Search

Record beta and density values have been obtained at the Small Tight Aspect Ratio Tokamak in the United Kingdom Atomic Energy Agency (UKAEA) Fusion Culham Science Centre by using Oak Ridge National Laboratory's (ORNL's) neutral beam injector for plasma heating. This result has improved the prospects for a future spherical tokamak (ST) fusion core device. To address the physics issues of ST plasmas and the technology of neutral beam heating, ORNL neutral beam injectors have been installed on the Mega Amp Spherical Tokamak (MAST) at UKAEA Culham. The goal of the injectors is to provide a neutral beam heating power of 5 MW for 0.5 s, or up to 4 MW for 5 s. To achieve 5-s operation at the required power level of 4 MW, the existing oxide-filament cathode must be replaced with a cathode having long-pulse capability. In 1983 ORNL developed an advanced positive ion source having long-pulse capability for 50-A and 80-keV hydrogen ion beams. The indirectly heated cathode technology developed for the advanced positive ion source will be utilized to fulfill requirements of long-pulse neutral beam heating on MAST plasmas. The cathode utilizes an electron emitter made of lanthanum oxide (La 2 O 3 ) doped molybdenum. The cathode is heated by a graphite heater and insulated by a heat shield. The heat shield is made of multiple layers of tantalum sheet. Details of design and performance of such long-pulse cathodes are reported and discussed.

An electron cyclotron resonance (ECR) multicusp plasmatron has been developed by feeding a multicusp bucket arc chamber with a compact ECR plasma source. This novel source produces large (about 25 cm diam), uniform (to within ±10%), dense (>1011 cm−3) plasmas of argon, helium, hydrogen, and oxygen. It has been operated to produce an oxygen plasma for etching 12.7 cm (5 in.) positive photoresist‐coated silicon wafers with uniformity within ±8%. Results and potential applications of this new ECR plasma source for plasma processing of thin films are discussed.An electron cyclotron resonance (ECR) multicusp plasmatron has been developed by feeding a multicusp bucket arc chamber with a compact ECR plasma source. This novel source produces large (about 25 cm diam), uniform (to within ±10%), dense (>1011 cm−3) plasmas of argon, helium, hydrogen, and oxygen. It has been operated to produce an oxygen plasma for etching 12.7 cm (5 in.) positive photoresist‐coated silicon wafers with uniformity within ±8%. Results and potential applications of this new ECR plasma source for plasma processing of thin films are discussed.

The emittances of hydrogen and deuterium negative ion beams produced by volume ion sources have been measured in a transverse plane normal to the beam trajectory. The extraction voltage was varied from 10 to 40 kV, and the transverse magnetic field in the Penning discharges was varied from 0.1 to 0.2 T. Measurements were made on beams with current densities up to 60 mA/cm2 at Oak Ridge National Laboratory with an emittance scanner originally developed at Los Alamos National Laboratory. The beam profile at the scanner can be used to improve the accuracy of the emittance measurements. Other factors affecting emittance measurements are discussed. This analysis may be applicable to other ion sources.

A concept for a current drive system that is based on negative ions with beam energies >1 MeV is presented. Preliminary physics calculations, which are discussed, show that the core current necessary for stability enhancement can be achieved by beams with energy ranging from 1 to 3 MeV. Further study and experiments will better define the optimum energy. Work under way at Oak Ridge National Laboratory, at AccSys Technology Inc., and at collaborating institutes in the United States, Canada, and the Federal Republic of Germany is continuing to define systems, their elements, configurations, and operational scenarios deemed appropriate for such devices as ITER (International Thermonuclear Experimental Reactor) ARIES (Advanced Reactor Innovation and Evaluation Study), and other future steady-state tokamaks. The cost of the RF-accelerated beam should be quite competitive with DC beam concepts being considered for current drive. Not only would the cost per unit power for the RF concept be attractive but the development costs and time also should be quite reasonable. >

