Calculation of helium stopping powers in the intermdiate energy region

A model for calculation of helium stopping powers is developed which takes into account different charge fraction contributions. The neutral part contribution is treated according to the ordinary Firsov theory, whereas for the charged part of the ion beam earlier classical stopping power calculations for point charges by Kührt and Wedell are used.     

Fusion burning waves in degenerate plasmas

The outcome of fusion burning waves in non-degenerate plasmas is limited by the strength of ion–electron Coulomb collisions and subsequent energy loss mechanisms as electron heat conduction and radiation emission. In this Letter, an analysis is presented on the degeneracy effects in the stopping power of suprathermal charged particles and in the energy transmitted from ions to electrons by Coulomb collision. Main results of this analysis is that very powerful fusion burning waves can be launched into previously compressed degenerate plasmas. This can be specially suitable for proton–boron fusion, but it also applicable to any type of fusion reaction, where ignition can be triggered by an incoming ion beam or another external source of energy deposited in a small fraction of the compressed plasma (fast ignition).     

Stopping of heavy ions in plasmas at strong coupling

Standard approaches to the energy loss of ions in plasmas like the dielectric linear response or the binary collision model are strictly valid only in the regimes where the plasma is close to ideal and the coupling between projectile-ion and the plasma target is sufficiently weak. In this review we explore the stopping power in regimes where these conditions are not met. Actually relevant fields of application are heavy ion driven inertial fusion and the cooling of beams of charged particles by electrons. The conventional linear mean-field treatments are extended by many-body methods and particle simulations to account for strong correlations between the particles and for nonlinear coupling. We report the following important results in connection with the stopping at strong coupling: The energy loss of an ion scales with its charge approximately like Z^1.5, the effective screening length depends on Z and is larger than the Debye length. Slow highly charged ions are surrounded by a cloud of electrons trapped by many body collisions. Quantum effects like the wave nature of the electrons and Pauli-blocking reduce the stopping power by mollifying the effective interactions.     

Experimental observation of excited state muon transfer in mixtures of hydrogen isotopes

Molecular dynamic (MD) computer simulations are used to investigate the stopping of heavy ions in strongly coupled electron plasmas. Our results show, that in this regime collisions between the electrons as well as non-linear screening effects yield at low ion velocities a dependence of the stopping power on the ion chargeZ which scales like Z^1.43 instead of the usual Z² ln(const/Z)-scaling for weak coupling. This is connected with an enhanced local density of electrons around a highly charged, slow ion.Supported by the Bundesministerium für Bildung und Forschung (BMBF), the Gesellschaft für Schwerionenforschung Darmstadt (GSI) and the European Community.     

Laser ion source activities at Brookhaven National Laboratory

In Brookhaven National Laboratory (BNL), we have been developing laser ion sources for diverse accelerators. Tabletop Nd:YAG lasers with up to several Joules of energy are mainly used to create ablation plasmas for stable operations. The obtained charge states depend on laser power density and target species. Two types of ion extraction schemes, direct plasma injection scheme (DPIS) and conventional static extraction, are used depending on the application. We optimized and selected a suitable laser irradiation condition and a beam extraction scheme to meet the requirement of the following accelerator system. We have demonstrated to accelerate more than 5?×?10¹⁰ of C⁶⁺ ions using the DPIS. We successfully commissioned a low-charge ion beam provider to the user facilities in BNL. To achieve higher current, higher charge state and lower emittance, further studies will continue.     

碰撞辐射稳态等离子体电荷态分布的一种扩展模型

通过等离子体中离子激发-退激发平衡关系,构造一种离子激发组态之间满足的非Boltzmann分布,利用这个分布作为权函数对原子过程速率系数进行平均,构造出一个扩展的碰撞辐射稳态模型.利用该模型计算从低Z到高Z元素等离子体平均离子电荷随电子温度的变化.进而研究非Boltzmann分布对平均电离度和激发组态相对密度的影响.结果表明,它对相对激发组态密度的影响非常显著. 关键词： 扩展的碰撞辐射稳态 概率分布 能级动理学     

Conformity between linear response and binary collision treatments of an ion energy loss in a magnetized quantum plasma

In this paper the energy loss of a heavy ion moving in a magnetized quantum electron plasma is considered within the linear response and binary collision treatments. Treating the electron-ion interaction force as a small perturbation to the electron nth Landau level we show within the second order perturbation theory the conformity between these two models.Received: 8 August 2003PACS: 52.40.Mj Particle beam interactions in plasmas - 34.50.Bw Energy loss and stopping power - 03.65.Nk Scattering theory - 52.20.Hv Atomic, molecular, ion, and heavy-particle collisions     

Determination of charge states of single swift heavy projectiles by high-energy delta-electrons

The effective charge state is an important particle parameter which is required for the calculation of many effects concerning the interaction between radiation and matter such as an estimate of the radial dose of swift heavy projectiles, stopping power and so on. A new method for the determination of effective charge states of heavy ions is based on the measurement of the number of high-energy delta-electrons which are ejected from a target by the penetrating ion. These electrons are detectable with a CCD-detector and their number can be correlated to the effective charge state of the projectile for known particle velocities. This method is even applicable to operation with single swift heavy ions within statistical bounds.     

