Laser-accelerated Proton Beams Research Articles

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.

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.

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.

Future laser-accelerated proton beams at ELI-Beamlines as potential source of positron emitters for PET

The development of novel compact PET radionuclide production systems is of great interest to promote the diffusion of PET diagnostics, especially in view of the continuous development of novel, fast and efficient, radiopharmaceutical methods of labeling. We studied the feasibility to produce clinically-relevant amounts of PET isotopes by means of laser-accelerated proton sources expected at the ELI-Beamlines facility where a PW, 30 fs, 10 Hz laser system will be available. The production yields of several positron emitters were calculated through the TALYS software, by taking into account three possible scenarios of broad proton spectra expected, with maximum energies ranging from about 8 MeV to 100 MeV. With the hypothesized proton fluencies, clinically-relevant amounts of radionuclides can be obtained, suitable to prepare single doses of radiopharmaceuticals exploiting modern fast and efficient labeling systems.

Ion acceleration and plasma jet formation in ultra-thin foils undergoing expansion and relativistic transparency

At sufficiently high laser intensities, the rapid heating to relativistic velocities and resulting decompression of plasma electrons in an ultra-thin target foil can result in the target becoming relativistically transparent to the laser light during the interaction. Ion acceleration in this regime is strongly affected by the transition from an opaque to a relativistically transparent plasma. By spatially resolving the laser-accelerated proton beam at near-normal laser incidence and at an incidence angle of 30°, we identify characteristic features both experimentally and in particle-in-cell simulations which are consistent with the onset of three distinct ion acceleration mechanisms: sheath acceleration; radiation pressure acceleration; and transparency-enhanced acceleration. The latter mechanism occurs late in the interaction and is mediated by the formation of a plasma jet extending into the expanding ion population. The effect of laser incident angle on the plasma jet is explored.

Manipulation of the spatial distribution of laser-accelerated proton beams by varying the laser intensity distribution

We report on a study of the spatial profile of proton beams produced through target normal sheath acceleration using flat target foils and changing the laser intensity distribution on the target front surface. This is done by either defocusing a single laser pulse or by using a split-pulse setup and irradiating the target with two identical laser pulses with variable spatial separation. The resulting proton beam profile and the energy spectrum are recorded as functions of the focal spot size of the single laser pulse and of the separation between the two pulses. A shaping of the resulting proton beam profile, related to both an increase in flux of low-energy protons in the target normal direction and a decrease in their divergence, in one or two dimensions, is observed. The results are explained by simple modelling of rear surface sheath field expansion, ionization, and projection of the resulting proton beam.

The stopping power of relativistic electrons and laser-accelerated proton beams for fast ignition of DT and D3He and P11B fuels

The understanding of basic physics of processes associated with the beam in fast ignition is very important. In this paper energy deposition of 1 MeV relativistic electrons study by calculating stopping power in D3He plasma with uniform density 300 g cm−3 and compare with DT plasma in identical condition. The results show energy deposition in D3He plasma is more than DT plasma. Scattering due to of background electrons decreases the penetration depth from 0.38 to 0.24 g cm−2 in D3He plasma and from 0.51 to 0.33 g cm−2 in DT plasma. Nuclear reaction of protons with the boron-11 nuclei (p–11B) is the most promising of all the reactions that can be used for completely neutronless power generation in a fusion reactor. The level of radioactivity associated with concomitant and secondary reactions is negligible, while for D–T reactor 80% of the fusion power is released in neutrons and neutron yield of D–3He is about 5%. Note, D–3He reaction is neutronless, but neutrons are born as a result of D–D branch and the secondary reaction of tritium and deuterium. From a technical point of view the lack of neutrons in the reactor mixture p–11B is very attractive because it removes a major problem of the first wall. Therefore in this paper proton beam is proposed in fast ignition approach using P11B fuel at uniform density 300gcm−3 with considering Maxwellian energy distribution. The stopping power and total range of proton beam are calculated. The rate of energy transfer between ions and electrons and bremsstrahlung loss power with considering relativistic corrections in P11B fuel are exanimated. The results show that total stopping power of protons in P11B fuel at different temperatures is a function of proton energy and it decreases with rising temperature at constant EP. Bonus energy and total deposited energy is significant at smallerEP and higher Te.

