08 Feb

Fusion Reactions

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Contents

• Introduction
• Why nuclear fusions are important as an energy source?
• Types of Fusion Reactions
• Significance
• Some Caveats
• India and Fusion
• Key Limitations for India

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Introduction

• Fusion is the energy source of the Sun and Stars. A fusion reaction occurs when two atoms of lighter nuclei combine to form an atom with heavier nucleus. The mass of the resulting atom is slightly less than the combined mass of the constituent atoms, and this lost mass is released in the from of energy as per Einstein’s mass-energy equivalence relation (E=mc²).
• Fusion takes place at very high temperature (for e.g. Sun’s core has a temperature of 15 million degree C)
  • What is the need of extremely high temperature?
    • to overcome the electrical repulsive force
• Till date we don’t have any stable fusion reactor.
  • Development of thermonuclear energy power plants has been difficult:
  • Three conditions must be fulfilled to achieve fusion in a laboratory:
    • Very High Temperature (on the order of 15 million degrees C)
    • Sufficient Plasma particle density (to increase the likelihood that collisions do occur)
    • Sufficient confinement time (to hold the plasma, which has the propensity to expand, within a defined volume)
  • Note: Twentieth century fusion science identified the most efficient fusion reaction in the laboratory setting to be reaction between two hydrogen isotopes, deuterium (D) and tritium (T), as the D-T reaction produces the higher energy gain at the “lowest temperatures”.

Why nuclear fusions are important as an energy source?

• Easily available raw material
• Most efficient known from of energy production in the universe – it produces four times more energy than a standard Uranium-based fission reaction.
• Nuclear Fusion is a clean and green route to produce energy, as it doesn’t involve any remnant waste products.
• Long term energy security

USA’s Attempt:

• In Dec 2022, an experiment at US National Ignition Facility (NIF), within the Livermore National Laboratory, Livermore, California, achieved a fusion ignition by successfully conducting a fusion test that produced 153% (1.53 gain) as much energy as went into
  triggering it.
• In July 2023, in a repeat of the above experiment, scientists were able to generate more energy with nearly a factor of 2 in gain compared with energy of the incoming lasers.

Types of Fusion Reactions:

• For fusion reaction to happen in reactors, the high temperature must be created artificially.
• There are two different ways of achieving this: Inertial Confinement Method and Magnetic Confinement Method:
  1) Inertial Confinement Method: In this method, high energy laser beams are focused onto a pellet of the fuel (D-T), which creates extreme temperatures required for fusion inside it. The outer mass of the pallet explodes and is responsible for confining the reaction.
  ­ E.g., The NIF reactions
  2) Magnetic Confinement Fusion (MCF): It uses a magnetic field to contain plasma, which prevents the particles from hitting the reactor walls which could otherwise cause them to slow down.
  • Magnetic confinement uses a torus-shaped reactor called tokamak, in which a hydrogen plasma is heated to a high temperature and the nuclei are guided by strong magnetic fields to fuse. ITER is a famous example of an experiment trying to achieve fusion using magnetic confinement.
    3) Some other variants also exist such as those which use a combination of these methods (Magnetized Target Fusion) and those that combine fission with fusion (Hybrid Fusion)
• The NIF Breakthrough:
  • In Dec 2022, NIF was finally able to achieve ‘breakeven’, or a net positive energy gain.
  • In July 2023, it was able to replicate its efforts, but now with a bigger gain (almost 2)
  • In both these achievements inertial confinement was employed.
• In NIF’s set up, high-power lasers fire pulses at a 2 mm wide capsule inside a 1-cm long cylinder called hohlraum, in less than 10 billionths of a second. The capsule holds deuterium and tritium atoms.
• As the pulse strikes the hohlraum’s inside, the latter heats up and releases x-rays, which heat the nuclei to millions of degrees centigrade and compress them to billions of Earth atmosphere. This technique is called inertial confinement method because the nuclei’s inertia creates a short window between implosion and explosion in which the strong nuclear force dominates, fusing the nuclei.
• Specifically, when two hydrogen-2 nuclei fuse, they yield a helium-4 nucleus, a neutron and 17.6 MeV of energy.

Significance:

• Fusion ignition is one of the most impressive feats of the 21st century and is an engineering marvel beyond belief.

Some Caveats:

• First: NIF experiment is highly sophisticated and required very high precision. Even small changes in the experiment may negatively impact the output. So, for long term use, they
  will have to reproduce these results again and again.
• Second: For fusion reaction to be truly gainful, the energy released by the reactions needs to be greater than the energy going into the lasers, about 300 megajoules, and not just the energy delivered to the hohlraum. This hasn’t been achieved yet. The energy transferred to plasma is just 1%, the rest is all lost in other processes. “Future research will need to focus on reaching the next major milestone – a target gain of G > 100, which is required to run a power plant efficiently.
• Third: The road to a power plant from the NIF’s current achievement isn’t well understood.

India and Fusion:

• India has become one of the major players in fusion technology and has been one of the pioneers in its development.
• The Plasma Physics Program was initiated by the GoI in 1982 to conduct research at MCF,
  which later evolved into the Institute for Plasma Research (IPR) in 1986 and led to the creation of India’s own tokamak, ADITYA, in 1989.
• Subsequently, it also developed a large semi-indigenous tokamak called the Steady State Superconducting Tokamak (SST-1) which was fully commissioned in 2013. IPR has also
  revealed its plans for a successor, the SST-2, due in 2017.
• In 2005, India became the 7th member to join the International Thermonuclear Experiment Reactor (ITER) project, a global initiative attempting to build the world’s largest tokamak
  reactor.
• ITER-India has been set up under the supervision of IPR and is responsible for fulfilling India’s commitment to the project. It has already provided the world’s largest cryostat, a vacuum application stainless steel vessel, to house the reactor, along with a host of other equipment.

Key Limitations for India:

• Lack of Private Investment: it is primarily because of Atomic Energy Act, 1962, which puts the brunt of developing and running nuclear power stations on the government.
  • However, a recent government panel convened by NITI aayog has recommended overturning the ban of foreign investment and allowing greater participation of private players.

Conclusion:

The NIF experiment has opened up a new avenue for achieving nuclear fusion through the means of inertial confinement and it would be fruitful for India to take notice and invest in this technology since it’s clear that this is where the future lies.