Magnetic geometry and physics of advanced divertors: The X-divertor and the snowflake

Abstract

Advanced divertors are magnetic geometries where a second X-point is added in the divertor region to address the serious challenges of burning plasma power exhaust. Invoking physical arguments, numerical work, and detailed model magnetic field analysis, we investigate the magnetic field structure of advanced divertors in the physically relevant region for power exhaust—the scrape-off layer. A primary result of our analysis is the emergence of a physical “metric,” the Divertor Index DI, which quantifies the flux expansion increase as one goes from the main X-point to the strike point. It clearly separates three geometries with distinct consequences for divertor physics—the Standard Divertor (DI = 1), and two advanced geometries—the X-Divertor (XD, DI > 1) and the Snowflake (DI < 1). The XD, therefore, cannot be classified as one variant of the Snowflake. By this measure, recent National Spherical Torus Experiment and DIIID experiments are X-Divertors, not Snowflakes.

Optimization of experimental snowflake configurations on TCV

“…Promising experimental results on advanced configurations have been obtained in TCV [5], [6], DIII-D [7] and NSTX [8]- [9], and the possibility to create snowflake configurations 1 R. Ambrosino is with Consorzio CREATE and the Dipartimento di Ingegneria (DI), Università degli Studi di Napoli Parthenope, Napoli, Italy. email: ambrosino@uniparthenope.it 2 R. Albanese is with Consorzio CREATE and the Dipartimento di Ingegneria Elettrica e Tecnologie dell'Informazione (DIETI), Università degli Studi di Napoli Federico II, Napoli, Italy 3 S. Coda, J.-M. Moret and H. Reimerdes are with Ecole Polytechnique Fèdèrale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, CH-1015 Lausanne, Switzerland 4 M. Mattei is with Consorzio CREATE and the Dipartimento di Ingegneria Industriale e dell'Informazione (DIII), Seconda Università di Napoli, Aversa (CE), Italy has been considered in EAST for the experimental campaign 2014 [10].…”

Comment on “Magnetic geometry and physics of advanced divertors: The X-divertor and the snowflake” [Phys. Plasmas 20, 102507 (2013)]

“…Our next concern is related to the concept of a "divertor index" introduced in Ref. 1. The index characterizes the flux expansion (contraction) along the flux surface between the point nearest to the main null and the strike point.…”

“…Our second concern is related to the discussion of the relation between the SF and XD given in Ref. 1. Here, we present our view of this relation.…”

Taming the Heat Flux Problem: Advanced Divertors Towards Fusion Power

“…It is, perhaps, a commonly shared concern that the next great obstacle to the realization of fusion power may be the power exhaust problem [1][2][3][4] that becomes progressively more severe as we advance towards reactor conditions. The idea that innovative magnetic geometries, called advanced divertors (AD) [5][6][7][8][9][10][11][12][13][14][15], may present a most direct way to meet the daunting technological challenges of heat flux and erosion on material surfaces, is steadily gaining widespread acceptance in the community.…”

“…The X-divertor (XD) [1][2][3][4]6] introduces a second X-point near the divertor plate to enhance the poloidal flux expansion and line length (Fig. 1a).…”