J. Plasma Physics: page 1 of 22. c  Cambridge University Press 2014 doi:10.1017/S0022377814000890 1 The hot hELicon eXperiment (HELIX) and the large experiment on instabilities and anisotropy (LEIA) E. E. Scime 1 †, P. A. Keiter 2 , M. M. Balkey 1 , J. L. Kline 3 , X. Sun 4 , A. M. Keesee 1 , R. A. Hardin 5 , I. A. Biloiu 6 , S. Houshmandyar 7 , S. Chakraborty Thakur 8 , J. Carr, Jr. 9 , M. Galante, 10 D. McCarren 1 and S. Sears 1 1 Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA 2 Department of Atmospheric and Space Sciences, University of Michigan, Ann Arbor, MI 48109, USA 3 Los Alamos National Laboratory, Los Alamos, NM 87545, USA 4 Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026, China 5 Wacker Polysilicon North America LLC, Charleston, TN 37310, USA 6 US Army Research Laboratory, Adelphi, MD 20783, USA 7 Department of Physics, Gonzaga University, Spokane, WA 99258, USA 8 Center for Energy Research, University of California, San Diego, CA 92093, USA 9 Department of Physics, Texas Lutheran University, Seguin, TX 78155, USA 10 Department of Physics, University of Wisconsin, Madison, WI 53706, USA (Received 4 March 2014; revised 14 May 2014; accepted 19 September 2014) The West Virginia University Hot hELIcon eXperiment (HELIX) provides variable density and ion temperature plasmas, with controllable levels of thermal anisotropy, for space relevant laboratory experiments in the Large Experiment on Instabilities and Anisotropy (LEIA) as well as fundamental studies of helicon source physics in HELIX. Through auxiliary ion heating, the ion temperature anisotropy (T ⊥ /T || ) is variable from 1 to 20 for parallel plasma beta (β =8πnkT i  /B 2 ) values that span the range of 0.0001 to 0.01 in LEIA. The ion velocity distribution function is measured throughout the discharge volume in steady-state and pulsed plasmas with laser induced fluorescence (LIF). The wavelengths of very short wavelength electrostatic fluctuations are measured with a coherent microwave scattering system. Operating at low neutral pressures triggers spontaneous formation of a current-free electric double layer. Ion acceleration through the double layer is detected through LIF. LIF-based velocity space tomography of the accelerated beam provides a two- dimensional mapping of the bulk and beam ion distribution functions. The driving frequency for the m = 1 helical antenna is continuously variable from 8.5 to 16 MHz and frequency dependent variations of the RF coupling to the plasma allow the spontaneously appearing double layers to be turned on and off without modifying the plasma collisionality or magnetic field geometry. Single and multi-species plasmas are created with argon, helium, nitrogen, krypton, and xenon. The noble gas plasmas have steep neutral density gradients, with ionization levels reaching 100% in the core of the plasma source. The large plasma density in the source enables the study of Aflv´ en waves in the HELIX device. † Email address for correspondence: escime@wvu.edu