Laser-accelerated Proton Research Articles

Laser-Generated Proton Beams for High-Precision Ultra-Fast Crystal Synthesis

We present a method for the synthesis of micro-crystals and micro-structured surfaces using laser-accelerated protons. In this method, a solid surface material having a low melting temperature is irradiated with very-short laser-generated protons, provoking in the ablation process thermodynamic conditions that are between the boiling and the critical point. The intense and very quick proton energy deposition (in the ns range) induces an explosive boiling and produces microcrystals that nucleate in a plasma plume composed by ions and atoms detached from the laser-irradiated surface. The synthesized particles in the plasma plume are then deposited onto a cold neighboring, non-irradiated, solid secondary surface. We experimentally verify the synthesizing methods by depositing low-melting-material microcrystals - such as gold - onto nearby silver surfaces and modeling the proton/matter interaction via a Monte Carlo code, confirming that we are in the above described thermodynamic conditions. Morphological and crystallinity measurements indicate the formation of gold octahedral crystals with dimensions around 1.2 μm, uniformly distributed onto a silver surface with dimensions in the tens of mm2. This laser-accelerated particle based synthesis method paves the way for the development of new material synthesis using ultrashort laser-accelerated particle beams.

Considerations on employing a PMQ-doublet for narrow and broad proton energy distributions

Abstract We simulated a doublet of permanent magnet quadrupoles (PMQs) to estimate the sensitivity on positioning precision and its impact on the spectral properties of transported protons. The study guided the construction and testing of a focusing setup for laser-accelerated proton bunches with energies between 6 and 10 MeV. Our results shed light on possible applications that may arise from broad input particle spectra.

Characterization of online high dynamic range imaging for laser-driven ion beam diagnostics using visible light

Abstract Laser-driven acceleration of particle beams is an emerging modality under research for biomedical applications. The spatially resolved diagnostics of laser-accelerated proton bunches is crucial for their application. The RadEye detector, featuring up to 10 cm x 5 cm area of online complementary metal-oxide-semiconductor (CMOS) detector made of 48 μm pixels, is established for x-ray, proton and ion beam diagnostics. We exploit the usually undesired ‘Image lag’ phenomenon of incomplete pixel reset to generate 2D-images with a larger dynamic range than the single frame range of 12-bit. Using 532 nm laser pulses and computer simulations for single-slit diffraction, calibration factors to stack multiple readouts were successfully derived to quantitatively reconstruct spatial information about an optical beam and hence extend the dynamic range of the detector compared to a single frame. The final goal is focus quantification for a permanent magnet quadrupole system for protons and terawatt (TW-class) laser focus diagnostics.

Manipulation of laser-accelerated proton beam profiles by nanostructured and microstructured targets

Nanostructured and microstructured thin foils have been fabricated and used experimentally as targets to manipulate the spatial profile of proton bunches accelerated through the interaction with high intensity laser pulses (6 x 1019 W/cm(2)). Monolayers of polystyrene nanospheres were placed on the rear surfaces of thin plastic targets to improve the spatial homogeneity of the accelerated proton beams. Moreover, thin targets with grating structures of various configurations on their rear sides were used tomodify the proton beam divergence. Experimental results are presented, discussed, and supported by 3D particle-in-cell numerical simulations.

Laser proton accelerator with improved repeatability at Peking University

The repeatability of laser proton accelerator is mainly limited by laser plasma interaction, laser target coupling and laser parameter variation. In our recent experiments performed on the Compact Laser Plasma Accelerator at Peking University, gain of proton beams with improved repeatability is demonstrated. In order to control the laser plasma interaction in pre-plasma, cross polarized-wave generation technique is employed to provide a laser pulse with an ultrahigh contrast of 10−10 A semi-automatic laser and target alignment system with a sensitivity of few microns is employed. The repetition rate of the laser pro-ton accelerator is at the level of 0.1 Hz which is beneficial to decrease laser parameter variation. The shot-to-shot variation of proton energies is about 9% for a level of confidence of 0.95.

