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Metrology inside a D/T burning fusion reactor must necessarily be conducted remotely since the in-vessel environment would be highly radioactive due to neutron activation of the torus walls. A technique based on frequency modulated coherent laser radar (FM CLR) for such remote metrology is described. Since the FM CLR relies on frequency shift to measure distances, the results are largely insensitive to surface reflectance characteristics. Results of measurements in TFTR and NSTX fusion devices using a prototype FM CLR unit, capable of remotely measuring distances (range) up to 22 m with better than 0.1-mm precision, are provided. These results illustrate that the FM CLR can be used for precision remote metrology as well as viewing. It is also shown that by conducting Doppler corrected range measurements using the CLR, the motion of objects can be tracked. Thus, the FM CLR has the potential to remotely measure the motion of plasma facing components (PFCs) during plasma disruptions.

A frequency modulated Coherent Laser Radar ranging diagnostic is being used on the National Spherical Torus Experiment (NSTX) for precision metrology. The distance (range) between the 1.5 μm laser source and the target is measured by the shift in frequency of the linearly modulated beam reflected off the target. The range can be measured to a precision of

Next generation fusion reactors require accurate measuring systems to verify sub-millimeter alignment of plasma-facing components in the reactor vessel. A metrology system capable of achieving such...

This paper identifies the requirements for the International Thermonuclear Experimental Reactor metrology and viewing system, and describes a remotely operated precision surface mapping system. A metrology system capable of achieving sub-millimeter accuracy must operate in a reactor vessel that has high gamma radiation, high vacuum, elevated temperature, and magnetic field. A coherent, frequency modulated laser radar system is under development to meet these requirements. The metrology/viewing sensor consists of a compact laser optics module linked through fiber optics to the laser source and imaging units, located outside the harsh environment. The deployment mechanism is a remotely operated telescopic-mast. Gamma irradiation to 107 Gy was conducted on critical sensor components at Oak Ridge National Laboratory, with no significant impact to data transmission, and analysis indicates that critical sensor components can operate in a magnetic field with certain design modifications. Plans for testing key components in a magnetic field are underway.

We describe the development of a novel Doppler laser radar (DOLAR) for remote measurement of flow velocity (0–10 m/s) and film thickness of liquid metal walls, currently being studied for their superior heat handling and self-healing characteristics. Small fluctuations in flow velocity(∼mm/s) and flow thickness (∼50 μm) that may arise during plasma discharges can also be measured. The DOLAR is also designed for non intrusive mapping of features of plasma-facing solid surfaces with very high precision (∼50 μm). It can also measure the motion of structural components of a fusion reactor during plasma discharges and during plasma disruptions. The device utilizes frequency modulation laser radar principles for precision range measurements. Compensation of Doppler frequency shift is used to measure flow velocity. The DOLAR probe head is designed with acousto-optic and piezoelectric devices for operation in the harsh fusion environment.

DIII-D currently operates with a single- or double-null open divertor and graphite walls. Active particle control with a divertor cryopump has demonstrated density control, efficient helium exhaust, and reduction of the inventory of particles in the wall. Gas puffing of D{sub 2} and impurities has demonstrated reduction of the peak divertor beat flux by factors of 3--5 by radiation. A combination of active cryopumping and feedback-controlled D{sub 2} gas puffing has produced similar divertor heat flux reduction with density control. Experiments with neon puffing have shown that the radiation is equally-divided between a localized zone near the X-point and a mantle around the plasma core. The density in these experiments has also been controlled with cryopumping. These experimental results combined with modeling were used to develop the new Radiative Divertor for DIII-D. This is a double-null slot divertor with four cryopumps to provide particle control and neutral shielding for high-triangularity advanced tokamak discharges. UEDGE and DEGAS simulations, benchmarked to experimental data, have been used to optimize the design.

A particle exhaust scheme, employing a cryocondensation pump in the outboard divertor region under a baffle, has been installed and operated in the DIII-D tokamak. The cryopump provides toroidally symmetric pumping at a rate of 30000 to 40000 l/s for D{sub 2} in the pressure range of 1 to 4 mTorr. Pressures in the 2 to 3 mTorr range are routinely observed under the baffle. This translates to particle exhaust throughputs of nearly 100 Torr l/s. The exhaust throughput could be controlled by selecting the position of the plasma strike region with respect to the opening to the baffle chamber. The pump has been used quite effectively for plasma density control. 19 refs., 9 figs., 1 tab.

