Showing papers in "Fusion Science and Technology in 2007"
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TL;DR: The Wendelstein 7X (W7-X) stellarator as mentioned in this paper, which at present is being built at Max-Planck-Institut fur Plasmaphysik, Greifswald, aims at demonstrating the inherent inherent ste...
Abstract: The Wendelstein 7X (W7-X) stellarator (R = 5.5 m, a = 0.55 m, B < 3.0 T), which at present is being built at Max-Planck-Institut fur Plasmaphysik, Greifswald, aims at demonstrating the inherent ste...
180 citations
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TL;DR: The theoretical framework of quasi-optical propagation power absorption and driven current of a Gaussian beam of electron cyclotron (EC) waves in a general tokamak equilibrium implemented in the co...
Abstract: The theoretical framework of quasi-optical propagation power absorption and driven current of a Gaussian beam of electron cyclotron (EC) waves in a general tokamak equilibrium implemented in the co...
120 citations
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TL;DR: The Mercury laser project as discussed by the authors developed key technologies within an architectural framework that demonstrates basic building blocks for scaling to larger multi-kilojoule systems for inertial fusion energy (IFE) applications.
Abstract: Hundred-joule, kilowatt-class lasers based on diode-pumped solid-state technologies, are being developed worldwide for laser-plasma interactions and as prototypes for fusion energy drivers. The goal of the Mercury Laser Project is to develop key technologies within an architectural framework that demonstrates basic building blocks for scaling to larger multi-kilojoule systems for inertial fusion energy (IFE) applications. Mercury has requirements that include: scalability to IFE beamlines, 10 Hz repetition rate, high efficiency, and 10 9 shot reliability. The Mercury laser has operated continuously for several hours at 55 J and 10 Hz with fourteen 4 x 6 cm 2 ytterbium doped strontium fluoroapatite amplifier slabs pumped by eight 100 kW diode arrays. A portion of the output 1047 nm was converted to 523 nm at 160 W average power with 73% conversion efficiency using yttrium calcium oxy-borate (YCOB).
115 citations
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TL;DR: An overview of the key themes in the Alcator C-Mod tokamak research program are given, which include energy, particle and momentum transport, wave-plasma interactions, boundary and divertor physics and technology, macrostability including disruptions and their mitigation, and advanced toKamak scenarios with profile control and noninductive current drive.
Abstract: To introduce this special issue, this paper gives a brief overview of the key themes in the Alcator C-Mod tokamak research program. These include energy, particle and momentum transport, wave-plasm...
102 citations
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TL;DR: In this article, a review of divertor physics in C-Mod is presented, along with the three regimes of parallel transport, sheath limited, conduction limited, and detached, and their effects on plasma pressure along the magnetic field in the scrape-off layer.
Abstract: Many important contributions to the understanding of divertor physics are presented in this review of Alcator C-Mod research. The three regimes of parallel transport, sheath limited, conduction limited, and detached, were identified experimentally, along with their effects on plasma pressure along the magnetic field in the scrape-off layer. The extensive probe and bolometric coverage of the divertor allowed detailed characterization of the physics of detachment. The ability to dissipate ITER-like parallel power densities with extremely high divertor radiation emissivities (>40 MW/m3) was demonstrated under high-recycling and detached divertor conditions. The vertical plate divertor concept, developed and applied first on C-Mod, allowed the effect of divertor geometry to be studied, with the result that the vertical-plate and deep-slot geometries have a lower detachment threshold than the standard, flat-plate divertor. High-density (ne > 1 × 1021 m-3) divertor conditions allowed recombination to be...
101 citations
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TL;DR: In this article, the physics and technology of wave-particle-interaction experiments in the ion cyclotron range of frequencies (ICRF) and the lower hybrid (LH) range of frequency (LHRF) were reviewed.
Abstract: This paper reviews the physics and technology of wave-particle-interaction experiments in the ion cyclotron range of frequencies (ICRF) and the lower hybrid (LH) range of frequencies (LHRF) on the ...
