高强度紫外激光驱动的质子加速

正超强脉冲激光驱动等离子体加速产生强流脉冲质子束,在高能量密度物理和惯性约束聚变等领域有着重要的研究意义。本文研究了超短脉冲激光加速质子的物理过程,研究了激光强度、激光波长、激光对比度、薄膜靶厚度等对超短脉冲激光驱动薄膜靶加速质子束的影响。研究了紫外超短脉冲激光在质子加速过程中的优势,高对比度的紫外激光有效抑制等离子体对质子加速的影响,波长短,具有高临界密度和更好的激光吸收效率,可产生具有超高密度梯度的高密度等离子体,有利于提高超热电子密度,提高质子加速的束流强度和能量转换效率。P极化激光以45°入射角入     

紫外超短激光驱动铜薄膜靶产生质子的实验研究

在中国原子能科学研究院的放电泵浦的紫外KrF超短脉冲激光放大装置上,开展了紫外超短脉冲激光与铜薄膜靶相互作用加速产生质子束的实验研究。紫外超短脉冲激光输出能量为30 mJ、波长为248 nm、脉冲宽度为500 fs,采用离轴抛物面镜聚焦获得激光聚焦功率密度为1.2×10¹⁷ W/cm²。激光以45°入射5 μm厚的铜薄膜靶,质子最大能量超过300 keV。紫外超短脉冲激光的高对比度和高吸收效率是紫外激光加速的优点。     

飞秒激光-薄膜靶相互作用中快电子和快质子前向发射的研究

采用飞秒激光与金属薄膜靶相互作用,测量了前向(靶背方向)发射的快电子和快质子.实验显示:快电子主要沿靶背法线附近发射且有较大的发散角,这与PIC模拟的结果一致;快质子发射方向与快电子大体一致,但其发散角远小于快电子.原因在于电子产生和加速在靶前(激光辐照面),在输运中受过密等离子体和靶的散射;而质子来源于靶背的含H污染物,并由靶法线鞘加速机制(TNSA)加速,未受散射地到达探测器.快电子和快质子能谱给出的快电子有效温度和质子最大能量较好地满足定标关系Emax=αTh,其中α≈2.     

电子磁谱仪法测量超热电子温度

利用超热电子磁谱仪测量了紫外超短脉冲激光与固体等离子体相互作用产生超热电子的能谱,在无预脉冲、激光强度为1017 W/cm2 条件下,紫外超短脉冲激光与固体(Cu)等离子体相互作用产生超热电子的能谱呈双温麦克斯韦分布,超热电子温度为81 keV,激光吸收的主导机制为真空吸收。     

紫外超短脉冲激光与固体靶相互作用产生超热电子能谱测量

利用电子磁谱仪测量紫外超短脉冲激光与固体等离子体相互作用产生超热电子的能谱,在无预脉冲、激光强度为1017 W/cm2的条件下,紫外(248 nm)超短(440 fs)脉冲激光与固体(Cu)等离子体相互作用产生超热电子的能谱呈双温麦克斯韦分布, 超热电子温度为81 keV,激光吸收的主导机制为真     

超热电子能谱测量

采用180电子磁谱仪方法测量了超短(120 fs)红外(744 nm)脉冲激光与固体等离子体相互作用产生的超热电子能谱。激光参数为无预脉冲、45斜入射的P激化光,靶为5 mm的铜,靶表面经机械抛光,靶上功率密度为1016 W/cm2。谱仪设置在入射激光的正反射方向,测量到的能谱采用 Maxwellian(e     

固体径迹探测器CR39的标定

固体径迹探测器广泛应用于科学和技术方面，CR39是其中使用很频繁的一种塑料探测器。由于电子和伽马光子在CR39中的碰撞截面很小，远小于中子、质子或其他离子的碰撞截面，因此可认为固体径迹探测器CR39对电子和光子不响应，而仅对中子、质子或其他离子响应，这给CR39在实验中的应用带来很大优点。在超短超强脉冲激光与等离子体相互作用的实验中，会产生大量的强伽马射线、热电子或超热电子，而在有些实验如超短超强脉冲激光加速产生高能质子束的研究中，需单独对质子束的通量、角分布、能谱等参数进行详尽的测量。     

