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Dmitri Mossessian

Dmitri Mossessian
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127
Publications
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3,154
Citations
Citations since 2016
2 Research Items
882 Citations
2016201720182019202020212022020406080100120140
2016201720182019202020212022020406080100120140
2016201720182019202020212022020406080100120140
2016201720182019202020212022020406080100120140

Publications

Publications (127)
Chapter
This chapter discusses multiple definitions of the yield curve and provides a conceptual understanding on the construction of yield curves for several markets. It reviews several definitions of the yield curve and examines the basic principles of the arbitrage-free pricing as they apply to yield curve construction. The chapter also reviews cases in...
Chapter
This chapter presents an overview of the modern state of term structure modeling techniques. It provides an analytical framework that is applicable to all short rate models and considers them from the point of view of the classic approach of pricing by replication. The market price of risk and its relation to the drift of a short rate model are imp...
Article
Full-text available
The sources of neutrals at the outer midplane of the plasma are discussed. We find that both the flux of neutrals escaping the divertor through leaks and ion recycling at main chamber surfaces appear to contribute. The ion flux to the walls is larger than the flux entering the divertor and comparable to recycling at the divertor plate. The cause of...
Article
Full-text available
An overview of the diagnostics installed on the Al-cator C-Mod tokamak is presented. Approximately 25 diagnostic systems are being operated on C-Mod. The compact design of the machine and the cryostat enclos-ing the vacuum vessel and magnetic field coils make access challenging. Diagnostics are used to study four focus areas: transport, plasma boun...
Article
Full-text available
Local edge electron parameters are measured in the Alcator C-Mod tokamak, during discharges in which input power is continuously ramped up and down, leading to transitions from the low-confinement (L) to high confinement (H) mode and back to L- mode. This allows measurement of the accessible portions of the non-monotonic flux- gradient relationship...
Article
ABSTRACT H-mode research on Alcator C-Mod is described, with a focus on the edge transport bar- rier (ETB). ETB pedestals are characterized using several diagnostics, leading to a thorough description of profile structure in H-mode. L-H transition criteria are discussed, along with the fast evolution of the pedestal following the L-H transition. H-...
Article
Spontaneous toroidal rotation of impurity ions has been observed in the core ofAlcator C-Modplasmas with no external momentum input. The magnitude of the rotation ranges from -60 km/s (countercurrent) in limiter L-mode discharges to + 140 km/s (cocurrent) in ion cyclotron range of frequencies-heated H-mode plasmas. The core rotation in L-mode plasm...
Article
Full-text available
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 the Alcator (linear) regime have been confirmed, and the saturated confinement regime has been shown to be equivalent to that of L-mode. For auxiliary he...
Article
Full-text available
The object of this review is to summarize the achievements of research on the Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 (1994) and Marmar, Fusion Sci. Technol. 51, 261 (2007)] and to place that research in the context of the quest for practical fusion energy. C-Mod is a compact, high-field tokamak, whose unique design and oper...
Article
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Similarity plasmas are studied in JET, ASDEX Upgrade and ALCATOR C-Mod to test the validity of dimensional constraints for core profiles and profiles at the plasma edge in H-modes with and without large dge Localised Modes and at the H-mode transition. Core and H-mode edge profiles in the studied comparison pairs of pulses match within uncertaintie...
Article
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 (countercurrent) in limiter L-mode discharges to + 140 km/s (cocurrent) in ion cyclotron range of frequencies-heated H-mode plasmas. The core rotation in L-mode pla...
Article
Full-text available
Edge transport barrier (ETB) studies on the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511 (1994)] investigate pedestal scalings and the radial transport of plasma and neutrals. Pedestal profiles show trends with plasma operational parameters such as total current IP. A ballooning-like IP2 dependence is seen in the pressure gradient, despite calculat...
Article
Full-text available
Plasma profiles across the separatrix and scrape-off layer (SOL) in Alcator C-Mod are examined for a range of plasma densities, currents and magnetic fields in Ohmic L-mode discharges and for a subset of conditions in Ohmic H-mode discharges. In all plasmas, electron pressure gradient scale lengths ( ) exhibit a minimum value just outside the separ...
Article
Full-text available
During the operation of the Alcator C-Mod tokamak three common classifications of H-mode are observed: 1) ELM-free H-mode, 2) ELMy H-mode, and 3) so-called ``enhanced D alpha'' (EDA) H-mode accompanied by a quasi-coherent mode (QCM) edge relaxation mechanism. In all cases, the transition to H-mode occurs concurrently with the formation of edge temp...
