1. 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.

2. 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.

3. 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

4. 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.

5. 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 (4core 2thread): 8 MPI process.
GPU : GTX titan : GPU is used only to solve Poisson eq.
RAM : 16GB
13s per PIC cycle.

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

7. 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.

8. 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.

9. 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.

10. 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).

12. 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

13. 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.

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

15. 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.