Solar Proton Monitoring Experiment More Complex Phenomenon
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\ PROT0N ~ j.W. Kohl \ uring recent years it has become obvious that are severely handicapped by a lack of spatial D solar conditions have a major influence on the and/or temporal coverage. This results in much near-earth environment. For this reason there has data in which the measuring conditions are so been an increasing effort in the study of the solar restricted that correlations become very difficult, flare processes, from the solar flare mechanism to if not impossible. What were, and are, needed are the various effects experienced in space and on easily repeatable experiments to make similar earth. A solar flare, which has been defined as "a measurements in different regions of space over a sudden short-lived brightening of a localized area long period of time. of the chromosphere,» now is recognized as a far The Solar Proton Monitoring Experiment more complex phenomenon. Solar flares occur in (SPME) is intended to provide continuous long the solar chromosphere in the vicinity of complex term monitoring of the energetic protons emitted by sunspot groups. Models for the flare process have the sun. SPME was orignially conceived by C.O. assumed the source of energy to be magnetic, Bostrom of APL and D.]. Williams, D .E. Hagge, thermal, kinetic, and some others, with new and F.B. McDonald of Goddard Space Flight models appearing regularly. In any case, a flare Center (GSFC). It cons·ists of instrumentation is due to an instability leading to various phases of suitable for measuring proton fluxes and spectra particle acceleration, storage, and release, accom in an energy range associated with solar-activity panied by radiative emissions in a complex time changes, both near the earth and in interplanetary sequence still comparatively uncertain. The study space during at least half of a solar cycle. Data of the energy release in the form of X -rays, ultra from the radiation monitoring program is made violet, visible light, radio noise bursts, and parti available to scientists in related disciplines through cles may someday evolve into a unified theory. In the Solar-Geophysiml Data Bulletins published the meantime these separate disciplines involve monthly by the Environmental Science Services many separate investigations by the scientific Administration (ESSA), Institute for Environ community in which most individual experiments mental Research for use in correlation studies. 2 APL Technical Digest I nstrumentation has been developed to provide data over long periods of time on the radiation environment near earth and in interplanetary space. This article presents a description of the particle detectors used and a few of the preliminary observations obtained with this instrumentation on-board rockets and satellite IMP F. Variations of particle flux and energy during periods of differing solar activity provide information on the magnetic configuration in space and near earth, and on particle interactions with the earth 's magnetosphere. Future flights of similar instrumentation may improve our understanding of solar-terrestrial relationships. Such studies will lead to increased knowledge of units, each of which functions in a different energy the fundamental physical processes involved in region. Although preliminary results from SPME solar-geophysical phenomena, such as: solar ac have caused some changes, most of the basic units celeration processes, interactions in the interplane as used onboard SPICE rockets (the Solar Particle tary medium, interplanetary magnetic configura Intensity and Composition Experiment version of tions, and interactions with the earth 's magnetic SPME) and satellite Explorer 34(IMP F ) remained field . unchanged. The changes consist of more resolution Besides the strictly scientific, such a program in energy ranges and the addition of more detectors has other uses, such as its ability to serve as a rather than actual detector changes. For this warning system of radiation hazards. With in reason, a very brief description of each of the initial creased knowledge, it might be possible to predict four detector units of SPME follows (see Fig. 1): both the probability and the effects of solar events SPME-Detector Unit 7: This unit is a set of three with a greater reliability than exists at present. 