Mirror Trap Research Articles

Deuterium ion beam focusing for the point neutron source development

This work is a continuation of the studies on the point neutron source development. In the neutron source scheme proposed, neutron emission occurs in a relatively small region (less than 1 mm) as a result of the D–D fusion reaction initiated when the focused deuterium ion beam hits the deuterium-loaded target. The main goal of the project is to develop a simple and compact device that can be used in the high-quality fast neutron radiography. In the scheme proposed, the ion beam is extracted from the dense ECR discharge plasma that is confined in the simple magnetic mirror trap. After upgrading the extraction system and the magnetic lens, the deuterium ion beam with a total current in the focal plane of up to 150 mA was obtained, which considerably exceeds the current obtained previously. The numerical simulations of the beam magnetic focusing were performed using the IBSimu code and the results were compared to the experimental data.

Terrella for advanced undergraduate laboratory

A terrella developed for the undergraduate Advanced Laboratory course in the University of Wisconsin-Madison Physics Department is described. Our terrella consists of a permanent magnet, mounted on a pedestal in a vacuum chamber, surrounded by electrodes that may be biased in various ways. The system can confine a plasma, which may, in some ways, be considered as a toy model of the plasma confined in the Earth's magnetosphere. Our axisymmetric plasma forms in a region where the magnitude of the magnetic field B is 14 G ≤B≤ 550 G; for typical operation, the neutral gas pressure is p∼10−4 Torr. The plasma is created by thermionic emission from a hot filament. Available diagnostics are a swept Langmuir probe, a spectroscopic fiber and visible-wavelength spectrometer, and visible imaging. In two four-hour laboratory sessions, students are guided through vacuum pumpdown, connection of electrical circuits, establishment of plasma, acquisition of data, analysis of data, and critique of data. In this paper, we present student measurements of radial profiles of electron temperature Te and density ne as well as imaging of mirror trapping and ∇B drift and curvature drift. We conclude by outlining some opportunities for additional terrella-based student experiments.

Measurements of axial energy loss from magnetic mirror trap

The work represents a next step in studies of longitudinal energy losses from linear magnetic plasma confinement devices. The paper describes the experimental technique that has been developed and used to measure the absolute values of longitudinal particle and energy density fluxes from an open magnetic mirror trap. Using this technique, it was possible to measure and account for the secondary electron emission coefficient from plasma-facing end plate, and perform a comparison with the existing theory of energy confinement in open traps. It is shown that the average energy transported by an ion-electron pair leaving the trap is close to theoretically predicted minimum value of 6–8 electron temperatures. As confirmed by the measured dependencies, this conclusion is valid in a broad range of parameters and the threshold value of the magnetic expansion ratio does not exceed its theoretically predicted minimum of .

Self, other and individuation: resolving narcissism through the lunar and solar paths of the Rosarium.

This paper describes narcissism as our natural, infant-like behaviour, and specifies three characteristics relating to the evacuation and avoidance of distress, to control, and to distancing from relationship. It suggests that the processes of incarnation and individuation represent the development of the early ego and the 'resolution' of these narcissistic ways of being, including escape from the 'mirror trap'. The development of the early, controlling 'homunculus-ego' entails the loosening and broadening of ego-identifications and the ego becoming subject to the Self. This is an embodied-relational-social-spiritual process outlined in detail by the full 20 woodcuts of the Rosarium Philosophorum, and specifically the lunar (relational) and solar (self-expressive) paths, which are explored herein. These processes are illustrated with respect to the interaction between infant and caregiver, clinical vignettes and examples from the political sphere.

Investigation of ion acceleration effect influence on formation of ambipolar potential profile in the expander region.

This paper presents a study of plasma flux characteristics flowing out from the gas-dynamic mirror trap along the magnetic field lines to a metal wall. The main feature of the current work is that the effect of ion acceleration by ambipolar potential is considered in the expander region. The developed model also takes into account a possibility of transition from the collisional expansion of electron flow in the vicinity of the magnetic plug to the collisionless regime. The developed model allows calculation of the ambipolar potential profile and plasma characteristics in the expander region.