A better understanding of helium transport in the plasma core and edge in enhanced confinement regimes is now emerging from recent experimental studies on DIII-D. Overall, the results are encouraging. Significant helium exhaust ({tau}*{sub He}/{tau}{sub E} {approximately} 11) has been obtained in a diverted, ELMing H-mode plasma simultaneous with a central source of helium. Detailed analysis of the helium profile evolution indicates that the exhaust rate is limited by the exhaust efficiency of the pump ({approximately}5%) and not by the intrinsic helium transport properties of the plasma. Perturbative helium transport studies using gas puffing have shown that D{sub He}/X{sub eff}{approximately}1 in all confinement regimes studied to date (including H-mode and VH-mode). Furthermore, there is no evidence of preferential accumulation of helium in any of these regimes. However, measurements in the core and pumping plenum show a significant dilution of helium as it flows from the plasma core to the pumping plenum. Such dilution could be the limiting factor in the overall removal rate of helium in a reactor system.

The He generated as a result of D/T burn in a fusion reactor must be exhausted from the plasma to avoid fuel dilution effects. In view of this, transport and exhaust studies of He in fusion plasmas are getting increasing attention in recent years. In fusion plasmas, the exhaust gas will be a combination of D2 and He, with He forming only a small fraction (about 10%). The cryosorption pumping characteristics of pure He and a mixture of D2 and He (90% D2) have been investigated using a cryosorption pump with condensed layers of Ar as sorbent. A cryocondensation pump cooled by liquid He at 4.3 K, and located in the outboard divertor region of the DIII‐D tokamak, was used for the experiment. The investigation was conducted in a pressure regime that is relevant for particle exhaust from fusion plasmas. The experiment revealed that (1) the cryosorption pumping speed of pure He drops precipitously if the Ar/He ratio falls below about 20; (2) the pumping speed for He in a D2/He mixture decreases in an exponential manner with the amount of D2 pumped; (3) increasing the thickness of Ar in the range of 1–12 μm had little effect on the pumping speed for He in a D2/He mixture; and (4) for a pumping surface coated with a thick (≳2 μm) layer of Ar, surrounded by a radiation shield having a transparency factor of about 6, a He pumping speed in the range of 15–25 m3 s−1 m−2 in the mTorr pressure range for a pulse duration of about 5 s can be obtained after pumping about 80 Torr l of D2.

Significant exhaust of thermal helium in a diverted, H-mode deuterium plasma has been demonstrated for the first time on the DIII-D tokamak using an in-vessel cryopump conditioned with an argon frost. The helium, introduced via gas puffing, is observed to reach the plasma core and then is readily removed from the plasma with a time constant of ∼8–15 energy confinement times. Detailed analysis of the helium profile evolution indicates that the exhaust rate is limited by the exhaust efficiency of the pump (∼5%) and not by the intrinsic helium transport properties of the plasma. Additional studies focusing on the recycling properties of helium relative to deuterium in the divertor region indicate some dependence of the helium concentration in the divertor pumping plenum on the divertor outer strike-point (OSP) position in Ohmic discharges. However, the helium concentration in the plenum appears to have little dependence on OSP position in beam-heated, ELMing H-mode discharges.

A better understanding of helium transport in the plasma core and edge in enhanced confinement regimes is now emerging from recent experimental studies on DIII-D. Overall, the results are encouraging with significant helium exhaust obtained in a diverted, ELMing H-mode plasma, with {tau}*{sub He}/{tau}{sub E} {approximately} 10 and transport studies indicating that D{sub He}/{Chi}{sub eff} {approximately} 1 in all plasma conditions studied to date. However, measurements in the core and pumping plenum show a significant dilution of helium as it flows from the plasma core to the pumping plenum. Such dilution could be the limiting factor in the overall removal rate of helium in a reactor system.

