Numerical study of potential heat flux mitigation effects in the TCV snowflake divertor

We report on EMC3-Eirene simulations of the plasma and neutral particle transport the TCV boundary layer of a series of snowflake (SF) equilibria characterized by the normalized poloidal flux coordinate rho(x2) of the secondary X-point x(2). We refer to a snowflake plus (SF+) for rho(x2) 1 and a single-null (SN) for vertical bar rho(x2)-1 vertical bar >> 0. Four effects are identified that have the potential to mitigate the heat flux density at the outer strike point in a LFS SF- where x(2) is located on the low field side of the primary X-point x(1): (1) a scrape-off layer heat flux splitting, (2) an impurity radiation cloud forming at x(2) (3) the increased connection length to the outer target and (4) increased transport between x(1) and x(2). The LFS SF- is thus expected to tolerate a larger power flux P-sep over the separatrix than a comparable SN configuration.

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