The features of the characteristic electromagnetic plasma bunches oscillations in the long magnetic mirror

The aim of this work was to study the spectrum of LF and HF oscillations generated by plasma bunches created and confined in the volume of a microwave cavity immersed in the magnetic field of a mirror trap. The registration of electrostatic oscillations in the plasma was carried out using two flat electrodes mounted diametrically opposite in the central part of the cavity close to its wall. This diagnostic showed the presence of low-frequency oscillations with frequencies of 130 kHz and 450 kHz. The oscillation spectrum in the microwave range was recorded at the minimum of the magnetic trap using a real-time spectrometer and a loosely coupled loop antenna. The registration of the spectra in the 40 MHz band revealed a regular change in the frequency of the fundamental oscillation mode of the cavity and the presence of two harmonics of the synchrotron radiation of the plasma bunch at frequencies of 2.25 GHz and 4.52 GHz, respectively. According to the obtained data, the parameters of the formed bunch (density, shape, volume, energy spectra of plasma components) can be restored.

Status of the gasdynamic ion source for multipurpose operation (GISMO) development at IAP RAS.

A new experimental facility named GISMO (Gasdynamic Ion Source for Multipurpose Operation) was constructed at the IAP RAS to continue investigations in the field of gasdynamic ion sources. The source utilizes 28 GHz/10 kW gyrotron radiation for heating magnetically confined plasma. Magnetic field configuration provided by a fully permanent magnet system is much like a simple mirror trap. The GISMO source is aimed at the production of bright ion beams with hundreds of milliamperes current. The facility has been tested for continuous-wave (CW) operation with 2 kW of heating power to check durability of a microwave injection system and the plasma chamber. A 2-electrode extraction system with an integrated Einzel lens was designed for a formation of CW high current beam with up to 100 kV accelerating voltage. The first results on ion beam production at GISMO are presented together with the general progress status of the facility.

The Use of Streak Photography, X-Ray Radiography, and Radiometric and Spectrometric Measurements to Study Plasma Bunches Generated under Gyroresonant Interactions

Results of experimental studies of relativistic plasma bunches obtained under gyromagnetic autoresonance (GA) and confined in a magnetic mirror trap are provided. The main attention is paid to observations of the radiation generated by plasma bunches at different stages of their lives in different spectral ranges using streak photography and X-ray imaging techniques. The original method of accounting for the instrument function in X-ray spectroscopic analysis and radiometric measurements is applied within the quantum energy range of 0.2–2 MeV to take account of considerable distortion caused by the Compton scattering in the detector.

Parameters of plasma bunches generated in a long mirror trap under conditions of gyromagnetic autoresonance

Temporal evolution of the spectrum and intensity of bremsstrahlung generated by the plasma bunches formed in a symmetric long mirror trap under conditions of gyromagnetic autoresonance was studied experimentally in detail. Bremsstrahlung was detected by two identical detectors installed in the axial and radial directions with respect to the stationary magnetic field. The results show that the radiation is spatially inhomogeneous. The parameters of the spectra measured in the radial direction strongly depend on the amplitude of the pulsed magnetic field, while the spectra measured in the longitudinal direction are determined mainly by the ECR conditions in the phase of filling the trap with the primary plasma. The integrated intensities, obtained with allowance for the refined form factors of the generated bunches recorded using the high-speed photochronography, made it possible to determine the number of primary plasma particles trapped in the autoresonance mode.

Computer simulation of diamagnetic regime in open magnetic trap

Preliminary results of numerical simulation of transition to regime of diamagnetic confinement in an axially-symmetric mirror trap are presented. Author’s two-dimensional modification of hybrid Particle-in-Cell model is used in the simulations. Formation of region with hot dense plasma and very small magnetic field is demonstrated. Evolution of plasma and magnetic field, as well as structure of the formed region are discussed and compared with simple analytical estimations.

Time resolved X-ray emission diagnostics in an axis-symmetric simple mirror trap

Time resolved characterization of plasma X-ray emission represents an innovative technique to characterize non-equilibrium phases in Electron Cyclotron Resonance Ion Sources (ECRIS). Indeed, although ECRIS plasmas are usually in dynamical equilibrium, many relevant phenomena are characterized by fast transients and require a dedicated diagnostics to be fully investigated. In particular, time resolved diagnostics can be applied to characterize the X ray emission during the plasma turn on and off and during the turbulence phenomena induced by Cyclotron-Maser instability. This paper presents the experimental set-up used during the last campaign at measurement carried out at the Istituto Nazionale Fisica Nucleare -Laboratori Nazionali del Sud (INFN-LNS), together with the main achieved results. Particular relevance will be given to the characterization of the afterglow phase, which highlighted the existence of two electron populations characterized by different mean lifetime. Evidences of X-ray bursts emission in the afterglow phase, compatible with Cyclotron Maser instability, will be also shown.

