Adu. Space Res. Vol.2, No.7, pp.27-30, 1983 O273-1177/83/070027-04503.OO/0 Printed in Great Britain. All rights reserved. Copyright © COSPAR THE ION ENERGY AND MASS ANALYZER ON BOARD THE 'INTERCOSMOS-BULGARIA-1300' SATELLITE P. Nenovski*, Y. Semkova*, R. Koleva*, S. Chapkunov*, N. Kanchev*, N. Tabov*, A. Kanchev*, O. Vaisberg**, V. Smirnov**, G. Zastenker** and A. Leibov** *Central Laboratory for Space Research, Bulgarian Academy of Sciences, Sofia, Bulgaria **Space Research Institute, Mosco w, U.S.S.R. ABSTRACT An original instrument for ion energy distribution measurement in ionospheric plasma above the F-layer was designed and launched on board the'INTERCOSMOS - BULGARIA-13OO' satellite. The instrument performs differential energy analy- sis of ion species within the two energy ranges of 1 - 27 eV/q and O,2-8keV/~ INTRODUCTION An ion energy and mass spectrometer is an instrument which samples ions in the vicinity of the spacecraft, separates the different ion speciestand mea- sures their energy distribution and concentration. The existing instruments of this type, e.g. that on board GEOS-I~I~ or the retarding ion mass spectrome- ter on board the Dynamics Explorer, perform an integro-differentialenergya- nalysis of the thermal ions by the use of retarding potentials. HoweveDthere are many flow situations in aeronomy and space physics where the species ve- locity distributions depart significantly from the equilibrium Maxwellian form (see e.g. /2J ). There are many reasons why we should know the form of these distribution functions : many chemical reactions are energy depen - dent, the excitation rates of various auroral processes depend on the number of particles in the tail of the ion and electron distribution functions, and finally, the form of the species distribution function has important implica- tions for modelling plasma and neutral gas behaviour E3J. The form of the ener- gy distribution function can be measured by an instrument performing differen- tial energy analysis of the ionized components, in particular of the ion spe- cies. On the other hand, measurement of the mass spectrum of the low energy ions (with energies in the keY range) will give us a general idea about the direct penetration of solar ions (He and He + ) from the solar wind to the ionosphere and about the mechanisms of magnetospheric acceleration and precipitation of protons and 0 + ions. The ion energy and mass analyzer on board the 'INTERCOSMOS-BULGARIA-1300' sa- tellite is designed to measure the energy distribution of the different ion species at the height of about 900 km in the energy range - 27 eV/q and 0.2 - 8 keV/q in the mass range 1 - 64 amu. INSTRUMENT DESCRIPTION The outline of the ion energy and mass analyzer discussed are shown in Fig.l. It consists of an energy analyzing part, a system for accelerating and focus- ing the ions (OS) and a mass analyzing part which is a magnetic deflector(MA). The energy analyzing part comprises two channels : a channel for measuring thermal ions in the energy range 1 - 27 eV/q(TEC) and a channel for measuring low energy ions with energy 0.2 - 8 keV/q(LEC). The entrance aperture of TEC is oriented to look parallel to the velocity vector of the spacecraft and that of LEC-normal to the velocity vector and away from the Earth . Each channel is comprised of an entrance slit, a grid plasma-repelling system, a collimator and a cylindrical electrostatic deflector. The thermal ions are analyzed by energy per charge in a 12OO-cylindrical deflector (3) the analyzing surfaces of which are made of gold-plated brass grids with 82% transparency.The energy analyzing part of LEC represents a 90°-cylindrical deflector (4)combined with 27