The best features of two independently developed surface-plasma negative ion sources with separated function (independently controlled plasma generation and negative ion emission), have been combined in an optimized configuration; as a result, we propose to add a new mode of operation that will allow a 50-fold reduction in the negative ion temperature. The process of Cs injection developed for the semiplanotron negative ion source at the Budker Institute of Nuclear Physics (BINP), Novosibirsk, along with the hot cathode, first anode configuration and neutral gas injection of the ion source development at Oak Ridge National Laboratory, combines the best features of both for the continuous wave (CW) high-density, low-pressure generation of negative ions. Converter-generated cw negative ion densities of 750 mA/cm/sup 2/ are expected from the existing data base. These ions are generated with a temperature of about 7 eV; focusing these ions by a factor of 5 increases the current density to 3500 mA/cm/sup 2/ (with some mutual neutralization loss included). The ion temperature becomes 50 eV; however, according to Liouville's theorem, the brightness of the beam remains at a value of 100 mA/cm/sup 2/ eV (Volume ion sources with a cw current per channel of 100 mA, have a brightness one-third this value.) The configuration of the source geometry and atomic gas control is optimized for maximum charge exchange reduction of the ion temperature by a factor of 50. The configuration involves appropriate shaping of the converter, anode slot, and hot cathode use of a supersonic gas jet of HO, and pumping the jet into the source. Increasing the beam brightness to 1000 mA/cm/sup 2/ eV corrects for a factor of four loss in recovery of charge-exchanged ions. The concept proposed here results in a net cw brightness increase of 10, which is about 30-times greater than that otherwise available.

Summary form only given. The features of improved versions of surface plasma sources (SPS) with cesium catalysis for negative ion production are discussed. The advantages of semiplanotron SPS (BINP, Novosibirsk) with the drift of a thin layer high dense plasma in crossed fields and a hot cathode discharge SPS (SITEX, ORNL) with magnetic field and low gas density are optimized configurations. Close discharge configuration have a Penning multicharge ion source with sputtered electrode opposite an emission slit. The form of emitter surface should be optimized for low aberration geometrical focusing of the secondary negative ion to the emission hole in magnetic field. A supersonic jet of atoms, crossed emission hole, will be used for deep cooling of the negative ion flux with big energy spread from the emitter by resonant charge-exchange with the cold atoms of a jet. The fast pumping of atoms directly in source chamber will keep the gas density low and the destruction of negative ions low. Intense beams of hydrogen isotopes with a temperature less than 1 eV and an emission current density up to 1 A/cm can be reached in a continuously operated SPS with cylindrical emitter and emission slit parallel to the magnetic field. A similar configuration is adequate as an efficient ionizer for nuclear polarized negative ion beam production from low energy polarized atoms after sextupole focusing, optical pumping, or supercold accumulation.

Surface processing techniques involving high energy ion implantation have achieved commercial success for semiconductors and biomaterials. However, wider use has been limited in good part by economic factors, some of which are related to the line‐of‐sight nature of the beam implantation process. Plasma source implantation (or plasma immersion ion implantation) is intended to remove some of the limitations imposed by directionality of beam systems and also to help provide economies of scale. The present paper will outline relevant technologies and areas of expertise that exist at Oak Ridge National Laboratory in relation to possible future needs in materials processing. Experience in generation of plasmas, control of ionization states, pulsed extraction, and sheath physics exist. Contributions to future technology can be made either for the immersion mode or for the extracted beam mode. Existing facilities include the High Power Test Facility, which could conservatively operate at 1 A of continuous current...

The emittances of hydrogen and deuterium negative ion beams produced by volume ion sources have been measured in a transverse plane normal to the beam trajectory. The extraction voltage was varied from 10 to 40 kV, and the transverse magnetic field in the Penning discharges was varied from 0.1 to 0.2 T. Measurements were made on beams with current densities up to 60 mA/cm2 at Oak Ridge National Laboratory with an emittance scanner originally developed at Los Alamos National Laboratory. The beam profile at the scanner can be used to improve the accuracy of the emittance measurements. Other factors affecting emittance measurements are discussed. This analysis may be applicable to other ion sources.

Experimental comparison is made of four plasma grids, each with a specific aperture geometry, in an attempt to improve the ion optics of a multiple aperture ion source. It is clearly shown that a simple notch geometry outperforms the other candidates with a high transmission efficiency (∼68%) to a 2° target at high perveance (∼9.6 μperv).

Several different axisymmetric aperture shapes have been studied, experimentally and theoretically, for use in the plasma electrode employed in extracting ions from a plasma. Compared to a cylindrical bore aperture, a class of shapes opening away from the source plasma resulted in smaller beam divergence (due to reduced aberration fields), while a class opening toward the source plasma resulted in higher beam power density at optimum divergence. The minimum half‐width‐half‐maximum divergence obtained for the former class was 0.57° at a beam energy of 27 kV, as compared to 1° obtained for a conventional cylindrical bore aperture.