We summarize results from DIII-D in regard to issues for reactor application of H-mode. Recently, DIII-D has begun to operate a cryopump (D{sub 2} pumping speed = 31,000 {ell}/s at a pressure of 2 mTorr). Initial results are very favorable for density control in H-mode. The plasma density could be reduced by 50%. Energy confinement is unchanged so the temperature rises in proportion to the density drop. Ability to access these less collisional plasmas in H-mode is favorable to current drive application. With the all-graphite wall, impurity accumulation has been eliminated. The exceedingly good confinement of VH-mode offers the possibility of retaining good confinement while radiating copious power from the plasma edge using injected noble gas impurities.

A collaborative program has been initiated on DIII-D to study helium (He) transport and exhaust in H-mode plasmas. To simulate the presence of He ash in DIII-D, a 50 ms He puff is injected into a DIII-D plasma, resulting in a He concentration of approximately 15%. The time dependence of the He density profiles in the plasma core is measured with charge-exchange recombination spectroscopy and the He spatial distribution on the divertor floor is studied with an impurity monitor array. The dependence of core transport diffusivities as a function of edge-localized modes (ELM) frequency has been studied and the first demonstration made of He exhaust from an ELMing H-mode plasma in a diverted tokamak. A measured value of tau *He/ tau E of 14 was obtained, which is within the acceptable range for a fusion reactor.

The Advanced Toroidal Facility (ATF) torsatron [Fusion Technol. 10, 179 (1986)] has completed experiments focusing on microwave scattering measurements of density fluctuations and transport studies utilizing the modulation of dimensionless parameters. Microwave scattering measurements of electron density fluctuations in the core of low‐collisionality electron cyclotron heated (ECH) plasmas show features that might be evidence of trapped electron instabilities. Starting from gyro‐Bohm scaling, the additional dependence of confinement on the dimensionless parameters ν* and β (collisionality and beta) has been investigated by modulating each of these parameters separately, revealing the additional favorable dependence, τE∝τgBν*−0.18β+0.3.

A particle exhaust scheme using a cryocondensation pump in the advanced divertor configuration of the DIII-D tokamak is described. In this configuration, the pump is located inside a baffle chamber...

The DIII‐D tokamak is being upgraded to allow for divertor biasing, baffling, and pumping experiments. This paper gives an overview of the new diagnostics added to DIII‐D as part of this advanced divertor program. They include tile current monitors, fast reciprocating Langmuir probes, a fixed probe array in the divertor, fast neutral pressure gauges, and Hα measurements with TV cameras and fiber optics coupled to a high‐resolution spectrometer.

This paper identifies the requirements for a remotely operated precision laser ranging system for the International Thermonuclear Experimental Reactor. The inspection system is used for metrology and viewing, and must be capable of achieving submillimeter accuracy and operation in a reactor vessel that has high gamma radiation, high vacuum, elevated temperature, and magnetic field levels. A coherent, frequency modulated laser radar system is under development to meet these requirements. The metrology/viewing sensor consists of a compact laser-optic module linked through fiberoptics to the laser source and imaging units, located outside the harsh environment. The deployment mechanism is a remotely operated telescopic mast. Gamma irradiation up to 10/sup 7/ Gy was conducted on critical sensor components with no significant impact to data transmission, and analysis indicates that critical sensor components can operate in a magnetic field with certain design modifications. Plans for testing key components in a magnetic field are underway.

The plasma facing surfaces in ITER must be aligned to millimeter accuracy with respect to the magnetic flux surfaces to prevent impurity influx into the plasma and to avoid component damage. Checking of in-vessel component alignment during initial assembly, operation, and subsequent maintenance is anticipated. A fully remote metrology system is necessary, particularly since major remote operations such as shield blanket exchange and divertor cassette replacement are planned. The metrology system must be compatible with the ITER in-vessel environment of high gamma radiation (/spl sim/10/sup 6/ R/hr), super-clean ultra-high-vacuum (/spl sim/10/sup -8/ Torr), and elevated temperature (/spl sim/200/spl deg/C). A fast scanning rate is required since the plasma facing surface in ITER is very large (/spl sim/1500 m/sup 2/). A coherent FM laser radar based metrology system, developed by Coleman Research Corporation, is being adopted to accomplish this task. Conceptually, this metrology system consists of a compact (few cm/sup 3/) remotely deployed laser transceiver optics module, linked through fiber optics to the laser source and imaging units that are located outside the biological shield. Range measurements conducted on a variety of surfaces using the system have yielded sub-millimeter accuracy. Therefore, the technique will easily meet the precision requirement for the ITER application. Computer simulations have been carried out to determine the optimum number of units required for complete mapping of the plasma facing surfaces. Most in-vessel components of the system appear to be radiation hardenable and vacuum compatible. Details of the system and developments required to make it fully compatible for ITER metrology application will be elaborated.

