Markus Roth
Institute for Nuclear Physics, Technische Universität Darmstadt, Germany
The quest for laser-based high-energy ions and secondary radiation for applications like material research or even cancer treatment has been going on for some years. Recently, using high contrast short pulse lasers like the LANL 200 TW TRIDENT laser and the concept of relativistic transparency, a breakthrough has been achieved with ion energies exceeding 100 MeV and the production of intense neutron pulses [1], only about three orders of magnitude weaker than the LANSCE neutron pulses.
Based on the new mechanism’s advantages, a laser-driven deuteron beam is used to achieve a new record in laser-neutron production in intensity, energy and directionality. Thus, we demonstrated the use of short pulse lasers to use the resulting hard X-Rays and neutrons of different energies to radiograph an unknown object and to determine its material composition [2]. Neutron generation,
e.g. for deuterium break-up reaction in Be or copper, scale exponentially with energy of the deuterium beam, which scales with the energy of the accelerating laser and result in a collimated beam, allowing e.g. a much higher fraction of produced neutrons to be captured by the moderator and delivered to the application. With available laser power increasing by an order of magnitude every past decades and and enormous increase in repetition rate and therefore average power, pulsed neutron sources achieving or even exceeding the neutron output of LANSCE or even SNS are conceivable. At present, high rep rate lasers are developed which either a) scale up to 30 times the energy of TRIDENT [3] or b) operate at multi Hertz levels [4] at slightly lower energies. Since comparably little shielding is required, targets for laser neutron sources can be very compact, allowing moderator to sample/detector distances of a meter or even less, further increasing the flux on the sample. Investment and operational cost as well as real estate foot-print for the necessary laser systems are all a small fraction of those for the particle accelerators or reactors required for present neutron sources.
Furthermore, recent advantages in electron acceleration with lasers allowed to produce multi-GeV electrons and hard X-ray pulses (>30 keV) already demonstrated for phase contrast imaging [5]. Excluding the laser, the hard X-ray source has only a length of 1cm and a micro-CT with better than 50 micrometer resolution was recently demonstrated in one of the first experiments ever to utilize
synchrotron-like X-rays produced by compact lasers. While synchrotrons produce continuous radiation, laser based system can produce pulses, thus reducing the total dose received by the object. We present the current understanding of the neutron and X-ray generation process with laser pulses and describe the landscape and developments of available laser sources. We quantitatively compare the initial experiments in laser neutron and X-ray generation with existing conventional sources. An overview and outlook on the developments in laser technology will be presented and the potential for neutron and X-ray production will be outlined.
Systems like the 10 PW lasers at ELI in Europe could lead the path for a robust diagnostic system for MARIE with high versatility and scientific opportunities.
[1] M. Roth et al., Phys. Rev. Lett., 110, p. 044802 (2013)
[2] D. Jung et al., Physics of Plasmas 20, 056706 (2013) [3] ELI-BEAMS, L4 Beamline
[4] DIPOLE Laser system, Rutherford Appleton Laboratory, UK
[5] J.M.Cole et al., NATURE Scientific RepoRts | 5:13244