New Delhi: Fusion energy physicists at the Princeton Plasma Physics Laboratory (PPPL) have advanced the use of boron powder as a shield for the inner tungsten walls of tokamaks to withstand the heat and pressure of fusion plasma. Tungsten is usually applied to coat the plasma-facing parts of fusion reactors as it is resistant to the stress.
Due to their high energy, plasma can knock out tungsten atoms and will introduce them into plasma, which will cool down and slow down the fusion reaction. Sodium, particularly in the form of a fine powder, has been successfully used to prevent tungsten walls from sputtering and thereby stabilise the plasma.
Using Boron from a Single Point
The PPPL’s team, led by Joseph Snipes, the deputy head for Tokamak Experimental Science, came up with a manner in which boron can be inserted into the tokamak like salt in a shaker. The boron ionises at the edges while within the plasma and forms a thin layer on the walls of the reactor. It also protects the tungsten atoms from being sputtered into the plasma, which minimises the cooling effect on the fusion process. The boron layer also efficiently traps tritium, a radioactive hydrogen isotope that must be contained within specific levels in ITER for nuclear reasons.
New Computer Models Prove Efficiency
In parallel with the experiments, a PPPL staff research physicist, Florian Effenberg, coordinated the work on the simulation of boron powder behaviour in the DIII-D tokamak. This framework also includes three computer models that are used to predict plasma behaviour, movement of boron powder, and its interaction with the walls of the tokamak. Interestingly, the simulations show that boron could be spread evenly on the walls of the reactor if it was sprinkled from a single source; the protection layer can be maximised with minimal use of boron.
Towards ITER’s Tungsten Walls
These advances help scientists get closer to using boron injection in the ITER tokamak, which will have tungsten walls unlike the DIII-D. The subsequent step of the study will generalise the PPPL’s models to the more complex ITER reactor and explore the potential variation in the efficiency of boron with tungsten. This contribution from Oak Ridge National Laboratory as well as ITER and its main idea is to set up an efficient wall conditioning approach that will enable the reactor and foster long-term fusion.
This study is a major step toward improving the durability and performance of a fusion reactor. The reduction of tungsten contamination could be achieved by boron injection, which might enhance the reactor performance and make fusion energy almost clean and practical.