Diagnosis of tuberculosis in body fluids remains an enigma. This study is an attempt to evaluate various modalities like smear, culturePCR for the same. Out of 110 samples of body fluids, 68(61.8%) were negative by all the modalities, 11(10%) could be diagnosed by all modalities. 25(22.72%) were diagnosed by PCR alone. 3(2.7%) showed a growth on culture alone while 3 cases (2.7%) could be demonstrated only on smear.

A frequency modulated Coherent Laser Radar ranging diagnostic is being used on the National Spherical Torus Experiment (NSTX) for precision metrology. The distance (range) between the 1.5 {micro}m laser source and the target is measured by the shift in frequency of the linearly modulated beam reflected off the target. The range can be measured to a precision of < 100{micro}m at distances of up to 22 meters. A description is given of the geometry and procedure for measuring NSTX interior and exterior surfaces during open vessel conditions, and the results of measurements are elaborated.

The objective of this study on bladder lesions was to assess the relationship of (a) the proliferative activity measured by AgNOR counts, and (b) the loss of cell adhesion leading to acquisition of invasive properties as assessed by E-Cadherin expression. Paraffin embedded tissue biopsies from normal urothelium and malignant urothelial lesions were randomly selected from our surgical pathology files. AgNORs were analysed by the silver staining method and E_cadherin expression by immunohistochemistry. An increase in MP AgNOR counts was observed from normal through benign to malignant tumors. A corresponding decrease in E Cadherin expression was noticed from normal through different grades of transitional cell carcinoma (TCC). A correlation was found between a high P AgNOR and decreased E_cadherin expression with stromal and muscle invasive tumors. It is deduced that when low grade tumors show a high P AgNOR and loss of E_cadherin expression, it is a significant indicator of the possible aggressive behavior in terms of stromal or muscle invasion and progression to a higher grade in future.

One hundred cervical tissues including 72 malignancies (68 squamous cell carcinomas, 3 adenocarcinomas, 1 neuro-endocrine carcinoma), 24 cases of CIN of various grades and 4 normals were examined for the presence of Human Papilloma virus (HPV) types by non isotopic in-situ hybridisation. Biotinylated probes to HPV types 16 and 18 were used in all the cases and 31 and 33 in 15 squamous Carcinomas. HPV DNA sequences were detected in 55/72 (76.4%) of the malignant lesions, of which among squamous Carcinomas. HPV 16 alone was present in 12 of 68 cases (17.64%) and type 18 in 15 of 68 cases (22.0%). 20/68 (29.4%) showed both types 16 and 18. Of the 15 cases examined for types 31 and 33.5 cases showed presence of both types. All three adenocarcinomas were negative for HPV 16, but positive for HPV 18. The solitary case of Neuroendocrine Carcinoma showed only HPV 18. Of the 24 CINS, type 16 was detected in 7/24 cases (29.1%) type 18 in 2/24 (8.3%) cases and both types in 1/24 (4.1%). None of the normal cases showed positive signals for HPV. The overall results show a slight preponderance of HPV 18 in this group of carcinoma of cervix studied and correlate with poor differentiation and greater aggressive behaviour of cervical cancer which is the most common type of cancer among women in this country.

A high throughput cryocondensation pump has been installed inside the DIII-D plasma chamber as part of the Advanced Divertor Program. During normal plasma discharges the pumping surface temperature must remain sufficiently low (

A cryocondensation pump for the DIII-D advanced diverter program is to be installed in the vacuum vessel in the fall of 1992. The purpose of the cryopump is to remove gas from the diverter, reduce recycling to the plasma, and to provide reduced density plasmas for experimental study. The pump is designed for a pumping speed of 50,000 l/s at 0.4 mtorr. The major pump components are toroidally continuous to minimize inductive voltages, thereby greatly reducing the risk of any electrical breakdown during disruptions. The cryopump consists of a 25mm Inconel tube, 10m long, cooled by liquid helium. It is surrounded by liquid nitrogen-cooled shields and a segmented ambient temperature radiation/particle shield. The outer nitrogen shield has a toroidally discontinuous copper coating to enhance thermal conductivity while maintaining a high toroidal electrical resistance to minimize electromagnetic loads during disruptions. The pump is cooled by 10 g/s of liquid helium at an inlet pressure of 115 kPa and temperature of 4.35 K. The pump is subjected to a steady-state heat load of

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.