Article
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Since it is uncertain if ITER operation is compatible with type-I edge localized modes (ELMs), the study of alternative ELM regimes is an urgent issue. This paper reports on experiments on JET aiming to find scenarios with small ELMs and good confinement, such as the type-II ELMs in ASDEX Upgrade, the enhanced D-alpha H-mode in Alcator C-mod or the...
Article
Full-text available
Research on the Alcator C-Mod tokamak has emphasized RF heating, self-generated flows, momentum transport, scrape-off layer (SOL) turbulence and transport and the physics of transport barrier transitions, stability and control. The machine operates with P-RF up to 6 MW corresponding to power densities on the antenna of 10 MW m(-2). Analysis of rota...
Article
Full-text available
Factor of ~2 higher power thresholds for low-to high-confinement mode transitions (L-H) with unfavorable x-point topologies in Alcator C-Mod [Phys. Plasmas 1, 1511 (1994)] are linked to flow boundary conditions imposed by the scrape-off layer (SOL). Ballooning-like transport drives flow along magnetic field lines from low-to high-field regions with...
Article
Full-text available
The recently upgraded phase-contrast imaging (PCI) diagnostic is used to characterize the transition from the low (L) to the enhanced Dα (EDA) high (H) confinement mode in Alcator C-Mod [ I. H. Hutchinson, R. Boivin, F. Bombarda et al., Phys. Plasmas 1, 1511 (1994) ] plasmas. PCI yields information on line integrated density fluctuations along vert...
Article
An alternative method of absolute calibration of Thomson scattering (TS) systems is described. The method is based on the measurements of electron cyclotron emission (ECE) from the plasma. If the plasma density reaches some critical value the emission at some frequencies is cut off and an abrupt loss of signal is registered by the ECE diagnostic. T...
Article
The observed toroidal rotation in Alcator C-Mod Ohmic L-mode plasmas has been found to depend strongly on the magnetic configuration. For standard discharges with a lower single null and the ion B × ∇B drift downward, and with BT = 5.4 T, IP = 0.8 MA and ne = 1.4 × 1020 m−3, the core toroidal rotation is measured to be in the range of 10–20 km s−1...
Article
Edge profile data for H-mode discharges in 6 tokamaks have been analysed with the main focus on the edge density profile as well as electron temperature and density gradient lengths and steep gradient zone widths. A uniform procedure of data treatment and assignment of the separatrix position via power balance allowed to put the multi-machine data...
Article
Pedestal-forming edge transport barriers (ETBs) in tokamak plasmas and the physics governing them are linked to the enhancement of confinement obtained in H-mode plasmas. Studies on Alcator C-Mod employ experimental measurements and simple 1-D transport models in order to better understand ETB physics. We examine the influences of ionization and ch...
Article
Recent experimental results from the new Compact Neutral Particle Analyzer (CNPA) and a completed multi-detector upgrade of the diagnostic are presented. The CNPA uses Si diodes to detect charge-exchanged (CX) induced energetic (>20keV) neutral particles for ICRF hydrogen minority tail temperature diagnosis. A diagnostic neutral beam (DNB) provides...
Article
The core Thomson scattering (TS) diagnostic is used to study profiles of the electron temperature and density in the core plasma region on the Alcator C-Mod tokamak. Results of the profile measurements will be presented as well as comparison with T_e, ne measurements from other diagnostics. Systematic analysis of Z_eff behavior in different plasma...
Article
Full-text available
At certain values of the edge rotational transform, ι a = 1/q a , the confinement time of plasmas in the Wendelstein 7-AS (W7-AS) stellarator was found to be very sensitive to small modifications of ι a . Since ι a could be changed reproducibly by e.g. a small plasma current, these transitions provided a means to perform systematic investigations o...
Article
Full-text available
Mode conversion MC of long wavelength fast electromagnetic magnetosonic waves fast wave, or FW into shorter wavelength electrostatic ion-Bernstein, or IBW or slow electromagnetic ion cyclotron, or ICW waves is of great interest in laboratory, magnetic fusion and space physics experiments. Such processes are particularly important in multi-ion speci...
Article
Full-text available
Edge profiles during the L H transition and pedestal evolution in the Alcator C-Mod tokamak have been measured with high spatial and time resolution. For input power near the threshold, periodic 'dithering' cycles are seen, and the sustained transition occurs in a series of steps that appear related to this oscillatory behaviour. Even at a higher p...
