Journal of Physics B: Atomic and Molecular Physics, 1974
Excitation of the ground state vibrational modes of CO2 has been studied in an electron impact ex... more Excitation of the ground state vibrational modes of CO2 has been studied in an electron impact experiment in the energy range 3-5 eV. A series of oscillations is observed in the excitation functions of the elastic and vibrational channels which was previously assumed to result from vibrational excitation of an intermediate negative ion (shape resonance). The oscillations were seen to move towards higher energies with increasing vibrational quantum number when observed in the symmetric stretch channel. This leads us to propose that the structure is due to an interference effect in the negative ion wavefunction (boomerang model).
Journal of Physics B: Atomic, Molecular and Optical Physics, 2002
ABSTRACT We report measured absolute single and double charge-exchange cross sections for 3He2+ o... more ABSTRACT We report measured absolute single and double charge-exchange cross sections for 3He2+ on CO at ion impact energies between 1 and 14 keV (velocities between 254 and 949 km s-1). A retarding-field method is used for charge-state analysis of the ion beam after traversing the target gas cell. Cross sections are determined from absolute measurements of current ratios and the CO target gas pressure. For testing the experimental technique, proton-electron capture cross sections are measured at energies between 2.5 and 7 keV. The measured He2+ and H+ cross sections are compared to available data.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2003
ABSTRACT We report measured absolute single and double charge-exchange cross sections (CSs) for F... more ABSTRACT We report measured absolute single and double charge-exchange cross sections (CSs) for Feq+ ions with He at the ion impact energy of 7.0 × q keV for q = 5–13. The range of ion velocities is 350 km s−1 for q = 5, to 560 km s−1 for q = 13, comparable to typical solar wind velocities. A retarding-field method is used for charge-state analysis of the ion beam after traversing the stationary target gas cell. The CSs are determined from absolute measurements of the ion currents and He target gas pressure.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2012
Here we report on the first dual-beam experiment employing a hydrogen atom beam for sample exposu... more Here we report on the first dual-beam experiment employing a hydrogen atom beam for sample exposure and an ion beam for analysis, enabling in situ and real time studies of hydrogen atom interaction with materials. The erosion of an amorphous hydrogenated carbon (a-C:H) layer by deuterium atoms at 580 K sample temperature was studied and the uptake of deuterium during the erosion process was measured in real time. The deuterium areal density increased at the beginning to 7.3×10 15 at.cm-2 , but then stabilized at a constant value of 5.5×10 15 at.cm-2. Formation of a polymerlike deposit on an a-C:H layer held at room temperature and subjected to the deuterium atom beam was observed and also studied in-situ. For both erosion and deposition studies an a-13 C:H layer on top of a Si substrate was used as a sample, making the experiments isotopically fully specified and thereby differentiating the deposited from the original layer and the interacting D atoms from H atoms present in the layer and in the residual vacuum. From the deposition study it was shown that carbon in the deposited layer originates from carbon-carrying species in the background vacuum that interact with hydrogen atoms. The areal density of the carbon at the surface was determined from the energy shift of the Si edge in the RBS spectrum. The cross-section for 7 Li on D at 4.3 MeV Li ion energy and at a recoil angle of 30 o was also determined to be (236±16)×10-27 cm 2 /sr. This is a factor of 3±0.2 times higher than the Rutherford elastic cross-section.
The role of neutral molecules in edge plasma is discussed with special emphasis on the vibrationa... more The role of neutral molecules in edge plasma is discussed with special emphasis on the vibrationally excited hydrogen. Neutral molecules are formed mostly by surface processes on the walls and then released to the edge plasma where they take part in volumetric reactions with other particles. Typically these molecules are formed in excited states and data are needed for their reactions on the wall and in the volume. Processes in edge plasma determine particle and energy flux what is especially critical issue in tokamak divertor region. Various cross sections and reaction rates are needed for modelling edge plasma and its interaction with walls.
