Surface Plasma Source Research Articles

Comparative Analysis of High-Frequency Plasma Drivers with Various Protective Screens for Atomic Injectors with Multi-Second Pulse Duration

Atomic beam injection is one of the main methods of plasma heating in thermonuclear facilities. An injector of high-energy hydrogen atoms for plasma heating based on the acceleration and neutralization of negative hydrogen ions is being developed at the Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences. The injector uses a surface plasma source, in which a plasma flow is created using a radio-frequency driver: an induction radio-frequency (RF) discharge, ignited inside a cylindrical ceramic chamber when an RF voltage is applied to an external antenna. As a part of this work, a new version of the RF driver is being developed. A protective screen is used to prevent overheating and erosion of the ceramic wall of the driver. The operation of RF driver with different protective screens is studied. These screens reduce the efficiency of RF power transmission into the discharge, but make it possible the operation of the ion source in multi-second or steady-state pulses.

Water Surface Plasma Source for Large Area Water Treatment by Using Volume Dielectric Barrier Discharge

The concept of a water surface plasma source (WSPS) was proposed to directly interact plasmas with water for large area water treatment, which is the type of volume dielectric barrier discharge (vDBD) with plate-to-plate. One electrode is submerged in water, while the other is floated in air, which is covered with a dielectric material. The characteristics of the WSPS were investigated by using a complementary metal–oxide–semiconductor (CMOS) camera, voltage and current probes, and optical emission spectroscopy (OES). The electrochemical parameters of plasma-activated water (PAW, 2 L) after plasma treatment times of 3 min by the WSPS were analyzed by using a multiparameter meter. As results, the formation of the water wave due to plasma generation, caused by the effect of the induced polarization forces, was observed at the WSPS. By comparison with the tap water, the applied voltage of the distilled water required higher than 130% for stable operation of the WSPS due to lower electrical conductivity (EC). As gap distance between dielectric plate and water surface increased, the applied voltage increased. In addition, an increase of 2 mm in the water level from the lower electrode required an approximately 5% increase in applied voltages for the ignition and stable plasma generation of the WSPS. The dominant peaks that were for N2 species system in the spectrum of plasmas at the WSPS were analyzed by using the OES. In the case of distilled water, the pH values decreased from 6.25 to 4.24 and the EC increased from 2.00 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$22.33 ~\mu \text{S} \cdot $ </tex-math></inline-formula> cm by using multiparameter meter during plasma treatment, whereas in the case of tap water, the effects on the pH and EC were insignificant.

Development of a surface plasma method for negative ion beams production

By now, the fluxes of accelerated negative ions of steel an indispensable tool for accelerators, plasma physics, solid state physics, chemistry, biology, medicine, important areas of new technique and technology. It arouses increased interest to the development of intensive sources of these particles.The cesiation effect - a significant increase in the emission of negative ions from the discharge with a simultaneous decrease in the flux of accompanying electrons below the current of negative ions after adding a small amount of cesium or other substances with a low ionization potential to the discharge was discovered 50 years ago, on July 1, 1971 in the Budker Institute of Nuclear Physics (BINP), Novosibirsk, Russia.The cesiation effect has opened the door to high-intensity, high-brightness negative ion beams production. The efficiency of generating beams of negative ions was significantly increased due to the invention at the BINP of geometric focusing of generated negative ions. Based on the cesiation effect a surface-plasma method for producing beams of negative ions was developed at the BINP, which provided the creation of surface plasma sources of negative ions for accelerators with a current of hundreds of mA and sources for Controlled Nuclear Fusion with a current of tens of A. (the previous intensity record was 5 mA).Surface plasma sources are being developed all over the world in England, France, Germany, Switzerland, Italy, Japan, Korea, China, India, USA, Canada, Sweden, Spain, New Zealand, Russia, Ukraine, Finland with investments in billions of USD. Specialists in surface plasma sources are trained at the Plasma Physics Department of Novosibirsk State University.

ISIS Penning source extraction studies reveal the 3-dimensional Child-Langmuir effect.

The standard 1X ISIS negative Penning surface plasma source has reliably produced an H- beam for ISIS operations for 35 years. In order to meet the 60 mA, 2 ms, and 50 Hz beam current and duty cycle required for the front end test stand (Letchford et al., in Proceedings of IPAC2015, Richmond, VA, USA, 2015), a 2X scaled source has been developed [Faircloth et al., AIP Conf. Proc. 2052, 050004 (2018)]. The 2X source has a plasma chamber twice the linear dimensions of the 1X source. This paper investigates the comparison between different emission areas (plasma electrode aperture dimensions) for both the 1X and 2X sources. Slit and circular extraction schemes are studied. A 3D Child-Langmuir relationship is observed where the space charge limited current density depends on the aspect ratio of the extraction aperture.

