Development of short-pulsed high-field electromagnetic dipoles for laser-based proton therapy

Introduction
During the last years, the new technology of laser based particle acceleration was developed at such a rate that medical application for cancer therapy becomes conceivable. Promising more compact and economic accelerators, the laser technology however generates intense ultra-short (~ ps) pulsed proton beams with large divergence and broad energy spectrum. Within the German joint research project “onCOOPtics” the clinical applicability of such pulsed proton beams is investigated including the development of a laser accelerator and a suitable beam transport.
Methods
A compact beam transport system was designed enabling an efficient transport of proton pulses from generation to treatment site. The initially divergent proton beam is captured by a cylindrical electromagnet (solenoid), deflected by 45° dipole magnets and formed by quadrupole magnets, whereas the spectrum is shaped by adaptable lead apertures. For realization, electromagnetic dipoles with magnetic fields of up to 10 T are required to deflect up to 220 MeV protons. These field strengths are achieved by in-house developed non-ferrous dipoles that consist of 80 copper coils in 12 layers and are operated at peak currents of up to 20 kA. To handle the high currents and the generated heat the dipoles are externally cooled and operated in 1 ms short pulses synchronized with the laser repetition frequency.
Results
The prototype of a short-pulsed electromagnetic dipole magnet was designed and manufactured. Results of the experimental characterization and first performance tests at a conventional Tandem accelerator are under way.
Conclusion
Pulsed electromagnetic dipoles as crucial components of a compact beam line for laser-accelerated protons are engineered. Following validation of their suitability at a conventional accelerator the dipoles will be implemented and further tested at a laser accelerator. Together with improvement of the dipole the design of quadrupoles will start.