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Title: Plasma/liquid metal interactions during tokamak operation.

Abstract

One of the critical technological challenges of future tokamak fusion devices is the ability for plasma-facing components to handle both normal and abnormal plasma/surface interaction events that compromise their lifetime and operation of the machine. Under normal operation plasma/surface interactions that are important include: sputtering, particle implantation and recycling, He pumping and ELM (edge localized modes)-induced erosion. In abnormal or off-normal operation: disruptions and vertical displacement events (VDEs) are important. To extend PFC lifetime under these conditions, liquid-metals have been considered as candidate PFCs (Plasma-Facing Components), including: liquid lithium, tin-lithium, gallium and tin. Liquid lithium has been measured to have nonlinear increase of physical sputtering with rise in temperature. Such increase can be a result of exposure to ELM-level particle fluxes. The significant increase in particle flux to the divertor and nearby PFCs can enhance sputtering erosion by an order of magnitude or more. In addition from the standpoint of hydrogen recycling and helium pumping liquid lithium appears to be a good candidate plasma-facing material (PFM). Advanced designs of first wall and divertor systems propose the application of liquid-metals as an alternate PFC to contend with high-heat flux constraints of large-scale tokamak devices. Additional issues include PFC operation under disruptionsmore » and long temporal instabilities such as VDEs. A comprehensive two-fluid model is developed to integrate core and SOL (scrape-off layer) parameters during ELMs with PFC surface evolution using the HEIGHTS package. Special emphasis is made on the application of lithium as a candidate plasma-facing liquid-metal.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
957382
Report Number(s):
ANL/ET/CP-116239
TRN: US201002%%950
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Conference
Resource Relation:
Journal Name: Fusion Sci. Technol.; Journal Volume: 47; Journal Issue: 3 ; Apr. 2005; Conference: 16th ANS Topical Meeting on the Technology of Fusion (TOFE); Sep. 14, 2004 - Sep. 16, 2004; Madison, WI
Country of Publication:
United States
Language:
ENGLISH
Subject:
08 HYDROGEN; DIVERTORS; FIRST WALL; GALLIUM; HELIUM; HYDROGEN; LIFETIME; LIQUID METALS; LITHIUM; PUMPING; RECYCLING; SOLS; SPUTTERING; TOKAMAK DEVICES

Citation Formats

Hassanein, A., Allain, J. P., Insepov, Z., Konkashbaev, I., and Energy Technology. Plasma/liquid metal interactions during tokamak operation.. United States: N. p., 2005. Web.
Hassanein, A., Allain, J. P., Insepov, Z., Konkashbaev, I., & Energy Technology. Plasma/liquid metal interactions during tokamak operation.. United States.
Hassanein, A., Allain, J. P., Insepov, Z., Konkashbaev, I., and Energy Technology. 2005. "Plasma/liquid metal interactions during tokamak operation.". United States. doi:.
@article{osti_957382,
title = {Plasma/liquid metal interactions during tokamak operation.},
author = {Hassanein, A. and Allain, J. P. and Insepov, Z. and Konkashbaev, I. and Energy Technology},
abstractNote = {One of the critical technological challenges of future tokamak fusion devices is the ability for plasma-facing components to handle both normal and abnormal plasma/surface interaction events that compromise their lifetime and operation of the machine. Under normal operation plasma/surface interactions that are important include: sputtering, particle implantation and recycling, He pumping and ELM (edge localized modes)-induced erosion. In abnormal or off-normal operation: disruptions and vertical displacement events (VDEs) are important. To extend PFC lifetime under these conditions, liquid-metals have been considered as candidate PFCs (Plasma-Facing Components), including: liquid lithium, tin-lithium, gallium and tin. Liquid lithium has been measured to have nonlinear increase of physical sputtering with rise in temperature. Such increase can be a result of exposure to ELM-level particle fluxes. The significant increase in particle flux to the divertor and nearby PFCs can enhance sputtering erosion by an order of magnitude or more. In addition from the standpoint of hydrogen recycling and helium pumping liquid lithium appears to be a good candidate plasma-facing material (PFM). Advanced designs of first wall and divertor systems propose the application of liquid-metals as an alternate PFC to contend with high-heat flux constraints of large-scale tokamak devices. Additional issues include PFC operation under disruptions and long temporal instabilities such as VDEs. A comprehensive two-fluid model is developed to integrate core and SOL (scrape-off layer) parameters during ELMs with PFC surface evolution using the HEIGHTS package. Special emphasis is made on the application of lithium as a candidate plasma-facing liquid-metal.},
doi = {},
journal = {Fusion Sci. Technol.},
number = 3 ; Apr. 2005,
volume = 47,
place = {United States},
year = 2005,
month = 4
}