超短激光与薄膜靶作用加速产生质子初步研究

物理学家利用高能粒子加速器进行了多方面的研究，但高能粒子加速器庞大且耗资巨大。随着超短超强激光的发展，现在的激光的功率密度可达到10^22W／cm^2。许多实验室利用不同功率密度的激光与固体靶、薄膜靶及气体等相互作用，进行加速产生高能粒子的研究。其中，利用超短超强激光与薄膜薄相互作用加速产生质子是一重要的研究课题，利用超热电子加速产生超热电子，     

超短脉冲激光与固体等离子体相互作用实验研究

实验研究了超短脉冲激光（744nm/120fs/12mJ）与固体（Cu）等离子体相互作用产生超热电子的能谱与角分布,利用电子磁谱仪与成像板（IP）探测器测量能谱,采用IP在入射平面内测量角分布。在无预脉冲、P极化激光45°斜入射下,采用Maxwellian分布拟合得到的超热电子温度为46keV,超热电子主要沿靶法线方向发射。产生超热电子的主导机制为真空加热,等离子体的电荷分离势约为70keV。     

超短超强激光与不同厚度的铝膜作用加速质子的实验研究

介绍了功率密度4×10¹⁶W/cm²,脉宽120 fs情况下超短超强激光分别与5和2.1 μm薄膜铝靶作用加速质子的实验。采用CR-39固体径迹探测器和Thomson谱仪结合测量得到质子能谱,并对实验结果进行分析。测得的5 μm铝靶的质子最大能量约为140 keV,2.1 μm铝靶的质子最大能量约为170 keV。2.1 μm铝靶的质子产额较5 μm铝靶的高1个量级。     

Effect of Foil Target Thickness in Proton Acceleration Driven by an Ultra-Short Laser

Proton acceleration experiments were carried out by a 1.2 x 101s W/cm2 ultra-short laser interaction with solid foil targets.The peak proton energy observed from an optimum target thickness of 7μm in our experiments was 2.1 MeV.Peak proton energy and proton yield were investigated for different foil target thicknesses.It was shown that proton energy and conversion efficiency increased as the target became thinner,on one condition that the preplasma generated by the laser prepulse did not have enough shock energy and time to influence or destroy the target rear-surface.The existence of optimum foil thickness is due to the effect of the prepulse and hot electron transportation behavior on the foil target.     

Candidates for Laser Fusion Energy with Minimized Radioactivity

The new candidates for laser fusion energy with minimized radioactivity were presented. The possibility of side-on laser ignition of H–¹¹B with negligible radioactivity encouraged to study the fusion of solid state H–⁷Li fuel which again turns out to be only about ten times more difficult than the side-on ignition of solid deuterium–tritium using petawatt-picosecond laser pulses at anomalous interaction conditions if very high contrast ratio. Updated cross sections of the nuclear reaction are included. In other words, the specific approach discussed here involves inducing a fusion burn wave without radioactivity by laser-driven impact of a relatively large block of plasma on the outside of a solid density H–¹¹B and H–⁷Li targets.     

Magneto-inertial Approach to Direct-drive Laser Fusion

A magneto-inertial fusion (MIF) approach to inertial confinement fusion (ICF), based on laser-driven magnetic-flux compression (LDFC) is described. This approach benefits from both the high-energy-density characteristic to ICF and the thermal insulation of the fuel by magnetic fields, typical of MFE. The reduction in thermal-conduction losses in the hot spot of an imploding target that has trapped and amplified a pre-seeded magnetic flux leads to increased hot-spot temperatures at lower implosion velocities than required in conventional ICF. This can lead to ignition designs with larger energy gains. This work describes the main concept and the use of a compact magnetic-pulse system to seed a macroscopic magnetic field into cylindrical DD-filled targets, which are radially driven with the OMEGA laser. The compression of the internal magnetic flux is measured with proton deflectometry. Magnetohydrodynamic simulations predict compression of a 0.1-MG seed field to multi-megagauss values, at which levels the radial electron thermal conduction in the hot spot is significantly inhibited. Initial benchmark experiments are described.     

Proton acceleration from picosecond-laser interaction with a hydrocarbon target

As an intense picosecond laser pulse irradiates a hydrocarbon target, the protons therein can be accelerated by the radiation pressure as well as the sheath field behind the target. We investigate the effect of the laser and hydrocarbon target parameters on proton acceleration with two/threedimensional particle-in-cell simulations. It is found that the resulting two-ion species plasma can generate a multiple peaked charge-separation field that accelerates the protons. In particular, a smaller ca...     

