Modern COTS electronics are widely used for space missions because it’s difficult to find equivalent space electronics or in some cases space electronics is not available for modern IC’s like FPGAs, SoC, DAC/ADC etc. And nowadays it is a trend to plan space missions with “small” spacecrafts like CubeSats (NanoSats) to reduce cost and time to start mission. So, it’s possible to do single event effects radiation test for COTS electronics at proton accelerators only because it’s faster and less expensive than heavy ion test.
The other reason to do proton accelerator test is a spacecraft orbit: if it’s a low-Earth orbit it’s possible to take into account only proton Van Allen belt, South Atlantic anomaly and Solar protons so proton accelerator test is closer to real space environment. Galactic and Solar heavy ions could be taken into account by means of simple semiempirical models (for example Petersen or Barak models) or focused laser test.
Medical proton facility “PROMETEUS” primarily used for cancer therapy was certified for space electronics radiation test by Specialized Electronic Systems (SPELS, Moscow). The accelerator has proton energy from 30 MeV to 250 MeV with ±0.15% error, minimum proton beam diameter is about 2 mm and proton flux is about 107…109 particles/(cm2×bunch).