Charge-state distribution of ions in a vacuum arc discharge plasma in a high magnetic field

It is shown that the fraction of multiply charged metal ions generated in a vacuum arc discharge plasma grows substantially in a high magnetic field. This effect was observed for more than 30 different cathode materials. A relation is established between growth of the mean charge of the ions and increases in the burning voltage of the arc. It is demonstrated that the burning voltage of the vacuum arc can be ultimately increased to 160 V. Zh. Tekh. Fiz. 68, 39–43 (May 1998)     

Particles formation in an expanding plasma

Interaction of a laser beam with a target generates a high velocity expanding plasma plume, solid debris and liquid nano- and microparticles. They are produced from plasma recombination and vapor condensation and can be deposited on optical elements located nearby the target. Two distinct kinds of particles were observed depending on the temperature achieved in the plasma plume: large micrometer-size fragments for temperatures lower than the critical temperature, and very small nanometer-size particles for higher temperatures. The paper presents experimental observations of fragments and nanoparticles in plasma plumes and a comparison with models.     

The effect of excited atomic states on the harmonic generation in a photoionized plasma

Owing to the conservation by the electrons of the memory of their intra-atomic states, a photoionized plasma arising in the mode of suppression of the ionization barrier exhibits a pronounced dependence of the efficiency of generation of the third and fifth harmonics of the pumping field on such states of electrons. For the maximal values of generation efficiency, this dependence is directly proportional to the tenth power of the principal quantum number of excited ns states of electrons.     

The effect of hadronization on the instabilities in an expanding parton plasma

The growth rate for instabilities in an expanding parton plasma is investigated by using a quasiparticle transport model including hadronization. The coupled Boltzmann equations for partons and pions with time dependent mean field masses and source terms are solved in the Bjorken boost invariant picture. Hadronization modifies the known instability in the parton plasma created by the mean field in two ways: In the beginning, hadronization increases the rate Γ of instability, but then Γ→ 0 when the hadronization is dominating the time evolution. Received: 11 January 1999     

Electron diamagnetic effect on axial force in an expanding plasma: experiments and theory

The axial force imparted from a magnetically expanding current-free plasma is directly measured for three different experimental configurations and compared with a two-dimensional fluid theory. The force component solely resulting from the expanding field is directly measured and identified as an axial force produced by the azimuthal current due to an electron diamagnetic drift and the radial component of the magnetic field. The experimentally measured forces are well described by the theory.     

膨胀等离子体云的粒子密度时空分布

为了获得超高速碰撞产生等离子体粒子密度的时空分布特性,利用点电荷电场的1维理论模型,综合运用质量守恒方程、动量守恒方程、能量守恒方程和麦克斯韦方程,推导出了等离子体在膨胀过程中粒子密度的时空分布规律。通过对超高速碰撞2024-T4铝靶实验采集的原始数据分析,得到了超高速碰撞2024-T4铝靶产生膨胀等离子体云粒子密度的时空演化规律。     

膨胀等离子体云的粒子密度时空分布

为了获得超高速碰撞产生等离子体粒子密度的时空分布特性,利用点电荷电场的1维理论模型,综合运用质量守恒方程、动量守恒方程、能量守恒方程和麦克斯韦方程,推导出了等离子体在膨胀过程中粒子密度的时空分布规律。通过对超高速碰撞2024-T4铝靶实验采集的原始数据分析,得到了超高速碰撞2024-T4铝靶产生膨胀等离子体云粒子密度的时空演化规律。     

Photon and dimuon pairs in an expanding quark-gluon plasma

Diphotons and dimuons escaping the interaction regions in ultra-relativistic heavy-ion collisions are studied in a thermodynamical framework. The relevance of such an analysis for quark-gluon plasma diagnostics is highlighted.     

Cadmium ion excitation in an expanding He-Cd plasma

Space-time characteristics of radiation, temperature, and electron concentration are studied for segmented excitation and subsequent recombination in an expanding He-Cd plasma. It is shown that recombination processes play the dominant role in excitation of levels. The collision of metastable helium and cadmium atoms is significant in populating the cadmium ion 4²F_{5/2, 7/2} levels.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 35–39, July, 1986.     

Particle energization in an expanding magnetized relativistic plasma

Using a 21 / 2-dimensional particle-in-cell (PIC) code to simulate the relativistic expansion of a magnetized collisionless plasma into a vacuum, we report a new mechanism in which the magnetic energy is efficiently converted into the directed kinetic energy of a small fraction of surface particles. We study this mechanism for both electron-positron and electron-ion (m(i)/m(e)=100, m(e) is the electron rest mass) plasmas. For the electron-positron case, the pairs can be accelerated to ultrarelativistic energies. For electron-ion plasmas, most of the energy gain goes to the ions.     

