Collector-based measurement of gas desorption and secondary electron emission induced by 0–1.4 keV electrons from LHC-grade copper at 15 K

CERN's Large Hadron Collider cryomagnets embed a 1.9 K UHV chamber lined with a 5-20 K beam-screen (BS) that intercepts the synchrotron radiation and electron cloud (EC). The low-energy EC irradiates the BS and desorbs gas, creating a dynamic vacuum effect. A novel setup controllably reproduces this by irradiating an unbaked as-received BS copper sample at 15 K with 0-1.4 keV electrons, representing a slice of the EC spectrum. This collector-based setup is qualified using a HOPG reference for secondary electron yield (SEY) and N-15(2) as a tracer in low-energy electron stimulated desorption (ESD) measurements. Measurement at 15 K revealed sub-10 eV ESD thresholds and a maximum around 300 eV of 0.18 H-2/e(-) and 0.13 CO/e(-). Irradiation with 300 eV and 1 keV electrons at similar to 8.10(-4) C.mm(-2) conditioned ESD and SEY alike. Similar dose at 17 eV only caused minor SEY reduction and no ESD decline. The as-received H-2 and CO2 yields at 300 eV decreased 5-150x between 15 and 265 K, respectively..