Line Cusp Research Articles

Behavior of ion acoustic solitons in a two-electron temperature plasma of a multi-pole line cusp plasma device (MPD)

This article presents the experimental observations and characterization of ion acoustic solitons (IASs) in a unique multi-pole line cusp plasma device (MPD), in which the magnitude of the pole-cusp magnetic field can be varied. In addition, by varying the magnitude of the pole-cusp magnetic field, the proportion of the two-electron-temperature components in the filament-produced plasmas of the MPD can be varied. The solitons are experimentally characterized by measuring their amplitude-width relation and Mach numbers. The nature of the solitons is further established by making two counter-propagating solitons interact with each other. Later, the effect of the two-temperature electron population on soliton amplitude and width is studied by varying the magnitude of the pole cusp-magnetic field. It has been observed that different proportions of two-electron-temperature significantly influence the propagation of IASs. The amplitude of the solitons has been found to be inversely proportional to the effective electron temperature (Teff).

Characterization of Plasma Discharge in a Multi Dipole Line Cusp Magnetic Field Created by an RF Source Coupled by a Spiral Antenna

A detailed characterization of RF–plasma discharge in the multi-cusp plasma device (MPD) having a multi-dipole line cusp magnetic field (MMF: <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{0})$</tex-math> </inline-formula> has been experimentally demonstrated using the externally employed four turns high power spiral antenna. The experimentally measured input impedance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 0.37 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$+$</tex-math> </inline-formula> j80 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega )$</tex-math> </inline-formula> of the complete antenna system along with the MPD is found to be in good validation with the CST–MWS simulated result ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 0.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$+$</tex-math> </inline-formula> j88 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega )$</tex-math> </inline-formula> . The cusp magnetic field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{0})$</tex-math> </inline-formula> along the MPD chamber is also validated and has a good agreement with the simulated results for the magnet current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 150 A. The antenna is then made to resonate at 13.56 MHz using an external L-type matching network (MN) along with an RF source. It is found that the plasma density shifts to a maximum ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n_e \sim3.2$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{17}$</tex-math> </inline-formula> /m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{3})$</tex-math> </inline-formula> value at the argon-filled pressure of 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-3}$</tex-math> </inline-formula> mbar for large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$B_{0}$</tex-math> </inline-formula> and RF power of 1 kW. Further, the input resistances of the antenna with a vacuum ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_v $</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 0.27 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega )$</tex-math> </inline-formula> and plasma ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{p} $</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 0.55 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega )$</tex-math> </inline-formula> inside the MPD under the matched condition are also measured experimentally using the Rogowski coil. This concluded that the RF power coupling efficiency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\eta )$</tex-math> </inline-formula> with the Argon plasma is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 68%. A plasma with nearly a uniform density of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.7\,\times\, 10$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{17}$</tex-math> </inline-formula> /m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{3}$</tex-math> </inline-formula> is obtained up to a radial distance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 5 cm from the MPD center at the constant RF power of 800 W for the Argon-filled pressure and magnet current of 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-3}$</tex-math> </inline-formula> mbar and 100 A respectively.

Effects of axial magnetic field in a magnetic multipole line cusp ion source

Experiments have been performed to study the effects of axial magnetic field on plasma and ion beam parameters in a magnetic multipole line cusp ion source. Studies performed on ring cusp and Kaufmann type ion sources suggest that the axial component of magnetic field may help in improving the ion extraction current at a low discharge power. The line cusps ion sources have been used since long to produced uniform beams, however, they lack axial component of the magnetic field. These ion sources generally suffer from low efficiency possibly due the absence of axial magnetic field. In this work, an additional magnetic coil is added at various axial positions between the back-plate and the plasma grid of the multipole line cusp ion source. We have investigated the effects of axial magnetic field on the discharge efficiency and source parameters like beam current and uniformity in the multipole line cusp ion source. The beam profiles are obtained using an eleven-channel faraday cup array to estimate the effects of the axial magnetic field on beam uniformity and divergence. Initial studies suggest a reduction of beam divergence with increasing axial magnetic field. A significant rise in the beam current and the discharge current is also observed when the axial magnetic field is increased. Particle trajectory simulation using the CST-Studio suite is utilised in understanding the role of confinement of primary electrons behind the improved performance of the ion source.