87 citations
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TL;DR: An overview of the diagnostics installed on the Alcator C-Mod tokamak is presented in this article, where several advanced and novel diagnostics contribute to the investigation of C-mod plasmas, e.g., electron cyclotron emission, phase contrast imaging, gas puff imaging, probe measurements, and active magnetohydrodynamic antennas.
Abstract: An overview of the diagnostics installed on the Alcator C-Mod tokamak is presented. Approximately 25 diagnostic systems are being operated on C-Mod. The compact design of the machine and the cryostat enclosing the vacuum vessel and magnetic field coils make access challenging. Diagnostics are used to study four focus areas: transport, plasma boundary, waves, and macrostability. There is significant overlap between these topics, and they all contribute toward the burning plasma and advanced tokamak thrusts. Several advanced and novel diagnostics contribute to the investigation of C-Mod plasmas, e.g., electron cyclotron emission, phase-contrast imaging, gas puff imaging, probe measurements, and active magnetohydrodynamic antennas.
82 citations
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TL;DR: In this paper, Electron Bernstein waves (EBWs) were used to provide efficient off-axis heating and CD in spherical tokamaks, and the EBWs were combined with a non-nolenoid start-up technique.
Abstract: Burning plasma spherical tokamaks (STs) rely on off-axis current drive (CD) and nonsolenoid start-up techniques. Electron Bernstein waves (EBWs) may provide efficient off-axis heating and CD in hig...
57 citations
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TL;DR: In this article, a 12-meter-long solenoid with 55 corrugation cells with mirror ratio B max /B min = 4.8/3.2 T was used for fast ion heating, issues of plasma stability and confinement were discussed.
Abstract: Recent results of the experiments at GOL-3 facility are presented. In present configuration of the device, plasma with a density of 10 14 ÷10 16 cm -3 is confined in a 12-meter-long solenoid, which comprises 55 corrugation cells with mirror ratio B max /B min =4.8/3.2 T. The plasma in the solenoid is heated up to 2-4 keV temperature by a high power relativistic electron beam (∼1 MeV, ∼30 kA, ∼8 μs, ∼120 kJ) injected through one of the ends. Mechanism of experimentally observed fast ion heating, issues of plasma stability and confinement are discussed.
54 citations
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TL;DR: In this paper, the ability of ITER electron cyclotron (EC) wave launchers to drive localized current at various plasma locations is analyzed by means of beam-tracing codes, looking at extended physics application of EC current drive in ITER and at possible synergy between the two launchers.
Abstract: The ability of ITER electron cyclotron (EC) wave launchers to drive localized current at various plasma locations is analyzed by means of beam-tracing codes, looking at extended physics application of EC current drive in ITER and at possible synergy between the two launchers Calculations for an improved design of the upper launcher, based on four upper ports and front steering mirrors allowing both optimum focusing of the beams and an extended plasma deposition region, show that narrow, high peak current density profiles may be maintained over the radial range 04 40 deg), the power deposition and current drive location by this launcher is limited to rho(p) <= 055 Moreover, it is shown that performance close to the center can be improved with a poloidal tilt of the low and top front mirrors The main aim of this study is to provide guidance to the design of both launchers in order to optimize their performance, depending on the physics application
47 citations
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TL;DR: In this article, global and local transport experiments in ohmic, L-mode and H-mode regimes on the Alcator C-Mod tokamak were summarized, and earlier results derived for energy confinement scaling in...
Abstract: Global and local transport experiments in ohmic, L-mode and H-mode regimes on the Alcator C-Mod tokamak are summarized. For ohmic plasmas, earlier results derived for energy confinement scaling in ...
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TL;DR: In this article, the authors used the heavy ion beam probe diagnostic in the TJ-II stellarator to study directly the plasma electric potential with good spatial (up to 1 cm) and temporal resolution.