Simulations of radiation pressure ion acceleration with the VEGA Petawatt laser

The Spanish Pulsed Laser Centre (CLPU) is a new high-power laser facility for users. Its main system, VEGA, is a CPA Ti:Sapphire laser which, in its final phase, will be able to reach Petawatt peak powers in pulses of 30fs with a pulse contrast of 1:1010 at 1ps. The extremely low level of pre-pulse intensity makes this system ideally suited for studying the laser interaction with ultrathin targets. We have used the particle-in-cell (PIC) code OSIRIS to carry out 2D simulations of the acceleration of ions from ultrathin solid targets under the unique conditions provided by VEGA, with laser intensities up to 1022Wcm−2 impinging normally on 20–60nm thick overdense plasmas, with different polarizations and pre-plasma scale lengths. We show how signatures of the radiation pressure-dominated regime, such as layer compression and bunch formation, are only present with circular polarization. By passively shaping the density gradient of the plasma, we demonstrate an enhancement in peak energy up to tens of MeV and monoenergetic features. On the contrary linear polarization at the same intensity level causes the target to blow up, resulting in much lower energies and broader spectra. One limiting factor of Radiation Pressure Acceleration is the development of Rayleigh–Taylor like instabilities at the interface of the plasma and photon fluid. This results in the formation of bubbles in the spatial profile of laser-accelerated proton beams. These structures were previously evidenced both experimentally and theoretically. We have performed 2D simulations to characterize this bubble-like structure and report on the dependency on laser and target parameters.

Guiding and collimation of laser-accelerated proton beams using thin foils followed with a hollow plasma channel

It is proposed that guided and collimated proton acceleration by intense lasers can be achieved using an advanced target—a thin foil followed by a hollow plasma channel. For the advanced target, the laser-accelerated hot electrons can be confined in the hollow channel at the foil rear side, which leads to the formation of transversely localized, Gaussian-distributed sheath electric field and resultantly guiding of proton acceleration. Further, due to the hot electron flow along the channel wall, a strong focusing transverse electric field is induced, taking the place of the original defocusing one driven by hot electron pressure in the case of a purely thin foil target, which results in collimation of proton beams. Two-dimensional particle-in-cell simulations show that collimated proton beams with energy about 20 MeV and nearly half-reduced divergence of 26° are produced at laser intensities 1020 W/cm2 by using the advanced target.

Self-Consistent Simulation of Transport and Energy Deposition of Intense Laser-Accelerated Proton Beams in Solid-Density Matter.

The first self-consistent hybrid particle-in-cell (PIC) simulation of intense proton beam transport and energy deposition in solid-density matter is presented. Both the individual proton slowing-down and the collective beam-plasma interaction effects are taken into account with a new dynamic proton stopping power module that has been added to a hybrid PIC code. In this module, the target local stopping power can be updated at each time step based on its thermodynamic state. For intense proton beams, the reduction of target stopping power from the cold condition due to continuous proton heating eventually leads to broadening of the particle range and energy deposition far beyond the Bragg peak. For tightly focused beams, large magnetic field growth in collective interactions results in self-focusing of the beam and much stronger localized heating of the target.

Feasibility study of using laser-generated neutron beam for BNCT

The feasibility of using a laser-accelerated proton beam to produce a neutron source, via (p,n) reaction, for Boron Neutron Capture Therapy (BNCT) applications has been studied by MCNPX Monte Carlo code. After optimization of the target material and its thickness, a Beam Shaping Assembly (BSA) has been designed and optimized to provide appropriate neutron beam according to the recommended criteria by International Atomic Energy Agency. It was found that the considered laser-accelerated proton beam can provide epithermal neutron flux of ∼2×106n/cm2 shot. To achieve an appropriate epithermal neutron flux for BNCT treatment, the laser must operate at repetition rates of 1kHz, which is rather ambitious at this moment. But it can be used in some BNCT researches field such as biological research.

Simultaneous observation of angularly separated laser-driven proton beams accelerated via two different mechanisms

We present experimental data showing an angular separation of laser accelerated proton beams. Using flat plastic targets with thicknesses ranging from 200 nm to 1200 nm, a laser intensity of 6×1020 W cm−2 incident with an angle of 10°, we observe accelerated protons in target normal direction with cutoff energies around 30 MeV independent from the target thickness. For the best match of laser and target conditions, an additional proton signature is detected along the laser axis with a maximum energy of 65 MeV. These different beams can be attributed to two acceleration mechanisms acting simultaneously, i.e., target normal sheath acceleration and acceleration based on relativistic transparency, e.g., laser breakout afterburner, respectively.

