ESTIMATION OF SPACE CHARGE INFLUENCE ON RESOLUTION OF ION-MOBILITY SPECTROMETER

The paper presents an analytical model describing the dynamics of ion cloud, taking into account the action of space charge during a motion in ion mobility spectrometer — starting from the reaction region, where the shutter forms an ion pulse, and the further drift of the formed ion pulse towards the collector. The presented model lets to estimate the degree of influence of the space charge on possible ion losses and the resolution of ion mobility spectrometer. The effect of the space charge becomes noticeable, starting with the ion density of 106 cm–3. Comparison of the results obtained using the analytical model with the results of numerical solution of the initial equations shows that they practically coincide.

Runaway of electrons and initiation of explosive electron emission during pulse breakdown of high-pressure gases

We propose a scenario of the initiation of explosive electron emission on the boundary of the electrode and a high-pressure gas. According to this scenario, positive ions are formed due to the gas ionization by field-emission electrons and accumulated in the vicinity of protrusions of micron size at the cathode. The distance between the ion cloud and the emitting surface decreases with increasing pressure which results in a growth of the local field. As a consequence, an explosive growth of the emission current density occurs for a dense gas (the gas with the pressure of tens of atm). As a result, explosive-emission centers can be formed in dozens of ps. These centers give a start to plasma channels expanding towards the anode. Runaway electron flow generated near the channel heads ionizes the gas gap, causing its subnanosecond breakdown.

Counter differential rigid-rotation equilibrium of electrically non-neutral two-fluid plasma with finite pressure

We derive the two-dimensional counter-differential rotation equilibria of two-component plasmas, composed of both ion and electron ( $e^-$ ) clouds with finite temperatures, for the first time. In the equilibrium found in this study, as the density of the $e^{-}$ cloud is always larger than that of the ion cloud, the entire system is a type of non-neutral plasma. Consequently, a bell-shaped negative potential well is formed in the two-component plasma. The self-electric field is also non-uniform along the $r$ -axis. Moreover, the radii of the ion and $e^{-}$ plasmas are different. Nonetheless, the pure ion as well as $e^{-}$ plasmas exhibit corresponding rigid rotations around the plasma axis with different fluid velocities, as in a two-fluid plasma. Furthermore, the $e^{-}$ plasma rotates in the same direction as that of $\boldsymbol {E \times B}$ , whereas the ion plasma counter-rotates overall. This counter-rotation is attributed to the contribution of the diamagnetic drift of the ion plasma because of its finite pressure.

A simulation study of excitation contour of a linear trap with spatial harmonics

The process of nonlinear resonant excitation of ion oscillations in a linear trap is studied. There is still no detailed simulation of the resonance peak in the literature. We propose to use the excitation contour to describe the collective ion resonance. The excitation contour is a resonant mass peak obtained by the trajectory method with the Gaussian distribution of the initial coordinates and velocities. The following factors are considered: excitation time, low order hexapole and octopole harmonics with amplitudes A3 and A4, the depth of the initial ion cloud position. These multipoles are used for selective ion ejection from linear ion trap. All these factors affect the ion yield and the shape of the contours. Obtained data can be useful for control of such processes as ion fragmentation, ion isolation, ion activation, and ion ejection. Simulated resonance peaks are important for the theoretical description of the ion collective nonlinear resonances.

Velocity distribution of 43Ca+ion cloud in the low temperature limit in a quadrupole Penning Trap

Penning trap has electric field created by DC voltage applied between ring and end cap electrodes and magnetic field is applied along symmetry axis, as the electric field confines ions in the axial direction through an electric potential minimum and the magnetic field confines the ions in the radial direction. The trapping potential created by the DC voltage applied between the end cap and ring electrodes in the low temperature limit is cancelled by Coulomb interaction of ions and the total energy is mainly kinetic energy of ions. The velocity distribution of 43Ca+ ions along axial direction, in radial plane and total velocity distribution due to resulting motion of both axial and radial motion of ions in low temperature limit in a Quadrupole Penning trap are presented here. These results reveal the properties of 43Ca+ ion cloud and are useful to study confining techniques for different types of ions in low temperature limit and a qubit can be encoded in the hyperfine ground states of 43Ca+ isotope for ion trap quantum computation.

Possible Mechanisms of String Formation in Complex Plasmas at Elevated Pressures

Possible mechanisms of particle attraction providing formation of the field aligned microparticle strings in complex plasmas at elevated gas pressures are theoretically investigated in the light of the Plasmakristall-4 (PK-4) experiment on board the International Space Station. The particle interaction energy is addressed by two different approaches: (i) using the dynamically screened wake potential for small Mach numbers derived by Kompaneets et al., in 2016, and (ii) introducing effect of polarization of the trapped ion cloud by discharge electric fields. Is is found that both approaches yield the particle interaction energy which is independent of the operational discharge mode. In the parameter space of the performed experiments, the first approach can provide onset of the particle attraction and string formation only at gas pressures higher than 40–45 Pa, whilst the mechanism based on the trapped ion effect yields attraction in the experimentally important pressure range 20–40 Pa and may reconcile theory and observations.

Energy distribution of an ion cloud in a quadrupole Penning Trap

Ions are confined in Penning trap by the combination of electric field and magnetic field, as the electric field confines ions in the axial direction through an electric potential minimum and the magnetic field applied along the axis of the trap confines the ions in the radial direction. In the high temperature limit Coulomb interaction of ions can be neglected and the total energy is due to the electrostatic potential energy of the charge of ions and kinetic energy due to thermal energy. However, in the low temperature limit the trapping potential created by the dc voltage applied between the end cap and ring electrodes is cancelled by Coulomb interaction of ions and the total energy is mainly kinetic energy of ions. The probability density of energy distribution of ions along axial direction, in radial plane and total probability density of energy distribution due to resulting motion of both axial and radial motion of ions under high temperature and low temperature limits in a Quadrupole Penning trap are presented here. These results reveal the energy properties of ion cloud and are useful to carry out accurate measurement experiments on single stored particle, antiparticles with energy related parameters, under high temperature and low temperature limits in a Quadrupole Penning trap.

Ion cloud expansion after hypervelocity dust impacts detected by the MMS spacecraft

<p>Dust grains impacting with high velocities the spacecraft body can be partly or totally evaporated and create clouds of charged particles. Presence of electrons and ions generated by such hypervelocity impacts can consequently influence the spacecraft potential and/or measurements of on-board scientific instruments. Electric field instruments are able to register signals generated by dust impacts as short pulses in the measured electric field. These signals can be used for detection of dust grains by the spacecraft without dedicated dust detectors. This dust detection method has been successfully used for data collected by many spacecraft as Voyager, Cassini, Wind, STEREO, MAVEN, and MMS. On the other hand, our understanding of this complex process comprising from dust grain evaporation, generation of charged particles, to impact cloud expansion and signal detection is still not complete.</p><p>We present a study of events related to dust impacts on the spacecraft body detected by electric field probes operating simultaneously in the monopole (probe-to-spacecraft potential measurement) and dipole (probe-to-probe potential measurement) configurations by the Earth-orbiting MMS spacecraft. The presented study is focused on events when expanding ions affect not only the potential of the spacecraft body but also one or more electric probes on the end of antenna booms. Expanding ions can influence electric probes located far from the spacecraft body only when the spacecraft is located in tenuous ambient plasma as inside of the Earth’s magnetosphere. This analysis can confirm if these events are really connected to dust impacts and gives us some information about ion expansion velocity, and improve our knowledge of dust impact process.</p>