Abstract: The heavy ion beam probe diagnostic is used in the TJ-II stellarator to study directly the plasma electric potential with good spatial (up to 1 cm) and temporal (up to 2 μs) resolution. Singly charged heavy ions, Cs + , with energies of up to 125 keV are used to probe the plasma column from the edge to the core. Both electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI)-heated plasmas (P ECRH = 200 to 400 kW, P NBI = 200 to 400 kW, E NBI = 28 keV) have been studied. Low-density ECRH [n = (0.5 to 1.1) X 10 19 m -3 ] plasmas in TJ-II are characterized by positive plasma potential on the order of 1000 to 400 V. A negative electric potential appears at the edge when the line-averaged density exceeds 0.5 X 10 19 m -3 . Further density rises are accompanied by a decrease in the core plasma potential, which becomes fully negative for plasma densities n ≥ 1.5 X 10 19 m -3 . The NBI plasmas are characterized by a negative electric potential across the whole plasma cross section from the core to the edge. In this case, the absolute value of the central potential is on the order of -500 V. These results show a clear link between plasma potential and density in the TJ-II stellarator.
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TL;DR: In this paper, correlation radiometry techniques have been developed to detect the small-amplitude, high-frequency electron temperature fluctuations to which standard electron cyclotron emissions are correlated.
Abstract: Over the past 15 years, correlation radiometry techniques have been developed to detect the small-amplitude, high-frequency electron temperature fluctuations to which standard electron cyclotron em...
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TL;DR: In this paper, the edge transport barrier (ETB) pedestals are characterized using several diagnostics, leading to a thorough description of the performance of the ETB pedestals and their properties.
Abstract: H-mode research on Alcator C-Mod is described, with a focus on the edge transport barrier (ETB). ETB pedestals are characterized using several diagnostics, leading to a thorough description of prof...
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TL;DR: In this paper, an agitation method that includes both bouncing and rolling the spherical mandrels during deposition, and by reducing the coating rate, consistent columnar grain structure has now been obtained up to 170 mm.
Abstract: Various morphologies have been observed in sputter-deposited Be ablator capsules, including nodular growth, cone growth and twisted grain growth. By devising an agitation method that includes both bouncing and rolling the spherical mandrels during deposition, and by reducing the coating rate, consistent columnar grain structure has now been obtained up to 170 mm. Low mode deformation of the shells is observed on thin CH mandrels, but is suppressed if stiffer mandrels are used. Ablator density measured by weighing and x-ray radiography is 93%–95% of bulk density of Be. Transmission electron microscopy shows 100.200 nm size voids in the film and striations inside the grains. Be shells produced with rolling agitation have met most of the NIF specifications. Some of the few remaining issues will be discussed.
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TL;DR: In this article, the development of a 1MW-class continuous-wave gyrotron for the self-ignition experiment of fusion plasma and its confinement at the International Thermonuclear Experimental Reactor (ITER) is presented.
Abstract: Recent progress on the worldwide development of gyrotrons for fusion application is presented After breakthroughs of gyrotron technologies in the 1990s, significant progress has been made in the 2000s, in particular, on a long-pulse gyrotron for a wide range of frequencies from 84 to 170 GHz And, activities for advanced gyrotrons, for example, a high-power gyrotron using a coaxial resonator, a multifrequency gyrotron, etc, have proceeded With this progress have come improvements of gyrotron components such as a high-efficiency mode converter, a wide-band window, etc The gyrotrons have been applied to major fusion devices for heating and magnetohydrodynamics controls At present, the development of a 1-MW-class continuous-wave gyrotron is in the scope, which is applicable for the self-ignition experiment of fusion plasma and its confinement at the International Thermonuclear Experimental Reactor (ITER)
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TL;DR: The main-line hohlraum design now has a He gas fill, a wall of U-Au layers, and no shields as were formerly used between the capsule and the laser entrance holes as discussed by the authors.
Abstract: Targets intended to produce ignition on NIF are being simulated and the simulations used to set specifications for target fabrication. Recent design work has focused on refining the designs that use 1.0 MJ of laser energy, with ablators of Be(Cu), CH(Ge), and diamond-like C. The main-line hohlraum design now has a He gas fill, a wall of U-Au layers, and no shields as were formerly used between the capsule and the laser entrance holes. The emphasis in this presentation will be on changes in the requirements over the last year, and on the characteristics of the diamond-ablator design. Complete tables of specifications have been prepared for all of the targets. All the specifications are rolled together into an error budget indicating adequate margin for ignition with all of the designs.
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TL;DR: In this article, the authors have developed a production process for both standard density (100 mg/cc) and high density (180-200 mg/c) resorcinol formaldehyde (RF) foam shells with a triple orifice droplet generator.