It is known that micron‐ and submicron‐sized metallic particles are released from the electrode surfaces when a vacuum gap is subjected to a high dc stress. It is also well known that larger particles (> 10 μm) are generated within the interelectrode gap when a vacuum gap is subjected to conditioning or severe prebreakdown current flow. This paper examines the role of such particles in inducing the breakdown of a vacuum gap. While the larger particles induce breakdown by way of a trigger discharge, it is shown that the smaller particles can initiate breakdown because of effects associated with impact. The various effects associated with the high‐speed impact of a metallic microparticle on a target electrode, viz., cratering, production of metal vapor, and production of thermally generated plasma and their relative significance on vacuum breakdown, are examined.

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).

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...

Several types of thin polymer film insulation are being evaluated for possible use in superconducting underground transmission cables. Measurements are reported on the partial discharge inception voltages of threelayer disc samples of 102-?m polyethylene and 61-?m polycarbonate for temperatures and pressures of the helium impregnant ranging from 5.0 K and 0.3 MPa to 11.5 K and 1.5 MPa. Butt gaps are simulated by punching 1 mm diameter holes in some of the layers. The effect of aluminized shielding around the holes is discussed. The observed inception voltages vary strongly with the helium conditions, increasing rapidly as the density increases. The results suggest that the voltage is capacitively divided between the polymer layers and helium-filled gaps, with partial discharge occurring when the breakdown strength of the helium is exceeded.

Two electrostatic detectors are designed to search for the presence of microparticles of dimensions greater than 10 μm, in an ultrahigh-vacuum test gap (≈7 mm), when a high dc voltage (> 100 kV) is applied across the gap. The experiments with both the detectors revealed that such microparticles are not generated in detectable numbers, within the vacuum gap, prior to breakdown.

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...

According to Cranberg's hypothesis, tiny aggregates of metallic matter called microparticles, emanating from the electrode surfaces, are responsible for the breakdown of a vacuum gap under high dc stress. Experiments are carried out using a scanning electron microscope to see whether such particles appear within the interelectrode gap prior to breakdown. It was observed that micron‐ and submicron‐sized particles are released in abundance well below the breakdown voltage. Investigations were continued to identify the microparticles with the electrode materials using an electron microprobe analyzer. It was found that the microparticles were composed of the electrode materials. Direct examination of the electrode surfaces, after application of the voltage, under the scanning electron microscope also showed features suggesting that the microparticles are released from the electrode surfaces.

Beam power transmission and grid loading characteristics of a two‐stage neutral beam source are presented. The dependence of power deposition on the target, the grids, and the gas cell was studied over a wide range of extraction perveance values with the accel‐to‐extraction gap field ratio as the other parameter. The results show that the power transmission improves remarkably with increasing field ratio. For sufficiently large field ratios (≈2.5), more than 80% of the input IV power was collected on a target located 4 m downstream and subtending 2 ° half angle to the source. The sum of the grid loading is approximately double that of single‐stage accelerators; the plasma grid loading is the highest, followed by ground grid, accel grid, and extraction grid in that order.

The underlying mechanisms involved in the heat loading on the accelerator grids and plasma chamber components of multimegawatt ion sources are experimentally identified. Utilizing numerical techniques, a new accelerator geometry is designed to minimize the heat loading on various source components and maximize the beam brightness. Measurements on an ion source employing this accelerator geometry, during extraction of quasi‐steady‐state beam pulses of 3.2‐MW power, show significantly reduced heat loadings on all its components.

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.

