Laser-driven Proton Beams Research Articles

Laser-driven acceleration of a 94.8 MeV uniform proton beam enhanced by a thin axial absorber rod

Laser-based proton accelerators offer promising advantages for many sensitive applications due to their compact size. However, achieving uniform beams with a narrow energy spread remains a challenge. Here, a beamline simulation is performed using the racein and codes to optimize the spectral and spatial characteristics of a laser-driven proton beam. This beamline, comprised of four magnetic quadrupoles and equipped with a thin axial absorber rod in conjunction with an energy selection aperture for narrowing the energy spread, a carbon scatterer foil for beam spot smoothing, and an angular selection aperture for beam collimation, effectively transports a selected proton beam energy within the range of 50–250 MeV. In this work, laser-accelerated protons with a wide energy spread were transported through the proposed beamline, which was optimized for 109 MeV protons. The protons emerged well-collimated with a significantly narrowed energy spread of 94.8±3.9 MeV (a reduction from the intended 109 MeV due to passage through the scatterer) and a homogenized, 11 mm diameter beam spot while maintaining a transmission efficiency above 2.2%. Published by the American Physical Society 2024

Laser-driven high-energy proton beams from cascaded acceleration regimes

Laser-driven ion accelerators can deliver high-energy, high-peak current beams and are thus attracting attention as a compact alternative to conventional accelerators. However, achieving sufficiently high energy levels suitable for applications such as radiation therapy remains a challenge for laser-driven ion accelerators. Here we generate proton beams with a spectrally separated high-energy component of up to 150 MeV by irradiating solid-density plastic foil targets with ultrashort laser pulses from a repetitive petawatt laser. The preceding laser light heats the target, leading to the onset of relativistically induced transparency upon main pulse arrival. The laser peak then penetrates the initially opaque target and triggers proton acceleration through a cascade of different mechanisms, as revealed by three-dimensional particle-in-cell simulations. The transparency of the target can be used to identify the high-performance domain, making it a suitable feedback parameter for automated laser and target optimization to enhance stability of plasma accelerators in the future.

Emittance growth analysis of laser-driven broad energy spectral proton beams

Emittance growth analysis of laser-driven broad energy spectral proton beams

Deep learning approaches for modeling laser-driven proton beams via phase-stable acceleration

Deep learning (DL) has recently become a powerful tool for optimizing parameters and predicting phenomena to boost laser-driven ion acceleration. We developed a neural network surrogate model using an ensemble of 355 one-dimensional particle-in-cell simulations to validate the theory of phase-stable acceleration (PSA) driven by a circularly polarized laser driver. Our DL predictions confirm the PSA theory and reveal a discrepancy in the required target density for stable ion acceleration at larger target thicknesses. We discuss the physical reasons behind this density underestimation based on our DL insights.

Proof-of-Principle of Absolute Dosimetry Using an Absorbed Dose Portable Calorimeter with Laser-Driven Proton Beams

Charged particle beams driven to ultra-high dose rates (UHDRs) have been shown to offer potential benefits for future clinical applications, particularly in the reduction of normal-tissue toxicity. Studies of the so-called FLASH effect have shown promise, generating huge interest in high dose rate radiation studies. With laser-driven proton beams, where the duration of the proton burst delivered to a sample can be as short as hundreds of picoseconds, the instantaneous dose rates are several orders of magnitude higher than those used for conventional radiotherapy. The dosimetry of these beam modalities is not trivial, with conventional active detectors, such as ionisation chambers, experiencing saturation effects making them unusable at the extremely high dose rates. Calorimeters, measuring the radiation-induced temperature rise in an absorber, offer an ideal candidate for the dosimetry of UHDR beams. However, their application in the measurement of laser-driven UHDR beams has so far not been trialled, and their effective suitability to work with the quasi-instantaneous and inhomogeneous dose deposition patterns and the harsh environment of a laser-plasma experiment has not been tested. The measurement of the absorbed dose of laser-driven proton beams was conducted in a first-of-its-kind investigation, employing the VULCAN-PW laser system of the Central Laser Facility (CLF) at the Rutherford Appleton Laboratory (RAL), using a small-body portable graphite calorimeter (SPGC) developed at the National Physical Laboratory (NPL) and radiochromic films. A small number of shots were recorded, with the corresponding absorbed dose measurements resulting from the induced temperature rise. The effect of the electromagnetic pulse (EMP) generated during laser–target interaction was assessed on the system, showing no significant effects on the derived signal-to-noise ratio. These proof-of-principle tests highlight the ability of calorimetry techniques to measure the absorbed dose for laser-driven proton beams.

