Neutral Beam Ion Source Research Articles

Beam extraction characteristics of a low-energy, high-current pulsed ion source of a versatile experiment spherical torus neutral beam injector

A neutral beam (NB) ion source aimed to inject a 0.5-MW NB has been developed for Versatile Experiment Spherical Torus (VEST) plasma heating. Beam energy is generally limited to less than ∼20 keV to reduce particle orbit loss and beam shine-through. To meet this power demand, high-current ion beam extraction is important to achieve the required performance of the ion source. In this study, a 0.7-MW ion source was designed, fabricated, assembled, and optimized at the NB test stand in Korea Atomic Energy Research Institute (KAERI) considering the beam power losses in the beamline components. The ion source comprises a multicusped-bucket-type plasma generator and a multislot-triode-type ion accelerator with an extraction area of 12 cm × 46 cm. The characteristics of arc discharge and beam extraction were investigated using hydrogen gas to obtain the optimum operating parameters of the arc power, filament voltage, gas pressure, extraction voltage, and suppression voltage. The ion source was then conditioned and performance tests were primarily completed. Results of the experiments show that the ion source can extract sufficient ion beam power that is than 0.75 MW (50 A/15 keV) with 100-kW arc power. The arc efficiency and beam perveance were estimated to be 0.6 A/kW and 20–25 μP, respectively. Moreover, the design goal of delivering a 0.5-MW NB into the VEST plasma will be achievable based on the optimum operating conditions. This ion source has been installed in the VEST NB injection system at Seoul National University and its commissioning is ongoing.

Development of data acquisition and over-current protection systems for a suppressor-grid current with a neutral-beam ion source

Neutral beam injection is one of the effective auxiliary heating methods in magnetic-confinement-fusion experiments. In order to acquire the suppressor-grid current signal and avoid the grid being damaged by overheating, a data acquisition and over-current protection system based on the PXI (PCI eXtensions for Instrumentation) platform has been developed. The system consists of a current sensor, data acquisition module and over-current protection module. In the data acquisition module, the acquired data of one shot will be transferred in isolation and saved in a data-storage server in a txt file. It can also be recalled using NBWave for future analysis. The over-current protection module contains two modes: remote and local. This gives it the function of setting a threshold voltage remotely and locally, and the forbidden time of over-current protection also can be set by a host PC in remote mode. Experimental results demonstrate that the data acquisition and over-current protection system has the advantages of setting forbidden time and isolation transmission.

Manufacturing, assembly and tests of SPIDER Vacuum Vessel to develop and test a prototype of ITER neutral beam ion source

The SPIDER experiment (Source for the Production of Ions of Deuterium Extracted from an RF plasma) aims to qualify and optimize the full size prototype of the negative ion source foreseen for MITICA (full size ITER injector prototype) and the ITER Heating and Current Drive Injectors. Both SPIDER and MITICA experiments are presently under construction at Consorzio RFX in Padova (I), with the financial support from IO (ITER Organization), Fusion for Energy, Italian research institutions and contributions from Japan and India Domestic Agencies. The vacuum vessel hosting the SPIDER in-vessel components (Beam Source and calorimeters) has been manufactured, assembled and tested during the last two years 2013–2014.The cylindrical vessel, about 6m long and 4m in diameter, is composed of two cylindrical modules and two torispherical lids at the ends. All the parts are made by AISI 304L stainless steel.The possibility of opening/closing the vessel for monitoring, maintenance or modifications of internal components is guaranteed by bolted junctions and suitable movable support structures running on rails fixed to the building floor. A large number of ports, about one hundred, are present on the vessel walls for diagnostic and service purposes.The main working steps for construction and specific technological issues encountered and solved for production are presented in the paper. Assembly sequences and tests on site are furthermore described in detail, highlighting all the criteria and requirements for correct positioning and testing of performances.