700-J.L-thick, silicon surface-barrier detectors It can be appreciated how important both warning connected in parallel and mounted on orthogonal and prediction might be to manned spacecraft and axes. The effective surface area of each individual to supersonic transports in high-altitude flights detector is 0.8 cm2, with the total providing a large over the polar caps. area sensitive to incoming particles over a 211" steradian solid angle. The energy threshold is set Description of Experiments by the 5.6-mm-thick hemispherical copper shield Since the purpose of the SPME is to provide a surrounding the detector to detect all protons with number of self-consistent packages for various energy greater than 60 Mev. spacecraft to allow monitoring of protons over a Detector Unit 2: This unit is identical to Unit 1 wide flux and spectral range, it was decided to except for the shielding thickness. In this case, the keep the packages as simple as possible. This is 1.6-mm-thick copper dome sets the threshold to accomplished by the use of four separate detector measure protons with energy greater than 30 Mev. September - O ctober 1968 3 DETECTOR DETECTOR DETECTOR DETECTOR UNIT NO. 1 UNIT NO.4 UNIT NO. 3 UNIT NO. 2 Fig. I-The four particle-detector units of the IMP F version of SPME. The Ep ~ 60 Mev and the Ep ~ 30 Mev dODles are shown with a black, protective coating which is reDloved before flight. Detector Unit 3: This unit uses a cubic 3mm x detector. The detector housing incorporates a col 3mm x 3mm lithium-drifted ·solid-state detector. limator which reduces the look-angle to a cone of The look-angle is a 27r steradian hemisphere. The 60° full angle. The electronic discrimination in this energy threshold for protons is set by the 0.63-mm unit is so arranged that there are two channels of thick aluminum shield to measure protons of output information. One channel measures pro energy :::: 10 Mev. tons in an energy "window," 1.0 ~ Ep ~ 10 Mev. Detector Unit 4: This detector is a nominal The second channel of data is the " upper-level" of 100-J.L-thick silicon surface-barrier detector. The the 100-J.L detector and measures particles depos sensitive surface area is 200 mm2. The only shield iting more than 3.6 Mev in the detector. A conse ing on this unit is a 1/4 mil aluminized mylar film quence of this scheme is that with the appropriate to provide an opaque shield over the light-sensitive correction for the proton component (the spectral CHANNEL 1 CHARGE SENSITIVE PREAMPLIFIER CHANNEL 2 CHARGE SENSITIVE PREAM PLI FI ER CHANNEL 3 CHARGE .; .a SENSITIVE ..JW ..J" PREAMPLIFIER Z W Z Z -< Z :J: -< DISCRIMINATOR (,) 0 CHANNEL 4 4a CHARGE SENSITIVE PREAMPLIFIER DISCRIMINATOR 4b Fig. 2-Block diagraDl of the IMP F SPME electronics. 4 APL Technical Digest 100r-------~--------~--------~--------~------~--------~--------~--------~------~ 50 -50 f----_+_ MAGNETOPAUSE EXPLORER 34 (IMP-F) -100L-______~ _________L ________ ~ ________L_ ______ ~ _________L ________ ~ ________~ ______~ 250 200 150 100 50 o - 50 - 100 - 150 -200 Y(1 0 3 KM) Fig. 3-Projection onto the ecliptic plane (as seen from the north ecliptic pole) of the IMP F orbit from May 27 through June 5,1967. Also shown is the orbit of satellite 1963 38C, not to scale. qualities of which can be calculated from the data to test the system, while the other two successful in Units 1, 2, and 3), the " upper-level" channel flights were made in the decay phase of the may provide information on alpha particles. September 2, 1966 flare event. Each of the four detector units described above EXPLORER 34 (IMP F )- I ~1P F, with its version has its own preamp-amplifier-discriminator, the of SPME, was launched on May 24, 1967 into a outputs of which are sent to the data-processing highl y elliptical orbit perpendicular to the ecliptic electronics. A block diagram of the Explorer 34 plane. The orbit has an apogee of'"'-' 34 Re (earth (IMP F) version of the SPME package is shown radii), a perigee of '"'-' 250 km, and an orbital in Fig. 2. It has been previously mentioned that period of '"'-' 4 days. At launch, the sun-earth-probe SPME packages have been flown in SPICE rockets angle was approximately 104° and was changing and satellite IMP F. Descriptions of these vehicles at roughly 1° per day. The integral detector Units follow. 1, 2, and 3, are mounted with their symmetry axes SPICE-The SPICE sounding rocket program parallel to the satellite spin axis, which is perpen was instituted to carry emulsions into the solar dicular to the ecliptic plane. The differential flux cosmic ray flux incident on the polar cap; it also detector, Unit 4, looks out perpendicular to the served as a pre-satellite test for the SPME. As spin axis and undergoes several rotations in one will be shown later, the flights provide important data collection period integrating over all azimuth secondary information. Data have been obtained angles. Thus, no directional information is avail able. As mentioned previously, the IMP F data from three fli ghts of N ike-Apache rockets launched from Ft. Churchill, Manitoba, Canada, at geo from detector Units 1, 2, and 3 are made available magnetic latitude 67°N, reaching altitudes of to the scientific community on a monthly basis approximately 160 km. The nose cones were so with a six-month lag time for data processing. constructed that they would provide no excess Observations shielding material around the detectors while Analysis of the data from the SPME program is above the atmosphere.