Ion energy containment of ICRF-heated plasmas in the GAMMA10 central cell

This thesis describes investigations of the ion temperature,neutral particle density,and ion energy confinement in ICRF-heated plasmas in the central cell of the GAMMA10 tandem mirror on the basis of measurements of charge exchange neutral particles emitted from the plasma. A charge exchange neutral particle analyzer(CX-NPA) has been used for measuring the ion temperature in the central cell.Calibration experiments for the CX-NPA were carried out to confirm the characteristics of the analyzer,usiug a hydrogen ion source. In low density plasmas such as the GAMMA10 plasmas,it has been proved that the density profile of neutral hydrogen atoms estimated from the Hα emission is not consistent with that calculated by a neutral particle transport code (DEGAS).For solving this problem on the DEGAS code,the original DEGAS code was modified so as to take into account the dissociative-excitation processes of neutral hydrogen molecules.Furthermore,the conventional method for the estimation of the density of neutral hydrogen atoms from the Hα　emission is modified so as to take into consideration the direct Hα emission through the above processes.The density profile of neutral hydrogen atoms estimated from the Hα line intensity using this method agreed well with the calculated result by the modified DEGAS code.It was proved that the radial profile of neutral particles can be determined by the modified DEGAS code in low density plasmas. For the interpretation of the experimental results of the energy spectrum and the count-rate profile of the charge exchange neutral particles measured with the CX-NPA,the following three effects were newly included in the conventional method for obtaining the ion temperature radial profile;(1) the anisotropy of pitch angle distribution of ions,(2) charge exchange reaction with neutral hydrogen molecules,(3) ion finite Larmor radius.The experimental results were explained well using this improved method.This method may be applicable to the analysis of temperature of alpha particles with large Lamor radius in a fusion plasma. In the typical hot-ion mode plasmas,the radial profile of ion temperature was obtained by applying the above improved method.Using the radial profile of ion temperature and the other plasma parameters,the ion energy loss caused by the classical processes(electron drag,and charge exchange reactions) was calculated with taking into account of the effects of the ion finite Larmor radius and the anisotropy of the ion pith angle distribution.This calculation was applied to the ion energy loss in the non-steady state plasma.A simulation code was developed for investigating the time evolution of the ion energy balance including the above classical processes.This simulation results were compared with the results in the experiments where the ICRF power was decreased stepwise with various ICRF powers.On applying the ECRH for the heating of electrons,the significant increase of the diamagentism was observed in these experiments.The cause of the increase of the diamagnetism is discussed in this thesis by using the simulation code. The ICRF power dependence of the time evolution of the diamagnetism during the ICRF power decrease was examined.In the cases where the ICRF power were 90kW and 133kW,the time behaviors of the diamagnetism agreed well with the simulation results.This indicates that the ion energy loss is mainly explained by the classical processes.In the case where the ICRF power was 160kW,the diamagnetism saturated at about 7.0x10-5 Wb after the rapid increase of the diamagnetism during the ECRH.This indicates that the ion energy loss mechanism due to some non-classical processes,like an instability,may be taking place,and they should be taken into consideration in the analysis.For explaning the above discrepancy,the ion energy loss mechanism due to the ion thermal conduction was included in the simulation code.It is found that the time evolution of the diamagnetism can be explanied by the following two mechanisms:(1)a temporal change of the ICRF heating power;(2)the ion energy loss induced by the thermal conduction which increases with the diamagnetism.Further investigations,however,are required in order to clarify the responsible mechanism of the diamagnetism saturation. From the analysis of the ion temperature,it was shown that plasmas with the high ion temperature(-10keV) at the plasma center were achieved in high magnetic field strength experiments.The reason for the achievement of the high ion temperature is discussed from the viewpoint of the ion energy loss by the classical processes.The saturation of the diamagnetism was also observed in various magnetic field strength experiments when the ICRF power was increased.The ICRF power was increased stepwise when the diamagnetism saturated.From the analysis of ion temperature radial profile,no significant increase of the ion temperature in the plasma center,and the appreciable broadening of the ion temperature profile were observed during the higher ICRF power phase.While,no broadening of the ion temperature profile was observed under the low diamagnetism condition.The following two mechanisms can be considered as the cause of the broadening during the ICRF power increase at the diamagnetism saturation:(1) the change of the radial profile of the ICRF heating power,(2)the occurrence of the ion thermal conduction and convection. The diamagnetism degradation was observed in both the additional gas puffing experiments and the stepwise application of higher ICRF power experiment.The ion temperature analysis clarified that the appreciable decrease of the ion temperature near the plasma center occurred with the degradation of the diamagnetism.The degradation with the additional gas puffing will be discussed from the standpoint of the ion energy loss due to the charge exchange reactions,using the modified DEGAS code with including the axial variation of the neutral particle density.From the results of the systematic investigation on the diamagnetism degradation,the relationship between the maximum diamagnetism(ion temperature)and the plasma density profile in the central cell is also discussed.Thesis (Ph.D. in Physics)--University of Tsukuba, (A), no. 1358, 1995.3.2

