Electron Cyclotron Resonance Discharge Research Articles

Design of the electron cyclotron resonance (ECR) plasma source for the space plasma environment research facility.

The Space Plasma Environment Research Facility (SPERF) was built in Harbin to study the three-dimensional magnetic reconnection and wave-particle interactions relevant to space physics in laboratory settings. A 2.45GHz Electron Cyclotron Resonance (ECR) plasma source is adopted in the device to simulate the Earth's magnetosphere and achieve the scientific goals. In this paper, the design of the ECR plasma source is presented. The structures of the microwave source, the microwave transfer system, and the antenna are introduced. Additionally, the resonant surfaces are computed to predict the locations of microwave absorption. The absorption mechanisms of the microwave in the SPERF are also discussed. The discharge experiment demonstrates the utility of the ECR source in simulating the Earth's magnetosphere. The successful operation of the source indicates that the ECR discharge is a powerful tool for creating a plasma environment in a large plasma experimental device.

On matching a microwave radiation with the plasma of an electron cyclotron resonance discharge

This article proposes a scheme for matching microwave radiation with a magnetized plasma of an electron cyclotron resonance (ECR) discharge in an open magnetic trap, using the effect of depolarization—the transformation of the ordinary wave into the extraordinary one upon reflection from the metal walls of a plasma chamber. An analysis of the efficiency of such a transformation is carried out, and it is shown that for grazing (less than 15° with metal surface) angles of incidence; it is possible to achieve an efficiency exceeding 90%.

Self-mode transition, oscillation and inverse hysteresis in ECR discharges

Positive and negative feedback of microwave (MW) ECR (electron cyclotron resonance) discharges in cross magnetic field were manipulated by a three-stub coaxial tuner. Unstable ECR discharges in the positive feedback region, such as the self-mode transition between the ordinary (O)-wave mode and extraordinary (X) one, inverse hysteresis, and oscillation, were investigated using a time-resolved MW power meter, high speed camera, and thermocouple. In the positive feedback region, the self-O → X wave mode discharge transition can be driven under the “hot” wall condition, while the counterpart, namely the self-X → O wave mode transition, is observable for the “cold” wall; the inverse hysteresis and oscillation take place at low and moderate gas flow rates, respectively. The mechanism underlying the self-mode transitions and instabilities is the discharge shift due to the gas heating effect. For MW ECR discharges to become stable, as indicated in previous experiments, they should be mismatched in the negative feedback region.

Effects of magnetic field configurations on the minimized ECR ion thrusters for micro-Newton and wide-range operations

Space-based gravitational wave detection missions require precise thrusts over a wide-range of 1–100 μN. In this study, the axial ring-cusp magnetic field configuration is used to design a miniature electron cyclotron resonance ion thruster with a radius of 5 mm. Two typical configurations, i.e., open-type and closed-type, are compared in terms of electron density, electron temperature, and thrust for micro-Newton and wide-range operations. The results show that the open-type achieves high performances owing to the high efficiency of absorption of input microwave power. The lower limit of the mass flow rate in the electron cyclotron resonance (ECR) discharge is expanded to a very low value of 3 × 10−2 sccm to achieve 1 μN in the open-type. The thrust in the open-type could be tuned in a wide-range of 1–119 μN, meeting the requirement.

Critical behavior near the instability threshold of an electron cyclotron maser formed in a mirror magnetic trap.

High-power electron cyclotron resonance discharge in a laboratory open trap is frequently accompanied by growth of electron cyclotron instabilities. We study a simple universal model that explains some of the stability conditions of such plasma observed experimentally, in particular, its crucial dependence on localization of the rf power deposition zone with respect to a minimum of B. An instability threshold seems to be sensitive to particular details of electron losses in a velocity space. Comparing theoretical predictions for the threshold condition with available measurements sheds light on a structure of fast-electron losses in ongoing experiments.

Vacuum Ultraviolet Emission from a Plasma of Continuous Electron Cyclotron Resonance Discharge

Vacuum Ultraviolet Emission from a Plasma of Continuous Electron Cyclotron Resonance Discharge

Probe experiment on basic plasma parameter investigation in a quasi-gasdynamic ion source GISMO

Plasma parameters in a 28 GHz gasdynamic continuous electron cyclotron resonance discharge (ECR) with a high volumetric energy input were investigated with a Langmuir probe. The knowledge of the dependencies of plasma density and temperature on external parameters is useful for tuning the ECR source to the desired mode of operation. The design features of the plasma chamber and the configuration of the magnetic field made it possible to use the approximation a non-magnetized flat probe to calculate the temperature and electron density at various gas pressures and power of the heating microwave. A movable tungsten probe was used, allowing for studying plasma parameters along the magnetic field at various distances from the plasma electrode. At high powers, the electron density in the plug turned out to be close to the cutoff density (about 10 13 cm − 3). A fraction of warm ( > 30 eV) electrons, appearing at high powers, was found, which explains the formation of a pure proton beam in a number of experiments at the same facility. The abrupt increase in the temperature of the warm fraction with power was also found, which makes it of great interest to perform experiments on a multi-charged ions production in heavy gases.

