Laser Ion Acceleration
Theoretical and Computer Simulation Study of High Energy Ion Acceleration with a Shot Intense Laser Pulses
Tech Area / Field
- PHY-PLS/Plasma Physics/Physics
8 Project completed
Senior Project Manager
Malakhov Yu I
VNIITF, Russia, Chelyabinsk reg., Snezhinsk
- FIAN Lebedev / Quantum Radiophysics Department of the Lebedev Physical Institute of Russian Academy of Sciences, Russia, Moscow
- University of Michigan / Center for Ultrafast Optical Science, USA, MI, Ann Arbor\nUniversity of Alberta, Canada, AB, Edmonton
Project summaryDevelopments in laser technology have enabled high power lasers to produce multi-terrawatt picosecond and femtosecond pulses, which allow examining the fundamental physics of high intensity (I > 1019 W/cm2) laser radiation interaction with matter and properties of laser-produced plasma. Recently an interest has developed in the use of intense lasers with ultra-short pulse for ion acceleration up to multi-MeV energies. Experiments held in the laboratories all around the World (in the USA, Great Britain, France, Japan) have proven the possibility of transformation of the laser energy to collimated ultra-fast ion bunches with high efficiency (up to 10%) when focusing ultra-short laser pulses of intensity 1019–1020 W/cm2 on solid or gaseous targets. Among potential applications of the laser ion acceleration are: the development of a compact proton source for radiography and imaging, medicine isotope production, experiments in nuclear physics at extremely short time scales, new methods in nuclear medicine.
The commonly recognized effect responsible for ion acceleration is the charge separation in plasma due to high-energy electrons motion driven by the laser inside the target. The electrons can be accelerated up to relativistic energies due to several processes such as stimulated forward Raman scattering, resonant absorption, laser wakefield, ponderomotive acceleration by standing or propagating laser pulse, “vacuum heating” due to Lorentz force or Brunel effect, self modulated laser wakefield via Raman backscatter, and betatron resonance provided by laser pulse channeling. Because of such numerous mechanisms of electric field generation the different regimes of ion acceleration are possible.
Our basic interest in the project is to investigate the mechanisms of ion acceleration in the interaction of laser pulse with solid target depending on laser pulse and plasma parameters, the ion beam propagation through the target and target design. The main goad object of project is to formulate practical recommendations on optimization of ion yield with given characteristics for laser intensities of current interest 1019–1021 W/cm2. Such optimization is needed for investigation of prospects of laser-accelerated ion for development compact proton source for actual application in technology and medicine. Laser accelerated proton beams could be used as a tool for radiography and imaging. The proton radiotherapy may also get a big potentiality with this novel method of laser ion acceleration. The latter application is supposed to be a matter of main concern in our project.
A branch of radiology, proton therapy employs fast protons as a tool for the treatment of various, mainly oncological, diseases. The features of tissue ionization by protons (Bragg peak) facilitate a further step towards solving the principal challenge in radiology: to deliver a sufficiently high and homogeneous dose to virtually any tumor, while sparing healthy neighboring tissues organs and structures. The state of proton therapy is still defined by conventional method by using radio-frequency waves for ion acceleration.
A proton beams was first used for radiation treatment at Lawrence Berkeley Laboratory, USA, in 1954. More then 20 proton therapy facilities have been brought into operation since that time. With the some expectation, almost all facilities mentioned utilize dedicated external proton beams from physics research accelerators. A modern radiological pision of a large oncology hospital occupies an area of hundreds or thousands of square meters. The frequent transportation of patients from hospital to physics centers for irradiation considerably reduced both the numbers and categories of patients and the number of clinicians capable of participating in the work. The necessity of sharing beam time between treatment and physics experiments, and impractical accelerator schedules for daily-uninterrupted clinical work worsened the treatment conditions and imposed severe constraints on clinical practice. The use of huge non-specialized experimental accelerators proved to be very expensive. Economic competition even with the most expensive alternative treatment was absolutely out of the question. The future of proton therapy should deal with the construction of hospital-based facilities with dedicated medical proton accelerators.
The USA, Russia, UK, France, and Japan researchers have announced recently a new method to accelerate ions by using powerful light from a table-top laser instead of the conventional accelerator. The new technique allows to accelerate ions in almost a million times shorter distance than a cyclotron, which uses huge electromagnets to accelerate atomic particles around a circular path before releasing them at a target. This new technique may eventually make ion accelerators much more affordable to clinics and hospitals as well as providing doctors with new cancer-treatment capabilities. This smaller source may permit the irradiation of a small group of cells, enabling biological research on the early stages of the growth of tumors. The range of proton energy of the interest for practical radiotherapy is 70 - 100 MeV that is rather close to maximum proton energy already measured in the experiments.
The possibility of application of laser-accelerated ion beams for hadron therapy has been marked in talks made by USA, Japan and Germany scientists at the IFSA-2001 conference which was held in Japan ( Kyoto, September, 2001). However, there is still a big gap between the results of current investigations and the desired parameters. We believe that systematic study of ion generation proposed in our project will have significant impact on the optimization of laser accelerated ion beams to make the idea of its practical use to be true.
