Disruption mitigation in tokamak reactor via reducing the seed electrons of avalanche

Abstract

Disruption mitigation technology remains the key factor for ensuring safe and reliable operation in future large tokamaks including ITER. A novel approach analyzed in this paper aims at mitigating the runaway avalanche (RA) development by reducing the population of runaway seeds using the tungsten projectile injection into the ITER plasma just after the thermal quench. As opposed to the scenario currently discussed by the ITER team, the approach does not involve injecting a large mass of deuterium into the tokamak vacuum vessel for collisional suppression of the RA current generated. This should significantly reduce the operational problems of the ITER technological systems dealing with fueling and pumping, isotope separation, plasma heating, etc. Collecting seeds and runaways by the projectile injected might reduce the avalanche current in ITER below the level of 1 MA and its magnetic energy by more than two orders of magnitude. A tungsten rod being 8 mm inside of the square section and 80 mm in length that crosses the plasma volume with the velocity of 0.8 km s−1 radially or tangentially seems appropriate for ITER disruption conditions. Simulations of the projectile interaction with the ITER post TQ plasma revealed that its surface temperature remains below the tungsten melting point. It is also found that a railgun using the toroidal magnetic field of the tokamak is the optimal way to accelerate such a projectile.

Corrigendum: Simulations of stand-off runaway electron beam termination by tungsten particulates for tokamak disruption mitigation (2024 Nucl. Fusion 64 056019)

“…We regret the omission in the original article, and thank the authors of the cited article for bringing this matter to our attention. We also find the possibility of using the injected tungsten rod from [2] to terminate the runaways, as opposed to the cloud of tungsten particulates in [1] intriguing. In that context, it is of interest to mention another possibility of a retractable tungsten metal arm that can be swung out for deployment in runaway termination, which would remove the need for post-mitigation recovery of tungsten debris in injection schemes.…”

“…This can be contrasted with another interesting idea [3] of using small tungsten pellets coated with a low Z material for depleting the runaway seeds as an option for upgrade of the ITER Disruption Mitigation System. Interested readers are referred to those two papers [2,3] on the tungsten injection for runaway seed removal/reduction, and the related issue of not shortening the current quench excessively.…”

“…In the original article, [1] we inadvertently omitted a reference [2] which previously introduced the concept of tungsten injection for 'Disruption Mitigation in Tokamak Reactor via Reducing the Seed Electrons of Avalanche.' In that reference, the authors have proposed injection of a tungsten cylinder of 80 mm by 8 mm dimensions, by rail guns, to absorb the runaway seed population.…”