Vadim Dudnikov

Surface Plasma Sources with Helicon Plasma Generators

A Surface Plasma Source (SPS) with plasma generation by a saddle type antenna is discussed. The following features of the helicon discharge with a saddle type antenna in magnetic field are identified: efficient plasma generation in resonant condition, low gas density, strong separation of plasma from the wall, possibility to control plasma flux distribution by magnetic field configuration. Applications of saddle type antenna in SPS for accelerators for Homeland Security and for Neutral Beam Injectors (NBI) are considered.

Relevance of Volume and Surface Plasma Generation of Negative Ions in Gas Discharges

The relative contribution of volume and surface‐plasma generation in emission of H− ions in gas discharge sources is analyzed. At the present time, it is generally accepted that surface‐plasma generation of extracted H− ions dominates over volume processes in discharges with admixture of cesium or other catalysts with low ionization potential. We will attract attention to the evidence, that surface‐plasma generation can be significantly enhanced in high density discharges without cesium after electrode activation by high temperature conditioning in discharge. With this optimization of conditions for surface‐plasma generation of emitted H−, an emission current density was increased up to ∼1 A/m2 in discharges without cesium. Diffusion of impurities with low ionization potential can be the reason for the observed enhancement of H− emission. Such optimization allows considerable improvement of H−/D− source characteristics. Volume generation of extracted H− in high density discharges is suppressed by the high...

Compact surface plasma sources for heavy negative ion production

Features of a compact surface plasma source designed for heavy negative ion beam production are considered. Discharges in crossed E×B fields with hollow cathodes were used for efficient plasma generation. Production of heavy negative ion beams by plasma interaction with the surface of spherical focusing emitters made of different materials, such as copper and lanthanum hexaboride, with cesium catalysis are presented. The dynamics of emitter activation is discussed. dc ion beams with current up 0.9 mA have been extracted from the compact surface plasma sources with a 12-mm-diam LaB6 emitter and a emission aperture of 3 mm diam. Minimizing plasma and gas thickness between emitter and emission aperture is essential for minimizing negative ion destruction and maximizing high intensity beam production. A small mass analyzer and secondary ion mass spectroscopy were used to quantify boron ion yield. Presence of atomic and molecular boron negative ions is confirmed. The estimated emittance of the 0.5 mA heavy neg...

Beam-Based Production of 178m2Hf

In this study, the production yield for the reaction 176Yb(9Be, α3n)178Hf was explored using the FN tandem injected superconducting LINAC at SUNY at Stony Brook at a 9Be energy of 65 MeV. By comparing the experimental yield of 178Hf ground state γ rays with those of 180W as a function of energy, the cross section for production of the incomplete fusion γ rays in 178Hf was evaluated. Coincidence measurements were made to get information about the population strength of the high spin states in 178Hf. From these measurements, the maximum cross section for the reaction 176Yb(9Be, α3n)178m2Hf is estimated to be no larger than 5 mb.

An intense, compact fourth-generation positron source based on using a 2 MeV proton accelerator

A method of producing an intense source of e+’s that uses the internal pair production decay of the 6.05 MeV, 0+ first excited state of O16 is described. The first excited state decays overwhelmingly by this process with the competing decays of double gamma-ray emission and atomic electron internal conversion contributing about 1 decay in 104. The most effective way to produce this excited state of 16O in terms of compactness, power consumption, and general ease of operation is to use the strong proton-induced resonance on F19 at 1.89 MeV. This resonance is the most favorable low-energy proton resonance in F19 for populating the 6.05 MeV, 0+ state. We predict low-energy e+ beams with intensity of 107–108/s by using off-the-shelf accelerator technology producing a 2 MeV proton beam with average currents of 1 to 5 mA.

Detection of Hidden Explosives Using Resonant Gamma Rays From In‐Flight Annihilation of Fast Positrons

Gamma rays with tunable energies can be produced by the in‐flight annihilation of fast positrons. The kinetic energy of the positron beam determines the gamma‐ray energy of annihilation photons emitted in a narrow cone in the forward direction. These photons can be used for nuclear resonant fluorescence determination of explosive materials rich in 14N selecting gamma rays with energies that match excited states in 14N and then observing the emitted nuclear fluorescence.

Surface-plasma generation of negative ions in gas discharges without cesium

Surface-plasma generation (SPG) of negative ions in gas discharges is extremely sensitive to small admixture of uncontrolled impurities. An efficiency of SPG was greatly improved by injection into discharge a small amount of cesium or other substances with low ionization potential. For explanation of anomalistic H− generation in discharges without the addition of cesium it is important to identify the sources of important impurities. Generation of H− ion in different ion sources is analyzed. Sources of impurities catalyzing SPG are proposed. A higher probability of cold H− extraction is outlined and explained. A proposal for enhanced H− generation in discharges without cesium is presented. Further experiments for identification of the dominant mechanism of H− generation are discussed.

Relative Contribution of Volume and Surface-Plasma Generation of Negative Ions in Gas Discharges

Surface-plasma generation of extracted H-ions in gas discharges without the addition of cesium is analyzed. At the present time, it is common consensus that surface-plasma generation of extracted H-ions dominates above volume processes in discharges with the admixture of cesium or other catalysts with low ionization potential. We will present evidence that surface-plasma generation can be enhanced in high density discharges without cesium after electrode activation by high temperature conditioning in the discharge. The diffusion of impurities with low ionization potential is the presumed cause of the observed H-emission enhancement. For the effective generation of H-ion beams in discharges without cesium, it is necessary to optimize surface-plasma generation of extracted H-ions. Such optimization allows considerable improvement of H-/D-sources characteristics.

Laser Triggered Synchronizable X‐Ray System for Real Time Study of Shock Waves in Condensed Materials

A laser excited, sub‐nanosecond, pulsed, electron beam system is described. The system consists of a high voltage pulser and a coaxial laser triggered gas or liquid spark gap. The spark gap discharges into a pulse forming line designed to produce and maintain a flat voltage pulse for 1 ns or greater duration on the cathode of a photodiode. A synchronized pulsed laser is used to illuminate the photo‐cathode to produce an electron beam with very high brightness, short duration and current at or near the space charge limit. The system can be configured to operate at energies from less than 500 keV to 1 MeV and pulse width from less than 10 ps to 1000 ps and higher. This laser controlled electron beam system can be used to produce synchronizable monochromatic fluorescent or broad spectrum Bremsstrahlung x‐rays for shock wave studies.

Optimization of surface plasma sources for efficient production of negative ions with high emission current density

The main mechanism of negative ion formation in a Surface Plasma Source (SPS) is secondary emission of sputtered and scattered particles accompanied by capture of electrons from the electrodes. In the first, pulsed, versions of the SPS, adding a small amount of cesium increased the emission current density for light ions up to 3.7 A/cm2 with a flat emitter and up to 8 A/cm2 after optimization of geometrical focusing. Since this power density was too high for DC operation, LBL developed a large volume SPS with a hot cathode discharge, a large emitter-emission aperture gap and low emission current density. The LBL type of SPS was used for some accelerators and for heavy negative ion production with emission current density of 10 mA/cm2. Researchers at Budker Institute of Nuclear Physics (BINP) developed a small SPS optimized for long time DC operation. In the BINP source, DC H− current up to 2.5 mA and heavy ion current up to 1 mA have been extracted from a 1 mm diameter aperture using an improved SPS that ...