Stable high repetition-rate laser-driven proton beam production for multidisciplinary applications on the advanced laser light source ion beamline.

Laser-driven proton accelerators are relevant candidates for many applications such as material science or medicine. Today, there are multi-hundred-TW table-top laser systems that can generate relativistic peak intensities >1018 W/cm2 and routinely reach proton energies in the MeV range. However, for most desired applications, there is still a need to optimize the quality and stability of the laser-generated proton beam. In this work, we developed a 0.625Hz high repetition-rate setup in which a laser with 2.5% RMS energy stability is irradiating a solid target with an intensity of 1019 to 1020 W/cm2 to explore proton energy and yield variations, both with high shot statistics (up to about 400 laser shots) and using different interaction targets. Investigating the above-mentioned parameters is important for applications that rely on specific parts of the proton spectrum or a high ion flux produced over quick multi-shot irradiation. We demonstrate that the use of a stable "multi-shot mode" allows improving applications, e.g., in the detection of trace elements using laser-driven particle-induced x-ray emission.

Cascaded solenoid acceleration of vortex laser-driven collimated proton beam

Efficient cascaded proton acceleration driven by an intense Laguerre–Gaussian (LG) laser is realized in combined three-dimensional particle-in-cell simulations and CST STUDIO SUITE (CST) simulations. CST simulations show that there is no divergent force component in the transverse direction in the coil center. Therefore, the collimated proton beam driven by the LG laser in the first stage benefits from the uniform beam acceleration in the second stage. By contrast, the proton beam with larger divergence disperses to the outside of the coil because of the divergent force near the coil wire in the Gaussian laser case. Finally, a quasi-monoenergetic proton beam with a higher flux is generated by the LG laser, which is much better than the Gaussian laser case. The obtained proton beam can potentially be used in some special applications, such as proton radiography, fast ignition of fusion targets, biomedical applications, and production of warm dense matter.

Proton Bragg curve and energy reconstruction using an online scintillator stack detector.

Real-time measurement and characterization of laser-driven proton beams have become crucial with the advent of high-repetition-rate laser acceleration. Common passive diagnostics such as radiochromic film (RCF) are not suitable for real-time operation due to time-consuming post-processing; therefore, a novel approach is needed. Various scintillator-based detectors have recently gained interest as real-time substitutes to RCF-thanks to their fast response for a wide range of dose deposition rates. This work introduces a compact, scalable, and cost-effective scintillator-based device for proton beam measurements in real-time suitable for the laser-plasma environment. An advanced signal processing technique was implemented based on detailed Monte Carlo simulations, enabling an accurate unfolding of the proton energy and the depth-dose deposition curve. The quenching effect was accounted for based on Birks' law with the help of the Monte Carlo simulations. The detector was tested in a proof-of-principle experiment at a conventional cyclotron accelerating protons up to 35MeV of energy. The signal comparison with a standard RCF stack was also performed during the test of the device, showing an excellent agreement between the two diagnostics. Such devices would be suitable for both conventional and laser-driven proton beam characterization.

Optically tunable proton acceleration with a controlled prepulse in ultrashort intense laser double-foil target interaction

Competition and transition of the dominated mechanisms for proton acceleration were investigated in experiments by optically tuning the preplasma density profile using an additional femtosecond pre-ablation laser beam. Two groups of proton beams with angular separation were measured along the laser propagation axis and target normal direction from a vacuum-gapped double-foil target. A transition of proton acceleration from a target normal sheath acceleration regime to relativistically induced transparency (RIT) domination was observed when increasing the prepulse intensity. Two-dimensional particle-in-cell simulations qualitatively verify the experimental observations that a proton component along the laser axis is mainly generated by the RIT induced breakout afterburner from the tailored pre-expanded ultrathin front-layer foil with spatial-intensity distribution improvement by the second-layer foil. Our method can be popularized in manipulating the laser-driven proton acceleration and beam spatial quality for wide applications.

