Collisionless microinstabilities in stellarators II - numerical simulations

Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-$J$ geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment (NCSX) and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilizing in the energy budget. These results suggest that imperfectly optimized stellarators can retain most of the stabilizing properties predicted for perfect maximum-$J$ configurations.Comment: 15 pages, 40 figure

Collisionless microinstabilities in stellarators I - analytical theory of trapped-particle modes

This is the first of two papers about collisionless, electrostatic micro-instabilities in stellarators, with an emphasis on trapped-particle modes. It is found that, in so-called maximum-$J$ configurations, trapped-particle instabilities are absent in large regions of parameter space. Quasi-isodynamic stellarators have this property (approximately), and the theory predicts that trapped electrons are stabilizing to all eigenmodes with frequencies below the electron bounce frequency. The physical reason is that the bounce-averaged curvature is favorable for all orbits, and that trapped electrons precess in the direction opposite to that in which drift waves propagate, thus precluding wave-particle resonance. These considerations only depend on the electrostatic energy balance, and are independent of all geometric properties of the magnetic field other than the maximum-$J$ condition. However, if the aspect ratio is large and the instability phase velocity differs greatly from the electron and ion thermal speeds, it is possible to derive a variational form for the frequency showing that stability prevails in a yet larger part of parameter space than what follows from the energy argument. Collisionless trapped-electron modes should therefore be more stable in quasi-isodynamic stellarators than in tokamaks.Comment: 9 pages, 1 figur

The Spatial Distribution of New York State’s Older Population: Let’s Keep New York’s Older Adults Safe and Healthy during the Coronavirus Pandemic

This brief addresses the concern for older adults\u27 health during the COVID-19 outbreak, highlights the distribution of this population throughout New York State, and recommends ways to keep them safe during this time

Domestic Violence is Prevalent among U.S. Adolescents and Young Adults

Rates of domestic violence are high among adolescents and young adults in the U.S. This data slice describes the geographic distribution of reported domestic violence incidents among adolescents and young adults in the U.S in 2019 and identifies the most common types of incidents

Automatic generation: A way of ensuring PLC and HMI standards

Preparing an automatic production system takes a lot of time and to be able to decrease this time virtual simulation studies are used more and more frequently. However, even if more work is performed in a virtual environment a problem is still that the same work is done more than one time in different software tools due to the lack of integration between them. The present paper presents a case study that investigates how a newly developed tool called SIMATIC Automation Designer can be used in order to close the gap between the mechanical design and the electrical design. SIMATIC Automation Designer is a Siemens software that can generate PLC code and HMI screens. The result shows that by generating PLC code and HMI screens automatically, it is possible to get the same structure and naming standard in every PLC and HMI project. This will ensure a corporate standard and will be a quality assurance of the PLC code and HMI screens

Available energy from diffusive and reversible phase space rearrangements

Rearranging the six-dimensional phase space of particles in plasma can release energy. The rearrangement may happen through the application of electric and magnetic fields, subject to various constraints. The maximum energy that can be released through a rearrangement of a distribution of particles can be called its available or free energy. Rearrangement subject to phase space volume conservation leads to the classic Gardner free energy. Less free energy is available when constraints are applied, such as respecting conserved quantities. Also, less energy is available if particles can only be diffused in phase-space from regions of high phase-space density to regions of lower phase-space density. The least amount of free energy is available if particles can only be diffused in phase space, while conserved quantities still need to be respected.Comment: 7 pages, 3 figure

The Public Health Crisis of Law Enforcement’s Over-Use of Force

The overuse of police force has public health implications. The rates of injury and death sustained while in law enforcement custody should be collected as a part of the public health strategy to minimize the over-use of force

Stroke: Identifying Symptoms and Acting Fast to Save Lives and Prevent Permanent Disabilities

Stroke is the 5th leading cause of death in the United States. Strokes and their long-term effects are preventable. Recognizing the symptoms of stroke and acting quickly can prevent death and minimize long-term disabilities. Family members and bystanders have an important role to play. This issue brief describes stroke symptoms and prevention guidelines, summarizes the information 9-1-1 callers should be prepared to provide when someone is having a stroke, and discusses the importance of acting quickly to save lives and long-term damage

Accidental Drownings are Predictable and Preventable

Drowning is the 3rd leading cause of unintentional injury-related death in the world for all age groups, with one third of fatal and nonfatal drownings occurring with the hours of 4pm and 8pm. This data slice gives helpful advice on how to stay safe while cooling off