Electrostatic Plasma Lens Research Articles

Self-sustained focusing of high-density streaming plasma

We describe our observations of the transport through an electrostatic plasma lens of a wide-aperture, high-current, low energy, metal-ion plasma flow produced by a cathodic arc discharge. The lens input aperture was 80 mm, the length of the lens was 140 mm, and there were three electrostatic ring electrodes located in a magnetic field formed by permanent magnets. The lens outer electrodes were grounded and the central electrode was biased up to −3 kV. The plasma was a copper plasma with directed (streaming) ion energy 20–40 eV, and the equivalent ion current was up to several amperes depending on the potential applied to the central lens electrode. We find that when the central lens electrode is electrically floating, the current density of the plasma flow at the lens focus increases by up to 40%–50%, a result that is in good agreement with a theoretical treatment based on plasma-optical principles of magnetic insulation of electrons and equipotentialization along magnetic field lines. When the central lens electrode is biased negatively, an on-axis stream of energetic electrons is formed, which can also provide a mechanism for focusing of the plasma flow. Optical emission spectra under these conditions show an increase in intensity of lines corresponding to both copper atoms and singly charged copper ions, indicating the presence of fast electrons within the lens volume. These energetic electrons, as well as accumulating on-axis and providing ion focusing, can also assist in reducing the microdroplet component in the dense, low-temperature, metal plasma.

Modelling of new generation plasma optical devices

Abstract The paper presents new generation plasma optical devices based on the electrostatic plasma lens configuration that opens a novel attractive possibility for effective high-tech practical applications. Original approaches to use of plasma accelerators with closed electron drift and open walls for the creation of a cost-effective low-maintenance plasma lens with positive space charge and possible application for low-cost, low-energy rocket engine are described. The preliminary experimental, theoretical and simulation results are presented. It is noted that the presented plasma devices are attractive for many different applications in the state-of-the-art vacuum-plasma processing.

Recent development of plasma optical systems (invited).

The article devotes a brief description of the recent development and current status of an ongoing research of plasma optical systems based on the fundamental plasma optical idea magnetic electron isolation, equipotentialization magnetic field lines, and the axi-symmetric cylindrical electrostatic plasma lens (PL) configuration. The experimental, theoretical, and simulation investigations have been carried out over recent years collaboratively between IP NASU (Kiev), LBNL (Berkeley, USA), and HCEI RAS (Tomsk). The crossed electric and magnetic fields inherent the PL configuration that provides the attractive method for establishing a stable plasma discharge at low pressure. Using PL configuration, several high reliability plasma devices were developed. These devices are attractive for many high-tech applications.

Focusing intense electron beams using a positive space charge cloud plasma lens

An original plasma-optical device for focusing and manipulating negatively charged particle beams by a dynamic cloud of non-magnetized free positive ions and magnetically isolated electrons produced by a toroidal plasma source such as an anode layer thruster has recently been proposed and explored. In such systems, the electrons are separated from the ions by the relatively strong magnetic field in the discharge channel. The accelerated ions are weakly affected by the magnetic field, owing to their mass. Here, we describe the current status of ongoing research and development of a wide-aperture electrostatic plasma lens with a positive space charge cloud for focusing and manipulating large-area, high-current electron beams. The new modified magnetic system was simulated, designed and tested for minimal aberrations. In this work, we present new simulation results of the further lens development.

Electrostatic Plasma Lens Focusing of an Intense Electron Beam in an Electron Source With a Vacuum Arc Plasma Cathode

In this paper, we present the research results on focusing and transport of an intense (up to 100 A) nonrelativistic (up to 20 kV) pulsed electron beam using an axially symmetric device with a high-current plasma lens configuration. The electron source is based on electron extraction from the plasma of a hollow-anode vacuum arc discharge. The arc is initiated by a dielectric surface flashover. The emission hole is covered with a fine mesh grid. The beam is extracted and accelerated in a diode-type electro-optical system formed between the grid surface and an open anode plasma boundary. The anode plasma is produced in an electron beam transport channel through residual gas ionization by beam electrons and a plasma lens discharge. The plasma lens configuration of crossed electric and magnetic fields provides an attractive means to obtain a stable low-pressure plasma discharge. This geometry allows the compression of the electron beam in diameter from 6 to 1 cm with more than 100- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm A}/{\rm cm}^{2}$</tex></formula> beam current density at the collector.

Invited Review Article: The electrostatic plasma lens

The fundamental principles, experimental results, and potential applications of the electrostatic plasma lens for focusing and manipulating high-current, energetic, heavy ion beams are reviewed. First described almost 50 years ago, this optical beam device provides space charge neutralization of the ion beam within the lens volume, and thus provides an effective and unique tool for focusing high current beams where a high degree of neutralization is essential to prevent beam blow-up. Short and long lenses have been explored, and a lens in which the magnetic field is provided by rare-earth permanent magnets has been demonstrated. Applications include the use of this kind of optical tool for laboratory ion beam manipulation, high dose ion implantation, heavy ion accelerator injection, in heavy ion fusion, and other high technology.

