Impurity Transport in a Mixed-Collisionality Stellarator Plasma.

Area of Science:

• Plasma physics
• Fusion energy research
• Magnetically confined plasmas

Background:

• Impurity accumulation in fusion plasmas degrades performance through excessive radiation.
• Traditionally, stellarators were thought to always accumulate impurities, unlike tokamaks which utilize temperature screening.

Purpose of the Study:

• To investigate the possibility of outward impurity flux (temperature screening) in stellarator plasmas.
• To challenge the long-held assumption of inevitable impurity accumulation in stellarators.

Main Methods:

• Analytical techniques were employed to study impurity transport.
• A new numerical code was developed and utilized to support analytical findings.

Main Results:

• Temperature screening, an outward impurity flux driven by temperature gradients, was shown to occur in stellarator plasmas.
• This screening effect was observed in a relevant operating regime with highly collisional impurities and low bulk plasma collisionality.

Conclusions:

• Stellarators can indeed benefit from temperature screening, mitigating impurity accumulation.
• The findings suggest new possibilities for optimizing stellarator performance and achieving sustained fusion energy.