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S Schiller - One of the best experts on this subject based on the ideXlab platform.
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static and dynamic polarizability and the stark and blackbody radiation frequency shifts of the molecular Hydrogen Ions h 2 hd and d 2
Physical Review A, 2014Co-Authors: S Schiller, D Bakalov, A K Bekbaev, V I KorobovAbstract:We calculate the DC Stark effect for three molecular Hydrogen Ions in the non-relativistic approximation. The effect is calculated both in dependence on the rovibrational state and in dependence on the hyperfine state. We discuss special cases and approximatIons. We also calculate the AC polarisabilities for several rovibrational levels, and therefrom evaluate accurately the black-body radiation shift, including the effects of excited electronic states. The results enable the detailed evaluation of certain systematic shifts of the transitIons frequencies for the purpose of ultra-high-precision optical, microwave or radio-frequency spectroscopy in ion traps.
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The electric quadrupole moment of molecular Hydrogen Ions and their potential for a molecular ion clock
Applied Physics B, 2014Co-Authors: D Bakalov, S SchillerAbstract:The systematic shifts of the transition frequencies in the molecular Hydrogen Ions are of relevance to ultra-high-resolution radio-frequency, microwave and optical spectroscopy of these systems, performed in ion traps. We develop the ab initio description of the interaction of the electric quadrupole moment of this class of molecules with the static electric field gradients present in ion traps. In good approximation, it is described in terms of an effective perturbation Hamiltonian. An approximate treatment is then performed in the Born–Oppenheimer approximation. We give an expression of the electric quadrupole coupling parameter valid for all Hydrogen molecular ion species and evaluate it for a large number of states of H _2 ^+ , HD^+, and D _2 ^+ . The systematic shifts can be evaluated as simple expectation values of the perturbation Hamiltonian. Results on radio-frequency, one-photon electric dipole (E1), and two-photon E1 transitIons between hyperfine states in HD^+ are reported. For two-photon E1 transitIons between rotationless states, the shifts vanish. For a large subset of rovibrational one-photon transitIons, the absolute values of the quadrupole shifts range from 0.3 to 10 Hz for an electric field gradient of 10^8 V/m^2. We point out an experimental procedure for determining the quadrupole shift which will allow reducing its contribution to the uncertainty of unperturbed rovibrational transition frequencies to the 1 × 10^−15 fractional level and, for selected transitIons, even below it. The combined contributIons of black-body radiation, Zeeman, Stark and quadrupole effects are considered for a large set of transitIons, and it is estimated that the total transition frequency uncertainty of selected transitIons can be reduced below the 1 × 10^−15 level.
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rovibrational spectroscopy of trapped molecular Hydrogen Ions at millikelvin temperatures
Physical Review A, 2006Co-Authors: Bernhard Roth, J. C. J. Koelemeij, H Daerr, S SchillerAbstract:We report a high-resolution spectroscopic study of molecular Ions at millikelvin temperatures. We measured several rovibrational infrared transitIons in HD{sup +} molecular Ions, stored in a radio-frequency trap and sympathetically cooled to {approx_equal}20 mK by laser-cooled Be{sup +} Ions. We observed hyperfine splitting of the lines, in good agreement with theoretical predictIons. The transitIons were detected by monitoring the decrease in ion number after selective photodissociation of HD{sup +} Ions in the upper vibrational state. The method described here is expected to be generally applicable.
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production of ultracold trapped molecular Hydrogen Ions
Physical Review Letters, 2005Co-Authors: P J Blythe, Bernhard Roth, U Frohlich, H Wenz, S SchillerAbstract:We have cooled ensembles of the molecular Hydrogen Ions H2+, H3+, and all their deuterated variants to temperatures of a few mK in a radio frequency trap, by sympathetic cooling with laser-cooled beryllium Ions. The molecular Ions are embedded in the central regIons of Coulomb crystals. Mass spectroscopy and molecular dynamics simulatIons were used to accurately characterize the properties of the ultracold multispecies crystals. We demonstrate species-selective purification of multispecies ensembles. These molecules are of fundamental importance as the simplest of all molecules, and have the potential to be used for precision tests of molecular structure theory, tests of Lorentz invariance, and measurements of electron to nuclear mass ratios and their time variation.
U Fantz - One of the best experts on this subject based on the ideXlab platform.
