Divertor

A divertor is a component in a fusion reactor, most commonly a tokamak, that is used to remove heat and exhaust impurities from the plasma. It serves as a crucial part of the exhaust system, protecting the main plasma-facing components of the reactor from excessive heat load and erosion. The divertor is specifically designed to channel the particle and heat flux away from the main plasma chamber and direct it to a dedicated target area.

Functionality:

The primary functions of a divertor are:

• Heat Removal: The divertor removes a significant fraction of the heat generated in the fusion plasma, which is exhausted as hot particles. Without a divertor, this heat would directly impinge on the walls of the reactor, potentially damaging them.

• Impurity Control: The divertor intercepts and neutralizes impurities (e.g., helium ash from fusion reactions, sputtered material from the reactor walls) that contaminate the plasma. These impurities can dilute the fuel and radiate energy, thus reducing the efficiency of the fusion reaction. The divertor reduces the concentration of these impurities in the main plasma.

• Plasma Detachment: By promoting a plasma detachment regime near the target plates, the divertor can spread the heat load over a larger area, reducing the peak heat flux to manageable levels. Plasma detachment involves the creation of a dense, cold plasma near the divertor target, which radiates a significant amount of the heat, preventing it from reaching the target plates.

Design and Operation:

Divertors are typically located in a region of the tokamak with a strong magnetic field gradient. Magnetic field lines are configured to intersect the divertor target plates, guiding the plasma exhaust along these lines.

Common divertor configurations include:

• Single-null divertor: One set of target plates is used to intercept the diverted plasma.

• Double-null divertor: Two sets of target plates are used, one above and one below the midplane of the tokamak, allowing for more symmetric heat distribution.

Divertors are typically made of materials with high heat resistance and low sputtering yields, such as tungsten or carbon-based materials. Advanced divertor concepts, such as liquid metal divertors, are also being explored to handle the extreme heat fluxes expected in future fusion reactors.

Importance:

The divertor is a critical component for the successful operation of future fusion power plants. Efficient and reliable divertor operation is essential for maintaining plasma purity, protecting reactor components, and achieving sustained fusion reactions. The development and optimization of divertor technology is a major research area in fusion energy.