Role of Kinetic Instability in Runaway-Electron Avalanches and Elevated Critical Electric Fields.

The effects of kinetic whistler wave instabilities on the runaway-electron (RE) avalanche is investigated. With parameters from experiments at the DIII-D National Fusion Facility, we show that RE scattering from excited whistler waves can explain several poorly understood experimental results. We find an enhancement of the RE avalanche for low density and high electric field, but for high density and low electric field the scattering can suppress the avalanche and raise the threshold electric field, bringing the present model much closer to observations. The excitation of kinetic instabilities and the scattering of resonant electrons are calculated self-consistently using a quasilinear model and local approximation. We also explain the observed fast growth of electron cyclotron emission signals and excitation of very low-frequency whistler modes observed in the quiescent RE experiments at DIII-D tokamak. Simulations using ITER parameters show that by controlling the background thermal plasma density and temperature, the plasma waves can also be excited spontaneously in tokamak disruptions and the avalanche generation of runaway electrons may be suppressed.

"I Just Roll Over, Pick Myself Up, and Carry On!" Exploring the Fall-Risk Experience of Canadian Masters Athletes.

OBJECTIVES: The risk of falling increases in adults aged 65 years and older. A common barrier to take up physical activity in sedentary older adults is the fear of falls and injury. Experiences of master athletes can provide insights into management of the risk of falling. The purpose of this phenomenological study was to explore the fall-risk experience of masters athletes actively competing in sport. METHODS: Masters athletes aged 55 years and older (N = 22) described their experiences in semistructured interviews. Data were analyzed through an interpretive-constructivist paradigm using inductive content analysis. RESULTS: Five dominant themes emerged: acceptance, learning, awareness, resilience, and self-fulfillment. Participants of this study reported an acceptance of the risk they take in sport for falls and injuries in their pursuits for self-fulfillment. DISCUSSION: Findings indicate that master athletes accept the risk for falls and injuries in sport, find ways to adapt, and continue to compete because it is self-fulfilling. Sharing their experiences might inspire other older adults to get active as a rewarding means of remaining independent.