Characterization of a Multicusp Ion Source With Two-Grid Extraction System for Studying Extraction and Transport of Ion Beam

A low-energy multipole line cusp ion source with two-grid extraction system has been developed and characterized for studying the role of the charge exchange processes on ion beam extraction, transport, and neutralization. The ion source is operated for extraction of Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ion beam of current 50–240 mA at energies 850–1650 eV. The characterization of the ion beam is carried out at various axial positions along a 200–815-mm beam path with a background pressure of 4– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> Torr. An 11-channel Faraday cup array is used to measure the radial profiles of ion current density and angular beam divergence at these positions. The beam divergences are found to be in the range of 6°–15° for beam perveance of 0.50– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.75\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−9</sup> AV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3/2</sup> . The attenuation of ion beam current along the beam path is observed due to the charge exchange neutralization of the energetic ions in the presence of high background pressure. Since ion current density along the beam path can be reduced by both the charge exchange processes and beam divergence, the accounting of beam particles, i.e., energetic ions and neutrals, at larger distances is difficult by the measurements of ion current density using the Faraday cup alone. The flux of energetic particles (energetic ions and fast neutrals) is therefore obtained by a thrust measurements on a beam target fixed at a distance of 800 mm from the ion source. The neutralization of the ion beam obtained by the emission of electrons from a hot filament neutralizer is also investigated in the presence of the charge exchange processes. Space-charge neutralization is provided initially by the secondary electrons emitted from the vessel walls or by the charge exchange processes even without the neutralizer operating at the desired temperature. However, the current neutralization is achieved only by the electrons emitted from the hot filament neutralizer operating in a space-charge-limited mode.

Characterization of argon plasma in a variable multi-pole line cusp magnetic field configuration

This paper presents a detail characterization of argon plasma confined by a multi-pole line cusp magnetic field (MMF) over a large cylindrical volume (1 m axial length and 40 cm diameter) (Patel et al 2018 Rev. Sci. Instrum. 89 043510) and various magnetic field scaling with magnet current obtained from the magnetic field simulation in the vacuum. From the experimental results, it has been observed that in this field configuration the confinement of the primary electrons increases and leak width (plasma escaping through the cusp) of plasma decreases with increasing the magnetic field. As a result the mean density, particle confinement time and the stability of the plasma increase with increasing magnetic field values. In addition to this, it has been also observed that the radial uniformity of the plasma density across the magnetic field explicitly depends on the magnetic field values of MMF. Moreover, the nature of turbulence in a quiescent argon plasma has been identified.

Effect of a magnetic cusp configuration on the ion species ratio in a NBI ion source

In arc discharge plasma, ion species ratio depends on plasma density and ion confinement time. To increase an atomic ion species ratio in an NBI (neutral beam injector) ion source, various ion sources have been designed with a higher ratio of plasma volume to effective ion loss area for increasing ion confinement time. In such designs, most NBI ion sources have a large arc chamber with strong cusp magnetic field. KSTAR NBI ion source also has a large arc chamber with a strong azimuthal line cusp configuration but its atomic ion (H+) beam fraction is small because its normal operation power levels of the arc discharges are comparatively lower than those of other NBI ion sources. In particular, the H2+ ion beam fraction is relatively large at about 40%. This means that there are many primary electrons in the beam extraction region. Through several Ele-orbit code simulations, it was found that some magnetic cusp configurations are effective in preventing primary electrons from nearing the plasma grid facing a plasma and having a high voltage potential. To reduce the molecular ion fraction in KSTAR NBI ion source and consequently increase its atomic ion fraction, experiments regarding the application of several new magnetic cusp configurations to the arc chamber were performed. Experimental results show that the new magnetic cusp configuration can increase the atomic ion fraction to approximately 80%, despite the low arc operation power at KSTAR NBI ion source.

Experimental observation of drift wave turbulence in an inhomogeneous six-pole cusp magnetic field of MPD

This paper presents a detailed study on the controlled experimental observation of drift wave instabilities in an inhomogeneous six pole cusp magnetic field generated by an in-house developed multi-pole line cusp magnetic field device [Patel et al., Rev. Sci. Instrum. 89, 043510 (2018)]. The device is composed of six axially symmetric cusps and non-cusp (in between two consecutive magnets) regions. The observed instability has been investigated in one of these non-cusp regions by controlling the radial plasma density gradient with changing pole magnetic field which is a unique feature of this device. It has been observed that the frequency of the instability changes explicitly with the density gradient. Moreover, the scale lengths of plasma parameters, frequency spectrum, cross-correlation function, and fluctuation level of plasma densities have been measured in order to identify the instability. The cross field drift velocity due to fluctuation in plasma parameters has been measured from the wave number-frequency S (kz, ω) spectrum and verified with the theoretical values obtained from density scale length formula. Further, from the S (kz, ω) spectrum, it has been found that the drift velocity alternates the sign in the consecutive non-cusp regions.

