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Pumpout of argon ions by ICRF waves has been observed in C-Mod deuterium L- and I-mode plasmas that had a substantial hydrogen fraction. The effect is manifested by a reduction of core argon x-ray brightness up to a factor of 90% on time scales of tens of milliseconds following injection of ICRF power. For Ar16+, the pumpout is strongest for hydrogen minority concentrations between 0.25 and 0.4, when the ICRF waves are not expected to result in minority heating. Modeling with the TORIC code suggests that the pumpout process occurs when the H/D mode conversion layer overlaps with the 2nd harmonic impurity resonance layer. The magnitude of the argon pumpout is independent of ICRF power above an apparent threshold of ∼500 kW, independent of electron density and appears to decrease as the plasma current is increased. Potential application as a heavy impurity control tool in reactors is discussed.

The SPARC tokamak project, currently in engineering design, aims to achieve breakeven and burning plasma conditions in a compact device, thanks to new developments in high-temperature superconductor technology. With a magnetic field of 12.2 T on axis and 8.7 MA of plasma current, SPARC is predicted to produce 140 MW of fusion power with a plasma gain of Q ≈ 11, providing ample margin with respect to its mission of Q > 2. All tokamak systems are being designed to produce this landmark plasma discharge, thus enabling the study of burning plasma physics and tokamak operations in reactor relevant conditions to pave the way for the design and construction of a compact, high-field fusion power plant. Construction of SPARC is planned to begin by mid-2021.

Synthesis of reversible sequential circuits is a very new research area. It has been shown that such circuits can be implemented using quantum dot cellular automata. Other work has used traditional designs for sequential circuits and replaced the flip-flops and the gates with their reversible counterparts. Our earlier work uses a direct feedback method without any flip-flops, improving upon the replacement technique in both quantum cost and ancilla inputs. We present here a further improved version of the direct feedback method. Design examples show that the proposed method produces better results than our earlier method in terms of both quantum cost and ancilla inputs. We also propose the first technique for online testing of single line faults in sequential reversible circuits.

We present an overview and analysis of existing work in the design of online testable reversible logic circuits, as well as propose new approaches for the design of such circuits. We explain how previously proposed approaches are unnecessarily high in overhead and in many cases do not provide adequate fault coverage. Proofs of the correctness of our approaches are provided, and discussions of the advantages and disadvantages of each design approach are given. Experimental results comparing our approaches to existing work are presented as well. Both approaches that we propose have better fault coverage and significantly lower overheads than previous approaches.

Tungsten will be an important element in nearly all future fusion reactors because of its presence in plasma facing components. This makes tungsten a good candidate for a diagnostic element for ion temperature and toroidal velocity measurement, and it makes understanding tungsten emissions important for tokamak power balance. The effect of tungsten on tokamak plasmas is investigated at the Alcator C-Mod tokamak using VUV, bolometry, and soft X-ray spectroscopy. Tungsten was present in Alcator C-Mod as a plasma facing component and through laser blow-off impurity injection. Quasi-continuum emission previously seen at other tokamaks has been identified. Theoretical predictions are presented of tungsten emission that could be expected in future Alcator C-Mod measurements. Furthermore, spectra of highly charged tungsten ions have been studied at the SuperEBIT electron beam ion trap. This emission could prove useful for spectroscopic diagnostics of future high-temperature fusion reactor plasmas.

Reversible logic is being suggested as a possibility for overcoming potential power loss and heat dissipation problems that the computing industry may soon be at a loss to overcome. However, for reversible logic to be a solution we must have techniques for synthesizing function descriptions to reversible circuits. This paper presents an improved ESOP-based reversible logic synthesis approach which leverages situations where cubes are shared by multiple outputs and ensures that the implementation of each cube requires just one Toffoli gate. It has the potential to minimize both gate count and quantum cost, and in fact our experimental results show that this technique can reduce the quantum cost up to 75% compared to results from the existing work.

Reversible logic has been suggested as one solution to the problem of power consumption in today's electronic devices. This paper addresses the issue of designing reversible latches and provides an overview and analysis of some proposed designs.