Characteristics and parameter optimization of electron beam radiography

The electron beam produced by an ultra-short, high-intensity laser pulse is of properties of small source size, short duration, and quasi-monoenergetic energy, and will play a unique role in radiographic diagnostics. By analyzing the scattering processes of electrons in materials and performing Monte-Carlo simulations, electron radiography for probing target surface non-uniformities or material interfaces is studied for electron energy ranging from 100 keV to several hundreds of MeV, and the results are compared with those of proton radiography and X-ray radiography, respectively. Features and parameter optimization of electron radiography are obtained, and some applications are suggested. By taking advantage of inelastic scattering or energy loss of charged particles, target surface nonuniformities could be diagnosed by a charged-particle beam whose range is close to the target thickness. Such a diagnosis would produce a higher detection contrast than that by absorption-type X-ray radiography. For a proton beam, a target thickness variation as small as 0.1% could be detected due to a more evident Bragg peak of the stopping power near its range. Nevertheless, the energy of laser-accelerated proton beams being up to 100 MeV would limit the applications. For an electron beam, since a thickness variation of 0.3% could be detected, its energy over 1 GeV has been realized by laser acceleration, the electron radiography could be extended to diagnose thicker targets. When using an electron beam to radiograph a thin or a foil target, for example, of thickness on the order of 100 μm, a spatial resolution of 11 μm or better could be achieved due to the reduced elastic scattering and angular deflection. By taking advantage of elastic scattering of electrons, an electron beam whose range is much greater than the target thickness could be used to diagnose a target interface composed of different materials or even a multilayered capsule, and a higher contrast of the electron fluence modulation at interfaces would be realized than that by absorption-type X-ray radiography, which is caused by stronger scattering of electrons as the electron scattering cross section is several orders of magnitude greater than that of X-ray scattering such as the Thomson scattering. As a laser-produced electron beam is prone to have an ultrafast pulse duration of 100’s of femtoseconds or less, it is anticipated that the electron radiography will produce an ultrasfast temporal resolution. These results and conclusions would be helpful to the applications and parameter optimization of electron radiography.

Effective generation of the spread-out-Bragg peak from the laser accelerated proton beams using a carbon-proton mixed target.

Conventional laser accelerated proton beam has broad energy spectra. It is not suitable for clinical use directly, so it is necessary for employing energy selection system. However, in the conventional laser accelerated proton system, the intensity of the proton beams in the low energy regime is higher than that in the high energy regime. Thus, to generate spread-out-Bragg peak (SOBP), stronger weighting value to the higher energy proton beams is needed and weaker weighting value to the lower energy proton beams is needed, which results in the wide range of weighting values. The purpose of this research is to investigate a method for efficient generating of the SOBP with varying magnetic field in the energy selection system using a carbon-proton mixture target. Energy spectrum of the laser accelerated proton beams was acquired using Particle-In-Cell simulations. The Geant4 Monte Carlo simulation toolkit was implemented for energy selection, particle transportation, and dosimetric property measurement. The energy selection collimator hole size of the energy selection system was changed from 1 to 5mm in order to investigate the effect of hole size on the dosimetric properties for Bragg peak and SOBP. To generate SOBP, magnetic field in the energy selection system was changed during beam irradiation with each beam weighting factor. In this study, our results suggest that carbon-proton mixture target based laser accelerated proton beams can generate quasi-monoenergetic energy distribution and result in the efficient generation of SOBP. A further research is needed to optimize SOBP according to each range and modulated width using an optimized weighting algorithm.

The Energy Selection System for the laser-accelerated proton beams at ELI-Beamlines

ELI-Beamlines is one of the four pillars of the ELI (Extreme Light Infrastructure) pan-European project. It will be an ultrahigh-intensity, high repetition-rate, femtosecond laser facility whose main goals are the generation and applications of high-brightness X-ray sources and accelerated charged particles. In particular medical and multidisciplinary applications with laser-accelerated beams are treated by the ELIMED task force, a collaboration between different research institutes. A crucial goal for this network is represented by the design and the realization of a transport beamline able to provide ion beams with suitable characteristics in terms of energy spectrum and angular distribution in order to perform dosimetric tests and biological cell irradiations.A first prototype of transport beamline has been already designed and some magnetic elements are already under construction. In particular, an Energy Selector System (ESS) prototype has been already realized at LNS-INFN. This paper reports about the studies of the ESS properties as, for instance, energy spread and transmission efficiency, carried out using the GEANT4 Monte Carlo code.

