2 40-70 50-85 55-90 90-130
3 70-110 85-115 90-130 130-185
4 110-150 115-170 130-185 185-245
5 150-220 170-225 185-240 245-315
6 220-290 225-300 240-315 315-395
7 290-390 300-395 315-415 395-510

Table 1. Ranges of energy intervals for EM-1-1 and EM-1-2.