Generation Of Proton Beams Research Articles

Energetic electron and ion generation from interactions of intense laser pulses with laser machined conical targets

The generation of energetic electron and proton beams was studied from the interaction of high intensity laser pulses with pre-drilled conical targets. These conical targets are laser machined onto flat targets using 7–180 µJ pulses whose axis of propagation is identical to that of the main high intensity pulse. This method significantly relaxes requirements for alignment of conical targets in systematic experimental investigations and also reduces the cost of target fabrication. These experiments showed that conical targets increase the electron beam charge by up to 44 ± 18% compared with flat targets. We also found greater electron beam divergence for conical targets than for flat targets, which was due to escaping electrons from the surface of the cone wall into the surrounding solid target region. In addition, the experiments showed similar maximum proton energies for both targets since the larger electron beam divergence balances the increase in electron beam charge for conical targets. 2D particle in cell simulations were consistent with the experimental results. Simulations for conical target without preplasma showed higher energy gain for heavy ions due to ‘directed coulomb explosion’. This may be useful for medical applications or for ion beam fast ignition fusion.

超薄靶激光质子加速实验研究

The generation of proton beams from thin-foil targets on SILEX-Ⅰ is studied. It shows that prepulse has a profound effect on the maximum proton energy. The thinner the target is, the more sensitive it is to the prepulse. Under the laser intensity of 1018 to 3×1019 W/cm2, the maximum proton energy is 0.54 MeV with 190 nm CH target and 3.15 MeV with 3 μm Cu target (back surface plated with 4 μm CH) respectively. Besides, the effect of laser polarization on proton acceleration is also studied. The maximum proton energy accelerated by a circularly polarized laser pulse is a little lower than that by a P-polarized laser pulse with the same laser power density. The mechanism is consistent with target normal sheath acceleration.

Quasi-monoenergetic proton beam generation from a double-layer solid target using an intense circularly polarized laser

AbstractMonoenegetic ion beam generation from circularly polarized laser-pulse interaction with a double-layer target is considered. The front layer consists of heavy-ion plasma, and the rear layer is a small thin coating of light-ion plasma. Particle-in-cell simulation shows that the multi-dimensional effects in the ion radiation pressure acceleration are avoided and a highly monoenergetic light-ion beam can be produced. Our simulations reveal that the charge-mass ratio of heavy ions in the front layer and the thicknesses of both layers can strongly affect the proton energy spectra.

Modernization of the injector for a multibeam proton accelerator

Within the program for the development of high-current charged-particle accelerators with a high acceleration rate, an injector for a 19-beam proton accelerator with a multibeam ion injection mode is described. The injector contains an ion gun with a duoplasmatron-type H2 ion source and a multiaperture ion-optical system regulating the inclination of the ion-beam current tubes at the inputs of the corresponding channels of the accelerating structure. The cold-cathode ion source contains a system for transporting plasma from the cathode to its output aperture in magnetic fields of complex configurations, which allows stable pulsed generation of proton beams with a current amplitude of up to 3 A at an operating gas pressure in the discharge chamber of 0.2 Torr and a decrease in the flow of unionized gas emerging from the source to 2 cm3/h. It is shown that the developed ion source and the ion-optical system make it possible to increase the phase density of the beam current at the inputs of the accelerating-structure channels and to change the divergence angles.

Efficient Production of Proton Beam in Laser-Illuminated Tailored Microstructured Target

In a proton beam generation by a laser-foil interaction, significant improvement of energy-conversion efficiency from laser to proton beam is presented by particle simulations. When an intense short-pulse laser illuminates the thin-foil target, the foil electrons are accelerated around the target by the ponderomotive force. The hot electrons generate a strong electric field, which accelerates the foil protons, and the proton beam is generated. In this paper, a tailored multihole thin-foil target is proposed in order to increase the energy-conversion efficiency from laser to protons. The multiholes transpiercing the foil target enhance the laser-proton energy-conversion efficiency significantly. Particle-in-cell 2.5-dimensional simulations present that the total laser-proton energy-conversion efficiency becomes 9.3% for the tailored multihole target, although the energy-conversion efficiency is 1.5% for a plain thin-foil target. The maximum proton energy is 10.0 MeV for the multihole target and is 3.14 MeV for the plain target. The transpiercing multihole target serves a new method to increase the energy-conversion efficiency from laser to ions.

