G. Yu. Yushkov

Simple and inexpensive time-of-flight charge-to-mass analyzer for ion beam source characterization

We describe the design, electronics, and test results of a simple and low-cost time-of-flight ion charge-to-mass analyzer that is suitable for ion source characterization. The method selects a short-time sample of the beam whose charge-to-mass composition is then separated according to ion velocity and detected by a remote Faraday cup. The analyzer is a detachable device that has been used for rapid analysis of charge-to-mass composition of ion beams accelerated by voltages of up to about 100kV.We describe the design, electronics, and test results of a simple and low-cost time-of-flight ion charge-to-mass analyzer that is suitable for ion source characterization. The method selects a short-time sample of the beam whose charge-to-mass composition is then separated according to ion velocity and detected by a remote Faraday cup. The analyzer is a detachable device that has been used for rapid analysis of charge-to-mass composition of ion beams accelerated by voltages of up to about 100kV.

The ‘‘TITAN’’ ion source

TITAN is a new type of ion source capable of generating high current, wide aperture beams of gas and metal ions from a broad range of elements: Mg, Al, Ti, Cr, Fe, Co, Ni, Sm, Zn, W, Pb, Ta, Re, Y, C, He, N, Ar, and Xe. A specific feature of the TITAN ion source is the use of two kinds of arc discharges, each with cold cathodes, to produce plasma for ion beam extraction. Metal ions are generated by means of the vacuum arc in the metal vapor formed in cathode spots. Gas ions, on the other hand, are provided by a low‐pressure constricted arc discharge. In a pulsed mode of operation the extraction voltage of the source ranges from 10 to 100 kV. The pulsed beam current for gas and metal ions is on the order of 1 A at pulse repetition rates up to 50 pulses per second and pulse duration of ∼400 μs. For dc operation and at an extraction voltage up to 10 kV, the ion current is as high as hundreds of milliamperes. This work outlines briefly the ion source, its design, and certain physical peculiarities observed wh...

Measurements of the total ion flux from vacuum arc cathode spots

The ion current from different cathode materials was measured for 50-500 A of arc current. The ion current normalized by the arc current was found to depend on the cathode material, with values in the range from 5% to 19%. The normalized ion current was generally greater for elements of low cohesive energy. The ion erosion rates were determined from values of ion current and ion charge states, which were previously measured in the same ion source. The absolute ion erosion rates ranged from 16-173 /spl mu/g/C.

The 100‐kV gas and metal ion source for high current ion implantation

The TITAN ion source is a new kind of source which can produce high current beams of both metal and gas ions simultaneously or separately. Ion beams of the elements Mg, Al, Ti, Ca, Cr, Fe, Co, Ni, Zn, Sn, Ta, Re, Y, C, He, N, Ar, and Xe have been generated. To obtain metal ions a vacuum arc is used in metal vapors created in ‘‘cathode spots.’’ To obtain gas ions a contragated arc discharge in gas current is used. The source extraction voltage is controlled within 10–100 kV. The ion current of both gas and metal was ≂1 A. The source operates in a frequency‐pulse regime at a pulse‐repetition frequency as high as 50 pps. At its normal operation the source provides a dose of 1016 ions/cm2 per minute on a 250‐cm2 area surface. The source is constructed according to the program on development of new technologies and is intended for high current surface modification and production of exotic surface alloys. At present, TITAN ion sources are utilized to modify physical‐mechanical parameters of different surfaces. ...

Enhanced ion charge states in vacuum arc plasmas using a “current spike” method

Ion charge state distributions of vacuum arc ion sources are correlated to the arc operating voltage. An enhancement of ion charge state via an increase of the arc voltage can be achieved utilizing the transient processes that accompany an arc current spike. A current spike of 100–1000 A and several microseconds width was produced on top of the main arc current pulse (100 A, 250 μs). The ion charge state distribution was measured by charge-to-mass spectrometry. The measured charge state distributions were used as input data to the plasma model of partial local Saha equilibrium, giving the time-dependent electron temperature of the plasma at the freezing zone near the cathode spot.