We present the numerical model for determining particle concentration in partially dissociated lo... more We present the numerical model for determining particle concentration in partially dissociated low pressure neutral hydrogen gas in a metal reaction cell where flowing gas is partially dissociated by a hot tungsten filament. Neutral hydrogen atoms and molecules in different vibrational states are taken into account. Available parameters for relevant surface processes (thermal dissociation, atom recombination, adsorption/desorption and vibrational relaxation) are used as initial input parameters. Calculated particle concentration distributions are compared to experimental data and qualitative agreement is obtained. Such a model is needed as a tool for indepth understanding and interpretation of results from our specific experiment and thus in turn enabling checking and evaluating rates and cross sections for the above surface processes.
Plasma facing components in ITER and in future fusion reactors will be exposed to 14 MeV neutrons... more Plasma facing components in ITER and in future fusion reactors will be exposed to 14 MeV neutrons producing radiation defects in the bulk of materials. Tungsten is one of most favorable materials for fusion applications at the present time. Hydrogen solubility in tungsten is very low and retention of hydrogen isotopes in tungsten is determined by trapping in defects. Therefore, radiation defects can play an important role in tritium retention in tungsten. To simulate neutron damage irradiation by 20 MeV W 6+ ions have been used in this work. The irradiation of W with W ions was done at IPP. After pre-irradiation with W ions at different damage levels, polycrystalline tungsten samples were exposed to low-energy deuterium (D) plasma at IPP [1] and to atomic D beam at Jožef Stefan Institute [2] in a wide range of temperatures between 300 and 800 K. D depth profiles were measured by nuclear reaction analysis (NRA) and total D retention by thermal desorption spectroscopy (TDS). NRA data ...
We have measured the cross-section for the 1 H( 7 Li,[FORMULA]) 4 He reaction at lithium beam ene... more We have measured the cross-section for the 1 H( 7 Li,[FORMULA]) 4 He reaction at lithium beam energies from 0.34 to 1.05MeV. Hydrogen was forced by diffusion into Pd and PdAg alloy foils. A large electron screening effect was observed only when foils were under tensile stress. A dependence of the screening potential on hydrogen concentration or Hall coefficient of the metallic host could not be established.
Thermal desorption of deuterium from mixed C:W and C:W:Al layers was studied in situ by Nuclear R... more Thermal desorption of deuterium from mixed C:W and C:W:Al layers was studied in situ by Nuclear Reaction Analysis (NRA) and mass spectrometry during linear sample heating. The deuterium thermal desorption was correlated by decrease of the proton signal at single 3 He probing beam energy (2.5 MeV) and increase of the masses 3 and 4 in the mass spectrum. Main deuterium desorption in C:W mixed layer takes place at relatively high temperature, around 1000 K, what is higher than typical desorption temperatures for W and amorphous deuterated carbon films. The deuterium depth profile in the layer was measured before and after heating and some deuterium was found to remain after the experiment. Deuterium atom absorption in multilayer film (200 nm of C on top of 500 nm W on graphite substrate) exposed to deuterium atom beam for one day was also studied by the same procedure.
The radiative lifetime of the 2s22p2 S0 level in O 2+ has been measured via the magnetic-dipole (... more The radiative lifetime of the 2s22p2 S0 level in O 2+ has been measured via the magnetic-dipole (M1) transition 2s2p S0 ! P1 at 232.17 nm. Data were recorded in a Kingdon trap, with the source of ions a 14 GHz electron cyclotron resonance ion source. The lifetime of the S0 level was found to be 540 27 ms. This is in good agreement with a previous measurement and with a number of theoretical calculations. Metastable lifetimes, when combined with collisional excitation rates, can provide a diagnostic for electron density Ne in a stellar or solar plasma. Subject headings: atomic data — atomic processes
The influence of light hydrocarbons on vibrational excitation of H2 generated in a special source... more The influence of light hydrocarbons on vibrational excitation of H2 generated in a special source of excited molecules has been studied. Vibrational spectrometer based on analysis of variation of H yield produced by dissociative electron attachment in 0-5 eV electron energy range is employed. Molecule dissociation on the hot tungsten filament and atom recombination on cooled walls is used for production of molecular excitation in the source and specific influence of CH4, C2H4 and C2H6 on vibrational distribution of hydrogen molecules from the source is presented here. Vibrational relaxation of H2(v) is observed when mixture of CH4 and H2 is introduced to the source. On the other hand, production of vibrationally excited H2 molecules is observed when C2H4 (ethene) and C2H6 (ethane) are present alone in the source, due to the thermal dissociation of these two molecules on the hot filament. This effect was not found for CH4. Studied processes are relevant for the modelling of edge plas...
