Experiments and Analysis of Effect of Gas Injection During Coupling of Lower Hybrid Waves in HT-7

Good coupling of lower hybrid waves （LHW）was viewed during the gas （D₂ and CD₄） injection around the antenna, and the reflection coefficient of LHW was mostly decreased to 6%. The effects of LHW coupling and density are not the same when gas is injected in different pipes, because the key factor for the good coupling is the increase of local density in the scrape-off layer (SOL). The comparison between effects of D₂ and CH₄ on wave-plasma coupling shows coupling is a little better with D₂ puffing and D₂ gives higher electron density in the SOL than CH₄. This is becauseD₂ makes a greater contribution to the increase of density.