Complex of Facilities for Studying Interaction of Hydrogen Isotopes with Materials

In the National Research Center “Kurchatov Institute,” a complex of laboratory facilities was created for studying experimentally the interaction of hydrogen isotopes with materials. The complex includes equipment for sample preparation, facilities for plasma irradiation using distributed electron cyclotron resonance and helicon discharges, facilities for plasma-driven and gas-driven permeation measurements, a setup for thermal desorption analysis, and a multipurpose laboratory facility for solving a variety of short-term tasks. The teams of each experimental facility include students. Students of the third and fourth years from several technical universities come to the laboratory complex as interns. Depending on their personal abilities and preferences, the students are involved in different engineering, experimental, and theoretical tasks. After getting master’s degrees, the most motivated and gifted students continue their education as PhD students and work in experimental teams.

Kinetic whistler instability in a mirror-confined plasma of a continuous ECR ion source

Kinetic instabilities in a dense plasma of a continuous electron cyclotron resonance (ECR) discharge in a mirror magnetic trap at the Gasdynamic Ion Source for Multipurpose Operation (GISMO) setup are studied. We experimentally define unstable regimes and corresponding plasma parameters, where the excitation of electromagnetic emission is observed, accompanied by the precipitation of energetic electrons from the magnetic trap. A comprehensive experimental study of the precipitating electron energy distribution and plasma electromagnetic emission spectra, together with theoretical estimates of the cyclotron instability increment proves that under the experimental conditions, the observed instability is related to the excitation of whistler-mode waves, which are a driver of losses of energetic electrons from the magnetic trap. The results of this study are important for the further development of the GISMO electron cyclotron resonance ion source facility and for the improvement of its parameters as an ion source. Also, this research on plasma kinetic instabilities is of fundamental interest and provides experimental tools to simultaneously study plasma electromagnetic activity and corresponding changes in a resonant electron energy distribution.

Numerical simulation of magnetic field and channel configuration effect on cusped field thruster with electron cyclotron resonance discharge enhancement

Cusped field thrusters with electron cyclotron resonance discharge enhancement have great potential in micro-Newton propulsion field. According to the magnetic field and channel configuration, the thruster can be divided into 1-stage thruster, 2-stage thruster and 3-stage thruster. The ionization region and acceleration region of the 1-stage thruster are located at the channel upstream, which causes a large amount of wall power deposition, resulting in poor performance. Due to the shorter channel of the 2-stage thruster, it is easier for electrons to reach the ECR layer on the near-antenna region to obtain energy to promote ionization, compared with 3-stage thruster. In addition, the magnetic cusp number of the 2-stage thruster wall is lower than that of the 3-stage thruster, reducing the total wall power deposition. It is necessary to use 2-stage short channel configuration to design the thruster.

Foundations of magnetized radio-frequency discharges

This is the second part of a set of two papers on radio-frequency (RF) discharges, part of a larger series on the foundations of plasma and discharge physics. In the first paper (Chabert et al 2021 Plasma Sources Sci. Technol. 30 024001) the two basic configurations of RF discharges commonly used in industrial applications, the capacitive and the inductive discharges, are presented. The introduction of an external magnetic field to these discharges results in not only a quantitative enhancement of their capabilities but also leads to qualitatively different interaction mechanisms between the RF field and the plasma. This provides rich opportunities for sustaining dense plasmas with high degrees of ionization. On one hand, the magnetic field influences significantly the particle and energy transport, thus providing new possibilities for control and adjustment of the plasma parameters and opening even lower operation pressure windows. On the other hand, when the magnetic field is introduced also in the region where the plasma interacts with the RF field, qualitatively new phenomena arise, that fundamentally change the mechanisms of power coupling to the plasma—the electromagnetic energy can be transported as waves deeper into the plasma volume and/or collisionlessly absorbed there by wave resonances. The characteristics of these discharges are then substantially different from the ones of the standard non-magnetized RF discharges. This paper introduces the physical phenomena needed for understanding these plasmas, as well as presents the discharge configurations most commonly used in applications and research. Firstly, the transport of particles and energy as well as the theory of waves in magnetized plasmas are briefly presented together with some applications for diagnostic purposes. Based on that the leading principles of RF heating in a magnetic field are introduced. The operation and the applications of various discharges using these principles (RF magnetron, helicon, electron cyclotron resonance and neutral loop discharges) are presented. The influence of a static magnetic field on standard capacitive and inductive discharges is also briefly presented and discussed.