Design of a Prototype Positive Ion Source with Slit Aperture Type Extraction System

The neutral beam injector group at IPR aims at developing an experimental positive ion source capable of delivering H+ ion beam having energy of 30 – 40 keV and carrying an ion beam current of 5 A. The slit aperture based extraction system is chosen for extracting and accelerating the ions so as to achieve low divergence of the ion beam (< 0.5°). For producing H+ ions a magnetic multi-pole bucket type plasma chamber is selected. We calculated the magnetic field due to cusp magnets and trajectories (orbits) of the primary electrons to investigate the two magnetic configurations i.e. line cusp and checker board. Numerical simulation is also carried out by using OPERA-3D to study the characteristic performance of the slit aperture type extraction-acceleration system. We report here the results of the studies carried out on various aspects of the design of the slit aperture type positive ion source.

Horizontal profile of a moving red line cusp aurora

AbstractAuroral emission at a wavelength of 630.0 nm (red line) has a long radiative time. In this study, we show how this long radiative time controls the horizontal extent of a moving mesoscale aurora, which is typical of the cusp. Using high time resolution (4 s) observations by an all‐sky imager at Longyearbyen, Svalbard, and observations by the European Incoherent Scatter Svalbard Radar (ESR), we examined the auroral emission enhancements obtained in the cusp during an interval of southward interplanetary magnetic field on 27 November 2011. Simultaneous observations from the all‐sky imager and the ESR clearly show the manner in which auroral emission regions passed through the radar's field of view. When the front edge of the moving auroral structure intersected the radar's field of view, the ESR electron temperature was enhanced. A few minutes later, the ESR electron temperature dropped to the background level, indicating that the mesoscale electron precipitation region shifted away from the radar's field of view. At that time, the auroral emission in the radar's field of view decreased but still had adequate intensities. These results provide evidence demonstrating that moving cusp auroral emission occurs behind the electron precipitation region as well as inside that region. We interpreted this feature semiquantitatively by using the equation of continuity of the density of the excited atomic oxygen. Our model indicates that the maximum intensity in the moving auroral structure occurs at a point along the trailing edge of the electron precipitation region and that the velocity of that region is important for determining how the 630.0 nm aurora emissions extend horizontally.

Characterization of electron temperature by simulating a multicusp ion source

Multicusp ion sources are used in cyclotrons and linear accelerators to produce high beam currents. The structure of a multicusp ion source consists of permanent magnets, filaments, and an anode body. The configuration of the array of permanent magnets, discharge voltage of the plasma, extraction bias voltage, and structure of the multicusp ion source body decide the quality of the beam. The electrons are emitted from the filament by thermionic emission. The emission current can be calculated from thermal information pertaining to the filament, and from the applied voltage and current.The electron trajectories were calculated using CST Particle Studio to optimize the plasma. The array configuration of the permanent magnets decides the magnetic field inside the ion source. The extraction bias voltage and the structure of the multicusp ion source body decide the electric field. Optimization of the electromagnetic field was performed with these factors. CST Particle Studio was used to calculate the electron temperature with a varying permanent magnet array. Four types of permanent magnet array were simulated to optimize the electron temperature. It was found that a 2-layer full line cusp field (with inverse field) produced the best electron temperature control behavior.

An arithmetic Hilbert–Samuel theorem for singular hermitian line bundles and cusp forms

AbstractWe prove arithmetic Hilbert–Samuel type theorems for semi-positive singular hermitian line bundles of finite height. This includes the log-singular metrics of Burgos–Kramer–Kühn. The results apply in particular to line bundles of modular forms on some non-compact Shimura varieties. As an example, we treat the case of Hilbert modular surfaces, establishing an arithmetic analogue of the classical result expressing the dimensions of spaces of cusp forms in terms of special values of Dedekind zeta functions.

