Plasma Lens for ion-beam focusing

Worldwide, there are 28.5 million new cancer cases each year with over 10 million deaths, which is predicted to increase by almost 64% by 2040. X-ray based radiotherapy is used in 40% of cures (second only to invasive surgery) and proton beam therapy (PBT) can offer significant therapeutic benefits with a reduced risk of damage to healthy tissues.

The LhARA, the Laser-hybrid Accelerator for Radiobiological Applications, collaboration [1] is developing a facility that is affordable and capable of exploring the mechanisms and biological response to ionising radiation at high dose rates. Proton beam therapies typically use rates <10 Gy/min with tailored beam characteristics to spare healthy tissues, but the use of so-called “FLASH” (dose rates >40 Gy/s) radiotherapy offers an exciting development.

Exploiting the target normal sheath acceleration (TNSA) mechanism resulting when a high repetition (10 Hz), high power, laser is directed at the rear of a thin target, a continuous stream of high intensity, ultra-short (10s ns), proton bunches of up to 20 MeV will be directed downstream. Capture and tailoring of the broad energy, highly divergent, beam will be achieved with the aid of non-traditional, non-neutral electron plasmas as electrostatic beam elements.

Here we present details of the proposed facility, recent progress towards numerically modelling the large (1 m long, 5 cm radius), high density (5E15 m^-3), electron plasma required to efficiently capture the protons (and other heavy ions), and validating the numerical results against experiment.

1. Aymar G. et al. LhARA: The Laser-hybrid Accelerator for Radiobiological Applications. Front. Phys. 8 (2020) 567738