Obravnavali bomo rekombinacijo vodikovih atomov na površini. To je proces, pri katerem dva atoma ... more Obravnavali bomo rekombinacijo vodikovih atomov na površini. To je proces, pri katerem dva atoma na površini med seboj interagirata, se vežeta v molekulo, ki nato kot prosti delec zapusti površino. Sproščene molekule lahko nastanejo ali z rekombinacijo dveh atomov, ki sta adsorbirana na površini ali z direktno rekombinacijo enega atoma s površine z drugim atomom, ki prileti iz okolǐskega plina. Molekule, nastale z rekombinacijo, so lahko v vzbujenih vibracijskih stanjih. Zasedenost posameznih vibracijskih stanj je odvisna od materiala in temperature površine, pogojev v okolǐskem plinu ter od mehanizma rekombinacije. Zaradi pomanjkanja eksperimentalnih podatkov še danes ni popolnoma znano, kateri mehanizem rekombinacije je dejansko odgovoren za opaženo zasedenost tudi visokih vibracijskih stanj. Da bi prispevali k razumevanju procesa rekombinacije vodika na površinah, razvijamo aparaturo, s katero bomo lahko analizirali vibracijsko-rotacijsko zasedenost tako nastalih molekul.
This paper presents preliminary results of adjusting parameters of Hypocycloidal Electron Monochr... more This paper presents preliminary results of adjusting parameters of Hypocycloidal Electron Monochromator in Stepwise Electron Laser Excitation (SELE) experiment at the Institute of Physics, Belgrade.
Detailed knowledge of surface processes on plasma facing components is of high importance for und... more Detailed knowledge of surface processes on plasma facing components is of high importance for understanding and modelling of the edge plasma in tokamaks. This requires information on the kind of emitted particles as well as their state of excitation. While this was to more extent studied for carbon materials much less is known for metals (ITER relevant W) and especially at higher temperatures relevant to divertor operation and transient heat load phenomena. The production of vibrationally excited molecules by hydrogen atom (H and D) recombination is a subject of a present studies. A vibrational spectrometer is used for determination of vibrational excitation of hydrogen molecules. It was recently upgraded by single-stage differential pumping thus separating the detector and the reaction chamber. Recent results with new experimental arrangement are presented and compared to the results obtained with the old experimental set-up.
A sensitive electron-impact spectrometer has been used to study vibrational excitation of the gro... more A sensitive electron-impact spectrometer has been used to study vibrational excitation of the ground state of ${\mathrm{N}}_{2}$ through the first excited doublet state $A^{2}\ensuremath{\Pi}_{u}$ of ${\mathrm{N}}_{2}^{\ensuremath{-}}$. Oscillations are observed in both the cross sections of the parent state $A{^{3}\ensuremath{\Sigma}_{u}}^{+}$ and the ground state. The absolute values of these cross sections have been measured. The observations are readily accounted for by calculations which use the "boomerang model." The resonant cross sections for excitation of the vibrational levels of the parent state vary in the same way as the direct Franck-Condon factors between the $A{^{3}\ensuremath{\Sigma}_{u}}^{+}$ and the ground states of the neutral molecule, whereas the observed intensities of the vibrational levels of the ground state are almost constant.
