Search results for "plasma physics"
showing 10 items of 393 documents
Precision mass measurements using a penning trap and highly charged ions produced in an electron beam ion source
1997
A method for precision mass measurements in a Penning trap using highly charged ions produced in an electron beam ion source (CRYSIS) has been developed. The cyclotron frequencies for O8+, 7+, 6+, 5+ and Ar18+, 17+, 16+, 15+, 14+, 13+ ions have been determined by the excitation of the sum frequency v+ + v−. In addition to CRYSIS ions, H+, H2+ and He+ ions were produced by electron bombardment of the H2 rest gas or helium gas introduced through an UHV leak valve into an auxiliary ion trap (or a pre-trap). A technique for fast (seconds) interchanging of the ion species in the precision trap has been implemented to reduce the long term magnetic field drift.
Production of hydrogen negative ions in an ECR volume source: balance between vibrational excitation and ionization
2018
International audience; The operation of an ECR-driven (2.45 GHz) hydrogen negative ion source is studied. Electron densities and temperatures are investigated with electrostatic probes and negative ion densities are measured with laser photodetachment. Vacuum ultraviolet irradiance measurements are focused on molecular transitions to the ground state while high-resolution visible emission spectroscopy is used to study the transitions between excited states for both molecules and atoms. The standalone operation of the source is found to be more efficient in higher pressures (12 mTorr) where negative ion densities are as high as 4×109 cm−3. Further investigation on the operation of the sou…
VUV diagnostic of electron impact processes in low temperature molecular hydrogen plasma
2015
Novel methods for diagnostics of molecular hydrogen plasma processes, such as ionization, production of high vibrational levels, dissociation of molecules via excitation to singlet and triplet states and production of metastable states, are presented for molecular hydrogen plasmas in corona equilibrium. The methods are based on comparison of rate coefficients of plasma processes and optical emission spectroscopy of lowest singlet and triplet transitions, i.e. Lyman-band ($B^1\Sigma^+_u \rightarrow X^1\Sigma^+_g$) and molecular continuum ($a^3\Sigma^+_g \rightarrow b^3\Sigma^+_u$), of the hydrogen molecule in VUV wavelength range. Comparison of rate coefficients of spin-allowed and/or spin-f…
Gas sensing properties of multiwall carbon nanotubes decorated with rhodium nanoparticles
2011
International audience; In the present work, multiwalled carbon nanotubes were decorated with rhodium nanoparticles using a colloidal solution in the post-discharge of an RF atmospheric plasma of argon (Ar) or argon/oxygen (Ar:O 2). The properties of these hybrid materials towards the room temperature detection of NO 2 , C 2 H 4 , CO, C 6 H 6 and moisture were investigated and discussed in view of compositional and morphological studies. It was found that the presence of oxygen in the plasma treatment is essential to significantly enhance the gas response of Rh-decorated multiwalled carbon nanotubes and to avoid response saturation even at low gas/vapor concentrations. These desirable effec…
Depolarization Field in Thin Ferroelectric Films With Account of Semiconductor Electrodes
2005
Within the framework of the phenomenological Ginzburg-Landau theory influence of semiconductor electrodes on the properties of thin ferroelectric films is considered. The contribution of the semiconductor electrodes with different Debye screening length of carriers is included in the functional of free energy. The influence of highly doped semiconductor electrodes on the depolarization field and the film properties was shown to be great.
Third-harmonic generation in the skin layer of a hot dense plasma
2003
The third-harmonic generation of a pump wave, resulting from the electron-ion collision frequency dependence on the electric field in the skin layer of a hot dense plasma is investigated. The relation of the current third harmonic with the high-frequency field in the skin layer is established for arbitrary ratios of the electron-ion collision frequency to the field frequency. For arbitrary ratios of these two frequencies, the field structure inside the skin layer is determined, and the field of the wave irradiated by the plasma at tripled frequency, too, is calculated. It has permitted us to find the explicit dependencies of the third-harmonic generation efficiency on the plasma and pump fi…
Ferroelectric plasma source as an exciting source for rare earth elements
2003
The plasma sources basing on electrical discharges near the surfaces of ferroelectric materials have been described. It was shown that the ferroelectric plasma sources are especially useful for investigations in the field of optical spectroscopy. They have been found to be especially useful for exciting the atoms and ions or rare earth elements.
On the sensitivity of ion traps for spectroscopic applications
1979
Ba+ ions, created by surface ionization near one endcap of an rf quadrupole trap were slowed down by collisions with the background gas. At He pressures of 10−6 mbar or more 2% of the primary ions could be trapped. The sensitivity of ion detection by fluorescence radiation allows spectroscopic experiments, starting from less than 107 particles. The observation of the ground-state hyperfine splitting of137Ba+ is given as an example.
Photoelectron emission induced by low temperature hydrogen plasmas
2018
Experimental results of low temperature hydrogen plasma induced photoelectron emission measurements comparing two different plasma heating methods are summarized. By exposing the samples to the vacuum ultraviolet radiation of a filament-driven multi-cusp arc discharge ion source and a 2.45 GHz microwave-driven ion source, it has been measured that the total photoelectron emission from various metal surfaces is on the order of 1 A per kW of plasma heating power, which can be increased by a factor of 2–3.5 with a thin layer of alkali metal. The possible effects of the photoelectrons on the plasma sheath structure are studied with a 1D collisionless model extended to include the contribution o…
Study of Gasdynamic Electron Cyclotron Resonance Plasma Vacuum Ultraviolet Emission to Optimize Negative Hydrogen Ion Production Efficiency
2019
Negative hydrogen ion sources are used as injectors into accelerators and drive the neutral beam heating in ITER. Certain processes in low-temperature hydrogen plasmas are accompanied by the emission of vacuum ultraviolet (VUV) emission. Studying the VUV radiation therefore provides volumetric rates of plasma-chemical processes and plasma parameters. In the past we have used gasdynamic ECR discharge for volumetric negative ion production and investigated the dependencies between the extracted H$^-$ current density and various ion source parameters. It was shown that it is possible to reach up to 80 mA/cm$^2$ of negative ion current density with a two electrode extraction. We report experime…