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D

Glossary

Alcator: A tokamak device in the United States.

Alfvén waves: A low-frequency, transverse wave (lower in frequency than the gyration frequencies of electrons and ions) in which the plasma and magnetic field move together.

ASDEX: A tokamak device in Germany.

Beta (β): Ratio of the pressure of the plasma to the “pressure” (energy density) of the confining magnetic field.

Charge exchange: Mechanism by which an ion in an overall charge-neutral beam takes the charge from a plasma ion.

DIII-D: A tokamak device in the United States.

ELM: An instability at the edge of a plasma that is operating in the H-mode.

Flux surfaces: Surfaces, usually nested, on which magnetic field lines lie.

FRC: A magnetic confinement configuration where currents generated by the plasma's pressure cause the magnetic field to reverse, resulting in self-confinement.

Fusion-grade: A plasma with a temperature of the order of 100 million degrees, or around 10 keV.

Gyrofluid: A fluid-like description of plasma dynamics constructed from a finite number of velocity moments of the gyrokinetic equations. This construction includes collisionless damping due to resonant particle interactions.

Gyrokinetic: A reduced description of plasma dynamics obtained by averaging out the fast gyrating motion of particles around field lines.

Gyroradius: The radius of gyration of a particle around a magnetic field.

H-mode: Operational regime in which tokamak confinement, even with external heating, is significantly higher than tokamak confinement in L-mode. The H-mode enhances confinement results through the formation of a transport barrier at the plasma edge.



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OCR for page 94
Page 94 D Glossary Alcator: A tokamak device in the United States. Alfvén waves: A low-frequency, transverse wave (lower in frequency than the gyration frequencies of electrons and ions) in which the plasma and magnetic field move together. ASDEX: A tokamak device in Germany. Beta (β): Ratio of the pressure of the plasma to the “pressure” (energy density) of the confining magnetic field. Charge exchange: Mechanism by which an ion in an overall charge-neutral beam takes the charge from a plasma ion. DIII-D: A tokamak device in the United States. ELM: An instability at the edge of a plasma that is operating in the H-mode. Flux surfaces: Surfaces, usually nested, on which magnetic field lines lie. FRC: A magnetic confinement configuration where currents generated by the plasma's pressure cause the magnetic field to reverse, resulting in self-confinement. Fusion-grade: A plasma with a temperature of the order of 100 million degrees, or around 10 keV. Gyrofluid: A fluid-like description of plasma dynamics constructed from a finite number of velocity moments of the gyrokinetic equations. This construction includes collisionless damping due to resonant particle interactions. Gyrokinetic: A reduced description of plasma dynamics obtained by averaging out the fast gyrating motion of particles around field lines. Gyroradius: The radius of gyration of a particle around a magnetic field. H-mode: Operational regime in which tokamak confinement, even with external heating, is significantly higher than tokamak confinement in L-mode. The H-mode enhances confinement results through the formation of a transport barrier at the plasma edge.

OCR for page 94
Page 95 ITG: Instability driven by the gradient of the ion temperature. JET: A tokamak device in Europe in which deuterium/tritium fusion experiments have been completed. JT-60U: A tokamak device in Japan. L-mode: Operational regime in which tokamak confinement is degraded when the plasma is heated. MHD: A model of a plasma as a fluid in a magnetic field. Ideal MHD is when the fluid is taken to have zero resistivity, in which case the plasma and magnetic field are constrained to move together. This limit maximizes plasma stability. Motional Stark effect: A plasma diagnostic that measures the polarization of light due to Stark splitting of atomic energy levels. MRX: The Magnetic Reconnection Experiment is a small laboratory experiment located at the Princeton Plasma Physics Laboratory. The goal of MRX is to investigate the fundamental physics of magnetic field line reconnection, an important process in magnetized plasmas in space and in the laboratory. Radio-frequency waves: A generic designation for waves in a plasma driven by external electromagnetic power sources and having frequencies anywhere from kilohertz (Alfvén waves) to multigigahertz (electron-cyclotron waves). Reconnection: A process in which the reversed components of adjacent magnetic field lines cross-connect with each other, releasing magnetic energy into high-velocity flows. Reversed-field pinch: A magnetic confinement configuration with toroidal symmetry, where the magnetic field in the toroidal direction and that in the transverse field are equally strong and the former reverses direction inside the plasma. Sawtooth: Periodic instability of the core of tokamaks in which a slow increase in the electron temperature is followed by a fast decline. Separatrix: A bounding line in magnetic topology across which the direction of a field line reverses. Spherical torus: Doughnut-shaped magnetic confinement configuration in which the magnetic fields in the toroidal and transverse directions are comparable. Spheromak: Spherical magnetic confinement configuration in which the magnetic fields in the long and short directions of the doughnut are comparable in strength and the fields are primarily generated by internal plasma currents. Stellarator: Magnetic confinement configuration in which all of the confining magnetic fields are created by external coils, usually in the form of helical coils wound into a torus. Tearing mode: Small-amplitude version of magnetic field line reconnection. TFTR: A tokamak device in the United States in which deuterium/tritium fusion experiments have been carried out. Tokamak: Doughnut-shaped magnetic confinement configuration in which the magnetic field in the toroidal direction is much stronger than in the transverse direction. TRACE: The Transition Region and Coronal Explorer is a NASA Small Explorer mission to image the solar corona and transition region at high angular and temporal resolution.