Rayleigh scattering is used in order to deduce the gas temperature from neutral density measurements inside a microwave discharge in argon. Rayleigh scattering is a powerful non-intrusive method which provides direct heavy particle density measurements with a very high spatial resolution. The gas pressure ranges from 1 to 40 torr and the microwave power ranges from 35 to 900 W. We show that temperature gradient is very sharp at the edge of the plasma column: T g drops to nearly room temperature within 3 cm. In contrast, T g is nearly constant in the bulk of the plasma region. The gas temperature is determined over a large range of power and pressure conditions. We show that the gas temperature in the centre of the tube, ranging from 300 to 2500 K, is a linear function of the averaged power density per unit of length. Analytical calculations are in good agreement with experimental results.

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