Commencing from 1997 a theoretical group involved in project is conducting the research on ion acceleration by relativistic intense short laser pulses. Several mechanisms of ion generation (“vacuum heating” due to Lorentz force, “Coulomb explosion”, ponderomotive acceleration by propagating laser pulse), ion acceleration during adiabatic expansion of a plasma bunch, fast ion cumulating in the focus of sub-picosecond laser and laser triggered nuclear transformations have been considered. Theoretical results were checked in the experiments performed in the Center for Ultrafast Optical Science, University of Michigan, on ion acceleration and laser triggered nuclear reactions.
In 1994-97 years the RFNC-VNIITF scientists under support ISTC through ISTC Project #0107 had carried out theoretical studies of intense ultra-short laser pulses interaction with matter including the positron generation, target heating by fast electrons and fluorescent K- radiation generation. The numerical code PM2D (2-dimensional relativistic PIC code) for simulation of charged particles dynamics and electromagnetic fields generation at high intensity laser interaction with matter was developed at RFNC-VNIITF. The PM2D code was used to study fast electron dynamics; electromagnetic waves generation, and positron jets formation at intense ultra-short laser pulses interaction with matter.
This studies benefit to the investigation of generation of high velocity ion jets, its propagation in matter and prospects of laser-accelerated proton scheme for hadron’s therapy. The performed works give evidence of project team competence in theory and numerical simulation of processes that proceeded at high-intensity laser-plasma interaction. The efforts of project team are directed now to investigation of the new applications of short laser pulses to technology and medicine. That is why we propose this project with the aim to develop a code package suitable for self-consistent modeling of ion generation and propagation through the target, study the efficiency of ion generation, and elaboration of a target design for proton therapy.
The proposed researches are of fundamental importance for the basic study of laser-plasma interaction at relativistic intensities and will be addressed to the following problems:
- Development of a physical model of the high electric field generation in the interaction of high-intensity short laser pulses with solid targets, electron and ion acceleration, and their propagation through the dense plasma.
- Development of 2D and 3D numerical codes for modeling of ion generation in the interactions of laser pulse with plasma based on the pic method and finite difference with adaptive mesh refinement;
- Investigation of the fast electron propagation through the matter including effects of ionization due to breakdown in a strong charge separation electric field and with self-consistent conductivity and return currents;
- Optimization of the laser parameters and the target design including multistage ion acceleration to find most optimum schemes to achieve well-collimated ion beams with the energy reliable to the hadron’s therapy concept.
The most fundamental model will include kinetic description of the particles in the laser and self-consistent electromagnetic fields that provide a first principles description of the laser-plasma interaction at extremely high incident intensities. This model will be implemented through multidimensional fully relativistic particle-in-sell (PIC) simulations. The 3D parallel PIC code will be a backbone for modeling of laser-plasma coupling and particle generation. Our advanced numeric study will be based on adaptive mesh refinement scheme which has already demonstrated significant advantage in accuracy for 3D parallel hydrodynamic simulations but is still aside of implementation in the PIC codes. Particle transport from the near critical density region to dense medium, ionization of the medium, and return current formation will be studied theoretically and by using the 2D-parallel hybrid code simulation. This code will deal with the solution to Maxwell equations on regular cylindrical mesh (by finite-difference method) and kinetics of electrons and ions accounting for ionization and particle collisions. The latter will be modeled by using PIC simulations, Lagrange hydrodynamic code and Monte-Carlo method.
The research proposed would be the first one among self-consistently models with accounting of the most important physical processes responsible for ion acceleration and propagation including laser-plasma, field-matter, and particle-matter interactions. Expected results will contribute to the knowledge of the problem of intense short laser pulse interaction with plasma and could make significant support to the international efforts on development of laser-accelerated high-energy ion beams for technology and medical applications. The realization of the project and analyzes of the experimental data will enable to formulate recommendations for practical implementation of laser accelerated proton beams to hadron’s therapy for the treatment of cancer diseases.
Contacts were established with Japanese group from Institute of Laser Engineering (ILE, University of Osaka), French group from LULI laboratory of Ecole Polytechnique and USA group from the Center for Ultrafast Optical Science, University of Michigan (CUOS). These groups are well known due to their deep studies of intense laser interaction with matter. The leading experts in this field, Prof. Kunioki Mima (ILE), Prof. Jean-Claude Gauthier (LULI), and Dr.A.Maksimchuk, kindly have agreed recently to participate in the project as collaborators. The project will enable constant exchange of the information between American, French, Japanese and Russian scientists. The collaborators will significantly influence on theoretical work and numerical modeling within the scope of this project. The main results of the project will be published in the scientific journals.
The project will address the general ISTC objectives:
- it offers for the weapon scientists from RFNC — VNIITF an opportunity to apply their professional skills to a peaceful activities related to development of new technologies;
- it encourages integration of the RFNC — VNIITF weapon scientists into the international scientific community;
- the project bears in itself a particular commercial potential, as it creates scientific background for development of new methods for the treatment of cancer diseases using the laser-accelerated proton beams.
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