Field-reversed Configuration Confinement Research Articles

A numerical survey of parameters to reach ignition condition for axial compression of a large-sized field reversed configuration

Field reversed configuration (FRC) is widely considered as an ideal target plasma for magneto-inertial fusion. However, its confinement and stability, both proportional to the radius, will deteriorate inevitably during radial compression. Hence, we propose a new fusion approach based on axial compression of a large-sized FRC. The axial compression can be made by plasma jets or plasmoids converging onto the axial ends of the FRC. The parameter space that can reach the ignition condition while preserving the FRC’s overall quality is studied using a numerical model based on different FRC confinement scalings. It is found that ignition is possible for a large FRC that can be achieved with the current FRC formation techniques if compression ratio is greater than 50. A more realistic compression is to combine axial with moderate radial compression, which is also presented and calculated in this work.

Formation of hot, stable, long-lived field-reversed configuration plasmas on the C-2W device

TAE Technologies’ research is devoted to producing high temperature, stable, long-lived field-reversed configuration (FRC) plasmas by neutral-beam injection (NBI) and edge biasing/control. The newly constructed C-2W experimental device (also called ‘Norman’) is the world’s largest compact-toroid (CT) device, which has several key upgrades from the preceding C-2U device such as higher input power and longer pulse duration of the NBI system as well as installation of inner divertors with upgraded electrode biasing systems. Initial C-2W experiments have successfully demonstrated a robust FRC formation and its translation into the confinement vessel through the newly installed inner divertor with adequate guide magnetic field. They also produced dramatically improved initial FRC states with higher plasma temperatures (Te ~ 250 + eV; total electron and ion temperature >1.5 keV, based on pressure balance) and more trapped flux (up to ~15 mWb, based on rigid-rotor model) inside the FRC immediately after the merger of collided two CTs in the confinement section. As for effective edge control on FRC stabilization, a number of edge biasing schemes have been tried via open field-lines, in which concentric electrodes located in both inner and outer divertors as well as end-on plasma guns are electrically biased independently. As a result of effective outer-divertor electrode biasing alone, FRC plasma is well stabilized and diamagnetism duration has reached up to ~9 ms which is equivalent to C-2U plasma duration. Magnetic field flaring/expansion in both inner and outer divertors plays an important role in creating a thermal insulation on open field-lines to reduce a loss rate of electrons, which leads to improvement of the edge and core FRC confinement properties. An experimental campaign with inner-divertor magnetic-field flaring has just commenced and early result indicates that electron temperature of the merged FRC stays relatively high and increases for a short period of time, presumably by NBI and E × B heating.

Improved Confinement of C-2 Field-Reversed Configuration Plasmas

C-2 is a unique, large compact-toroid (CT) device at Tri Alpha Energy that produces field-reversed configuration (FRC) plasmas by colliding and merging oppositely directed CTs. Significant progress has recently been made on C-2, achieving ~5 ms stable plasmas with a dramatic improvement in confinement, far beyond the prediction from the conventional FRC scaling. This stable, long-lived FRC plasma state is called the high-performance FRC (HPF) regime. The key approaches to achieve the HPF regime are as follows: (i) dynamic FRC formation by collision/merging of super-Alfvénic CTs, (ii) effective control of stability and transport by end-on plasma guns and neutral-beam (NB) injection, and (iii) active wall conditioning using titanium and lithium gettering systems. Moreover, further improvement in FRC confinement has been obtained with improved open-field-line plasma properties such as a lower fluctuation level, reduced transport rates in radial/axial directions, and lower background neutral density as well as recycling. This open-field-line plasma improvement, mainly obtained by higher magnetic fields in the formation and mirror-plug sections, allows for better NB coupling to the core-FRC plasma. In the recent HPF regime there is a sufficiently large fast-ion population that appears to improve FRC confinement properties as well as stability; the FRC particle and global energy confinement times both increased by ~30% and ~80%, respectively, compared to that of the previously obtained HPF regime.

Field Reversed Configuration Confinement Enhancement through Edge Biasing and Neutral Beam Injection

Field reversed configurations (FRCs) with high confinement are obtained in the C-2 device by combining plasma gun edge biasing and neutral beam injection. The plasma gun creates an inward radial electric field that counters the usual FRC spin-up. The n = 2 rotational instability is stabilized without applying quadrupole magnetic fields. The FRCs are nearly axisymmetric, which enables fast ion confinement. The plasma gun also produces E × B shear in the FRC edge layer, which may explain the observed improved particle transport. The FRC confinement times are improved by factors 2 to 4, and the plasma lifetimes are extended from 1 to up to 4 ms.

