Power exhaust in the snowflake divertor for L- and H-mode TCV tokamak plasmas

Abstract

The snowflake (SF) divertor is a plasma configuration that may enable tokamak operation at high performance and lower peak heat loads on the plasma-facing components than a standard single-null divertor. This paper reports on the results of experiments performed on the TCV tokamak in both the low- and high-confinement regimes, wherein the divertor configuration was continuously varied between a standard single-null and a ‘SF-plus’, which features auxiliary strike points (SPs) in the private flux region of the primary separatrix. The measured edge properties show that, in L-mode, the fraction of the exhaust power reaching the additional SPs is small. During edge-localized modes, up to ∼20% of the exhausted energy is redistributed to the additional SPs even at an x-point separation of 0.6 times the plasma minor radius, thereby reducing the peak heat flux to the inner primary SP by a factor of 2–3. The observed behaviour is qualitatively consistent with a proposed model for enhanced cross-field transport through the SF's relatively large region of low poloidal field by instability-driven convection.

Radiative snowflake divertor studies in DIII-D

“…Previously, similar observations were made in TCV [5] and NSTX [8]. In the DIII-D H-mode discharges, the majority of ELMs were Type I ELMs with DW ELM =W ped $ 0:02 À 0:1, with a few larger ELMs.…”

“…standard divertor) and has a strong impact on edge plasma properties. Experiments performed in the TCV [3][4][5], NSTX [6][7][8] and DIII-D tokamaks [9] are providing data to support the physics basis for the SF divertor concept development for future high-power facilities. Initial experiments in DIII-D and NSTX at high divertor power density demonstrated significantly reduced divertor heat flux with the SF-minus divertor and compatibility with high performance operation (H98y2P1).…”

Modification of SOL profiles and fluctuations with line-average density and divertor flux expansion in TCV

“…A new 32-chords divertor spectroscopy system (DSS) [23] has been installed for extracting information on recombination and electron temperature from Balmer series spectra. This information can be combined with radiation measurements estimated from Bolometry [24] and absolute extreme ultraviolet (AXUV) bolometric camera sightlines [25]. An array of wall-mounted Langmuir probes (LPs) [26] covers the inner and outer wall as well as the floor.…”

Tokamak Power Exhaust with the Snowflake Divertor: Present Results and Outstanding Issues

“…This unique snowflake divertor property was observed experimentally [18,[20][21][22] and is highly beneficial for inter-ELM and ELM peak heat flux mitigation. The associated transport mechanism in the divertor null region is not well understood.…”