Abstract
The authors have experimentally observed a dissipative universal instability caused by the presence of magnetically trapped electrons and excited by finite Larmor radius effects. The experiment is performed in a linear device having two magnetic mirrors. An ion cyclotron resonance scheme is used to heat the ions (protons) from one to ten eV in order to enhance the effect of finite ion Larmor radius. Ion Landau damping is observed to become important in the case of hot ions and short magnetic mirror cell length. The measured real frequency ( omega R approximately 25 kHz) and fluctuation amplitude (n/n0 approximately 25%) are found to vary in the same manner as the frequency and growth rate predicted by a linear theory, taking into account the finite axial structure of the mode.