Initial results of LOC to SOC transition experiment in HL-2A tokamak*

Dedicated experiment of LOC (linear Ohmic confinement) to SOC (saturated Ohmic confinement) transition was carried out in the HL-2A tokamak during the last campaign. The line-averaged density was ramped up from 0.6x10$^{19}$/m$^{3}$ to 1.5x10$^{19}$/m$^{3}$ under limiter configuration. The energy confinement time was observed to linearly increase with density and then saturate around line-averaged density $\sim$ 1.0x10$^{19}$/m3 (density in the core is around 2.0x10$^{19}$/m$^{3}$). The Shimomura density threshold was estimated as 1.9x10$^{19}$/m$^{3}$. A Langmiur probe array was plunged into the plasma during the whole density ramp up period, which measured the particle and momentum fluxes during the transition. Data from DBS and ECE will also be presented. The transition under divertor configuration was not found during density ramp up all the way to the density limit.