CTOF measurements and Monte Carlo analyses of neutron spectra for the backward direction from a lead target irradiated with 200-1000 MeV protons

A calorimetric-time-of-flight technique was used for real-time, high-precision measurement of neutron spectra at an angle of 175^o from the initial proton beam direction, which hits a face plane of a cylindrical lead target of 20 cm in diameter and 25 cm thick. A comparison was performed between the neutron spectra predicted by the MARS, RTS&T, MCNP6, and the MCNPX 2.6.0 transport codes and that measured for 200, 400, 600, 800, and 1000 MeV protons. Neutron spectra were measured within the energy range from 0.7 to 250 MeV almost continuously. The transport codes tested here describe with different success the measured spectra, depending on the energy of the detected neutrons and on the incident proton energy, but all the models agree reasonably well with our data.     

Enhancement of proton collimation and acceleration by an ultra-intense laser interacting with a cone target followed by a beam collimator

A special method is proposed of a laser-induced cavity pressure acceleration scheme for collimating, accelerating and guiding protons, using a single-cone target with a beam collimator through a target normal sheath acceleration mechanism. In addition, the problems involved are studied by using two-dimensional particle-in-cell simulations. The results show that the proton beam can be collimated, accelerated and guided effectively through this type of target. Theoretically, a formula is derived for the combined electric field of accelerating protons. Compared with a proton beam without a beam collimator, the proton beam density and cut-off energy of protons in the type II are increased by 3.3 times and 10% respectively. Detailed analysis shows that the enhancement is mainly due to the compact and strong sheath electrostatic field, and that the beam collimator plays a role in focusing energy. In addition, the simulation results show that the divergence angle of the proton beam in type II is less than 1.67 times that of type I. The more prominent point is that the proton number of type II is 2.2 times higher than that of type I. This kind of target has important applications in many fields, such as fast ion ignition in inertial fusion, high energy physics and proton therapy.     

Neutronics Calculations in Pellets and Blankets of Laser Fusion Reactor Concept SENRI-I

The neutronic properties of SENRI-I, a reference design of laser fusion reactor proposed by Institute of Engineering, Osaka University, are discussed on the basis of the one-dimensional neutron transport calculations in burning DT plasmas and blankets. The softening of the fusion neutron energy spectrum, the neutron heating and the neutron multiplication are studied and discussed for the compressed DT pellets with various thickness of fuel plasmas and lead or lead-polyethylene tampers.

The neutronic and thermal features in the blanket of the SENRI-I design are also examined. The tritium breeding ratio is high enough (~1.6), depending on the neutron energy spectrum from a pellet. The maximum temperature increase per 1,000 MJ DT fusion reactions is ~3°C in the inner liquid Li layer and ~1.5°C in the stainless steel first wall. A parametric study is also presented on the effect of varying the thickness of the inner Li blanket ΔRⁱ to examine the thickness required for the enough tritium breeding ratio and energy deposition.     

Energy and flux measurements of laser-induced silver plasma ions by using Faraday cup

Silver(Ag)plasma has been generated by employing Nd∶YAG laser(532 nm,6 ns)laser irradiation.The energy and flux of ions have been evaluated by using Faraday cup(FC)using time of flight(TOF)measurements.The dual peak signals of fast and slow Ag plasma ions have been identified.Both energy and flux of fast and slow ions tend to increase with increasing irradiance from 7 GW cm-2 to 17.9 GW cm-2 at all distances of FC from the target surface.Similarly a decreasing trend of energies and flux of ions has been observed with increasing distance of FC from the target.The maximum value of flux of the fast component is 21.2×1010cm-2,whereas for slow ions the maximum energy and flux values are 8.8 keV,8.2×1012 cm-2 respectively.For the analysis of plume expansion dynamics,the angular distribution of ion flux measurement has also been performed.The overall analysis of both spatial and angular distributions of Ag ions revealed that the maximum flux of Ag plasma ions has been observed at an optimal angle of～15°.In order to confirm the ion acceleration by ambipolar field,the self-generated electric field(SGEF)measurements have also been performed by electric probe;these SGEF measurements tend to increase by increasing laser irradiance.The maximum value of 232 V m-1 has been obtained at a maximum laser irradiance of 17.9 GW cm-2.