A rectangular ion source is being developed for producing 120‐keV/25‐A hydrogen ion beams for pulse durations up to 10 s. It consists of a plasma generator with a rectangular arc chamber (25×35 cm cross section) and an ion accelerator with rectangular grids (10×25 cm hole pattern). The plasma generator is a modified duoPIGatron type. It has been operated at 120 V, 1100 A, and 10 s arc durations to produce a dense and uniform plasma sufficient for supplying a 25‐A ion beam current. The electron emitter used is either a LaB6 hollow cathode or a LM (molybdenum doped with La2O3) indirectly heated cathode. The ion accelerator having four (or three) rectangular grids with multiple circular apertures has been utilized to form high‐energy ion beams above (or below) 80 keV. With substantial improvements in water cooling and mechanical stability, this ion accelerator has been operated reliably to deliver long‐pulse ion beams with energies in excess of 100 keV and pulse lengths of many seconds. The results of measur...

The effect of an insulator coating on the plasma electrode of a duoPIGatron ion source on ion‐beam optics was examined theoretically and experimentally. The effect of a preacceleration potential, applied between the insulated electrode and the target cathode of the source plasma, on ion optics was also examined. A principal result is that this electrode arrangement with precel gives a much lower beam divergence than the same arrangement without precel. Detailed comparisons between the data and calculations are presented.

In an effort to develop a plasma source capable of producing a dense, quiescent, uniform plasma for extracting tens of amperes of hydrogen ions, experimental and theoretical studies on a duoPIGatron ion source have been pursued. A study of plasma generation in the duoPIGatron was begun and a discharge model was subsequently developed to explain observed source behavior. The discharge model is based on two plasmas, a cathode plasma and a PIG plasma separated by a double layer of ions and electrons, and is similar to the existing model for a duoplasmatron. This discharge model is reviewed and the importance of the double layer on plasma generation in the duoPIGatron is discussed. Source electrode modifications suggested by the model resulted in a low noise level of about ±5% and a low‐denisty nonuniformity of about ±10% over a 10‐cm diameter at a high hydrogen plasma denisty of roughly 2×1012 cm−3. This source has been operated reliably to produce a hydrogen ion beam of 15 A at 40 keV. Initial operation of ...

The results of a systematic investigation of the power flow along the Oak Ridge National Laboratory/Princeton Large Torus (ORNL/PLT) neutral beam line, using an intense modified duoPIGatron source with a 22‐cm active grid diameter and 1799 circular apertures that provide 53% transparency, are reported. The variation of power deposited on the different components of the beam line is measured over a wide range of perveance values. The maximum efficiency for beam power transmitted through a 20×25‐cm aperture located 4.1 m downstream was found to be 41%. This efficiency was raised to 53% when a voltage of about 175 V was applied to preaccelerate the ions entering the extraction apertures. Transmission efficiencies approaching 60% were obtained using shaped apertures on the plasma grid. Higher efficiencies should be attainable when used for PLT injection since the acceptance angle for the Princeton tokamak is 11% higher than that of the test facility. Detailed analysis of the results using straight circular ap...

The injection of neutral hydrogen or deuterium particles continues to be the most promising means of heating magnetically confined fusion plasmas to ignition temperatures. Neutral beam injection systems that employ positive ion sources presently operate at energies of about 40-50 keV/nucleon at 60 A [Princeton Large Torus (PLT)] or 100 A [Princeton Divertor Experiment (PDX) or the Oak Ridge National Laboratory (ORNL) Impurities Study Experiment (ISX)] with about 60% conversion efficiency. However, the desire for multisecond beams in the 80-keV/nucleon energy range at ~ 10 MW/module has emphasized the need for technological advances in several areas. At such beam energies, as much as 75% of the initial beam energy is retained in the unneutralized ion components. As a result, two questions immediately come to mind: (1) how can one dispose of this energy; or better still, (2) how can one efficiently recover this energy? The conventional way of treating such a problem is to deflect the ions out of the neutral beam and onto water-cooled plates or beam dumps. This method has worked satisfactorily for 40-keV/nucleon beams in excess of 1.5 MW and ~0.5 s. However, the power per unit area to be disposed of in the high power, multisecond beams mentioned above is beyond present-day technology.

