Deposition of lithium on a plasma edge probe in TFTR. Behavior of lithium-painted walls interacting with edge plasmas

Hirooka, Y.; Ashida, Kan; Kugel, H.; Walsh, D.S.; Wampler, W.R.; Bell, M.G.; Conn, R.W.; Hara, Masanori; Luckhardt, S.; Matsuyama, Masao; Mansfield, D. K.; Mueller, D.; Skinner, C.H.; Walters, T.; Watanabe, Kuniaki

doi:10.1016/s0022-3115(99)00053-7

Cited by 3 publications

(1 citation statement)

References 21 publications

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“…Intercalation (mixing) of lithium into graphite was evident, and lithium was preferentially sputtered over carbon, leading to an order of magnitude reduction in net carbon sputtering yield. Materials mixing in the carbon and lithium systems appears to be a key process to successful lithium wall conditioning [687]. Renewed interest in liquid lithium as a plasma facing material [55] makes these low recycling regimes relevant to fusion reactor studies.…”

Section: Wall Conditioningmentioning

confidence: 99%

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

et al. 2001

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The major increase in discharge duration and plasma energy in a next step DT fusion reactor will give rise to important plasma-material effects that will critically influence its operation, safety and performance. Erosion will increase to a scale of several centimetres from being barely measurable at a micron scale in today's tokamaks. Tritium co-deposited with carbon will strongly affect the operation of machines with carbon plasma facing components. Controlling plasma-wall interactions is critical to achieving high performance in present day tokamaks, and this is likely to continue to be the case in the approach to practical fusion reactors. Recognition of the important consequences of these phenomena stimulated an internationally co-ordinated effort in the field of plasma-surface interactions supporting the Engineering Design Activities of the International Thermonuclear Experimental Reactor project (ITER), and significant progress has been made in better understanding these issues. The paper reviews the underlying physical processes and the existing experimental database of plasma-material interactions both in tokamaks and laboratory simulation facilities for conditions of direct relevance to next step fusion reactors. Two main topical groups of interaction are considered: (i) erosion/redeposition from plasma sputtering and disruptions, including dust and flake generation and (ii) tritium retention and removal. The use of modelling tools to interpret the experimental results and make projections for conditions expected in future devices is explained. Outstanding technical issues and specific recommendations on potential R&D avenues for their resolution are presented.

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Section: Wall Conditioningmentioning

confidence: 99%

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

et al. 2001

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Rapid diffusion of lithium into bulk graphite in lithium conditioning

Itou

Toyoda

Morita³

et al. 2001

Journal of Nuclear Materials

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Observations concerning the injection of a lithium aerosol into the edge of TFTR discharges

et al. 2001

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A new method of actively modifying the plasma-wall interaction was tested on the Tokamak Fusion Test Reactor. A laser was used to introduce a directed lithium aerosol into the discharge scrape-off layer. The lithium introduced in this fashion ablated a n d migrated preferentially to the limiter contact points. This allowed the plasma-wall interaction to be influenced in situ and in real t i m e by external means. Significant improvement in energy confinement and fusion neutron production rate as well as a reduction in t h e plasma Z eff have been documented in a neutral-beam-heated plasma. The introduction of a metallic aerosol into the plasma e d g e increased the internal inductance of the plasma column and also resulted in prompt heating of core electrons in Ohmic plasmas. Preliminary evidence also suggests that the introduction of a n aerosol leads to both edge poloidal velocity shear and edge electric field shear. . I n t r o d u c t i o nIt has been well documented that the fusion performance of discharges in the Tokamak Fusion Test Reactor (TFTR) was strongly dependent on the physical and chemical condition of the graphite surface forming its limiter [1,2]. In particular, the highperformance supershot mode of operation was attainable at high currents (>2.0 MA) only when the graphite inner wall had previously been "scoured" by repeated discharges heated by high-power neutral beam injection (NBI) in order to render the limiter surface free of loosely-bound carbon and loosely-adsorbed hydrogenic material. At the end of a series of such pre-conditioning discharges, plasma fueling from the limiter typically reached a minimum.Moreover, only when this low-recycling condition had been attained did high levels of fusion performance become accessible.It has also been well documented that dramatic improvements in supershot fusion performance were attainable by the deposition of elemental lithium (Li) onto the limiter surface once it had been brought into the low-recycling condition. This deposition was carried out in earlier experiments by the injection and ablation of a few small (3 mg each) Li pellets [3,4,5,6]. In order to improve plasma performance during NBI, Li pellets were typically injected into the Ohmic phase of discharges and the ablated Li was allowed to 3 condense out of the plasma column and onto the limiter surface before the application of auxiliary heating. While the use of Li pellets did improve plasma performance, the technique was, nonetheless, highly perturbing. In order to reduce the perturbation to the plasma, brief but successful experiments with a Li effusion oven were also carried out on TFTR and are described elsewhere [7,8].While the use of an oven did result in an increase in the amount of Li deposited onto the inner wall as compared to pellet injection, deposition could only take place between discharges and not during the discharge of interest.In this work, an alternate wall-conditioning technique is described in which Li was injected into the scrape-off layer (SOL), during pl...

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Deposition of lithium on a plasma edge probe in TFTR. Behavior of lithium-painted walls interacting with edge plasmas

Cited by 3 publications

References 21 publications

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

Rapid diffusion of lithium into bulk graphite in lithium conditioning

Observations concerning the injection of a lithium aerosol into the edge of TFTR discharges

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