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modelling the ion source for iter nbi from the generation of negative Hydrogen Ions to their extraction
Plasma Sources Science and Technology, 2014Co-Authors: D Wunderlich, U Fantz, S Mochalskyy, P FranzenAbstract:The neutral beam injection (NBI) system for ITER is based on a large (Asource = 1.9 × 0.9 m2) negative Hydrogen or deuterium ion source. In this source negative Ions are produced in a low-pressure (pfill ≈ 0.3 Pa) plasma by conversion of atoms and protons on a caesiated molybdenum surface with low work function. Then the negative Ions are transported through the plasma to the extraction system where extraction of these Ions and co-extraction of electrons also take place. This paper describes the status of the modelling activities connected with the negative ion test facilities of IPP Garching. It is illustrated that these modelling activities constitute a strong support of the experimental activities connected with the development of the negative ion source for ITER NBI. Several numerical codes developed in the past years—in close collaboration with the experiment—and their results are introduced. Focus is laid on the production, transport and extraction of negative Hydrogen Ions and on the inevitable co-extraction of electrons.
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influence of cesium on the plasma parameters in front of the plasma grid in sources for negative Hydrogen Ions
THIRD INTERNATIONAL SYMPOSIUM ON NEGATIVE IONS BEAMS AND SOURCES (NIBS 2012), 2013Co-Authors: R Friedl, U FantzAbstract:The cesium dynamics in ion sources for negative Hydrogen Ions based on surface conversion mainly determine the performance of the neutral beam injection (NBI) heating system for fusion. To investigate the role of the evaporated cesium in the Hydrogen plasma, which e.g. causes a decrease of the co-extracted electron current, experiments at a flexible laboratory setup (planar inductively coupled plasma) have been performed aiming at the direct influence of cesium on the plasma parameters in the plasma volume. In order to distinguish between effects resulting from the high atomic mass and those from plasma and surface chemistry, xenon admixtures (similar mass to Cs) were also investigated. A comprehensive set of diagnostics is applied simultaneously: optical emission and white light absorption spectroscopy, Langmuir probe measurements and residual gas analysis. As expected admixtures of xenon lead to a reduction of Te and an increase of ne. For cesium, however, the major effect is a remarkably reduction of n...
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magnetic filter field dependence of the performance of the rf driven ipp prototype source for negative Hydrogen Ions
Plasma Physics and Controlled Fusion, 2011Co-Authors: P Franzen, U Fantz, D Wunderlich, L Schiesko, M Froschle, Nnbi TeamAbstract:The ITER neutral beam system requires a negative Hydrogen ion beam of 48 A with an energy of 0.87 MeV and a negative deuterium beam of 40 A with an energy of 1 MeV. The beam is extracted from a large RF driven ion source with the dimension of 1.9 × 0.9 m2. An important role for the transport of the negative Hydrogen Ions to the extractor and the suppression of the co-extracted electrons is the magnetic filter field in front of the extractor. For the large ITER source the filter field will be generated by a current of up to 4 kA flowing through the first grid of the extractor. The extrapolation of the results obtained with the small IPP RF prototype source, where the filter field has a different 3D structure as it is generated by permanent magnets, is not straightforward. Furthermore, the filter field is by far not optimized due to the technical constraints of the RF source. Therefore, a frame that surrounds the ion sources and hosts permanent magnets was constructed for a fast and flexible change of the filter field. First results in Hydrogen show that a minimum field of 3 mT in front of the extractor is needed for a sufficiently large number of extracted negative Hydrogen Ions, whereas sufficient co-extracted electron suppression is achieved by a source integrated magnetic field of more than 1.0 mTm.
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pic code for the plasma sheath in large caesiated rf sources for negative Hydrogen Ions
Plasma Sources Science and Technology, 2009Co-Authors: D Wunderlich, R Gutser, U FantzAbstract:Powerful negative Hydrogen ion sources are required for heating and current drive at ITER. The physics of the production and extraction of high negative ion currents is much more complex than that for positive Ions. One of the most relevant parameters is the shape of the plasma sheath, which determines the velocity of surface produced negative Ions and thus the probability of the Ions to reach the extraction system. In order to investigate the influence of Hydrogen atoms, positive and negative Hydrogen Ions and positive caesium Ions on the plasma sheath, a 1d3v particle in cell code (PIC) code for the plasma close to the extraction system has been developed. For typical plasma parameters of such ion sources, surface conversion of impinging atoms is the main negative ion production channel, while conversion of positive Ions plays a minor role. Due to the formation of a potential minimum close to the surface, the emission of negative Ions into the plasma is space charge limited. As a consequence, the flux of negative Ions can be increased only by increasing the density of positive Hydrogen Ions. At identical plasma parameters, an isotope effect is determined by the mass of the particles only, resulting in lower fluxes of negative deuterium Ions compared with Hydrogen. A small amount of positive Cs does not change the plasma sheath and the H− flux significantly.