Journal of Physics B: Atomic and Molecular Physics, 1974
Excitation of the ground state vibrational modes of CO2 has been studied in an electron impact ex... more Excitation of the ground state vibrational modes of CO2 has been studied in an electron impact experiment in the energy range 3-5 eV. A series of oscillations is observed in the excitation functions of the elastic and vibrational channels which was previously assumed to result from vibrational excitation of an intermediate negative ion (shape resonance). The oscillations were seen to move towards higher energies with increasing vibrational quantum number when observed in the symmetric stretch channel. This leads us to propose that the structure is due to an interference effect in the negative ion wavefunction (boomerang model).
Journal of Physics B: Atomic, Molecular and Optical Physics, 2002
ABSTRACT We report measured absolute single and double charge-exchange cross sections for 3He2+ o... more ABSTRACT We report measured absolute single and double charge-exchange cross sections for 3He2+ on CO at ion impact energies between 1 and 14 keV (velocities between 254 and 949 km s-1). A retarding-field method is used for charge-state analysis of the ion beam after traversing the target gas cell. Cross sections are determined from absolute measurements of current ratios and the CO target gas pressure. For testing the experimental technique, proton-electron capture cross sections are measured at energies between 2.5 and 7 keV. The measured He2+ and H+ cross sections are compared to available data.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2003
ABSTRACT We report measured absolute single and double charge-exchange cross sections (CSs) for F... more ABSTRACT We report measured absolute single and double charge-exchange cross sections (CSs) for Feq+ ions with He at the ion impact energy of 7.0 × q keV for q = 5–13. The range of ion velocities is 350 km s−1 for q = 5, to 560 km s−1 for q = 13, comparable to typical solar wind velocities. A retarding-field method is used for charge-state analysis of the ion beam after traversing the stationary target gas cell. The CSs are determined from absolute measurements of the ion currents and He target gas pressure.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2012
Here we report on the first dual-beam experiment employing a hydrogen atom beam for sample exposu... more Here we report on the first dual-beam experiment employing a hydrogen atom beam for sample exposure and an ion beam for analysis, enabling in situ and real time studies of hydrogen atom interaction with materials. The erosion of an amorphous hydrogenated carbon (a-C:H) layer by deuterium atoms at 580 K sample temperature was studied and the uptake of deuterium during the erosion process was measured in real time. The deuterium areal density increased at the beginning to 7.3×10 15 at.cm-2 , but then stabilized at a constant value of 5.5×10 15 at.cm-2. Formation of a polymerlike deposit on an a-C:H layer held at room temperature and subjected to the deuterium atom beam was observed and also studied in-situ. For both erosion and deposition studies an a-13 C:H layer on top of a Si substrate was used as a sample, making the experiments isotopically fully specified and thereby differentiating the deposited from the original layer and the interacting D atoms from H atoms present in the layer and in the residual vacuum. From the deposition study it was shown that carbon in the deposited layer originates from carbon-carrying species in the background vacuum that interact with hydrogen atoms. The areal density of the carbon at the surface was determined from the energy shift of the Si edge in the RBS spectrum. The cross-section for 7 Li on D at 4.3 MeV Li ion energy and at a recoil angle of 30 o was also determined to be (236±16)×10-27 cm 2 /sr. This is a factor of 3±0.2 times higher than the Rutherford elastic cross-section.
The role of neutral molecules in edge plasma is discussed with special emphasis on the vibrationa... more The role of neutral molecules in edge plasma is discussed with special emphasis on the vibrationally excited hydrogen. Neutral molecules are formed mostly by surface processes on the walls and then released to the edge plasma where they take part in volumetric reactions with other particles. Typically these molecules are formed in excited states and data are needed for their reactions on the wall and in the volume. Processes in edge plasma determine particle and energy flux what is especially critical issue in tokamak divertor region. Various cross sections and reaction rates are needed for modelling edge plasma and its interaction with walls.
