Particle Transport in a DIII-D RMP H-mode plasma using gas puff modulations

We extract time-dependent particle transport coefficients at the plasma edge in an H-mode discharge with applied resonant magnetic perturbations on DIII-D. Particle transport, while difficult to quantify, is critical in determining the density profile. To separate diffusive and convective contributions, a perturbative technique is used to assess particle transport using time-dependent density changes. Previous analysis on DIII-D ^[1] assumed particle transport to be unaffected by small modulations but work on AUG indicates that this assumption is false and both heat and particle transport are altered by density modulation with a relative amplitude of around 10%.^[2] A discharge without ELMs is studied by applying RMPs to enhance particle transport in the pedestal region to prevent the pedestal from reaching the critical density gradient which triggers an ELM. Under conditions of constant density near the separatrix, the relationship between the density gradient and the fueling source is investigated. By setting the source term to zero, we estimate the minimal increase in diffusivity that is necessary to explain the observed flattening of the density gradient. Better understanding of particle transport enables us to more accurately predict the density profile for high-performance tokamak operation.



References

1. A.M. Rosenthal NF 2024 64 036006
   
   C.U. Schuster NF 2024 63 092001

Supported by US DOE under DE-FC02-04ER54698, DE-SC0019302, DE-AC02-09CH11466, DE- SC0024523 and DE-SC0014264