Ion cyclotron emission and fast wave destabilization by a proton beam on the Large Plasma Device*

Resonant interaction between energetic-ions and plasma waves is a fundamental topic of importance in space and laboratory plasma physics (e.g., interaction of protons and alpha particle with Alfven-ion-cyclotron and fast-magnetosonic waves in the solar wind, aurora and magnetic fusion plasmas). We report results on the spontaneous generation of fast Alfvén waves and high-harmonic electrostatic waves in the lower-hybrid range of frequencies by an intense proton beam. A proton beam (15 keV, 10 A) has been injected into a large magnetized plasma (n ≈ 10¹⁰ – 10¹³ cm^-3, T_e ≈ 5.0-15.0 eV, B = 0.6–1.8 kG, He⁺ and H⁺ ions, 19 m long, 0.6 m diameter) for performing fast-ion studies on the Large Plasma Device (LAPD). The beam forms a helical orbit (pitch-angle ≈ 7°–55°) and propagates with an Alfvénic speed (beam-speed/Alfvén-speed = 0.2–3.0). The role of resonant processes in destabilizing these waves were examined by recording the mode-structure of these waves and relevant parameters of plasma using a variety of diagnostic tools (retarding-field energy analyzer, three-axis magnetic-loop, Dipole, and Langmuir probes). This presentation will particularly focus on the excitation of waves with right-handed polarization that cover a broad spectrum above the beam gyro-frequency.