The charge-exchange neutralization efficiency of positive ion-based neutral beams used in plasma heating applications decreases as the beam energy increases. Direct energy recovery from the remaining charged particles can be accomplished by electrostatically decelerating the positive ions; the space-charge neutralizing electrons are constrained from being accelerated by the application of a transverse magnetic field. A finite difference nonlinear sheath analysis is used to analyze the transverse magnetic field electron suppression experiments carried out at Oak Ridge National Laboratory in the early 1980s. A double plasma model, which assumes an equilibrium Boltzmann distribution of electrons at both the neutralizer potential and the ion collector potential, is used to study the experimental data obtained from operating 40 keV, 10 A ion beam energy recovery experiments. The effects of the magnetic field strength, ion “boost” energy, and ion beam current density are examined in detail.

The properties of an intense 50‐kV neutral‐beam system are discussed. The salient features of this system are a transmission efficiency of 76% of the extracted ion beam through a 30×34 cm aperture that is 4.5 m from the ion source, a transmitted neutral power of 1.8 MW H0 (2.0 MW D0) at extraction parameters of 50 kV/100 A/0.1 s (53 kV/85 A/0.1 s), a proton fraction of ∼80%, an ion‐source arc efficiency of ∼1.3 A/kW, an ion‐source gas efficiency of ∼35%, and a reliability of ≳90%.

Conceptual and preliminary engineering design for the National RF Test Facility at Oak Ridge National Laboratory (ORNL) has been completed. The facility will comprise a single mirror configuration embodying two superconducting development coils from the ELMO Bumpy Torus Proof-of-Principle (EBT-P) program on either side of a cavity designed for full-scale antenna testing. The coils are capable of generating a 1.2-T field at the axial midpoint between the coils separated by 1.0 m. The vacuum vessel will be a stainless steel, water-cooled structure having an 85-cm-radius central cavity. The facility will have the use of a number of continuous wave (cw), radio-frequency (rf) sources at levels including 600 kW at 80 MHz and 100 kW at 28 GHz. Several plasma sources will provide a wide range of plasma environments, including densities as high as approx. 5 x 10/sup 13/ cm/sup -3/ and temperatures on the order of approx. 10 eV. Furthermore, a wide range of diagnostics will be available to the experimenter for accurate appraisal of rf testing.

The magnetic multipole line-cusp device developed by MacKenzie and associates has been adapted for use as a neutral beam ion source. It has produced high-density, large volume, quiescent, uniform hydrogen plasmas, which makes it a potential candidate for use as a plasma generator for neutral beam injectors. The device is a water-cooled cylindrical copper discharge chamber (25 cm in diameter by 36 cm long) with one end enclosed by a set of extraction grids with a 15-cm-diam multi-aperture pattern. The chamber wall serves as an anode and is surrounded by an external system of rare-earth cobalt magnets arranged in a line-cusp geometry of 12 cusps; plasma is produced by electron emission from a hot cathode assembly. This source has achieved extracted beam currents of 12 A at 18.5 kV, radial plasma density uniformities of +/-5% over a 15-cm diameter, noise levels of less than +/-0.5%, and arc efficiencies (beam current/arc power) of 0.6 A/kW.

A quasi‐steady‐state (pulse duration of 30 s) ion source of the duoPIGatron type has been developed for fusion applications. It was designed to deliver an 80‐keV hydrogen ion beam of low beamlet divergence (Θrms= 0.26°) at a current density of 0.19 A cm−2. Hydrogen ion beams of 40 to 48 A were extracted at beam energies of 77 to 80 keV for 30‐s‐long pulses. The reliability and stability of the ion source operation were demonstrated by extracting about 600 beam pulses at full power and full pulse length. The ion source was also operated with deuterium as the working gas, and the optimum current at 80 keV was found to be about 33 A, in agreement with the expected inverse square‐root scaling of current density with atomic mass.

The next-generation fusion devices based on the tokamak confinement concept are expected to emphasize steady-state operation. Such future reactors may include designs like the International Thermonuclear Experimental Reactor (ITER) and that of the recent International Tokamak Reactor (INTOR) program. Effective means of non-inductive plasma current drive would therefore be necessary. This paper describes a neutral beam concept for a current drive system (which will heat the plasma as well) that is based on negative ions and has a beam energy > 1 MeV. Such systems, at much lower power levels, are also being considered for alpha diagnostics. Preliminary physics calculations show that the plasma core current necessary for stability enhancement can best be achieved in these future reactor-like machines with tangentially injected beams having energies ranging from 1 to 4 MeV. Further study and experiments will better define the optimum energy. Studies of how to accomplish beams of this energy led to the system described in this paper.