Energetic laser-driven proton beams from near-critical-density double-layer targets under moderate relativistic intensities

Double-layer targets composed of near-critical-density carbon nanotube foams (CNFs) and solid foils have shown their advantages in laser-driven ion acceleration under high relativistic intensity. Here, we report the experimental and numerical results on the laser-accelerated proton beams from such targets under moderate relativistic intensities I∼5×1019W/cm2. 40-TW femtosecond laser pulses were used to irradiate CNF-based double-layer targets. Compared to single-layer targets, significant enhancements on the cutoff energy and numbers of ions were observed. It was found that the CNF layer also leads to a larger divergence angle and a more homogeneous spatial distribution profile of the proton beam. Particle-in-cell simulations reveal the reason for the enhanced proton acceleration. It is found that the lateral electric field and the strong magnetic field built by the directly accelerated electrons from the CNF layer contribute to the enlarged divergence angle.

Automated control and optimization of laser-driven ion acceleration

Abstract The interaction of relativistically intense lasers with opaque targets represents a highly non-linear, multi-dimensional parameter space. This limits the utility of sequential 1D scanning of experimental parameters for the optimization of secondary radiation, although to-date this has been the accepted methodology due to low data acquisition rates. High repetition-rate (HRR) lasers augmented by machine learning present a valuable opportunity for efficient source optimization. Here, an automated, HRR-compatible system produced high-fidelity parameter scans, revealing the influence of laser intensity on target pre-heating and proton generation. A closed-loop Bayesian optimization of maximum proton energy, through control of the laser wavefront and target position, produced proton beams with equivalent maximum energy to manually optimized laser pulses but using only 60% of the laser energy. This demonstration of automated optimization of laser-driven proton beams is a crucial step towards deeper physical insight and the construction of future radiation sources.

Time-of-flight spectroscopy for laser-driven proton beam monitoring

Application experiments with laser plasma-based accelerators (LPA) for protons have to cope with the inherent fluctuations of the proton source. This creates a demand for non-destructive and online spectral characterization of the proton pulses, which are for application experiments mostly spectrally filtered and transported by a beamline. Here, we present a scintillator-based time-of-flight (ToF) beam monitoring system (BMS) for the recording of single-pulse proton energy spectra. The setup’s capabilities are showcased by characterizing the spectral stability for the transport of LPA protons for two beamline application cases. For the two beamline settings monitored, data of 122 and 144 proton pulses collected over multiple days were evaluated, respectively. A relative energy uncertainty of 5.5% (1upsigma) is reached for the ToF BMS, allowing for a Monte-Carlo based prediction of depth dose distributions, also used for the calibration of the device. Finally, online spectral monitoring combined with the prediction of the corresponding depth dose distribution in the irradiated samples is demonstrated to enhance applicability of plasma sources in dose-critical scenarios.

Transmission and homogenization of laser-driven proton beams with broadband spectra