Surface-plasma method for the production of negative ion beams

Increased interest in the development of negative ions sources is related to the emergence of important applications of negative-ion beams. These are, first of all, tandem accelerators, high-energy implantation and accelerator-based mass spectrometry, supercollimated beams, charge-exchange injection into cyclic accelerators and storage rings, charge-exchange extraction of beams from cyclotrons, injectors of high-energy neutrals in plasma systems, and charge-exchange beam separation. The development of sources of negative ions and their use in academic research and industry are reviewed. Physical bases and designs of surface-plasma sources of negative ions, as well as the history of their development, are presented.

Breakdown Oscillations of the ISIS H− Penning Ion-Source Hydrogen–Cesium Discharge

The ISIS Penning ion source is a pulsed dc discharge surface plasma source delivering a 55-mA beam of negative hydrogen ions (H−) in 250- ${ mu }\text{s}$ pulses to the ISIS accelerator for neutron and muon physics at 50-Hz pulse repetition rate. The H− ions are extracted from the hydrogen–cesium discharge sustained by a current-regulated pulsed power supply delivering a current of 50–60 A. The discharge exhibits an ignition transient that requires the pulselength to be prolonged to 700 ${ mu }\text{s}$ to extract a clean H− beam pulse. The current and voltage fluctuations during the breakdown oscillation enhance the sputtering damage of the ion-source cathodes, thus contributing to the lifetime limitation of the device. It has been hypothesized that the breakdown oscillations are due to cesium dynamics causing the surface work function and electron emission from the cathode surfaces to fluctuate periodically. Experiments with the ISIS H− Penning ion source, reported here, reveal that the breakdown oscillations are primarily driven by the discharge power supply and its auxiliary circuits, whereas cesium dynamics have only a minor effect on the ignition transient. The conclusion is derived from careful characterization of the discharge current–voltage characteristics, optical emission measurements combined with a 0-D model, and comparison of different discharge geometries. Engineering solutions to mitigate the breakdown oscillations are presented and the potential effect of the applied modifications on the molybdenum cathode erosion by cesium sputtering is estimated.

Study of continuous wave 33 keV H- beam transport through the low energy beam transport section.

The transport of a continuous wave 33 keV negative ion beam through the low energy beam transport section, designed for beam injection into the tandem accelerator, was studied. The continuous wave H- beam, produced by the Penning surface-plasma source with hollow cathodes and cesium addition, was separated and focused by the 90° bending magnet and then transported through the 0.8 m long transport tube, equipped with beam electrical and optical diagnostics. The beam current was measured by a water-cooled Faraday cup at the transport tube exit. Beam sizes and profiles were measured by CCD cameras looking into the beam from the back and sides. The additions of hydrogen, argon, and xenon to the transport tube and to the bending magnet chamber in the pressure range of 10-6 to 10-4 Torr were tested. The influence of gas addition on the beam space charge compensation and beam transport was studied. A mechanism for the H- beam focusing due to space charge overcompensation and beam compression by the positive charge, produced with positive ion accumulation in the beam, is discussed.

Spectroscopic characterization of H 2 and D 2 helicon plasmas generated by a resonant antenna for neutral beam applications in fusion

A new generation of neutral beam systems will be required in future fusion reactors, such as DEMO, able to deliver high power (up to 50 MW) with high (800 keV or higher) neutral energy. Only negative ion beams may be able to attain this performance, which has encouraged a strong research focus on negative ion production from both surface and volumetric plasma sources. A novel helicon plasma source, based on the resonant birdcage network antenna configuration, is currently under study at the Swiss Plasma Centre before installation on the Cybele negative ion source at the Institute for Magnetic Fusion Research, CEA, Cadarache, France. This source is driven by up to 10 kW at 13.56 MHz, and is being tested on a linear resonant antenna ion device. Passive spectroscopic measurements of the first three Balmer lines α, β and γ and of the Fulcher-α bands were performed with an f/2 spectrometer, for both hydrogen and deuterium. Multiple viewing lines and an absolute intensity calibration were used to determine the plasma radiance profile, with a spatial resolution <3 mm. A minimum Fisher regularization algorithm was applied to obtain the absolute emissivity profile for each emission line for cylindrical symmetry, which was experimentally confirmed. An uncertainty estimate of the inverted profiles was performed using a Monte Carlo approach. Finally, a radiofrequency-compensated Langmuir probe was inserted to measured the electron temperature and density profiles. The absolute line emissivities are interpreted using the collisional–radiative code YACORA which estimates the degree of dissociation and the distribution of the atomic and molecular species, including the negative ion density. This paper reports the results of a power scan up to 5 kW in conditions satisfying Cybele requirements for the plasma source, namely a low neutral pressure, Pa and magnetic field G.

