Question

Explain why achievement of nuclear fusion in the laboratory requires a temperature of about 100 million degrees Celsius, which is much higher than that in the interior of the sun ( 15 million degrees Celsius).

Short answer

Laboratory conditions lack the pressure of the sun, requiring higher temperatures to achieve fusion.

Step-by-step solution

Understand Nuclear Fusion

Nuclear fusion involves combining small atomic nuclei to form a larger nucleus, releasing a large amount of energy in the process. It requires a significant overcoming of the electrostatic repulsion between positively charged nuclei to get them close enough to allow the strong nuclear force to bind them together.

Compare Conditions in the Sun and Laboratory

The core of the sun has extreme pressure and density, which are natural conditions that promote nuclear fusion at relatively lower temperatures (~15 million degrees Celsius). In contrast, the laboratory setup lacks these conditions and primarily relies on temperature to increase particle kinetic energy.

Consider Particle Kinetic Energy

Higher temperatures in the laboratory are used to increase the kinetic energy of the particles. With sufficient energy, particles can overcome the electrostatic repulsion without the immense pressure present in the sun, which aids in initiating the fusion process.

Achieving Sufficient Collision Probability

In laboratory conditions, the temperature needs to be much higher (~100 million degrees Celsius) to achieve a sufficient rate of successful collisions between nuclei necessary for sustained fusion, compensating for the absence of solar-like pressure.

Conclusion

The discrepancy in required temperatures stems from the absence of the intense gravitational pressure of the sun in laboratory conditions, necessitating higher temperatures to achieve fusion through increased particle kinetic energy.

Key concepts

Nuclear Force

The nuclear force is a powerful interaction that keeps atomic nuclei together. It operates at an incredibly short range, approximately one femtometer (a millionth of a billionth of a meter). This force is what allows protons and neutrons within an atomic nucleus to stay bound despite the repulsion between positively charged protons. Without the nuclear force, atomic nuclei would not be stable.
In nuclear fusion, the goal is to bring two nuclei close enough for the nuclear force to take over and bind them together, releasing energy in the process. However, bringing these positive charges close requires overcoming their natural tendency to repel each other. This is where the nuclear force shows its crucial role in fusion, serving as the ultimate glue for new atomic formations.

Electrostatic Repulsion

Electrostatic repulsion is a force that acts between charged particles. Protons, being positively charged, naturally push away from one another due to this force. For nuclear fusion to occur, particles must overcome electrostatic repulsion, which is a significant challenge.
In the sun, the immense gravitational pressure helps overcome this repulsion. However, in the lab, without extreme pressure, scientists must find alternative methods to bring nuclei together. By applying immense heat, they increase the chances that particles will have either enough speed or energy to collide, enabling the nuclear force to cluster them. This makes understanding electrostatic repulsion a key topic in fusion research.

Kinetic Energy

Kinetic energy is the energy that an object possesses due to its motion. In the context of nuclear fusion, it refers to the energy of the atomic nuclei moving at high speeds. The greater the kinetic energy, the faster and more forceful the nuclei move and collide.
To achieve fusion in the lab, scientists raise the kinetic energy of particles by increasing the temperature. This energy boost helps particles reach velocities where they can overcome electrostatic repulsion. Thus, kinetic energy plays a vital role in facilitating the conditions necessary for fusion reactions.

Temperature Conditions

Temperature conditions are crucial in determining the feasibility of nuclear fusion. High temperatures correspond to high kinetic energy levels. In laboratory fusion experiments, reaching about 100 million degrees Celsius is essential.
This extreme temperature is necessary because the lab environment lacks the solar core's intense pressure, which aids fusion at "only" 15 million degrees. By creating temperatures much higher than those in the sun, the laboratory compensates for this absence, ensuring particles collide with enough energy to initiate and sustain fusion reactions. The disparity in temperature conditions reflects the need to balance different environmental pressures to achieve successful fusion.

Laboratory Fusion Experiments

Laboratory fusion experiments aim to replicate the conditions necessary for nuclear fusion on Earth. Unlike the sun, where gravitational forces naturally support fusion at lower temperatures, laboratories must artificially create extreme conditions.
Experiments often involve heating fuel to extreme temperatures to compensate for the lack of pressure found in the sun. High temperatures ensure particles have enough kinetic energy to overcome electrostatic repulsion and collide sufficiently to trigger fusion. Achieving consistent nuclear fusion in a lab remains a significant scientific challenge, but each experiment brings researchers closer to harnessing this potential energy source. Understanding these experimental nuances is essential as scientists continue to explore fusion's applications.