This paper proposes templates for positive and negative control Toffoli gates for post synthesis optimization of reversible circuits. Templates 1 − 5 can be applied to two adjacent Toffoli gates T 1(C 1,t 1) and T 2(C 2,t 2) where C i is the set of controls, |C 1| = |C 2|, and |t 1| = |t 2|. Templates 6 − 7 can be applied to two different size Toffoli gates T 1(C 1,t 1) and T 2(C 2,t 2) where C i is the set of controls, |C 1| = |C 2| and t i is the target, |t 1| = |t 2|. When applying our templates to circuits generated by the improved shared cube synthesis approach [14] a reduction in quantum cost was achieved for 98 of the 122 circuits. On average a 16.82% reduction in quantum cost was achieved, and in some cases up to 49.60% reduction was obtained.

Trace non-recycling impurities have been injected into Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] plasmas in order to determine impurity transport coefficients. Subsequent impurity emission has been observed with spatially scanning x-ray and Vacuum Ultra-Violet (VUV) spectrometer systems. Measured time-resolved brightness profiles of helium- and lithium-like transitions have been compared with those calculated from a transport code which includes impurity diffusion and convection in conjunction with an atomic physics package for individual line emission. During Low-Confinement-Mode (L-mode) plasmas, the transport can be characterized by pure diffusion, with coefficients ∼5000 cm2/s, reflecting the ∼20 ms decay in the x-ray and VUV line brightnesses. During High-Confinement-Modes (H-modes), the impurity confinement times are much longer, and the modelling requires that there be a strong inward convection (of order 1000 cm/s) near the plasma edge, with greatly reduced diffusion (o...

This paper presents some new considerations for spectral techniques for classification of Boolean functions. These considerations incorporate discussions of the feasibility of extending this classification technique beyond n=5. A new implementation is presented along with a basic analysis of the complexity of the problem. We also note a correction to results in this area that were reported in previous work.

The evolution of wireless networks and mobile devices has resulted in increased concerns about performance and security of mobile payment systems. In this paper we propose a new secured architecture for two-party mobile payments, e.g. mobile banking. The proposed architecture employs a lightweight cryptography system that combines public key and symmetric key cryptography systems (ECDSA and AES), as well as a multi-factor authentication mechanism. These are coupled with a transaction log strategy to satisfy the properties of confidentiality, authentication, integrity and non-repudiation. Compared to some existing mobile payment platforms the proposed architecture is a lightweight secured mechanism that is more suitable for two-party banking transactions over resource-limited mobile devices.

Many systems exist that store and manipulate data; however, many do no have sufficient support for spatial data Many data structures are proposed that are intended specifically for spatial data; however, software implementations have not performed as well as hoped. This work presents a feasibility study investigating the use of a FPGA for the implementation of a structure to support spatial search and retrieval.

Recent work has begun to investigate the advantages of using reversible logic for the design of circuits. The majority of work, however, has limited itself to combinational logic. Researchers are just now beginning to suggest possibilities for sequential implementations. This paper performs a closer analysis of three latch designs proposed in previous work and suggests advantages and disadvantages of each

Although many researchers are investigating techniques to synthesize reversible combinational logic, there is little work in the area of sequential reversible logic. We present an analysis of a basic memory element, the RS-latch, and a number of possible implementations. We then go on to introduce four reversible flip-flop designs based on the reversible RS-latch implementation.

An implementation of an algorithm for string matching, commonly used in DNA string analysis, using configurable technology is proposed. The design of the circuit allows for pipelining to provide a performance increase. The proposal is unique in that we suggest a design that is specific to certain parameters of the problem, but may be reused for any particular instance of the problem that matches these parameters. The use of a field programmable gate array allows the implementation to be instance specific, thus ensuring maximal usage of the hardware. Analysis and preliminary results based on a prototype implementation are presented.

H-mode experiments on Alcator C-Mod [I.H. Hutchinson, et al., Phys. Plasma 1 (1994) 1511] which exhibit an internal transport barrier (ITB), have been examined with gyrokinetic simulations, near the ITB onset time. Linear simulations support the picture of ion and electron temperature gradient (ITG, ETG) microturbulence driving high {chi}{sub i} and {chi}{sub e}, respectively, and that stable ITG correlates with reduced particle transport and improved ion thermal confinement on C-Mod. In the barrier region ITG is weakly unstable, with a critical temperature gradient higher than expected from standard models. Nonlinear calculations and the role of E x B shear suppression of turbulence outside the plasma core are discussed in light of recent profile measurements for the toroidal velocity. The gyrokinetic model benchmarks successfully against experiment in the plasma core.

