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We have investigated the supersonic flow of dense plasma, formed by a pulsed vacuum arc, in a magnetic field of about 1 T using probe and optical diagnostics. Two separate magnetic field configurations were examined—an axial field with either converging or diverging lines of force. We find that for a low-current arc of from 0.4 to 1 kA and pulse duration of 270 $\mu \text{s}$ , the diverging magnetic field leads to increased plasma flow velocity by about a factor of 2.5, whereas the converging magnetic field reduces the velocity by about the same amount. For a high-current arc of from 5 to 30 kA and pulse duration of $40~\mu \text{s}$ , the plasma flow velocity increases, although the effect of increased field strength on flow velocity is less significant. Here, we describe these observations and other effects of magnetic field on the parameters of the vacuum arc plasma flow. [ABSTRACT FROM AUTHOR]

A plasma assistance system was investigated with the goal to operate high power impulse magnetron sputtering (HiPIMS) at lower pressure than usual, thereby to enhance the utilization of the ballistic atoms and ions with high kinetic energy in the film growth process. Gas plasma flow from a constricted plasma source was aimed at the magnetron target. Contrary to initial expectations, such plasma assistance turned out to be contraproductive because it led to the extinction of the magnetron discharge. The effect can be explained by gas rarefaction. A better method of reducing the necessary gas pressure is operation at relatively high pulse repetition rates where the afterglow plasma of one pulse assists in the development of the next pulse. Here we show that this method, known from medium-frequency (MF) pulsed sputtering, is also very important at the much lower pulse repetition rates of HiPIMS. A minimum in the possible operational pressure is found in the frequency region between HiPIMS and MF pulsed sputtering. [ABSTRACT FROM AUTHOR]

Short-pulse high-current discharges in vacuum were investigated with the goal to maximize the ion charge state number. In a direct extension of previous work [G. Y. Yushkov and A. Anders, Appl. Phys. Lett. 92, 041502 (2008)], the role of pulse length, rate of current rise, and current amplitude was studied. For all experimental conditions, the usable (extractable) mean ion charge state could not be pushed beyond 7+. Instead, a maximum of the mean ion charge state (about 6+ to 7+ for most cathode materials) was found for a power of 2–3 MW dissipated in the discharge gap. The maximum is the result of two opposing processes that occur when the power is increased: (i) the formation of higher ion charge states and (ii) a greater production of neutrals (both metal and nonmetal), which reduces the charge state via charge exchange collisions. [ABSTRACT FROM AUTHOR]

Cathodic arc plasmas are considered fully ionized and they contain multiply charged ions, yet gaseous and metal neutrals can be present. It is shown that they can cause a significant reduction of the ion charge states as measured far from the cathode spots. Several cathode materials were used to study the evolution of the mean ion charge state as a function of time after arc ignition. The type of cathode material, arc current amplitude, intentionally increased background gas, additional surfaces placed near the plasma flow, and other factors influence the degree of charge state reduction because all of these factors influence the density of neutrals. In all cases, it was found that the mean ion charge state follows an exponential decay of first order, [formula], where A is a parameter describing the importance of the decay, τ is the characteristic decay time, and Qss is a steady-state value approached for continuous arc operation. The extrapolated values Q(t→0) indicate surprisingly high mean charge states as produced at cathode spots and not “skewed” by charge exchange collisions with neutrals. [ABSTRACT FROM AUTHOR]

We have explored the generation of high-charge-state ion beams by a vacuum arc ion source. A pulsed vacuum arc with current up to several kiloamperes and pulse duration about $1~\mu \text{s}$ was used. In a vacuum arc ion source with bismuth cathode and at a background pressure of about $40~\mu $ Pa, a bismuth ion beam was formed with a maximum charge state Bi19+. For an ion accelerating voltage of 60 kV, this corresponds to a maximum bismuth ion energy of over 1 MeV. [ABSTRACT FROM AUTHOR]

