Overview of C-2W: high temperature, steady-state beam-driven field-reversed configuration plasmas

Abstract

TAE Technologies, Inc. (TAE) is pursuing an alternative approach to magnetically confined fusion, which relies on field-reversed configuration (FRC) plasmas composed of mostly energetic and well-confined particles by means of a state-of-the-art tunable energy neutral-beam (NB) injector system. TAE’s current experimental device, C-2W (also called ‘Norman’), is the world’s largest compact-toroid device and has made significant progress in FRC performance, producing record breaking, high temperature (electron temperature, T e > 500 eV; total electron and ion temperature, T tot > 3 keV) advanced beam-driven FRC plasmas, dominated by injected fast particles and sustained in steady-state for up to 30 ms, which is limited by NB pulse duration. C-2W produces significantly better FRC performance than the preceding C-2U experiment, in part due to Google’s machine-learning framework for experimental optimization, which has contributed to the discovery of a new operational regime where novel settings for the formation section and the confinement region yield consistently reproducible, hot, and stable plasmas. An active plasma control system has been developed and utilized in C-2W to produce consistent FRC performance as well as for reliable machine operations using magnets, electrodes, gas injection, and tunable NBs. The active control system has demonstrated stabilization of FRC axial instability. Overall FRC performance is well correlated with NBs and edge-biasing system, where higher total plasma energy is obtained by increasing both NB injection power and applied-voltage on biasing electrodes. C-2W divertors have demonstrated a good electron heat confinement on open-field-lines using strong magnetic mirror fields as well as expanding the magnetic field in the divertors (expansion ratio > 30); the energy lost per electron ion pair, η e ∼ 6–8, is achieved, which is close to the ideal theoretical minimum.

A New Device Concept of Magnetic Confinement Deuterium–Deuterium Fusion

“…C-2 series device experiments show that the current carried by high-energy ions plays an important role in stability. [8] The Spitzer resistance of ions can be used to estimate the corresponding current diffusion time: [9] 𝜏𝜂 = 𝜇0𝜎 ⊥ (𝑅s/2) 2 ∼ 1.25 s, where 𝜎 ⊥ is the resistance of plasma perpendicular to the magnetic field line. The characteristic length is 𝑅s/2.…”

Enhancing historical electron temperature data with an artificial neural network in the C-2U FRC

“…L1 regularization applies a penalty to the cost function equal to the sum of absolute value of the model weights [23]. Equation (4) shows the effect of regularization on the mean absolute error (MAE) cost function…”

“…While the mechanism for this mitigation is presently unknown, one strong possibility is the increase in neutral beam power from C-2U to C-2W. Neutral beam injection has been demonstrated experimentally to stabilize FRCs against instabilities [28,29], and the neutral beam injection power was increased by a factor of 2, from 10 MW on C-2U to 20 MW on C-2W [3,4]. Other parameters, such as the increased electric field from biasing or increased neutral beam energy may also play a role in the mitigation of the micro-burst in C-2W [4].…”

“…Neutral beam injection has been demonstrated experimentally to stabilize FRCs against instabilities [28,29], and the neutral beam injection power was increased by a factor of 2, from 10 MW on C-2U to 20 MW on C-2W [3,4]. Other parameters, such as the increased electric field from biasing or increased neutral beam energy may also play a role in the mitigation of the micro-burst in C-2W [4]. Examination of this effect in C-2U and C-2W is still ongoing, and a more thorough investigation of the physics of the micro-burst in beam-driven FRCs is likely the subject of future work.…”

“…decommissioned in 2016, so that it may be compared more directly to data from C-2W [4], the present device.…”