Open Trap Research Articles

Mathematical modelling of beam dynamics in diamagnetic confinement regime of open trap

The paper is devoted to the mathematical modelling of a beam injected into an open magnetic trap in the diamagnetic mode. The two-dimensional axially symmetric hybrid numerical model with the kinetic approximation for the ion component of the plasma and the MHD approximation for magnetized electrons is used. In the numerical experiments, the possibility of formation of the cavity in the magnetic field was shown. A detailed study of the evolution of the ion beam continuously injected into the trap is done, the dependencies on time, moment of injection and beam temperature are presented. The obtained results may be used for the data analysis of the laboratory experiments in open magnetic systems.

Formation of Starting Plasma Flow in an Open Trap Using Arc Plasma Gun

Formation of Starting Plasma Flow in an Open Trap Using Arc Plasma Gun

Charge exchange radiation diagnostic with gas jet target for measurement of plasma flow velocity in the linear magnetic trap

The study of longitudinal fluxes of energy and particles is one of the most important fundamental problems in the physics of open magnetic traps. The solution to this problem is the key to the successful implementation of fusion power in linear magnetic systems. The plasma electrostatic ambipolar potential largely determines the physics of longitudinal transport of particles and energy. In this work, we used the spectroscopic method CXRS (Charge eXchange Recombination Spectroscopy) to measure the plasma ion velocity distribution via the analysis of light emitted in this atomic process. The experiments were carried out in the gas dynamic trap (GDT), which is a linear plasma confinement system with an axially symmetric magnetic field configuration. We measured plasma potential and ion temperature of two plasma components: the main (hydrogen and deuterium) and the helium impurity. The paper presents the emission spectra of the lines H-α (656.28 nm) and He-I (667.8 nm). This method was applied for the first time to measure the spatial profile of the ambipolar potential in an open magnetic trap.

Development of fast-ion collective Thomson scattering diagnostics for the GDT experiment

In this paper, we describe hardware developed for the collective Thomson scattering (CTS) diagnostic for the large open magnetic trap GDT (Budker Institute, Russia) used in fusion researches. The diagnostic utilizes 400 kW/54.5 GHz gyrotron as a source of probe radiation and is aimed at the reconstruction of fast ion distributions over transverse and longitudinal velocities driven by high-power neutral beam injection. Formation and manipulation of the probe beam and collection of the scattered microwave radiation are done with large-aperture quasi-optical mirror systems. The receiving complex consists of two identical channels for simultaneous detection of scattering in two complement geometries. Each channel includes a highly sensitive radiometer/spectrum analyzer with the band of 54.470 ± 0.550 GHz, the noise temperature of 0.35 eV, the sensitivity less than 0.025 eV, the frequency/time resolution of 5–50 MHz/10 μs, and narrow-band notch filter providing at least -40 dB rejection in the band of 25 MHz with a central frequency tunable in 54.470 ± 0.050 GHz for protection of the input RF circuit from a backlight of powerful gyrotron radiation.

Recovery of the Two-Dimensional Ion Distribution Function in a Magnetic Mirror from Measurements of Collective Thomson Scattering Spectra

A method is proposed for tomography of the distribution function of energetic ions that are adiabatically trapped in an open magnetic trap, according to the diagnostic data by the method of collective Thomson scattering. This method is based on measurements of the scattering spectra from successive plasma cross sections corresponding to different values of the magnetic-field strength along a single line of force. It is shown that the problem of restoring the ion distribution function in the velocity space from the measurement data in this situation is reduced to an integral equation of the first kind that allows an analytical solution. Several ways to construct exact and approximate solutions of the resulting integral equation are considered.

Long-pulse plasma source for SMOLA helical mirror

A plasma gun for forming a plasma stream in the open magnetic mirror trap with additional helicoidal field SMOLA is described. The plasma gun is an axisymmetric system with a planar circular hot cathode based on lanthanum hexaboride and a hollow copper anode. The two planar coils are located around the plasma source and create a magnetic field of up to 200 mT. The magnetic field forms the magnetron configuration of the discharge and provides a radial electric insulation. The source typically operates with a discharge current of up to 350 A in hydrogen. Plasma parameters in the SMOLA device are Ti ~ 5 eV, Te ~ 5–40 eV and ni ~ (0.1–1) × 1019 m−3. Helium plasma can also be created. The plasma properties depend on the whole group of initial technical parameters: the cathode temperature, the feeding gas flow, the anode-cathode supply voltage and the magnitude of the cathode magnetic insulation.

