In this series, we will be reviewing the nuclear options to achieve a net carbon footprint of zero, it will be intriguing to start with the latest in fusion research, before examining the more traditional based (e.g. fission), which should come in the following articles.
Known as ionised gases, a mixture of negative and positive charge and yet a big mystery to control and made use of in nuclear fusion research
The mysterious fourth state of matter otherwise known as plasma has been drawing attention lately. But what is plasma? Plasma refers to an ionised gas, which is a mixture of positive and negative charge particles and occasionally includes neutral ones. Its origin in physics goes back to 1920 with the works of pioneers Irving Langmuir, Lewi Tonks and Harold Mott-Smith. The fourth state of matter has come a long way since then, and its properties are the foundation of nuclear fusion research.
An important aspect of the plasma is its temperature, and it refers to the thermal motion or the velocity of the particles inside the ionised gas. The higher the temperature is, the faster the particles be. If one was to make a collective distribution, it would fit a Maxwell-Boltzmann velocity function. Plasma is usually made of different particles (electrons and protons), and each has a different velocity distribution, simply because they have different masses. For example, a 100,000,000 degree Celsius, refers to a plasma with a collective velocity of 10 kilo-electron Volt, and that is 1386.7 km/sec.
But how does a Fusion Reactor work?
The aim of fusion reactors is to create, contain and confine the plasmas as the first step. Once the first step is achieved, the plasma is heated up to reach conditions where the ignition can happen.
In nuclear fusion research, and for the purpose of power generation, plasma gets trickier to deal with. This is because there are several factors that are always considered, which are heat capacity, confinement, pressure, time, density, and many others. As we examined previously [please see the previous article in this series], research in nuclear fusion started in the thirties involving powerful magnets in devices known as Magnetically Confined Fusion (MCF), and later in the sixties with the development of the lasers, Inertial Confinement Fusion (ICF). ICF will be discussed in upcoming commentaries. Both methods involve similar goals of maintaining plasma, containing heat, increasing the temperature, and of course, ignition, and as a general rule, they are denoted by factor Q, which is simply the ratio of energy gain versus the energy which is lost. Lastly, the Lawson Criterion refers to the conditions for the reactor to reach ignition, which simply refers to a self-sustaining nuclear fusion.
Ideally one would want to have plasmas at higher pressures and possibly operate at larger currents. Simply, the higher the pressure, the closest we get to the Q factor, therefore higher power output is achieved. Spherical Tokamaks (ST) are one of the ideal candidates, with a much higher ratio of thermal plasma pressure to the magnetic pressure, known as beta. This is very desirable and simply means less energy is required to generate magnetic fields hence, better confinement is achieved.
The notable STs are ST40 (at Tokamak Energy ltd), the first privately funded tokamak, and publicly funded facilities of National Spherical Torus eXperiment (NSTX) at Princeton Plasma Physics Laboratory (PPPL), and Mega Ampere Spherical Tokamak (MAST) at CCFE.