Midplane Edge Research Articles

Ion cyclotron emission due to collective instability of fusion products and beam ions in TFTR and JET

Ion cyclotron emission (ICE) has been observed from neutral beam heated TFTR, and JET tritium experiments at sequential cyclotron harmonics of both fusion products and beam ions. The emission originates from the outer midplane plasma, where fusion products and beam ions are likely to have a drifting ring-type velocity-space distribution that is anisotropic and sharply peaked. Fusion product driven ICE in both TFTR and JET can be attributed to the magnetoacoustic cyclotron instability, which involves the excitation of obliquely propagating waves on the fast Alfven/ion Bernstein branch at cyclotron harmonics of the fusion products. Differences between ICE observations in JET and TFTR appear to reflect the sensitivity of the instability growth rate to the ratio vbirth/cA where vbirth is the fusion product birth speed and cA is the local Alfven speed for fusion products in the outer midplane edge of TFTR supershots, vbirth < cA for alpha particles in the outer midplane edge of JET, the opposite inequality applies. If sub-Alfvenic fusion products are isotropic or have undergone even a moderate degree of thermalization, the magnetoacoustic instability cannot occur. In contrast, the super-Alfvenic alpha particles that are present in the outer midplane of JET can drive the magnetoacoustic cyclotron instability even if they are isotropic or have a relatively broad distribution of speeds. These conclusions may account for the observation that fusion product driven ICE in JET persists for longer than fusion product driven ICE in TFTR. Moreover, the time evolution of the maximum growth rate, obtained using the Sigmar model for the alpha particle distribution and TFTR data for the fusion product source rate, closely follows the observed time evolution of the ICE amplitude in TFTR supershot discharges. Other observed features of fusion product driven ICE that match the linear instability include the scaling with fusion product density, doublet splitting of spectral peaks, the relative strength of certain harmonics and source localization. A separate mechanism is proposed forthe excitation of beam driven ICE in TFTR: electrostatic ion cyclotron harmonic waves, supported by stronglysub-Alfvénic beam ions, can be destabilized by a low concentration of such ions with a very narrow spread ofvelocities in the parallel direction. Sufficiently narrow distributions are likely to exist in the edge plasma, close tothe point of beam injection.

Ion cyclotron emission on the Tokamak Fusion Test Reactor

Preliminary observations of ion cyclotron emission (ICE) have been made in D-T plasmas on the Tokamak Fusion Test Reactor, using an array of seven rf probes located at the top and bottom of the torus. Fusion product line emission has been identified, and appears to originate at the low field equatorial plane, near the radius of the outboard limiter. While the peak intensity of D-T fusion product ICE exhibits a correlation with overall neutron production, the time evolution of the ICE signal does not follow that of the neutron rate. During high power neutral beam injection, beam-species ICE is also observed, with frequencies corresponding to the outer midplane edge of the plasma.

A mechanism for beam-driven excitation of ion cyclotron harmonic waves in the Tokamak Fusion Test Reactor

A mechanism is proposed for the excitation of waves at harmonics of the injected ion cyclotron frequencies in neutral beam-heated discharges in the Tokamak Fusion Test Reactor (TFTR) [Proceedings of the 17th European Conference on Controlled Fusion and Plasma Heating (European Physical Society, Petit-Lancy, Switzerland, 1990), p. 1540]. Such waves are observed to originate from the outer midplane edge of the plasma. It is shown that ion cyclotron harmonic waves can be destabilized by a low concentration of sub-Alfvénic deuterium or tritium beam ions, provided these ions have a narrow distribution of speeds parallel to the magnetic field. Such a distribution is likely to occur in the edge plasma, close to the point of beam injection. The predicted instability gives rise to wave emission at propagation angles lying almost perpendicular to the field. In contrast to the magnetoacoustic cyclotron instability proposed as an excitation mechanism for fusion-product-driven ion cyclotron emission in the Joint European Torus (JET) [Phys. Plasmas 1, 1918 (1994)], the instability proposed here does not involve resonant fast Alfvén and ion Bernstein waves, and can be driven by sub-Alfvénic energetic ions. It is concluded that the observed emission from TFTR can be driven by beam ions.

Analysis of a symmetric laminate with mid-plane free edge delamination under torsion: theory and application to the edge crack torsion (ECT) specimen for mode III toughness characterization

A shear deformation theory is developed to analyze a symmetric laminate with mid-plane edge delamination under torsion loading. The theory is based on an assumed displacement field which includes shear deformation. The governing equations and boundary conditions are obtained from the principle of virtual work. Closed-form solutions for the compliance and strain energy release rate are obtained. The theory is used to analyze a mid-plane Edge Crack Torsion (ECT) specimen used for characterizing the mode III delamination behavior of composites. The prediction of the present theory for a [90, (±45)n, (±45)n, 90]s class of laminates is compared with existing test data, and good agreement is observed. In addition, the Classical Lamination Theory (CLT) is found to be less accurate for the analysis of the edge crack torsion specimen. The layup effect on the behavior of some ECT specimens is analyzed using the present theory.

