We report on the first experimental verification of the traveling-wave-like picture of a magnetic-field and an associated electric potential hill propagating non-diffusively in low resistivity plasma. High spatial resolution spectroscopic method, developed here, allowed for obtaining the detailed shape of the propagating magnetic-field front. The measurements demonstrated that the ion separation, previously claimed, results from the reflection of the higher charge-to-mass ratio ions from the propagating potential hill and from climbing the hill by the lower charge-to-mass ratio ions. This ion dynamics is found to be consistent with the observed electron density evolution.

We apply three fluid plasma evolution equations to the problem of magnetic field propagation in a planar plasma opening switch. For certain initial conditions in which Hall parameter H ∼ 1, magnetic field penetration due to the Hall field, initially, as expected, either opposes or adds to the hydromagnetic pushing, depending on the polarity of the magnetic field relative to the density gradient. Later, however, the plasma pushing by the magnetic field is found in the case studied here to modify the plasma density in a way that the density gradient tends to align with the magnetic field gradient, effectively turning off the Hall effect. The penetration of the magnetic field then ceases and plasma pushing becomes the dominant process.

Mehlhorn, T. A. (2016). Electron density evolution during a fast, non-diffusive propagation of a magnetic field in a multi-ion-species plasma. Physics of Plasmas, 23(12), [122126]. DOI: 10.1063/1.4972536 DOI:10.1063/1.4972536 Document status and date:Published: 01/12/2016 Document Version: Publisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at:openaccess@tue.nl providing details and we will investigate your claim. Electron density evolution during a fast, non-diffusive propagation of a magnetic field in a multi-ion-species plasma Electron density evolution during a fast, non-diffusive propagation of a magnetic field in a multi-ion-species plasma We present spectroscopic measurements of the electron density evolution during the propagation of a magnetic-field front (peak magnitude $8 kG) through low-resistivity, multi-ion species plasma. In the configuration studied, a pulsed current, generating the magnetic field, is driven through a plasma that pre-fills the volume between two electrodes. 3D spatial resolution is achieved by local injection of dopants via an optimized laser blow-off technique. The electron density evolution is inferred from the intensity evolution of Mg II and B II-III dopant line-emission. The Doppler-shifted line-emission of the light boron, accelerated by the magnetic field is also used to determine the electric-potential-hill associated with the propagating magnetic field. Utilizing the same spectral line for the determinat...

We present high-resolution observations of a magnetic-field front (peak magnitude ~ 8 kG) propagating through lowresistivity, multi-ion species plasma (mainly protons and carbon ions, electron density ~ 2.5x10 14 cm -3 and temperature ~ 6 eV). Diagnostic methods are developed in order to reveal the details of the interaction, including the evolution of the magnetic-field front and plasma properties. These methods are based on controlled injection of trace-element ions (via an optimized laser blow-off) and new analysis approach that allows for obtaining the magnetic field from the velocity evolution of trace-element ions. A sub-mm resolution is achieved, which is comparable to the electron skin-depth. Moreover, the newly developed method enables the determination of relatively low-intensity fields of ~ 1 kG, otherwise impractical to measure spectroscopically by the common Zeeman method under such highly transient, lowdensity conditions. Here, we briefly describe the diagnostic method and the main results. The structure of the propagating magnetic field front is reconstructed and its width (~ 10 mm) is used for estimating the plasma conductivity. We find that the magnetic-field front structure and velocity remain nearly constant when the field propagates a length scale of the order of the front width. This allows the analysis of the associated electric potential hill in the moving frame of the magnetic field. Using the properties of the potential hill we derive the details of the ion dynamics according to their charge-to-mass (Z/m) ratios. Ions of relatively low Z/m ratios (C II-III) are penetrated by the magnetic field, whereas ions of high Z/m ratios (protons and C V-IV) are reflected off the field-front at different field magnitudes. The measured electron density evolution agrees with the predicted ion dynamics. ________________________________ *

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