Parametrically Induced Nonlinear Wave-Particle Scattering and Plasma Heating near the Lower Hybrid Frequency

Abstract

PHYSICAL REVIEW LETTERS 3 JUNE 1974the modulation voltage V m . In summary, preliminary observations have demonstrated a nonlinear interaction of an ionbeam-mode, plasma system. The measured amplitude oscillations are found to be consistent with the ion-beam trapping model. The physical implications of the results are as follows: (1) A modulated ion beam can excite large-amplitude coherent oscillations and subsequent trapping of the beam occurs. (2) The beam ions become bunched in space analogous to the nonlinear interactions of an electron beam and plasma. 7 (3) This spatial bunching provides an effective mechanism for the generation of higher harmonics and could be of interest in spreading the wave spectrum and providing effective coupling of energy into plasmas by means of ion beams.We thank Dr. N. L. Oleson for helpful and rewarding discussions. *Work supported in part by the U. S. Atomic Energy Commission and Tampa Electric Company. *J. H. Malmberg and C. B. Wharton, Phys. Rev. Lett.Most parametric instabilities studied up to date in a plasma have involved the excitation of resonant electron and ion modes by a "pump" rf field. 1 That is, each of the excited modes satisfies a linear dispersion relationship in the absence of the external rf field. In this Letter we report experimental observations of a new type of parametric instability which involves the excitation of lower-hybrid waves and nonresonant low-frequency modes (ion quasimodes) when the "pump" rf field is near the lower hybrid frequency. 19, 755 (1967). """ 5 T. M. O'Neil, Phys. Fluids 8, 225 (1965). 3 L. M. Al'tshul and V. I. Karpman, Zh. Eksp. Teor. . ^n such multipole devices, the plasma is supported at the edge by strong short-range magnetic fields which are produced by permanent magnets spaced completely around the plasma. This arrangement leads to higher plasma densities at lower neutral pressures and lower discharge currents, and to plasmas which are highly uniform in density. See, for example, R. Limpaecher and K. R. MacKenzie, Bull. Amer. Phys. Soc. Ij5, 1222 (1971); R. J. Taylor, D. R. Baker, and H. Ikezi, Phys. Rev. Lett. 24, 206 (1970). 10 For example, B. D. Fried and A. Y. Wong, Phys. Fluids 9, 1084 (1966). n R. A. Stern, J. F. Decker, and P. M. Platzman, Phys. Rev. Lett. 32, 359 (1974).Physically, the mechanism for instability is quite similar to that which drives the nonlinear Landau growth. 2 We can view the interaction as a scattering of a particle with a photon and a plasmon, in which a photon is absorbed followed by the emission of a plasmon; the particle carries off the difference of the wave energy and momentrum. The growth rate of the instability is maximum when the parallel phase velocity (along the confining magnetic field) of the ion quasimode is of the order of the electron thermal velocity.Experimental and theoretical studies of a new type of parametric instability involving the excitation of ion quasimodes (due to nonlinear wave-particle scattering) have been carried out when the "pump" frequency is near the lower hybrid...

Nonlinear wave effects in laboratory plasmas: A comparison between theory and experiment

“…A unified treatment of the problem of parametric coupling of waves in a magnetic field has been undertaken by Aliev et al (1966), Amano and Okamoto (1969), and Porkolab ( , 1974. These authors used the Vlasov equation, which can be solved after transformation to the oscillating frame of reference.…”

“…(y+y )(y+y ) i x t( l)xa ( 1) The purely growing mode is obtained by assuming~, = 0, ts ((u"k) = 0, in which case the growth rate near threshold is (Porkolab, 1974) 4k so that y~EO (since p,~E,). For large electric fields (i.e.…”

“…The growth rate is (Porkolab, 1974 ([e(~) [' (4.17) where~e(&u)~' = a"'(~)+ a g~), etc. Depending upon which term is the largest, the growth rate is &~Epp (~l or y~EO/X &, , &z.…”

Evolution of electron beam generated waves resulting in transverse ion heating and filamentation of the plasma

“…The role of lower hybrid (LH) waves in the transverse heating of ions has been known since the mid-1970s in connection with plasma heating in fusion machines [e.g., Chang and Porkolab, 1974]. In connection with the observation of the transversely accelerated ions in the auroral plasma [Klumpar, 1979], Chang and Coppi [ 1981 ] suggested that the auroral electron beam driven LH waves might transversely accelerate ions leading to the formation of ion conics.…”

Anomalous Absorption of Electromagnetic Energy through Parametrically Induced Lower-Hybrid Turbulence

“…4 In this Letter I report further theoretical results concerning the saturation of lower-hybrid turbulence triggered by a whistler pump wave, 3 * 4 and ion and electron heating in a plasma of thermonuclear interest.…”