  Refractive Interstellar Scintillation (RISS) effects on pulsar signals are
powerful techniques for discriminating between different models that have been
proposed for the power spectrum of plasma density fluctuations in the
Interstellar Medium. The nature of the spectrum is considered to be a major
input for understanding the underlying mechanism of interstellar plasma
turbulence. Data from our long-term pulsar scintillation observations using the
Ooty Radio Telescope (ORT) at 327 MHz are used to investigate the nature of the
spectrum in the Local Interstellar Medium. The emerging picture is that the
spectrum is Kolmogorov-like ($ \beta \approx 11/3 $) in the spatial scale range
$\sim 10^6$ m to $\sim 10^{11}$ m, and there is evidence for excess power at
larger spatial scales ($ \sim 10^12 - 10^13 $ m).