Conference:
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  • One of the critical technological challenges of future tokamak fusion devices is the ability for plasma-facing components to handle both normal and abnormal plasma/surface interaction events that compromise their lifetime and operation of the machine. Under normal operation plasma/surface interactions that are important include: sputtering, particle implantation and recycling, He pumping and ELM (edge localized modes)-induced erosion. In abnormal or off-normal operation: disruptions and vertical displacement events (VDEs) are important. To extend PFC lifetime under these conditions, liquid-metals have been considered as candidate PFCs (Plasma-Facing Components), including: liquid lithium, tin-lithium, gallium and tin.Liquid lithium has been measured to have nonlinearmore » increase of physical sputtering with rise in temperature. Such increase can be a result of exposure to ELM-level particle fluxes. The significant increase in particle flux to the divertor and nearby PFCs can enhance sputtering erosion by an order of magnitude or more. In addition from the standpoint of hydrogen recycling and helium pumping liquid lithium appears to be a good candidate plasma-facing material (PFM). Advanced designs of first wall and divertor systems propose the application of liquid-metals as an alternate PFC to contend with high-heat flux constraints of large-scale tokamak devices. Additional issues include PFC operation under disruptions and long temporal instabilities such as VDEs. A comprehensive two-fluid model is developed to integrate core and SOL (scrape-off layer) parameters during ELMs with PFC surface evolution using the HEIGHTS package. Special emphasis is made on the application of lithium as a candidate plasma-facing liquid-metal.« less
  • The particle confinement time in tokamaks, {tau}{sub p}, is at least an order of magnitude less than the length of the discharge. In order to maintain a constant density during the discharge, it is necessary to provide an external hydrogen fueling source. On Phaedrus-T, approximately 4 {times} 10{sup 17} hydrogen atoms per millisecond must be puffed into the vessel to maintain a constant density. Ion impact onto materials within the vacuum vessel causes sputtering and gas desorption, and these processes provide an additional uncontrolled fueling source. On the Phaedrus-T tokamak, high power rf operation increases the sputtering and gas desorptionmore » rates. This increased gas influx, called rf fueling, can lead to disruptions or create ambiguity in interpreting the nature of the rf physics. Antenna designs have played a critical role in determining the amount rf fueling that occurs. On Phaedrus-T, insulating boron nitride (BN) protection limiters intercept the plasma flow to the antenna straps. Early versions of the Phaedrus-T antennas completely surrounded the antenna straps with BN. 100 kW operation led to an influx of up to 7 {times} 10{sup 17} electrons per millisecond which caused the plasma density to rise uncontrollably. The present BN shield design possessed only side limiters which prevent plasma flow along the magnetic lines from reaching the straps. The net influx has been reduced to less than 1 {times} 10{sup 17} electrons per millisecond for 400 kW operation. Results documenting the reduced rf fueling are presented.« less
  • Power loadings experienced by tokamak plasma facing components during normal operation and during off-normal events are discussed. A model for power and particle flow in the tokamak boundary layer is presented and model predictions are compared to infrared measurements of component heating. The inclusion of the full three-dimensional geometry of the component and of the magnetic flux surface is very important in the modeling. Experimental measurements show that misalignment of component armor tile surfaces by only a millimeter can lead to significant localized heating. An application to the design of plasma facing components for future machines is presented. Finally, thermalmore » loads expected during tokamak disruptions are discussed. The primary problems are surface melting and vaporization due to localized intense heating during the disruption thermal quench and volumetric heating of the component armor and structure due to localized impact of runaway electrons. 39 refs., 8 figs., 1 tab.« less
  • Recent progress in understanding of disruptions and in developing methods to avoid disruption damage is presented. Nearly complete mitigation of conducted heat loads has been achieved with high-Z gas jet shutdown. The resulting local radiation heat flash melting in the main chamber might be a concern in ITER, especially with beryllium walls. During the current quench, significant vessel forces can occur due to halo currents I-halo; however, these are found to fall reliably below a boundary of (halo current fraction times halo current peaking factor) <0.7 both experimentally and numerically. Numerical simulations indicate that runaway electrons (REs) could cause seriousmore » damage to hard-to reach components in ITER, making their suppression a high priority. During the current quench, less than 20% of the density required for collisional suppression of REs appears to have been achieved. Collisional suppression of REs may have been achieved, however, in full-current RE beams with gas injection. (C) 2010 Elsevier B.V. All rights reserved.« less