Electron tomography is a well-established technique for three-dimensional structure determination of (almost) amorphous specimens in life sciences applications. With the recent advances in nanotechnology and the semiconductor industry, there is also an increasing need for high-resolution three-dimensional (3D) structural information in physical sciences. In this article, we evaluate the capabilities and limitations of transmission electron microscopy (TEM) and high-angle-annular-dark-field scanning transmission electron microscopy (HAADF-STEM) tomography for the 3D structural characterization of partially crystalline to highly crystalline materials. Our analysis of catalysts, a hydrogen storage material, and different semiconductor devices shows that features with a diameter as small as 1-2 nm can be resolved in three dimensions by electron tomography. For partially crystalline materials with small single crystalline domains, bright-field TEM tomography provides reliable 3D structural information. HAADF-STEM tomography is more versatile and can also be used for high-resolution 3D imaging of highly crystalline materials such as semiconductor devices.
A compact scintillator-based imaging neutral particle analyzer (INPA) that provides energy and radially resolved measurements of confined fast ions has been designed and built in the DIII-D tokamak. The system measures charge-exchanged energetic neutrals by viewing an active neutral beam source through a 1D pinhole camera with a rear collimating slit that defines the neutral particle collection sightline and radial positions probed in the plasma. The incident neutrals are ionized by ultra-thin carbon stripping foils of 10 nm thickness with the local tokamak magnetic field acting as a magnetic spectrometer to disperse the ions onto a scintillator. The strike position on the phosphor is determined by the fast ion energy and sightline while the intensity of emitted light from the phosphor is proportional to the ion flux. Fast camera measurements of the scintillator provide 2D images of the escaping neutrals mapped to energy and radial position in the plasma. The INPA system images a broad radial range from the plasma core to edge and deuterium energies up to 80 keV, with energy resolution of ∼7.5 keV and pitch angle resolution of ∼5°. The first data obtained from the INPA demonstrates that the system has excellent signal to noise ratio and provides unprecedented details of phase space dynamics.
A: A novel imaging neutral particle analyzer (INPA) which provides energy-resolved radial profiles of confined fast ions on the DIII-D tokamak is discussed. The INPA measures chargeexchanged energetic neutrals by viewing an "active" neutral beam through a 1D pinhole camera with a rear collimating slit that defines the neutral particle collection sightlines. The incident neutrals are ionized by 10 nm thick carbon stripping foils and the local tokamak magnetic field acts as a magnetic spectrometer to disperse ions onto a phosphor scintillator. A fast (160 Hz) CCD camera provides 2D images of the escaping neutrals mapped to energy and radial position in the plasma. The INPA typically probes passing orbits with an energy resolution of ≈7.5 keV (E = 20 − 80 keV) and a spatial resolution that ranges from 4 cm half width at half max (HWHM) in the core to 3 cm at the plasma edge. The INPA clearly resolves fast ion transport in localized regions of phase space due to individual sawteeth and a replenishing before each event. Extension to proton and triton DD fusion product measurements in high-performance DIII-D plasmas is analyzed and simulations show peak signals which are 10 −6 lower than that from neutral beam ions for the same configuration. Possible modifications to increase fusion product signals are discussed along with upgrades to improve the overall diagnostic performance. K: Plasma diagnostics -charged-particle spectroscopy; Nuclear instruments and methods for hot plasma diagnostics 1Corresponding author.
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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