| 1. |
- Fenstermacher, M.E., et al.
(författare)
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DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L-H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.
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| 2. |
- Elahipanah, Hossein, et al.
(författare)
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Design optimization of a high temperature 1.2 kV 4H-SiC buried grid JBS rectifier
- 2017
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Ingår i: 11th European Conference on Silicon Carbide and Related Materials, ECSCRM 2016. - : Trans Tech Publications Inc.. - 9783035710434 ; , s. 455-458
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Konferensbidrag (refereegranskat)abstract
- 1.2 kV SiC buried grid junction barrier Schottky (BG-JBS) diodes are demonstrated. The design considerations for high temperature applications are investigated. The design is optimized in terms of doping concentration and thickness of the epilayers, as well as grid size and spacing dimensions, in order to obtain low on-resistance and reasonable leakage current even at high temperatures. The device behavior at temperatures ranging from 25 to 250ºC is analyzed and measured on wafer level. The forward voltage drop of 1.1 V at 100 A/cm2 and 3.8 V at 1000 A/cm2 is measured, respectively. At reverse voltage of 1 kV, a leakage current density below 0.1 μA/cm2 and below 0.1 mA/cm2 is measured at 25 and 250ºC, respectively. This proves the effective shielding effect of the BG-JBS design and provides benefits in high voltage applications, particularly for high temperature operation.
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| 3. |
- Hjort, T., et al.
(författare)
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High temperature capable SiC Schottky diodes, based on buried grid design
- 2014
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Ingår i: International Conference and Exhibition on High Temperature Electronics. ; , s. 158-160
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Konferensbidrag (refereegranskat)abstract
- Electrical characteristics of 4H-SiC Schottky barrier diodes, based on buried grid design are presented. The diodes, rated to 1200V/10A and assembled into high temperature capable T0254 packages, have been tested and studied up to 250°C. Compared to conventional SiC Schottky diodes, Ascatron’s buried grid SiC Schottky diode demonstrates several orders of magnitude reduced leakage current at high temperature operation.
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| 4. |
- Lim, Jang-Kwon, et al.
(författare)
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A theoretical and experimental comparison of 4H- and 6H-SiC MSM UV photodetectors
- 2012
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Ingår i: Silicon Carbide and Related Materials 2011. - : Trans Tech Publications Inc.. - 9783037854198 ; , s. 1207-1210
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Konferensbidrag (refereegranskat)abstract
- This paper reports on fabrication and modeling of 4H- and 6H-SiC metal-semiconductor-metal (MSM) photodetectors (PDs). MSM PDs have been fabricated on 4H-SiC and 6H-SiC epitaxial layers, and their performance analyzed by MEDICI simulation and measurements. The simulations were also used to optimize the sensitivity by varying the width and spacing of the interdigitated electrodes. The fabricated PDs with 2 ÎŒm wide metal electrodes and 3 ÎŒm spacing between the electrodes exhibited, under UV illumination, a peak current to dark current ratio of 10 5 and 10 4 in 4H-SiC and 6H-SiC, respectively. The measured spectral responsivity of 6H-SiC PDs was higher compared to that of 4H-SiC PDs, with a cutoff at 407 nm compared to 384 nm in 4H-SiC PDs. Also the peak responsivity occurred at a shorter wavelength in 6H material. A high rejection ratio between the photocurrent and dark current was found in both cases. These experimental results were in agreement with simulation.
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| 5. |
- Bhat, N. D. R., et al.
(författare)
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Observations of Low-frequency Radio Emission from Millisecond Pulsars and Multipath Propagation in the Interstellar Medium
- 2018
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Ingår i: Astrophysical Journal, Supplement Series. - : American Astronomical Society. - 1538-4365 .- 0067-0049. ; 238:1
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Tidskriftsartikel (refereegranskat)abstract
- Studying the gravitational-wave sky with pulsar timing arrays (PTAs) is a key science goal for the Square Kilometre Array (SKA) and its pathfinder telescopes. With current PTAs reaching sub-microsecond timing precision, making accurate measurements of interstellar propagation effects and mitigating them effectively has become increasingly important to realize PTA goals. As these effects are much stronger at longer wavelengths, low-frequency observations are most appealing for characterizing the interstellar medium (ISM) along the sight lines toward PTA pulsars. The Murchison Widefield Array (MWA) and the Engineering Development Array (EDA), which utilizes MWA technologies, present promising opportunities for undertaking such studies, particularly for PTA pulsars located in the southern sky. Such pulsars are also the prime targets for PTA efforts planned with the South African MeerKAT, and eventually with the SKA. In this paper we report on observations of two bright southern millisecond pulsars, PSR J0437-4715 and PSR J2145-0750, made with these facilities; MWA observations sampled multiple frequencies across the 80-250 MHz frequency range, while the EDA provided direct-sampled baseband data to yield a large instantaneous usable bandwidth of similar to 200 MHz. Using these exploratory observations, we investigate various aspects relating to pulsar emission and ISM properties, such as spectral evolution of the mean pulse shape, scintillation as a function of frequency, chromaticity in interstellar dispersion, and flux density spectra at low frequencies. Systematic and regular monitoring observations will help ascertain the role of low-frequency measurements in PTA experiments, while simultaneously providing a detailed characterization of the ISM toward the pulsars, which will be useful in devising optimal observing strategies for future PTA experiments.