Diagnostics of hot electrons leaving the ECR plasma sustained by the high-power gyrotron

Energy distribution of electrons in the electron-cyclotron resonance (ECR) discharge has a complicated shape as a function of various parameters that still remains unknown. Meanwhile, it is an important plasma characteristic. There are some methods and approaches, which give the possibility to measure or estimate the properties of the distribution. One of them, similar to the ion mass spectrometry [1], was used in this work to obtain the energy distribution of electrons escaping the magnetic confinement in the non-classical continuous ECR ion source with high (up to 50–100 W/cm3) specific energy input along with bremsstrahlung spectra. A threshold-like behaviour was discovered, which comprised of the bursts of energetic electrons, bremsstrahlung and, supposedly, the development of kinetic instabilities, once the energy input exceeds a certain level.

High power vacuum ultraviolet source based on gasdynamic ECR plasma

We report experimental results of vacuum ultraviolet (VUV) emission from the plasma of an electron cyclotron resonance (ECR) discharge in hydrogen, sustained by millimeter-wavelength radiation of a gyrotron. The considered discharge is characterized with the high plasma density (1013 cm−3 order of magnitude) and, at the same time, the high electron average energy (10–300 eV), which makes it possible to significantly increase the efficiency of VUV re-emission of the energy deposited into the plasma by the microwave radiation. Experiments were performed with the plasma confined in a simple mirror trap and heated by pulsed gyrotron radiation of 37.5 GHz/100 kW under the ECR condition. The measured volumetric VUV emission power of Lyman-alpha line (122 10 nm) overlapping with the Werner band, Lyman band (160 10 nm), and molecular continuum (180 20 nm) reached 45, 25, and 55 W/cm3, respectively. The total absolute radiation power in these three ranges integrated over the plasma volume is estimated to be 22 kW, i.e., 22% of the incident microwave power, which matches theoretical predictions. The development of effective technological VUV sources of a kilowatt power level is expected to be the next step following the optimization of the conditions of the ECR hydrogen discharge sustained by powerful gyrotron radiation.

Effects of gas adsorbed on solid surface during gas breakdown in electron cyclotron resonance discharges

The microwave breakdown power (P wb) in an ECR plasma source was not merely determined by pressure (gas flow rate), but found to vary with the time interval between two successive breakdowns. The measured P wb dropped rapidly from a high value at a short time interval to a low level at a long time interval. The obtained dependence of P wb on pressure (gas flow rate) exhibited distinct features: the normal monotonicity and abnormal non-monotonicity at the short and long time intervals, respectively. The effective zone in the antenna’s surface, bombarded by hot electrons heated in the ECR layer, was validated by (1) masking the antenna with a film having a variable radius; (2) calculating the distribution of the vertical component of the microwave electric field with respect to the static magnetic field; and (3) imaging glows of transient breakdown discharges with a fast camera. The reduction in P wb was mainly attributed to the enhanced emission of δ-electrons from the gas-adsorbed antenna under the bombardment of energetic electrons coming from the ECR layer. The correlation between the dynamic gas coverage and the emission coefficient of δ-electrons was established to understand the abnormal ECR breakdown features.

Comparative analysis of the plasma parameters of ECR and combined ECR + RF discharges in the TOMAS plasma facility

The toroidal magnetized system (TOMAS) plasma facility aims at complementary research on wall conditioning methods, plasma production and plasma–surface interaction studies. This paper explores for the first time the parameters in helium electron-cyclotron resonance (ECR) plasma and combined ECR + radio-frequency (RF) discharges in TOMAS. The ECR discharge in this work, at 2.45 GHz and 87.6 mT, is the main one for creating and maintaining the plasma, while the addition of RF power at 25 MHz allows to broaden the achievable electron temperature and density at a given gas flow, as evidenced by triple Langmuir probe measurements. This effect of the combined ECR + RF discharge provides flexibility to study particular aspects of wall conditioning techniques relevant to larger devices, or to approach plasma conditions relevant to fusion edge plasmas for particular surface interaction studies.