Ion beam technology has advanced immensely during the past 15 years in connection with the application of neutral beam injection heating for fusion research. Ion sources have been scaled up along with necessary modifications, yielding currently a few megawatts of extraction power (e. g., 40 keV-60 A, 0.3-sec pulse). The entire neutral beam injection system has become a multidisciplinary technology including plasma physics, accelerator and beam physics, pumping technology, heat transfer, electrical engineering, and so on. Since the neutral beam injection heating of fusion plasmas has been proved the most viable means of increasing the plasma temperature to ignition, the future demand and requirements are rising with the size of fusion plasma devices. A brief review of the state of the art of neutral beam technology is presented and the direction of the future neutral beam field is discussed.

Multimegawatt neutral beams of hydrogen or deuterium atoms are needed for fusion machine applications such as MFTB-B, TFTR-U, DIII-U, and FED (INTOR or ETR). For these applications, a duoPIGatron ion source is being developed to produce high-brightness deuterium beams at a beam energy of approx. 120 keV for pulse lengths up to 30 s. A long-pulse plasma generator with active water cooling has been operated at an arc level of 1200 A with 30-s pulse durations. The plasma density and uniformity are sufficient for supplying a 60-A beam of hydrogen ions to a 13- by 43-cm accelerator. A 10- by 25-cm tetrode accelerator has been operated to form 120-keV hydrogen ion beams. Using the two-dimensional (2-D) ion extraction code developed at Oak Ridge National Laboratory (ORNL), a 13- by 43-cm tetrode accelerator has been designed and is being fabricated. The aperture shapes of accelerator grids are optimized for 120-keV beam energy.

Scaling studies for a SITEX negative ion source to produce 200-keV, 10-A, long pulse D/sup -/ beams are under way at Oak Ridge National Laboratory (ORNL). Designs have been restricted to the use of established techniques and reasonably welldemonstrated scaling. The results show that the 1-A SITEX source can be directly scaled to produce 200-keV, 10-A long pulse ion beams with a source power efficiency of less than or equal to5 kW of total plasma generator power per ampere of D/sup -/ beam generated. Extracted electron-to-D/sup -/ ratios should be less than or equal to0.06, with all extracted electrons recovered at less than or equal to10% of the first gap potential energy difference. The close-coupled accelerating structure will be 5 cm long and have five electrodes with 21 slits each, with a 50-kV/cm field in each gap. No decel electrode was included because of the transverse magnetic field. Electrons formed in each gap by the about16% charge-exchange loss of D/sup -/ in the total accelerator column will be collected by electron recovery structures associated with the gaps at an average energy of 50% of a gap's potential energy difference. Atomic gas efficiency will be greater than or equal to67%. Beammore » divergence calculations using the ORNL optics code give theta /SUB rms/ = + or -0.4/sup 0/. The ion source magnetic field provides momentum dispersion of the extracted beam, separating out both the electrons and all heavy ion impurities and low energy D/sup 0/ particles formed by charge exchange in the accelerating column. A D/sub 2/ gas neutralization cell and a charge separation magnet provide 1 MW of D/sup 0/ beam at 200 keV for injection. The overall beam line dimensions are 2.2 X 1.0 X 5.0 m (H X W X L).« less