An analytical reconstruction model of the spread-out Bragg peak using laser-accelerated proton beams

With the development of laser technology, laser-driven proton acceleration provides a new method for proton tumor therapy. However, it has not been applied in practice because of the wide and decreasing energy spectrum of laser-accelerated proton beams. In this paper, we propose an analytical model to reconstruct the spread-out Bragg peak (SOBP) using laser-accelerated proton beams. Firstly, we present a modified weighting formula for protons of different energies. Secondly, a theoretical model for the reconstruction of SOBPs with laser-accelerated proton beams has been built. It can quickly calculate the number of laser shots needed for each energy interval of the laser-accelerated protons. Finally, we show the 2D reconstruction results of SOBPs for laser-accelerated proton beams and the ideal situation. The final results show that our analytical model can give an SOBP reconstruction scheme that can be used for actual tumor therapy.

DOSIMETRIC EVALUATION OF LASER-DRIVEN X-RAY AND NEUTRON SOURCES UTILIZING XG-III PS LASER WITH PEAK POWER OF 300 TERAWATT.

Current short-pulse high-intensity lasers can accelerate electrons and proton/ions to energies of giga-electron volts. For certain advanced applications, laser-accelerated electrons and protons are optimised for high-energy X-ray and neutron generation at the XG-III picosecond (ps) laser beamline. These energetic X-ray and neutron beams can significantly affect radiation safety at the facility; therefore, proper evaluation of the radiological hazards induced by laser-driven X-ray and neutron sources is required. This study presents a dosimetric evaluation of laser-driven X-ray and neutron sources at the XG-III ps laser beamline. The 'source terms' of the laser-accelerated electrons and protons are characterised utilising the particle-in-cell method and an analytical model, respectively. The Monte Carlo code FLUKA is used to calculate prompt and residual dose yields due to all radiation field components and the number of residual activated nuclei. Our results can provide a reference for radiation hazard analysis at short-pulse high-intensity laser facilities worldwide.

Measurement of the equation of state of solid-density copper heated with laser-accelerated protons.

We present equation of state (EOS) measurements of solid-density copper heated to 5-10 eV. A copper sample was heated isochorically by hydrogen ions accelerated from an adjacent foil by a high intensity pulsed laser, and probed optically. The measured temperature and expansion are compared against simulations using the most up-to-date wide range EOS tables available.

Laser-Accelerated Proton Beams as Diagnostics for Cultural Heritage

This paper introduces the first use of laser-generated proton beams as diagnostic for materials of interest in the domain of Cultural Heritage. Using laser-accelerated protons, as generated by interaction of a high-power short-pulse laser with a solid target, we can produce proton-induced X-ray emission spectroscopies (PIXE). By correctly tuning the proton flux on the sample, we are able to perform the PIXE in a single shot without provoking more damage to the sample than conventional methodologies. We verify this by experimentally irradiating materials of interest in the Cultural Heritage with laser-accelerated protons and measuring the PIXE emission. The morphological and chemical analysis of the sample before and after irradiation are compared in order to assess the damage provoked to the artifact. Montecarlo simulations confirm that the temperature in the sample stays safely below the melting point. Compared to conventional diagnostic methodologies, laser-driven PIXE has the advantage of being potentially quicker and more efficient.

The radiobiology of laser-driven particle beams: focus on sub-lethal responses of normal human cells

Accelerated proton beams have become increasingly common for treating cancer. The need for cost and size reduction of particle accelerating machines has led to the pioneering investigation of optical ion acceleration techniques based on laser-plasma interactions as a possible alternative. Laser-matter interaction can produce extremely pulsed particle bursts of ultra-high dose rates (⩾ 109 Gy/s), largely exceeding those currently used in conventional proton therapy. Since biological effects of ionizing radiation are strongly affected by the spatio-temporal distribution of DNA-damaging events, the unprecedented physical features of such beams may modify cellular and tissue radiosensitivity to unexplored extents. Hence, clinical applications of laser-generated particles need thorough assessment of their radiobiological effectiveness. To date, the majority of studies have either used rodent cell lines or have focussed on cancer cell killing being local tumour control the main objective of radiotherapy. Conversely, very little data exist on sub-lethal cellular effects, of relevance to normal tissue integrity and secondary cancers, such as premature cellular senescence. Here, we discuss ultra-high dose rate radiobiology and present preliminary data obtained in normal human cells following irradiation by laser-accelerated protons at the LULI PICO2000 facility at Laser Lab Europe, France.