Spatial and temporal characteristics of X-ray emission from hot plasma driven by a relativistic femtosecond laser pulse

AbstractWe present the temporal and spatial characterization of X-ray sources (at ~1 keV) driven by a 200 TW, 30 fs, 800 nm laser pulse on SILEX-I laser facility at Research Center of Laser Fusion. For laser copper foil interaction with laser intensity between 6 × 1018 W/cm2and 3 × 1019 W/cm2, the X-ray images show cone-like jet structures. While the yield of X-rays is strongly dependent on the laser intensity, the plasma expansion length is weakly dependent on the laser intensity, and the open angle of the cone-like jet is not correlated to the laser intensity. The formation of the jet structure is attributed to the plasma transverse confine by the self-induced quasi-static magnetic field. An X-ray pedestal 4 ns preceding the main pulse was observed. The correlation between X-ray pedestal and collimated proton beam generation was found.

Different effects of a laser prepulse on the proton generation between plastic and metal targets irradiated by an ultraintense laser pulse

The effect of a laser prepulse on the generation of proton beams is compared between plastic and metal targets by irradiating a 30fs, 2.4×1018W∕cm2 Ti:sapphire laser pulse. Proton energies generated from both target materials increase as the pulse duration of the laser prepulse decreases. However, it was found that there are distinct differences with respect to target materials. In the case of aluminum targets, as target thickness decreases, proton energy gets higher, which is well described by an isothermal expansion model. However, in the case of Mylar® targets, no such dependence on target thickness could be observed, and the highest maximum proton energies are higher by factors of 1.5 to 3 than those from aluminum targets or those predicted by the isothermal expansion model. Such characteristics of the proton beams from Mylar® targets can be accounted for by a bulk acceleration model, or acceleration by a resistively induced electric field.

High-Quality Energetic Proton Beams from an Intense Laser-Plasma Interaction with a Micro-Structured Slab Target

High-quality energetic proton-beam generation from the interaction of a high-intensity short-pulse laser with an overdense plasma slab has been studied by using a two-dimensional, fully electromagnetic and relativistic particle-in-cell simulation. The collimation and the beam divergence of the accelerated protons are expected to strongly depend on the spatial coupling between the laser pulse and the target plasma. In this work, with a proper micro-modification of the target structure, improved beam quality, including the collimation, the forward directionality and the beam divergence, are clearly demonstrated. For a detailed analysis, the relativistic momentum distribution, the spatial density map and the angular distribution of the accelerated protons are considered.

Generation of intense proton beams from plastic targets irradiated by an ultraintense laser pulse

Proton beams generated from thin aluminum and Mylar foil targets that are irradiated by a 30fs Ti:sapphire laser pulse with an intensity of 2.2x10;{18}Wcm;{2} were investigated. Protons from the Mylar targets were observed to have an energy higher by a factor of 2 and were higher in number by an order of magnitude as compared with those generated from the aluminum targets. The maximum proton energy of 1.3+/-0.12MeV obtained from the Mylar target was found to be similar with previous observations that used laser pulses with different intensities. To address the anomalous behavior of the maximum proton energy for plastic targets, an acceleration model is proposed. In this model, the protons are accelerated by a resistively induced electric field in the front of the target, which can account for the experimental observations.

Ultraintense proton beams from laser-induced skin-layer ponderomotive acceleration

The results of studies of high-intensity proton beam generation from thin (1–3 μm) solid targets irradiated by 0.35 ps laser pulse of energy up to 15 J and intensity up to 2×1019 W/cm2 are reported. It is shown that the proton beams of terawatt power and intensity around 1018 W/cm2 at the source can be produced when the laser-target interaction conditions approach the skin-layer ponderomotive acceleration requirements. The proton beam parameters remarkably depend on the target structure and can be significantly increased with the use of a double-layer Au/PS target (plastic covered by 0.1–0.2 μm Au front layer).

