Nuclear Fusion

Technology Roadmap Sections and Deliverables

• 2NCF - Nuclear Fusion

Roadmap Overview

Fusion power refers to the generation from the energy released by merging, or fusing, two atomic nuclei to generate energy. The energy generated from this reaction comes from the difference in mass between the two individual nuclei and the resulting lighter nucleus; this difference in mass is converted to energy according to Einstein’s famous equation, E=mc2. There are different atoms that can be combined to generate fusion energy, but the most common reaction explored for commercial purposes involves two isotopes of hydrogen, deuterium, and tritium, in a reaction referred to as DT fusion. These two isotopes are brought in close proximity in a fusion reactor at over 100 million Celsius and combine to produce helium, releasing high-energy neutrons that can be captured to generate heat and run a conventional turbine to generate electricity.

D+T -> 4He+n

where

• D: Deuterium
• T: Tritium
• He: Helium
• n: neutron

Fusion reactions occur when two or more nuclei come close enough to each other for a long enough time that the nuclear forces attracting the nuclei exceed the electrostatic forces pulling them apart, fusing them into a heavier nucleus. To realize nuclear fusion for energy generation, there are technical challenges, such as plasma control and energy supply, to create and maintain high temperatures and high pressure.

There are multiple reactor concepts being explored to enable a fusion reaction, which involve the use of a strong magnetic field (magnetic confinement), powerful lasers (inertial confinement), or a hybrid of inertial and magnetic confinement methods (e.g., magneto-inertial confinement). The main applicable markets for fusion power are the electricity market, industrial heat, and space propulsion.

[1]

Design Structure Matrix (DSM) Allocation

The 2LCNF tree shows us that Laser Confined Nuclear Fusion is part of larger global Nuclear Fusion Power initiative to harness fusion power. The DSM and tree both show that 2LCNF requires the following technologies at the subsystem level 3: 3LAS Laser, 3TAR ICF Targets, 3DIA Diagnostics, 3CTP Cryogenic Target Positioning, and 3CHB Target Chamber. Each level 3 subsystem also require enabling technologies shown as level 4 systems.

Roadmap Model using OPM

The OPM and OPL of one possible fusion technology system are depicted below. This technology assists in harnessing nuclear energy to generate power with lower risk than nuclear generation in a controlled environment and produces less radioactive waste.

Object Process Language1

Object Process Language1

Object Process Language1

Figures of Merit

The table below shows a list of FOMs of nuclear fusion.

Gain factor(Q-Value) and Triple product is fusion-specific figures of merit. The Q-value is a crucial metric for evaluating the performance and viability of a fusion device. A device with a high Q-value suggests a significant net energy gain, increasing its potential as a practical energy source.

Gain factor (Q-Value) = (Energy produced by fusion reactions) / (External energy input to the plasma)

The other is figures of merit relevant to the electricity market: Cost per Kilowatt, Levelized cost of electricity (LCOE), Power density, Carbon Emissions, Net capacity factor, and Ramp rate. These metrics of fusion energy are vital indicators of its competitiveness compared to other energy sources such as solar, wind, and fossil fuels.

Triple product

Triple product can be used to compare performance across various approaches to fusion, such as magnetic confinement schemes, inertial confinement schemes, and magneto-inertial schemes, being independent of the scheme used to create the fusion plasma. It is defined as the product of three factors: plasma density, temperature, and confinement time. Triple produc is expressed as:

Triple product ((m^-3) * eV * s) =density(1/m^3) × temperature(eV) × confinement time (s)

Where

• Density is the number of nuclei per unit volume
• Temperature is the kinetic energy of the particles in the plasma (the unit for temperature in fusion contexts is usually expressed in electron volts (eV))
• Confinement Time is the average time that a particle remains in the plasma before escaping.

The triple product is the main figure of merit used to measure progress in fusion energy research. Even though cost-per-KW is more appropriate when comparing power generation technologies, fusion technology is at too early stages to come up with reliable estimates of cost and progress over time. Figure 1 below shows the record values for a given fusion confinement concept along with the theoretical limit [1]. This theoretical limit occurs due to operational limits in plasma density, and a parameter called beta, β, the ratio of plasma pressure to magnetic pressure [2].

Figure 1. Triple product achieved for various fusion confinement concepts [1]

The rate of improvement was estimated for Magnetic Confinement fusion (red line in Figure 1); this is shown in Figure 2. The rate of improvement was found to be uneven, with large values at the beginning ~200% and then slowing down to about 35%. This decreased rate of improvement is well documented in the literature and is attributed to the international research community focusing on the International Thermonuclear Experimental Reactor (ITER). This particular confinement method appears to be in the portion of the S curve with slower progress. In contrast, the Inertial confinement fusion (black line in Figure 2) appears to be in the rapid progress phase (the rate of improvement was not calculated)

Figure 2. Rate of improvement for the triple product of magnetic confinement fusion. Raw data obtained from ref. [1].

Bibliography

[1] S. E. Wurzel, "Progress toward fusion energy breakeven and gain as measured against the Lawson criterion," Physics of Plasmas, 2022

[2] A. Costley, "On the fusion triple product and fusion power gain," Nuclear Fusion, Volume 56, Number 6