Anomalous direction for skyrmion bubble motion

Magnetic skyrmions are localized topological excitations that behave as particles and can be mobile, with great potential for novel data storage devices. In this work, the current-induced dynamics of large skyrmion bubbles is studied. When skyrmion motion in the direction opposite to the electron flow is observed, this is usually interpreted as a perpendicular spin current generated by the spin Hall effect exerting a torque on the chiral N\'{e}el skyrmion. By designing samples in which the direction of the net generated spin current can be carefully controlled, we surprisingly show that skyrmion motion is always against the electron flow, irrespective of the net vertical spin-current direction. We find that a negative bulk spin-transfer torque is the most plausible explanation for the observed results, which is qualitatively justified by a simple model that captures the essential behaviour. These findings demonstrate that claims about the skyrmion chirality based on their current-induced motion should be taken with great caution

Experimental studies of the arc chamber short circuit failure mechanism on the DIII-D neutral beam system

Here we report on efforts to improve performance and longevity of the Neutral Beam Injection (NBI) system by initiating a R&D program aimed at studying the most common failure mechanism for the ion sources. To this end a filament driven plasma chamber has been constructed with plasma parameters similar to the arc chamber of NBI ion sources. A preliminary report of an investigation into the most common failure is presented here: The failure mechanism observed during helium operations on DIII-D is the result of electrical breakdown of the insulation material that separates the filament plates from the anode. The fault is reproduced in a table top experiment analogous to the DIII-D NBI ion source in key parameters and proposals for amelioration of the issue are discussed

Experimental studies of the arc chamber short circuit failure mechanism on the DIII-D neutral beam system

\u3cp\u3eHere we report on efforts to improve performance and longevity of the Neutral Beam Injection (NBI) system by initiating a R&D program aimed at studying the most common failure mechanism for the ion sources. To this end a filament driven plasma chamber has been constructed with plasma parameters similar to the arc chamber of NBI ion sources. A preliminary report of an investigation into the most common failure is presented here: The failure mechanism observed during helium operations on DIII-D is the result of electrical breakdown of the insulation material that separates the filament plates from the anode. The fault is reproduced in a table top experiment analogous to the DIII-D NBI ion source in key parameters and proposals for amelioration of the issue are discussed.\u3c/p\u3

Anomalous direction for skyrmion bubble motion

Magnetic skyrmions are localized topological excitations that behave as particles and can be mobile, with great potential for novel data storage devices. In this work, the current-induced dynamics of large skyrmion bubbles is studied. When skyrmion motion in the direction opposite to the electron flow is observed, this is usually interpreted as a perpendicular spin current generated by the spin Hall effect exerting a torque on the chiral N\'{e}el skyrmion. By designing samples in which the direction of the net generated spin current can be carefully controlled, we surprisingly show that skyrmion motion is always against the electron flow, irrespective of the net vertical spin-current direction. We find that a negative bulk spin-transfer torque is the most plausible explanation for the observed results, which is qualitatively justified by a simple model that captures the essential behaviour. These findings demonstrate that claims about the skyrmion chirality based on their current-induced motion should be taken with great caution