We present the numerical model for determining particle concentration in partially dissociated lo... more We present the numerical model for determining particle concentration in partially dissociated low pressure neutral hydrogen gas in a metal reaction cell where flowing gas is partially dissociated by a hot tungsten filament. Neutral hydrogen atoms and molecules in different vibrational states are taken into account. Available parameters for relevant surface processes (thermal dissociation, atom recombination, adsorption/desorption and vibrational relaxation) are used as initial input parameters. Calculated particle concentration distributions are compared to experimental data and qualitative agreement is obtained. Such a model is needed as a tool for indepth understanding and interpretation of results from our specific experiment and thus in turn enabling checking and evaluating rates and cross sections for the above surface processes.
Plasma facing components in ITER and in future fusion reactors will be exposed to 14 MeV neutrons... more Plasma facing components in ITER and in future fusion reactors will be exposed to 14 MeV neutrons producing radiation defects in the bulk of materials. Tungsten is one of most favorable materials for fusion applications at the present time. Hydrogen solubility in tungsten is very low and retention of hydrogen isotopes in tungsten is determined by trapping in defects. Therefore, radiation defects can play an important role in tritium retention in tungsten. To simulate neutron damage irradiation by 20 MeV W 6+ ions have been used in this work. The irradiation of W with W ions was done at IPP. After pre-irradiation with W ions at different damage levels, polycrystalline tungsten samples were exposed to low-energy deuterium (D) plasma at IPP [1] and to atomic D beam at Jožef Stefan Institute [2] in a wide range of temperatures between 300 and 800 K. D depth profiles were measured by nuclear reaction analysis (NRA) and total D retention by thermal desorption spectroscopy (TDS). NRA data ...
We have measured the cross-section for the 1 H( 7 Li,[FORMULA]) 4 He reaction at lithium beam ene... more We have measured the cross-section for the 1 H( 7 Li,[FORMULA]) 4 He reaction at lithium beam energies from 0.34 to 1.05MeV. Hydrogen was forced by diffusion into Pd and PdAg alloy foils. A large electron screening effect was observed only when foils were under tensile stress. A dependence of the screening potential on hydrogen concentration or Hall coefficient of the metallic host could not be established.
Thermal desorption of deuterium from mixed C:W and C:W:Al layers was studied in situ by Nuclear R... more Thermal desorption of deuterium from mixed C:W and C:W:Al layers was studied in situ by Nuclear Reaction Analysis (NRA) and mass spectrometry during linear sample heating. The deuterium thermal desorption was correlated by decrease of the proton signal at single 3 He probing beam energy (2.5 MeV) and increase of the masses 3 and 4 in the mass spectrum. Main deuterium desorption in C:W mixed layer takes place at relatively high temperature, around 1000 K, what is higher than typical desorption temperatures for W and amorphous deuterated carbon films. The deuterium depth profile in the layer was measured before and after heating and some deuterium was found to remain after the experiment. Deuterium atom absorption in multilayer film (200 nm of C on top of 500 nm W on graphite substrate) exposed to deuterium atom beam for one day was also studied by the same procedure.
The radiative lifetime of the 2s22p2 S0 level in O 2+ has been measured via the magnetic-dipole (... more The radiative lifetime of the 2s22p2 S0 level in O 2+ has been measured via the magnetic-dipole (M1) transition 2s2p S0 ! P1 at 232.17 nm. Data were recorded in a Kingdon trap, with the source of ions a 14 GHz electron cyclotron resonance ion source. The lifetime of the S0 level was found to be 540 27 ms. This is in good agreement with a previous measurement and with a number of theoretical calculations. Metastable lifetimes, when combined with collisional excitation rates, can provide a diagnostic for electron density Ne in a stellar or solar plasma. Subject headings: atomic data — atomic processes
The influence of light hydrocarbons on vibrational excitation of H2 generated in a special source... more The influence of light hydrocarbons on vibrational excitation of H2 generated in a special source of excited molecules has been studied. Vibrational spectrometer based on analysis of variation of H yield produced by dissociative electron attachment in 0-5 eV electron energy range is employed. Molecule dissociation on the hot tungsten filament and atom recombination on cooled walls is used for production of molecular excitation in the source and specific influence of CH4, C2H4 and C2H6 on vibrational distribution of hydrogen molecules from the source is presented here. Vibrational relaxation of H2(v) is observed when mixture of CH4 and H2 is introduced to the source. On the other hand, production of vibrationally excited H2 molecules is observed when C2H4 (ethene) and C2H6 (ethane) are present alone in the source, due to the thermal dissociation of these two molecules on the hot filament. This effect was not found for CH4. Studied processes are relevant for the modelling of edge plas...
