Experimental and numerical investigations of mechanisms for Auroral Kilometric Radiation S.L. M c Conville 1 , D.C. Speirs 1 , K. M. Gillespie 1 , R. Bingham 1,2 , K. Ronald 1 , A.W. Cross 1 , A.D.R. Phelps 1 , C.W. Robertson 1 , C.G. Whyte 1 , R.A. Cairns 3 , I. Vorgul 3 and B.J. Kellett 2 1 SUPA Department of Physics, University of Strathclyde, Glasgow, G4 0NG, Scotland 2 Space Physics Division, CCLRC, Rutherford Appleton Laboratory, Didcot, OX11 0QX, England 3 School of Mathematics and Statistics, University of St. Andrews, St. Andrews, KY16 9SS, Scotland Introduction Magnetic field lines at the Earth’s poles create regions of increasing field which magnetically compresses electrons as they descend towards the ionosphere. This produces a horseshoe shaped distribution function in velocity space which has been observed by satellites [1]. Research has shown this distribution to be unstable to a cyclotron maser type instability [2] and the emitted radiation is observed to be polarised in the extraordinary mode. We present results of experimental and computational investigations [3] of radiation emissions from an electron beam with a horseshoe distribution in velocity space to compare with the astrophysical observations. Results are presented using an electron beam of energy 75keV with a cyclotron frequency of 4.45GHz and 85keV and 11.7GHz frequency, compressed using magnet coils to mimic the naturally occurring phenomenon. The radiation output from the experiment which was observed to be close to the cyclotron frequency and electron transport measurements confirmed that the horseshoe distribution function was obtained. Experimental measurements of the antenna pattern radiated from the output window allowed the TE mode structures excited by the beam to be analysed demonstrating the radiation to be polarised and propagating perpendicular to the static magnetic field and the efficiency was estimated to be ~2% in close agreement to the predictions of the 2D and 3D versions of the PiC code KARAT. The efficiency was also comparable with estimates of the astrophysical phenomenon. Method and Apparatus To investigate the driving mechanisms believed to cause the process of auroral kilometric radiation in a controlled environment, use has been made of the fact that the theoretical models of the beam wave interaction process predicts that the process scales with the 34th EPS Conference on Plasma Phys. Warsaw, 2 - 6 July 2007 ECA Vol.31F, P-2.088 (2007)