Characteristics of a high-power RF source of negative hydrogen ions for neutral beam injection into controlled fusion devices

An injector of hydrogen atoms with an energy of 0.5–1 MeV and equivalent current of up to 1.5 A for purposes of controlled fusion research is currently under design at the Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences. Within this project, a multiple-aperture RF surface-plasma source of negative hydrogen ions is designed. The source design and results of experiments on the generation of a negative ion beam with a current of >1 A in the long-pulse mode are presented.

Inductively driven surface-plasma negative ion source for N-NBI use (invited).

The long-pulse surface-plasma source prototype is developed at Budker Institute of Nuclear Physics for negative-ion based neutral beam injector use. The essential source features are (1) an active temperature control of the ion-optical system electrodes by circulation of hot thermal fluid through the channels, drilled in the electrode bodies, (2) the concaved transverse magnetic field in the extraction and acceleration gaps, preventing the electrons trapping and avalanching, and (3) the directed cesium deposition via distribution tubes adjacent to the plasma grid periphery. The long term effect of cesium was obtained just with the single cesium deposition. The high voltage strength of ion-optical system electrodes was improved with actively heated electrodes. A stable H(-) beam with a current ∼1 A and energy 90 keV was routinely extracted and accelerated.

Saddle antenna radio frequency ion sources.

Existing RF ion sources for accelerators have specific efficiencies for H(+) and H(-) ion generation ∼3-5 mA/cm(2) kW, where about 50 kW of RF power is typically needed for 50 mA beam current production. The Saddle Antenna (SA) surface plasma source (SPS) described here was developed to improve H(-) ion production efficiency, reliability, and availability. In SA RF ion source, the efficiency of positive ion generation in the plasma has been improved to 200 mA/cm(2) kW. After cesiation, the current of negative ions to the collector was increased from 1 mA to 10 mA with RF power ∼1.5 kW in the plasma (6 mm diameter emission aperture) and up to 30 mA with ∼4 kW RF. Continuous wave (CW) operation of the SA SPS has been tested on the test stand. The general design of the CW SA SPS is based on the pulsed version. Some modifications were made to improve the cooling and cesiation stability. CW operation with negative ion extraction was tested with RF power up to ∼1.2 kW in the plasma with production up to Ic = 7 mA. A stable long time generation of H(-) beam without degradation was demonstrated in RF discharge with AlN discharge chamber.

Compact surface plasma H⁻ ion source with geometrical focusing.

Factors limiting operating lifetime of a Compact Surface Plasma Sources (CSPS) are analyzed and possible treatments for lifetime enhancement are considered. Increased cooling permeate increased discharge power and increased beam intensity and duty factor. A design of an advanced CSPS with geometrical focusing of H(-) flux is presented.

Effect of Plasma Temperature and Nonlinearity of the Adiabatic Compressibility Index on Flow Parameters for Hypersonic Aerosol Expansion Following a Plasma Disruption

Future fusion reactors are expected to experience hard current disruptions that quench the confined plasma and depositing the energy on the plasma facing materials, thus causing surface ablation and the evolving aerosol expands into the reactor chamber. The plasma flow following a disruption event can be simulated experimentally and computationally using confined capillary discharges, which generate heat fluxes (up to ~80 GW/m2) typical to those expected in fusion reactors during a disruption. Computational technique to investigate the effect of plasma temperature on the adiabatic compressibility index has been investigated using a pulsed disruptive capillary electrothermal plasma source with a converging–diverging transition nozzle at the exit attached to the expansion regions. The plasma is formed in the capillary due to thermal decomposition of the ablating inner wall followed by subsequent ionization of the decomposed material. This work is particular to the cases where the ejected particulates coming out from a heat-load affected surface or arc-triggered plasma source orifice are at the sonic speed. The converging section in the nozzle provides a transition from the capillary exit subsonic condition to sonic state, which allows for observing the effect of temperature on the supersonic isentropic expansion. Mathematical model has been developed for effective atomic number (Z eff ) as function of the plasma temperature and has been used to model the adiabatic compressibility index (γ p ) of the plasma. Plasma parameters along the axial direction of the flow in the transition and the expansion regions are obtained.

