Cusp Magnetic Field Research Articles

Operating Characteristics of a Wave-Driven Plasma Thruster for Cutting-Edge Low Earth Orbit Constellations

This paper outlines the development phases of a wave-driven Helicon Plasma Thruster for cutting-edge Low Earth Orbit (LEO) constellations. The two-stage ambipolar electric propulsion (EP) system combines the efficient ionization of an ultra-compact helicon reactor with plasma acceleration based on an ambipolar electric field provided by a magnetic nozzle. This paper reveals maturation challenges associated with an emerging EP system in the hundreds-watt class, followed by outlook strategies. A 3 cm diameter helicon reactor was operated using argon gas under a time-modulated RF power envelope ranging from 250 W to 500 W with a fixed magnetic field strength of 400 G. Magnetically enhanced inductively coupled plasma reactor characteristics based on half-wavelength right helical and Nagoya Type III antennas under capacitive (E-mode), inductive (W-mode), and wave coupling (W-mode) were systematically investigated based on Optical Emission Spectroscopy. The operation characteristics of a wave-heated reactor based on helicon configuration were investigated as a function of different operating parameters. This work demonstrates the ability of two-stage HPT using a compact helicon reactor and a cusped magnetic field to outperform today’s LEO spacecraft propulsion.

Magnetic controlled arc welding technology: a review

PurposeThe purpose of this study is to optimize and improve conventional welding using EMF assisted technology. Current industrial production has put forward higher requirements for welding technology, so the optimization and improvement of traditional welding methods become urgent needs.Design/methodology/approachExternal magnetic field assisted welding is an emerging technology in recent years, acting in a non-contact manner on the welding. The action of electromagnetic forces on the arc plasma leads to significant changes in the arc behavior, which affects the droplet transfer and molten pool formation and ultimately improve the weld seam formation and joint quality.FindingsIn this paper, different types of external magnetic fields are analyzed and summarized, which mainly include external transverse magnetic field, external longitudinal magnetic field and external cusp magnetic field. The research progress of welding behavior under the effect of external magnetic field is described, including the effect of external magnetic field on arc morphology, droplet transfer and weld seam formation law.Originality/valueHowever, due to the extremely complex physical processes under the action of the external magnetic field, the mechanism of physical fields such as heat, force and electromagnetism in the welding has not been thoroughly analyzed, in-depth theoretical and numerical studies become urgent.

Discharge characterization of two-region arc plasma (TRAP) ion source

The Korea Atomic Energy Research Institute (KAERI) is developing a novel Two-Region Arc Plasma Ion Source (TRAP) as a negative hydrogen (deuterium) ion source for a Neutral Beam Injection (NBI) system in a fusion tokamak. The TRAP ion source is based on a two-region configuration, comprising a high energy electron region that creates highly vibrationally excited molecules and a low electron temperature region that generates negative ions by attaching electrons to molecules. This configuration can be achieved by optimizing the filament position and magnetic cusp field. In order to optimize the TRAP configuration, the plasma parameters are investigated under various operating conditions, such as filament position, gas pressure, and arc power. Electron density and temperature are determined using Langmuir probe measurements. In this paper, the detailed experimental results are described and discussed.

Investigation on weld forming, microstructure and mechanical characteristics of dissimilar steel GTAW under novel composite magnetic field

During dissimilar steel welding, differences in magnetic permeability and thermophysical parameters between materials result in significant disparity in heat distribution on both sides of weld and poor weld formability. To solve the welding quality problems caused by significant disparity in heat distribution, a novel composite magnetic field consisting of longitudinal magnetic field (LMF) and cusp magnetic field (CMF) is applied to dissimilar steel welding. In this study, the influence of novel magnetic field on the mechanical characteristics, microstructure, and weld formation of dissimilar steel gas tungsten arc welding (GTAW) welds was investigated. It was found that arc deflection is influenced by both the material properties and LMF. When longitudinal exciting current (IL) was 0.5A, the weld melting zone tended to be symmetrical. On the premise that IL remained unchanged at 0.5A, as cusp exciting current (IC) increased from 0A to 5A: the weld fusion zone always remained symmetrical; The arc compression degree, weld penetration, melting area of weld and weld penetration/width ratio significantly increased, while the weld width progressively reduced; The heat-affected zone's (HAZ) width of the base metals and the mean grain size in the HAZ are significantly reduced; The mean microhardness of the weld metal (WM) and tensile properties are also significantly improved. The study results enrich the research foundation on heat input regulation in dissimilar steel GTAW, providing experimental evidence and theoretical support for resolving welding quality issues caused by welding conditions with different material properties.