Laser-accelerated ion beam diagnostics with TOF detectors for the ELIMED beam line

Laser-accelerated ion beams could represent the future of particle acceleration in several multidisciplinary applications, as for instance medical physics, hadrontherapy and imaging field, being a concrete alternative to old paradigm of acceleration, characterized by huge and complex machines. In this framework, following on from the ELIMED collaboration, launched in 2012 between INFN-LNS and ELI-Beamlines, in 2014 a three-years contract has been signed between the two institutions for the design and the development of a complete transport beam-line for high-energy ion beams (up to 60 MeV) coupled with innovative diagnostics and in-air dosimetry devices. The beam-line will be installed at the ELI-Beamlines facility and will be available for users. The measurement of the beam characteristics, such as energy spectra, angular distributions and dose-rate is mandatory to optimize the transport as well as the beam delivery at the irradiation point. In order to achieve this purpose, the development of appropriate on-line diagnostics devices capable to detect high-pulsed beams with high accuracy, represents a crucial point in the ELIMED beamline development. The diagnostics solution, based on the use of silicon carbide (SiC) and diamond detectors using TOF technique, will be presented together with the preliminary results obtained with laser-accelerated proton beams.

Focusing effect of channel target on ultra-intense laser-accelerated proton beam

In laser proton acceleration, the inevitable transverse divergence of proton beam restricts its applications in many fields. In this paper, a structured target with a properly wide channel attached to the backside of a foil is proposed, and the interaction of the ultra-short laser pulse with the structured channel target is investigated via two-dimensional particle-in-cell simulation. The simulations show that for the structured channel target, electrons on the front surface are heated by the incident high-intensity laser pulse and then the induced hot electrons transport through the target to the rear surface, building an electrostatic field in the longitudinal direction to accelerate the protons to high energies as the typical target normal sheath acceleration scheme. In the case of the structured channel target, the simulation results indicate that a strong transverse electrostatic field is created by charge separation along the inner surface of the channel while hot electrons propagate along the channel side walls under the guidance of self-induced magnetic and electric fields, which can focus the emitted proton beam transversely, leading to a smaller divergence. By comparing the channel target case with the traditional foil target case under the same conditions, it is found that the divergence angle of the proton beam from the channel target is reduced significantly. Protons with energies above 3 MeV have a divergence angle of 5.3° at the time of 500 fs in the channel target case, while the value is 17.1° in the foil case for a laser intensity of 5.4×1019 W/cm2. Additionally, the effect of the channel target on the maximum proton energy is considered. The simulation results of the energy spectra reveal that the maximum proton cut-off energy of the channel target is about 1 MeV lower than that of the foil target. This small energy loss is due to the refluxing of the cold electrons on the channel walls, which suppresses the increasing of the sheath potential. Therefore, it is concluded that the focusing electric field can work on the proton beam effectively, leading to a better collimation with conserving the proton energy by using the proposed channel target. Especially when the inner diameter of the channel target is comparable to the laser focal spot size, the proton beam can be confined to a small divergence, and a relatively higher laser energy conversion efficiency can be ensured as well.