Beam current in extraction system of neutral beam ion source on HL-2A

In the extraction process of neutral beam ion source, the production of extraction current and deceleration current is analyzed and it is helpful for obtaining reliable extraction power and heat deposition power on the grids surface. Based on the electric connection way of the extraction grids of neutral beam ion source on HL-2A and the basic physical process during ion beam extraction, beam extraction process is analyzed and the principle sources of deceleration current are given. Through analyzing the results in gas pressure scanning experiment, it is found that with gas pressure increasing, deceleration current increases, and the ratio of deceleration current to extraction current increases approximately linearly. A physical model is set up based on the process of extracted ion beam coming through the extraction grids. The dependence of the ratio of deceleration current to the acceleration current on the discharge gas pressure is calculated, and the result is consistent with the experimental result which shows the rationality of the analysis method.

HL-2A装置中性束离子源引出系统束流分析

HL-2A装置中性束离子源引出系统束流分析

The dependence of extracted current on discharge gas pressure in neutral beam ion sources on HL-2A tokamak

The discharge gas pressure is a key factor to influence the extracted current of ion source. In this paper, the dependence of extracted current on discharge gas pressure was investigated in detail at different arc discharge currents. The discharge gas pressure with a very broad range (0.1 Pa-2.7 Pa) was scanned for the first time. It is turned out that, with the increasing of discharge gas pressure, the extracted current increases and the arc voltage decreases at different arc currents; however, when the discharge gas pressure exceeds a certain value, the extracted current decreases. For the same discharge gas pressure, the higher the arc current, the higher the arc voltage and the extracted current are. The arc efficiency was also calculated, and its dependence on gas pressure was almost the same with the dependence of extracted current on gas pressure, but at the same discharge gas pressure, the lower the arc current, the higher the arc efficiency is and the lower the extracted current is.

Numerical simulation for the accelerator of the KSTAR neutral beam ion source

Recent experiments with a prototype long-pulse, high-current ion source being developed for the neutral beam injection system of the Korea Superconducting Tokamak Advanced Research have shown that the accelerator grid assembly needs a further upgrade to achieve the final goal of 120keV/65A for the deuterium ion beam. The accelerator upgrade concept was determined theoretically by simulations using the IGUN code. The simulation study was focused on finding parameter sets that raise the optimum perveance as large as possible and reduce the beam divergence as low as possible. From the simulation results, it was concluded that it is possible to achieve this goal by sliming the plasma grid (G1), shortening the second gap (G2-G3), and adjusting the G2 voltage ratio.

Criticality in the fabrication of ion extraction system for SST-1 neutral beam injector

For the heating of plasma in steady-state superconducting tokamak (SST-1) (Y.C. Saxena, SST-1 Team, Present status of the SST-1 project, Nucl. Fusion 40 (2000) 1069–1082; D. Bora, SST-1 Team, Test results on systems developed for the SST-1 tokamak, Nucl. Fusion 43 (2003) 1748–1758), a neutral beam injector is provided to raise the ion temperature to ∼1 keV. This injector has a capability of injecting hydrogen beam with the power of 0.5 MW at 30 keV. For the upgrade of SST-1, power of 1.7 MW at 55 KeV is required. Further, beam power is to be provided for a pulse length of 1000S. We have designed a neutral beam injector (S.K. Mattoo, A.K. Chakraborty, U.K. Baruah, P.K. Jayakumar, M. Bandyopadhyay, N. Bisai, Ch. Chakrapani, M.R. Jana, R. Onali, V. Prahlad, P.J. Patel, G.B. Patel, B. Prajapati, N.V.M. Rao, S. Rambabu, C. Rotti, S.K. Sharma, S. Shah, V. Sharma, M.J. Singh, Engineering design of the steady-state neutral beam injector for SST-1, Fusion Eng. Des. 56 (2001) 685–691; A.K. Chakraborty, N. Bisai, M.R. Jana, P.K. Jayakumar, U.K. Baruah, P.J. Patel, K. Rajasekar, S.K. Mattoo, Neutral beam injector for steady-state superconducting tokamak, Fusion Technol. (1996) 657–660; P.K. Jayakumar, M.R. Jana, N. Bisai, M. Bajpai, N.P. Singh, U.K. Baruah, A.K. Chakraborty, M. Bandyopadhyay, C. Chrakrapani, D. Patel, G.B. Patel, P. Patel, V. Prahlad, N.V.M. Rao, C. Rotti, V. Sreedhar, S.K. Mattoo, Engineering issues of a 1000S neutral beam ion source, Fusion Technol. 1 (1998) 419–422) satisfying the requirements for both SST-1 and its upgrade. Since intense power is to be transported to SST-1 situated at a distance of several meters from the ion source, the optical quality of the beam becomes a primary concern. This in turn, is determined by the uniformity of the ion source plasma and the extractor geometry. To obtain the desired optical quality of the beam, stringent tolerances are to be met during the fabrication of ion extractor system. SST-1 neutral beam injector is based on positive ion source. The extraction system consists of three grids, each having extraction area of (width) 230 mm × (height) 480 mm and 774-shaped apertures of 8-mm diameter. To obtain horizontal focal length of 5.4 m and vertical of 7 m, each grid consists of two halves with 387 apertures. Two halves are inclined at an angle of 1.07 ± 0.01°. For long pulse operation, active water cooling is provided by in-laid down of dense network of 22 wavy semicircular ( r = 1.1 ± 0.05 mm) cooling channels in the space available between the apertures. The required flatness of the copper plate is 100 μm and positioning tolerance of aperture is ±60 μm. The measurement obtained after fabrication is compared with the specifications. It is pointed out that fabrication within set tolerance limit could be achieved only through process of fabrication and high-resolution measurements.