<p indent="0mm">Over the past few decades, laser accelerators made continuous progress. Thanks to the ultra-high electric field gradient (100 GV/m) generated by the interaction of laser and plasma, protons can be accelerated to MeV energy at a micron scale, being expected to be a new generation of widely used compact accelerators. The laser-driven proton beam has the characteristics of μm-level size (point source), ampere-level peak current, broadband energy spectrum, and large divergence angle. Irradiation applications need a uniform dose distribution, requiring the transformation from a point source to a large area of uniformly distributed particles. Increase of utilization efficiency requires that beams with energy spread as large as possible can be transmitted, while the chromatic aberrations pose a challenge to the homogenization of the beams, including the homogenization of the beams with the same energy and different initial divergence angles, and the homogenization of the beams with different energies. The weak focusing of the constant gradient magnetic field can focus in the horizontal and vertical directions at the same time, and analyze the energy in the horizontal direction. The integration of focusing and energy analysis can achieve achromatic transmission, or significantly reduce the influence of chromatic aberrations. This paper studies the transmission characteristics of proton beams in weak-focusing magnetic fields. The homogenized transformation for protons with the same energy in the horizontal direction from a point to a large area by point-to-parallel imaging is demonstrated. Point-to-parallel imaging is not a necessary condition for homogenization; transformation without point-to-parallel imaging in the vertical direction also obtains good homogeneity. The conditions for positional achromaticity in the horizontal direction are explored, and the transmission and homogenization of proton beams with 20% energy spread can be achieved with appropriate design. In positional achromatic transmission, the chromatic aberrations still have influence, causing the proton beam with large energy spread to deviate from the center of the beamline in the horizontal direction. In order to reduce the influence of chromatic aberrations, a special steering magnet is designed after the weak-focusing magnet to correct the divergence angle in the horizontal direction. The relationship between the correction amount of divergence angle and the position in the horizontal direction is obtained through parameter scanning, which can be well fitted by a 4 order polynomial. After correcting the divergence angle, the proton beam with large energy spread returns to the center of the beamline at the beamline exit. With a slit and energy spectrum shaping, proton beams with 80% energy spread can be obtained for irradiation with better uniformity. When the deflection radius is designed to be <sc>0.65 m,</sc> the weak-focusing beamline can transmit proton beams with <sc>1–20 MeV</sc> energy, 80% energy spread, and an initial divergence angle of ±50 mrad. After changing the magnetic field direction, electron beams with <sc>1–200 MeV</sc> energy, 40% energy spread can be transmitted. The transmission and homogenization of the proton beam with 80% energy spread greatly improves the utilization efficiency. Higher energy particle beams can be delivered using superconducting or pulsed magnet technology. The study found that the influence of chromatic aberrations is much larger in the beam transmission with a quadrupole triplet lens (strong focusing), and as energy cannot be accurately analyzed, it is difficult to improve. In comparison, the weak-focusing magnetic fields have significant advantages for beam homogenization.

Assessment of the reliability of deconvolution procedures for RCF spectroscopy of laser-driven ion beams

Laser-driven ion beams are defined by a number of unique features, including a large spread in energy. A stack configuration of radiochromic films (RCF) can be utilized to characterize such beams through measurements of their energy spectra. A spectroscopic procedure is reported that allows the proton energy density within each active layer of a radiochromic film (RCF) stack to be retrieved. This is based upon on a deconvolution algorithm developed through Geant4 Monte Carlo simulations to correct the contributions of energy depositions within a given film layer. Through Monte Carlo calculations, the spectrum retrieved from a simulated film stack can be retrieved and compared with a known energy spectrum, providing an examination of the efficacy of this tool. Application of the developed deconvolution procedure thus offers the potential to correctly reconstruct the incident energy spectrum of a laser-driven proton and ion beam from a stack of irradiated RCF.

Beamline design with weak-focusing magnetic field for applications of laser-driven proton beams

&lt;sec&gt;With the development of high-power laser technology, laser plasma acceleration has developed rapidly due to its excellent acceleration structure. Nearly one-hundred-MeV proton beams and several GeV electron outputs are obtained. The laser-driven proton beams have excellent quality of μm-scale sizes and ps-scale pulse lengths. Owing to the existence of the accelerating laser field, direct application is difficult, so the proton beams need to be transmitted to the application terminal through the beamline. However, the wide energy spectrum and large divergence angle bring difficulties in transmitting the beam. The weak focusing in the constant gradient magnetic field is neglected in the transmission of laser-driven particle beams because of the relatively weak focusing force. But weak focusing has special advantages: simultaneous focusing in the horizontal direction and the vertical direction, energy analysis in the horizontal direction, focusing force in the horizontal and vertical direction distributed by the field index &lt;i&gt;n&lt;/i&gt;, and smaller influence of chromatic aberration effect.&lt;/sec&gt;&lt;sec&gt;In this paper, we propose the beam transmission with weak-focusing magnet. The requirements for the focusing of proton beams with the same energy and different divergence angles in the &lt;i&gt;X&lt;/i&gt; direction and &lt;i&gt;Y&lt;/i&gt; direction in the weak-focusing magnetic field are explored by studying the linear beam dynamics of the beams. Then the conditions of precise energy analysis for particle beams with large divergence angle can be determined. For beams with 2% energy spread, the lengths of the drift space before and after the weak-focusing magnet and deflection radius are scanned to find out the minimum beam size and the shortest pulse length after transmission. It is found that a certain combination of drift space and deflection radius can minimize the beam size or the pulse length. Focusing and energy selection can be achieved while compressing the pulse length and effectively reducing the size of the beamline, which has significant advantages. When the deflection radius is 0.65 m, the proton beam with 20 MeV energy, 2% energy spread, and an initial divergence angle of ±50 mrad has the root-mean-square size of 108 μm in both the &lt;i&gt;X&lt;/i&gt; direction and the &lt;i&gt;Y&lt;/i&gt; direction, and a pulse length of 154 ps at the application terminal.&lt;/sec&gt;&lt;sec&gt;Comparing with common beam transmission elements such as quadrupole lenses and deflection magnets, the laser-accelerated ion beam benefits from the integration of focusing and energy analysis of weak-focusing magnetic fields (focusing and energy analysis exist at the same time and continuously change with deflection angle), as well as the horizontal and vertical focusing forces can be distributed by the magnetic field index &lt;i&gt;n&lt;/i&gt; (the larger the &lt;i&gt;n&lt;/i&gt;, the stronger the focusing force in the vertical direction is and the weaker the focusing force in the horizontal direction). When the proton beam is transmitted in a weak-focusing magnetic field, the advantages of the focusing element and the energy selection element are combined, so the influence of the chromatic aberration effect can be reduced, the pulse length can be compressed, and the beamline size can be effectively reduced.&lt;/sec&gt;