Calculation of the Tangential View of an H-Alpha Intensity Profile in the Large Helical Device

A tangential image of an H-alpha intensity profile in a large helical device (LHD) plasma is investigated by a neutral particle transport simulation using a detailed 3-D grid model including the geometry of the helical plasma and the vacuum vessel. The calculated image of the H-alpha intensity profile calculated by the simulation quite agrees with the observed image, which strongly suggests that there is no significant abnormal neutral particle sources in typical plasma discharge operation in LHD

A Study on the Placement of Variables in a Modified Constellation Graph

In this study, we proposed a method of variable placement in a modified constellation graph. In the graph, p variables are arranged at equal intervals on the circumference of a semicircle,and the vectors of length xij ( i=1, 2, …, n; j=1, 2, …, p) are concatenated. This modified constellation graph has the advantage of providing an easier understanding of the object characteristics than is possible using the constellation graph. However, results of the modified constellation graph are affected by the placement of the variables; therefore, it is necessary to determine their optimum placement. In this study, we proposed to place the variables such that the covariance or horizontal distance of the objects is as large as possible. In addition, the proposed method was applied to an achievement survey.departmental bulletin pape

Visible Images Induced by the Three-Dimensionally Complicated Structure of the Plasma Periphery in the Large Helical Device

The magnetic components produced by nonaxisymmetric superconducting coils in the Large Helical Device produce a complicated magnetic structure in the plasma periphery, which strongly depend on the configuration of electric currents in the magnetic coils. A tangentially viewing charge-coupled device camera has observed line emission of doubly ionized carbon CIII. The dependence of the 3-D distribution of the CIII emission on magnetic configurations will be discussed

Surface Nanofabrication in Photosensitive Polymers at the diffraction limit of light and down to 47 nm by Metal Tip-Enhanced Near Field light : Light Induced Nanomovement of Polymers