Medical research and multidisciplinary applications with laser-accelerated beams: the ELIMED netwotk at ELI-Beamlines

Laser accelerated proton beams represent nowadays an attractive alternative to the conventional ones and they have been proposed in different research fields. In particular, the interest has been focused in the possibility of replacing conventional accelerating machines with laser-based accelerators in order to develop a new concept of hadrontherapy facilities, which could result more compact and less expensive. With this background the ELIMED (ELIMED: ELI-Beamlines MEDical applications) research project has been launched by LNS-INFN researchers (Laboratori Nazionali del Sud-Istituto Nazionale di Fisica Nucleare, Catania, IT) and ASCR-FZU researchers (Academy of Sciences of the Czech Republic-Fyzikální ústar, Prague, Cz), within the pan-European ELI-Beamlines facility framework. Its main purposes are the demonstration of future applications in hadrontherapy of optically accelerated protons and the realization of a laser-accelerated ion transport beamline for multidisciplinary applications. Several challenges, starting from laser-target interaction and beam transport development, up to dosimetric and radiobiological issues, need to be overcome in order to reach the final goals. The design and the realization of a preliminary beam handling and dosimetric system and of an advanced spectrometer for high energy (multi-MeV) laser-accelerated ion beams will be shortly presented in this work.

Improved spectral data unfolding for radiochromic film imaging spectroscopy of laser-accelerated proton beams.

An improved method to unfold the space-resolved proton energy distribution function of laser-accelerated proton beams using a layered, radiochromic film (RCF) detector stack has been developed. The method takes into account the reduced RCF response near the Bragg peak due to a high linear energy transfer (LET). This LET dependence of the active RCF layer has been measured, and published data have been re-interpreted to find a nonlinear saturation scaling of the RCF response with stopping power. Accounting for the LET effect increased the integrated particle yield by 25% after data unfolding. An iterative, analytical, space-resolved deconvolution of the RCF response functions from the measured dose was developed that does not rely on fitting. After the particle number unfold, three-dimensional interpolation is performed to determine the spatial proton beam distribution for proton energies in-between the RCF data points. Here, image morphing has been implemented as a novel interpolation method that takes into account the energy-dependent, changing beam topology.

Passive tailoring of laser-accelerated ion beam cut-off energy by using double foil assembly

A double foil assembly is shown to be effective in tailoring the maximum energy produced by a laser-accelerated proton beam. The measurements compare favorably with adiabatic expansion simulations, and particle-in-cell simulations. The arrangement proposed here offers for some applications a simple and passive way to utilize simultaneously highest irradiance lasers that have best laser-to-ion conversion efficiency while avoiding the production of undesired high-energy ions.

Weighing the neutrino

We investigate the potential of short-baseline experiments in order to measure the dispersion relation of the (muon) neutrino, with a prospect of eventually measuring the neutrino mass. As a byproduct, the experiment would help to constrain parameters of Lorentz-violating effects in the neutrino sector. The potential of a high-flux laser-accelerated proton beam (e.g., at the upcoming ELI facility), incident on a thick target composed of a light element to produce pions, with a subsequent decay to muons and muon-neutrinos, is discussed. We find a possibility for a muon neutrino mass measurement of unprecedented accuracy.

Development of an energy selector system for laser-driven proton beam applications

Nowadays, laser-driven proton beams generated by the interaction of high power lasers with solid targets represent a fascinating attraction in the field of the new acceleration techniques. These beams can be potentially accelerated up to hundreds of MeV and, therefore, they can represent a promising opportunity for medical applications. Laser-accelerated proton beams typically show high flux (up to 1011 particles per bunch), very short temporal profile (ps), broad energy spectra and poor reproducibility. In order to overcome these limitations, these beams have be controlled and transported by means of a proper beam handling system. Furthermore, suitable dosimetric diagnostic systems must be developed and tested. In the framework of the ELIMED project, we started to design a dedicated beam transport line and we have developed a first prototype of a beam line key-element: an Energy Selector System (ESS). It is based on permanent dipoles, capable to control and select in energy laser-accelerated proton beams. Monte Carlo simulations and some preliminary experimental tests have been already performed to characterize the device. A calibration of the ESS system with a conventional proton beam will be performed in September at the LNS in Catania. Moreover, an experimental campaign with laser-driven proton beam at the Centre for Plasma Physics, Queens University in Belfast is already scheduled and will be completed within 2014.