The Oak Ridge National Laboratory (ORNL) SITEX (Surface Ionization with Transverse Extraction) negative ion source utilizes a 100-V/20-A reflex arc discharge in a 1300-gauss magnetic field to generate Cs+ ions and H+ or D+ ions, depending on the beam required. A shaped molybdenum plate is placed directly behind the arc column. Cesium coverage on this plate is used to minimize the surface work function, which requires two-thirds of a monolayer coverage. Cesium coverage ia adjusted both by cesium flow control into the arc discharge chamber and by temperature control of the converter using gaseous-helium cooling channels in the converter plate. Normal converter operational temperatures are 300/sup 0/ to 500/sup 0/C H/sup -//D/sup -/ beams are generated at the biased converter surface (-150 V with respect to the anode) by Cs/sup +/ sputtering of absorbed hydrogen or deuterium and by the reflection-conversion mechanism of H/sup +//D/sup +/ ions which strike the converter surface at 150 eV. The negative ions are accelerated through the 150-V plasma sheath at the converter surface and are focused by the converter geometry and magnetic field so as to pass through the exit aperture with minimum angular divergence. The ion optics of the SITEX accelerator has beenmore » calculated using the ORNL 3-D optics code and results in a divergence perpendicular to the slot of theta/sub perpendicular rms/ = 0.35/sup 0/ and parallel to the slot of theta/sub parallel rms/ = 0.18/sup 0/. This beam divergence should be adequate for injection into a radio frequency quadrupole (RFQ) for further acceleration.« less

A duoplasmatron ion source is modified to provide a large plasma surface with a uniform density at a target cathode. The target cathode and the acceleration and deceleration electrodes are gridded or multi-apertured and are spaced in close proximity each to the others with the apertures being in alignment. With such an arrangement, it is possible to extract multi-ampere bright ion beams at energies of tens of KeV. Conversion of the ion beam to a neutral particle beam can be readily accomplished by addition of a gas cell.

A hydrogen arc has been developed which produces a low‐density plasma column. The electrodes of the arc discharge are geometrically arranged such that the plasma drifts through a hole in the arc anode along a flux tube of the confining magnetic field.A differentially‐pumped vacuum system was constructed which achieved a base pressure of 2.5×10−10 Torr in the inner liner region while at liquid‐nitrogen temperature. A density of about 1010 particles cm−3 can be achieved in the plasma column contained in the inner liner region, down field from the arc chamber, with a gas flow of 2 cm3 min−1 into the arc chamber. At this flow, the pressure in the inner liner rises to 3×10−9 Torr. The ion‐to‐neutral density ratio under these conditions is about 30 to 1 in the inner liner region.

For several years, we have been empirically producing steady-state, mirror-confined hot-ion plasmas with ${T}_{i}\ensuremath{\approx}\mathrm{a}$ few keV and ${n}_{i}\ensuremath{\approx}\frac{{10}^{13}}{{\mathrm{cm}}^{3}}$. We describe here the ion-heating mechanism, which is an instability having a fine-grained azimuthal structure covering a broad band of frequencies around ${\ensuremath{\omega}}_{\mathrm{pi}}$, having a rapid growth rate on the order of ${\ensuremath{\omega}}_{\mathrm{pi}}$, and being driven by an intense radial dc electric field. It does not require that ${T}_{e}g{T}_{i}$.

A model of an ion source for producing large spacecharge-neutralized beams is preserted. Experiments show that coaxially injected electrons overcome space charge, thereby increasing ion output. Ideally, ions and electrons emerge together with the same density and velocity, forming a neutralized beam. (auth)

A method is described for making positive‐ion‐based neutral‐beam injection viable at energies of ≲100 keV per nucleon by recovering the energy of residual charged particles as electrical energy. The concept of transverse magnetic field blocking of electrons has been shown to be successful, and preliminary experimental results are presented.

Beam parameters have been measured for both the Surface Ionization with Transverse Extraction (SITEX) and Volume Ionization with Transverse Extraction (VITEX) H−/D− ion sources. Both sources use a reflex discharge to generate the main plasma. Beam energies up to 18 keV were used for pulse lengths up to several seconds. For SITEX, Faraday cup magnetically analyzed D− beam currents of 110 mA at extraction densities of 48 mA/cm2 and at a source ion temperature of 4 eV have been measured. For the VITEX results, Faraday cup magnetically analyzed beam currents of up to 80 mA at extraction densities of 27 mA/cm2 and at a source ion temperature of 0.5 eV have been measured. Virtually all extracted electrons were recovered at an energy of 10–30% of the accel beam energy, and there were none in the analyzed beam.

Surface ionization with Transverse Extraction (SITEX) and Volume Ionization with Transverse Extraction (VITEX) ion sources are being developed to produce intense beams of light negative ions for neutral particle beam applications. The salient feature of these ion sources is their ability to form intense negative‐ion beams. With the objective of improving the performance of these sources, an experimental study of their plasma properties has been conducted. The effects of various electrodes in the plasma generator were investigated. Low electron and ion temperatures (below 1 eV) and positive plasma potential up to +6V have been measured. The measured distributions of plasma density and potential reveal the existence of multichamber characteristics in the source plasma. The significant discharge characteristics and the plasma properties associated with the performance of SITEX and VITEX ion sources are discussed.