Injection of energetic neutrals of hydrogen and deuterium has been used effectively to heat plasma in several fusion experiments. All applications to date have used neutral beams with pulse lengths in the subsecond range. The injected power extends into the megawatt level, approaching 10 MW in the case of PDX and D-III, with beam energies in the range of 20 to 80 keV. Key tokamak experiments are planned in which neutral beam injection will be applied at power levels extending toward the 25-MW range. A major difference in the injectors being planned for the future from those operating today lies in their need for longer pulse lengths. Extending the pulse lengths at higher power levels and a high beam brightness is the major goal of the neutral beam development laboratories. Other development areas include improving the atomic fraction in the beam to nearly 100%, increasing the beam brightness, and reducing the impurity content in the beam. Lifetime and reliability are also important considerations. This paper summarizes the advances made in each of these areas and elaborates on the work at Oak Ridge National Laboratory. Neutral injection parameters for a variety of fusion devices are also presented.

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%.

The energy spectrum and impurity content of a high‐power neutral beam are measured by implanting the beam into high‐purity silicon crystals. The depth distribution of the beam particles is then measured by secondary ion mass spectrometry (SIMS); the penetration depth is a function of the incident particle energy. This is one of the few measurement techniques that can determine neutral beam energy components directly. From the results, percentages of atomic and molecular ions in the source plasma can be inferred. Use of deuterium as the source gas provides insight into the role of residual hydrogen in the ion source and accelerating grids and in the SIMS analysis. The principal impurities are carbon and oxygen. Preliminary data indicate that carbon can originate from both methane and carbon monoxide, while oxygen can come from molecular oxygen, carbon monoxide, and water. Results are given and future plans are discussed.

The effects of geometrical parameters (aspect ratio, aperture size, gaps) and electrical parameters (voltage distribution, beam energy) on single‐beamlet profiles are investigated theoretically and experimentally on a two‐stage ion accelerator over both a broad range of beam conditions and a wide range of angles (0 to ±11.5°). In general, the intensity distribution is non‐Gaussian. Under optimum conditions, divergence angles half‐width at half maximum less than 0.5° could be achieved even with large holes (0.9 mm). Shaping the plasma grid reduced the non‐Gaussian wings and improved the beam transmission efficiency.

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.

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.

A centrifugal method for fractionating fine (

A high‐heat‐flux target has been developed for intercepting multimegawatt, multisecond neutral beams at Oak Ridge National Laboratory (ORNL). Water‐cooled copper swirl tubes are used for the heat transfer medium; these tubes exhibit an enhancement in burnout heat flux over conventional axial flow tubes. The target consists of 126 swirl tubes [each 0.95 cm in outside diameter (o.d.) with 0.16‐cm‐thick walls and ≊1 m long] arranged in a V shape and inclined with respect to the beam axis. In tests with the ORNL long‐pulse ion source (13×43‐cm grid), the target has handled up to 3‐MW, 30‐s beam pulses with no deleterious effects. The peak power density was estimated at ≊15 kW/cm2 normal to the beam axis (>5 kW/cm2 maximum on tube surfaces). The water flow rate through the tubes was 0.33 l/s (5.2 gal/min) per tube (axial flow velocity=11.6 m/s) with a corresponding pressure drop of 1.14 MPa (165 psi). To date, the target has absorbed an estimated 25 000 full‐power (≊3 MW) pulses for a cumulative time of ≊100 0...

The role of low‐velocity microparticles (diameters 109 V/m) are possible at the cathode surface. The emission current not only causes partial neutralization of the initial charge on the microparticle, but also raises the temperature (> 2000°K) of the particle surface. As a consequence, a significant increase in gas pressure (∼ 100 Torr) in the microvolume between the cathode and the particle is possible, resulting in a discharge between the two. Such a discharge could act as a trigger for the breakdown of the main gap. Other possible processes that could arise due to the onset of melting or boiling of the bombarded surface, and which may lead to breakdown of the entire gap, are also 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 .

Hydrogen ion beam optics in a two-stage linear acceleration system is studied by examining the beam divergence as a function of the voltage and gap distribution, the beam perveance, the background gas pressure, the aspect ratio, and the total accelerating energy (60-110 keV). The system consists of four electrodes with single, cylindrical, straight-bore apertures acting as an extraction-accel-decel column. An optimum relation between the field ratio and the extraction perveance is obtained from measurements for the minimum beam divergence condition. The HWHM divergence angle is0.3 degrees under optimum conditions. Qualitative agreement between the measurements and a previous theoretical study is noticed. A potential application of the results to high energy neutral beam injectors for fusion research is also discussed.