Optimization of grain-selection behavior in the spiral selector during Cusp-magnetic-field-assisted directional solidification of single-crystal superalloy

Cusp magnetic field (CMF) could overcome the damage of the longitudinal or transverse magnetic fields on the directional growth of dendrites in single crystal (SC) superalloy, which shows the promising prospects in the industrial application. The SC preparation is obtained by the spiral selector in industry. Thus, the work investigates the effect of CMF on the grain selection of SC superalloy with starter-block heights and temperature gradients in the spiral selector for the first time. The results show that the favorable effect of CMF on SC selection in the spiral selector is all related with the starter-block heights at the temperature gradients. At the high starter-block height, the CMF decreases the height of the selected SC in the spiral section and optimizes the selected orientation. The less grains in the entrance make the favorable effect of CMF on SC selection be realized in the spiral section. The CMF effect on SC selection in the spiral selector origins from the change of the flow field structure near the liquid-solid interface. It not only enhances the effect of grain competition and selection in the high starter block but also makes the liquid-solid interface less tilt for favorably competition growth of dendrites in the spiral channel. The investigation provides a new means and a theory instruction for optimizing the SC selection in the spiral selector.

Influence of cusp magnetic field configuration on plasma parameters of radio frequency driven negative ion source for CRAFT NNBI

Radio Frequency (RF) driven negative ion source is the preferred ion source for negative ion based Neutral Beam Injection system (NNBI). The plasma generator, which consists of RF driver(s) and an expansion chamber, is one of the key parts for NNBI. The distribution of cusp magnetic field which is generated by permanent magnets installed at the lateral wall of the expansion chamber is a common issue, due to the great influence on electron density, electron temperature and spatial uniformity of plasma density in the extraction area. Two kinds of configuration of cusp magnetic field (checkerboard type and symmetric type) and three types of arrangement of permanent magnets (with three, four and five rows of magnets) have been carried out with the approach of finite element and the experimental performance. On the RF negative ion source testbed, a moveable Langmuir probe has been adopted to investigate the characteristic of electron density and temperature near the extraction area. Since the symmetric type with three rows of permanent magnets generates the distribution of cusp magnetic field that contribute to extract the plasma from RF driver and improve the probability of particle collision easily, the higher electron density and the lower electron temperature was obtained via simulation. The experimental conclusion is that the symmetric type with three rows of permanent magnets leads to a higher electron density and lower electron temperature, showing a great agreement with simulation results. The results are helpful to optimize the structure and performance of high power ion source, and provide support for the development of large area RF negative ion sources with multi-driver.

Effect of a permanent-magnet-induced cusp field on a magnetic nozzle radio frequency plasma thruster

A cusp magnetic field is formed upstream of a radio frequency antenna by using a permanent magnet (PM) array in a radio frequency plasma source attached to a diffusion chamber, while an expanding magnetic field configuration downstream of the source is maintained by placing a solenoid near the source tube’s exit, resembling a magnetic nozzle plasma thruster. The PM array is composed of 16 neodymium magnets and is designed to be movable axially, providing a movable axial location of the cusp field. The source is operated at a frequency of 13.56 MHz and an rf power of up to 2.6 kW in low-pressure argon. A force exerted on a target plate located downstream of the source is assessed by a pendulum target technique, showing that the force is increased if the cusp field is closer to the radio frequency antenna. The result is consistent with the previously reported result for the cusp field configuration applied by two sets of solenoids, while the present configuration can reduce the consumed electricity for the upstream solenoid.

ISOLATION OF ELECTRONS BY THE MAGNETIC FIELD OF A CUSP FOR HIGH-DENSITY ION BEAM ACCELERATION

2.5D numerical simulation was carried out of the process of ions isolation from electrons of a compensated ion beam by the cusp magnetic field of the before entering the accelerating gap located in the region of zero magnetic field of the cusp, followed by the compensation of the accelerated ion beam with new electrons and transportation of the compensated ion beam to the next section of the linear induction ion accelerator. In contrast to the previously simulated compensated high-current ion beam with an energy of 250 keV (now non-existent), the equivalent plasma flow of a traditional coaxial plasma gun with real parameters: density 1010…1012 cm-3 and velocity 107 cm/s was considered as an injected compensated ion beam.

Three-Dimensional Simulation of Melt Convection and Oxygen Transport in CZ-Si Crystal Growth with Cusp Magnetic Fields

The application of magnetic fields has become a standard control technique in the CZ-Si growth industry. To investigate the impact of cusp-shaped magnetic fields (CMF) on heat and mass transfer in the melt, a series of transient three-dimensional simulations were conducted for the growth of a 100 mm CZ-Si crystal with a cylindrical crucible. The turbulent melt motion was modeled using the large eddy simulation (LES) method. Six configurations of CMF with various zero-Gaussian plane (ZGP) positions were examined and numerically compared. The computed results showed that different ZGP positions resulted in distinct types of melt convection, buoyant plumes, and thermal waves. Additionally, it was observed that the studied CMF configurations effectively reduced oxygen dissolution from the crucible wall along with oxygen impurity incorporation into the crystal. These findings demonstrate the potential for precise control of the heat and mass transfer process in CZ-Si growth through the application of suitable CMF.