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simulatIons for the generation and extraction of negative Hydrogen Ions in rf driven ion sources
NEGATIVE IONS BEAMS AND SOURCES: Proceedings of the 1st International Symposium#N#on Negative Ions Beams and Sources, 2009Co-Authors: R Gutser, U Fantz, D Wunderlich, P Franzen, B Heinemann, R Nocentini, N I TeamAbstract:The injection of energetic neutral Hydrogen atoms plays an important part for plasma heating in fusion experiments. In order to fulfill the requirements of the ITER neutral beam injection (NBI), a RF‐driven ion source based on the generation of negative Ions prior to neutralization has been successfully developed at IPP Garching. Negative Hydrogen Ions are generated on a cesiated converter surface (plasma grid) by neutral particles and positive Ions and are then transported to the extraction apertures, where the ion beam formation process takes place. Numerical models are necessary to include the relevant physical aspects of these processes. The Monte Carlo transport code CSFLOW is used to describe the dynamical behavior of the cesium distribution on the source walls during vacuum operation. The negative ion transport process is simulated by means of the probabilistic ion transport code TRAJAN, focussing on the effects of aperture diameter variatIons in mono‐ and multiaperture extraction systems. A simula...
Nnbi Team - One of the best experts on this subject based on the ideXlab platform.
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magnetic filter field dependence of the performance of the rf driven ipp prototype source for negative Hydrogen Ions
Plasma Physics and Controlled Fusion, 2011Co-Authors: P Franzen, U Fantz, D Wunderlich, L Schiesko, M Froschle, Nnbi TeamAbstract:The ITER neutral beam system requires a negative Hydrogen ion beam of 48 A with an energy of 0.87 MeV and a negative deuterium beam of 40 A with an energy of 1 MeV. The beam is extracted from a large RF driven ion source with the dimension of 1.9 × 0.9 m2. An important role for the transport of the negative Hydrogen Ions to the extractor and the suppression of the co-extracted electrons is the magnetic filter field in front of the extractor. For the large ITER source the filter field will be generated by a current of up to 4 kA flowing through the first grid of the extractor. The extrapolation of the results obtained with the small IPP RF prototype source, where the filter field has a different 3D structure as it is generated by permanent magnets, is not straightforward. Furthermore, the filter field is by far not optimized due to the technical constraints of the RF source. Therefore, a frame that surrounds the ion sources and hosts permanent magnets was constructed for a fast and flexible change of the filter field. First results in Hydrogen show that a minimum field of 3 mT in front of the extractor is needed for a sufficiently large number of extracted negative Hydrogen Ions, whereas sufficient co-extracted electron suppression is achieved by a source integrated magnetic field of more than 1.0 mTm.
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cavity ring down spectroscopy on a high power rf driven source for negative Hydrogen Ions
Plasma Sources Science and Technology, 2009Co-Authors: M Berger, U Fantz, S Christkoch, Nnbi TeamAbstract:Cavity ring-down spectroscopy (CRDS) is a very sensitive diagnostic technique for absorption measurements. It is capable of measuring the absolute line-of-sight (LOS) integrated density of negative Hydrogen Ions (H−, D−) which induce a weak absorption (α 10−6 cm−1) along a LOS in plasmas containing negative Hydrogen Ions. CRDS has been applied to a high power rf driven negative ion source which is now the reference source for the ITER neutral beam injection system. The rf source operates at low pressure (typically 0.3 Pa). Negative Hydrogen Ions are produced mainly by the conversion of Hydrogen particles at a caesium coated surface achieving negative ion densities comparable to the electron density near the surface. It is shown that CRDS very reliably measures the absolute volume density of negative Hydrogen Ions in these sources. The densities range from 1016 m−3 in volume operation to 1017 m−3 in caesium seeded operation. The measured volume density close to the extraction system and the extracted current density change consistently while varying different source parameters, such as the total pressure or the input power applied to the source. Results are shown for measurements in Hydrogen and deuterium discharges with caesium seeding. An additional absorption is measured in the afterglow of the discharge and is attributed to the caesium dimer Cs2.
