In the course of the Preliminary Tritium Experiment in JET, where combined deuterium and tritium neutral beam injection generated a DT fusion power of 1.7 MW, ion cyclotron emission (ICE) was measured in the frequency range Y I 180 MHz. The ICE spectra contain superthermal, narrow, equally spaced emission lines, which correspond to successive cyclotron harmonics of deuterons or alpha particles at the outer midplane, close to the last closed flux surface at major radius R -4.0 m. Above about 100 MHz the lines merge into a relatively intense continuum. The ICE signal fluctuates rapidly in time, and is extinguished whenever a large amplitude edge localized mode (ELM) occurs.In pure deuterium and mixed DT discharges ICE spectra are similar in form, but on changing from pure D to mixed D + T neutral beam injection at constant power, the intensity of the ICE rises in proportion to the increased neutron flux: this indicates that fusion alpha particlesand not beam ionsprovide the free energy to generate ICE. The JET ICE database, which now extends over a range of six decades in signal intensity, shows that the time averaged ICE power increases almost linearly with total neutron flux. The rise and fall of the neutron flux during a single discharge is closely followed by that of the ICE signal, which is delayed by a time of the order of the fusion product slowing down time. This feature is well modelled by a TRANSP code simulation of the density of deeply trapped fusion products reaching the plasma edge. Calculations reveal a class of fusion products, born in the core, which make orbital excursions of sufficient size to reach the outer midplane edge. There, the velocity distribution has a ring structure, which is found to be linearly unstable to relaxation to obliquely propagating waves on the fast Alfv6n-ion Bernstein branch at all ion cyclotron harmonics. The paper shows how ICE provides a unique diagnostic for fusion alpha particles.
Recent results on investigations of Alfvén eigenmodes, fast ion confinement and fast ion diagnostics in JT-60U are presented. It was found that toroidicity induced Alfvén eigenmodes (TAEs) were stable in negative shear discharges with a large density gradient at the internal transport barrier (ITB). If the density gradient was small at the ITB, multiple TAEs appeared around the q = 2 surface (pitch minimum) and showed a large frequency chirping (∆f ≈ 80 kHz). In low-q positive shear discharges, the location of the TAEs changed from outside to inside the q = 1 surface, owing to a temporal change of the q profile. A significant depression of the megaelectronvolt ion population was observed only with high-n (n up to 14) multiple TAEs inside the q = 1 surface. Non-circular triangularity induced Alfvén eigenmodes were observed for the first time. Considerable depression of the triton burnup was observed in negative shear discharges. Orbit following Monte Carlo simulations indicated that ripple loss was responsible for the enhanced triton losses. The fast ion stored energies in ICRF heated negative shear discharges were comparable to those of positive shear plasmas. Tail ion temperatures in high (second to fourth) harmonic ICRF heating experiments were first analysed with an MeV neutral particle analyser. The behaviour of MeV ions produced by ICRF heating was studied with gamma ray diagnostics. A scintillating fibre detector system for detecting the 14 MeV neutron emission was developed for the triton burnup studies. Ion cyclotron emission measurements discriminating between parallel and perpendicular components of the electric field were carried out for the first time.
Fusion performance of reversed shear discharges with an L-mode edge has been significantly improved in a thermonuclear dominant regime with up to 2.8 MA of plasma current in the JT-60U tokamak. The core plasma energy is efficiently confined due to the existence of persistent internal transport barriers formed for both ions and electrons at a large minor radius of r͞a ϳ 0.7 near the boundary of the reversed shear region. In an assumed deuterium-tritium fuel, the peak fusion amplification factor defined for transient conditions involving the dW ͞dt term would be in excess of unity. [S0031-9007(97)04592-4] PACS numbers: 52.55.Fa, 52.55.PiThe reversed shear discharges are considered attractive for a steady state operation with a large bootstrap current fraction in tokamak reactors as proposed for SSTR [1] and ITER [2], since it would be possible to match the hollow current profile to a bootstrap current profile in a steady state. While the central magnetic shear in tokamak plasmas is naturally reversed during a sufficiently long discharge duration with a large bootstrap current fraction [3], the forced shear reversal operation by enhancing a skin current effect has become important for establishing a controlled approach to the steady state [4].In nuclear fusion research, critical conditions in which fusion power produced in plasmas is equal to loss power from the plasmas have been pursued as a crucial milestone ultimately towards the commercial use of thermonuclear fusion energy. In order to determine whether the reversed shear scenario is workable, it is crucially important to demonstrate the fusion-relevant performance, particularly in the thermonuclear fusion regime with the shear reversal operation. So far, however, most of the previous experiments addressing high fusion reactivity in tokamaks have been limited to a hot-ion regime with substantial beam-thermal reactions for deuterium plasmas in TFTR supershot [5], JET hot-ion H mode [6] and JT-60U high-b p H mode [7], and deuterium-tritium (D-T) plasmas in TFTR supershot [8]. Although fusion performance has been recently enhanced with strong profile and shaping control in deuterium reversed shear plasmas with an H-mode edge in DIII-D [9], the projected D-T fusion power is substantially below the loss power from the plasma. In the present paper, it is shown that fusion performance has been significantly improved in JT-60U for reversed shear discharges with an L-mode edge in a thermonuclear fusion regime, so that the transient fusion amplification factor defined as below would be in excess of unity.In JT-60U, the experimental campaign of the reversed shear discharges aiming at high fusion amplification factor ͑Q͒ has been intensively performed with D beams into D plasmas. The confinement properties for the reversed shear discharges created in JT-60U are characterized by (i) the significant reduction of heat and particle transport for electrons as well as ions around the internal transport barrier (ITB), (ii) a large extension of the enhanced confinement region up...
JET was extensively modified in the 1992/93 shutdown. The new pumped divertor and many new systems were brought into operation early in 1994. Operations have progressed to 4 MA plasma current and, with substantial additional heating, H-mode confinement results confirm the expected scaling. The high power handling capability of the pumped divertor with sweeping is estimated at 20 MW for 20 s. H-mode plasmas have large Type I ELMs. With lower hybrid heating alone, 2 MA full current drive has been achieved with good efficiency, and with ICRF power, effective heating and direct electron heating have been demonstrated.
The authors present a case of Osteogenesis Imperfecta, emphasizing the clinical and epidemiological characteristics, forms of classification and treatment of the disease. This is an important case not only to the knowledge of pediatricians and orthopedists, but also for other professionals involved with the problem. This article has been jointly described by the Departments of Pediatrics and Neonatology of the Girassol Clinic in Luanda Capital of the Republic of Angola, Africa.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.