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| 6. |
- Reshanov, S. A., et al.
(författare)
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Full epitaxial trench type buried grid SiC JBS diodes
- 2014
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. ; , s. 289-293
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Konferensbidrag (refereegranskat)abstract
- The paper presents the advanced concept of fully epitaxial SiC junction barrier Schottky (JBS) diodes. It combines trench etching with embedded epitaxial re-growth and enables cost-efficient manufacturing. Fabricated devices are rated for 20A / 1200V and have leakage currents below 0.1μA at 1000V blocking voltage.
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| 7. |
- Wang, Q., et al.
(författare)
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Compacted nanoscale sensors by merging ZnO nanorods with interdigitated electrodes
- 2011
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Ingår i: Proc SPIE Int Soc Opt Eng. - : SPIE. - 9780819486059
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Konferensbidrag (refereegranskat)abstract
- ZnO nanorods (NRs) sensors utilizing hybrid or monolithic integration of the NRs on nanoscale or microscale interdigitated electrodes (IDEs) were fabricated and characterized. The IDEs with their finger electrode width ranging from 50 nm to 3 μm were formed on SiO2/Si substrates by nanoimprint lithography or conventional photolithography and metallization techniques, whereas the ZnO NRs were grown by chemical synthesis method. The average diameter of the ZnO NRs is about 100 nm, and their length can be varied from 2 to 5 μm by controlling growth time. When sensing targets, such as molecules or nanoparticles, bind onto the ZnO NRs, the conductance between IDEs will change. As probing test, II-VI quantum dots (QDs) were attached on the ZnO NRs, and clear responses were obtained by measuring and comparing current-voltage (I-V) characteristic of the sensor before and after binding the QDs.
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| 8. |
- Bakowski, M., et al.
(författare)
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Merits of Buried Grid Technology for Advanced SiC Device Concepts
- 2011
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Ingår i: GALLIUM NITRIDE AND SILICON CARBIDE POWER TECHNOLOGIES. - : The Electrochemical Society. - 9781607682622 ; , s. 155-162
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Konferensbidrag (refereegranskat)abstract
- Selected examples of the use of buried grid technology for SiC devices are discussed. First example is development of normally-off and normally-on JFETs, Second the development of Schottky barrier diodes for 250 degrees C operation. Other examples are efficient junction termination and avalanche UV detectors. Experimental results are used in support of simulations.
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| 9. |
- Haglöf, Fredrik, et al.
(författare)
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Experimental study of carbides in the Ti-Cr-C system
- 2019
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Ingår i: Journal of Materials Science. - : Springer. - 0022-2461 .- 1573-4803. ; 54:19, s. 12358-12370
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Tidskriftsartikel (refereegranskat)abstract
- The Ti-Cr-C system has been studied by producing samples within the MC-M3C2-M7C3 (M=Ti, Cr) and MC-M3C2-graphite equilibria. The main purpose was to determine the solubility of Cr in MC; however, the solubility of Ti in M3C2 and M7C3 was also of interest, as well as the C content in MC. Heat treatments have been performed at 1673 and 1773 K for 300 h. Thereafter, the phase compositions have been measured with energy-dispersive X-ray spectroscopy (EDS) and wavelength-dispersive X-ray spectroscopy (WDS). X-ray diffraction (XRD), in combination with Rietveld refinement, has been used to determine the lattice parameter for MC. Density functional theory (DFT) calculations were performed to estimate the lattice parameter for MC as a function of composition, and the Rietveld refined lattice parameters for MC have then been recalculated to compositions in order to verify the EDS measurements. The results show that the EDS and XRD measurements give equal results. One conclusion is that, with the current conditions, 300 h is a sufficient heat treatment time in order to reach thermodynamic equilibrium. The other main conclusion is that the solubility of Cr in MC, in general, was overestimated by previous studies due to too short heat treatment times, but also that the solubility is very temperature dependent, especially for the MC-M3C2-graphite equilibrium. This clear temperature dependence was not taken into account in the existing thermodynamic description found in the literature.
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| 10. |
- Yuan, Zimo, et al.
(författare)
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Localized Lifetime Control of 10 kV 4H-SiC PiN Diodes by MeV Proton Implantation
- 2022
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Ingår i: Materials Science Forum. - : Trans Tech Publications Ltd. - 1662-9752. - 9783035727609 ; , s. 442-446
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Konferensbidrag (refereegranskat)abstract
- In this paper, proton implantation with different combinations of MeV energies and doses from 2×109 to 1×1011 cm-2 is used to create defects in the drift region of 10 kV 4H-SiC PiN diodes to obtain a localized drop in the SRH lifetime. On-state and reverse recovery behaviors are measured to observe how MeV proton implantation influences these devices and values of reverse recovery charge Qrr are extracted. These measurements are carried out under different temperatures, showing that the reverse recovery behavior is sensitive to temperature due to the activation of incompletely ionized p-type acceptors. The results also show that increasing proton implantation energies and fluencies can have a strong effect on diodes and cause lower Qrr and switching losses, but also higher on-state voltage drop and forward conduction losses. The trade-off between static and dynamic performance is evaluated using Qrr and forward voltage drop. Higher fluencies, or energies, help to improve the turn-off performance, but at a cost of the static performance. © 2022 The Author(s).
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