Electrostatic plasma lens for focusing negatively charged particle beams

We describe the current status of ongoing research and development of the electrostatic plasma lens for focusing and manipulating intense negatively charged particle beams, electrons, and negative ions. The physical principle of this kind of plasma lens is based on magnetic isolation electrons providing creation of a dynamical positive space charge cloud in shortly restricted volume propagating beam. Here, the new results of experimental investigations and computer simulations of wide-aperture, intense electron beam focusing by plasma lens with positive space charge cloud produced due to the cylindrical anode layer accelerator creating a positive ion stream towards an axis system is presented.

Positive-Space-Charge Lens for Focusing and Manipulating High-Current Beams of Negatively Charged Particles

We describe a new approach for the creation of effective axially symmetric plasma tools for focusing and manipulating high-current negatively charged particle beams, negative ions, and electrons. This approach is based on the fundamental plasma-optical concept of magnetic and electrostatic insulation of electrons and nonmagnetized positive ions providing controlled uncompensated positive-space-charge cloud formation. The recent advances in the creation of negative ion sources have led to the problem of elaboration and creation of focusing tools capable of manipulating high-current negative ion beams. We describe novel experimental, theoretical, and computer simulation results of the application of the magnetic electron insulation concept for the creation of the positive-space-charge electrostatic plasma lens. The described results open up an attractive possibility to use this lens for focusing high-current negative ion beams.

Recent advances in plasma devices based on plasma lens configuration for manipulating high-current heavy ion beams

We describe new results of development of novel generation cylindrical plasma devices based on the electrostatic plasma lens configuration and concept of electrons magnetic insulation. The crossed electric and magnetic fields plasma lens configuration provides us with the attractive and suitable method for establishing a stable plasma discharge at low pressure. Using plasma lens configuration in this way some cost-effective plasma devices were developed for ion treatment and deposition of exotic coatings and the effective lens was first proposed for manipulating high-current beams of negatively charged particles. Here we describe operation and features of these plasma devices, and results of theoretical consideration of mechanisms determining their optimal operation conditions.

Advances in Novel Plasma Devices Based on the Plasma Lens

We review some new results in the development of novel cylindrical plasma devices based on the electrostatic plasma lens configuration and the concepts of electron magnetic insulation and magnetic field line equipotentialization. The plasma lens configuration of crossed electric and magnetic fields provides an attractive method for establishing a stable plasma discharge at low pressure. Use of the plasma lens configuration in this way has been explored, and a number of easily maintained low-cost plasma devices for ion treatment and deposition of exotic coatings have been developed. These devices make use of permanent magnets and possess considerable flexibility with respect to spatial configuration. They can be operated as a stand-alone tool for ion treatment of substrates, or as part of an integrated processing system together with cylindrical magnetron sputtering, for coating and deposition. Here, we describe the operation and features of some cylindrical plasma devices based on the plasma lens configuration, the results of theoretical investigations of the plasma discharge characteristics, and experimental investigations of the physical mechanisms determining optimal operating conditions for these devices.

Experimental study of electron vortex structures in an electrostatic plasma lens

Results are presented from experimental studies of electron vortex bunches in a cold ion-beam plasma consisting of strongly magnetized electrons and a beam of almost free positive ions. The existence of electron vortex bunches was detected from local minima of the electric potential on surfaces perpendicular to the magnetic field lines. It is found that the vortices have the form of magnetic-field-aligned filaments, in which electrons rotate with a velocity significantly exceeding both the velocity of the vortex as a whole and the electron velocity in the ambient plasma. It is shown that, in a sufficiently strong magnetic field, the accumulation of electrons in the vortices terminates when the condition for the longitudinal confinement of electrons by the electric field fails to hold.

Plasma Devices Based on the Plasma Lens&amp;#x2014;A Review of Results and Applications

We review some novel developments of the electrostatic plasma lens and some new plasma devices based on the plasma-optical idea of magnetic insulation of electrons and equipotentialization along magnetic field lines. The plasma lens configuration of crossed electric and magnetic fields provides an attractive and simple method in establishing a stable plasma discharge at low pressure and has been used to develop some cost-effective low-maintenance plasma devices for ion cleaning, surface activation, and polishing of substrates prior to film deposition. Recent embodiments of these devices use permanent magnets and possess considerable flexibility with respect to spatial configuration.

Simulating optimal structure of the magnetic field of electrostatic plasma lens

The paper considers the motion of electrons in the curvilinear magnetic field of a plasma lens. This motion is modeled mathematically on the assumption that the force acting on the electron is central in a moving coordinate frame. The existence conditions for optimal and stable equipotentials are studied.