D Wunderlich - One of the best experts on this subject based on the ideXlab platform.
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modelling the ion source for iter nbi from the generation of negative Hydrogen Ions to their extraction
Plasma Sources Science and Technology, 2014Co-Authors: D Wunderlich, U Fantz, S Mochalskyy, P FranzenAbstract:The neutral beam injection (NBI) system for ITER is based on a large (Asource = 1.9 × 0.9 m2) negative Hydrogen or deuterium ion source. In this source negative Ions are produced in a low-pressure (pfill ≈ 0.3 Pa) plasma by conversion of atoms and protons on a caesiated molybdenum surface with low work function. Then the negative Ions are transported through the plasma to the extraction system where extraction of these Ions and co-extraction of electrons also take place. This paper describes the status of the modelling activities connected with the negative ion test facilities of IPP Garching. It is illustrated that these modelling activities constitute a strong support of the experimental activities connected with the development of the negative ion source for ITER NBI. Several numerical codes developed in the past years—in close collaboration with the experiment—and their results are introduced. Focus is laid on the production, transport and extraction of negative Hydrogen Ions and on the inevitable co-extraction of electrons.
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magnetic filter field dependence of the performance of the rf driven ipp prototype source for negative Hydrogen Ions
Plasma Physics and Controlled Fusion, 2011Co-Authors: P Franzen, U Fantz, D Wunderlich, L Schiesko, M Froschle, Nnbi TeamAbstract:The ITER neutral beam system requires a negative Hydrogen ion beam of 48 A with an energy of 0.87 MeV and a negative deuterium beam of 40 A with an energy of 1 MeV. The beam is extracted from a large RF driven ion source with the dimension of 1.9 × 0.9 m2. An important role for the transport of the negative Hydrogen Ions to the extractor and the suppression of the co-extracted electrons is the magnetic filter field in front of the extractor. For the large ITER source the filter field will be generated by a current of up to 4 kA flowing through the first grid of the extractor. The extrapolation of the results obtained with the small IPP RF prototype source, where the filter field has a different 3D structure as it is generated by permanent magnets, is not straightforward. Furthermore, the filter field is by far not optimized due to the technical constraints of the RF source. Therefore, a frame that surrounds the ion sources and hosts permanent magnets was constructed for a fast and flexible change of the filter field. First results in Hydrogen show that a minimum field of 3 mT in front of the extractor is needed for a sufficiently large number of extracted negative Hydrogen Ions, whereas sufficient co-extracted electron suppression is achieved by a source integrated magnetic field of more than 1.0 mTm.
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pic code for the plasma sheath in large caesiated rf sources for negative Hydrogen Ions
Plasma Sources Science and Technology, 2009Co-Authors: D Wunderlich, R Gutser, U FantzAbstract:Powerful negative Hydrogen ion sources are required for heating and current drive at ITER. The physics of the production and extraction of high negative ion currents is much more complex than that for positive Ions. One of the most relevant parameters is the shape of the plasma sheath, which determines the velocity of surface produced negative Ions and thus the probability of the Ions to reach the extraction system. In order to investigate the influence of Hydrogen atoms, positive and negative Hydrogen Ions and positive caesium Ions on the plasma sheath, a 1d3v particle in cell code (PIC) code for the plasma close to the extraction system has been developed. For typical plasma parameters of such ion sources, surface conversion of impinging atoms is the main negative ion production channel, while conversion of positive Ions plays a minor role. Due to the formation of a potential minimum close to the surface, the emission of negative Ions into the plasma is space charge limited. As a consequence, the flux of negative Ions can be increased only by increasing the density of positive Hydrogen Ions. At identical plasma parameters, an isotope effect is determined by the mass of the particles only, resulting in lower fluxes of negative deuterium Ions compared with Hydrogen. A small amount of positive Cs does not change the plasma sheath and the H− flux significantly.
