3 Irradiation Facilities and Telemetry

For SEL qualification and SET characterization testing, heavy ion species were provided and delivered by the MSU Facility for Rare Isotope Beams⁽⁴⁾ (FRIB) using a linear particle accelerator ion source. Ion beams were delivered with high uniformity over a 17mm × 18mm area for the in-air station. A current-based measurement is performed on the collimating slits, which intercept 90-95% of the total beam, and this measurement is cross-calibrated against Faraday cup readings. These measurements are real-time continuous and establish dosimetry and integrated fluence. In-vacuum and in-air scintillating viewers are used for measurement of the beam size and distribution. An ion flux of 10⁵ ions / s-cm² was used to provide heavy ion fluences to 10⁷ ions / cm² for most runs. Ion flux was reduced to 10⁴ ions / s-cm² for some runs, to show SEL immunity at multiple flux rates and to explore the effect of flux rate on transient event counts.

For SET testing, the FRIB "degrader wheel" was employed to adjust the ion energy. The wheel is positioned between the beam "window" or output, and the device under test. The wheel features multiple slots where a foil degrading element of known thicknesses can be loaded. When the wheel is rotated to an "open" slot, only the 70mm air gap and the copper foil in the LINAC path serve to degrade the ion energy. When the wheel is remotely rotated to a slot with a given aluminum degrading foil thickness, the ions pass through the aluminum foil as well, and are slowed accordingly. This decreases the effective ion range in silicon, but increases the effective Linear Energy Transfer (LET_eff) in MeV-cm²/mg, effectively shifting along the Bragg curve. Use of the degrader wheel allows multiple LET_eff values to be achieved per beam species and LINAC energy level, reducing the switching time and improving testing throughput.