Article
Full-text available
The time evolution of toroidal rotation velocity profiles has been measured in Alcator C-Mod [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] plasmas using a tangentially viewing x-ray spectrometer array. The strong co-current toroidal rotation in enhanced Dα (EDA) high confinement mode (H-mode) plasmas is observed to propagate in from the edge on...
Article
Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas. The time evolution of core impurity toroidal rotation velocity profiles has been measured with a tangentially viewing crystal x-ray spectrometer array. Following the L-mode to EDA (enhanced Dα) H-mode transition in both Ohmic and ion cyclotron range of frequencies heat...
Article
Full-text available
We review and test the peeling–ballooning model for edge localized modes (ELMs) and pedestal constraints, a model based upon theoretical analysis of magnetohydrodynamic (MHD) instabilities that can limit the pedestal height and drive ELMs. A highly efficient MHD stability code, ELITE, is used to calculate quantitative stability constraints on the p...
Article
ICRF mode conversion (MC) in H(3He, D) and D(H) plasmas have been studied in detail in Alcator C-Mod. In H(3He, D) plasma, the mode converted ion cyclotron wave (MC ICW) was observed in tokamak plasmas for the first time using a phase contrast imaging system. The MC ICW was observed in the low field side of the ion-ion hybrid layer, and generally h...
Article
Full-text available
Research on the Alcator C-Mod tokamak [1] is focused on high particle- and power-density plasma regimes to understand particle and energy transport in the core, the dynamics of the H-mode pedestal, and scrape-off layer and divertor physics. The auxiliary heating is provided exclusively by RF waves, and both the physics and technology of RF heating...
Conference Paper
Full-text available
The DIII-D research program is developing the scientific basis for advanced tokamak (AT) modes of operation in order to enhance the attractiveness of the tokamak as an energy producing system. Since the last international atomic energy agency (IAEA) meeting, we have made significant progress in developing the building blocks needed for AT operation...
Article
Details of interactions between plasma and neutral atomic species at the tokamak plasma edge are crucial to the assessment of local transport and the consequent profiles of plasma temperature and density. Since edge quantities directly affect core plasma confinement, it is important to evaluate the influence of these edge neutral-plasma interaction...
Article
The "quasi-coherent" (QC) mode is believed to be responsible(A.E. Hubbard, Phys. Plasmas 8 (2001) p. 2033.) for the reduced particle confinement in the enhanced D_alpha (EDA) H-mode. The QC mode has a frequency between 60-150 kHz and is localized to the pedestal density gradient region(A. Mazurenko, et al., PRL 89 (2002) p 225004.). The associated...
Article
Internal transport barrier (ITB) plasmas with peak pressures of 0.25 MPa and pressure gradients as large as 2.5 MPa m−1 have been produced in Alcator C-Mod using off-axis ion cyclotron range of frequencies (ICRF) heating. The onset of the ITBs is apparent when the pressure gradient exceeds 1.0 MPa m−1, which is similar to the JET criterion of ρs/L≥...
Article
Localized direct electron heating (EH) by mode-converted (MC) ion cyclotron range of frequencies (ICRF) waves in D(H) tokamak plasmas has been clearly observed for the first time in Alcator C-Mod. Both on- and off-axis (high field side) mode conversion EH (MCEH) have been observed. The MCEH profile was obtained from a break-in-slope analysis of ele...
Article
For steady state high-confinement-mode (H-mode) operation, a relaxation mechanism is required to limit build-up of the edge gradient and impurity content. Alcator C-Mod [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] sees two such mechanisms—EDA (enhanced D-alpha H mode) and grassy ELMs (edge localized modes), but not large type I ELMs. In EDA th...
Article
Experiments were carried out to study the similarity of H-mode (high confinement mode) physics on the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] and DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] tokamaks comparing plasmas with matched local edge dimensionless parameters (β, ρ∗, ν∗, q95) and shape (ε, κ, δ). It was obs...
Article
The Thomson scattering (TS) diagnostics set has been upgraded to deliver measurements of electron temperature (Te) and density (ne) with improved temporal and spatial resolution. Two 30 Hz, 1.3 J Nd-doped yttrium–aluminum–garnet (Nd:YAG) lasers share a vertical beam path through the tokamak plasma and are fired in an alternating fashion, allowing t...
Article
Scientific and technical activities on JET focus on the issues likely to affect the ITER design and operation. Our understanding of the ITER reference mode of operation, the ELMy H-mode, has progressed significantly. The extrapolation of ELM size to ITER has been re-evaluated. Neoclassical tearing modes have been shown to be meta-stable in JET, and...
