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In this Tutorial, surface and double charge exchange negative ion sources for producing negative ion beams of different ion species will be described. The need for negative ions as the beam particles of tandem Van de Graaf accelerators and that for charge exchange injection of hydrogen negative ions into high-energy proton accelerators requires the development of these ion sources, which are then enlarged to generate ampere level broad beams to heat up, after neutralization, the fusion experiment plasmas confined in magnetic field. The physical mechanisms leading to the formation of various negative ion species, such as hydrogen, helium, alkali metals, and halogens will be presented, and the ion source designs are analyzed based on the knowledge of fundamental processes related to negative ion formation and destruction. The use of negative ion sources in accelerators, nuclear fusion research, technology, and medicine will also be presented. [ABSTRACT FROM AUTHOR]

The AC component of a beam current extracted from a negative hydrogen (H−) ion source was detected through a 0.1 mm wide, 66.5 mm long entrance slit to observe the spatial distribution. An internal antenna type multicusp source driven by a 2 MHz radio frequency (RF) power delivered beams to an electrostatic accelerator coupled to a pair of magnetic lenses. The local beam intensity measured by a Faraday cup after the entrance slit exhibited an oscillation showing two main frequency components: the RF power supply frequency and the frequency two times the driving RF. The frequency spectrum of the detected signal showed sharp peaks at 2 MHz, 4 MHz, and 6 MHz as well as at 3 MHz and 5 MHz. A 1 mm displacement of the Faraday cup slit position from the center of the beam axis increased the oscillation amplitude, corresponding to a larger amplitude of the AC component at the beam edge. [ABSTRACT FROM AUTHOR]

Angle-resolved energy distribution functions of positive and negative hydrogen ions produced from a rough-finished Si surface under 1 keV proton irradiation have been measured. The corresponding distribution from a crystalline surface and a carbon surface are also measured for comparison. Intensities of positive and negative ions from the rough-finished Si are substantially smaller than those from crystalline Si. The angular distributions of these species are broader for rough surface than the crystalline surface. No significant temperature dependence for positive and negative ion intensities is observed for all samples in the temperature range from 300 to 400 K. [ABSTRACT FROM AUTHOR]

Energy straggling in a charge exchange cell, which is frequently used for negative ion production, was studied experimentally and compared with the results of theoretical evaluation. The change of the energy spectrum of a He+ beam due to charge exchange processes in argon gas was measured in the energy range of 2–6 keV. Energy straggling by multiple collisions is expressed by the energy loss formula due to inelastic and elastic processes. The impact parameter is related to the elastic scattering angle, and the geometry of the charge exchange cell and other components of the beam transportation system determines the maximum acceptable scattering angle. The energy spread was evaluated taking the integral limit over the impact parameter into consideration. The theoretical results showed good agreement with those of actual measurement. [ABSTRACT FROM AUTHOR]

The effect upon extraction of negative hydrogen ions (H-) due to electric field near the extractor hole of a H- source is studied experimentally and theoretically. Probe measurements show that the extraction electric field penetrates into the plasma in the region near the extractor hole. Based on this observation a three-dimensional H- trajectory calculation that takes into account the local electric field distribution near the plasma electrode has been carried out. The validity of the trajectory calculation was examined by comparing the results with experimentally measured changes in H- current detected by a Faraday cup due to irradiation of a pulse laser beam in the region close to the extractor hole. The calculation results qualitatively explain the changes in H- current observed in the experiment. The calculation results also predict that the amount of H- current passing through the extractor hole changes with the electric field: the penetration of the electric field substantially enhances the H- extraction current, because it produces an electric field to attract H- toward the extraction hole. [ABSTRACT FROM AUTHOR]

Preliminary test bench results to study the beam quality extracted from a compact multicusp He+ ion source for He- beam production are reported. The bench is a part of the beam diagnostic system equipped with energy analyzers, emittance meters, focusing beam optics, an alkali-metal charge-exchange cell, a neutral particle energy analyzer, a double focusing magnetic momentum analyzer, a postaccelerator, and a drift tube. Utilizing the front end of the bench, the transverse emittance and the energy distribution function of a He+ beam extracted from a multi-line-cusp magnetic-field ion source 8 cm in diameter and 9 cm in length were measured. The results indicated that improvements in both formation of the plasma meniscus and reinforcement of pumping in the extraction region are necessary to produce a higher brightness He+ beam. [ABSTRACT FROM AUTHOR]

A method to estimate H- density and velocity in the extraction region of a negative ion source plasma without a Langmuir probe is developed. It utilizes the laser photodetachment with a Faraday cup (PD-FC). The H- parameters estimated by PD-FC are compared to the results measured by laser-photodetachment with a Langmuir probe (PD-LP). The result shows that H- velocity estimated by PD-FC is in good agreement with the PD-LP result. Meanwhile, H- density estimated by PD-FC is twice larger than the PD-LP result. Though a more detailed research, including more effects that are ignored in this study, is needed for H- density measurement, PD-FC will be a very useful tool for H- measurements especially near an extraction hole in negative ion sources. [ABSTRACT FROM AUTHOR]

