title: Density profile measurements with X-mode lower cut-off reflectometry in ASDEX             Upgrade.
abstract: Despite the fact that density profile measurements using X-mode lower cut-off             reflectometry are foreseen to be used on ITER, little or no experience is available             within the reflectometry community and to our knowledge no results on this subject have             been published so far. In ASDEX Upgrade the multichannel broadband reflectometer is             equipped with both O- and X-mode channels. While X-mode operation was designed for upper             cut-off reflection, it is observed that for both high magnetic field and high density             discharges the lower cut-off becomes accessible. Here we present reflectometry             measurements obtained in ASDEX Upgrade using X-mode lower cut-off and compare both the             resulting group delay and density profile with O-mode measurements performed             simultaneously over the same plasma region. The possible use of this comparison to             provide estimates of the magnetic field is briefly discussed.
authors.affiliation: Associação EURATOM/IST, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisboa, Portugal. pvarela@ipfn.ist.utl.pt
authors.forename: P
authors.initials: P
authors.lastname: Varela
authors.forename: M
authors.initials: M
authors.lastname: Manso