Monte Carlo method has been used to calculate neutral atom density distributions in Tokamaks. Numerical results for HT-6B, HT-6M are in good agreements with the experimental data.

When the ion cyclotron resonance heating is adopted in Tokamak, in order to protect the antenna in a better way, the antenna is usually placed in the cavity.The boundary condition in cavity is more complex, so the coupling calculation is comparatively more difficult. The two dimension strip shape antenna in cavity is calculated. The variation of coupling impedance of such antenna with its sizes has been investigated.