Marginal Discrepancy as Affected by Selective Placement of Die-Spacer: An In Vitro Study

An increase in the marginal discrepancy is seen after cementation with a luting agent and provision of cement space with a die-spacer is the most preferred method to avoid it. Recommended thickness of die-spacer is 25-40μm. Smaller die-spacer thickness was consistently found at the axio-occlusal line angles as compared to the other surfaces which has been postulated to that the spacer paint tends to flow away from the sharp line angles and cusp tips as a result of increased surface tension. The absence of adequate relief spaces in these areas impedes the flow of cement beyond the occlusal portion of the casting, which would result in incomplete seating because of hydraulic pressure. Fifty stone dies were duplicated from a steel die and were divided into five groups of sample size 10, where the die-spacer was selectively placed. Measurements were taken at four points, 90° apart from each other with the help of optical microscope. Later all the castings were cemented using Glass Inomer cement as a luting agent, under a 10kg static load and measurements were recorded. Statistical analysis showed samples with no spacer had the maximum pre and post cementation gap while the least discrepancy was seen in group with additional layer of die-spacer painted over the axio-occlusal line angle. The results were highly significant which clearly indicated the superiority of this group over others. Within limitations of the study, it can be said that application of additional layer of die-spacer at the axio-occlusal line angle will help in decreasing the post cementation marginal discrepancy in full cast metal crowns.

A three-dimensional particle-in-cell/Monte Carlo computer simulation based on negative hydrogen ion source

Based on the analysis of the plasma physics mechanism in negative hydrogen ion source, the particle-in-cell algorithm is studied and optimized and a high efficient storage method of particles is designed. Using the Monte Carlo collision model, considering the plasma potential and coulomb collisions between charged particles, the full three-dimensional particle-in-cell/ Monte Carlo algorithm (PIC/MCC) is developed. With the magnetic charge model, using the FDTD method, the line cusp magnetic field is calculated. With the negative hydrogen ion source JT-60U and considering the main reactions in the negative hydrogen ion source, the full three-dimensional PIC/MCC simulation algorithm is verified by simulation.

Low beta confinement in a Polywell modelled with conventional point cusp theories

The magnetic field structure in a Polywell device is studied to understand both the physics underlying the electron confinement properties and its estimated performance compared to other cusped devices. Analytical expressions are presented for the magnetic field in addition to expressions for the point and line cusps as a function of device parameters. It is found that at small coil spacings, it is possible for the point cusp losses to dominate over the line cusp losses, leading to longer overall electron confinement. The types of single particle trajectories that can occur are analysed in the context of the magnetic field structure which results in the ability to define two general classes of trajectories, separated by a critical flux surface. Finally, an expression for the single particle confinement time is proposed and subsequently compared with simulation.

Studies on plasma direct energy converters for thermal and fusion-produced ions using slanted cusp magnetic and distributed electric fields

Two types of direct energy converters, cusp direct energy converter (CUSPDEC) and travelling-wave (TW) DEC, used to produce electricity from thermal ions and fusion products in an advanced fuelled fusion, are investigated using small-scale devices. In CUSPDEC, magnetized electrons are deflected along the field lines of the cusp magnetic field to the line cusp region and collected by an electron collector, while weakly magnetized ions can traverse the separatrix and enter into the point cusp region. Thus, ions are separated from electrons, and flow into an ion collector to produce dc power. Efficiencies of energy conversion of separated ions with large thermal spread of energy are measured to be ∼55%. An additional lateral electrode, together with the existing collector, constitutes a two-stage ion collector that provides distributed ion-decelerating fields. From the measured voltage–current characteristics, the efficiency of this collector is estimated to be improved to 65–70%, which is consistent with the calculation. Fusion-produced fast ions enter into TWDEC and are velocity-modulated by RF fields, bunched and then decelerated by RF travelling-wave fields on the decelerator to produce RF power. The TWDEC device has shown that the energies of ions of 3–6 keV can be decreased by 10–15% for a one-wavelength decelerator. This would give a total efficiency of 60–70% for a full-length decelerator. A novel system is being investigated for further improvement, in which the incoming ions are deflected transversely, according to each energy, to form a fan-shaped beam and a distributed electrode array for modulation and deceleration generates travelling-waves appropriate to each ion path depending on the energy.