Spin Squeezing in a Tunneling-Dissipative Bose-Hubbard Dimer

We investigate spin squeezing of a Bose-Einstein condensate in an open symmetrical double-well trap with dissipation in the tunneling process, which can be treated as a tunneling-dissipative Bose-Hubbard dimer. Perturbation technique based on the system is applied. Its shown that more squeezing can be achieved by increasing the tunneling rate and the dissipation.

Performance improvement of particle-in-cell method for numerical modelling of open magnetic system

The work is connected with numerical simulation of plasma dynamics in open magnetic trap in diamagnetic regime. The hybrid particle-in-cell model we develop allows to perform numerical experiments for the high ratio of Larmor radius of the ions and the one of the electrons due to the combining of the kinetic description for the ions and MHD description for the electron plasma component. The disadvantage of the model is the stability condition and the corresponding requirements for the time step. In practice a doubling of the grid nodes in each direction leads to the decrease of the time step x6 times. For the characteristic times of the plasma processes 102 reciprocal ion cyclotron frequencies the computations required few days for grids 100x500. The processing of the particle data takes more than 85% of the total computation time, thus its effective realization yields significant gain in performing. In our algorithm we combine the dynamic load balance and vectorized computations of densities and current densities. We present the results of numerical experiments on its basis including the highly non-uniform particle distribution in the domain and the increasing of the particle number due to the beam injection.

Simulations of fusion neutron source based on the axially symmetric mirror trap for the thorium hybrid reactor

The axially symmetric open mirror trap is considered as a neutron source for the hybrid thorium reactor. Plasma parameters are optimized in order to achieve the maximum neutron yield in the volume surrounded by the subcritical fuel assembly while meeting the stability criteria. For plasma consisting of equal amounts of deuterium and tritium isotopes, in the fuel assembly region, the neutron yield was found to be 0.6 × 1017 n/s at an input power of 20 MW, and it will increase to 2.6 × 1017 n/s if the input power increases two times. In optimal regimes, the plasma parameters were close to those achieved in experiments at the GDT facility.

Граничные условия в источнике электронного пучка на поверхности анодной плазмы со сверхзвуковым потоком ионов

A solution for the one-dimensional Poisson problem for a layer on the surface of a plasma ion emitter is obtained. The case of plasma with a directed ion velocity greater than the ionic sound one is considered. Moreover, the plasma surface is irradiated with an electron beam. As applied to the parameters of deuterium plasma flowing out of a gas dynamic open magnetic trap GDT, a physical model of a layer with boundary conditions on the plasma surface is formulated. It allows a two-dimensional numerical simulation of the source of an electron beam injected into a trap.

Numerical study of diamagnetic regime in open magnetic trap

The article presents a two-dimensional axially symmetric numerical model of a diamagnetic plasma confinement regime in a linear magnetic system as applied to laboratory experiments at the BINP SB RAS, Novosibirsk. The model is based on the kinetic approximation for the ion components of the background plasma and the injected beam. The MHD approximation is used for the electron component, taking into account the mechanisms of energy dissipation due to conductivity and thermal conductivity. The particle-in-cell method is used to solve the Vlasov equation. The dependences of the magnetic field profile and plasma density on the current of the ion beam and its energy are found.

Linear Transformation of Electromagnetic Waves in Large-Scale Axially Symmetric Trap

The results are presented from studies of the efficiency of the quasi-optical wave beam tunneling through the opacity region in the vicinity of the plasma cutoff surface in the inhomogeneous magnetoactive plasma in the geometry corresponding to a large-scale axially symmetric open trap. In this geometry, the distinctive features are considered of the linear transformation of normal waves in two cases: the transformation of the left-handed polarized wave, which is typical of the toroidal traps, and the transformation of the right-handed polarized waves, which is possible when the plasma density gradient is not orthogonal to the magnetic field. Different effects limiting the achievable transformation efficiency are studied, and the possible approaches to the transformation efficiency optimization are considered.

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 .