The properties of an intense neutral beam injector, the modified duoPIGatron ion source, are discussed and compared with other injectors. For this source (a) beam composition for hydrogen is approximately (85+/-5) % monatomic, (b) nucleon gas efficiency is 50%, (c) the electrical efficiency of ion generation is 1.1 A/kW, and (d) up to 52% of the input power is delivered in the ion and neutral beam to a target subtending a half angle of 1.8 degrees x1.4 degrees .

Solving the Poisson‐Vlasov equations ∇2φ=∫fdv−e−φ (1) (v×B+∇φ) ⋅ ∇v f=v ⋅ ∇f=0 (2) where the magnetic field, B, is assumed constant, we optimize the optical system of a SITEX negative ion source in ∞ slot geometry. Algorithms designed to solve the above equations were modified to include the curved emitter boundary data appropriate to a negative ion source. Other configurations relevant to negative ion sources are examined.

A sciopticon based on the pinhole-camera effect is being used to determine individual beamlet contributions to the quality of neutral beams extracted from multiaperture ion sources. The technique outlined in this note can be used to study the effects on beam optics of nonhomogeneous source plasma density or acceleration gap nonuniformities, grid nonparallelism or aperture misplacement, and space-charge blowup or scattering in the neutralizer cell.

A proof-of-principle experiment on direct recovery of residual hydrogen ions based on a magnetic electron suppression scheme is described. Ions extracted from a source plasma a few kilovolts above the ground potential (approx. 20 A) are accelerated to 40 keV by a negative potential maintained on a neutralizer gas cell. As the residual ions exit the gas cell, they are deflected from the neutral beam by a magnetic field that also suppresses gas cell electrons and then recovered on a ground-potential surface. Under optimum conditions, a recovery efficiency (the ratio of the net recovered current to the available full-energy ion current) of 80% +- 20% has been obtained. Magnetic suppression of the beam plasma electrons was rather easily achieved; however, handling the fractional-energy ions originating from molecular species (H/sub 2//sup +/ and H/sub 3//sup +/) proved to be extremely important to recovery efficiency.

Thin, pure, hard carbon films about 1 pm thick have been deposited on a water-cooled copper plate installed in a continuous-wave (cw) plasma source with graphite walls. The transparent, glassy films were observed after several thousand multisecond pulses of intense hydrogen discharges. The properties of these films and the operating conditions of the plasma, source are described. Many ion beam and rf sources are available in the Fusion Energy Division of the Oak Ridge National Laboratory (ORNL). The potential application of these plasma sources to growing large, thick diamond films is discussed.

The Oak Ridge National Laboratory (ORNL) Fusion Energy Division (FED) negative ion development program has concentrated on the use of Penning discharges in a strong magnetic field. Extraction from the discharge has taken place both perpendicular and parallel to the confining magnetic field. The former has received by far the greater development effort. The ion source produced is called VITEX for Volume Ionization with Transverse EXtraction. Attempts to extract parallel to themagnetic field have recently begun and the ion source principle has been labeled Ringatron. A plan view of a Penning discharge as used in VITEX is shown in Fig. 1. An elevation view is shown in Fig. 2. A thin sheet plasma of thickness D(1) is formed with energetic electrons of density on the order of 1013 cm-3. A secondary cold plasma of thickness D(2) is formed in the region immediately surrounding the energetic electron sheet due to diffusion. Negative ions formed in the discharge may be extracted transverse to the magnetic field with suitable electrodes as shown in Fig. 2. Probe studies coupled with geometrical variations on the thickness of D(1) and D(2) indicate that the two chamber model of Hiskesl is a valid production mechanism. A variation to the extraction geometry of VITEX is to take the sheet plasma of energetic electrons and wrap it around into a cylinderical annulus as shown in Fig. 3. Thus, excited molecular neutrals are fed into the core of the discharge from the entire annulus. The core is similar to the region D(2) of the VITEX geometry. Negative ions produced in the core are free to drift along the magnetic field to the extraction electrodes at which point they are accelerated parallel to the magnetic field. This source is called Ringatron due to the ring or annular nature of the discharge.

