J. H. Kamperschroer

Measurements of neutral beam species, impurities, spatial divergence, energy dispersion, pressure, and reionization using the TFTR U.S. Common Long Pulse Ion Source

Results are given from the first comprehensive and complementary measurements using the final production U.S. Common Long Pulse Ion Sources mounted on both the TFTR neutral beam test beamline and the TFTR neutral beam injection system, with actual tokamak experimental conditions, power systems, controls, and operating methods. The set of diagnostics included water calorimetry, thermocouples, vacuum ionization gauges, photodiodes, neutron, gamma‐ray, and charged particle spectroscopy, optical multichannel analysis, charge exchange spectroscopy, Rutherford backscatter spectroscopy, and implantation/secondary ion mass spectroscopy. These systems were used to perform complementary measurements of neutral beam species, impurities, spatial divergence, energy dispersion, pressure, and reionization. The measurements were performed either in the neutralizer region, where the beam contained both ions and neutrals, or in the region of the output neutral beam. The average of the neutral particle ratios in the range f...

Multiple track Doppler-shift spectroscopy system for TFTR neutral beam injectors

A Doppler‐shift spectroscopy system has been installed on the TFTR neutral beam injection system to measure species composition during both conditioning and injection pulses using short and long pulse ion sources. Two intensified vidicon detectors and two spectrometers are utilized in a system capable of resolving data from up to 12 ion sources simultaneously. By imaging the light from six ion sources onto one detector, a cost‐effective system has been achieved. Fiber optics are used to locate the diagnostic in an area remote from the hazards of the tokamak test cell allowing continuous access, and eliminating the need for radiation shielding of electronic components. Automatic hardware arming and interactive data analysis allow beam composition to be computed between tokamak shots for use in analyzing plasma heating experiments. Measurements have been made using lines of sight into both the neutralizer and the drift duct. Analysis of the data from the drift duct is both simpler and more accurate since only neutral particles are present in the beam at this location. Comparison of the data taken at these two locations reveals the presence of partially accelerated particles possessing an estimated 1/e half‐angle divergence of 15° and accounting for up to 30% of the extracted power from the short pulse ion sources. Operation with long pulse ion sources indicates a higher atomic composition, fewer partially accelerated particles, and somewhat reduced neutralization line densities.

TFTR neutral beam injected power measurement

Energy flow within TFTR neutral beamlines is measured with a waterflow calorimetry system capable of simultaneously measuring the energy deposited within four heating beamlines (three ion sources each), or of measuring the energy deposited in a separate neutral beam test stand. Of the energy extracted from the ion source on the well‐instrumented test stand, 99.5±3.5% can be accounted for. When the ion deflection magnet is energized, however, 6.5% of the extracted energy is lost. This loss is attributed to a spray of devious particles onto unmonitored surfaces. A 30% discrepancy is also observed between energy measurements on the internal beamline calorimeter and energy measurements on a calorimeter located in the test stand target chamber. Particle reflection from the flat plate calorimeter in the target chamber, which the incident beam strikes at a near‐grazing angle of 12°, is the primary loss of this energy. A slight improvement in energy accountability is observed as the beam pulse length is increased...

Doppler-shifted neutral beam line shape and beam transmission

Analysis of Doppler‐shifted Balmer‐α line emission from the Tokamak Fusion Test Reactor’s (TFTR) neutral beam injection systems has revealed that the line shape, which is a direct measure of the velocity distribution function, is well approximated by the sum of two Gaussians, or, alternatively, by a Lorentzian. For the sum of two Gaussians, the wide‐divergence part of the distribution contains 40% of the beam power and has a divergence five times that of the narrow part. Assuming a narrow 1/e‐divergence of 1.3° (based on fits to the beam shape on the calorimeter), the wide part has a divergence of 6.9°. The entire line shape is also well approximated by a Lorentzian with a half‐maximum divergence of 0.9°. Up to now, most fusion neutral beam modelers have assumed a single Gaussian velocity distribution, at the extraction plane, in each direction perpendicular to beam propagation. This predicts a beam transmission efficiency from the ion source to the calorimeter of 97%. Waterflow calorimetry data, however,...