Manipulating the Laser-Driven Proton Bunch with Plasma Wakefield

With the advantages of short duration and extreme brightness, laser proton accelerators (LPAs) show great potential in many fields for industrial, medical, and research applications. However, the quality of current laser-driven proton beams, such as the broad energy spread and large divergence angle, is still a challenge. We use numerical simulations to study the propagation of such proton bunches in the plasma. Results show the bunch will excite the wakefield and modulate itself. Although a small number of particles at the head of the bunch cannot be manipulated by the wakefield, the total energy spread is reduced. Moreover, while reducing the longitudinal energy spread, the wakefield will also pinch the beam in the transverse direction. The space charge effect of the bunch is completely offset by the wakefield, and the transverse momentum of the bunch decreases as the bunch transports in the plasma. For laser-driven ion beams, our study provides a novel idea about the optimization of these beams.

Numerical investigation of spallation neutrons generated from petawatt-scale laser-driven proton beams

Laser-driven neutron sources could offer a promising alternative to those based on conventional accelerator technologies in delivering compact beams of high brightness and short duration. We examine this through particle-in-cell and Monte Carlo simulations that model, respectively, the laser acceleration of protons from thin-foil targets and their subsequent conversion into neutrons in secondary lead targets. Laser parameters relevant to the 0.5 PW LMJ-PETAL and 0.6–6 PW Apollon systems are considered. Owing to its high intensity, the 20-fs-duration 0.6 PW Apollon laser is expected to accelerate protons up to above 100 MeV, thereby unlocking efficient neutron generation via spallation reactions. As a result, despite a 30-fold lower pulse energy than the LMJ-PETAL laser, the 0.6 PW Apollon laser should perform comparably well both in terms of neutron yield and flux. Notably, we predict that very compact neutron pulses, of ∼10 ps duration and ∼100 μm spot size, can be released provided the lead convertor target is thin enough (∼100 μm). These sources are characterized by extreme fluxes, of the order of 1023 n cm−2 s−1, and even ten times higher when using the 6 PW Apollon laser. Such values surpass those currently achievable at large-scale accelerator-based neutron sources (∼1016 n cm−2 s−1), or reported from previous laser experiments using low-Z converters (∼1018 n cm−2 s−1). By showing that such laser systems can produce neutron pulses significantly brighter than existing sources, our findings open a path toward attractive novel applications, such as flash neutron radiography and laboratory studies of heavy-ion nucleosynthesis.

