The following analysis is based on the review of publicly available scientific journal papers written and published by scientists at each of the identified companies as well as recent “poster presentations” at meetings such as the October-November 2016 American Physical Society Division of Plasma Physics, conference held in San Jose, CA, and others. The following descriptions and challenges may be updated from time to time as new information is obtained.
This information is provided solely as an example of the State-Of-The-Art practiced by the private sector as readily known in the public domain based on our best judgment analysis. This information is not meant to be used in any financial analysis of these firms.
Helion Energy
Helion Energy aims to repetitively compress a field-reversed-configuration (FRC) plasma using a pulsed magnetic field that is generated by external coils. Advantages of their approach include (i) being at slightly higher fuel density than steady-state magnetic-confinement concepts (which requires shorter energy confinement times), (ii) using a magnetic field to compress and heat their fuel (which avoids the need to repetitively form an imploding liner), and (iii) having a geometry that is amenable to highly efficient direct conversion of the fusion products to electricity.
Challenges:
-Demonstrate both global plasma stability and a sufficient energy confinement time at the Lawson-relevant fuel densities and temperatures. These challenges are significant in that they have less to do with engineering and more to do with fundamental limits of plasma physics.
-In addition, these challenges are orders of magnitude more difficult for D3He rather than DT fuel.
-Furthermore Helion aims to self-generate 3He (which is not available in relevant quantities on Earth) in a “breeding reaction from DD. How the reaction is started without 3He needs significant investigation and work.
Tri Alpha
Tri Alpha Energy (TAE) aims to create a steady-state field-reversed-configuration at low densities typical of mainstream magnetic fusion, i.e., tokamaks. One of their key innovations is to inject high-energy beam ions into their FRC, which has recently been shown to provide global stability, an important achievement. Being an FRC, it does have the advantage of a favorable geometry for fusion-heat extraction and efficient direct conversion to electricity.
Challenges:
-The beam ions are supposed to improve the energy confinement time, which is a major challenge and remains to be demonstrated.
-Unless TAE demonstrates energy confinement that is better than a tokamak (which would be challenging and unexpected), it will likely need to be a large device, making it more costly than other higher-density approaches such as Helion or General Fusion.
– As with Helion, Tri Alpha’s challenges for reaching Lawson conditions are exacerbated if they use p11B rather than DT fuel. P11B is at least another order of magnitude more difficult than D3He
General Fusion
General Fusion’s approach belongs to a class of pulsed, high-fuel-density concepts called magneto-inertial fusion (MIF), which is theoretically a low-cost minimum for achieving triple product Lawson conditions. Their specific approach is to compress a magnetized plasma via acoustically driven shock implosions through a liquid-metal vortex, which would also serve as the reactor coolant and tritium-breeding medium. This is a particularly elegant aspect of General Fusion’s approach. Another advantage is the relatively low cost of their pressurized-gas-driven piston drivers.
Challenges:
-Must form a suitable target in a reactor-relevant manner
-Must achieve global stability of their target in a manner compatible with repetitive compressions
-Must achieve sufficient energy confinement time exceeding the relative slow implosion time by a fair margin.
Tokamak Energy
Tokamak Energy seeks to use novel, high-temperature superconducting tape and compact tokamak geometry to achieve a simpler and modular design that could potentially benefit from the tokamak’s advanced performance while reducing the cost/size of a conventional tokamak by an order of magnitude.
Challenges:
-Achieving triple product Lawson conditions in a sustained manner overlap with those of the traditional tokamak (JET, PPPL NSTX, MIT Alcator, ITER and the like,) namely achieving sufficient stability, confinement time, global disruptions, and also steady-state plasma interactions with the “first wall” (even if it is a liquid).
-Susceptibility to magnetic quenches causing machine damage
Magneto-Inertial Fusion Technologies, Inc (MIFTI)
MIFTI proposes to use a concept called the staged Z pinch, in which a cylindrical plasma is magnetically imploded onto gaseous DT fuel. Shock heating of the gaseous DT fuel is supposed to play a key role in providing effective, stable compressions of the fuel, and diffusion of the exterior magnetic field into the core is supposed to reduce the rate of heat loss from the fuel. An axial magnetic field can be added to help with reducing heat transport from the fuel.
Challenges:
-Overcoming known Z-pinch instabilities that are well-studied over 60+ years of controlled fusion research, and in the difficulty in achieving a high enough repetition rate for economical fusion.
– A discussion of potential discrepancies in mathematical calculations in MIFTI published papers is discussed on page 38, paragraph 3, of “The Ignition Design Space of Magnetized Target Fusion,” Irvin R. Lindemuth, Ph.D., December 28, 2015.
Lockheed Martin Compact Fusion
Lockheed Martin aims for a mirror-based concept operating at high beta (ratio of plasma pressure to magnetic pressure) and densities typical of tokamaks. It aims to have a field-free interior at fusion pressures supported by a steep pressure and magnetic-field gradient at the boundary. This geometry is to be sustained in part by coils internal to the main plasma.
Challenges:
-achieving sufficient stability, especially at the sharp edge boundary
-achieving sufficient energy confinement time, despite having coils interior to the plasma (a general no-no if you want good plasma confinement)
-being low density, requires higher confinement time and therefore larger sizes, which makes the “compact” goal difficult
LPP Fusion – Focus Fusion
LPP aims to use a variant of the Z pinch called the Dense Plasma Focus (DPF), which is a known effective source of beam-target (not thermonuclear) neutrons. To achieve energy gain in a DPF requires thermonuclear neutrons and electrical current of more than 10 MA. This is another case of going against the history of 60+ years of controlled fusion research, where Z pinches are known to suffer all sorts of instabilities, precluding them to pinch down to the small sizes needed to attain triple product Lawson conditions. LLP’s work has centered on p11B which, due to cross sectional diameters, is many orders of magnitude more difficult to achieve triple product Lawson criterion than DT.