Ion target impact energy during Type I edge localized modes in JET ITER-like Wall

TY - JOUR

T1 - Ion target impact energy during Type I edge localized modes in JET ITER-like Wall

AU - Guillemaut, C.

AU - Jardin, A.

AU - Horacek, J.

AU - Autricque, A.

AU - Arnoux, G.

AU - Boom, J.

AU - Brezinsek, S.

AU - Coenen, J. W.

AU - De La Luna, E.

AU - Devaux, S.

AU - Eich, T.

AU - Giroud, C.

AU - Harting, D.

AU - Kirschner, A.

AU - Lipschultz, B.

AU - Matthews, G. F.

AU - Moulton, D.

AU - O'Mullane, M.

AU - Stamp, M.

PY - 2015/8/1

Y1 - 2015/8/1

N2 - The ITER baseline scenario, with 500 MW of DT fusion power and Q = 10, will rely on a Type I ELMy H-mode, with ΔW = 0.7 MJ mitigated edge localized modes (ELMs). Tungsten (W) is the material now decided for the divertor plasma-facing components from the start of plasma operations. W atoms sputtered from divertor targets during ELMs are expected to be the dominant source under the partially detached divertor conditions required for safe ITER operation. W impurity concentration in the plasma core can dramatically degrade its performance and lead to potentially damaging disruptions. Understanding the physics of plasma-wall interaction during ELMs is important and a primary input for this is the energy of incoming ions during an ELM event. In this paper, coupled Infrared thermography and Langmuir Probe (LP) measurements in JET-ITER-Like-Wall unseeded H-mode experiments with ITER relevant ELM energy drop have been used to estimate the impact energy of deuterium ions (D+) on the divertor target. This analysis gives an ion energy of several keV during ELMs, which makes D+ responsible for most of the W sputtering in unseeded H-mode discharges. These LP measurements were possible because of the low electron temperature (Te) during ELMs which allowed saturation of the ion current. Although at first sight surprising, the observation of low Te at the divertor target during ELMs is consistent with the 'Free-Streaming' kinetic model which predicts a near-complete transfer of parallel energy from electrons to ions in order to maintain quasi-neutrality of the ELM filaments while they are transported to the divertor targets.

AB - The ITER baseline scenario, with 500 MW of DT fusion power and Q = 10, will rely on a Type I ELMy H-mode, with ΔW = 0.7 MJ mitigated edge localized modes (ELMs). Tungsten (W) is the material now decided for the divertor plasma-facing components from the start of plasma operations. W atoms sputtered from divertor targets during ELMs are expected to be the dominant source under the partially detached divertor conditions required for safe ITER operation. W impurity concentration in the plasma core can dramatically degrade its performance and lead to potentially damaging disruptions. Understanding the physics of plasma-wall interaction during ELMs is important and a primary input for this is the energy of incoming ions during an ELM event. In this paper, coupled Infrared thermography and Langmuir Probe (LP) measurements in JET-ITER-Like-Wall unseeded H-mode experiments with ITER relevant ELM energy drop have been used to estimate the impact energy of deuterium ions (D+) on the divertor target. This analysis gives an ion energy of several keV during ELMs, which makes D+ responsible for most of the W sputtering in unseeded H-mode discharges. These LP measurements were possible because of the low electron temperature (Te) during ELMs which allowed saturation of the ion current. Although at first sight surprising, the observation of low Te at the divertor target during ELMs is consistent with the 'Free-Streaming' kinetic model which predicts a near-complete transfer of parallel energy from electrons to ions in order to maintain quasi-neutrality of the ELM filaments while they are transported to the divertor targets.

KW - edge localized modes

KW - JET ITER-like wall

KW - magnetic confinement fusion

UR - http://www.scopus.com/inward/record.url?scp=84938864486&partnerID=8YFLogxK

U2 - 10.1088/0741-3335/57/8/085006

DO - 10.1088/0741-3335/57/8/085006

M3 - Article

SN - 0741-3335

VL - 57

JO - Plasma Physics and Controlled Fusion

JF - Plasma Physics and Controlled Fusion

IS - 8

M1 - 085006

ER -