Document Type

Conference Paper

Journal/Book Title/Conference

14th Spacecraft Charging Technology Conference

Publication Date

Spring 4-2016

Abstract

Accurate determination of the absolute electron yields of conducting and insulating materials are essential for models of spacecraft charging and related processes involving charge accumulation and emission due to electron beams and plasmas. Apparatus using low-fluence pulsed electron beam sources and various methods to minimize charge accumulation have been developed at facilities around the world. This study presents a round robin comparison of such tests performed in CSIC at Instituto de Ciencia de Materiales de Madrid, LaSeine at Kyushu Institute of Technology, DESSE at ONEREA, and the Space Environment Effects Materials (SEEM) test facility at Utah State University. The primary objectives of the study were to determine the consistency and uncertainties of these absolute yields measurements, and to investigate the effects of the similarities and differences of the diverse facilities.

Measurements were made of the absolute total, secondary and backscattered electron yields at normal incidence over the full range of incident energies accessible with each group’s instrumentation (a full range of ~5 eV to ~30 keV). Electron emission spectra at specific incident electron energies were also measured. Measurements were made for identical samples with reproducible sample preparation of two standard materials: (1) the elemental conductor Au (25 μm thick 6N high purity Au foils) and (2) the polymeric insulator polyimide (25 μm thick Kapton HNTM). Studies of the effects on electron yield of Au surface contamination—as measured with Auger Electron Spectroscopy and other techniques—were made for samples: (1) as received, (2) subject to a simple standard cleaning procedure, (3) subsequently baked out under ultrahigh vacuum, and (4) after Ar ion sputter cleaning and thermal annealing. Similarly, studies of the effects of absorbed water and volatile compounds on electron yield were made for polyimide samples: (1) unbaked and (2) subjected to a vacuum bake out.

An outline of measurement and analysis techniques used by each laboratory is presented, along with methods used to calibrate the incident energies and absolute yields measured with their different electron detectors. The effects of different charge minimization and neutralization methods are compared. Various empirical and physics-based models to characterize the electron yield curves are used to parameterize the yield data. The values determined at each laboratory for the maximum yield and energy at this yield, the first and second crossover energies, and the asymptotic yield at high energy are also compiled and compared.

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