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@unpublished{wolf:cool2021-s303,
author = {A. Wolf},
title = {{Electron Cooling of Molecular Rotations in the Low-Energy Electrostatic Ion Storage Ring CSR}},
booktitle = {Proc. COOL'21},
language = {english},
intype = {presented at the},
series = {Workshop on Beam Cooling and Related Topics},
number = {13},
venue = {Novosibirsk, Russia},
publisher = {JACoW Publishing, Geneva, Switzerland},
month = {11},
year = {2021},
note = {presented at COOL'21 in Novosibirsk, Russia, unpublished},
abstract = {{In the CSR at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, a cryogenic electrostatic storage ring for ions up to 300 keV kinetic energy per charge,* a merged and velocity-matched electron beam was used to cool the rotational states of CH⁺ molecular ions in a 300 keV stored beam. Diagnostics of the relative populations in the J = 0, 1 and 2 rotational levels was achieved by photodissociation in a laser beam with a wavelength close to the CH⁺ dissociation threshold. During a storage time up to 10 minutes, slow spontaneous rotational cooling to the J = 0 ground state occurs by radiative emission of rotationally excited CH⁺ ions. Applying electrons in the electron cooling geometry (11.8 eV beam energy) at a density near 7·10⁺⁵ per cm³ and a temperature near 2.3 meV boosted the rotational cooling rate by a large factor (~4). Using the laser-based rotational population measurements, the electron-induced rotational cooling rates could be measured.** This presents the first detailed measurement of rotationally inelastic collision cross sections on a molecular ion, as important for the diagnostics of cold astrophysical media. - Presented for the research team.**}},
}