Origin of the Delayed Current Onset in High-Power Impulse Magnetron Sputtering

Repetitive pulses of voltage and current are applied in high-power impulse magnetron sputtering. The current pulse usually lags the applied voltage by a significant time, which, in some cases, can reach several tens of microseconds. The current time lag is generally highly reproducible and jitters less than 1% of the delay time. This work investigates the time lag experimentally and theoretically. The experiments include several different target and gas combinations, voltage and current amplitudes, gas pressures, pulse repetition rates, and pulse durations. It is shown that, in all cases, the inverse delay is approximately proportional to the applied voltage, where the proportionality factor depends on the combination of materials and the conditions selected. The proportionality factor contains the parameters of ionization and secondary-electron emission. The statistical time lag is negligible, while the formative time lag is large and usually dominated by ion motion (inertia), although, at a low pressure, the long free path of magnetized electrons causing ionization contributes to the delay.

Multiple ionization of metal ions by ECR heating of electrons in vacuum arc plasmas

A joint research and development effort has been initiated, whose ultimate goal is the enhancement of the mean ion charge states in vacuum arc metal plasmas by a combination of a vacuum arc discharge and electron cyclotron resonance (ECR) heating. Metal plasma was generated by a special vacuum arc mini-gun. Plasma was pumped by high frequency gyrotron-generated microwave radiation. The results have demonstrated substantial multiple ionization of metal ions. For a lead plasma, ECR heating increased the maximum attainable ion charge state from Pb2+ up to Pb6+. The confinement parameter was as high as ∼109 cm−3 s. Further increase of the ion charge states will be attained by increasing the vacuum arc plasma density and optimizing the ECR heating conditions.

Study of directed ion velocities in a vacuum arc by an emission method

Directed ion velocities in a vacuum arc discharge plasma are measured on the basis of a study of the ion emission current response to a rapid change of arc current. It is shown that these velocities are about 106 cm/s, are determined by the cathode material, and are almost independent of the ion charge number. Applying a magnetic field results in an increase in the directed ion velocity. As the gas pressure increases, the directed ion velocity decreases; this is the only case where the directed velocities are observed to depend on the ion charge number.

Electron-beam enhancement of the metal vapor vacuum arc ion source

We report detailed investigations of the electron-beam metal vapor vacuum arc (E-MEVVA) ion source. The experiments were performed in Moscow and Tomsk with nearly the same design of ion sources. We recently reported the first conclusive demonstration of electron-beam enhancement of MEVVA performance using lead and bismuth cathodes, which yielded maximum ion charge states of Pb7+ and Bi8+ for E-MEVVA, as compared to Pb2+ and Bi2+ for conventional MEVVA operation. In this article we report extensive results for additional cathode materials, further details of the Moscow and Tomsk ion sources, and a discussion of electron beam effects on E-MEVVA performance. These results can be considered as a proof of the E-MEVVA principle.

Hybrid gas-metal co-implantation with a modified vacuum arc ion source

Energetic beams of mixed metal and gaseous ion species can be generated with a vacuum arc ion source by adding gas to the arc discharge region. This could be an important tool for ion implantation research by providing a method for forming buried layers of mixed composition such as e.g. metal oxides and nitrides. In work to date, we have formed a number of mixed metal-gas ion beams including Ti+N, Pt+N, Al+O, and Zr+O. The particle current fractions of the metal-gas ion components in the beam ranged from 100% metallic to about 80% gaseous, depending on operational parameters. We have used this new variant of the vacuum arc ion source to carry out some exploratory studies of the effect of Al+O and Zr+O co-implantation on tribology of stainless steel. Here we describe the ion source modifications, species and charge state of the hybrid beams produced, and results of preliminary studies of surface modification of stainless steel by co-implantation of mixed Al/O or Zr/O ion beams. 5 figs, 21 refs.