Observation of Doppler shifted Tα emission from TFTR tritium neutral beams

195 tritium ion source shots were injected into Tokamak Fusion Test Reactor (TFTR) high power plasmas during December 1993–March 1994. In addition, four highly diagnosed pulses were fired into the calorimeter. Analysis of the Doppler shifted Tα emission of the beam in the neutralizer has revealed that the extracted ion compositions for deuterium and tritium are indistinguishable: 0.72±0.04 D+; 0.22±0.02 D+2; 0.07±0.01 D+3 compared to 0.72±0.04 T+; 0.23±0.02 T+2; 0.05±0.01 T+3. The resultant tritium full‐energy neutral fraction is higher than for deuterium due to the increased neutralization efficiency at lower velocity. To conserve tritium, it was used only for injection and a few calorimeter test shots, never for ion source conditioning. When used, the gas species were switched to tritium only for the shot in question. This resulted in an approximately 2% deuterium contamination of the tritium beam and vice versa for the first deuterium pulse following tritium. Data from the calorimeter shots indicate th...

Measurement of thermal ion profiles in TFTR neutral beamlines

A technique is described whereby the ion dumps inside the TFTR Neutral Beam Test Stand were used to measure thermal profiles of the full‐, half‐, and third‐energy ions. 136 thermocouples were installed on the full‐energy ion dump, allowing full beam contours. Additional linear arrays across the widths of the half‐ and third‐energy ion dumps provided a measure of the shape, in the direction parallel to the grid rails, of the half‐ and third‐energy ions, and, hence, of the molecular ions extracted from the source. As a result of these measurements, it was found that the magnet was more weakly focusing, by a factor of 2, than expected, explaining past overheating of the full‐energy ion dump. Hollow profiles on the half‐ and third‐energy ion dumps were observed, suggesting that extraction of D+2 and D+3 is primarily from the edge of the ion source. If extraction of half‐energy ions is from the edge of the accelerator, a divergence parallel to the grid rails of 0.6°±0.1° is deduced. It is postulated that a non...

Operation of a TFTR ion source with a ground potential gas feed into the neutralizer

TFTR long pulse ion sources have been operated with gas fed only into the neutralizer. Gas for the plasma generator entered through the accelerator rather than directly into the arc chamber. This modification has been proposed for tritium beam operation to locate control electronics at ground potential and to simplify tritium plumbing. Source operation with this configuration and with the nominal gas system that feeds gas into both the ion source and the center of the neutralizer are compared. Comparison is based upon accelerator grid currents, beam composition, and neutral power delivered to the calorimeter. Charge exchange in the accelerator can be a significant loss mechanism in both systems at high throughput. A suitable operating point with the proposed system was found that requires 30% less gas than used presently. The extracted D+, D+2, and D+3 fractions of the beam were found to be a function of the gas throughput; at similar throughputs, the two gas feed systems produced similar extracted ion fr...

Near‐field characterization of hydrogen and helium operation on the TFTR diagnostic neutral beam

An optical multichannel analyzer has been used to measure beam divergence and composition. This measurement is usually performed near the center of the neutralizer or beyond the magnet. In the past, these locations suffered difficult beam composition analysis and low light intensity, respectively. It has been determined that the light emission is relatively independent of neutralizer line density in the near field, allowing near‐field measurements to overcome both difficulties. At optimum perveance, but under conditions of high gas throughput, the helium 1/e divergence angle was measured to be 1.5°. Further investigation found that the divergence decreased with gas throughput down to 1.25°. Minimum divergences for the full‐, half‐, and third‐energy hydrogen components were 1.1°, 1.2°, and 1.4°, respectively. Relative neutral hydrogen particle fluxes available for injection into TFTR are a function of perveance. At maximum perveance, the full‐, half‐, and third‐energy atom fractions were 0.25±0.04, 0.5±0.0...

Low Z impurity ion extraction from Tokamak Fusion Test Reactor ion sources

Tokamak Fusion Test Reactor (TFTR) deuterium neutral beams have been operated unintentionally with significant quantities of extracted water ions. Water has been observed with an optical multichannel analyzer. These leaks were thermally induced with the contamination level increasing linearly with pulse length. Up to 6% of the beam current was attributed to water ions, corresponding to an instantaneous value of 12% at the end of a 1.5 s pulse. A similar contamination is observed during initial operation of ion sources exposed to air. Operation of new ion sources typically produces a contamination level of ∼2%, with cleanup to undetectable levels in 50–100 beam pulses. Approximately 90% of the water extracted from ion sources with water leaks was deuterated, implying that there is the potential for tritiated water production during TFTR’s forthcoming DT operation. It is concluded that isotope exchange in the plasma generator takes place rapidly, most likely as the result of surface catalysis. The primary c...

Diagnostics for TFTR neutral beam species measurement

Five diagnostic systems were used for initial species measurements during tokamak fusion test reactor (TFTR) neutral beam test stand operations involving four ion sources, as well as several different configurations and operating conditions. Initial results were obtained for total neutral species fractions at the beamline input and the beamline output, differential radial profiles of species fractions, angular divergences of species components, species radial power density profiles, and beam impurity components for various conditions.