Various probing beams have been developed and used for plasma diagnostics in thermonuclear fusion research for magnetic confinement The required beam current, beam size, energy, beam characteristics such as divergence, energy spread, and emittance, etc., as well as ion species are different depending on the purpose of diagnostics, target plasma size and parameters. Hydrogen beams are used for charge-exchange recombination spectroscopy (CHERS) and motional stark effect (MSE) spectroscopy. Suitable beam energy for CHERS ranges in the area of 50 keV/amu, and a small beam divergence is required for MSE measurements. Heating beams are often used as diagnostic beams by sharing. Neutral lithium probing beams have been used as effective tools for measurement of density and fluctuations. A heavy ion beam probe (HIBP), made from alkali metal ions, is injected directly without neutralization to measure plasma potential and density, as well as their fluctuations. Recent progress in magnetic fusion experiments has resulted in advancement of the development of negative ion sources, such as He¯ and Li¯ sources for alpha-particle measurement, because of their advantages with regard to efficient neutralization in the high-energy region, and an Au¯ source for HIBP with the application of tandem acceleration. [ABSTRACT FROM AUTHOR]

The wall production contribution to the negative hydrogen ion formation in multicusp ion sources has been investigated using the photodetachment diagnostic (for determining the negative ion density and temperature), negative ion and electron extraction, and vacuum ultraviolet (VUV) emission spectroscopy. The wall material was modified either by depositing thin films from filaments made of different material or by depositing fresh material of the same filament. Thus we show that a fresh tantalum film leads to enhanced negative ion density and enhanced temperature of the hot negative ion population. The slow poisoning effect due to argon additive also indicates the presence of the wall contribution to H- formation. The study of the VUV spectra with different wall materials indicates the presence of vibrationally excited states of H2. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We study influence of electric field penetration into H- ion source plasma with three-electrode beam extraction system. Clear change in the plasma potential due to the field penetration is observed in case of low gap voltage between a plasma electrode and an extraction electrode. Influence of lens voltage on the second electrode, which is normally utilized to focus the extracted beam, on ion source plasma is evaluated separating contributions of H- density in the plasma and extraction probability of H- ions from the plasma by two kinds of photodetachment techniques. In our operation condition, we found that the lens voltage is also useful to enhance the H- density in the plasma, though it negatively affects the extraction probability. [ABSTRACT FROM AUTHOR]

We investigate influence of H- initial transport direction and kinetic energy on H- extraction probability with three-dimensional Monte Carlo calculation. As a result, lower energy H- ions are strongly trapped by the electrical potential structure, so that initial condition of H- transport direction is cancelled by alignment of the electric field; thus, it has lower influence for H- extraction probability. Besides, the potential hill induced by the beam extraction voltage more effectively enhances H- extraction probability for the lower energy H- ions. The correlation between the magnitude of the local plasma potential near the extraction region and the mean velocity of H- ions in the region should determine the H- extraction probability from the ion source. [ABSTRACT FROM AUTHOR]

A strongly focusing high-intensity He+ ion source equipped with three concave electrodes has been designed and constructed as the beam source for a high-energy He0 neutral beam probe system to diagnose fusion-produced alpha particles in thermonuclear fusion plasmas. The reduction of heat load onto the concave extraction electrodes is particularly important for a long pulse operation, as the heat load deforms the electrodes and thus the beam focal length. The effects on the arc efficiency (beam current/arc power) of the ion source due to the discharge filament structure (straight-type and L-shape-type filaments), size (filament diameters of 2 and 1.5 mm), number, and the locations have been studied. Choice of the appropriate filament structure improved the arc efficiency by 17%. [ABSTRACT FROM AUTHOR]

Performance of a compact He+ ion source was investigated before installing it to the experiment system developed for studying the efficiency of autodetachment neutralization from He- to He0. Dependence of the extracted ion current upon the plasma parameters and that upon the extraction voltage indicated that the source performance was limited by space charge effect. The beam emittance was measured with a multislit system for various operation conditions. The experimentally determined emittance agreed well with the emittance obtained from ion trajectories calculated with input plasma parameters measured by a Langmuir probe. The beam current density of 60 mA/cm2 and the emittance of less than 25π mm mrad are expected to deliver enough current to the downstream of the He- neutralizer system to clarify factors affecting the final He0 intensity. [ABSTRACT FROM AUTHOR]

A strongly focusing high-intensity He+ ion source has been designed and constructed as a beam source for a high-energy He0 beam probe system for diagnosis of fusion produced alpha particles in the thermonuclear fusion plasmas. The He+ beam was extracted from the ion source at an acceleration voltage of 18–35 kV. Temperature distributions of the beam target were observed with an IR camera. The 1/e-holding beam profile half-width was about 15 mm at optimum perveance (Perv) of 0.03 (Ibeam=2.4 A). A beam current about 3 A was achieved at an acceleration voltage of 26.7 kV with an arc power of 10 kW (Perv=0.023). [ABSTRACT FROM AUTHOR]