Characterization of the combination of microwave and laser ablation plasmas

The main aim of the present work is to report on the study of the combination of continuous plasma, formed by a microwave electron cyclotron resonance (ECR) discharge and the pulsed plasma obtained by the laser ablation of a solid target. Such arrangement allows studying the formation of materials in the form of thin films making use of the relatively high densities of the microwave discharge and the wide range of ion energies produced in the pulsed laser ablation plasmas. With this arrangement it is possible to deposit thin films of materials that in the usual microwave discharge require the use of dangerous and corrosive substances, as the required element is obtained from a pure solid target. Moreover, as the laser ablation process is carried out in plasma as the background gas, instead of a neutral gas, the presence of contaminants, such as oxygen can be significantly reduced. For the purpose of the present paper a nitrogen microwave ECR discharge was combined with the plasma created during the ablation of an aluminum target, in order to deposit AlN thin films. Plasma parameters were measured by a Langmuir probe, and the chemical species contained in the plasma were analyzed by optical emission spectroscopy (OES). The optical properties and chemical composition of the AlN thin films are reported.

Electron cyclotron resonance discharge enhancement in a cusped field thruster

Electron cyclotron resonance (ECR) is induced to enhance the discharging performance of a cusped field thruster, by feeding microwave into the channel. Due to a critical combination of ECR discharge and DC discharge, propellant utilization is significantly improved, with varying degrees of impact on other parameters. The DC mode, the ECR mode and the combined mode are achieved and analyzed respectively. A Faraday probe and a retarding potential analyzer are employed to diagnose the plume plasma, and approximate calculated thrust is given. Moreover, high frequency electric field simulation is carried out to indicate the microwave feeding process in different mass flow rate conditions, making use of a particle-in-cell simulation result. The result shows that the ECR enhancement is particularly effectual in low mass flow conditions, and the special plasma distribution in the cusped magnetic field leads to the propellant utilization trend in the combined mode.

Status of a point-like neutron generator development

In this paper we report on a high current density ion beam profile diagnostics with a slit-based system as a reliable method, capable of high thermal load applications. The task arose in frames of a point-like neutron source development for neutron radiography. In previous research, it was suggested to construct such a system as a D-D neutron generator based on the high current gasdynamic ion source, which utilises the plasma of electron cyclotron resonance discharge sustained by powerful millimeter wave gyrotron radiation. This device is able to produce focused D+ beams with a characteristic diameter of 1 mm, total current above 100 mA, and current density at a level of several A/cm2. Study of such intense beams profile to obtain the best focusing efficiency and minimize neutron producing area appeared to be a challenging task. The paper also demonstrates the possibility of fast neutron imaging with a point-like powerful neutron generator (neutron yield on the level of 1010 s−1).

Electron loss mechanisms in a miniature microwave discharge water neutralizer

This study analyzes the mechanism of electron loss at the discharge chamber wall of a microwave discharge neutralizer via three-dimensional particle-in-cell simulations with Monte Carlo collisions (PIC–MCCs). The neutralizer employs electron cyclotron resonance discharges with two ring-shaped permanent magnets and 4.2-GHz microwaves, where the plasma is confined by a magnetic mirror. The PIC–MCC simulation results show that the electron extraction efficiency of a water neutralizer can be increased by two times in an optimized magnetic field configuration, which is a higher increased rate than that of a xenon neutralizer. However, the efficiency of 20% is still low (e.g., less than half of the xenon one) because many electrons are lost to the magnet surface. The loss is determined to be due to approximately 5-times higher ratio of electrons inside the loss cone in the water neutralizer than that in the xenon neutralizer. The electron velocity distributions of each neutralizer clearly show that the water neutralizer has a larger fraction of electrons parallel to the magnetic field than the xenon neutralizer. This result is attributed to the large number of electron collisions in the water neutralizer owing to the high neutral gas pressure.

A novel technique for plasma diagnostics benchmarked by numerical simulations

Auxiliary electrons can be successfully used as a diagnostic probe to deduce characteristics and dynamics of magnetically confined plasmas typical of Electron Cyclotron Resonance and Microwave Discharge Ion Sources, as well as to improve their performances and/or stability. To this scope, numerical simulations are a powerful tool to predict the effect of the interaction of an electron beam with the plasma: this paper presents an alternative way to deduce the plasma density by joining the results of numerical simulations with the diagnostic of the beam transmitted through the plasma. As will be shown, the applied numerical code is able to describe the dynamics of an electron beam, generated by an e-gun, propagating inside a plasma trap, with a magnetic configuration typical of microwave discharge ion sources, focusing on several effects such as ionizations, heating, space charge etc. The role played by the position of the e-guns with respect to the magnetic field profile will be also underlined.