Generation of High-Current Proton Beams With a Low Energy Spread by Phase-Stable Acceleration (PSA)

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The acceleration of protons in the interaction of a circularly polarized laser pulse with a thin foil is investigated. For circular-polarization laser pulses, the quasi-equilibrium for electrons is established due to the light pressure and the electrostatic field built up at the interacting front of the laser pulse. The protons located within the skin depth of the laser pulse can be synchronously accelerated and bunched like phase-stable acceleration in a conventional radio-frequency accelerator, so that a high-current proton beam with a low energy spread is generated. It has been proved by 1-D particle-in-cell simulations. </para>

SU‐GG‐T‐525: Improved Proton Yield From a Laser‐Proton Accelerator

Purpose: To improve the energy output of the laser proton accelerator. To investigate how target position and thickness influence the final proton energy. To identify which set of laser parameters are most crucial to obtaining higher proton energies. Method and Materials: The experimental set‐up for generation of laser‐accelerated protons has been redesigned. The laser system is a chain of amplifiers capable of delivering up to 25TW in a 40fs pulse. The high‐power laser pulses are delivered to a thin (7μm – 20μm) Al or 7.5μm polyamide target in a shielded vacuum chamber. When the laser beam is focused by an off‐axis parabolic mirror of focal length of 15 cm, the light intensity on the target exceeds 2×1019 W/cm2. All experiments are conducted at oblique (45°) incidence with p‐polarized light. The energy of the generated protons is sampled by a range filter and the transmitted beam is registered on a CR39 track detector. Results: The proton spectra from targets with varying thickness and composition have been recorded. The maximum proton energy in excess of 2MeV was obtained for a 15μm Al target situated 50μm behind the focal plane of the laser beam. Comparison study in 7μm Al and 7.5μm polyamide targets has been conducted, resulting in slightly higher proton flux from the aluminum target and no measurable energy difference. Applying a simplified heat‐transfer model of target destruction we estimated that the laser pre‐pulse is at a level sufficient to destroy Al target of thickness below 14.5μm. Conclusion: The acceleration of protons using 25TW ultra‐short laser pulses to energies in excess of 2MeV has been experimentally demonstrated. The influence of various interaction parameters on the final proton energy has been evaluated. These experimental results are a new step toward the generation of therapeutic proton beams with controlled characteristics using lasers.

Phase space modulation of laser produced protons with a double-foil target generation of quasimonoenergetic proton beams

It is shown by one-dimensional particle-in-cell simulation that quasimonoenergetic protons can be generated from a double-solid-foil target irradiated by two ultrashort intense laser pulses. In this approach, one uses the first laser pulse irradiating on the first foil to generate the energetic protons, and one uses the second laser pulse irradiating on the second foil to generate an electrostatic field, which modulates the energy spectrum of protons from the first foil. Quasimonoenergetic protons with tunable energy peaks can be obtained by controlling the time delay and intensity of the second pulse as well as the distance between the two foils. It is also found that a preplasma on the second foil increases the peak energy. The dependence of the proton beam quality on the laser and target parameters is also discussed.

Ultrahigh-current proton beams from short-pulse laser-solid interactions

The results of studies of high-current proton beam generation from thin (1–3μm) solid targets irradiated by 0.35-ps laser pulse of intensity up to 2×1019 W/cm2 are reported. It is shown that the proton beams of multi-MA currents and multi-TA/cm2 current densities at the source can be produced when the laser-target interaction conditions approach the skin-layer ponderomotive acceleration requirements. The current and energy spectrum of protons remarkably depend on the target structure. In particular, using a double-layer Au/PS target (plastic covered by 0.1 − 0.2μm Au front layer) results in two-fold higher proton currents and higher proton energies than in the case of a plastic target.

Collimated ion beam by a tailored target illuminated by an intense short pulse laser

In a laser-foil interaction for an ion beam generation, suppression of a transverse proton beam divergence is realized by a tailored thin foil target, which has holes at the rear side of the target. The electron and proton clouds are limited in transverse by the plasma at the protuberant part. In this paper, we investigate the robustness of the hole target for the high quality proton beam generation in the laser-plasma interaction. The transverse edge effects of the ion cloud and the electron cloud deform the potential shape, which defines the proton extraction direction. Consequently the proton beam divergence is induced by the deformed potential shape. The protuberant part of the hole target shields the edge fields of the ion and electron clouds. The present work demonstrate that the hole target is robust against the additional contaminated proton source layers. The multiple-hole target is also robust against the laser alignment error and the target positioning error. The multiple-hole target may serve a robust target to produce a collimated proton beam in realistic experiments and uses.