Linear simulations of plasma microturbulence are used with recent radial profiles of toroidal velocity from similar plasmas to consider nonlinear microturbulence simulations and observed transport analysis on Alcator C-Mod. We focus on internal transport barrier (ITB) formation in fully equilibrated H-mode plasmas with nearly flat velocity profiles. Velocity profile data, transport analysis and linear growth rates are combined to integrate data and simulation, and explore the effects of toroidal velocity on benchmarking simulations. Areas of interest for future nonlinear simulations are identified. A good gyrokinetic benchmark is found in the plasma core, without extensive nonlinear simulations. RF-heated C-Mod H-mode experiments, which exhibit an ITB, have been studied with the massively parallel code GS2 towards validation of gyrokinetic microturbulence models. New, linear, gyrokinetic calculations are reported and discussed in connection with transport analysis near the ITB trigger time of shot No.1001220016.

Recent H-mode experiments on Alcator C-Mod [I.H. Hutchinson, et al., Phys. Plasmas 1 (1994) 1511] which exhibit an internal transport barrier (ITB), have been examined with flux tube geometry gyrokinetic simulations, using the massively parallel code GS2 [M. Kotschenreuther, G. Rewoldt, and W.M. Tang, Comput. Phys. Commun. 88 (1995) 128]. The simulations support the picture of ion/electron temperature gradient (ITG/ETG) microturbulence driving high xi/ xe and that suppressed ITG causes reduced particle transport and improved ci on C-Mod. Nonlinear calculations for C-Mod confirm initial linear simulations, which predicted ITG stability in the barrier region just before ITB formation, without invoking E x B shear suppression of turbulence. Nonlinear fluxes are compared to experiment, which both show low heat transport in the ITB and higher transport within and outside of the barrier region.

Recent H-mode experiments on NSTX [National Spherical Torus Experiment] and experiments on Alcator-CMOD, which also exhibit internal transport barriers (ITB), have been examined with gyrokinetic simulations with the GS2 and GYRO codes to identify the underlying key plasma parameters for control of plasma performance and, ultimately, the successful operation of future reactors such as ITER [International Thermonuclear Experimental Reactor]. On NSTX the H-mode is characterized by remarkably good ion confinement and electron temperature profiles highly resilient in time. On CMOD, an ITB with a very steep electron density profile develops following off-axis radio-frequency heating and establishment of H-mode. Both experiments exhibit ion thermal confinement at the neoclassical level. Electron confinement is also good in the CMOD core.

New symmetries of degree two are introduced, along with spectral techniques for identifying these symmetries. Some applications of these symmetries are discussed, in particular their application to the construction of binary decision diagrams and the implementation of Boolean functions.

Reconfigurable hardware has recently shown itself to be an appropriate solution to speeding up problems that are highly dependent on a particular complex or repetitive sub-algorithm. In most cases, these types of solutions lend themselves well to parallel solutions. The optimal design on field programmable gate arrays (FPGAs) for problems with algorithms or sub-algorithms that can be highly parallelised is investigated. In addition, a classification system is introduced, which categorises FPGA-based solutions into 'instance-specific' and 'parameter-specific'.

A mercuric iodide (HgI/sub 2/) detector has been used to obtain x-ray spectra in the energy range from 5 to 200 keV from the Alcator-C tokamak. During high-density Ohmic operation of Alcator-C, this detection system provides a reliable electron-temperature diagnostic. Nonthermal x-ray spectra above 20 keV are observed under certain conditions when a substantial amount of lower-hybrid rf (LHRF) power is injected. The magnitude of this nonthermal behavior strongly increases as the electron density is lowered and is more pronounced in deuterium plasmas than in hydrogen. Model electron distribution functions, which can give rise to the observed x-ray spectra, are discussed.

A new technique that makes use of a systolic array structure is proposed for solving the common approximate substring (CAS) problem. This approach extends the technique introduced in (Kent et al., 2006) from the computation of the edit-distance between two strings to the more encompassing CAS problem. The technique presented is validated and analyzed through simulation.

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.