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A low density plasma edge of small size divertor tokamak has been modeling by “B2SOLPS0.5.2 D” fluid transport code. The results of modeling are: 1) Formation of the strong “ITB” has detected more reliable with discovery that, low density plasma is necessary and important condition for it to form. 2) Reduction of plasma density play significantly role in the formation of the strong ITB as global parameter, possibly through change in the steep density gradient which stabilize “ITG” mode. 3) The radial electric field of small size divertor tokamak plasma edge is plasma density dependence and maximum radial electric field shear is found at low plasma density. 4) In the “NBI” discharge the toroidal (parallel) velocity at low plasma density is co-current and upward direction. 5) The structure of plasma pressure and radial electric field in quiescent H-mode are obtained.

The internal transport barrier “ITB” is a region characteristic by higher confinement in plasma core. The transport coefficients are strongly reduced in this region and steep density and temperature gradients are formed near last close flux surface (separatrix). The internal transport barrier “ITB” regime is an advanced operation scenario presently studied on the various tokamaks (e.g. JET [^{. }A great deal of progress has been made in recent years in theoretical modeling [1, 3-6] and experiment control^{ }[7-9] of “ITB”. However, the underlying mechanisms for “ITB” formation and sustainment are not yet fully understood^{ }[

The case of unbalance neutral beam injection for the for parameters of Small Size Divertor Tokamak (R = 0.3 m, a = 0.1 m, I = 50 KA, B_{T} = 1.7 T) was chosen for simulation by B2SOLPS0.5.2D fluid transport with average density (4 £ n_{i} £ 1) ´ 10^{19} m^{–}^{3} and temperature heating T_{i} = 3.443 KeV. The simulations were performed with B2SOLPS0.5.2D fluid transport code. As in similar codes the set of modified Braginski equations was solved [16,17]. The philosophy B2SOLPS0.5.2D fluid transport code (and other codes) is that the values of perpendicular transport coefficients are chosen to fit experimentally observed density, temperature radial profiles, density and temperature near the divertor plates. In the simulation presented below the perpendicular transport coefficients are replaced by the anomalous values: diffusion, electron, ion heat flux and perpendicular viscosity coefficients^{ }[16,17]. The perpendicular (anomalous) viscosity coefficient was taken in the form h = n·m_{i}·D. At the inner boundary flux surface, which was located few cm from the separatrix, the density, the electron and ion heat fluxes and the average toroidal momentum flux were specified [16,17]. The boundary heat fluxes were imposed independently from the toroidal momentum flux thus providing the opportunity to investigate the dependence of radial electric field on these parameters [16,17]. The anomalous values of the diffusion electron and ion heat conductivity coefficients were chosen equal for all sort of particle D = 0.5 m^{2}·s^{–1}, c_{e}_{, i }= 0.7 m^{2}·s^{–1}. The main results of simulation are:

1) The first result of simulated shows that, the typical profile of plasma density at outer mid-plane is shown Figures 1 and 2. From

2) The radial profile of the plasma density characteristic scale length (, h_{y} is one of the metric coefficient) is shown in

A possible explanation for the necessary condition of lower plasma density for steep plasma density and ITB formation is that, by slightly lowering the plasma density and keeping the temperature plasma heating and toroidal torque the same, the radial electric field shear and toroidal velocity will increase, possibly allowing the turbulence to be suppressed. Therefore, we conclude reduction of plasma density play significantly role as global parameter in the formation of strong ITB and steep density gradient which stabilize “ITG” mode.

3) The radial electric field profile for edge plasma of small size divertor tokamak at outer mid-plane is shown in

4) The parallel (toroidal) velocity at the outer mid-plane is shown in

5) The parallel (toroidal) velocity at the outer midplane is shown in ^{ }Pfirsch—Schlueter flux [

6) The radial profile for low plasma density QH (quiescent H) regime plasma pressure as shown in

The main simulation results demonstrated the following:

1) Formation of the strong “ITB” has detected more reliable with discovery that, low density plasma is necessary and important condition for it to form.

2) Reduction of plasma density play significantly role in the formation of the strong ITB as global parameter, possibly through change in the steep plasma density gradient which stabilize “ITG” mode.

3) The impact of change parallel (toroidal) rotation which transport from SOL to plasma core through separatrix on the structure of radial electric field is connected with plasma density reduction.

4) The radial electric field in edge plasma of small size divertor tokamak is plasma density dependence and the maximum radial electric field shear is found at low plasma density near separatrix.

5) The spikes in the radial electric field exist at the equatorial mid-plane in SN (Single Null) small size divertor tokamak. The existence of the spike is very important for L-H transition and turbulent suppression in single null small size divertor tokamak plasma edge.

6) In the “NBI” discharge the toroidal (parallel) velocity at low plasma density is co-current (upward) direction. The absolute value of toroidal rotation is larger for lower edge plasma density. The reason for the deviation of toroidal velocity at low plasma density from the toroidal velocity at high plasma density can be explaining according as follow: the difference in toroidal velocities at different plasma densities refer to unbalance toroidal (parallel) particle flux caused by radial flux from the plasma core goes to SOL and divertor plates. This result is interesting since they might help explain, The shear of toroidal velocity at low plasma density near separatrix is smaller in case of the high plasma density which explains the larger L-H transition than for high plasma density.

7) The parallel (toroidal) rotation in edge plasma of small size divertor tokamak is plasma density dependence.

8) The simulation results shows the nature of the QH-regime of small size divertor tokamak which allows us to obtain high enough radial electric field shear for turbulence suppression and strong ITB formation. The radial electric field well in QH-regime is so deep about ~100 k v/m and so narrow about (1 cm) compared with 20 - 40 k v/m in H-regime.

The simulation of small size divertor tokamak plasma edge in QH-regime by using the B2SOLPS0.5.2D fluid transport code is the subject of the future work.