Observation of very low frequency drift wave in ECR produced plasma in the MaPLE device

Plasma is produced by Electron Cyclotron Resonance(ECR) method using $2.45GHz$ microwave in the MaPLE device [R. Pal, S. Biswas et. al., Rev. Sci. Instrum. 81, 73507(2011)] Density fluctuation of the order of 40\% is created by modulating the microwave power at a frequency of $300 Hz$. Floating potential measurement shows the presence of $300 Hz$ frequency along with $600 Hz$ and $900 Hz$ frequencies. Amplitudes of the fluctuations are maximum at radial position $R=6cm$. Density gradient scale length gives the drift wave frequency close to $600 Hz$. Measurement of poloidal propagation confirms it to be a drift wave with mode no $m=2$ and wavelength $\lambda_{\perp}\approx 20cm$. Measured phase velocity in the poloidal direction is $1.3\times10^{4}cm/s$ which is about the electron diamagnetic drift velocity. This $600 Hz$ drift wave probably parametrically couples with $300 Hz$ pump wave and excite $300 Hz$ and $900 Hz$ frequencies. In the region between $R=8cm$ and $R=10 cm$, there is a high radial electric field which suppress both $300 Hz$ and $600 Hz$ fluctuations by $\bf{E \times B}$ flow. Poloidal flow measurement with mach probe also confirms about the presence of $\bf{E \times B}$ flow.