Abstract: Previously we have developed a production process for both standard density (100 mg/cc) and high-density (180-200 mg/cc) resorcinol formaldehyde (RF) foam shells with a triple orifice droplet generator. These foam shells are needed for direct drive inertial confinement laser fusion experiments on the OMEGA laser facility at the University of Rochester. Although this process has been developed into production mode, the yield of high density RF (HDRF) and standard density (SDRF) shells with acceptable wall uniformity has been poor. This yield depends on the type of RF shell that is being fabricated. For HDRF this yield is ~5% while for the SDRF shells the yield is ~30%. We have made improvements in the yield of these shells that meet the wall uniformity specification by modifying the composition of the outer oil solution (O2) in the microencapsulation emulsion. This improvement was achieved by a small addition (0.60 wt.%) of a styrene-butadiene-styrene (SBS) block copolymer into the outer oil (O2) s...
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TL;DR: In this paper, Radiography is used to measure the opacity of ablator shell fabrication, allowing the accurate determination of the total impurity effect in a lump sum, and by using the sputter target trace element information, the radial profile of oxygen is determined.
Abstract: In ablator shell fabrication, trace elements and impurities are introduced in the deposition and the pyrolysis process, which must be controlled below a critical level. However, it is the opacity, not the individual elements, which matters in an Inertial Confinement Fusion (ICF) implosion. Radiography measures the opacity, allowing the accurate determination of the total impurity effect in a lump sum. Furthermore, by using the sputter target trace element information, we can determine the radial profile of oxygen to ±0.4 at. %. Oxygen is very difficult to measure by any other method, but is critically important for beryllium process development such as mandrel removal. To ensure measurement accuracy, we use a local standard to remove fluctuation in film developing and a step wedge to calibrate the film model.
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TL;DR: In this article, various concepts for fast directional switches as well as their integration into transmission lines are discussed, and a resonant diplexer experiment is at present being prepared to be tested at high power in the electron cyclotron resonance heating (ECRH) system for Wendelstein 7X (W7-X).
Abstract: To combine powers from a set of gyrotrons and to switch the combined wave beam between a number of output channels, various kinds of multiplexers can be used. Especially, narrow-band frequency diplexers in connection with small frequency-shift keying of gyrotrons can be used to switch the millimeter-wave power between two output channels. This technique can, for example, be used for fast beam steering for synchronous stabilization of rotating neoclassical tearing modes in tokamaks. Beam steering can be performed by a multistage multiplexer, provided that phase-controlled sources are available. In the paper, various concepts for fast directional switches as well as their integration into transmission lines are discussed. Calculations and low-power measurements of prototypes are presented. A resonant diplexer experiment is at present being prepared to be tested at high power in the electron cyclotron resonance heating (ECRH) system for Wendelstein 7X (W7-X). Requirements and techniques for frequency control of the gyrotrons are discussed, and the results of preliminary frequency modulation experiments are shown. Finally, future prospects for the application of diplexers in large ECRH systems are discussed.
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TL;DR: In this paper, a consistent and conservative scheme designed by Ni et al. for the simulation of MHD flows with low magnetic Reynolds number has been implemented into a 3D parallel code of HIMAG based on solving t
Abstract: A consistent and conservative scheme designed by Ni et al. for the simulation of MHD flows with low magnetic Reynolds number has been implemented into a 3D parallel code of HIMAG based on solving t...
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TL;DR: In this article, trace nonrecycling impurities (scandium and CaF 2 ) have been injected into Alcator C-Mod plasmas in order to determine impurity transport coefficient profiles in a number of operating regimes.