The Fusion Energy Division of the Oak Ridge National Laboratory (ORNL) in cooperation with the Princeton Plasma Physics Laboratory (PPPL) designed, constructed, and tested four high power neutral beam injectors for application on the Princeton Large Torus (PLT). This system employs a modified duoPIGatron ion source which has produced ion beams with parameters up to 70 A, 45 keV, and 500 msec. Nominal extraction parameters were 60-A, 40-keV, and 300-msec pulses, simultaneously. Neutral power up to 750 kW for 100 msec was calorimetrically measured on a simulated PLT target behind a PLT-sized aperture of 20 x 25 cm located at 4.10 m. Initial performance of these beam lines on PLT was near these parameters. Calorimetric measurements of beam power delivered to the PLT torus with a 3.65-m beam line length and with 100-msec full power pulses indicate a 10 to 15% reionization loss when the beam line pulse is synchronized to the pulsed torus magnetic fields. Data taken at ORNL are presented to show that this power loss is approximately equal to that calculated on drift tube pressure measurements taken without drift tube magnetic fields.

The design of a high brightness penning ion source is discussed. A cylindrical configuration (RINGATRON) is used. This is shown to improve ion extraction across the magnetic field. It also leads to enhanced production density. Comparisons of the ringatron configuration with the duoplasmatron and the planar penning discharge configuration are made. (AIP)

Six high power (40 keV--60 A) injection systems, four for PLT (Princeton Plasma Physics Laboratory) and two for ISX (Oak Ridge National Laboratory) tokamaks, have been developed, fabricated, and operated. Each injector delivers 750 kW (1000 kW) of H (D) neutral power to the tokamak plasma. An in-depth system parameter study has revealed unique features: high atomic yield (approximately 85%), improved ion optics due to a preacceleration technique, near steady-state operation (up to 500 msec), and a possible technique to control species yield. Routine operation includes high duty cycle (approximately 10%), long filament lifetime (several months), high arc efficiency, and the reliability necessary for application on a fusion device. The program status and injection parameters will be discussed.

An emittance measurement employing two techniques are being made on SITEX. To this end, a 2-D calculation was performed to design the accelerator in order to reduce electric field abberations. The calculated normalized emittance is 6 x 10/sup -4/ IIcm mrad for an angular divergence theta/sub RMS/ approx. = 0.28/sup 0/. Status of the experimental findings are presented and a comparison made to the calculated value which will yield the ion sputter energy.

The technology of acceleration of MeV energy negative ion beams is discussed with respect to embodiments proposed. These embodiments are capable of producing multi-ampere negative ion beams with an overall current density consistent with the beam emittance and application requirements. Included in these considerations for the various concepts are: (1) status of data base support, (2) options for dealing with the issues specific to negative ion acceleration, (3) current per channel and multiplexing senarios, (4) efficiency, (5) beam emittance, and (6) extent and limitations of present concept development.

Parametric studies were made on a hot cathode reflex discharge H/sup -/ Surface Ionization source with Transverse Extraction (SITEX) in both the pure hydrogen and the mixed hydrogen-cesium mode. Extraction current density, beam current, gas efficiency, extracted electron-to-H/sup -/ current ratio, heavy negative ion impurities, optics, and long pulse operation were investigated as a function of time, arc voltage, arc current, converter voltage, H/sub 2/ gas flow, cesium feed rate, and plasma generator geometries. Initial results of the research were an extracted H/sup -/ beam current density of 56 mA/cm/sup 2/ at 23 mA for 5 s pulses and, gas efficiency of 3%, theta/sub perpendicular/ (1/e) approx. 2 +- 1/sup 0/, theta/sub parallel/ (1/e) approx. 1 +- 1/sup 0/, at a beam energy of 25 keV. Negative heavy ion beam impurities were reduced to < 1% at low current densities. H/sup -/ ions are produced prinicpally by positive ion surface conversion using elemental cesium fractional monolayer coverage on a molybdenum converter substrate, which is biased negatively with respect to the anode.

This paper describes the development of a long-pulse positive ion source that has been designed to provide high brightness deuterium beams (divergence ≈ 0.25° rms, current density ≈ 0.15 A cm-2) of 40-45 A, at a beam energy of 80 keV, for pulse lengths up to 30 s. The design and construction of the ion source components are described with particular emphasis placed on the long-pulse cathode assembly and ion accelerator.