An arbitrary order time-stepping algorithm for tracking particles in inhomogeneous magnetic fields

The Lorentz equations describe the motion of electrically charged particles in electric and magnetic fields and are used widely in plasma physics. The most popular numerical algorithm for solving them is the Boris method, a variant of the Störmer-Verlet algorithm. Boris method is phase space volume conserving and simulated particles typically remain near the correct trajectory. However, it is only second order accurate. Therefore, in scenarios where it is not enough to know that a particle stays on the right trajectory but one needs to know where on the trajectory the particle is at a given time, Boris method requires very small time steps to deliver accurate phase information, making it computationally expensive. We derive an improved version of the high-order Boris spectral deferred correction algorithm (Boris-SDC) by adopting a convergence acceleration strategy for second order problems based on the Generalised Minimum Residual (GMRES) method. Our new algorithm is easy to implement as it still relies on the standard Boris method. Like Boris-SDC it can deliver arbitrary order of accuracy through simple changes of runtime parameter but possesses better long-term energy stability. We demonstrate for two examples, a magnetic mirror trap and the Solev'ev equilibrium, that the new method can deliver better accuracy at lower computational cost compared to the standard Boris method. While our examples are motivated by tracking ions in the magnetic field of a nuclear fusion reactor, the introduced algorithm can potentially deliver similar improvements in efficiency for other applications.

Effect of ion acceleration on a plasma potential profile formed in the expander of a mirror trap

We consider a flow of completely ionized magnetized plasma streaming along divergent magnetic field lines from an open magnetic trap. An analytical model is proposed that takes into account a transition from a collisional (fluid) regime to a collisionless kinetic regime as the flow expands. This allows for study of the formation of a plasma potential along the magnetic field and the acceleration of ions in a self-consistent way. We show that ion acceleration may influence the potential profile; in particular, it significantly reduces the potential gap inside the Debye sheath near the plasma collector. This positive effect predicts low arcing in plasma absorbing units, which is important for all large-scale fusion-aimed experiments in mirror machines. Applications of the theory to smaller table-top machines are also considered.

Highly efficient electromagnetic emission during 100 keV electron beam relaxation in a thin magnetized plasma

In this paper, electromagnetic emissions produced by a beam-plasma system are investigated using particle-in-cell simulations for the particular case when the typical transverse size of both the 100 keV electron beam and the produced plasma channel is comparable to the radiation wavelength. The interest in this regime of beam-plasma interaction is associated with highly efficient generation of electromagnetic waves near the plasma frequency harmonics that has been recently observed in laboratory experiments on the GOL-3 mirror trap. It has been found that the radiation power only from the vicinity of the doubled plasma frequency in these experiments can reach 1% of the total beam power. Subsequent theoretical and simulation studies have shown that the most likely candidate for explaining such efficient generation of electromagnetic radiation is the mechanism of a beam-driven plasma antenna based on the conversion of the most unstable plasma oscillations on a longitudinal density modulation of plasma ions. In this paper, we investigate how effectively this mechanism can work in a real experiment at the GOL-3 facility, when a thin subrelativistic electron beam gets a large angular spread due to compression by a magnetic field, and the gas into which it is injected has macroscopic density gradients.

Multidiagnostics investigation of the role of the magnetic field profile in a simple mirror trap

The impact of the magnetic field profile on the operations of plasma-based Electron Cyclotron Resonance Ion Sources (ECRIS) has been debated and investigated for a long time, and a summary is given by the collection of the so-called ``magnetic scaling laws'', i.e., some rules-of-thumb providing the optimal configuration of the axial and radial confining magnetic fields. Anyway, the optimal configurations have been found just looking at the output beam currents and charge states. Only recently, more advanced experiments have shown that the optimal performances are related to some ``islands in the parameters space leading to a dense, energetic but stable plasma. A general, systematic characterization of plasma density and temperature as a function of the magnetic scaling, and for different energy domains (i.e., for cold, warm, and hot electrons) is not yet available. This paper presents a multidiagnostics characterization of a hydrogen plasma heated by microwaves at around 6.8 GHz via Electron Cyclotron Resonance, and confined in an axisymmetric simple mirror magnetic trap. Investigation of plasma response to solely the axial field profile gives the unique opportunity to decouple the effect of simple mirror field from the radial components that are, usually, provided by a hexapole. Optical emission spectroscopy, Langmuir probe, and an x-ray silicon drift detector were simultaneously used to evaluate the plasma density and temperature in different energy domains, thus exploring the electron energy distribution function from a few eV to hundreds of keV. Plasma parameters have been measured as a function of the magnetic field profile (in particular by varying the ratio ${B}_{\mathrm{min}}/{B}_{\mathrm{ECR}}$), of the microwave power and of the neutral pressure. Furthermore, for the same scaling, the relative abundances of $H$ atoms and ${H}_{2}$ have been estimated. Data show smooth trends of electron density and temperatures versus microwave power and neutral pressure, but strong and even nonlinear responses as a function of the magnetic field profile variation, allowing us to connect semiempirical scaling laws to changes in plasma parameters.

