high energies (hundreds of MeV), thus enhancing the population of HZE particles. The dosage level of HZE particles is very important for the question of radiation dosage for space workers and for the degradation of surfaces by sputtering, while the dosage level of relativistic electrons is significant for the rate of degradation of spacecraft instrumentation as well as for health problems of space workers. Suggestions for experimentation and for the utilization of targets of opportunity in this area are integrated into Sections 4.6.2 and 4.6.3. 4.4.2 Dumping of the Radiation Belts (Aikin, Cladis) A. Inner Belt Protons. Inner radiation belt protons may be precipitated into the stratosphere and mesosphere as a result of plasma turbulence caused by Ar ions from the ion thruster engine. Proton interaction with the atmosphere creates ionization at altitudes between 30 and 100 km, leading to a possible disruption of VLF communications and a modification of the ozone distribution. The magnitude of the effect is limited by the rate of repopulation of the inner belt protons. Since the mechanism for repopulation is the decay of albedo neutrons resulting from cosmic radiation, a long time, perhaps as much as 100 years, is required for repopulation. It is expected that following the initial dumping of the belt, subsequent precipitation will be limited by the low belt population. The amount of ozone destroyed initially needs to be calculated, but is less than that of the August 1972 Solar Proton Event. The high energy, inner-belt proton fluxes are very stable, and it is very unlikely that their distribution would be appreciably altered by the presence of the Ar+ beam or by an enhanced trapped Ar+ population. In fact, the enhanced plasma density would make the proton distribution more stable. If it is assumed, however, that the distribution were destabilized by some unknown mechanism, such that the protons were precipitated at the "strong" pitch-angle diffusion rate, the flux of precipitating protons of energy greater tjian 50 MeV (penetrating to 30 km) would be less than about 3 x 10J cm sec . This flux is about the highest that can be expected; and, at this rate, the proton reservoir would be depleted in about an hour. During the solar proton events of 3-11 August 1972, the flux of protons of energy 29-100 MeV incident on the atmosphere at high latitudes exceeded 2 x 103 cm-z sec-1, and it remained high for several days. Hence, it appears that the effects of the precipitation of the trapped energetic protons will be small in comparison to the effects produced by large solar proton events. B. Outer Belt Electrons. The precipitation of electrons from the outer radiation belt will cause atmospheric ionization at geomagnetic latitudes outside the equatorial zone. The magnitude and frequency of occurrence of the effect needs to be determined. Communications will be affected and some ozone will be destroyed. In fact, this is a relativistic electron precipitation (=REP) event, and it can be shown — see Bauer (1978), Figure 2-1 and Appendix E — that the effect of an REP on ozone is small compared to that of a solar proton event or to galactic cosmic rays.
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