Plasma containing deuterium ions has found wide application, for example and notably for generating neutron fluxes in nuclear fusion reactions. These reactions take place when a compressed plasma is heated to high temperature, or in nuclear reactions between energetic deuterium ion beams, obtained from deuterium-containing plasma, and a solid target containing heavy hydrogen isotopes. The vacuum arc discharge with composite cathode made of a metal saturated with deuterium provides one possible means for generating deuterium plasma. In the work described here, we have explored the mass-to-charge composition of the pulsed vacuum arc plasma formed from a zirconium cathode saturated with deuterium. The plasma composition is compared for cases when the cathode is deuterium-saturated and non-saturated, as well as for the case when an axial magnetic field of 0.5 T is applied in the arc cathode region. We show that the number of deuterium ions per zirconium ion in the vacuum arc plasma formed from a deuterium-saturated zirconium cathode is, on average, 1.4 which is two times greater than the number of deuterium atoms per zirconium atom in the cathode material. With a 0.5 Т magnetic field applied, this ratio increases up to 4.4. The results are discussed. [ABSTRACT FROM AUTHOR]

Thallium arc plasma was investigated in a vacuum arc ion source. As expected from previous considerations of cathode materials in the Periodic Table of Elements, thallium plasma shows leadlike behavior. Its mean ion charge state exceeds 2.0 immediately after arc triggering and diminishes to the predicted 1.60 and 1.45 after about 100 and 150 [micro]s, respectively. The most likely ion velocity is initially 8000 m/s and decays to 6500 and 6200 m/s after 100 and 150 [micro]s, respectively. Both ion charge states and ion velocities decay further toward steady-state values, which are not reached within the 300-[micro]s pulses used here. It is argued that the exceptionally high vapor pressure and charge exchange reactions are associated with the establishment of steady-state ion values. Index Terms--Cathodic vacuum arcs, ion charge states, ion velocity, thallium.

We report on the generation of boron-rich plasma by a pulsed vacuum arc with lanthanum hexaboride cathode. Two different ranges of arc current pulse duration and amplitude were investigated: the first one has pulse duration of 5–20 \mu \texts and arc current of 100–700 A and the second one has pulse duration of 300 \mu \texts and arc current of 140 A. The ion mass-to-charge spectrum of the plasma was investigated by both time-of-flight spectrometry and magnetic analysis. The results of measurements of the plasma ion composition for different arc parameters are presented and discussed. For all arc parameters considered, the fractional composition of boron and lanthanum ions agrees well with the stoichiometric composition of these elements into the lanthanum hexaboride cathode. [ABSTRACT FROM PUBLISHER]

Metal ions in the plasma of vacuum discharges are commonly multiply charged with ion charge states from 1+ to 3+, reaching 4+ and 5+ for some metals. The elevation of metal ion charge states in vacuum discharge plasma is an interesting challenge for plasma physics because it requires a deeper understanding of the processes leading to a more intense ionization of the electrode material. It also has practical implications, for example, for metal ion sources: elevation of ion charge state leads to a proportional increase in ion beam energy for a given accelerating voltage. During the last two decades, various techniques have been used to increase the ion charge states, including: 1) application of a strong magnetic field to the cathode region of the vacuum arc; 2) application of supplemental microwave power to the discharge plasma; 3) injection of an electron beam into the discharge area; and 4) application of a short current pulse to the discharge as to transiently increase the discharge voltage and power, emulating the conditions of a high-current vacuum spark. In this paper, we briefly survey the different techniques of metal ion charge state elevation and then present new experimental results by utilizing the spark regime and combining it with a strong pulsed magnetic field applied to the cathode region. Beams of ions with high charge state, up to a record Bi13+, were extracted from vacuum spark plasma. It is argued that the addition of a magnetic field to the spark plasma magnetizes the electrons and limits plasma expansion, which leads to an increase in the electron temperature relative to the free expansion case and to an increase in the likelihood of electrons to cause ionizing collisions. [ABSTRACT FROM PUBLISHER]

