Modeling of icrh slow wave propagation and absorption in Wendelstein 7-X stellarator

The propagation and absorption of slow waves in the plasma of the Wendelstein 7-X stellarator was investigated by the ray tracing. The aim of the work was to obtain a qualitative picture of the penetration into the plasma of a wave excited by the potential difference between the antenna conductors and the antenna box. For this, a ray code was used, which performs calculations in the magnetic configuration of the stellarator obtained by the VMEC code. A strong influence of the type of magnetic configuration (“higher mirror”, “lower mirror”, or standard configuration) on the propagation and absorption of a slow wave was found.Поширення і поглинання повільної хвилі в плазмі стеларатора Вендельштейн 7-Х було досліджено методом променевих траєкторій. Мета роботи – отримання якісної картини проникнення в плазму хвилі, що збуджується за рахунок різниці потенціалів між провідниками антени і антенним боксом. Для цього використаний променевий код, який виконував розрахунки в магнітній конфігурації стеларатора, що отримана кодом VMEC. Виявлено сильний вплив виду магнітної конфігурації (посилені гофри, зменшені гофри або стандартна конфігурація) на поширення і поглинання повільної хвилі.Распространение и поглощение медленной волны в плазме стелларатора Вендельштейн 7-Х было исследовано методом лучевых траекторий. Цель работы – получение качественной картины проникновения в плазму волны, возбуждаемой за счет разности потенциалов между проводниками антенны и антенным боксом. Для этого использован лучевой код, который выполнял расчеты в магнитной конфигурации стелларатора, полученной кодом VMEC. Обнаружено сильное влияние вида магнитной конфигурации (усиленные гофры, уменьшенные гофры или стандартная конфигурация) на распространение и поглощение медленной волны

2010-2011 Mostly Music: Bartok

https://spiral.lynn.edu/conservatory_mostlymusic/1011/thumbnail.jp

2010-2011 Mostly Music: Mozart

https://spiral.lynn.edu/conservatory_mostlymusic/1009/thumbnail.jp

2012-2013 Mostly Music: Mozart

https://spiral.lynn.edu/conservatory_mostlymusic/1017/thumbnail.jp

2017-2018 Mostly Music: Ludwig van Beethoven

https://spiral.lynn.edu/conservatory_mostlymusic/1030/thumbnail.jp

2018-2019 Mostly Music: Johann Sebastian Bach

https://spiral.lynn.edu/conservatory_mostlymusic/1031/thumbnail.jp

Validation of theory-based models for the control of plasma currents in W7-X divertor plasmas

A theory-based model for the control of plasma currents for steady-state operation in W7-X is proposed and intended for model-based plasma control. The conceptual outline implies the strength of physics-based models: it offer approaches applicable to future conditions of fusion devices or next-step machines. The application at extrapolated settings is related to the validity range of the theory model. Therefore, the predictive power of theory-based control models could be larger than for data-driven approaches and limitations can be predicted from the validity range for the prediction of bootstrap currents in W7-X. The model predicts the L/R response when density or heating power is changed. The model is based on neoclassical bootstrap current calculations and validated for different discharge conditions. While the model was found to be broadly applicable for conducted electron-cyclotron-heated discharges in W7-X, limits were found for cases when the polarization of the electron cyclotron heating was changed from X2 to O2-heating. The validity assessment attempts to quantify the potential of the derived model for model-based control in the operational space (density, heating power) of W7-X

Confinement degradation and plasma loss induced by strong sawtooth crashes at W7-X

Sawtooth-like crashes were observed during electron cyclotron current drive experiments for strikeline controls at the optimised superconducting stellarator Wendelstein 7-X (W7-X). The majority of the crashes did not have a relevant impact on plasma performance. However, a limited number of events, characterised by a large plasma volume affected by the instability, have been related to a strong deterioration performance and even to the premature termination of the plasma. The hot plasma core expelled during these sawtooth crashes can reach the plasma edge, where plasma surface interaction can occur and impurities can be released. The x-ray tomography shows a strong radiation increase starting from the edge and moving towards the inner plasma regions. This results in the cooling down and shrinking of the plasma, which eventually leads to a poor coupling of the ECRH to the electrons, that can in turn result in a plasma loss. A relation between the size and amplitude of the sawtooth crashes and the impurity increase is reported.EC/H2020/633053/EU/Implementation of activities described in the Roadmap to Fusion during Horizon 2020 through a Joint programme of the members of the EUROfusion consortium/Eurato