Design of follow-up superconducting Cusp magnetic field and system performance analysis of Czochralski single crystal furnace

This paper proposes a magnetic system structure for a single crystal furnace that addresses the issue of unreasonable distribution of magnetic field lines on the free surface caused by DHL (Distance between the lower edge of the heat shield and the liquid surface) fluctuation during early stages of crystal growth. The proposed structure adjusts with the fluctuation of the free surface during the crystal pulling process, enabling the magnetic system to positively impact the thermal system. The thermo-magnetic coupling in a 160-type single crystal furnace before and after magnetic system optimization was simulated using the finite element method. Numerical simulation was employed to compare the temperature gradient, S-L (solid–liquid) boundary temperature distribution, and radial oxygen content in the single crystal furnace before and after magnetic system optimization under the conditions of Cr (crystal rotation) and Gr (graphite crucible rotation). The results reveal that the optimized magnetic system helps adjust the shape of the S-L boundary, decrease the temperature gradient, and lower the oxygen levels at the S-L boundary. However, when the Gr is rotated at high speed, although the S-L interface becomes flatter, the temperature gradient and oxygen concentration at the boundary increase. On the other hand, When Cr is at high speed, the S-L boundary tends to become flatter and the temperature gradient at this boundary decreases, but the oxygen concentration at the S-L boundary increases. Compared to the original single crystal furnace with a fixed magnetic system, the single crystal furnace with a lifting magnetic system experiences a 6.34% reduction in radial temperature gradient and a 3.02% reduction in axial temperature gradient during the actual crystal pulling process parameters. The temperature gradient at the S-L boundary decreases by 36.50%, and the radial average oxygen concentration decreases by 26.58%. Furthermore, the temperature distribution of the crystal and melt becomes more uniform, the oxygen content at the S-L boundary is effectively controlled, and the overall crystal quality improves. These findings can serve as a reference for designing a new magnetic system for a single crystal furnace.

Comparison of vacuum-immersed helicon thrusters terminated by upstream magnetic and physical walls

Thrusts imparted by helicon thrusters terminated by a cusp magnetic field and a physical wall are compared in a laboratory experiment, where the configurations have source lengths of 26 cm and 17.5 cm, respectively. The thruster is typically operated at about 5 kW of radiofrequency power and argon gas is used as a propellant. The influence of the cusp magnetic field inside the source on the thrust is clearly observed for the long source length case, while it does not significantly affect the thrust for the short source length case. The results imply that the thrust enhancement by the cusp magnetic field is due to the geometrical isolation of the plasma from the physical wall, which reduces energy loss to the wall. Furthermore, it is observed that the high-potential plasma for the short source length case is indeed unstable due to microarcings, which occur with an interval time of about sub-second. It is shown that the occurrence of microarcings induces a temporal change in the plasma potential, while no drastic change in the electron temperature is observed.

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).

Influence of cusp magnetic field on the evolution of metallurgical and mechanical properties in GTAW of SS 304

Influence of cusp magnetic field on the evolution of metallurgical and mechanical properties in GTAW of SS 304

Functional optimization for a Beam Driven Plasma Neutralizer in DEMO Neutral Beam Injector

The Beam Driven Plasma Neutralizer (BDPN) has been proposed as a more efficient alternative to the gas neutralizer for negative-ion based Neutral Beam Injection (NNBI). In this paper we model the performance of an entire NNBI beamline with a BDPN. We simultaneously consider all the relevant physics and engineering aspects, the most important being the plasma density and degree of ionization inside the BDPN as a function of its geometry and feed gas flow, the geometrical transmission of the beamline, the dependence of the neutral gas distribution in the beamline on the geometry of the beamline components and gas flows, and the species evolution of the extracted D− beam through this neutral and charged particle distribution. Furthermore, we calculate the heat loads expected on the BDPN parts and on the NBI components located downstream of it and study the effect of the magnetic cusp field across the BDPN entrance on beamline transmission. While our results constitute an optimization only under the applied boundary conditions, we find that the beamline with a BDPN increases the system’s wall plug efficiency by about 13% to 0.34 from the 0.30 estimated for a gas neutralizer.