TH‐C‐M100F‐02: Beam of Laser‐Accelerated Protons: Generation and Characterization

Purpose: To experimentally demonstrate the generation of proton beams by a novel technique based on the interaction of high‐power laser pulses with thin solid‐state targets. To fully characterize the beam of particles emitted from the laser accelerator and to compare its properties with the theoretically predicted divergence and energy spectrum. Method and Materials: We have built an experimental set‐up for generation of laser‐accelerated protons. The high‐power laser pulses are produced by a chain of lasers and amplifiers and are delivered to the target in a shielded vacuum chamber. The sharply focused laser beam creates light intensity in excess of 1×1018 W/cm2. The cross‐section of the proton beam is directly imaged using a CR39 nuclear track detector situated at a fixed distance behind the target. The energy spectrum on the beam axis was recorded by a proton spectrometer (Thomson parabola) that was assembled and calibrated in our lab. An alternative method for energy evaluation utilizing a set of calibrated mylar range‐filters was used as well. Results: The angular distribution of the proton beam was determined from the CR39 images. Full divergence angle of 40° was measured, confirming the theoretical predictions. Our preliminary measurements were conducted at lower laser power (7 TW). Therefore, the energy spectrum of the proton beam revealed thermal (Maxwellian) distribution with cut‐off energy slightly less than 1 MeV. Conclusion: We demonstrated the acceleration of protons using powerful laser pulses and fully characterized the generated proton beam. Considerable improvements associated with increased laser intensity and novel target design are discussed as well. The experimental results presented here are the first step toward the generation of therapeutic proton beams with controlled characteristics using lasers.

Robustness of a tailored hole target in laser-produced collimated proton beam generation

A robustness of a thin-foil tailored hole target is demonstrated by particle simulations in laser-produced proton generation. The hole target has a hole at the target rear surface. When an intense short pulse laser illuminates the thin-foil target with the hole, transverse edge fields of an accelerated electron cloud and an ion cloud are shielded by a protuberant part of the hole so that the proton beam divergence is suppressed [Sonobe et al., Phys. Plasmas 12, 073104 (2005)]. This paper presents the robustness of the hole target against laser parameter changes in a laser spot size and in a laser pulse length against a contaminated proton source layer and against a laser alignment error. The 2.5-dimensional particle-in-cell simulations also show that a multiple-hole target is robust against a laser alignment error and a target positioning error. The multihole target may serve as a robust target for practical uses to produce a collimated proton beam.

Extension of atomic configuration sets of the Non-LTE model in the application to the Kα diagnostics of hot dense matter

High intensity short-pulse laser experiments are used for various applications from fast ignitor concept to proton beam generation. These systems produce substantial fluxes of energetic electrons, and the production of Kα spectrum by these energetic electrons has become a key diagnostics of interaction of short-pulse laser and solid-density matter. In general, spectral modeling is required to derive the thermal electron temperature from measured Kα spectrum and it is essential to use a Non-LTE (local thermodynamic equilibrium) model for this purpose. In this paper, we investigate the assumptions necessary for the application of the Non-LTE models and show that an extensive set of configurations is required to provide a valid Kα diagnosis of hot dense matter.

Measurement of the Electron Density Produced by the Prepulse in an Experiment of High Energy Proton Beam Generation

The characteristics of the preplasma, such as the electron density and its profile, were investigated from a measurement of the phase shift due to the preplasma in an experiment on high energy proton beam generation. The electron density and its profile were calculated from the measured phase shifts, and their dependences on the prepulse intensity and the time delay were investigated. Although the size of the electron density depended on the prepulse intensity, the maximum electron density ranged from 1.5 ◊ 10 19 to 2.1 ◊ 10 19 cm 3 , irrespective of the prepulse intensity and the time delay in the picosecond range. The analysis showed that a preplasma having an electron density of 10 19 cm 3 existed on a target before the main laser pulse arrived at the target for the

New epoch in the charged particle acceleration by relativistically intense laser radiation

The development of the ultraintense laser continues to open up new fields of physics. The laser accelerator development is now entering a new matured stage at which it becomes possible to manipulate in a controllable way the parameters of accelerated charged particle beams. In the electron acceleration the particle injection by breaking wake waves left by the laser pulse in underdense plasmas results in the quasi-monoenergetic beam production. When the ions are accelerated during the laser–matter interaction the tailored multi-layer foil targets provide conditions for the high quality proton beam generation.