We describe here our investigation of the mass-to-charge state of the plasma ions produced in a vacuum arc discharge with a composite cathode, which is a flat copper substrate coated with a hydrogen-saturated zirconium film of thickness 25–30 \mu \textm . It is shown that during the arc current pulse, the fractions of hydrogen and zirconium ions in the plasma decrease synchronously, while the copper ion fraction increases. The use of a film-coated cathode in a vacuum arc ion source allows generation of multicomponent gas and metal ion beams with a hydrogen ion fraction from several percent to several tens of percent. The lifetime of the cathode in terms of the total ion charge transported in the arc is as high as 1800 C. [ABSTRACT FROM PUBLISHER]

The angular distribution of the different cathode materials and gaseous ion flow from vacuum arc plasma is investigated. A metal-vapor-vacuum-arc-type ion source and a time-of-flight mass spectrometer were used. The experiments were performed using a range of different cathode materials, including C, Al, Zn, Cu, Ti, Co, Cr, W, Pb, \Cu0.7\Cr0.3, \W0.4\Co0.17\C0.43, and \Zn0.4\Pb0.6, over a range of vacuum arc discharge parameters. It was shown that, for all materials, the fraction of singly charged ions on the axis of the system is much less than that of multiply charged ions, but at the edges, the fraction of single-charged ions is greater than that of multiply charged ions; for composite cathodes consisting of light and heavy materials, there were substantially less light atoms on the axis than heavy atoms, while the opposite situation prevailed at the edges, but for cathodes with similar mass, the angular distributions of the materials were very close to each other. The velocities of ions of different materials in the composite cathode were different, but light ions had a higher velocity than those in a pure cathode plasma. With admission of gas, the angular distribution of \Ar^+ became more isotropic with increasing pressure, while the metal ion distributions changed only minimally. [ABSTRACT FROM AUTHOR]

High-charge-state heavy metal ion beams have been formed by high-power microwave heating of vacuum arc plasma confined in magnetic traps. Two types of magnetic traps were investigated: one is a simple mirror configuration, and the other is a cusp configuration with inherent “minimum-B ” structure. Pulsed high-power (>100 kW) gyrotrons with frequencies of 37.5 and 75 GHz were used for heating the vacuum arc plasma injected into the traps. Two different approaches were used for injecting the metal plasma—axial injection from a miniature arc source located on axis near the microwave window and radial injection from sources mounted radially at the midplane of the trap. High-charge-state heavy metal ion beams were extracted from the heated plasma. [ABSTRACT FROM AUTHOR]

Metal ions were extracted from pulsed discharge plasma operating in the transition region between vacuum spark and vacuum arc. At a peak current of about 4 kA, and with a pulse duration of 8 μs, we observed mean ion charges states of about 6 for several cathode materials. In the case of platinum, the highest average charge state was 6.74 with charge states present as high as 10, and with gold we found traces of charge state 11. At higher currents, nonmetallic contaminants started to dominate the ion beam, preventing further enhancement of the metal charge states. [ABSTRACT FROM AUTHOR]

Time-dependent ion charge state measurements for Pb and Bi cathodic arc plasmas revealed unexpected differences: the mean Bi ion charge state dropped much stronger and with a longer time constant. It is shown that the differences in thermal conductivity and vapor pressure led to much higher neutral density for Bi, which in turn can cause charge exchange collisions. The results have implications beyond Pb and Bi plasmas: most importantly, they imply that the “true” ion charge states, as emitted from the cathode spots, are higher than what is generally measured and published. [ABSTRACT FROM AUTHOR]

The noise of the burning voltage of cathodic arcs in vacuum was analyzed for a range of cathode materials (C, Mg, Ti, V, Ni, Cu, Zr, Nb, Ag, Hf, Ta, W, Pt, Bi, and Si). Cathodic arcs were generated in a coaxial plasma source, and the voltage noise was measured with a broadband measuring system. Each measurement was analyzed by fast Fourier transform, revealing a power spectrum ∼1/f2 for all cathode materials over several orders of magnitude of frequency f (brown noise). The absence of any characteristic time down to possible cutoffs at high frequencies supports a fractal model of cathode spots. The amplitude of colored noise scaled approximately linearly with the cathode’s cohesive energy, which is another manifestation of the cohesive energy rule. [ABSTRACT FROM AUTHOR]