Three-particle recombination coefficient of a weakly nonideal ultracold plasma in a high magnetic field

An expression for the recombination coefficient α _B in a weakly nonideal ultracold plasma in a high magnetic field has been proposed. According to this expression, α _B ∼ T _e ^−1.5 B ⁻², where T _e is the temperature of electrons and B is the strength of the magnetic field. Comparison of calculated values with experimental data including the results of the recent experiments on recombination in antihydrogen confirms the theoretical dependence.     

Collisional recombination coefficient in an ultracold plasma: Calculation by the molecular dynamics method

New results of the calculations of the distribution function and the electron diffusion coefficient in energy space are presented. We analyze all of the data obtained and calculate the temperature dependence of the recombination coefficient. This dependence coincides with the Gurevich-Pitaevsky analytical formula in the region of a weakly coupled plasma and begins to differ in the direction of a decline in the region of a strongly coupled plasma; the difference can reach several orders of magnitude.     

Electron beam dose distribution in a solenoid magnetic field

The results of simulation of irradiation of tissue-equivalent targets by 20-MeV electron beams in the presence of solenoid magnetic fields are discussed. These results are compared with the corresponding data obtained without magnetic fields. The data obtained can be used to solve beam therapy problems.     

Electron self-energy in a magnetic field

In the lowest order in the fine-structure constant, the electron self-energy in an external magnetic field can be written in the form of a double integral representation containing the exact information about the radiative shift and width of the energy levels, without approximation in the field strength. In the low-field expansion of the radiative shift, the leading term is conveniently interpreted in terms of the electron's anomalous magnetic moment, whilst in very strong fields the enhancement of the cyclotron motion makes the shift a positive, slowly increasing function of the field intensity. It follows that, even in superstrong magnetic fields, the electromagnetic interaction cannot give rise to an instability of the electron-positron vacuum.     

Quasiclassical distribution function of electrons in a homogeneous magnetic field

Vlasov's equation is used to find the classical nonrelativistic and relativistic distribution functions that describe an electron beam of bounded radius in a homogeneous magnetic field. In the quasiclassical approximation, by means of the exact wave functions of an electron in a homogeneous magnetic field, the quantum relativistic distribution function with allowance for the electron spin is found. The mean physical quantities that characterize the radially bounded electron beam are found as functions of the temperature and electron spin.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 50–56, July, 1976.It is a pleasant duty to thank Professor V. G. Bagrov for discussing the results.     

强磁场中超冷费米气体的相对论效应

由单粒子的弱相对论能谱及泊松公式,导出强磁场中费米气体的热力学势函数.在此基础上,运用热力学关系求解低温条件下系统的统计特征量的解析式,分析相对论效应对统计性质的影响机理.研究表明,磁场愈强,相对论效应愈明显.相对论效应引发的单调项与相应的振荡项的振幅相比,对总能,单调项远大于振幅;对化学势及磁矩,单调项与振幅几乎同一量级. 关键词： 强磁场 费米气体 相对论效应     

LEAD螺旋波射频等离子体电子能量分布函数的测量

通过电压扫描探针测量了LEAD装置螺旋波射频等离子体伏安特性曲线和电子能量分布函数,并对等离子体基本参数剖面如电子温度、密度、等离子体电位和鞘电位降系数等进行了计算.实验发现在LEAD装置半径5cm以内的位置电子能量分布函数都遵循麦克斯韦分布.而在半径7cm附近,即与射频源线圈处于相同径向位置,电子能量呈现出典型的双麦...     

Electron energy distribution function and dense-gas ionization in the presence of a strong field

The mechanism for dense-gas ionization is analyzed in the case when the deceleration of electrons by gas can be neglected in the equation of motion of a single electron. An expression for the electron energy distribution function in the presence of a strong field is derived. The characteristic width of the distribution corresponds to the energy acquired by the electron at a length determined by the inverse Townsend coefficient. The electron energy distributions are calculated for various distances form the cathode. It is demonstrated that the distribution becomes independent of the coordinate at a distance from the cathode that is significantly greater than the inverse Townsend coefficient. In this case, the distribution coincides with the distribution obtained with analytical calculations. The absence of the coordinate dependence is realized even in the presence of an extremely strong field when, in accordance with the commonly accepted point of view, the majority of electrons are runaway electrons.     

Electron energy distribution function in a collisional plasma heated by an electron beam

The electron energy distribution function for the non-resonant electrons in a collisional weakly ionized plasma is found, provided that the intensity of the Langmuir oscillation is spatially dependent. It is assumed that electron-electron collisions are responsible for energy loss.     

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)     

Phase transition in a plasma with anisotropic electron distribution in an external magnetic field

A phase transition is discussed that can occur in a plasma with substantially different transverse and longitudinal temperatures of electrons moving in a magnetic field, ?. The Debye cloud surrounding an ion sharply contracts as T_∥ decreases or the magnetic field increases. The effect of larger radiative electron-ion recombination cross sections compared with their theoretical values is explained; this effect is observed in storage rings with electron cooling systems (coolers). The role played by the phase transition in the crystallization of ion beams is discussed.     

Ultracold plasma expansion in a magnetic field

We measure the expansion of an ultracold plasma across the field lines of a uniform magnetic field. We image the ion distribution by extracting the ions with a high-voltage pulse onto a position-sensitive detector. Early in the lifetime of the plasma (<20 micros), the size of the image is dominated by the time-of-flight Coulomb explosion of the dense ion cloud. For later times, we measure the 2D Gaussian width of the ion image, obtaining the transverse expansion velocity as a function of the magnetic field (up to 70 G). We observe that the expansion velocity scales as B(-1/2), explained by a nonlinear ambipolar diffusion model with anisotropic diffusion in two different directions.     

Scattering amplitude and two-body loss of ultracold alkaline-earth atoms in a shaking synthetic magnetic field

The idea of manipulating the interaction between ultracold fermionic alkaline-earth (like) atoms via a laser-induced periodical synthetic magnetic field was proposed in Kanász-Nagy et al (2018 Phys. Rev. B 97, 155156). In that work, it was shown that in the presence of the shaking synthetic magnetic field, two atoms in ¹S₀ and ³P₀ states experience a periodical interaction in a rotated frame, and the effective inter-atomic interaction was approximated as the time-averaged operator of this time-dependent interaction. This technique is supposed to be efficient for ¹⁷³Yb atoms which have a large natural scattering length. Here we examine this time-averaging approximation and derive the rate of the two-body loss induced by the shaking of the synthetic magnetic field, by calculating the zero-energy inter-atomic scattering amplitude corresponding to the explicit periodical interaction. We find that for the typical cases with shaking angular frequency λ of the synthetic magnetic field being of the order of (2π) kHz, the time-averaging approximation is applicable only when the shaking amplitude is small enough. Moreover, the two-body loss rate increases with the shaking amplitude, and is of the order of 10⁻¹⁰ cm³ · s⁻¹ or even larger when the time-averaging approximation is not applicable. Our results are helpful for the quantum simulations with ultracold gases of fermionic alkaline-earth (like) atoms.