Internal plasma potential measurements of a Hall thruster using xenon and krypton propellant

For krypton to become a realistic option for Hall thruster operation, it is necessary to understand the performance gap between xenon and krypton and what can be done to reduce it. A floating emissive probe is used with the Plasmadynamics and Electric Propulsion Laboratory’s High-speed Axial Reciprocating Probe system to map the internal plasma potential structure of the NASA-173Mv1 Hall thruster [R. R. Hofer, R. S. Jankovsky, and A. D. Gallimore, J. Propulsion Power 22, 721 (2006); R. R. Hofer, R. S. Jankovsky, and A. D. Gallimore, J. Propulsion Power22, 732 (2006)] using xenon and krypton propellant. Measurements are taken for both propellants at discharge voltages of 500 and 600V. Electron temperatures and electric fields are also reported. The acceleration zone and equipotential lines are found to be strongly linked to the magnetic-field lines. The electrostatic plasma lens of the NASA-173Mv1 Hall thruster strongly focuses the xenon ions toward the center of the discharge channel, whereas the krypton ions are defocused. Krypton is also found to have a longer acceleration zone than the xenon cases. These results explain the large beam divergence observed with krypton operation. Krypton and xenon have similar maximum electron temperatures and similar lengths of the high electron temperature zone, although the high electron temperature zone is located farther downstream in the krypton case.

Electrostatic plasma lens for accelerator injection application

We describe the results of investigations of the suitability of the electrostatic plasma lens as a focusing element in the low-energy injection beam lines of particle accelerators. We have explored the focusing of high-current, wide-aperture, heavy-ion beams by a plasma lens. The results indicate that for optimal focusing conditions the lens does not increase the beam emittance nor the beam noise. The ion current density was increased by a factor of 30, up to 250mA∕cm2 in the work described here. We project that with an optimized ion extraction system, the plasma lens can provide an ion-beam current density of up to 400mA∕cm2 or more.

Large-scale electron vortex structure formation in a plasma lens

The first experimental data on the observation of electron vortices in an electrostatic plasma lens at a considerable radial gradient of electron density are reported. It is established that anharmonic potential waves of large amplitude appear and propagate in the azimuthal direction. The results of measurements of the electric field distribution show that electron bunches formed as a result of instability development contain trapped particles, which rotate at a large velocity around the centers of bunches, thus creating vortices. The main factor leading to limitation of the maximum amplitude of vortices in a strong magnetic field has been experimentally established.

Compression of large area, high-current ion beams by an electrostatic plasma lens

We describe the results of experimental investigations of factors restricting the maximum compression of multi-aperture heavy-ion beams focused by a high-current electrostatic plasma lens. We show that, under optimal conditions of the lens operation for which all negative factors are removed or suppressed, the compression of the ion beam is determined only by its initial emittance.

Effect of the electrostatic plasma lens on the emittance of a high-current heavy ion beam

We describe measurements we have made of the emittance of a high-current, moderate-energy ion beam after transport through a permanent-magnet electrostatic plasma lens. The results indicate the absence of emittance growth due to the lens, when the lens is adjusted for optimal beam focusing. The measured emittance for a 16 keV Cu{sup 2+} ion beam formed by a vacuum arc ion source was about 0.4 {pi} {center_dot} mm {center_dot} mrad at a beam current of 50 mA rising more-or-less linearly to 1.5 {pi} {center_dot} mm {center_dot} mrad at 250 mA, and was conserved in beam transport through the lens. These results have significance for the application of high-current ion sources and the electrostatic plasma lens to particle accelerator injection.

Vortex electron dynamics in a high-current plasma lens

An analytic study is made of the following problems: the instability of a plasma against the excitation of vortex turbulence, the turbulence saturation amplitude, the types and spatial structures of the nascent vortices, and their nonlinear growth rates in an electrostatic plasma lens for focusing high-current ion beams.

The low-field permanent magnet electrostatic plasma lens

We describe the status of ongoing research and development of the electrostatic plasma lens as used for the manipulation of high current broad beams of heavy ions of moderate energy. In some collaborative work at Lawrence Berkeley National Laboratory the lens was used to good effect for carrying out high dose ion implantation processing. In the process of this work a very narrow range of low magnetic field was found for which the ion-optical characteristics of the lens improved markedly. Subsequent theoretical analysis and computer modeling has led to an understanding of this phenomenon. These serendipitous results open up some attractive possibilities for the development of a new compact and low cost plasma lens based on permanent magnets rather than on current-driven field coils surrounding the lens volume. The development of this kind of lens, including both very low noise and minimal spherical aberration effects, may lead to a tool suitable for use in the injection beam lines of high current heavy ion linear accelerators. Here we briefly review the lens fundamentals, some characteristics of focusing heavy ion beams at low magnetic fields, and summarize recent theoretical and experimental developments, with emphasis on the relevance and suitability of the lens for accelerator injection application.