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| 2. |
- Fedosseev, V. N., et al.
(author)
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Upgrade of the resonance ionization laser ion source at ISOLDE on-line isotope separation facility : New lasers and new ion beams
- 2012
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 82:2, s. 02A903-
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Journal article (peer-reviewed)abstract
- The resonance ionization laser ion source (RILIS) produces beams for the majority of experiments at the ISOLDE on-line isotope separator. A substantial improvement in RILIS performance has been achieved through a series of upgrade steps: replacement of the copper vapor lasers by a Nd:YAG laser; replacement of the old homemade dye lasers by new commercial dye lasers; installation of a complementary Ti:Sapphire laser system. The combined dye and Ti:Sapphire laser system with harmonics is capable of generating beams at any wavelength in the range of 210-950 nm. In total, isotopes of 31 different elements have been selectively laser-ionized and separated at ISOLDE, including recently developed beams of samarium, praseodymium, polonium, and astatine.
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| 3. |
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| 4. |
- Wendt, M., et al.
(author)
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Current Limitation and Inertial Resistance of an Inhomogeneous Plasma Diode
- 2001
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In: Physica Scripta. - 0281-1847. ; 64, s. 372-381
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Journal article (peer-reviewed)abstract
- Inhomogeneous, collisionfree and bounded plasmas may support large potential drops even for steady electron motion. We present an experimental investigation of the exdended potential drops and transient current pulses, which form when a voltage drop U-a is suddenly applied to a magnetized, collisionfree plasma column with an axial ion density minimum. For well magnetized electrons the resistance at the current maximum agrees with the "intertial resistance" which is approximately proportional to U-a(1/2) for U-a much larger than the electron thermal temperature. The sharp drop following the current maximum is caused by the radial redistribution of the unmagnetized ions due to the transient radial electric field. For larger times (t > 10 omega (-1)(pi)) the measured resistance becomes approximately proportional to U-a as in the strong double layer that finally forms.
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| 5. |
- Kron, J., et al.
(author)
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Comparison of numerical simulation models for predicting temperature in solidification analysis with reference to air gap formation
- 2004
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In: International Journal of Cast Metals Research. - : Maney Publishing. - 1364-0461 .- 1743-1336. ; 17:5, s. 295-310
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Journal article (peer-reviewed)abstract
- As a result of its influence on heat transfer between cast part and mould, air gap formation is an important problem for many casting processes. The general explanation for gap formation is that, as a result of stresses and distortions that are created from inhomogeneous cooling, shrinkage of the casting and expansion of the mould occur. In this paper, different thermomechanical approaches are applied to a well defined casting process using three commercial and one in-house codes and their predictions are compared with experimental findings. The experimental data were obtained from the solidification and subsequent cooling of cylindrical castings of eutectic Al-13% Si and ternary Al-7% Si-0.3% Mg alloys. Based on these findings, the major differences between the predictions of the models and the actual formation of the air gap are discussed.
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| 7. |
- Schwellnus, F., et al.
(author)
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Study of low work function materials for hot cavity resonance ionization laser ion sources
- 2009
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 267:10, s. 1856-1861
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Journal article (peer-reviewed)abstract
- The selectivity of a hot cavity resonance ionization laser ion source (RILIS) is most often limited by contributions from competing surface ionization of the hot walls of the ionization cavity. In this article we present investigations on the properties of designated high temperature, low work function materials regarding their performance and suitability as cavity material for RILIS. Tungsten test cavities, impregnated with a mixture of barium oxide and strontium oxide (BaOSrO on W), or alternatively gadolinium hexaboride (GdB6) were studied in comparison to a standard tungsten RILIS cavity as being routinely used for hot cavity laser ionization at ISOLDE. Measurement campaigns took place at the off-line mass separators at ISOLDE/CERN, Geneva and RISIKO/University of Mainz.
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| 8. |
- Torvén, Staffan, et al.
(author)
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Experimental Investigations and Simulations of Quasi-Steady Potential Drops
- 2001
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In: Phys. Chem. of the Earth C. - 1464-1917. ; 26, s. 71-80
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Journal article (peer-reviewed)abstract
- Magnetic-field-aligned potential drops in the auroral zone have recently been interpreted in terms of "quasi-steady" states which are evaluated for a fixed, given ion density profile. Here we present experimental studies of such states, observed when a voltage drop is suddenly applied to an inhomogeneous plasma column with a homogeneous, axial magnetic field. The quasi-steady potential drops have a spatial extension related to the gradient length of the initial ion density and the potential profile steepens slowly to a U-shaped double layer on the ion time scale. They exist only when the applied voltage drop does not exceed a critical value which depends on the maximum difference in ion density. Higher voltage drops concentrate in a cathode sheath. Results from PIC-simulations and from a theoretical model, based on steady electron motion, are also presented. They agree excellently for times up to about an ion plasma period (omega (-1)(pi)) The theoretical current-voltage characteristic, which is determined by electron reflection at a virtual cathode formed in the plasma, agrees with the experiments up to about one omega (-1)(pi). However, already at about 4 omega (-1)(pi) the measured currents have dropped much below the theoretical values, and also the measured average potential profiles are inconsistent with steady acceleration of the electrons. The increased resistivity is associated with strong fluctuations.
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| 9. |
- Wendt, M., et al.
(author)
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Localization of the High Frequency Field in a Beam-Plasma Diode Due to Density Gradients
- 2001
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In: Physica Scripta. - 0281-1847. ; 63, s. 62-69
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Journal article (peer-reviewed)abstract
- An experimental study of the high frequency (hf) interaction of a strong, warm electron beam with an inhomogeneous, bounded plasma is presented and compared with particle-in-cell simulations. The density is highest in the center of the diode and decreases towards the boundaries. The electric field in the center is dominated by the unstable slow-space-charge wave, but experimental evidence is found, that reflected waves are present near the beam injection grid, where the oscillation frequency f is higher than the local plasma frequency f(pe)(x). The strong field at the resonance point (f = f(pe)(x)) is proposed to excite the unstable beam mode. Simulations confirm this picture by showing a concentration of the spectral power of the beam waves to the frequencies of the trapped Langmuir waves. Linear growth and Landau damping concentrate the beam wave to a 1.5-2 wavelengths wide region. Trapped Langmuir waves can accordingly determine the frequencies and position of the hf-field even for moderate density gradients and field strengths below the threshold for Langmuir collapse.
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