Investigation of the possibility of exceeding the Greenwald density limit during ECRH in T-10

In T-10 experiments, attempts were made to significantly exceed the Greenwald limit nGr during high-power (P ab=750 kW) electron-cyclotron resonance heating (ECRH) and gas puffing. Formally, the density limit ( nₑ )ₗᵢₘ exceeding the Greenwald limit (( nₑ )ₗᵢₘ / ( nₑ )ₗᵢₘ nGr . - nGr = 1.8) was achieved for q L=8.2. However, as q L decreased, the ratio ( nₑ )ₗᵢₘ / ( nₑ )ₗᵢₘ nGr . - nGr also decreased, approaching unity at q L≈3. It was suggested that the “current radius” (i.e., the radius of the magnetic surface enclosing the bulk of the plasma current I p), rather than the limiter radius, was the parameter governing the value of ( nₑ )ₗᵢₘ . In the ECRH experiments, no substantial degradation of plasma confinement was observed up to nₑ ~ 0.9( nₑ )ₗᵢₘ regardless of the ratio ( nₑ )ₗᵢₘ / ( nₑ )ₗᵢₘ nGr . - nGr . In different scenarios of the density growth up to ( nₑ )ₗᵢₘ , two types of disruptions related to the density limit were observed.