A new high performance field reversed configuration operating regime in the C-2 device

Large field reversed configurations (FRCs) are produced in the C-2 device by combining dynamic formation and merging processes. The good confinement of these FRCs must be further improved to achieve sustainment with neutral beam (NB) injection and pellet fuelling. A plasma gun is installed at one end of the C-2 device to attempt electric field control of the FRC edge layer. The gun inward radial electric field counters the usual FRC spin-up and mitigates the n = 2 rotational instability without applying quadrupole magnetic fields. Better plasma centering is also obtained, presumably from line-tying to the gun electrodes. The combined effects of the plasma gun and of neutral beam injection lead to the high performance FRC operating regime, with FRC lifetimes up to 3 ms and with FRC confinement times improved by factors 2 to 4.

Creation of a high-temperature plasma through merging and compression of supersonic field reversed configuration plasmoids

A new device, the Inductive Plasma Accelerator, was employed to simultaneously form and accelerate two oppositely directed field reversed configurations (FRCs) where the relative velocity (600 km s−1) of the plasmoids was much larger than their internal thermal motion. Upon collision all of the FRC directional energy was observed to be rapidly thermalized concurrent with complete magnetic reconnection of the two FRCs. Upon merging, the resulting FRC was compressed to kilovolt ion temperatures exhibiting a configuration lifetime better than predicted by past scaling of in situ formed FRCs. With the improved FRC confinement scaling, a pulsed plasma device based on this approach capable of achieving fusion gain is examined. For an FRC with a poloidal flux 20 mWb or greater, the fusion energy yield per pulse exceeds the plasma energy for compression fields of 10 T or more. The scaling is insensitive to the compression chamber radial scale, providing for the possibility of a very compact fusion neutron source.

Combined FRC and Mirror Plasma Studies in the C-2 Device

The Field Reversed Configuration (FRC) is a high-beta Compact Toroid that includes closed and open field line regions of poloidal magnetic field. Improving the transport properties of both regions is important for the overall FRC confinement and may be attempted in the C-2 device. The goal of this experiment is to explore FRC sustainment by combining heating and current drive from neutral beam injection and particle fueling from a pellet injector. Additions to the C-2 device may include magnetic mirror plugs, plasma guns, and electrically-biased limiters. These additions would permit us to explore combined FRC and mirror physics, with emphasis on improving the FRC confinement.

Modelling of Plasma Physics in the Fusion Reactor Based on a Field-Reversed Configuration

The compact torus/toroid (CT) as future fusion reactor is presented. The field reversed configuration (FRC) is alternative thermonuclear scheme with properties of compact tori as both open and closed systems. By plasma confinement method field reversed configuration is closed magnetic trap. Mathematical model of plasma core in the fusion reactor is shown. Power balance for the FRC confinement chamber is calculated. The formula for bremsstrahlung more accurate in the temperature range of advanced fuel is presented. D-3He-6Li fuel cycle is proposed and reactor schemes are discussed.

Confinement analyses of the high-density field-reversed configuration plasma in the field-reversed configuration experiment with a liner

The focus of the field-reversed configuration (FRC) experiment with a liner (FRX-L) is the formation of a target FRC plasma for magnetized target fusion experiments. An FRC plasma with density of 1023m−3, total temperature in the range of 150–300 eV, and a lifetime of ≈20μs is desired. Field-reversed θ-pinch technology is used with programed cusp fields at θ-coil ends to achieve non-tearing field line reconnections during FRC formation. Well-formed FRCs with density between (2–4)×1022m−3, lifetime in the range of 15–20μs, and total temperature between 300–500 eV are reproducibly created. Key FRC parameters have standard deviation in the mean of 10% during consecutive shots. The FRCs are formed at 50 mTorr deuterium static fill using 2 kG net reversed bias field inside the θ-coil confinement region, with external main field unexpectedly ranging between 15–30 kG. The high-density FRCs confinement properties are approximately in agreement with empirical scaling laws obtained from previous experiments with fill pressure mostly less than 20 mTorr. Analyses in this paper reveal that reducing the external main field modulation and∕or extending the θ-coil length in the FRX-L device are critical in achieving higher FRC parameters for application in magnetized target fusion.

