Shear Strength and Release of Large Cryogenic Pellets from the Barrel of a Shattered Pellet Injector for Disruption Mitigation

Gebhart, T. E.; Ghiozzi, A.G.; Velez, D. A.; Baylor, L. R.; Chilen, C.; Meitner, S. J.

doi:10.1080/15361055.2021.1874766

Cited by 7 publications

(9 citation statements)

References 7 publications

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“…Firing the pellet without a punch had a reliability issue, namely the pure D 2 pellets fired reliably but a large fraction ( 10%-20%) of Ne mixture pellets did not fire and were assumed to be stuck in the cold head of a barrel. This is due to the fact that the shear strength of neon is many times (∼5) higher than that of deuterium (the shear strength of argon is three to four times stronger than neon at much warmer temperatures) [65].…”

Section: Discussionmentioning

confidence: 99%

Interaction of SPI pellets with plasma on JET and associated disruptions

Gerasimov,

Baylor,

Boboc

et al. 2024

Phys. Scr.

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The presented data refer to the Shattered Pellet Injector (SPI) experiments carried out at JET in 2019-2020. This paper is a full journal version of the data originally presented as posters at TMPDM_2020 and EPS_2021. This paper presents various aspects of the interaction of pellets with plasma and associated disruptions. The experiment was performed with Ip = (1.1 - 3.1) MA plasmas and mainly with Ne + D2 pellet composition, but also with Ar pellets. The Current Quench (CQ) time, τ80-20, is the key characteristic of mitigation effectiveness. A pellet with a high content of Ne or Ar can reduce the CQ duration below the upper required JET threshold. Plasmas with high (thermal + internal poloidal magnetic) pre-disruptive plasma energy require a high content of Ne pellets to obtain a short CQ duration. Pellets with a small amount of Ne (and accordingly large amount of D), instead of causing a mitigated CQ, create the conditions for a “cold” Vertical Displacement Events (VDE).The SPI was applied to plasma with different status: mainly to normal (“healthy”) plasma, i.e. not prone to disruption, post-disruptive and VDE plasma. This study shows that SPI effectiveness in terms of CQ duration and, accordingly, EM loads does not depend on the state of the plasma, whether it is “healthy” or post-disruptive plasma. SPI has been shown to reduce axisymmetric vertical vessel reaction forces by about (30-40)% compared to unmitigated disruptions.On JET, the VDE, whether “hot” or “cold”, always creates the conditions for a toroidal asymmetry in the plasma, so the VDE on the JET is referred to as Asymmetric VDE (AVDE). The interrupting of VDE and prevention of AVDE with SPI has been demonstrated. Thus, the effectiveness of disruption mitigation using SPI has been confirmed.

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Section: Discussionmentioning

confidence: 99%

Interaction of SPI pellets with plasma on JET and associated disruptions

Gerasimov,

Baylor,

Boboc

et al. 2024

Phys. Scr.

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“…where T is the pellet temperature close to the barrel wall. Measured shear strength of protium, deuterium and neon solids were published in [18]. On the basis of these data the use of a punch mechanism for releasing the pellets was proposed [2].…”

Section: Propellant Valvementioning

confidence: 99%

“…Based on the shear strength of solid protium [18] modelling indicates that at least 12 bar-litre propellant gas should be injected into the barrel behind the pellet in order to launch protium pellets in the Support Laboratory [19]. In experiments it was found that even 3-4 bar-litre can launch a Protium pellet at 5 K temperature.…”

Section: Protium Pellet Launchmentioning

confidence: 99%

“…In experiments it was found that even 3-4 bar-litre can launch a Protium pellet at 5 K temperature. One possible reason for this discrepancy might be the fast pressure pulse on the pellet, in contrast to static shear strength measurements [18]. Another reason could be a pressure wave hitting the pellet if the valve opens quickly (full open in 1.5 ms), as observed in propellant valve laboratory tests [15].…”

Section: Protium Pellet Launchmentioning

confidence: 99%

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Production and launch studies of cryogenic pellets for the ITER disruption mitigation system

Zoletnik,

Bartók,

Buzás

et al. 2024

Nucl. Fusion

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A support laboratory has been set up to study pellet production, launch and shattering of cryogenic protium, deuterium, and neon pellets for the ITER Disruption Mitigation System (DMS), which plans to use 28.5 x 57 mm (diameter x length) protium, neon an mixture pellets in the Shattered Pellet Injectors. Such large protium pellets have not been produced and launched before, therefore the desublimation and launch process have been studied in detail in two steps. First 19 mm diameter pellets were produced, followed by the demonstration of the final pellet size. Pellet desublimation recipes were established for all pellet types, and it was found that, under certain conditions, even the large neon pellets can be launched with a propellent gas pulse, without requiring a mechanical punch device. This is attributed to cryogenic snow formation on the surface of the pellet. Conditions for the snow formation are studied and tendencies are understood using simple calculations.

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“…To support the design of the disruption mitigation system on ITER [4], the SPI is continued to be studied experimentally on DIII-D [5][6][7][8][9][10][11], as well as on J-TEXT [12,13], KSTAR [14][15][16], HL-2A [17], JET [18,19], ASDEX Upgrade [20], and also theoretically [21][22][23][24][25][26][27][28]. The main areas of research during past years were the design of SPI systems [12,20,[29][30][31][32][33][34][35], characterization of single [2, 3, 6, 10, 17-19, 24, 27, 36] and multiple injections [8, 14-16, 18, 19, 28], comparison with MGI [2,3,13,21,37], analysis of SPI interaction with runaway electrons (REs) [5,7,9,25,26] and effects of magnetohydrodynamic (MHD) activity on SPI …”

Section: Introductionmentioning

confidence: 99%

Density and temperature profiles after low-Z and high-Z shattered pellet injections on DIII-D

Lvovskiy,

Matsuyama,

O’Gorman

et al. 2023

Nucl. Fusion

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In this work we utilize the recently upgraded Thomson scattering diagnostic to resolve density and temperature plasma profiles after pure deuterium and mixed neon/deuterium shattered pellet injections (SPIs) on DIII-D. This allows us to study individual components of the staggered scheme proposed for disruption mitigation on ITER, consisting of a low-Z material SPI followed by a delayed high-Z SPI. Obtained spatio-temporal density profiles exhibit very different dynamics after dominantly neon and pure deuterium SPIs. The neon SPI causes a fast radiative plasma collapse in a few milliseconds and results in almost flat density profile once the impurity mixes with the plasma during and after the thermal quench (TQ). The deuterium SPI leads to a disruption delayed by ten and more milliseconds, but very limited core fueling can be observed before the disruption. Even during and after the TQ, the edge deuterium density significantly exceeds the core density. 1D transport modeling suggests that this poor core fueling can be explained by strong outward grad-B-induced drift of the injected deuterium. Preliminary simulations show that larger pellet shards and greater injected quantity can be used to improve the penetration of the low-Z material into the core. These results call for optimization and further evaluation of the staggered SPI on ITER.

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Shear Strength and Release of Large Cryogenic Pellets from the Barrel of a Shattered Pellet Injector for Disruption Mitigation

Cited by 7 publications

References 7 publications

Interaction of SPI pellets with plasma on JET and associated disruptions

Interaction of SPI pellets with plasma on JET and associated disruptions

Production and launch studies of cryogenic pellets for the ITER disruption mitigation system

Density and temperature profiles after low-Z and high-Z shattered pellet injections on DIII-D

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