Proton Beam Generated in PW Laser Interaction With Nano-Structure Array for Proton Therapy

In comparison with large and expensive conventional linear and circular accelerator, miniaturized laser-driven proton accelerator provides the potential to reduce the overall costs. This could allow a widespread use of the superior properties of protons and ions in radiation therapy. However, the key to success is to improve the particle energy which is not high enough to meet the requirement for the treatment. With the development of high-repetition-rate petawatt class laser technology matures gradually, different acceleration mechanisms have been able to raise the energy of protons to close to 100MeV.To confirm the feasibility of proton beam generated in petawatt-laser irradiating nano-array target, three-dimensional particle-in-cell (3D-PIC) simulations were performed with the QED-PIC code EPOCH. The simulation box has a size of 30 μm(x) × 20 μm (y) × 20 μm (z), which is sampled by cells of 1500 × 400 × 400 with 125 pseudo-electrons, eight pseudo-carbons, and four protons in each cell. The Gaussian laser pulse propagates along the x-direction with y-direction polarization, a wavelength λ0 of 1μm, a peak power of 50 PW, and a duration of 30 fs in full width at half maximum (FWHM). With an initial focal spot radius σ = 3μm. In order to reduce the computational requirements. The array wires have an initial density of ne = 300nc (where nc = 1.1 × 1021 cm-3 is the critical plasma density) and are attached to a 4-μm-thick CH foil. In these simulations, periodic boundary conditions were employed for the laser field in the transverse directions and absorbing boundary conditions for the particles.Three-dimensional particle-in-cell simulation show that the laser-driven proton beam keep quite different characteristics compared with other accelerators proton beam, such as ultra-short beam duration (ns), high strength (107 / cm2 / pulse), large divergence angle (2°) and poly real-energetic spectrum. Meanwhile, we show that under optimal interaction conditions protons can be accelerated up to relativistic energies of 300 MeV by a petawatt laser field. The proton acceleration is due to the dragging Coulomb force arising from charge separation induced by the ponderomotive pressure ∼light pressure! of high-intensity laser.We investigate the impact of nano-structure array on the proton spectrum for different laser-plasma conditions. Our simulated data show that the nanostructures lead to a significant enhancement of absorption over the entire range of laser plasma conditions investigated. At conditions that do not allow for efficient laser absorption by plane targets, nano-structure array is found to significantly enhance the proton cut-off energy and conversion efficiency.S. Wu: None. Z. Wang: None. X. Sun: None. W. Wang: None. F. Xiao: None. L. Zhao: None.

Carbon nanotubes embedded in a polyimide foil for proton acceleration with a sub-ns laser

A series of thin films made of aligned carbon nanotubes (CNTs) embedded in a polyimide substrate was designed, fabricated and used for the first time to accelerate protons and C ions by interaction with a sub-nanosecond, high power laser beam (600 J energy and 300 ps pulse width) with peak intensity of about 3 × 1016 W/cm2 on target. Each target was 5 µm thick, and the composite material contained CNTs aligned in different directions in the substrate. The results obtained from the analysis of a Thomson Parabola spectrometer, and of the spots imprinted by ions on a series of PM355 nuclear track detectors, indicate high energies (up to 3 MeV for protons and 9 MeV for C ions) and a marked influence of the CNTs’ orientation on the produced proton beam current. An increase of the proton fluxes, more than two orders of magnitude, was recorded with the targets containing CNTs aligned parallel to the target normal, in comparison to the other targets. The presented experimental results demonstrate that the laser-driven proton beam flux can be increased using ad hoc designed targets (with embedded and aligned nanotubes) and sub-nanosecond laser pulses with moderate intensities and poor temporal contrast, thus in an acceleration regime very far from those typically investigated experimentally using relativistic intensities (>5 × 1018 W/cm2) and short laser pulses (10 fs to 10 ps).

Improving laser-accelerated proton beam divergence by electric and magnetic fields induced in flat channel-like targets

Improving parameters of laser-driven proton and ion beams becomes one of the most important goals in the field of laser acceleration in order to fulfill requirements of foreseen applications. This work presents parametric 2D and 3D particle-in-cell simulations of various target designs in order to reduce proton beam divergence without significant drop in maximum energies or in proton number. The optimal target design proved to be a channel-like target which produces not only a long-lasting focusing transverse electric field in contrast to a flat foil, but also a magnetic quadrupole with strong octupole component inside the guiding channel. A combination of both electric and magnetic features results in a strong proton beam divergence reduction, accompanied by a higher uniformity of the beam, which is studied as a function of proton energy.