Improvement of Plasma Confinement on a Field-Reversed Configuration with Strong Mirror Field by Neutral Beam Injection

The first experiments of neutral beam (NB) injection into a field-reversed configuration (FRC) plasma have been performed at FIX (FRC Injection Experiment) device.1 The experimental results show that the configuration lifetime of a FRC have been expanded by about 200% compared with no NB injection case. These results indicate that several hundred kilo watts of NB injection saves several mega watts of global energy losses. For understanding these experimental phenomena, some numerical calculations have been performed. Numerically calculated ionization degree vs. distance along beam injection axis and beam trajectories show that the injected beam ions form dense regions around minimum │B│. These formed hot beam ions walls would play a role in improving these confinements on the edge layer. Some previous theoretical studies pointed out the existence of electrostatic effects in the FRC edge plasma confinements.6, 7 Since only several kilo watts NB injection improves FRC confinement, it seems that the injected hot beam ions encourage electrostatic effects on the edge layer.

Axial compression of a field reversed configuration plasma

A new concept for plasma heating using axial magnetic compression of a field reversedconfiguration (FRC) plasma is proposed. In this concept, the FRC plasma is compressed only axially,keeping the magnetic flux between the separatrix and the confining chamber (flux conserver) wallunchanged, while allowing the plasma to expand radially. A simple model based on an empiricalscaling law of FRC confinement and on the assumption that the compression is done adiabatically predicts that, in addition to heating the plasma, improved confinement will also be accomplished with this concept. This compression is done by energizing segmented mirror coils successively in such a way as to decrease the length of the confinement region between the coils. The apparatus for this axial compression was developed and an experiment was carried out. In this experiment the plasma was compressed by about 30% and the plasma lifetime of about 500 μs was increased by about 50 μs.

Particle end loss in the edge plasma of a field-reversed configuration

Plasma parameters, particle end loss flux, flow velocity, and pressure are measured using a radial array of magnetic probes and directional electrostatic probes, in order to investigate particle loss processes in the edge layer of a field-reversed configuration (FRC). A plasma flow toward the end region is detected outside the separatrix between the axial midplane and the end region. The exhaust flow is also found in the end region. These results imply that particles are lost radially across the separatrix and then axially to the end. Measured flow velocity in the end region agrees within an error of 20% with the fluid-theory prediction, in which isentropy and axial momentum balance along magnetic flux tubes are assumed. The existence of the sonic condition in the end region is also suggested, analogous to ordinary fluid flow in a nozzle. The magnetic flux embedded in the edge layer of the confinement region and in the end region agrees within an error of 30%. These results indicate the applicability of the magnetohydrodynamics (MHD) theory for particle end loss. The end loss time along the open field agrees with the MHD prediction within an error of 20%. The measured particle loss flux from the end region is explained by the MHD theory within an error of 20%. The plasma outside the separatrix is considered to behave as hydrodynamic flow through the magnetic loss channel, contrary to the previous work [L. C. Steinhaur, Phys. Fluids 29, 3379 (1986)]. It seems that the magnetic mirror field improves the particle confinement in the edge plasma of the FRC and thus assist the FRC confinement as previously predicted [Slough et al., Nucl. Fusion 24, 1537 (1984)].

Ideal-Magnetohydrodynamic-Stable Tilting in Field-Reversed Configurations

The tilting mode in field-reversed configurations (FRC) is examined using ideal-magnetohydrodynamic stability theory. Tilting, a global mode, is the greatest threat for disruption of FRC confinement. Previous studies uniformly found tilting to be unstable in ideal theory: the objective here is to ascertain if stable equilibria were overlooked in past work. Solving the variational problem with the Rayleigh-Ritz technique, tilting-stable equilibria are found for sufficiently hollow current profile and sufficient racetrackness of the separatrix shape. Although these equilibria were not examined previously, the present conclusion is quite surprising. Consequently checks of the method are offered. Even so it cannot yet be claimed with complete certainty that stability has been proved: absolute confirmation of ideal-stable tilting awaits the application of more complete methods.

Confinement of translated field-reversed configurations

The confinement properties of translating field-reversed configurations (FRC) in the FRX-C/T device [Phys. Fluids 29, ▪ ▪ ▪ ▪ (1986)] are analyzed and compared to previous data without translation and to available theory. Translation dynamics do not appear to appreciably modify the FRC confinement. Some empirical scaling laws with respect to various plasma parameters are extracted from the data. These are qualitatively similar to those obtained in the TRX-1 device [Phys. Fluids 28, 888 (1985)] without translation and with a different formation method. Translation with a static gas fill offers new opportunities such as improved particle confinement or refueling of the FRC particle inventory.