Development of an ultrathin liquid sheet target for laser ion acceleration at high repetition rates in the kilohertz range

A colliding microjet liquid sheet target system was developed and tested for pairs of round nozzles of 10,11 and 18μm in diameter.The sheet's position stability was found to be better than a few micrometers.Upon interaction with 50 mJ laser pulses,the 18μm jet has a resonance amplitude of 16μm at a repetition rate of 33 Hz,while towards 100 Hz it converges to 10μm for all nozzles.A white-light interferometric system was developed to measure the liquid sheet thickness in the target chamber both in air and in vacuum,with a measurement range of 182 nm±1μm and an accuracy of±3%.The overall shape and 3D shape of the sheet follow the Hasson±Peck model in air.In vacuum versus air,the sheet gradually loses 10%of its thickness,so the thinnest sheet achieved was below 200 nm at a vacuum level of 10±4mbar,and remained stable for several hours of operation.

Effects of density profile and multi-species target on laser-heated thermal-pressure-driven shock wave acceleration

The shock wave acceleration of ions driven by laser-heated thermal pressure is studied through one-dimensional particle-in-cell simulation and analysis. The generation of high-energy mono-energetic protons in recent experiments （D. Haberberger et al., 2012 Nat. Phys. 8 95） is attributed to the use of exponentially decaying density profile of the plasma target. It does not only keep the shock velocity stable but also suppresses the normal target normal sheath acceleration. The effects of target composition are also examined, where a similar collective velocity of all ion species is demonstrated. The results also give some reference to future experiments of producing energetic heavy ions.

Preparation of graphene on SiC by laser-accelerated pulsed ion beams

Laser-accelerated ion beams(LIBs) have been increasingly applied in the field of material irradiation in recent years due to the unique properties of ultra-short beam duration, extremely high beam current, etc. Here we explore an application of using laser-accelerated ion beams to prepare graphene. The pulsed LIBs produced a great instantaneous beam current and thermal effect on the SiC samples with a shooting frequency of 1 Hz. In the experiment, we controlled the deposition dose by adjusting the number of shootings and the irradiating current by adjusting the distance between the sample and the ion source. During annealing at 1100℃, we found that the 190 shots ion beams allowed more carbon atoms to self-assemble into graphene than the 10 shots case. By comparing with the controlled experiment based on ion beams from a traditional ion accelerator, we found that the laser-accelerated ion beams could cause greater damage in a very short time. Significant thermal effect was induced when the irradiation distance was reduced to less than 1 cm, which could make partial SiC self-annealing to prepare graphene dots directly. The special effects of LIBs indicate their vital role to change the structure of the irradiation sample.

On intense proton beam generation and transport in hollow cones

Proton generation,transport and interaction with hollow cone targets are investigated by means of two-dimensional PIC simulations.A scaled-down hollow cone with gold walls,a carbon tip and a curved hydrogen foil inside the cone has been considered.Proton acceleration is driven by a 10^(20) W·cm^(-2) and 1 ps laser pulse focused on the hydrogen foil.Simulations show an important surface current at the cone walls which generates a magnetic field.This magnetic field is dragged by the quasi-neutral plasma formed by fast protons and co-moving electrons when they propagate towards the cone tip.As a result,a tens of kT B z field is set up at the cone tip,which is strong enough to deflect the protons and increase the beam divergence substantially.We propose using heavy materials at the cone tip and increasing the laser intensity in order to mitigate magnetic field generation and proton beam divergence.

Feasibility study of laser-driven neutron sources for pharmaceutical applications

We predict the production yield of a medical radioisotope^(67)Cu using^(67)Zn(n,p)^(67)Cu and ^(68)Zn(n,pn)^(67)Cu reactions with fast neutrons provided from laser-driven neutron sources.The neutrons were generated by the p+9Be and d+9Be reactions with high-energy ions accelerated by laser–plasma interaction.We evaluated the yield to be(3.3±0.5)×10^(5) atoms for^(67)Cu,corresponding to a radioactivity of 1.0±0.2 Bq,for a Zn foil sample with a single laser shot.Using a simulation with this result,we estimated^(67)Cu production with a high-frequency laser.The result suggests that it is possible to generate^(67)Cu with a radioactivity of 270 MBq using a future laser system with a frequency of 10 Hz and 10,000-s radiation in a hospital.