Methods to determine the radiated power in SPI-mitigated disruptions in JET

Lovell, J.; Reinke, M.L.; Sheikh, U.; Sweeney, R.; Puglia, P.; Carvalho, P.; Baylor, L. R.; Contributors, Jet

doi:10.1063/5.0014654

Cited by 10 publications

(11 citation statements)

References 14 publications

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“…While the trends derived from these works have helped to build an understanding of mitigation performance dependencies, reactor class devices like ITER require absolute measurements to ensure the lifetime of the first wall and divertor. A recent work demonstrates that radiated power calculations in a small toroidal wedge containing a horizontal or vertical bolometer array suffers from errors up to ±50% when the location of the source in the poloidal plane is unknown [52]. The errors incurred from toroidal peaking are in principle unbounded with the usual small number of point-like measurements in the toroidal direction.…”

Section: Discussionmentioning

confidence: 99%

3D radiation, density, and MHD structures following neon shattered pellet injection into stable DIII-D Super H-mode discharges

et al. 2021

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Six nominally repeat neon shattered pellet injection (SPI) shutdowns of stable DIII-D Super H-modes are studied to understand the 3D properties of the radiation and impurity transport. The radiation efficiency and radiation peaking determine whether first wall melting is expected following disruption mitigation in ITER. Previous studies make use of axisymmetric approximations to infer radiation efficiencies, but validating the high efficiency required by ITER necessitates improved accuracy, and this work contributes by exploring the 3D radiation and density structures that will inform forward modeling. When the neon shatter plume produced by the SPI reaches the plasma edge, m/n = 3/1 and 2/1 island O-points are observed to align with the injection trajectory in five out of six cases, suggesting that the injected material seeds the island O-points. Field aligned neon structures emitting Ne-I line radiation drift at 1 km s−1 in the ion diamagnetic drift direction during the pre-thermal quench, tracking the motion of the m/n = 2/1 island O-point. Neon fragments penetrate to the q = 2 surface by the time of the thermal quench. Techniques to constrain the 3D emissivity are explored, and one method constrains a 3D flux tube that is consistent with the radiation data, and when mapped to the interferometers, intersects the lasers that measure the highest density. The resulting structure derived from the radiation measurements exists near the 2/1 island X-point. In five repeatable discharges, the peak of the radiation in the toroidal direction exists in a 120° toroidal sector where the injection occurs, in contrast with the outlier discharge where the toroidal peak exists in the complementary 240° toroidal sector far from the injector, and where a 50% lower density rise is observed. The n = 1 phase behavior is markedly different in the outlier discharge, suggesting a possible dependence of the radiation structure and the assimilation efficiency on MHD.

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Section: Discussionmentioning

confidence: 99%

3D radiation, density, and MHD structures following neon shattered pellet injection into stable DIII-D Super H-mode discharges

et al. 2021

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“…In fact, fast camera observations of the disrupting plasmas reveal a large helical structure during the TQ. Using radiation phantoms to match the individual line-of-sight measurements [12], the analysis can be improved, resulting in higher radiation efficiency [13]. However, in some cases the radiated fraction remains low.…”

Section: Thermal Load Mitigation Using Mixtures Of Deuterium and Neonmentioning

confidence: 99%

Shattered pellet injection experiments at JET in support of the ITER disruption mitigation system design

et al. 2021

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A series of experiments have been executed at JET to assess the efficacy of the newly installed Shattered Pellet Injection (SPI) system in mitigating the effects of disruptions. Issues, important for the ITER disruption mitigation system, such as thermal load mitigation, avoidance of runaway electron formation, radiation asymmetries during thermal quench mitigation, electromagnetic load control and runaway electron energy dissipation have been addressed over a large parameter range. The efficiency of the mitigation has been examined for the various SPI injection strategies. The paper summarises the results from these JET SPI experiments and discusses their implications for the ITER disruption mitigation scheme.

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“…This approach can lead to systematic errors if the radiation emission profile is poloidally peaked. The potential error arising from highly localised emission was calculated to be +/−50% for the vertical camera and +/−30% for the horizontal camera in the most extreme cases [12]. Due to its lower sensitivity to poloidal emission location, the radiated energies presented will be inferred from the horizontal camera and the data processed identically to past disruption mitigation experiments on JET [13].…”

Section: Diagnosticsmentioning

confidence: 99%

Disruption thermal load mitigation with shattered pellet injection on the Joint European Torus (JET)

et al. 2021

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Disruption mitigation remains a critical, unresolved challenge for ITER. To aid in addressing this challenge, a shattered pellet injection (SPI) system was installed on JET and experiments conducted at a range of thermal energy fractions and stored energies in excess of 7 MJ. The primary goals of these experiments were to investigate the efficacy of the SPI on JET and the ability of the plasma to assimilate multiple pellets. Single pellet injections produced a saturation in total radiated energy (W rad) with increasing injected neon content, suggesting total radiation of stored thermal energy. Further increases in injected neon quantities resulted in reduced cooling times and current quench (CQ) durations, indicating higher impurity assimilation. No significant variation in CQ duration or W rad was observed when varying the deuterium content at fixed neon quantities. Higher assimilation, inferred by shorter CQ durations, was measured when a mechanical punch was used to launch the pellets and this was attributed to a lower pellet velocity leading to higher solid content in the pellet plume and larger fragments penetrating deeper into the plasma. Radiation asymmetries averaged over the cooling time were inferred from Emis3D and ranged from 1.6 to 1.9. Asymmetries averaged over the entire disruption sequence were found to increase at higher thermal energy fractions. The radiated energy fractions decreased with increasing thermal energy fractions but this trend was eliminated when toroidal asymmetries were accounted for with Emis3D. Pure deuterium pellets were able to produce cooling times of up to 75 ms with a gradual loss in thermal stored energy of up to 80%. Experiments with multiple pellet injection indicated W rad can be increased through pellet superposition and density can be increased with an additional D2 injection without a reduction in W rad. KPRAD modelling accurately reproduced the cooling times and the CQ duration at high thermal energies. Assimilation estimates from KPRAD indicated CQ rates scale strongly whilst W rad scales weakly and saturates with assimilated neon content. Comparable W rad can be achieved with lower assimilated neon quantities as longer cooling times are attained. Thus reduced neon content can be preferential in a thermal load mitigation scheme as it may reduce radiation asymmetries and prevent flash melting.

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Methods to determine the radiated power in SPI-mitigated disruptions in JET

Cited by 10 publications

References 14 publications

3D radiation, density, and MHD structures following neon shattered pellet injection into stable DIII-D Super H-mode discharges

3D radiation, density, and MHD structures following neon shattered pellet injection into stable DIII-D Super H-mode discharges

Shattered pellet injection experiments at JET in support of the ITER disruption mitigation system design

Disruption thermal load mitigation with shattered pellet injection on the Joint European Torus (JET)

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