Fast plasma shutdown by killer pellet injection in JT-60U with reduced heat flux on the divertor plate and avoiding runaway electron generation

Yoshino, R.; Kondoh, T.; Neyatani, Y.; Itami, K.; Kawano, Y.; Isei, N.

doi:10.1088/0741-3335/39/2/008

Cited by 103 publications

(70 citation statements)

References 20 publications

(15 reference statements)

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“…It has been shown [8] that high-Z impurities, having large radiation rate coefficients, can radiate the energy of the plasma efficiently. This is true even when they are injected in low quantities, as with killer pellets [14] or low-pressure gas puffing [10]. As a result, the radiative fraction of the stored thermal energy is higher with argon than with helium, as can be seen in figure 1(b).…”

Section: Energy Removalmentioning

confidence: 96%

Using mixed gases for massive gas injection disruption mitigation on Alcator C-Mod

et al. 2011

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Abstract. Mixed gases are used for massive gas injection disruption mitigation on Alcator C-Mod in order to optimize radiation efficiency, halo current reduction, and response time. Gas mixtures of helium and argon (argon fraction 0-50%) are investigated in detail, as well as mixtures of deuterium, argon, krypton, and helium. Experiments show that injecting He/Ar mixtures leads to faster thermal and current quenches than with pure helium or argon injection, thus improving the time response of the disruption mitigation system and reducing the halo current. Small fractions of argon (∼5-10%) in helium also lead to optimized radiation fractions with large electron density increases in the core plasma. These results are consistent with the expectation that small fractions of argon will be entrained with the faster helium in the early phases of gas flow. The gas mixing allows one to simultaneously exploit the fast particle delivery rate of light helium gas and the large radiation capability of argon.

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Section: Energy Removalmentioning

confidence: 96%

Using mixed gases for massive gas injection disruption mitigation on Alcator C-Mod

et al. 2011

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“…These pellets are typically composed of moderate-Z or high-Z materials, and the pellet size and velocity are chosen such that the pellet can penetrate deep into the plasma core. Impurity pellet shutdown experiments demonstrating non-disruptive dissipation of the plasma thermal and/or magnetic energies have been performed in JT-60U [175][176][177], ASDEX-Upgrade [178,179], DIII-D [174,180,181], Alcator C-Mod [182], JET [183] and TFTR [184,185]. The efficacy of killer pellet shutdown clearly depends on having sufficient penetration of the pellet into the plasma, such that the resulting impurities are deposited more-or-less uniformly throughout the plasma cross-section.…”

Section: Other Plasma Disturbances Eg Elmsmentioning

confidence: 99%

“…These runaway electrons persist during current quench disruptions and can produce a current of up to about half of the pre-disruption plasma current in many present experiments, especially at low plasma densities, (e.g., TFTR [635], Tore Supra [636], JET [637,638] and JT-60U [175]). In present experiments, the magnitude of runaway electron generation varies, from none detectable to up to ≈50% of the initial plasma current.…”

Section: Runaway Electronsmentioning

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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“…Fast plasma shutdown by killer pellets has been demonstrated in several tokamak experiments [1,2,3], and it was shown that significant reduction of the thermal and mechanical loads on the vessel can be achieved. However, as the plasma cools down quickly, a large toroidal electric field is induced.…”

Section: Introductionmentioning

confidence: 99%

Runaway electron generation during plasma shutdown by killer pellet injection

Gál¹,

Fehér²,

Smith³

et al. 2008

Plasma Phys. Control. Fusion

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Abstract. Tokamak discharges are sometimes terminated by disruptions that may cause large mechanical and thermal loads on the vessel. To mitigate disruption-induced problems it has been proposed that "killer" pellets could be injected into the plasma in order to safely terminate the discharge. Killer pellets enhance radiative energy loss and thereby lead to rapid cooling and shutdown of the discharge. But pellets may also cause runaway electron generation, as has been observed in experiments in several tokamaks. In the present work, runaway dynamics in connection with deuterium or carbon pellet-induced fast plasma shutdown is considered. A pellet code which calculates the material deposition and initial cooling caused by the pellet is coupled to a runaway code, which determines the subsequent temperature evolution and runaway generation. In this way, a tool has been created to test the suitability of different pellet injection scenarios for disruption mitigation. If runaway generation is avoided, the resulting current quench times are too long to safely avoid large forces on the vessel due to halo currents.

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Fast plasma shutdown by killer pellet injection in JT-60U with reduced heat flux on the divertor plate and avoiding runaway electron generation

Cited by 103 publications

References 20 publications

Using mixed gases for massive gas injection disruption mitigation on Alcator C-Mod

Using mixed gases for massive gas injection disruption mitigation on Alcator C-Mod

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

Runaway electron generation during plasma shutdown by killer pellet injection

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