Uppsala University This is an accepted version of a paper published in European Physical Journal D: Atomic, Molecular and Optical Physics. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. Citation for the published paper: Ågren, O., Moiseenko, V., Noack, K., Hagnestål, A. (2012) "Radial Drift Invariant in Long-Thin Mirrors" European Physical Journal D: Atomic, Molecular and Optical Physics, 66(28) URL: http://dx.doi.org/10.1140/epjd/e2011-20477-4 Access to the published version may require subscription. Permanent link to this version: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-183360 http://uu.diva-portal.org