Advances in understanding the generation and evolution of the toroidal rotation profile on DIII-D

Recent experiments using DIII-D's capability to vary the injected torque at constant power have focused on developing the physics basis for understanding rotation through the detailed study of momentum sources, sinks and transport. Non-resonant magnetic braking has generally been considered a sink of momentum; however, recent results from DIII-D suggest that it may also act as a source. The torque applied by the field depends on the rotation relative to a non-zero 'offset' rotation. Therefore, at low initial rotation, the application of non-resonant magnetic fields can actually result in a spin-up of the plasma. Direct evidence of the effect of reverse shear Alfvén eigenmodes on plasma rotation has been observed, which has been explained through a redistribution of the fast ions and subsequent modification to the neutral beam torque profile. An effective momentum source has been identified by varying the input torque from neutral beam injection at fixed βN, until the plasma rotation across the entire profile is essentially zero. This torque profile is largest near the edge, but is still non-negligible in the core, qualitatively consistent with models for a so-called 'residual stress'. Perturbative studies of the rotation using combinations of co- and counter-neutral beams have uncovered the existence of a momentum pinch in DIII-D H-mode plasmas, which is quantitatively similar to theoretical predictions resulting from consideration of low-k turbulence. © 2009 IAEA, Vienna

Compatibility of internal transport barrier with steady-state operation in the high bootstrap fraction regime on DIII-D

Recent EAST/DIII-D joint experiments on the high poloidal beta tokamak regime in DIII-D have demonstrated fully noninductive operation with an internal transport barrier (ITB) at large minor radius, at normalized fusion performance increased by 30% relative to earlier work (Politzer et al 2005 Nucl. Fusion 45 417). The advancement was enabled by improved understanding of the 'relaxation oscillations', previously attributed to repetitive ITB collapses, and of the fast ion behavior in this regime. It was found that the 'relaxation oscillations' are coupled core-edge modes amenable to wall-stabilization, and that fast ion losses which previously dictated a large plasma-wall separation to avoid wall over-heating, can be reduced to classical levels with sufficient plasma density. By using optimized waveforms of the plasma-wall separation and plasma density, fully noninductive plasmas have been sustained for long durations with excellent energy confinement quality, bootstrap fraction ≥80%, βN ≤ 4, βP ≥ 3, and βT ≥ 2%. These results bolster the applicability of the high poloidal beta tokamak regime toward the realization of a steady-state fusion reactor

Compatibility of internal transport barrier with steady-state operation in the high bootstrap fraction regime on DIII-D

Recent EAST/DIII-D joint experiments on the high poloidal beta tokamak regime in DIII-D have demonstrated fully noninductive operation with an internal transport barrier (ITB) at large minor radius, at normalized fusion performance increased by 30% relative to earlier work (Politzer et al 2005 Nucl. Fusion 45 417). The advancement was enabled by improved understanding of the 'relaxation oscillations', previously attributed to repetitive ITB collapses, and of the fast ion behavior in this regime. It was found that the 'relaxation oscillations' are coupled core-edge modes amenable to wall-stabilization, and that fast ion losses which previously dictated a large plasma-wall separation to avoid wall over-heating, can be reduced to classical levels with sufficient plasma density. By using optimized waveforms of the plasma-wall separation and plasma density, fully noninductive plasmas have been sustained for long durations with excellent energy confinement quality, bootstrap fraction ≥80%, βN ≤ 4, βP ≥ 3, and βT ≥ 2%. These results bolster the applicability of the high poloidal beta tokamak regime toward the realization of a steady-state fusion reactor

Reconstruction after wide resection of the entire distal fibula in malignant bone tumours

In this study we present a series of patients (n = 11) with resection of the entire distal fibula in the case of sarcoma or metastasis. Moreover, we describe a new method to restore ankle stability with a tibiotalocalcaneal arthrodesis using a retrograde hindfoot nail (n = 4) in contrast to tibiotalar arthrodesis with screws (n = 5). The screw fixation failed in two patients due to osteopoenic bone. The crucial benefits of an arthrodesis with a retrograde nail are a stable arthrodesis, intramedullary stabilisation of the tibia and avoidance of extrinsic material in the wound area. An arthrodesis with a retrograde nail is a good alternative for reconstruction after a wide distal fibula resection. The additional arthrodesis of the subtalar joint was not associated with worse functional results in the MSTS and TESS scores