Simulation of Low-Earth-Orbit Radiation Environments with a 5 to 120 MeV Proton Cyclotron Beam Using a Proton Beam Modulator

In this paper we will describe the experimental results of a novel method for simulating the proton radiation of a low earth orbit with a cyclotron using a specially designed proton beam modulator. We will present details on the design of the proton beam modulator wheel and the experimental results of the irradiation of actual spaceflight electronic components with the modulated beam. Electronic devices on board spacecraft are generally susceptible to penetrating radiation encountered in the space environment. Since the proton radiation spectrum of a low earth orbit covers a rather wide range from 1 to 500 MeV, a proton beam range modulator was designed that simulates a proton spectrum from 5 to 120 MeV. This proton radiation energy range simulates the most damaging part of the spectrum. The spectrum from the cyclotron was mapped by means of a sodium iodide scintillator; those measurements confirmed our initial calculations of the proton spectral density and showed that the mean energy of the protons is centered at about 40 MeV. In this paper, we will present an analysis of the simulation of the low-earth-orbit proton energy spectrum and details concerning the design of the proton beam modulator. In order to verify the operation of the modulator used for simulating low-earth-orbit radiation, power conditioners using MOSFET power switches were subjected to the proton radiation. They were allowed to accumulate a total of 30 krads (Si) of proton radiation over the specified energy range.