Study On The Tokamak Local Neutral Beam Fastlon Loss Distribution And Active Control Of The Radial Electric Field By Local Beam Injection

Neutral beam injection(NBI)is an important heating method in tokamak plasma.The fast ions injected by the neutral beam heat the plasma while also causing orbit losses under the influence of the magnetic drift.High-energy fast ions hit the surface of the vessel wall and cause damage to the surface of the vessel wall and its components.Therefore,to study the corresponding relationship between the distribution of the lost beam ions and the beam cross-section injection position,modifying the neutral beam injection cross-section will help to reduce the beam ion orbit loss and impurity generation,which provides a reference for the high-power heating and long-pulse steady-state operation of the Tokamak fusion device.In order to study the orbit loss generated by the NBI,we need to calculate the orbits of fast beam ions.At present,the domestic programs for calculating the beam ion loss produced by NBI are borrowed from foreign programs.These foreign programs can give the total loss fraction and the deposition of the fast ion loss on the wall surface,but can not tell which initial ionization positions are.The location of the lost beam ions on the wall surface cannot tell which part of the beam in the cross section of the NBI produces how many lost ions.Foreign programs can only give results but cannot show the initial position of lost ions.Based on the neutral beam deposition calculation code TGCO and the orbit following code GYCAVA independently developed by the Institute of Plasma Physics,we have integrated and developed a set of neutral beam orbit calculation codes with independent intellectual property rights in China.The new codes can be used in the neutral beam orbit loss analysis,the loss distribution on the beam section and the corresponding loss distribution on the wall are given,and the radial electric field generated by the local neutral beam injection can also be calculated.The simulation results of the local neutral beam orbit loss show that the neutral beam fast ion loss fraction is unevenly distributed on the beam cross section and the wall surface.The maximum orbit loss fraction of the counter-current local beam is 58%,which is located in the upper part of the beam section,and the minimum orbit loss fraction of the counter-current local beam is 30%,which is located in the middle of the beam section,the average loss fraction is 42%.By tracing the orbit of the local beam,we found that the position of the lost ions of the local beam with a larger loss in the upper part of the beam section corresponds to the area with a higher heat load on the wall.By shielding the local beams with large losses in the beam section,the average orbit loss fraction can be reduced from 42%to 33%,and the maximum heat flow of the wall can be reduced from 0.3 MW/m2 to 0.12 MW/m2,the overall orbit loss of the neutral beam and the wall heat load have been significantly reduced.Under high-power neutral beam injection conditions,many devices have obtained the H-mode discharge modes.Experiments found that the improvement of the edge transport barrier(ETB)in the H-mode is related to the edge radial electric field and the electric field shear.In the experiment of forming an internal transport barrier under the condition of neutral beam injection on the DⅢ-D device,the existence of an internal radial electric field was also observed,which may be related to the fast ion motion generated by the neutral beam injection.We studied the particle orbits produced by the neutral beam,under the influence of magnetic drift,its orbit will deviate greatly from the initial deposited magnetic surface due to the higher energy of the beam ion,while the electrons generated by ionization basically stay on the initial deposition magnetic surface.The charge separation caused by the difference in the orbits of fast ions and electrons may form a radial electric field inside the plasma,and this electric field may be maintained by a neutral beam that is continuously injected.Therefore,the possibility and feasibility of actively generating and controlling the internal radial electric field by the local injection of neutral beams is studied,which is useful for the active generation and feasibility of the tokamak plasma in the future.It is of great significance to control the internal radial electric field and form a controllable internal transport barrier.Large-angle tangential injection of the local beam can deposit beam ions in a specific area inside the plasma,and generate electric charge separation to form an electric field.If the local beam is injected tangentially on the low-field side outside the magnetic axis of the tokamak,the innermost magnetic surface cut by the local beam is 0.2 m from the magnetic axis,7 cm wide,40 cm high,and the beam energy is 65 keV.When injected at the mid-plane position,peaking density distribution and electric field can be generated,and the intensity of the generated radial electric field is 44.81 kV/m,the electric field shear rate is 4.5 × 105 kV/m2,and the electric field shear can be controlled by the injection angle of the local beam.By improving the quality parameters of the neutral beam injection and the simultaneous injection of multiple local beams,the intensity of the radial electric field can be further improved.Through optimization,the radial electric field and electric field shear generated by the local beam injection,the width of the shearing area can reach or exceed the electric field level of the boundary Hmode,and this controllable internal radial electric field can meet the needs of improving confinement.injection.