To clarify the effect of polarization on electron cyclotron heating (ECH) in magnetized plasmas, experiments controlling the polarization of injected EC-waves are carried out in compact helical system (CHS). In the experiments, plasmas are generated and sustained only with 106.4GHz ECH power. Magnetic field at the magnetic axis is 1.9T so that the wave frequency is second harmonic. EC-waves are injected to CHS vacuum vessel aiming the magnetic axis from an outside port perpendicularly to the magnetic surface. In the transmission line for the power, a corrugated polarizer is installed. By rotating the polarizer, the direction of linear polarization of EC-wave can be changed arbitrarily. The polarization control affects both the density start-up delay time Tdelay measured from the start of power injection and the central electron temperature Te0 at the end of ECH pulse. Tdelay is minimized around the polarization direction of 90 degrees where the angle is measured from the toroidal direction. At the start-up phase, initial plasma volume is limited around the magnetic axis so that 90 degree polarization results in the second harmonic X-mode at the magnetic axis. On the other hand, Te0 shows its maximum around the polarization direction of 120 degrees. CHS plasma has the strong magnetic shear, and at the last closed magnetic surface (LCFS) the magnetic field direction has rather large angle of about 30 degrees. Then the optimized polarization direction for central electron heating for plasmas expanded to LCFS is the second harmonic X-mode for the plasma peripheral region. This result agrees with the theoretical prediction by taking the magnetic shear effect into account [1].

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