Ion Cyclotron Emission — a Natural Diagnostic for Fusion Alpha Particles

There exist strong observational links between ion cyclotron emission (ICE) and fusion reactivity in tokamak plasmas. These links originally emerged from deuterium discharges in the Joint European Torus (JET) and were demonstrated most recently in the Preliminary Tritium Experiment. They include the proportionality of ICE intensity to measured fusion reactivity over six decades in signal intensity; correlations in the time evolution of the ICE signal and neutron flux during discharges; the matching of the spectral peak frequencies to successive local ion cyclotron harmonics at the outer midplane edge; and correlations between ICE and the observed impact of magnetohydrodynamic activity, such as sawteeth and edge-localized modes, on energetic ions. The observations are broadly consistent with the excitation of the fast Alfvén wave through cyclotron resonance with the local non-Maxwellian fusion product population — the so-called magnetoacoustic cyclotron instability. The theory of this instability is extended to the regime of arbitrary k||, in which it is necessary to include both wave-particle cyclotron damping and the positive-energy loading due to resonant cyclotron harmonic waves supported by the thermal ions. The consequences of arbitrary k|| for the instability thresholds are described. An outline is given of the close similarities between ICE from tokamaks and signals at multiple ion cyclotron harmonics observed in the Earth’s magnetosphere, which apparently originate from regions where there is a ring-type population of energetic protons. This emission also appears to be explicable in terms of the magnetoacoustic cyclotron instability, and comparison with tokamak observations yields information on the distinction between features generic to the emission mechanism and those specific to particular magnetic geometries.

Influence of free-edge delaminations on the extension-twist coupling of elastically tailored composite laminates

A closed form solution is developed in order to analyze the influence of free-edge delaminations on elastically tailored composite laminates. The analysis is based upon a shear deformation theory and a sublaminate approach. The solution is applied to predict the influence of free-edge delamination on the behavior of a class of laminates exhibiting extension-twist coupling. Comparison of analytical predictions with test data from laminates with mid-plane and off mid-plane free edge delaminations is performed. The results indicate that free-edge delamination can have a significant influence on extension-twist coupling.

Ion cyclotron emission measurements during JET deuterium-tritium experiments

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 v ⩽ 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 tile last closed flux surface at major radius R approximately 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 particles-and not beam ions-provide 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 Alfven-ion Bernstein branch at all ion cyclotron harmonics. The paper shows how ICE provides a unique diagnostic for fusion alpha particles

Identification of ion cyclotron emission from fusion alpha particles during jet deuterium-tritium experiments

Summary form only given, as follows. In the course of the preliminary tritium experiment (PTE) in JET, where combined D and T neutral beam injection generated a DT fusion power of 1.7 MW, ion cyclotron emission (ICE) in the frequency range up to 180 MHz was measured using an ICRF heating antenna as probe. The ICE spectrum showed a number of superthermal narrow, equally spaced emission lines which correspond to deuteron or alpha -particle ion cyclotron harmonics at the outer mid-plane edge (major radius R approximately 4 m). DD and DT power spectra are similar in form, and show split lines which, above approximately 100 MHz, merge into a continuum. With tritium injection, the ICE power increased by a factor comparable to the increase of neutron flux, indicating that 3.5 MeV fusion alpha -particles provide the free energy for generating ICE. The ICE power increases almost linearly with neutron flux over a range of six decades. The evolution of the ICE follows the rise of the neutron flux, but is delayed by a time comparable with the slowing-down time of the alpha -particles. The ICE intensity is anti-correlated with large amplitude edge-localized modes.

Identification of ion cyclotron emission from fusion alpha particles during JET deuterium-tritium experiments

Summary form only given, as follows. In the course of the preliminary tritium experiment (PTE) in JET, where combined D and T neutral beam injection generated a DT fusion power of 1.7 MW, ion cyclotron emission (ICE) in the frequency range up to 180 MHz was measured using an ICRF heating antenna as probe. The ICE spectrum showed a number of superthermal narrow, equally spaced emission lines which correspond to deuteron or alpha -particle ion cyclotron harmonics at the outer mid-plane edge (major radius R approximately 4 m). DD and DT power spectra are similar in form, and show split lines which, above approximately 100 MHz, merge into a continuum. With tritium injection, the ICE power increased by a factor comparable to the increase of neutron flux, indicating that 3.5 MeV fusion alpha -particles provide the free energy for generating ICE. The ICE power increases almost linearly with neutron flux over a range of six decades. The evolution of the ICE follows the rise of the neutron flux, but is delayed by a time comparable with the slowing-down time of the alpha -particles. The ICE intensity is anti-correlated with large amplitude edge-localized modes.

Hygrothermal influence on mode I edge delamination in composites

A shear deformation theory is developed to calculate the interlaminar stresses and energy release rate associated with mid-plane edge delamination growth in graphite/epoxy laminates. The analysis includes the effect of residual thermal and moisture stresses. Results indicate that residual thermal stress increases the interlaminar stresses and strain energy release rate, while moisture content tends to alleviate thermal effects. Moreover, the value of moisture content at which the interlaminar stresses and strain energy release rate are totally alleviated is not affected by the stacking sequence.