A Network Based Telemetry Upgrade for the DIII-D Neutral Beam Power Diagnostics

Water flow calorimetry is utilized at DIII-D to quantify injected neutral beam power. As part of the system upgrades for the past year, the old CAMAC-based telemetry system for the WFC diagnostic was replaced by a fiber optic Ethernet-based telemetry system. The difficulty to obtain replacement CAMAC hardware and the prospect of lower noise and spurious signal sensitivity motivated the move to fiber optic Ethernet-based telemetry. The new system was installed and tested during the 2006 physics campaign startup phase. Both the CAMAC-based system and the new Ethernet-based system were used to acquire data from one common neutral beam ion source in the current year. System performance improvements are presented.

Control system for 5MW neutral beam ion source for SST1

This article describes the control system for a 5MW ion source of the NBI (neutral beam injector) for steady-state superconducting tokamak-1 (SST-1). The system uses both hardware and software solutions. It comprises a DAS (data acquisition system) and a control system. The DAS is used to read the voltage and current signals from eight filament heater power supplies and 24 discharge power supplies. The control system is used to adjust the filament heater current in order to achieve an effective control on the discharge current in the plasma box. The system consists of a VME (Verse Module Eurocard) system and C application program running on a VxWorks™ real-time operating system. A PID (proportional, integral, and differential) algorithm is used to control the filament heater current. Experiments using this system have shown that the discharge current can be controlled within 1% accuracy for a PID loop time of 20ms. Response of the control system to the pressure variation of the gas in the chamber has also been studied and compared with the results obtained from those of an uncontrolled system. The present approach increases the flexibility of the control system. It not only eases the control of the plasma but also allows an easy changeover to various operation scenarios.

Hydrogen and deuterium ion species mix and injected neutral beam power fractions of the TEXTOR–PINIs for 20–60 kV determined by Doppler shift spectroscopy

