Optimizing the Wall Thickness of a Rexolite Beam Pipe Towards a Proof of Concept Dielectric Wall Accelerator
Abstract
Purpose
To investigate the optimal wall thickness for a Rexolite beam pipe for a proof-of-concept dielectric wall accelerator (DWA). In a DWA, protons are accelerated by a virtual traveling wave, created by switching electric fields along a dielectric beam pipe. The beam pipe, therefore, requires operation under vacuum with a high surface flashover threshold.
Methods
A linear buckling study for a modular Rexolite beam pipe was conducted in COMSOL multiphysics 6.3. The outer diameter was constrained by the radially symmetric waveguides and kept at 2 cm. The wall thickness was varied between 0.2 and 4 mm, the first 5 buckling modes were extracted, and the maximal von Mises stress and displacement were recorded. Surface flashover and the accelerating field were investigated using the maximal electric field at the beam pipe-vacuum interface (Esf) and center (Eacc), respectively, for trapezoid voltage pulses with rise and flattop times of 1.2 and 2 ns, respectively, and peak amplitudes up to 25 kV.
Results
The minimal wall thickness for which 10-7 Pa could be maintained, without collapse was 0.4 mm and converged to a minimum for a wall thickness > 2.5 mm. Esf and Eacc decreased with increasing wall thickness. For all wall thicknesses simulated, using a 1 mm thick waveguide, Esf remained below the threshold (Eth) of 36 MV/m for a 7 mm Rexolite sample found in literature.
Conclusion
Simulations showed that the optimal wall thickness for the Rexolite beam pipe was 2.5 mm. For this wall thickness, Esf < 50∙Eth and Eacc is 165.73 kV/m for a 1 mm thick parallel plate waveguide. Construction of the beam pipe for experimental validation is ongoing.