Obravnavali bomo rekombinacijo vodikovih atomov na površini. To je proces, pri katerem dva atoma ... more Obravnavali bomo rekombinacijo vodikovih atomov na površini. To je proces, pri katerem dva atoma na površini med seboj interagirata, se vežeta v molekulo, ki nato kot prosti delec zapusti površino. Sproščene molekule lahko nastanejo ali z rekombinacijo dveh atomov, ki sta adsorbirana na površini ali z direktno rekombinacijo enega atoma s površine z drugim atomom, ki prileti iz okolǐskega plina. Molekule, nastale z rekombinacijo, so lahko v vzbujenih vibracijskih stanjih. Zasedenost posameznih vibracijskih stanj je odvisna od materiala in temperature površine, pogojev v okolǐskem plinu ter od mehanizma rekombinacije. Zaradi pomanjkanja eksperimentalnih podatkov še danes ni popolnoma znano, kateri mehanizem rekombinacije je dejansko odgovoren za opaženo zasedenost tudi visokih vibracijskih stanj. Da bi prispevali k razumevanju procesa rekombinacije vodika na površinah, razvijamo aparaturo, s katero bomo lahko analizirali vibracijsko-rotacijsko zasedenost tako nastalih molekul.
This paper presents preliminary results of adjusting parameters of Hypocycloidal Electron Monochr... more This paper presents preliminary results of adjusting parameters of Hypocycloidal Electron Monochromator in Stepwise Electron Laser Excitation (SELE) experiment at the Institute of Physics, Belgrade.
Detailed knowledge of surface processes on plasma facing components is of high importance for und... more Detailed knowledge of surface processes on plasma facing components is of high importance for understanding and modelling of the edge plasma in tokamaks. This requires information on the kind of emitted particles as well as their state of excitation. While this was to more extent studied for carbon materials much less is known for metals (ITER relevant W) and especially at higher temperatures relevant to divertor operation and transient heat load phenomena. The production of vibrationally excited molecules by hydrogen atom (H and D) recombination is a subject of a present studies. A vibrational spectrometer is used for determination of vibrational excitation of hydrogen molecules. It was recently upgraded by single-stage differential pumping thus separating the detector and the reaction chamber. Recent results with new experimental arrangement are presented and compared to the results obtained with the old experimental set-up.
A sensitive electron-impact spectrometer has been used to study vibrational excitation of the gro... more A sensitive electron-impact spectrometer has been used to study vibrational excitation of the ground state of ${\mathrm{N}}_{2}$ through the first excited doublet state $A^{2}\ensuremath{\Pi}_{u}$ of ${\mathrm{N}}_{2}^{\ensuremath{-}}$. Oscillations are observed in both the cross sections of the parent state $A{^{3}\ensuremath{\Sigma}_{u}}^{+}$ and the ground state. The absolute values of these cross sections have been measured. The observations are readily accounted for by calculations which use the "boomerang model." The resonant cross sections for excitation of the vibrational levels of the parent state vary in the same way as the direct Franck-Condon factors between the $A{^{3}\ensuremath{\Sigma}_{u}}^{+}$ and the ground states of the neutral molecule, whereas the observed intensities of the vibrational levels of the ground state are almost constant.
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