Improving efficiency of negative ion production in ion source with saddle antenna

Extraction of negative ions from a saddle antenna radio-frequency surface plasma source is considered. Several versions of new plasma generators with different antennas and magnetic field configurations were tested in the smal Oak Ridge National Laboratory Spallation Neutron Source Test Stand. The efficiency of positive ion generation in plasma has been improved to 200 mA/cm(2) kW from 2.5 mA/cm(2) kW. A small oven was developed for cesiation by cesium compounds and alloy decomposition. After cesiation, a current of negative ions to the collector was increased from 1 mA to 10 mA with 1.5 kW RF power in the plasma and longitudinal magnetic field Bl ∼ 250 G. The specific efficiency of H(-) production was increased to 20 mA/cm(2) kW from 2.5 mA/cm(2) kW.

Examining the Role of Ozone in Surface Plasma Sterilization Using Dielectric Barrier Discharge (DBD) Plasma

Dielectric barrier discharge (DBD) devices are known ozone generators. Authors have previously demonstrated a DBD surface plasma source, operating in air at atmospheric pressure, to achieve killing of vegetative cells in 2–3 min and sterilization in 20 min (bacterial spores). The aim of this paper is to examine the role of the ozone in surface DBD plasma sterilization. The role of ozone in plasma killing is examined by a) characterizing the rate of production/decay of ozone during DBD plasma generation, b) studying the effect of exposing bacteria (Escherichia coli) solely to the ozone thus produced. Our results indicate that while ozone plays a major role, the energy flux delivered to the electrodes is also crucial in the process of plasma sterilization.

The 25 mA continuous-wave surface-plasma source of H− ions

The ion source with the Penning geometry of electrodes producing continuous-wave beam of H(-) ions with current up to 25 mA was developed. Several improvements were introduced to increase source intensity, reliability, and lifetime. The collar around the emission aperture increases the electrons filtering. The apertures' diameters of the ion-optical system electrodes were increased to generate the beam with higher intensity. An optimization of electrodes' temperature was performed.

Surface plasma source with saddle antenna radio frequency plasma generator

A prototype RF H(-) surface plasma source (SPS) with saddle (SA) RF antenna is developed which will provide better power efficiency for high pulsed and average current, higher brightness with longer lifetime and higher reliability. Several versions of new plasma generators with small AlN discharge chambers and different antennas and magnetic field configurations were tested in the plasma source test stand. A prototype SA SPS was installed in the Spallation Neutron Source (SNS) ion source test stand with a larger, normal-sized SNS AlN chamber that achieved unanalyzed peak currents of up to 67 mA with an apparent efficiency up to 1.6 mA∕kW. Control experiments with H(-) beam produced by SNS SPS with internal and external antennas were conducted. A new version of the RF triggering plasma gun has been designed. A saddle antenna SPS with water cooling is fabricated for high duty factor testing.

Surface plasma source with anode layer plasma accelerator

Proposed plasma generation system can be used for high current negative ion beam production and for directed deposition by flux of sputtered neutrals and negative ions. The main mechanism of negative ion formation in surface plasma sources is the secondary emission from low work function surface bombarded by a flux of positive ion or neutrals. The emission of negative ions is enhanced significantly by introducing a small amount of cesium or other substance with low ionization potential. In the proposed source are used positive ions generated by Hall drift plasma accelerator (anode layer plasma accelerator or plasma accelerator with insulated channel, with cylindrical or race track configuration of emission slit). The target-emitter is bombarded by the ion beam accelerated in crossed ExB fields. Negative ions are extracted from the target surface with geometrical focusing and are accelerated by negative voltage applied between emitter and plasma, contacting with the plasma accelerator. Hall drift ion source has a special design with a space for passing of the emitted negative ions and sputtered particles through the positive ion source.

Forty years of surface plasma source development

The cesiation effect, a significant enhancement of negative ion emission from a gas discharge with decrease of co-extracted electron current below negative ion current, was observed for the first time on July 1, 1971 by placing into the discharge a compound with 1 mg of cesium. Subsequent developments of surface plasma sources (SPS) for highly efficient negative ion production caused by the interaction of plasma particles with electrodes on which the adsorbed cesium reduced the surface work function are described. In the last 40 years, the intensity of negative ion beams has increased by cesiation up to 10(4) times from 3 mA to tens of amperes. Here, the main attention is concentrated on earlier SPS developments because recent results are well known and widely available.

Features of semiplanotron surface plasma sources

Features of the semiplanotron surface plasma sources (SPS) with cesiation used for high efficient negative ion beam production from first development to modern condition are considered. Design features of semiplanotrons SPS with cylindrical and spherical geometric focusing and the features of the negative ion production in the semiplanotrons are reviewed. Several versions of semiplanotrons with efficiency up to 0.1 A of H(-) per kW of discharge power are discussed. Modifications of the semiplanotrons for dc operation and for heavy negative ion production are reviewed.