Effects of Magnetic Fields in Arc Welding, Laser Welding, and Resistance Spot Welding: A Review

The pictures show the effect of magnetic fields in different directions, including welding direction, transverse, longitudinal and cusp magnetic fields, on the shape of welding arc and molten pool. The magnetic field can significantly affect the arc morphology and droplet transfer, as well as the macro morphology and microstructure of the weld bead. Further information can be found in the article, number 2200682 by Yonghua Shi, and co-workers.

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.

Design of a Two-Region Arc Plasma ion source for Cs-free H-

The Korea Atomic Energy Research Institute (KAERI) is developing a new concept of cesium-free negative hydrogen (deuterium) ion source based on a Two-Region Arc Plasma (TRAP) ion source for a neutral beam injection (NBI) system in a fusion tokamak. The plasma generator of the ion source consists of magnetic cusp field bucket as an anode and filaments as a cathode. The main feature of the TRAP ion source is that the generated plasma has two regions (a high-energy electron region and a low-energy electron region) without an external magnetic filter field. This plasma is generated by optimization of the filament electron emission and magnetic cusp field. The plasma generator of the TRAP ion source has been designed to study the effects of two-region plasma generation and the resulting negative ion generation. An extractor (also called the pre-accelerator) was also designed. The extractor consists of four grids (G1, G2, G3, G4) and permanent magnets are employed to suppress co-extracted electron currents. The design of the TRAP ion source is finished and fabrications are currently in progress. This study discusses the main considerations and simulation results for the design of the TRAP ion source.

Thirty percent conversion efficiency from radiofrequency power to thrust energy in a magnetic nozzle plasma thruster

Innovations for terrestrial transportation technologies, e.g., cars, aircraft, and so on, have driven historical industries so far, and a similar breakthrough is now occurring in space owing to the successful development of electric propulsion devices such as gridded ion and Hall effect thrusters, where solar power is converted into the momentum of the propellant via acceleration of the ionized gases, resulting in a high specific impulse. A magnetic nozzle (MN) radiofrequency (rf) plasma thruster consisting of a low-pressure rf plasma source and a MN is an attractive candidate for a high-power electric propulsion device for spacecraft, as it will provide a long lifetime operation at a high-power level due to the absence of an electrode exposed to the plasma and a high thrust density. The high-density plasma produced in the source is transported along the magnetic field lines toward the open-source exit and the plasma is then spontaneously accelerated in the MN. By ejecting the plasma flow from the system, the reaction forces are exerted to the thruster structure including the source and the MN, and the spacecraft is resultantly propelled. The thruster will open the next door for space technologies, while the performance of the MN rf plasma thruster has been lower than those of the mature electric propulsion devices due to the energy loss to the physical walls. Here the thruster efficiency of about 30%, being the highest to date in this type of thruster, is successfully obtained in the MN rf plasma thruster by locating a cusp magnetic field inside the source, which acts as a virtual magnetic wall isolating the plasma from the source wall. The increase in the thrust by the cusp can be explained by considering the reductions of the loss area and the plasma volume in a thrust analysis combining a global source model and a one-dimensional MN model.

The effect of magnet core size on the performance of a cylindrical Hall thruster with the near-anode cusp magnetic field

Effect of magnet core size on the performance of a cylindrical Hall thruster with the near-anode magnetic field has been investigated. Experiments found that extending magnetic core and rising discharge voltage show similar effects on the ionization process. When the magnetic core ends flush with the anode and discharge voltage is fixed at 240 V, the upstream ionization related with the electron E × B drift is hardly established under an approximately axial magnetic field and the ionization region is located at the near-axial magnetic mirror field, the thruster manifests the highest propellant utilization efficiency (as high as 1.43), the lowest current utilization efficiency (0.54) and beam divergence efficiency (0.52). When the magnet core extends towards the thruster exhaust, the enhancement of upstream ionization results in significant enhancements in the current utilization efficiency (by 14.6%) and the beam divergence efficiency (by 27.1%). However, the reduction of magnetic mirror ionization also led to a reduction of propellant utilization efficiency (by 32.1%). Therefore, the anode efficiency varies non-monotonically (climbing up and then declining) and has an optimal solution: shorter magnet core performs higher anode efficiency in low voltage condition and longer magnet core performs higher anode efficiency in high voltage condition.

ACCELERATION OF A HIGH-CURRENT PROTON BEAM IN A LINEAR INDUCTION ACCELERATOR AT ITS COMPENSATION BY ELECTRON BEAMS

The dynamics of a high-current proton beam in the cusp magnetic field and in the uniform magnetic field of the drift region in the presence of an accelerating field in the cusp region and of two types of compensating electron beams (before and after the cusp) has been studied. It is shown that for the taken beam parameters and magnetic field it is impossible to accelerate a proton beam of the density higher than 1012 cm-3 with maintaining its initial transverse size and monoenergeticity.