The ion species fractions of the multimegawatt neutral beam ion sources for Torus Experiment for Technological Oriented Research (TEXTOR) were determined by Hα/Dα-light Doppler shift spectroscopy. The ion sources are modified Joint European Torus (JET) plug in neutral injectors (PINIs) with a three-grid acceleration system and a magnetic field in the plasma box produced by permanent magnets in checkerboard arrangement. The ion species mix of the extracted beam was measured for energies of 20–60 keV and beam currents of 13–100 A of hydrogen and deuterium produced by the two ion sources (PINI) mounted on the neutral beam injectors of TEXTOR. The maximum H+/D+ fraction at full power operation is 66%–69%. No significant difference between the two ion sources was found. The results of the hydrogen ion species mix are in good agreement with prior optical and momentum analysis made on the NI-Testbed. The additionally measured dependence of the extracted species mix from the source gas pressure is small in the pressure range above 3 μbar where the ion sources are usually operated. Measurements over the beam pulse length from 0.1 to 3 s show no change in the species mix. For calculating the deuterium ion species mix at low energies, several cross sections for Hα-light excitation, charge exchange, and dissociation available from the literature were extrapolated to about 3 keV per nucleon. The correction factors used for calculating the ion species fraction from the ratio of the relevant integrated Doppler shift light peaks are given as a function of the gas target density in the neutralizer and of the energy per nucleon. The optical spectrometers specially designed and constructed for neutral beam Hα-light Doppler shift spectroscopy give a sufficient resolution of 1 Å and enough light intensity also at smaller beam energies and currents. The subsequent injected neutral beam power fractions H0(E), H0(E/2), and H0(E/3) and the molecular fractions H02(E) and H02(2/3E) are given as a function of acceleration voltage considering the beam line transmission and 90% of equilibrium gas target density. The injected full energy neutral beam component at 55 keV is for hydrogen 48% or 0.7 MW and 66% or 1.1 MW for deuterium.

Fast neutral beam ion source coupled to a Fourier transform ion cyclotron resonance mass spectrometer

The coupling of an autoneutralizing SF−6 fast ion-beam gun to a Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometer is described. The fast neutral beam provides for secondary-ion-type FT/ICR mass analysis [e.g., production of abundant pseudomolecular (M+H)+ ions] of involatile samples without the need for external ion injection, since ions are formed at the entrance to the ICR ion trap. The design, construction, and testing of the hybrid instrument are described. The feasibility of the experiment (for both broadband and high-resolution FT/ICR positive-ion mass spectra) is demonstrated with tetra-butylammonium bromide and a Tylenol■ sample. The ability to analyze high molecular weight polymers with high mass resolution is demonstrated for Teflon■. All of the advantages of the fast neutral beam ion source previously demonstrated with quadrupole mass analysis are preserved, and the additional advantages of FT/ICR mass analysis (e.g., high mass resolving power, ion trapping) are retained.

Arc modulator for the TFTR neutral-beam ion source

A discussion is presented of the protection of the tokamak fusion reactor neutral-beam ion source, located at the Princeton Plasma Physics Laboratory. The system design is based on three operational protection requirements that include provisions for ion-source current pulse matching, ion-source fault current extinction, and metallic fault current extinction. A power circuit configuration satisfying these requirements is illustrated and briefly described. Simplified analytical expressions relating the protection requirements to the circuit parameters are developed. Experimental findings are in good agreement with a computer simulation of the circuit model, although several side effects introduced by the circuit configuration have been observed. The side effects observed include ion-source current overshoot and the existence of a negative ion source current. Modifications to counteract these side effects are briefly described. >

Modified perveance law for neutral-beam ion sources

The perveance law for ion sources is modified based on experimental data gained during the conditioning phase of three multiaperture ion sources for neutral-beam injection into TEXTOR. The ion sources are modified JET PINIs with a three-grid accel-decel extraction system designed for 55 kV, 88 A, 4.8 MW, operated in hydrogen. Results show that best agreement of the perveance law with the experimental data is achieved when the measured ion species mixture is used and, additionally, when the total width of the first acceleration gap, usually determined by the geometrical distance d1 between grid 1 and grid 2 and thickness D1 of grid 1, is enlarged by a third distance term r2, taking the effect of distortion of the electrical field lines at the decel grid into account. At perveance matched conditions, i.e., minimum beam divergence, the optimum value is found to be r′2 =0.8r2, where r2 is the aperture radius of the decel grid. The species fractions were measured by optical and magnetic spectrometry.

Development of large high-voltage pressure insulators for the princeton TFTR flexible transmission lines

Specially formulated insulator materials with improved strength and high-voltage properties were developed and used for critical components of the flexible transmission lines to the TFTR neutral beam ion sources. These critical components are plates which support central conductors as they exit the high-voltage power supply and enter the ion source enclosure. Each plate acts both as a high-voltage insulator and as a pressure barrier to the SF 6 insulating gas. The original plate was made of commercial glass-epoxy laminate which limited the plate voltage capacity. The newly developed insulator is made of specially-formulated cycloalphatic di-epoxide whose isotropic properties exhibit increased are resistance. It is cast in one piece with skirts which greatly increase the breakdown voltage. This paper discusses the design, fabrication and testing of the new insulator.

