0000000000594139
AUTHOR
Thomas Sunn Pedersen
Investigation of Space-Charge Phenomena in Gas-Filled Penning Traps
The centering of ions in Penning traps by a quadrupolar radiofrequency excitation in the presence of a buffer gas has been studied in the regime of high charge‐densities. It is found to deviate significantly from the single‐particle situation. In particular, the efficiency of the cooling process is affected as well as the resolving power. The behavior has been studied experimentally at the preparation trap REXTRAP and the high‐precision Penning trap setup ISOLTRAP both located at the on‐line mass separator ISOLDE at CERN. In addition, the phenomenon has been investigated numerically by a custom‐designed simulation.
Overview of first Wendelstein 7-X high-performance operation
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
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…