Hybrid Fusion-Fission System with Neutron Source Based on Deuterium Plasma

Development of hybrid fusion-fission systems appears today as a promising area in practical use of thermonuclear fusion energy. Thermonuclear plasma in such systems is the source of fast neutrons with the power gain factor Q < 1 power amplification factor in plasma. Hybrid system high amplification is generally achieved through nuclear reactions in the subcritical blanket surrounding plasma. Not only power could be produced in such a blanket, but also nuclear fuel, and waste of the nuclear fuel cycle could be disposed. The problem of systems using the thermonuclear reaction between deuterium and tritium lies in the lack of tritium reserves and in the limited possibilities of its production. Therefore, the work considers organization of a fuel cycle based on the deuterium-deuterium reaction. Options of a neutron source based on tokamak and linear system of the open trap type were examined. Magnitude of the socalled hybrid system electrical efficiency (ratio of the system electrical output to the blanket thermal power) was estimated. Calculations demonstrated fundamental possibility of realizing substantial neutron yield from deuterium plasma. To achieve acceptable performance, power gain in thermonuclear plasma should be Q = 0.5--1. In a tokamak of reasonable scale and when working on deuterium, the gain should be Q ~ 0.3. Potential advantages of linear systems associated with the possibility of high-pressure plasma confinement are presented

Collective Thomson scattering diagnostic for the GDT open magnetic trap

In this paper, we propose a collective Thomson scattering (CTS) diagnostic for fast ion measurements for the GDT (gas-dynamic trap) facility at the Budker Institute. The diagnostic utilizes the 54.5 GHz gyrotron usually used for electron cyclotron resonance heating as a source of probe radiation and is aimed at reconstruction of distributions over transverse and longitudinal velocities of NBI-driven ions in the plasma core. Here we present a feasibility study of this concept showing a possibility to receive a strong CTS signal of several hundred eVs for a wide range of GDT parameters. The main limitations come from the refraction of the probe and scattered radiation propagating in inhomogeneous plasma: to provide well-resolved CTS measurements the on-axis plasma density should be kept less than 1.5 · 1013 cm−3 while usual GDT discharges correspond to the density of (0.9 − 1.3)· 1013 cm−3.

Single probe diagnostics for the study of plasma parameters in the expander of an open magnetic trap

Method of plasma potential and electrons mean energy measurement by single Langmuir probe in highly fluctuated plasma of magnetic open trap is described. Diagnostics based on this method allows for two types of measurements: plasma potential in the emission probe mode, as well as current-voltage characteristics of the probe, followed by calculating the plasma potential and the average electron energy. All diagnostic elements, including pulse shape recorders, are fully galvanically isolated. Power supply is provided by battery placed on board of the measuring system. Control and synchronization are realized by means of optical communication lines. This diagnostic design allows measurements relate to plasma electrodes, the potential of which fluctuates with a frequency of up to hundreds of kilohertz.

Parallel Realization of the Hybrid Model Code for Numerical Simulation of Plasma Dynamics

The work is devoted to a parallel realization of a hybrid model for study of plasma dynamics in axially symmetric open magnetic traps. The model is based on MHD approximation for electron component of the plasma and on the kinetic approach for ion component. In the model the particle-in-cells method (PIC) with explicit numerical schemes on staggered grids for the cylindrical coordinate system is applied. The permanent injection of the particles, the long characteristic times, the necessary grid resolution and the conditional stability of the method required development of parallel version of the algorithm. In the parallelization we use the mixed decomposition with static load balancing. We present the parallel algorithm as well as results of the computational experiments on plasma dynamics in regime of diamagnetic confinement in an open magnetic trap.

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.

Method for Studying the Dynamics of Fast Frequency Sweeping Events in the Spectra of Non-Thermal Electromagnetic Plasma Emission

We developed an algorithm for processing of the dynamic spectra of plasma emission, which makes it possible to extract chirped elements with both increasing and decreasing frequencies. The algorithm was tested on a set of experimental data obtained by studying the emission spectra of the rarefied plasma of an electron cyclotron resonant discharge in an open magnetic trap. The efficiency of the method is close to 100% for signals with a signal-to-noise ratio of more than 30 dB and about 50% with a signal-to-noise ratio of 20 dB. This method can be used for automated analysis of dynamic emission spectra of both laboratory and space plasmas.

Nonlinear Interaction of Microwave Radiation with a Plasma Flow under Hybrid Resonance Conditions

We propose a simple model of quasi-one-dimensional steady-state nonequilibrium plasma flow propagating along the axis of an open magnetic trap and sustained by an rf electromagnetic field. The model makes it possible to analyze qualitatively possible regimes of the plasma flow in the presence of induced intrinsic rf field amplified due to geometrical resonance with the plasma flow and to determine the main features and key characteristics of nonlinear absorption of the external field energy.