The increase of H[sup -] current is observed, when the tantalum filaments are used instead of the tungsten filaments. In terms of the production rate of vibrational populations of hydrogen molecules with tungsten and tantalum filaments, we measured the Werner and Lyman emission bands (90-170 nm) the vacuum ultraviolet region to obtain the spectra of molecular hydrogen in an ion source, and observed a significant difference of spectrum between the two cases. From the pressure dependence, it is found that the production rate of vibrationally excited hydrogen molecules is well correlated with the H[sup -] density measured by photodetachment in hydrogen plasmas. [ABSTRACT FROM AUTHOR]

The gas mixture effect upon the negative ion temperature in negative ion sources has been studied by the laser photodetachment technique. The ion source is operated at hydrogen pressure from 0.05 to 2.0 Pa. Then argon gas is added up to 100% of the hydrogen pressure. Maximum enhancement of the negative ion density is observed at around a 20%-40% argon to hydrogen mixture in the low hydrogen pressure region. The recovery time for the electron current signal after photodetachment becomes longer when more argon is added to hydrogen plasmas, indicating a lower negative ion temperature. [ABSTRACT FROM AUTHOR]

Using the photodetachment technique we investigated the hydrogen negative ion density in the extraction region of a magnetically filtered multicusp ion source when argon is added to hydrogen. We found that the negative-ion density goes up at most by a factor of 1.5 when argon is added to low base hydrogen pressure (0.05 or 0.1 Pa), but goes down when argon is added to higher initial hydrogen pressure (0.5 or 1 Pa). Adding argon did not enhance the Werner and Lyman bands in the vacuum ultraviolet, which indicates that argon addition does not increase the production rate of vibrationally excited H[sub 2] molecules. The increase of the negative-ion density by adding argon into a low-pressure hydrogen discharge is probably due to the increase of the low-energy electron density. [ABSTRACT FROM AUTHOR]

The temporal change of the H[sup -] beam current extracted from a volume-production-type negative ion source by injecting a Nd-YAG laser beam into the ion source plasma was measured. The measured change was about 0.3% of the dc H[sup -] beam current. The validity of the method was confirmed using Ar plasma which showed no photodetachment signal. The contribution of the local H[sup -] density upon the extracted beam was investigated by changing the distance between the center of the laser beam and the plasma grid. The result showed that the contribution took the maximum at about 8 mm distance from the laser beam center to the plasma grid surface. [ABSTRACT FROM AUTHOR]

Focuses on development of a filament-type helium ion source. Alpha particle diagnostics; Test beam for electrostatic quadrupole transport experiments; Extracted beam current and emittance; Plasma parameters.

Attempts to measure spatial distributions of the current density of the ion beams extracted from an electron-stimulated-desorption-type powdery sample ion source. Localized ion emission at the powder surface; Deflection of the beam in the horizontal direction.

Describes the development of a double-charge exchange He[sup -] ion source. Extraction of a He[sup +] beam at a low energy; Relationship between the discharge current of the ion source and electrostatic field; Improvement of the ion source through the use of an active transport system for the He[sup +] beam.

A plasma sputter negative ion source was evaluated for its applicability for measuring the plasma potentials in fusion devices. Both the beam current density and the beam energy spread are key issues for this application. The energy spectra of self-extracted Au[sup -] beams from the source were measured under the condition of a constant work function of the production surface. The FWHM increases from 3 to 9 eV monotonically as the target voltage increases from 50 to 300 V, independently from the target surface work function of 2.2-3 eV. [ABSTRACT FROM AUTHOR]

Negative sodium ions and negative dimer ions of sodium are extracted from a sodium plasma. The extraction characteristics of Na[sup -] and Na[sup -, sub 2] from a low power discharge (about 1 W) through a single aperture (φl.5 mm) are described. Both extracted currents of Na[sup -] and Na[sup -, sub 2] increase with the temperature of the heat shield inside the discharge chamber. The current ratio of Na[sup -] to Na[sup -, sub 2] is almost constant independent of discharge voltage. By increasing the discharge power, the value of the bias voltage of the plasma electrode that gives the optimum extraction currents of Na[sup -] and Na[sup -, sub 2] increases. The extracted current of Na[sup -, sub 2] is lower than that of Na[sup -] by two orders of magnitude. [ABSTRACT FROM AUTHOR]

A beam of negative lithium ions (Li[sup -]) with a current density as high as 3 × 10[sup -5] A/cm² was extracted from a 5 cm diam, 7 cm long multicusp ion source. The extracted Li[sup -] current was correlated to the plasma temperature and density measured with Langmuir probes heated to avoid Li condensation. The neutral lithium flux from the ion source was measured with a Langmuir-Taylor detector, and it showed a linear correlation with the extracted Li[sup -] current. Further increase in efficiency to produce Li[sup -] current is expected by improving the plasma confinement of the ion source. [ABSTRACT FROM AUTHOR]