Resonant and near-threshold photoionization cross sections of Fe14+

Photoionization (PI) of Fe14+ in the range from 450 to 1100 eV was measured at the BESSY II storage ring using an electron beam ion trap achieving high target-ion area densities of 10(10) cm(-2). Photoabsorption by this ion is observed in astrophysical spectra and plasmas, but until now cross sections and resonance energies could only be provided by calculations. We reach a resolving power E/ΔE of at least 6500, outstanding in the present energy range, which enables benchmarking and improving the most advanced theories for PI of ions in high charge states.     

Density effects of heavy-ion stopping power in high temperature matter

Abstract

The stopping power and range for Xe ions in high temperature matter (partially ionized plasmas) have been calculated using the dielectric response function method. Calculations have been made for a target matter Al (Z = 13) over a wide range of temperatures and densities considering a finite temperature model. The stopping powers obtained have smaller values in comparison with those of a zero temperature model. The stopping power strongly depends on the density and temperature of the target material, and the projectile ion energy.     

强流重离子束驱动的高能量密度物理研究进展

强流高能离子束可以准等容加热任何高密度样品,制备出尺度大、状态均匀、内部无冲击波的高能量密度物质,为实验室研究高能量密度物理提供了一种独特的新手段。介绍了国内外典型的强流重离子加速器装置及其与高能量密度物理相关的关键参数设计和研究规划;展示了基于粒子和流体模拟的离子束驱动高能量密度物质产生和状态演化规律进展;介绍了一套兼具高时空分辨和高穿透力的高能电子成像诊断技术;分析了中低能区离子束与等离子体相互作用过程中的碰撞和电荷交换微观机制,以及激光加速超短超强离子束在等离子体中的非线性输运和欧姆能损机制。     

Beam purification techniques for low energy rare isotope beams from a gas cell

A linear gas stopping cell has been implemented at the NSCL as part of the Low Energy Beam and Ion Trap (LEBIT) facility. The gas stopping cell is used to convert relativistic ions into low energy ions suitable for use in ion trap experiments. A common undesired property of such systems is the production of beam contaminants through charge exchange of gas impurities with the He⁺ ions produced in the stopping process. These contaminants are of particular concern for Penning trap mass spectrometry, where the simultaneous trapping of ions with different masses can cause unwanted shifts in the measured cyclotron frequency of the desired ions. In order to minimize such effects, a multi-stage beam purification system has been implemented at LEBIT.     

Angular distribution of Cherenkov radiation from relativistic heavy ions taking into account deceleration in the radiator

Numerical methods are used to study the dependence of the structure and the width of the angular distribution of Vavilov-Cherenkov radiation with a fixed wavelength in the vicinity of the Cherenkov cone on the radiator parameters (thickness and refractive index), as well as on the parameters of the relativistic heavy ion beam (charge and initial energy). The deceleration of relativistic heavy ions in the radiator, which decreases the velocity of ions, modifies the condition of structural interference of the waves emitted from various segments of the trajectory; as a result, a complex distribution of Vavilov-Cherenkov radiation appears. The main quantity is the stopping power of a thin layer of the radiator (average loss of the ion energy), which is calculated by the Bethe-Bloch formula and using the SRIM code package. A simple formula is obtained to estimate the angular distribution width of Cherenkov radiation (with a fixed wavelength) from relativistic heavy ions taking into account the deceleration in the radiator. The measurement of this width can provide direct information on the charge of the ion that passes through the radiator, which extends the potentialities of Cherenkov detectors. The isotopic effect (dependence of the angular distribution of Vavilov-Cherenkov radiation on the ion mass) is also considered.     

Performance of 300 s-beam extraction in the KSTAR neutral beam injector

The first neutral beam injector (NBI-1) has been developed for the Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak. The first long pulse ion source (LPIS-1) has been installed in the NBI-1 for an auxiliary heating and current drive of KSTAR plasmas. The performance of 300 s ion beam extraction in the LPIS-1 was investigated on the KSTAR NBI-1 system, prior to the neutral beam injection for long pulse operation. The ion source consists of a magnetic bucket plasma generator with multi-pole cusp fields and a set of prototype tetrode accelerators with circular-type apertures. The inner volume of the plasma generator and accelerator column in the LPIS-1 is approximately 123 L. The nominal operation requirements for the ion source (IS) were a 100 kV/50 A deuterium beam and a 300 s pulse length. The extraction of ion beams was initiated by the formation of arc plasmas in the LPIS-1, called an arc-beam extraction method. A stable ion beam extraction of the LPIS-1 was achieved with 80 kV/27 A and a beam perveance of 1.19 microperv for a 300 s pulse length. Beam power deposition along the NBI-1 has been measured using water-flow calorimetry (WFC), and the sum of the deposited power on the ion source and beamline components was about 93% of the drained acceleration power (V_acc?I_acc). The beam power deposition was compared to the calculated results of the beam transport with re-ionization (BTR) code.     

