Mach numbers for gases and plasmas in a convergent-divergent cascaded arc

For a plasma, flowing through a cascaded arc channel with a varying cross-section, and flowing from a subsonic to a supersonic state, the sonic condition moves downstream and the plasma Mach number at the smallest cross section is less than one, although in case of a transonic isentropic gas flow the sonic condition is found at the smallest cross section. This shift in sonic condition is due to the lack of isentropic behavior of the plasma flow. Sources causing the anisentropy are viscosity, heat and ionization, of which ionization is vital for a plasma. It is found that the plasma Mach number is always lower than the corresponding gas Mach number. A quasi one-dimensional analysis and simulations with a two-dimensional plasma model, which support the analysis, are presented. © 1999 American Institute of Physics. © 1999 American Institute of Physic

Ionisation efficiency in a pinched cascaded arc channel

In the present study, we will focus on the improvement of the ion density at the arc outlet. Efficiency increases are necessary to obtain effective remote deposition, in which the plasma source and target area are decomposed. Remote deposition is easier to control than non-remote deposition and therefore preferable. The increase in the ionisation outflow will be obtained by creating a nozzle shaped cylindrical arc channel. Simulations were used to obtain the results. The arc plasma expands supersonically into a low pressure vessel. To simulate the existence of the expansion, a Ma=0.9 boundary condition is implemented at the arc outle

Ionisation efficiency in a pinched cascaded arc channel

In the present study, we will focus on the improvement of the ion density at the arc outlet. Efficiency increases are necessary to obtain effective remote deposition, in which the plasma source and target area are decomposed. Remote deposition is easier to control than non-remote deposition and therefore preferable. The increase in the ionisation outflow will be obtained by creating a nozzle shaped cylindrical arc channel. Simulations were used to obtain the results. The arc plasma expands supersonically into a low pressure vessel. To simulate the existence of the expansion, a Ma=0.9 boundary condition is implemented at the arc outle

RF discharge in argon with cylindrical dust particles

Kinetic computer simulations of the low pressure RF discharge in argon with cylindrical and spherical dust particles are carried out using PIC/MCC method. The Monte Carlo technique is used to describe electron and ion collisions with neutral atoms, ions, and dust particles. Obtained results show the remarkable influence of the dust particle shape on spatial distributions of RF discharge parameters including the ion density and the dust particle charge. Possible reasons of the influence can be a difference of the collection effective cross-section between spherical and cylindrical dust particles with equal surfaces as well as the balance of charged particles in dusty RF discharges.Кінетичне комп’ютерне моделювання радіочастотного розряду в аргоні з циліндричними і сферичними пиловими частинками проводилося з використанням PIC/MCC методу. Техніка Монте-Карло використовувалася для опису електронних і іонних зіткнень з нейтральними атомами і пиловими частинками. Отримані результати показують, що форма пилових частинок помітно впливає на просторові розподіли параметрів радіочастотного розряду, в тому числі на розподіли густини іонів і заряду пилових частинок. Можливими причинами цього впливу може бути різниця ефективних перетинів сферичних і циліндричних пилових частинок однакової поверхні, а також баланс заряджених частинок в запорошених радіочастотних розрядах.Кинетическое компьютерное моделирование радиочастотного разряда в аргоне с цилиндрическими и сферическими пылевыми частицами проводился с использованием PIC/MCC метода. Техника Монте-Карло использовалась для описания электронных и ионных соударений с нейтральными атомами и пылевыми частицами. Полученные результаты показывают, что форма пылевых частиц заметно влияет на пространственные распределения параметров радиочастотного разряда, в том числе на распределения концентрации ионов и заряда пылевых частиц. Возможными причинами этого влияния может быть разница эффективных сечений сферических и цилиндрических пылевых частиц с одинаковой поверхностью, а также баланс заряженных частиц в запыленных радиочастотных разрядах

Extreme hydrogen plasma densities achieved in a linear plasma generator

A magnetized hydrogen plasma beam was generated with a cascaded arc, expanding in a vacuum vessel at an axial magnetic field of up to 1.6 T. Its characteristics were measured at a distance of 4 cm from the nozzle: up to a 2 cm beam diameter, 7.5×1020 m-3 electron density, ~2 eV electron and ion temperatures, and 3.5 km/s axial plasma velocity. This gives a 2.6×1024 H+ m-2 s-1 peak ion flux density, which is unprecedented in linear plasma generators. The high efficiency of the source is obtained by the combined action of the magnetic field and an optimized nozzle geometry. This is interpreted as a cross-field return current that leads to power dissipation in the beam just outside the source

Transport of high fluxes of hydrogen plasma in a linear plasma generator

A study was made to quantify the losses during the convective hydrogen plasma transport in the linear plasma generator Pilot-PSI due to volume recombination. A transport efficiency of 35% was achieved at neutral background pressures below ~7 Pa in a magnetic field of 1.2 T. This efficiency decreased to essentially zero at higher pressures. At 1.6 T, the measured downstream plasma density was up to double the upstream density. Apparently plasma pumping and recycling at the target start to play a role under these increased confinement conditions. Feeding the plasma column at this field strength with a net current did not change the downstream density. This indicates that recycling sets the local plasma conditions