This paper discusses surface nanofabrication in azo-polymers. Nanoscale polymer movement is induced by a tightly focused laser beam in an azo-polymer film just at the diffraction limit of light. The deformation pattern which is produced by photoisomerization of the azo dye is strongly dependent on the incident laser polarization and the longitudinal focus position of the laser beam along the optical axis. The anisotropic nanofluidity of the polymer film and the optical gradient force played important roles in the light induced polymer movement. We also explored the limits of the size of the photo-induced deformation, and we found that the deformation depends on the laser intensity and the exposure time. The smallest deformation size achieved was 200 nm in full width of half maximum; a value which is nearly equal to the size of the diffraction limited laser spot. Beyond the limit of light diffraction, a nano protrusion was optically induced on the surface of the films by metal tip enhanced near-filed illumination. A silver coated tip was located inside the diffraction limited spot of a focused laser beam (460 nm), and an enhanced near-field, with 30 nm light spot, was generated in the vicinity of the tip due to localized surface plasmons. The incident light intensity was carefully regulated to induce surface nanodeformation by such a near-field spot. A nano protrusion with 47 nm full width of half maximum and 7 nm height was induced with a resolution beyond the diffraction limit of the light. The protrusion occurs because the film is attracted towards the tip end during irradiation. At the top of the protrusion, an anisotropic nanomovement of the polymer occurs in a direction nearly parallel to the polarization of the incident light, and suggests the existence at the tip end of not only a longitudinal, i.e., along the tip long axis, but also a lateral component of the electric field of light. The azo-polymer film helps map the electric field in the close vicinity of the tip.This paper discusses surface nanofabrication in azo-polymers. Nanoscale polymer movement is induced by a tightly focused laser beam in an azo-polymer film just at the diffraction limit of light. The deformation pattern which is produced by photoisomerization of the azo dye is strongly dependent on the incident laser polarization and the longitudinal focus position of the laser beam along the optical axis. The anisotropic nanofluidity of the polymer film and the optical gradient force played important roles in the light induced polymer movement. We also explored the limits of the size of the photo-induced deformation, and we found that the deformation depends on the laser intensity and the exposure time. The smallest deformation size achieved was 200 nm in full width of half maximum; a value which is nearly equal to the size of the diffraction limited laser spot. Beyond the limit of light diffraction, a nano protrusion was optically induced on the surface of the films by metal tip enhanced near-filed illumination. A silver coated tip was located inside the diffraction limited spot of a focused laser beam (460 nm), and an enhanced near-field, with 30 nm light spot, was generated in the vicinity of the tip due to localized surface plasmons. The incident light intensity was carefully regulated to induce surface nanodeformation by such a near-field spot. A nano protrusion with 47 nm full width of half maximum and 7 nm height was induced with a resolution beyond the diffraction limit of the light. The protrusion occurs because the film is attracted towards the tip end during irradiation. At the top of the protrusion, an anisotropic nanomovement of the polymer occurs in a direction nearly parallel to the polarization of the incident light, and suggests the existence at the tip end of not only a longitudinal, i.e., along the tip long axis, but also a lateral component of the electric field of light. The azo-polymer film helps map the electric field in the close vicinity of the tip

High Energy Particle Measurements during Long Discharge in LHD

The spatial resolved energy spectra can be observed during a long discharge of NBI plasma bycontinuously scanning the neutral particle analyzer. In these discharges, the plasmas are initiated by the ECH heating, after that NBI#2 (Co-injection) sustains the plasma during 40-60 seconds. The scanned pitch angle is from 44 degrees to 74 degrees. The injected neutral beam (hydrogen) energy of NBI#2 is only 130 keV because the original ion source polarity is negative. The shape of spectra is almost similar from 44 degrees to 53 degrees. However the spectra from 55 degrees are strongly varied. It reflects the injection pitch angle of the beam according to the simulation (53 degrees ot R* = 3.75 m in simulation). The beam keeps the pitch angle at incidence until the beam energy becomes to the energy, which the pitch angle scattering is occurred by the energy loss due to the electron collision. The low flux region can be observed around 10-15 keV, which is 15 times of the electron temperature. The energy region may be equal to the energy at which the pitch angle scattering is occurred. At the energy, the particle is scattered by the collision with the plasma ions and some of particles may run away from the plasma because they have a possibility to enter the loss cone. According to the simulation, the loss cone can be expected at the 10 keV with the small angular dependence. The depth of the loss cone is deep at the small pitch angle. The hollow in the spectrum may be concluded to be the loss cone as the tendency is almost agreed with the experimental result

Simulation Analysis of Transport of Boron Dust Particles Injected by Impurity Powder Dropper in the Large Helical Device

ORCID　0000-0003-0655-7347Boron dust particles were injected by an impurity powder dropper to improve plasma confinement and perform wall conditioning in the Large Helical Device. A fast-framing camera for monitoring dust particle trajectories in the peripheral plasma detected a change in the ablation positions of the dust particles depending on the plasma density and heating power. An analysis using a three-dimensional edge plasma simulation code (EMC3-EIRENE) and a dust transport simulation code (DUSTT) was applied to understand these observations. The simulations proved that the dust particle trajectories are more deflected toward the outboard side of the torus by the effect of the plasma flow in an upper divertor leg for higher plasma densities and higher plasma heating powers. The simulation successfully reproduced observations of the change in the ablation positions in the peripheral plasma.journal articl