A linear ion optics analysis applied to slit beams from doublet III ion sources

A linear analysis of slit beam optics is developed to yield relationship between the optimum perveance and other parameters including the voltage distribution in an accelerator column and the gap dimension. The result is applied to Doublet III neutral beam ion sources and is shown to be in fair agreement with the experimental result.

Gas flow measurements of a novel geometry for neutral beam neutralizers

The conductance and line density of a novel geometry (pumped geometry) for neutral beam neutralizers were measured and compared with a conventional (passive) neutralizer geometry in the transition flow regime. A passive neutralizer geometry is merely a duct attached to the ion source. For the pumped geometry, the top and bottom surfaces of the duct are replaced by a venetian blind geometry which opens into ballast vacuum pumping volumes. A one-half scale model with pumped neutralizer geometry was built and compared with a passive neutralizer geometry of comparable dimensions. A gas source was maintained at fixed pressure and the conductance and line density of the two geometries were measured. These measurements were repeated for several values of gas source pressure, covering the range of pressures typically used in neutral beam ion sources. With the vanes on the pumped neutralizer geometry opened to 55 deg and the gas source pressure ‘‘low,’’ i.e., in the range of pressures typical for ‘‘bucket-type’’ magnetic field ion sources, the amount of gas flowing from the exit of the pumped geometry was about 3 times less than the amount flowing from the passive geometry. As the source gas pressure was increased, the ratio of gas flow from the exit of the passive geometry to that of the pumped geometry increased also. At gas source pressures typical of magnetic field free ion sources, up to 5 times less gas flowed from the pumped geometry. On the other hand, the neutral gas line density of the pumped geometry was only 1.6 times less than that of the passive geometry, independent of the source gas pressure.

Experimental performance of a microwave cavity plasma disk ion source

The detailed description and performance characteristics of a microwave ion source are presented. This ion source utilizes an internally tuned, single-mode (or selective multimode) cylindrical cavity applicator to focus and match microwave energy into a disk-shaped discharge zone. The combination of mode focus control and variable, internal cavity matching allows the efficient operation and beam extraction over a wide range of pressures, powers and gaseous inputs. Experimental measurements of ion beam current versus accelerating voltage and input microwave power in xenon and oxygen gas are presented. Ion source specific energy and mass utilization versus experimental variables are also determined. The experimental performance demonstrates the ability of this ion source to extract an ion beam with a well matched, stable, and continuous operation over a wide range of input gases, low pressures, and over input gas flow rates in excess of 100 to a few sccm. Double Langmuir probe measurements in xenon gas indicate high degrees of ionization, and electron and ion concentrations in excess of 100 critical densities in the microwave discharge zone. This ion source has many potential uses such as spacecraft electric propulsion, material ion beam processing, and neutral beam ion sources.

Characteristics of a microwave plasma disk ion source

This letter describes an ion source using a cylindrical microwave cavity operating in a hybrid mode associated with the TE211 empty cavity mode. The design principles and associated electrical systems are also discussed. Extracted beam current versus accelerating voltage, and specific energy versus extracted beam current are displayed over the range of flow rates 20–80 sccm and absorbed powers 80–150 W. The results show the feasibility of this concept. The ion source has many potential uses such as space propulsion, material processing, and neutral beam ion sources.

Fabrication of extractor grids for neutral beam sources

The fabrication of tungsten wires for use in extractor grids on neutral beam ion sources is described. The tungsten wires are machined from 0.152-cm-diam tungsten wires into triangular wires by a three-step grinding process. These grid wires have been used in the neutral beam sources for Phaedrus (6 keV beams) and for the Wisconsin Levitated Octupole (15 keV beams). The beam angular divergence is comparable to that obtained from commercially supplied grid wires.