Experimental studies with two novel silicon detectors for the development of time-of-flight spectrometry of laser-accelerated proton beams

Laser-accelerated proton beams exhibit remarkably different beam characteristics as compared to conventionally accelerated ion beams. About 105 to 107 particles per MeV and msr are accelerated quasi-instantaneously within about 1 ps. The resulting energy spectrum typically shows an exponentially decaying distribution. Our planned approach to determine the energy spectrum of the particles generated in each pulse is to exploit the time-of-flight (TOF) difference of protons with different kinetic energies at 1 m distance from the laser-target interaction. This requires fast and sensitive detectors. We therefore tested two prototype silicon detectors, developed at the Centre for Medical Radiation Physics at the University of Wollongong with a current amplifier, regarding their suitability for TOF-spectrometry in terms of sensitivity and timing properties. For the latter, we illuminated the detectors with short laser pulses, measured the signal current and compared it to the signal of a fast photodiode. The comparison revealed that the timing properties of both prototypes are not yet sufficient for our purpose. In contrast, our results regarding the detectors’ sensitivity are promising. The lowest detectable proton flux at 10 MeV was found to be 25 protons per ns on the detector. With this sensitivity and with a smaller pixelation of the detectors, the timing properties can be improved for new prototypes, making them potential candidates for TOF-spectrometry of laser-accelerated particle beams.

Enhancement of laser intensity and proton acceleration using micro-tube plasma lens targets

A hollow, cylindrical, micron-scale structure is proposed to enhance and manipulate the laser plasma interaction. It is shown through 3-D particle-in-cell simulations that the incident laser pulse intensity is enhanced within the tube. A detailed study of the intensification optimizes the tube dimensions and provides a characterization of the in-tube intensity. By coupling the micro-tube plasma lens to a traditional flat interface, we show an increase in on-target intensity. We detail proton energy enhancement as a potential application of the micro-tube plasma lens target, where the tube structure focuses the light and provides additional electrons that enhance the accelerating sheath field.

1568P - Development of laser-driven proton beam therapy

ABSTRACT Aim: Proton beams by their advantageous dose profile over conventional photon and electron beams may provide higher dose conformity and better healthy tissue sparing. But due to high costs and huge size of existing facilities, proton therapy is limited to few centers. A novel proton acceleration, on µm scale by ultra-intense lasers, promises compact accelerators and beam delivery systems. Unlike conventional proton beams, laser-accelerated proton (LAP) beam is characterized by short ultra-intense pulses with peak dose rates exceeding conventional values by ∼9 orders of magnitude but low repetition rate, broad energy spread and large divergence. They require completely new techniques of beam transport, dose delivery and quality assurance along with radiobiological characterization. Methods: The presented work is an ongoing joint translational research project of several institutions in Germany aiming to establish LAP therapy. In parallel to the development of high power laser systems and laser targets to generate stable and reproducible LAP beams, a dedicated radiation oncology focused research program is being followed. Results: Laser-based technology was established for cell and small animal irradiation. The high power laser system DRACO was setup and optimized for long-term stable proton acceleration. A dedicated fixed-beam transport system with integrated energy selection and field shaping as well as real time dose monitoring was established. The suitability and reliability of all components was proven in systematic radiobiological studies over months. No overall difference in the biological effectiveness between laser-accelerated and conventional beams was detected to date. For translation towards patient irradiation, increase of proton energy from ∼25 to ∼230 MeV by increasing the laser power from ∼100 TW to ∼1 PW is required and the development of PW laser is in progress. Furthermore, a compact 360° isocentric proton gantry was designed, based on novel light-weight high-field pulsed magnets. This gantry is ∼2.5x smaller than conventional proton gantries. The necessary pulsed magnets are being developed together with novel dose delivery strategy for LAP. Conclusions: LAP therapy is a promising alternative, yet require substantial development with a clinical prototype in some years. Supported by German BMBF, no. 03Z1N511. Disclosure: All authors have declared no conflicts of interest.

Ultra-short laser-accelerated proton pulses have similar DNA-damaging effectiveness but produce less immediate nitroxidative stress than conventional proton beams.

Ultra-short proton pulses originating from laser-plasma accelerators can provide instantaneous dose rates at least 107-fold in excess of conventional, continuous proton beams. The impact of such extremely high proton dose rates on A549 human lung cancer cells was compared with conventionally accelerated protons and 90 keV X-rays. Between 0.2 and 2 Gy, the yield of DNA double strand breaks (foci of phosphorylated histone H2AX) was not significantly different between the two proton sources or proton irradiation and X-rays. Protein nitroxidation after 1 h judged by 3-nitrotyrosine generation was 2.5 and 5-fold higher in response to conventionally accelerated protons compared to laser-driven protons and X-rays, respectively. This difference was significant (p < 0.01) between 0.25 and 1 Gy. In conclusion, ultra-short proton pulses originating from laser-plasma accelerators have a similar DNA damaging potential as conventional proton beams, while inducing less immediate nitroxidative stress, which probably entails a distinct therapeutic potential.

