1. Description

2. Performance


The low energy plasma composition spectrometer AMEI-2 is built to be able to find in the low energy range of the phase space (E, q, j) and separate the fluxes of the major ion species in the magnetotail - H+, He++, He+ and O+, and analyse their energy and angular distributions. It scans an energy range 0.3 - 10 keV/q, respectively (m/q)*(E/q) = 0.3 - 160 a.m.u.*keV/q2. Masses m/q =1,2,4 and 16 are measured simultaneously. Energy bandpass is about 20%. Electrostatic angular scanning in one direction and the use of the spin of the satellite to sample the other angle give the ability to measure 2-D distributions for each ion specie several times per spin. Onboard identification of ion mass and flexible information capacities are provided.

The measurement cycle of the instrument is controlled by the "top of spin" signal and the 1/1024 part of spin period signals, produced by the BNS instrument. The 4p solid angle is separated into three parts: a solar cone with angle 80 degrees, an antisolar cone with angle of 44 degrees and a band (+25,-40) degrees perpendicular to the spin axis. The deflection voltages necessary to measure 210 energy-angular steps and mass spectra are programmed in the microcomputer. Sets of 128, 64 or 32 energy-angular steps can be selected by ground commands. Measurement cycle consists of angular scan in a given cone for one set of energies, and then the scans for the same sequence of energies are made for other angular ranges. In slow modes, measurements at each energy-angular step can be integrated over different ranges of azimuth angle, i.e. data obtained at each step for several measurement cycles are summed.

AMEI-2 is a joint Bulgarian-Russian instrument, developed and manufactured by STILL-BAS, Sofia and IKI-RAN, Moscow.

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AMEI-2 instrument is working since August 17, after the BNS instrument was switched on in automatic mode. We have some quota problems due to failure in the flag circuit to SSNI information system.
Though the instrument was designed for measurements in the tail, we had observed some events of ion beams in the magnetosheath. An example of measurements on August 26 is shown on the Figure.
AMEI-2 was in fast mode and performed 8 measurements cycles per spin, each spectrum measured within one 45 degrees azimuth sector. 4 consecutive spin periods are shown. One should remember that several polar angles are scanned for every energy, that is why spectra look ridged due to the fact that fluxes are narrow in polar angle. Except the main flow from the Sun, we can see significant proton fluxes in the perpendicular cone during the half the spin period. Alpha particles are observed flowing towards the and in the perpendicular direction. Notice, that these alpha fluxes are also seen during half of a spin period, but are shifted in phase from the proton fluxes.

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Last updated: 04 Nov 1995