Scaling of density fluctuations with magnetic field and ion mass

An improved CO2 laser collective scattering technique has been used to study the scaling of density fluctuations with magnetic field and ion mass in a linear magnetized plasma. Measurements are presented for H2, D2, He, Ne and Ar plasmas for magnetic fields of 0.1-0.3 T for frequencies 20 kHz< omega /2 pi <500 kHz and a wave vector range 3 cm-1<k<30 cm-1. The peak frequency omega pk of the fluctuations scales linearly with the magnetic field and decreases with increasing ion mass. The mean wave vector ktheta shows a similar but not so pronounced behaviour. The broadening of the frequency spectrum Delta omega increases with magnetic field and decreases with ion mass. A statistical dispersion relation is established for the different gases. Whereas the phase velocity of the fluctuations remains constant in the neon and argon plasma it increases with magnetic field in the hydrogen and deuterium plasma. The scaling n/n=1/kperpendicular to Ln fits the data noticeably better than the scaling Kperpendicular to rho s. Measurements of the time evolution of the fluctuations show that the peak frequency is generated at the beginning of each plasma pulse and remains constant in amplitude during the pulse. However, in a highly turbulent plasma frequencies with omega > omega pk grow exponentially to a saturated state. Compared to those obtained from measurements on Tokamaks, the author's results show similar behaviour regarding frequency, wavenumber and scaling of the density fluctuations in H2, D2 and He plasmas.