Linear propagation of dust acoustic modes in the presence of an electron beam

The physical and optical properties of plasmas are depended on dynamics of species in the discharge volume. Then, the presence of an electron beam, as a separate component, in a dusty plasma can modify the plasma structures through altering the discharge parameters. In this report, the linear propagation of acoustic modes in a collisionless dusty plasma contains electrons, ions and charged dust grains is investigated in the presence of an electron beam. Our analysis indicates that the electron beam can modify the dispersion relations of dust acoustic modes which resulted different data transportation in dusty plasmas. The obtained results are also examined for negative and positive charged dust grains with different number densities. The charge of dust grains represents an important role in the dynamics of the low frequency waves. Additionally, our findings reveal that the propagation of acoustic waves in dusty plasmas can be controlled by adjusting the electron number density of the beam and the cathode potential. Lastly, we obtian the destabilizing effects, originated from dust charge fluctuation, by reconsidering the dispersion relations of both dust acoustic modes.     

Results of vacuum cleaning techniques on the performance of LiFfield-threshold ion sources on extraction applied-B ion diodes at 1-10TW

Uncontrolled plasma formation on electrode surfaces limits performance in a wide variety of pulsed power devices such as electron and ion diodes, transmission lines, radio frequency (RF) cavities, and microwave devices. Surface and bulk contaminants on the electrodes in vacuum dominate the composition of these plasmas, formed through processes such as stimulated and thermal desorption followed by ionization. We are applying RF discharge cleaning, anode heating, cathode cooling, and substrate surface coatings to the control of the effects of these plasmas in the particular case of applied-B ion diodes on the SABRE (1 TW) and PBFA-X (30 TW) accelerators. Evidence shows that our LiF ion source provides a 200-700 A/cm² lithium beam for 10-20 ns which is then replaced by a contaminant beam of protons and carbon. Other ion sources show similar behavior. Our electrode surface and substrate cleaning techniques reduce beam contamination, anode and cathode plasma formation, delay impedance collapse, and increase lithium energy, power, and production efficiency. Theoretical and simulation models of electron-stimulated and thermal-contaminant desorption leading to anode plasma formation show agreement with many features from experiment. Decrease of the diode electron loss by changing the shape and magnitude of the insulating magnetic field profiles increases the lithium output and changes the diode response to cleaning. We also show that the LiF films are permeable, allowing substrate contaminants to affect diode behavior. Substrate coatings of Ta and Au underneath the LiF film allow some measure of control of substrate contaminants, and provide direct evidence for thermal desorption. We have increased lithium current density by a factor of four and lithium energy by a factor of five through a combination of in situ surface and substrate cleaning, substrate coatings, and field profile modifications     

Interactions of a Charged Particle with Parallel Two-Dimensional Quantum Electron Gases

By using the linearized quantum hydrodynamic (QHD) theory, electronic excitations induced by a charged particle moving between or over two parallel two-dimensional quantum electron gases (2DQEG) are investigated. The calculation shows that the influence of the quantum effects on the interaction process should be taken into account. Including the quantum statistical and quantum diffraction effects, the general expressions of the induced potential and the stopping power are obtained. Our simulation results indicate that a V-shaped oscillatory wake potential exists in the electron gases during the test charge intrusion. Meanwhile, double peaks will occur in the stopping power when the distance of two surfaces is smaller and the test charge gets closer to any one of the two sheets.     

Ionic Debye Screening in Dense Liquid Plasmas Observed for Li+p,d Reactions with Liquid Li Target

Thick target yields of a particles emitted in the ~6Li(d,a)~4 He and ~7Li(p,a)~4 He reactions were measured for Li target in the solid and liquid phase.Observed reaction rates for the liquid Li are always larger than those for the solid.This suggests that the stopping power of hydrogen ion in the liquid Li metal might be smaller than in the solid.Using the empirically obtained stopping power for the liquid Li,we have deduced the screening potentials of the Li+p and Li+d reactions in both phases.The deduced screening potential for the liquid Li is about 500 eV larger than for the solid.This difference is attributed to the effect of liquefied Li~+ ions.It is concluded that the ionic screening is much stronger than the electronic screening in a low-temperature dense plasmas.