Study of Plasma Meniscus and Beam Halo in Negative Ion Sources Using 3D3VPIC model Shu Nishioka Faculty of Science and Technology, Keio Univ. 1st year Master’s degree Today, I’d like talk to about my study, that is ‘Study of Plasma Meniscus and Beam halo in Negative Ion sources Using 3D 3V PIC model’ My name is Shu Nishioka, an I am 1st year Master’s degree student.

Simulation model B Geometry of simulation Model ・real size of simulation domain: ・Scale factor: In this study, I have developed 3D3V PIC model, it was based on Miyamoto sensei’s 2D3V PIC model. Miyamoto san already talked about backgroud, 2D result, So I’d like to talk about my detai of 3D3VPIC mode and Result. In this figure shows geometry of Simulation Model. Real size of domain, Scale factor, Number of meshes, mesh size, total Number of the SuperParticle is Likely here. I talk to about Magnetic filed in this sim Models,. we consider only PG magnetic filter field. Because I want to comparison between 2D3V PIC model that has already developed and 3DPICModel. PG magnetic filter is taken into account and it is Parallel to the y-axis. It was based on JT-60U NIS. ・Number of meshes: ・mesh size: ・Initial number of superparticles electron: Ne = 9×106　H+: NH+ = 1×107　 H-: NH- = 1×106 *PG magnetic filter is taken into account and it is parallel to the y-axis. It was based on JT-60U negative ion source.

Simulation model PIC calculation cycle Integration of the motions of the charged particles Solve the Poisson equation First-order particle weighting Then, here is the governing equation which is used in this model. Poisson eq, motion eq, and First order particle weithing. charged particle

Simulation model Boundary Condition Next, Boudary condition for Particles and any filed value is likely here. (黄色読む) ・ The periodic boundary conditions are used in the y and z directions. ・ The surface produced H- taken to be a parameter and launched at the PG surface by a given number of particles per time step.

Simulation model Computatinal resouce Current density density Magnetic flux density Electrostatic potential Velocity First 2D space coordinate Time Normalization Symbol Physical quantities 4.19×105 m/s Electron thermal velocity 5.64×1010 rad/s Electron plasma frequency 7.43×10-6 m Electron Debye length 1018m-3 Electron density 0.25 eV Hydrogen ion temperature 1 eV Electron temperature Value Symbol Physical parameters Then, physical quantities is normalized for to simple a calculation. Physical Parameter is here, and here is Computatinal resouce. Computatinal resouce CPU : Intel - Core i7-3820 @3.60GHz (4core 2thread): 8 MPI process. GPU : GTX titan : GPU is used only to solve Poisson eq. RAM : 16GB 13s per PIC cycle.

Result Ok, next, I’d like to toke about Result in this study.

Comparison between 2D3VPIC and 3D3VPIC ~ Electron density H- density Emittance diagram (at x=17mm) Magnetic filter field Plasma meniscus θ Fig.1 2D density profile of the 2D3V PIC model Emittance diagram (at x=17mm, z=0mm) Electron density H- density Magnetic filter field Plasma meniscus Fig. 2 2D density profile of the 3D3V PIC model ・Plasma Meniscus in the 2D model penetrates more deeply into the plasma source region and curvature is larger. ・The beam halo fraction to the total beam current is estimated to be 51.5% in the 2D model while around 6.3% in the 3D model.

Why is Penetration of the Meniscus small in the 3D model Potential Profile during vacuum condition 2D model Schematic view of 2Dmodel geometry 3D model 3Dmodel geometry ・The figure shows potential profile each 2D, 3D model during vacuum condition. In this 2D model, because extraction hole is modeled as a slit, the equipotential surface penetrate more deeply into the plasma source region. Therefore plasma meniscus penetrates deeply than 3D model.

Result ~perpendicular and parallel to PG filter field plane~ Emittance diagram (at x=17mm, z=0mm) Electron density H- density Magnetic filter field Plasma meniscus Fig. 2 2D density profile of the 3D3V PIC model (Z=0) Electron density H- density Emittance diagram (at x=17mm, z=0mm) Plasma meniscus Magnetic filter field Fig. 2 2D density profile of the 3D3V PIC model(Y=0) ・Asymmetry of the electron density profile due to the E×B drift is observed. ・Asymmetry of the plasma meniscus is observed. It induce asymmetry of negative ion current density profile.

Conclusion The H- beam halo ratio to extraction beam current is dependent on the penetration of plasma meniscus. 2. The ratio of beam halo is about 6% in the 3D3V-PIC model. This value reasonably agree with the experimental result1,2. 3. Asymmetricity of the electrons and negative ions due to the E×B drift is observed with 3D3V-PIC model. 1. K. Miyamoto, Y. Fujiwara, T. Inoue, N. Miyamoto, A. Nagase, Y. Ohara, Y. Okumura, and K. Watanabe, AIP conference proceedings, 380, 360 (1996) 2. H.P.L. de Esch, L. Svensson, Fusion Engineering and Design 86, 363 (2011).

Benchmark problem Geometry Physical parameter 19mm×17mm×17mm Include One PG aperture PG: hole Radius =14mm, thickness=2mm Peak value of the PG filter filed: 50Gauss Physical parameter Electron thermal velocity Electron plasma frequency Electron Debye length Electron density Hydrogen ion temperature Electron temperature Value Symbol Physical parameters

Effect of E×B drift Direction and magnitude of the E×B drift Electron density and direction of E×B Magnetic filter field ・The electron transport depends on along the direction of E×B drift close to PG.

Temporal Evolution of Extracted current (Am-2) Negative Ion Electron 1750 1500 1250 1000 750 500 250 J t ~ SP start

Definition of Plasma Meniscus The contour surface with defines Plasma Meniscus. This is almost same as the contour along which grad φ=0. The H+ ions cannot go forward beyond this contour and they return back towards the left hand side into the source region. On the other hand, H- ions is accelerated when beyond this contour, then they are extracted.