Space Sci Rev DOI 10.1007/s11214-013-9961-1 SPECIAL COMMUNICATION The Genesis Solar Wind Concentrator: Flight and Post-Flight Conditions and Modeling of Instrumental Fractionation Roger C. Wiens · Daniel B. Reisenfeld · Chad Olinger · Peter Wurz · Veronika S. Heber · Donald S. Burnett Received: 8 August 2012 / Accepted: 22 January 2013 © Springer Science+Business Media Dordrecht 2013 Abstract The Genesis mission Solar Wind Concentrator was built to enhance fluences of solar wind by an average of 20x over the 2.3 years that the mission exposed substrates to the solar wind. The Concentrator targets survived the hard landing upon return to Earth and were used to determine the isotopic composition of solar-wind—and hence solar—oxygen and nitrogen. Here we report on the flight operation of the instrument and on simulations of its performance. Concentration and fractionation patterns obtained from simulations are given for He, Li, N, O, Ne, Mg, Si, S, and Ar in SiC targets, and are compared with mea- sured concentrations and isotope ratios for the noble gases. Carbon is also modeled for a Si target. Predicted differences in instrumental fractionation between elements are discussed. Additionally, as the Concentrator was designed only for ions ≤ 22 AMU, implications of analyzing elements as heavy as argon are discussed. Post-flight simulations of instrumental fractionation as a function of radial position on the targets incorporate solar-wind veloc- ity and angular distributions measured in flight, and predict fractionation patterns for var- ious elements and isotopes of interest. A tighter angular distribution, mostly due to better Electronic supplementary material The online version of this article (doi:10.1007/s11214-013-9961-1) contains supplementary material, which is available to authorized users. R.C. Wiens ( ) · C. Olinger Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA e-mail: rwiens@lanl.gov D.B. Reisenfeld Department of Physics and Astronomy, University of Montana, Missoula, MT 59812, USA P. Wurz Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland V.S. Heber Department of Earth and Space Sciences, UCLA, 595 Charles Young Drive East, Los Angeles, CA 90095–1567, USA D.S. Burnett California Institute of Technology, 1200 California Boulevard, Pasadena, CA 91109, USA