0000000000430541
AUTHOR
R. Burhenn
showing 10 related works from this author
Major results from the first plasma campaign of the Wendelstein 7-X stellarator
2017
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 t…
Choice of the detectors for light impurities plasma studies at W7-X using ‘CO Monitor’ system
2019
Abstarct The ‘CO Monitor’ is a new spectrometer system dedicated for the continuous measurements of line intensities of carbon, oxygen, boron and nitrogen at the fusion plasma experiment Wendelstein 7-X (W7-X). Its main purpose is to deliver constant information about indicated elements with high time resolution (better than 1 ms), but low spatial resolution since the line shapes are not going to be investigated. The system consists of four independent channels, each equipped with dispersive element dedicated for measurement of selected line of interest. In order to perform the highest efficiency of the ‘CO Monitor’ system, it is essential to choose the proper detector type for this task. T…
Overview of diagnostic performance and results for the first operation phase in Wendelstein 7-X (invited)
2016
Wendelstein 7-X, a superconducting optimized stellarator built in Greifswald/Germany, started its first plasmas with the last closed flux surface (LCFS) defined by 5 uncooled graphite limiters in December 2015. At the end of the 10 weeks long experimental campaign (OP1.1) more than 20 independent diagnostic systems were in operation, allowing detailed studies of many interesting plasma phenomena. For example, fast neutral gas manometers supported by video cameras (including one fast-frame camera with frame rates of tens of kHz) as well as visible cameras with different interference filters, with field of views covering all ten half-modules of the stellarator, discovered a MARFE-like radiati…
Estimation of Photon Flux of the Oxygen Lyman-alpha Line Emitted from the W7-X Plasmas
2020
The low-Z impurities of the magnetic confined fusion plasmas can provide important information about the wall condition and plasma–wall interactions. In order to accomplish this aim, a special spectrometer called “C/O Monitor” was designed for the W7-X experiment. This system is dedicated to measure Lyman-α transitions of four low-Z impurities: carbon (3.4 nm), oxygen (1.9 nm), nitrogen (2.5 nm) and boron (4.9 nm). It is a high throughput and high time resolution spectrometer which allows to measure the line intensities evolution of indicated elements including information of the background (continuum). The designed spectrometer consists of two vacuum chambers positioned nearly horizontally…
Overview of first Wendelstein 7-X high-performance operation
2019
Abstract The optimized superconducting stellarator device Wendelstein 7-X (with major radius , minor radius , and plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. This paper reports on the results from the first high-performance plasma operation. Glow discharge conditioning and ECRH conditioning discharges in helium turned out to be important for density and edge radiation control. Plasma densities of with central electron temperatures were routinely achieved with hydrogen gas fueling, frequently terminated by a radiative collapse. In a first stage, plasma densities up to were reached with hydrogen pellet injec…
Confinement in Wendelstein 7-X limiter plasmas
2017
Observations on confinement in the first experimental campaign on the optimized Stellarator Wendelstein 7-X are summarized. In this phase W7-X was equipped with five inboard limiters only and thus the discharge length restricted to avoid local overheating. Stationary plasmas are limited to low densities <2–3 · 1019 m−3. With the available 4.3 MW ECR Heating core Te ~ 8 keV, Ti ~ 1–2 keV are achieved routinely resulting in energy confinement time τE between 80 ms to 150 ms. For these conditions the plasmas show characteristics of core electron root confinement with peaked Te-profiles and positive Er up to about half of the minor radius. Profiles and plasma currents respond to on- and off-axi…
Effect of spatial distribution of impurity ions on the signal of ‘C/O monitor for Wendelstein 7-X’ - an indicator of plasma wall interactions
2022
The ‘C/O monitor’ is a dedicated diagnostic system designed to monitor light impurities (B, C, N and O) in the Wendelstein 7-X (W7-X) stellarator. Its main goal is to provide fast (∼1 ms) information about the impurity level which is measured from a large plasma volume (high throughput). Its first subsystem dedicated to measure Lyman-α lines of H-like carbon (C5+ − 3.4 nm – used as PFC material) and oxygen (O7+ − 1.9 nm – common impurity absorbed by inner vessels’ walls) is going to be commissioned during the next Operational Phase of W7-X. Since the radiated photon intensity of a given impurity depends strongly on plasma kinetic parameters (Te, ne) and impurity transport, it is important t…
Technical challenges in the construction of the steady-state stellarator Wendelstein 7-X
2013
The next step in the Wendelstein stellarator line is the large superconducting device Wendelstein 7-X, currently under construction in Greifswald, Germany. Steady-state operation is an intrinsic feature of stellarators, and one key element of the Wendelstein 7-X mission is to demonstrate steady-state operation under plasma conditions relevant for a fusion power plant. Steady-state operation of a fusion device, on the one hand, requires the implementation of special technologies, giving rise to technical challenges during the design, fabrication and assembly of such a device. On the other hand, also the physics development of steady-state operation at high plasma performance poses a challeng…
Modelling of expected B, C, N and O Lyman-α line intensities emitted from W7-X plasmas and measured by means of the W7-X light impurity monitor system
2021
AbstractThe “C/O Monitor” for Wendelstein 7-X (W7-X) is a dedicated light impurity XUV spectrometer intended to measure Lyman-α transitions of hydrogen-like ions of four low-Z impurities—boron (4.9 nm), carbon (3.4 nm), nitrogen (2.5 nm) and oxygen (1.9 nm). Since the discussed diagnostic will deliver continuous information about the line intensities, it is crucial to understand the origin of the obtained signals with respect to the experimental plasma conditions (electron temperature and density). This, however, might be difficult because of the broad acceptance angle of the spectrometer and irregular shape of the plasma edge or SOL where the radiation is expected to mostly come from, depe…
XUV diagnostic to monitor H-like emission from B, C, N, and O for the W7-X stellarator
2019
The “C/O Monitor” system for the Wendelstein 7-X (W7-X) stellarator is a dedicated spectrometer with high throughput and high time resolution (order of 1 ms) for fast monitoring of content of low-Z impurities in the plasma. The observed spectral lines are fixed to Lyman-α lines of H-like atoms of carbon (3.4 nm), oxygen (1.9 nm), nitrogen (2.5 nm), and boron (4.9 nm). The quality of the wall condition will be monitored by the measurements of oxygen being released from the walls during the experiments. The strong presence of carbon is an indication for enhanced plasma-wall interaction or overload of plasma facing components. The presence of nitrogen (together with oxygen) may indicate a poss…