Nonlinear Processes in Geophysics www.nonlin-processes-geophys.net 1023-5809 1607-7946 11 2 2004 10.5194/npg-11-267-2004 http://www.nonlin-processes-geophys.net/11/267/2004/ http://www.nonlin-processes-geophys.net/11/267/2004/npg-11-267-2004.html http://www.nonlin-processes-geophys.net/11/267/2004/npg-11-267-2004.pdf 267 274 2004-04-14 Formation of quasi-power law weak Langmuir turbulence spectrum by harmonic generation P. H. Yoon Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA Langmuir wave turbulence generated by a beam-plasma interaction has been studied since the early days of plasma physics research. Despite a long history of investigation on this subject, among the outstanding issues is the generation of harmonic Langmuir waves observed in both laboratory and computer-simulated experiments. However, the phenomenon has not been adequately explained in terms of theory, nor has it been fully characterized by means of numerical simulations. In this paper, a theory of harmonic Langmuir wave generation is put forth and tested against the Vlasov simulation results. It is found that the harmonic Langmuir mode spectra exhibit quasi power-law feature implying a multi-scale structure in both frequency and wave number space spanning several orders of magnitude.