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Low-Voltage Tests of a Simple Pulse Line Ion Accelerator (PLIA) Structure

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Q Diot

Q Diot*, D Westerly , B Kavanagh , A Liu , M Miften , Univ. of Colorado Denver, Aurora, CO


TH-AB-FS4-2 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: Four Seasons 4

Purpose: Heavy ion radiotherapy offers potential advantages over x-rays for certain types of cancer; however, current methods for accelerating heavy ions are expensive and opportunities for translational research are severely limited. The pulse line ion accelerator (PLIA) is a helical slow-wave structure that can accelerate ions to energies suitable for cell and small animal irradiation at a fraction of the cost of conventional accelerators. In this work, we construct a low-voltage PLIA structure and characterize the travelling wave properties of the device in air.

Methods: A prototype PLIA tube was constructed and consists of a 22 gauge wire helix (pitch 0.7mm) wrapped around a piece of 1” diameter PVC pipe and placed inside of 3” diameter copper pipe. The axial length of the structure is 1.1m. We use a low voltage signal generator to inject pulse waveforms into the PLIA structure and measure the wave speed and wavelength (dispersion) at different frequencies.

Results: Electric field measurements made along the device illustrate the travelling wave nature of the PLIA structure. Wave speed measurements yield an axial phase velocity of 2.5 to 3.7 10^6m/s (0.8% to 1.2% C) for frequencies in the range of 50kHz to 20MHz, with higher frequencies showing a decrease in wave speed. The agreement with theoretical predictions is within 10%. Measurements suggest a 10V pulse @20MHz results in a wavelength of 15 cm in the structure and axial gradient of 267V/m. With a higher voltage prototype, a 200 kV pulse would produce a 5.3MV/m accelerating field.

Conclusion: Measurements of a low-voltage PLIA tube demonstrate the efficacy of the device as a slow-wave accelerator structure. Measurements of the wave characteristics are in good agreement with theory. Initial measurements suggest a PLIA with accelerating gradient of 3-5MV/m is feasible.

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