Energetic particle experiment DOK-2


The study of energetic particles acceleration and transport within the magnetosphere and on its boundaries is the main goal of DOK-2 experiment on Auroral Probe in a frame of INTERBALL project. Two particle spectrometers: DOK-2 and its small version - DOK-2S were installed on the main satellite and small subsatellite. Both function successfully since launch on 29 August, 1996. DOK-2 experiments on Tail and Auroral Probes of INTERBALL project continue our studies of energetic particle population on Prognoz 10 satellite in 1985 (Intershock project). Due to much higher energy, angular and time resolution, better separation of electrons and ions it is expected that DOK-2 experiment will allow to re-examine in more details energetic particle population and related processes in magnetosphere regions covered by the spacecraft orbit.

DOK-2 spectrometer

DOK-2 uses two pairs of energetic particle telescopes. Each telescope has a single, passively cooled, totally depleted, surface-barrier silicon detector. One detector of each pair (1e, 2e) is of 0.3 mm thick. Thin foil in front of detector protons with energies E < 400 keV so this detector measures electron spectrum in 20 - 420 keV range. The second detector (1p, 2p) of 0.15 mm thick is supplied with a broom magnet, deflecting electrons up to 1500 keV. It measures spectrum of ions (protons) in 20-850 keV range. Full aperture angles and geometric factors of electron telescopes are of 27o and 0.066 sm2*sr. For proton telescopes these values are 12.7o and 0.015 sm2*sr . Particle flux angular distribution is measured using spacecraft rotation with a 2 min period around the axis directed to the Sun (the angle ) and mechanical scanning of the second telescope pair in a plane containing the rotation axis (the angle ). So 3-dimensional particle distribution function is measured during each 2 min rotation period. About seven full scanning cycles are carried out for every rotation. The first detector pair (1e, 1p) is fixed in the antisolar direction. Moving detector pair (2e, 2p) can either scan from =45o to 180o (to a Sun direction) or stay in one of 4 positions: 45o, 90o, 135o and 180o.

Analogue electronics for each of 4 detectors consists of a charge sensitive preamplifier (in a cooled part of the instrument), a shaping pulse amplifier and 56-57 channel amplitude analyser AA (logarithmic ADC). The measurements base is formed of "elementary measurement" (EM) - one full 56-57 channel spectrum measured every 1 sec for each of 4 telescopes. This information is available only during the most informative Real Time mode of DOK-2. In storing modes there are two kinds of output information formed from EM's :

The mechanical scanning occurs only in Fast and Real Time modes. Transition from Monitoring to more informative Fast modes occurs automatically when particle flux variability is high enough or after a sharp increase of fluxes. Return to Monitoring mode is also automatic.

Telescope Energy values, keV Angle, deg
1e 21-26 39-48 76-95 180
2e 20-24 37-46 73-92 45-180
1p 22-28 46-60 101-132 180
2p 21-27 45-59 101-133 45-180

Experiment status

Spectrometer DOK-2 was switched on 5 hours after the launch on 29.08.1996 and is in a continuous operation up today. Tests of the instrument on 3.09.1996 showed normal function of all. As for Tail Probe some problems were with moving telescope mechanics. 2e and 2p-telescopes stay at =79o. All other systems both hardware and software are working normally.

DOK-2 data are processed at the Space Research Institute RAS, at the Institute of Experimental Physics SAS and at the Demokritos University of Thrace, Greece. DOK-2S data are processed at the Institute of Experimental Physics.

Examples of DOK-2 data.

Figures 1-7 show some examples of DOK-2 data for 1 hour time interval corresponding to the Auroral zone boundary intersection on 3.09.1996 11.00-12.00 UT. For this time interval:

=19169-17048 km,
Fig.1 shows time variation of the TP-parameters. Spin modulation of intensities for 1p-telescope (T=2 min) increasing to the end of the interval is due to great deviation of spin axis from X-axis of the SC in this period. At the beginning and in the middle of the interval 2p-detector detects the light reflected from the earth hat leads to periodical drops of intensities. Fig.2 and Fig.3 show series of successive spectra for electron telescopes which exhibit space-energy dispersion of electrons (peak slowly moves from 250 to 150 keV).
Analogous dispersion for protons is shown in Fig.4. Here as in Fig.5 there are narrow peaks in proton spectra corresponding to monoenergetic proton beams. Fig.6 and Fig.7 show existence of two components in proton spectra with a different spin modulations (different pitch angle distributions).

Fig.1 Fig.2 Fig.3 Fig.4
Fig.6 Fig.7 Fig.1

V.N. Lutsenko,
Space Research Institute, Russian Acad. of Sci., Profsojuznaja 84/32, 117810 Moscow, Russia.
K. Kudela (PI),
Institute of Experimental Physics, Slovak Acad. of Sci., Watsonowa 47 04353 Kosice, Slovakia.
E.T. Sarris,
Demokritos University of Thrace, Department of Electrical Engineering, 67100 Xanthi, Greece.

Correspondence to: V.N. Lutsenko. Phone: 7-095- 333-33-56, Fax: 7-095-310-70-23, E-mail: vlutsenk@volt.iki.rssi.ru