Abstract
Discharge characteristics and dynamic behaviors of a current-carrying line-tied (screw pinch) plasma have been experimentally studied. Besides its compactness, the novelty of this design is to utilize a single plasma source for both arc discharge and beam extraction, providing a plasma current of up to 2 kA with an injection voltage of 1.2 kV. The electron density and temperature of the screw pinch plasma were measured to be ∼1020 m−3 and ∼6 eV, respectively, depending on the operating parameters and magnetic field topology. The estimated Kruskal–Shafranov instability current limit of 1.58 kA was confirmed by high-speed camera measurement. The initial experimental results showed that the strength and topology of the magnetic field played a crucial role in the discharge characteristics and dynamic behaviors of the current-carrying line-tied plasma.
Highlights
Dynamic behaviors of plasmas injected into and interacting with a magnetic field draw considerable attention in many scientific research fields, such as screw pinches,1 plasma flux ropes,2 spheromaks,3,4 astrophysical jets,5 bipolar outflows associated with young stellar objects,6 active galactic nuclei,7 solar wind evolution,8 magnetotail physics,9 accretion disk dynamics,10 tokamak noninductive magnetic helicity injection,11 and neutral bean injectors
We developed a new device for investigating the dynamics of plasma injected into and interacting with a magnetic field
The discharge current measured at the gun cathode and the voltage difference between the anode and cathode waveforms are shown in Fig. 5, which showed that both plasma current and injection voltage waveforms were not flat due to the different values of inductance at each of the pulse forming network (PFN) stages since it was lab-designed
Summary
Dynamic behaviors of plasmas injected into and interacting with a magnetic field draw considerable attention in many scientific research fields, such as screw pinches, plasma flux ropes, spheromaks, astrophysical jets, bipolar outflows associated with young stellar objects, active galactic nuclei, solar wind evolution, magnetotail physics, accretion disk dynamics, tokamak noninductive magnetic helicity injection, and neutral bean injectors. Among many experimental devices, a magnetized current-carrying line-tied plasma (screw pinch) has been widely used to investigate the dynamics of plasma interacting with external and self-generating magnetic fields due to its simplicity and easiness of operation. The effect of magnetic field topology on the performance of the plasma current source and different plasma parameters was not considered in the experiment. They used many concentric plasma guns for the control of the plasma profile, which caused additional merging of the current filaments and coalescence of two magnetic ropes.. Another study by Furno et al investigated the effects of the boundary conditions on non-line-tied plasma sources.13 They found that the sheath resistance imposed a limitation on achieving perfect line-tied configurations and in doing so, there was a lower critical current for the onset of the kink.
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