Edge and scrape-off layer physics modeling for Wendelstein 7-X in preparation of the operation phases OP1.2 and OP2

The non-renewable energy sources coal, oil and natural gas that contribute the major share of the world's energy, will be running out in the next 40-80 years. With the growing energy demands especially in developing countries, which is likely to surpass that of the developed countries in next 50 years, an alternate energy source is the need to the hour. The nuclear fusion energy is foreseen as one of the potential candidates to solve the current global energy crisis. One of the major challenges faced by the fusion community is the problem of power exhaust. With the larger fusion devices to be built in the future, the heat load on the plasma facing components are expected to grow higher. The present work explores two numerical studies performed on the Wendelstein 7-X, the world's largest stellarator type fusion device, to cope with this problem. The first project on `'Numerical Studies on the impact of Connection Length in Wendelstein 7-X'' identifies magnetic configuration with long connection lengths, which could bring down the peak heat fluxes onto the divertor to manageable levels, by greater role of cross-field transport which may assist to get a wider heat deposition profile. The second project on `'Development of Heating Scenario to Reduce the Impact of Bootstrap Currents in Wendelstein 7-X'' advocates a novel self-consistent approach to reach high plasma density at full heating power without overloading the divertor during the transient phase of the evolution of the toroidal plasma current, by controlling two parameters; density and power. The aim of both the projects is to contribute to tackling the challenge of the tremendous power exhaust from fusion plasma which, if solved, will be a large step closer to a fusion power plant.Die nicht erneuerbaren Energiequellen Kohle, Öl und Erdgas, die den größten Anteil zur Energieerzeugung in der Welt beitragen, werden in den nächsten 40-80 Jahren knapp. Angesichts des wachsenden Energiebedarfs weltweit, insbesondere in Entwicklungsländern, welcher in den nächsten 50 Jahren den der Industrieländer voraussichtlich übertreffen wird, ist eine alternative Energiequelle in der nahen Zukunft von nöten/erforderlich. Die Kernfusionsenergie ist als einer der potenziellen Kandidaten zur Lösung der gegenwärtigen globalen Energiekrise vorgesehen. Eine der größten Herausforderungen für die Fusionsforschung ist das Problem der Energieabfuhr. Bei den größeren Fusionexperimenten, die in Zukunft gebaut werden sollen, wird erwartet, dass die Wärmebelastung der dem Plasma ausgesetzten Komponenten weiter steigt. Die vorliegende Arbeit besteht aus zwei numerischen Studien, die für Wendelstein 7-X, das weltweit derzeit größte Fusionexperiment vom Typ Stellarator, durchgeführt wurden, um zur Lösung dieses Problems beizutragen. Das erste Projekt trägt den Titel ``Numerical Studies on the impact of Connection Length in Wendelstein 7-X'' und identifiziert magnetische Konfigurationen mit langen Verbindungslängen, welche die Spitzenlast auf dem Divertor auf ein kontrollierbares Maß senken könnten, was dadurch erreicht werden würde, dass der senkrechte Transport eine größere Rolle einnimmt und dies zu einem breiteren Wärmedepositionsprofil führen könnte. Das zweite Projekt zur ``Development of Heating Scenario to Reduce the Impact of Bootstrap Currents in Wendelstein 7-X'' führt einen neuartigen, selbstkonsistent durchgeführten Ansatz ein. Um ein Plasma mit hoher Dichte bei hoher Heizleistung zu erreichen ohne den Divertor in der Entwicklungsphase des Toroidalstroms zuüberlasten, werden zwei Experimentparameter, die den Toroidalstrom mitbestimmen, abgestimmt angesteuert; Dichte und Heizleistung. Ziel beider Projekte ist es, einen Beitrag zur Bewältigung des Problems der enormen Leistungsabgabe aus Fusionsplasma zu leisten, die, wenn sie gelöst werden kann, uns einem Fusionskraftwerk einen großen Schritt näher bringen kann

Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000

Fusion energy research has in the past 40 years focused primarily on the tokamak concept, but recent advances in plasma theory and computational power have led to renewed interest in stellarators. The largest and most sophisticated stellarator in the world, Wendelstein 7-X (W7-X), has just started operation, with the aim to show that the earlier weaknesses of this concept have been addressed successfully, and that the intrinsic advantages of the concept persist, also at plasma parameters approaching those of a future fusion power plant. Here we show the first physics results, obtained before plasma operation: that the carefully tailored topology of nested magnetic surfaces needed for good confinement is realized, and that the measured deviations are smaller than one part in 100,000. This is a significant step forward in stellarator research, since it shows that the complicated and delicate magnetic topology can be created and verified with the required accuracy

Major results from the first plasma campaign of the Wendelstein 7-X stellarator

After completing the main construction phase of Wendelstein 7-X (W7-X) and successfully commissioning the device, first plasma operation started at the end of 2015. Integral commissioning of plasma start-up and operation using electron cyclotron resonance heating (ECRH) and an extensive set of plasma diagnostics have been completed, allowing initial physics studies during the first operational campaign. Both in helium and hydrogen, plasma breakdown was easily achieved. Gaining experience with plasma vessel conditioning, discharge lengths could be extended gradually. Eventually, discharges lasted up to 6 s, reaching an injected energy of 4 MJ, which is twice the limit originally agreed for the limiter configuration employed during the first operational campaign. At power levels of 4 MW central electron densities reached 3 1019 m-3, central electron temperatures reached values of 7 keV and ion temperatures reached just above 2 keV. Important physics studies during this first operational phase include a first assessment of power balance and energy confinement, ECRH power deposition experiments, 2nd harmonic O-mode ECRH using multi-pass absorption, and current drive experiments using electron cyclotron current drive. As in many plasma discharges the electron temperature exceeds the ion temperature significantly, these plasmas are governed by core electron root confinement showing a strong positive electric field in the plasma centre.Peer reviewe

Major results from the first plasma campaign of the Wendelstein 7-X stellarator

\u3cp\u3eAfter completing the main construction phase of Wendelstein 7-X (W7-X) and successfully commissioning the device, first plasma operation started at the end of 2015. Integral commissioning of plasma start-up and operation using electron cyclotron resonance heating (ECRH) and an extensive set of plasma diagnostics have been completed, allowing initial physics studies during the first operational campaign. Both in helium and hydrogen, plasma breakdown was easily achieved. Gaining experience with plasma vessel conditioning, discharge lengths could be extended gradually. Eventually, discharges lasted up to 6 s, reaching an injected energy of 4 MJ, which is twice the limit originally agreed for the limiter configuration employed during the first operational campaign. At power levels of 4 MW central electron densities reached 3 10\u3csup\u3e19\u3c/sup\u3e m\u3csup\u3e-3\u3c/sup\u3e, central electron temperatures reached values of 7 keV and ion temperatures reached just above 2 keV. Important physics studies during this first operational phase include a first assessment of power balance and energy confinement, ECRH power deposition experiments, 2nd harmonic O-mode ECRH using multi-pass absorption, and current drive experiments using electron cyclotron current drive. As in many plasma discharges the electron temperature exceeds the ion temperature significantly, these plasmas are governed by core electron root confinement showing a strong positive electric field in the plasma centre.\u3c/p\u3