Neutronless nuclear reaction at inertial confinement of the magnetized plasma of laser-accelerated protons and boron nuclei

It has been proposed to use the formation of a magnetized plasma of laser-accelerated ions and electrons at the irradiation of the curved surface of the inner cavity of the target by a petawatt laser pulse to initiate a neutronless nuclear reaction of protons with boron nuclei. The possibility of an additional increase in the intensity of the reaction owing to the compression of the plasma at the irradiation of the outer surface of the target by a second terawatt laser pulse synchronized in time with the plasma-forming pulse has been discussed. The parameters of laser pulses and a target have been determined at which the ignition of a pB plasma occurs; i.e., the energy released in reactions is equal to the energy of the plasma.

Fusion Energy and Stopping Power in a Degenerate DT Pellet Driven by a Laser-Accelerated Proton Beam**Supported by the Research Council of University of Guilan

In this paper, we have improved the fast ignition scheme in order to have more authority needed for high-energy-gain. Due to the more penetrability and energy deposition of the particle beams in fusion targets, we employ a laser-to-ion converter foil as a scheme for generating energetic ion beams to ignite the fusion fuel. We find the favorable intensity and wavelength of incident laser by evaluating the laser-proton conversion gain. By calculating the source-target distance, proton beam power and energy are estimated. Our analysis is generalized to the plasma degeneracy effects which can increase the fusion gain several orders of magnitude by decreasing the ion-electron collisions in the plasma. It is found that the wavelength of 0.53 μm and the intensity of about 1020 W/cm2, by saving about 10% conversion coefficient, are the suitable measured values for converting a laser into protons. Besides, stopping power and fusion burn calculations have been done in degenerate and non-degenerate plasma mediums. The results indicate that in the presence of degeneracy, the rate of fusion enhances.

Production of 68 Ge , 64 Cu , 86 Y , 89 Zr , 73 Se , 77 Br and 124 I positron emitting radionuclides through future laser-accelerated proton beams at ELI-Beamlines for innovative PET diagnostics

The development of innovative production pathways for high-Z positron emitters is of great interest to enlarge the applicability of PET diagnostics, especially in view of the continuous development of new radiopharmaceuticals. We evaluated the theoretical yields of 64 Cu , 86 Y , 89 Zr , 73 Se , 77 Br and 124 I PET isotopes, plus the 68 Ge isotope, parent of the 68 Ga positron emitter, in the hypothesis of production through laser-accelerated proton sources expected at the ELI-Beamlines facility. By means of the TALYS software we simulated the nuclear reactions leading to the above radionuclides, hypothesizing three possible scenarios of broad proton spectra, with maximum energies of about 9, 40 and 100 MeV. The production yields of the studied radionuclides, within the expected fluences, appear to be suitable for pre-clinical applications.

Laser-accelerated proton beam for fast ignition considering formation factor of a cloud and penetrability in P11B reaction

In this work proton beam is proposed in fast ignition of P11B fuel considering uniform density equal to 300 g cm−3. The total stopping power and range of protons are estimated by introducing the stopping power contribution of electrons and ions as a function of initial energy and temperature in the fuel. Also bonus energy and total deposition energy due to the additional fusion reactions are calculated. The bonus energy and total deposited energy are remarkable at smaller beam energy and higher electron temperature. Also this article show that the cross section of P11B fusion reaction is increased by increasing the penetrability of nuclei through the Coulomb barrier. In this approach, an intense laser field of more than 100 PW is required to distort the Coulomb barrier to obtain enough penetrability. We have calculated the penetrability of nuclei and the formation factor using available relations.