Abstract: Trace nonrecycling impurities (scandium and CaF 2 ) have been injected into Alcator C-Mod plasmas in order to determine impurity transport coefficient profiles in a number of operating regimes. Recycling Ar has also been injected to characterize steady-state impurity density profiles. Subsequent impurity emission has been observed with spatially scanning X-ray and vacuum ultraviolet spectrometer systems, in addition to very high spatial resolution X-ray and bolometer arrays viewing the plasma edge. Measured time-resolved brightness profiles of helium-, lithium-, and beryllium-like transitions have been compared with those calculated from a transport code that includes impurity diffusion and convection, in conjunction with an atomic physics package for individual line emission. Similar modeling has been performed for the edge observations, which are unresolved in energy. The line time histories and the profile shapes put large constraints on the impurity diffusion coefficient and convection velocity profiles. In L-mode plasmas, impurity confinement times are short (∼20 ms), with diffusivities in the range of 0.5 m 2 /s, anomalously large compared to neoclassical values. During Enhanced D α (EDA) H-modes, the impurity confinement times are longer than in L-mode plasmas, and the modeling suggests that there exists inward convection (≤50 m/s) near the plasma edge, with greatly reduced diffusion (of order 0.1 m 2 /s), also in the region of the edge transport barrier. These edge values of the transport coefficients during EDA H-mode are qualitatively similar to the neoclassical values. In edge localized mode-free H-mode discharges, impurity accumulation occurs, dominated by large inward impurity convection in the pedestal region. A scaling of the impurity confinement time with H-factor reveals a very strong exponential dependence. In internal transport barrier discharges, there is significant impurity accumulation inside of the barrier foot, typically at r/a = 0.5. Steady-state impurity density profiles in L-mode plasmas have a large up-down asymmetry near the last closed flux surface. The impurity density enhancement, in the direction opposite to the ion B X VB drift, is consistent with modeling of neoclassical parallel impurity transport.
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TL;DR: In this paper, the authors describe some of the engineering solutions required to produce a diverted tokamak capable of operation with a toroidal field of 8 T and plasma currents of up to 2 MA.
Abstract: We describe some of the engineering solutions required to produce a diverted tokamak capable of operation with a toroidal field of 8 T and plasma currents of up to 2 MA. Some design details of the toroidal field magnet, the ohmic heating magnet, the metal plasma-facing components, the rf heating and current drive systems, and the power and liquid nitrogen cooling systems are discussed. Vacuum, vessel bake, boronization, and wall-cleaning systems are also discussed. Finally, disruption research results from Alcator C-Mod are presented.
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TL;DR: In this paper, a He Cooled Molten Lithium (HCML) blanket with Ferritic Steel (FS) as a structural material was proposed for DEMO-relevant blanket concept.
Abstract: Through a consideration of the requirements for a DEMO-relevant blanket concept, Korea (KO) has proposed a He Cooled Molten Lithium (HCML) blanket with Ferritic Steel (FS) as a structural material ...
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TL;DR: The UW IEC D-D fusion device has achieved 115 kV pulses in excess of 2 ampere, with pulsed neutron rates of 1.8x10 9 n/s during a 0.5 ms pulse at 10 Hz.
Abstract: This paper overviews the work that has been done to date towards the development of a compact, reliable means to detect Highly Enriched Uranium (HEU) and other fissile materials utilizing a pulsed Inertial Electrostatic Confinement (IEC) D-D fusion device. To date, the UW IEC device has achieved 115 kV pulses in excess of 2 ampere, with pulsed neutron rates of 1.8x10 9 n/s during a 0.5 ms pulse at 10 Hz. MCNP modeling indicates that detection of samples of U-235 as small as 10 grams is achievable at current neutron production rates, and initial pulsed and steady-state HEU detection experiments have verified these results.
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TL;DR: In this paper, an investigation of MHD effects on Flibe simulant fluid (aqueous potassium hydroxide solution) flows has been conducted under the U.S.-Japan JUPITER II collaboration program using "FLIHY" pipe flow facility at UCLA.
Abstract: An investigation of MHD effects on Flibe simulant fluid (aqueous potassium hydroxide solution) flows has been conducted under the U.S.-Japan JUPITER-II collaboration program using "FLIHY" pipe flow facility at UCLA. Mean and fluctuating temperature profiles in a conducting wall pipe were measured for low Reynolds number turbulent flows using a thermocouples probe at constant heat flux condition. It is suggested that the temperature profiles are characterized by interaction between turbulence production, turbulence suppression due to magnetic field and thermal stratification occurred even under the situation where quite small temperature difference exists in the pipe cross-section.
