What is it about?
An analytical model of the current propagation in a helical coil with varying geometry is developed. It can be used for the post-acceleration and post-focusing of ions produced via the laser-driven Target Normal Sheath Acceleration and generation of electromagnetic pulses. We calculate the current that propagates in a helical coil and suggest improving its dispersion properties using a screening tube and with pitch and radius variation. The electromagnetic fields calculated with the analytical model are in agreement with Particle-in-Cell simulations. The model provides insights into the physics of current propagation in helical coils with varying geometries and enables a numerical implementation for rapid proton spectrum computations, which facilitate their design for future experiments.
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Why is it important?
In this work, we develop an analytic description of current propagation in a helical coil with a screening tube and varying geometry. The tube mitigates the coil dispersion and maintains a quasi-constant pulse shape and propagation velocity. In addition, a gradual increase of the coil pitch allows to accelerate the pulse along the propagation direction and maintain resonance with the accelerated particles over a longer distance. The model is implemented numerically in the code DoPPLIGHT, and its accuracy is demonstrated by comparing it with the results of PIC simulations. Good agreement is obtained for coils with a constant pitch and radius with and without a tube. Furthermore, the comparison is extended to the case of a linearly varying pitch. We demonstrated that coil screening and pitch stretching allows optimizing the proton acceleration. An increase in the number of high-energy protons by an order of magnitude was observed, together with an increase in the maximum proton energy by 20\% and a focusing of the particles on the coil axis.
Perspectives
I hope this article will permit scientific discussions, collaborations and will attract attention from physicist working on proton acceleration or travelling wave tube. Perhaps this article will also give rise to new ideas.
Clément Lacoste
CEA
Read the Original
This page is a summary of: Theoretical model of current propagation in a helical coil with varying geometry and screen tube, Matter and Radiation at Extremes, August 2024, American Institute of Physics,
DOI: 10.1063/5.0221820.
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