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simulatIons for the generation and extraction of negative Hydrogen Ions in rf driven ion sources
NEGATIVE IONS BEAMS AND SOURCES: Proceedings of the 1st International Symposium#N#on Negative Ions Beams and Sources, 2009Co-Authors: R Gutser, U Fantz, D Wunderlich, P Franzen, B Heinemann, R Nocentini, N I TeamAbstract:The injection of energetic neutral Hydrogen atoms plays an important part for plasma heating in fusion experiments. In order to fulfill the requirements of the ITER neutral beam injection (NBI), a RF‐driven ion source based on the generation of negative Ions prior to neutralization has been successfully developed at IPP Garching. Negative Hydrogen Ions are generated on a cesiated converter surface (plasma grid) by neutral particles and positive Ions and are then transported to the extraction apertures, where the ion beam formation process takes place. Numerical models are necessary to include the relevant physical aspects of these processes. The Monte Carlo transport code CSFLOW is used to describe the dynamical behavior of the cesium distribution on the source walls during vacuum operation. The negative ion transport process is simulated by means of the probabilistic ion transport code TRAJAN, focussing on the effects of aperture diameter variatIons in mono‐ and multiaperture extraction systems. A simula...
P Franzen - One of the best experts on this subject based on the ideXlab platform.
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modelling the ion source for iter nbi from the generation of negative Hydrogen Ions to their extraction
Plasma Sources Science and Technology, 2014Co-Authors: D Wunderlich, U Fantz, S Mochalskyy, P FranzenAbstract:The neutral beam injection (NBI) system for ITER is based on a large (Asource = 1.9 × 0.9 m2) negative Hydrogen or deuterium ion source. In this source negative Ions are produced in a low-pressure (pfill ≈ 0.3 Pa) plasma by conversion of atoms and protons on a caesiated molybdenum surface with low work function. Then the negative Ions are transported through the plasma to the extraction system where extraction of these Ions and co-extraction of electrons also take place. This paper describes the status of the modelling activities connected with the negative ion test facilities of IPP Garching. It is illustrated that these modelling activities constitute a strong support of the experimental activities connected with the development of the negative ion source for ITER NBI. Several numerical codes developed in the past years—in close collaboration with the experiment—and their results are introduced. Focus is laid on the production, transport and extraction of negative Hydrogen Ions and on the inevitable co-extraction of electrons.
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magnetic filter field dependence of the performance of the rf driven ipp prototype source for negative Hydrogen Ions
Plasma Physics and Controlled Fusion, 2011Co-Authors: P Franzen, U Fantz, D Wunderlich, L Schiesko, M Froschle, Nnbi TeamAbstract:The ITER neutral beam system requires a negative Hydrogen ion beam of 48 A with an energy of 0.87 MeV and a negative deuterium beam of 40 A with an energy of 1 MeV. The beam is extracted from a large RF driven ion source with the dimension of 1.9 × 0.9 m2. An important role for the transport of the negative Hydrogen Ions to the extractor and the suppression of the co-extracted electrons is the magnetic filter field in front of the extractor. For the large ITER source the filter field will be generated by a current of up to 4 kA flowing through the first grid of the extractor. The extrapolation of the results obtained with the small IPP RF prototype source, where the filter field has a different 3D structure as it is generated by permanent magnets, is not straightforward. Furthermore, the filter field is by far not optimized due to the technical constraints of the RF source. Therefore, a frame that surrounds the ion sources and hosts permanent magnets was constructed for a fast and flexible change of the filter field. First results in Hydrogen show that a minimum field of 3 mT in front of the extractor is needed for a sufficiently large number of extracted negative Hydrogen Ions, whereas sufficient co-extracted electron suppression is achieved by a source integrated magnetic field of more than 1.0 mTm.
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simulatIons for the generation and extraction of negative Hydrogen Ions in rf driven ion sources
NEGATIVE IONS BEAMS AND SOURCES: Proceedings of the 1st International Symposium#N#on Negative Ions Beams and Sources, 2009Co-Authors: R Gutser, U Fantz, D Wunderlich, P Franzen, B Heinemann, R Nocentini, N I TeamAbstract:The injection of energetic neutral Hydrogen atoms plays an important part for plasma heating in fusion experiments. In order to fulfill the requirements of the ITER neutral beam injection (NBI), a RF‐driven ion source based on the generation of negative Ions prior to neutralization has been successfully developed at IPP Garching. Negative Hydrogen Ions are generated on a cesiated converter surface (plasma grid) by neutral particles and positive Ions and are then transported to the extraction apertures, where the ion beam formation process takes place. Numerical models are necessary to include the relevant physical aspects of these processes. The Monte Carlo transport code CSFLOW is used to describe the dynamical behavior of the cesium distribution on the source walls during vacuum operation. The negative ion transport process is simulated by means of the probabilistic ion transport code TRAJAN, focussing on the effects of aperture diameter variatIons in mono‐ and multiaperture extraction systems. A simula...