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TL;DR: In this paper, the ASDEX upgrade tokamak experiment has been used for the first time in a fusion device, employing multifrequency gyrotrons, step-tunable in the range 105 to 140 GHz.
Abstract: A new multifrequency electron cyclotron resonance heating (ECRH) system is currently under construction at the ASDEX Upgrade tokamak experiment. This system will, for the first time in a fusion device, employ multifrequency gyrotrons, step-tunable in the range 105 to 140 GHz. In its final stage the system will consist of four gyrotrons with a total power of up to 4 MW and a pulse length of 10 s. The variable frequency will significantly extend the operating range of the ECRH system both for heating and current drive. The matching optics unit includes a set of phase-correcting mirrors for each frequency as well as a pair of broadband polarizer mirrors. The transmission line consists of nonevacuated corrugated HE 11 waveguides with inner diameter of 87 mm and has a total length of∼70 m. A fast steerable launcher enables the steering of the beam over the whole plasma cross section poloidally. The first two-frequency gyrotron has been installed recently. It is equipped with a single-disk diamond window. The next gyrotrons will be step-tunable with two additional frequencies between 105 and 140 GHz. They will require a broadband output window, which will be either a Brewster or a double-disk window.
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TL;DR: In this article, spontaneous toroidal rotation of impurity ions has been observed in the core of Alcator C-Mod plasmas with no external momentum input, and the magnitude of the rotation ranges from -60 km/s (countercur...
Abstract: Spontaneous toroidal rotation of impurity ions has been observed in the core of Alcator C-Mod plasmas with no external momentum input. The magnitude of the rotation ranges from -60 km/s (countercur...
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TL;DR: Spectroscopy of radiation emitted by impurities and hydrogen isotopes plays an important role in the study of magnetically-confined fusion plasmas, both in determining the effects of impurities on plasma behavior and in measurements of plasma parameters such as electron and ion temperatures and densities, particle transport, and particle influx rates.
Abstract: Spectroscopy of radiation emitted by impurities and hydrogen isotopes plays an important role in the study of magnetically-confined fusion plasmas, both in determining the effects of impurities on plasma behavior and in measurements of plasma parameters such as electron and ion temperatures and densities, particle transport, and particle influx rates. This paper reviews spectroscopic diagnostics of plasma radiation that are excited by collisional processes in the plasma, which are termed 'passive' spectroscopic diagnostics to distinguish them from 'active' spectroscopic diagnostics involving injected particle and laser beams. A brief overview of the ionization balance in hot plasmas and the relevant line and continuum radiation excitation mechanisms is given. Instrumentation in the soft X-ray, vacuum ultraviolet, ultraviolet, visible, and near-infrared regions of the spectrum is described and examples of measurements are given. Paths for further development of these measurements and issues for their implementation in a burning plasma environment are discussed.
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TL;DR: In this paper, the nuclear characteristics of a fusion-fission hybrid reactor such as tritium breeding ratio, energy multiplication factor, fissile fuel breeding, first wall radiation damage, and heat deposition have been investigated in a liquid first wall, blanket, and shield for the various mixture compositions of molten salt and heavy metals for blanket layer thicknesses of 20, 30, 40, and 50 cm.
Abstract: Three-dimensional analysis has been made using the MCNP Monte Carlo code and ENDF/B-VI nuclear data. The nuclear characteristics of a fusion-fission hybrid reactor such as tritium breeding ratio, energy multiplication factor, fissile fuel breeding, first wall radiation damage, and heat deposition have been investigated in a liquid first wall, blanket, and shield for the various mixture compositions of molten salt and heavy metals for blanket layer thicknesses of 20, 30, 40, and 50 cm. The neutron flux load at the first wall is assumed to be 10 MW/ m 2 . The flowing molten salt wall is composed of flibe (Li 2 BeF 4 ) as the main constituent with increased mole fractions of heavy metals, 2 to 10% ThF 4 and UF 4 . In terms of all parameters, the mixtures with UF 4 show better performance than the mixtures with ThF 4 . The atomic displacement and the helium, tritium production rates remain well below the presumable limits for all mixture compositions of molten salt and heavy metals and thicknesses of the blanket.