Article
A comparison of experimental measurements and theoretical studies of the quasicoherent (QC) mode, observed at high densities during enhanced D(alpha) (EDA) H mode in the Alcator C-Mod tokamak, are reported. The QC mode is a high frequency ( approximately 100 kHz) nearly sinusoidal fluctuation in density and magnetic field, localized in the steep de...
Article
We present turbulent transport simulations that are compatible with measurements in the core of typical C-Mod H-mode plasmas. Our two-species nonlinear gyrokinetic simulations of turbulent transport due to long wavelength electrostatic drift-type instabilities employ a flux-tube domain based on a realistic non-circular magnetic geometry. These GS2...
Article
A common method for determining electron temperature in a tokamak is to measure second harmonic electron cyclotron emission. This has implicit limitations, however, because cutoff of emission may occur when experiments operate with high electron density and low magnetic fields. This has been problematic in the internal transport barrier regime on C...
Article
For steady state H-mode operation, a relaxation mechanism is required to limit build-up of the edge gradient and impurity accumulation. The major relaxation mechanism seen on most of the existing tokamaks - large type I ELMs - drive high particle and energy fluxes that present a significant power load on the divertor plates. On Alcator C-Mod, howev...
Article
The Quasi-Coherent (QC) mode has been observed at high densities during enhanced D-alpha (EDA) H-Mode in the Alcator C-Mod tokamak. The QC mode is believed to be responsible for the reduced particle (and impurity) confinement during H-mode operation, so as to allow quasi-steady state operation of the tokamak. It has been proposed that the QC mode i...
Article
Edge transport barriers in tokamaks characterize the high confinement mode, or H-mode. The elevated electron temperature (T_e) and density (n_e) found just inside the plasma last closed flux surface (LCFS) are termed pedestals, and the region over which T_e, ne rise from their LCFS values to their pedestal values is indicative of transport barrier...
Article
Simultaneous high resolution measurements of the soft x-ray emission at the top and outboard edge of the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] are presented. Impurity density profiles are derived from these measurements. The impurity density varies considerably on a flux surface in the high confinement mode (...
Article
On the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511 (1994)], radial profiles of electron temperature (Te) and density (ne) are measured at the plasma edge with millimeter resolution Thomson scattering [Rev. Sci. Instrum. 72, 1107 (2001)]. Edge transport barriers in the high confinement regime (H mode) exhibit Te, ne pedestals with typical widths of...
Article
Double transport barrier plasmas comprised of an edge enhanced Dα (EDA) H-mode pedestal and an internal transport barrier (ITB) have been observed in Alcator C-Mod. The ITB can be routinely produced in ICRF heated plasmas by locating the wave resonance off-axis near |r/a|~0.5, provided the target plasma average density is above ~1.4×1020 m-3, and c...
Article
Co-current central impurity toroidal rotation has been observed in Alcator C-Mod plasmas with on-axis ICRF heating. The rotation velocity increases with plasma stored energy and decreases with plasma current. Very similar behaviour has been seen during ohmic H modes, which suggests that the rotation, generated in the absence of an external momentum...
Article
Full-text available
Research on the Alcator C-Mod tokamak is focused on exploiting compact high density plasmas to understand core transport and heating, the physics of the H mode transport barrier, and the dynamics of the scrape-off layer and divertor. Rapid toroidal acceleration of the plasma core is observed during ohmic heated H modes and indicates a momentum pinc...
Article
Double transport barrier modes (simultaneous core and edge transport barrier) have been observed with off-axis ion cyclotron range of frequencies (ICRF) heating in the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. An internal transport barrier (ITB) is routinely produced in enhanced DαH-mode (EDA) discharges where t...
Article
The dependence of the edge pedestal electron pressure on magnetic geometry is studied using the international pedestal database. For type I ELM discharges, the pressure normalized to B2 is found to scale roughly inversely with major radius and inverse aspect ratio. In addition, a strong increase in pressure with increasing shape is found when the p...
Article
Local edge electron parameters are measured in the Alcator C-Mod tokamak, during discharges in which input power is continuously ramped up and down, leading to transitions from the low-confinement mode (L-mode) to high-confinement mode (H-mode) mode and back to L-mode. This allows measurement of the accessible portions of the non-monotonic flux-gra...
Article
Under most operational conditions of Alcator C-Mod, the dominant type of H-mode is the steady state enhanced Dα (EDA) mode, characterized by good energy confinement, continuously degraded impurity confinement and absence of regular edge localized modes (ELMs). In this regime, a quasicoherent (QC) electromagnetic mode (kθ~5 cm-1, f~100 kHz) is obser...