Ion current density in an expanding laser plasma

The dependence of the ion current density in an expanding laser plasma on the parameters of the laser radiation, the target material, and the distance from the target is investigated theoretically. Calculations needed to design laser ion sources for accelerator technology are performed. An explanation for the two-peaked shape of the collector signals observed in some experiments with a laser plasma is given. Additional possibilities for obtaining information on the experimental conditions from collector signals are considered. Zh. Tekh. Fiz. 68, 28–32 (April 1998)     

Anomalous viscosity of an expanding quark-gluon plasma

We argue that an expanding quark-gluon plasma has an anomalous viscosity, which arises from interactions with dynamically generated color fields. We derive an expression for the anomalous viscosity in the turbulent plasma domain and apply it to the hydrodynamic expansion phase, when the quark-gluon plasma is near equilibrium. The anomalous viscosity dominates over the collisional viscosity for weak coupling and not too late times. This effect may provide an explanation for the apparent "nearly perfect" liquidity of the matter produced in nuclear collisions at the Relativistic Heavy Ion Collider without the assumption that it is a strongly coupled state.     

Formation of Rydberg atoms in an expanding ultracold neutral plasma

We study the formation of Rydberg atoms in expanding plasmas at temperatures of 1-1000 K and densities from 10(5)-10(10) cm(-3). Up to 20% of the initially free charges recombine in about 100 micros, and the binding energy of the Rydberg atoms approximately equals the increase in the kinetic energy of the remaining free electrons. Three-body recombination is expected to dominate in this regime, yet most of our results are inconsistent with this mechanism.     

Role of excited states in coherent harmonic bremsstrahlung in a photoionized plasma

It is established for a photoionized plasma formed in the barrier-suppression ionization regime that the preliminary population of the excited states of the ionizing atoms plays an important role. It is established that in this case an anomalously strong (several orders of magnitude) increase occurs in the efficiency of generation of the harmonics of the pump radiation. It is shown that a relative decrease of the harmonics generation efficiency occurs with time as a result of collisions of the electrons produced by ionization.     

Interaction between microwave oscillation and a photoionized semiconductor plasma in a two-layer waveguide

Theoretical studies are performed on the interaction between microwave electromagnetic radiation and a photoionized semiconductor plasma in a two-layer waveguide. The interaction between the characteristic wave types of oscillation and a photoexcited semiconductor plasma is investigated. The dependences of the reflection coefficient and phase of the microwave-frequency wave on the optical radiation intensity are obtained; the effect of the surface and of the geometric dimensions of semiconductor elements on these parameters is investigated.     

On “Fermi accelerated” ions from an expanding plasma sheath

Ions with a velocity equal to twice the expansion velocity of a sheath are observed. The acceleration mechanism is interpreted in terms of “Fermi acceleration”.     

A numerical study of an expanding plasma of quarks in a chiral model

We numerically solve the transport equations for a quark gas described by the the Nambu-Jona-Lasinio model. The mean field equations of motion, which consist of the Vlasov equation for the density and the gap equation for the mean field, are discussed, and energy and momentum conservation are proven. Numerical solutions of the partial differential equations are obtained by applying finite difference methods. For an expanding fireball the light quark mass evolves from small values initially to the value of 350 MeV. This leads to a depletion of the high energy part of the quark spectrum and an enhancement at low momenta. When collisions are included one obtains an equation of the Boltzmann type, where the transition amplitudes depend on the properties of the medium. These equations are given for flavor SU(3), i.e. including strangeness. They are solved numerically in the relaxation time approximation and the time evolution of various observables is given. Medium effects in the relaxation times do not significantly influence the shape of the spectra. The mass of the strange quark changes little during the expansion. The strangeness yield and the slope temperatures of the final spectra are studied as a function of the size of the initial fireball.     

Parton energy loss in an expanding quark-gluon plasma: Radiative vs. collisional

The radiative and collisional parton energy losses in an expanding quark-gluon plasma are compared. The radiative energy loss is calculated within the light-cone path integral approach [4]. The collisional energy loss is calculated using the Bjorken method with an accurate treatment of the binary collision kinematics. Our numerical results demonstrate that, for RHIC and LHC conditions, the collisional energy loss is relatively small in comparison with the radiative. An enhancement of the heavy quark radiative energy loss is found as compared to that of light quarks at high energies. The text was submitted by the author in English.