Second harmonic electromagnetic emission in a beam-driven plasma antenna

Generation of electromagnetic (EM) radiation near the second harmonic of the plasma frequency during the injection of an electron beam into a rippled-density plasma channel is investigated using both analytical theory and particle-in-cell simulations. The generating scheme is based on nonlinear interaction of the most unstable beam-driven potential plasma wave with its satellite arising due to scattering on the longitudinal modulation of plasma density. Resulting superluminal oscillations of electric current in a finite-size plasma channel radiate EM waves via the same mechanism which has been recently studied for the fundamental harmonic emission and reffered as a beam-driven plasma antenna. It is shown that theoretical predictions for the optimal plasma width and modulation period are confirmed by simulation results and the power conversion efficiency of the second harmonic emission reaches several percent. Such an efficient mechanism opens the path to explanation of laboratory experiments with a thin electron beam at the GOL-3 mirror trap as well as to developing the scheme of terahertz generation at the gigawatt power level.

Gasdynamic ECR ion source for negative ion production

H− ion sources are needed in various areas of accelerator technology, such as beam injection into cyclotrons and storage rings and as a part of neutral beam injectors for plasma heating in experimental facilities studying thermonuclear fusion. It was recently demonstrated that gasdynamic ion source based on ECR discharge in a simple mirror trap is very efficient for proton beam production [1]. Here we use the gasdynamic plasma source as the first stage driver of volumetric negative ion production through dissociative electron attachment (DEA) [2]. Experiments were performed with a pulsed 37 GHz / up to 100 kW gyrotron radiation in a dual-trap magnetic system, which consists of two identical simple mirror traps. The first trap was used for the plasma production under ECR condition. Dense hydrogen plasma flux from the first trap flows into the second trap through a perforated plate, which prevented the propagation of microwaves into the second one. The configuration helps to separate plasma volumes with “hot” and “cold” electrons. We present recent experimental results on this topic. A negative ion current density of 80 mA/cm2 through 1 mm plasma electrode was demonstrated.

Ion losses induced by Alfvén ion-cyclotron instability in mirror machine with skew neutral beam injection

The dynamic of ions in an axisymmetric mirror cell with a perturbed field is investigated. The spatial distribution of the perturbation was found in the framework of an analysis of the linear stage of the Alfvén ion cyclotron instability in a mirror trap with skew neutral beam injection. It is demonstrated that unstable perturbations do not cause losses of ions with maximal energy driving the instability. Main anomalous losses are longitudinal losses of ions with low transversal energy due to stochastic diffusion by the magnetic moment.

Study of the influence of magnetic field profile on plasma parameters in a simple mirror trap

This work presents the multiple diagnostics characterization of the plasma in an axis-symmetric simple mirror trap as a function of magnetic field profile (mirror ratios and magnetic field gradient), especially in the quasi-flat B field configuration that is typical of Microwave Discharge Ion Sources, and also of neutral gas pressure and microwave power. The simultaneous use of Optical Emission Spectroscopy, Langmuir Probe and X-ray diagnostics allows the characterization of the whole electron energy distribution function (EEDF), from a few eV to hundreds of keV . Results show non-linear behaviour under small variations of even one source parameter and strong influence on EEDF of the Bmin/BECR ratio. Benefit and next developments will be highlighted.

Plasma losses from mirror trap, initiated by microwave radiation under electron cyclotron resonance conditions

Plasma of a stationary electron cyclotron resonance (ECR) discharge sustained by gyrotron radiation at a frequency of 24 GHz and a power of up to 300 W in a mirror magnetic trap was studied. At pressures near the gas breakdown threshold, the extinction effect of an electron cyclotron discharge is observed with increasing radiation power. When the cyclotron resonance cross-section approaches the magnetic plug, the power threshold corresponding to the discharge extinction decreases. These experimental results confirm the presence of the effect of particles precipitation from the trap as a result of ECR interaction with gyrotron radiation. The experimental scaling of the extinction power dependence on the position of the ECR cross-section in a magnetic trap corresponds to the results of the estimates on the basis of the theory of particle precipitation in the quasilinear diffusion regime.