Plasma Direct Energy Converter for Thermal Ions Using a Slanted Cusp Magnetic Field and Two-Stage Deceleration

A direct energy converter (DEC) designed for thermal ions escaping from a fusion reactor consists of a cusp magnetic field and one-or two-stage decelerating electrodes. In this CUSPDEC, magnetized electrons are deflected along the field lines of the cusp magnetic field to the line cusp region and collected by an electron collector, while weakly magnetized ions can traverse the separatrix and enter into the point cusp region. Thus, ions are separated from electrons, and flow into an ion collector to produce DC power. A normal cusp magnetic field enables us to separate electrons and ions for low energy electrons from a test plasma source, but not for electrons with much higher energies from the tandem mirror GAMMA10. The reason for this is found that the high energy electrons do not follow the field lines due to a high potential applied to the ion collector for ion deceleration. Use of a slanted cusp field has resolved the difficulty resulting in good separation. The efficiency of energy conversion of separated ions with wide spread in energy is ~55 % for a one-stage decelerating electrode. An additional lateral electrode, together with the existing collector, constitutes a two-stage ion collector that provides distributed ion-decelerating fields. The system has revealed improvement in efficiency. From the measured voltage-current characteristics, the efficiency of this two-stage collector is estimated to have a value of 65-70 % at an optimum condition.

Study on an azimuthal line cusp ion source for the KSTAR neutral beam injector

In this study it is found that the cusp magnetic field configuration of an anode bucket influences the primary electron behavior. An electron orbit code (ELEORBIT code) showed that an azimuthal line cusp (cusp lines run azimuthally with respect to the beam extraction direction) provides a longer primary electron confinement time than an axial line cusp configuration. Experimentally higher plasma densities were obtained under the same arc power when the azimuthal cusp chamber was used. The newly designed azimuthal cusp bucket has been investigated in an effort to increase the plasma density in its plasma generator per arc power.

Growth of thin hydrocarbon films and hydrogen production in a cusp plasma device

A plasma device with a cusp magnetic field configuration and operating under steady state condition has been built to investigate surface deposition of hydrocarbon films at low temperature and, simultaneously, the cracking of methane in a plasma environment to hydrogen production. The gas (methane or a methane/argon mixture) has been fed to the plasma source (a cylindrical capacitively coupled rf type). The addition of a static magnetic field has increased the particle confinement time and, consequently, the hydrogen production rate. Here the preliminary results concerning the growth of thin hydrocarbon films and the dissociation of methane in the cusp plasma are presented. In our case, at the line and point cusp, we have a large flux of energetic particles as well as neutral, ions, thermal radicals that participate in the growth process. A fraction of the converted methane has been deposited on the substrates, at the line cusp, as amorphous hydrocarbon (a-C: H) film and amorphous carbon (a-C) film. The surface morphology of the film has been observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) has been used to determine the structure of the film. The results have indicated that the film has a prevalently amorphous structure with a presence of crystalline clusters.

A model of cusp magnetic-field compression by an expanding plasma fireball

The outward expansion of a hot plasma fireball initiated by a laser-driven pellet microexplosion in a spindle-cusp magnetic-field configuration is studied. The cusp magnetic field can protect the first wall of future inertial fusion energy containment vessels from the hot plasma ions and divert the expanded charged particles (waste energy) out of the system along open field lines. Closed-form solutions are derived for the compressed magnetic field in the case of a quasispherical expansion, and the maximum (stopping) radius of the field-free plasma cavity is calculated. For a 100-MJ-charged particle energy release per laser pulse, a rather low magnetic-field strength in the line cusp of 0.1 T can protect the first wall by stopping the fireball at a radius slightly less than the 6 m radius of the (spherical) target chamber wall.

Particle Discrimination Experiment for Direct Energy Conversion

A direct energy conversion system designed for D-3He fusion reactor based on a field reversed configuration employs a venetian-blind type converter for thermal ions to produce DC power and a traveling wave type converter for fusion protons to produce RF power. It is therefore necessary to separate, discriminate, and guide the particle species. For this purpose, a cusp magnetic field is proposed, in which the electrons are deflected and guided along the field line to the line cusp, while the ions pass through the point cusp. A small-scale experimental device was used to study the basic characteristics of discrimination of electrons and ions in the cusp magnetic field. Ions separated from electrons are guided to an ion collector, which is operated as a one-stage direct energy converter. The conversion efficiency was measured for cases with different values of mean and spread of ion energy. These experiments successfully demonstrate direct energy conversion from plasma beams using particle discrimination by a cusp magnetic field.