Enhanced helium exhaust during edge-localized mode suppression by resonant magnetic perturbations at DIII-D

Schmitz, O.; Abrams, T.; Briesemeister, A.; Bykov, I.; Chrystal, C.; Collins, C.; Evans, T.E.; Frerichs, H.; Grierson, B. A.; Moyer, R. A.; Paz-Soldan, C.; Thomas, D.M.; Unterberg, E.A.; Wade, M. R.

doi:10.1088/1741-4326/ab7d50

Cited by 7 publications

(6 citation statements)

References 22 publications

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“…For comparison, τ p /τ e ≈ 1.5 for the ELMy discharge without RMPs. This is consistent with experiments that have shown that RMPs reduce the particle confinement time in discharges with He impurity injection [27]. To study the impurity density evolution in more detail and to understand if the Al 13+ charge state density is indicative of the total impurity density, the STRAHL transport code is used.…”

Section: Evolution Of the Al Density Profilesupporting

confidence: 78%

Impurity transport in the pedestal of H-mode plasmas with resonant magnetic perturbations

Victor

Odstrčil

Paz-Soldan

et al. 2020

Plasma Phys. Control. Fusion

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Experiments on DIII-D show that resonant magnetic perturbations (RMPs) reduce the impurity confinement time in the H-mode pedestal below that of naturally ELMy plasmas. STRAHL modeling of discharges with aluminum laser blow off (LBO) injection show increased diffusion in the pedestal of H-mode discharges with RMPs. The increased diffusion from the RMPs provides improved impurity control compared to the naturally ELMy discharges and prevents the buildup of impurities near the edge of the plasma. Tungsten LBO injection into discharges with and without RMPs led to striking differences in the evolution of the discharge. The naturally ELMy discharge became ELM free and showed an increase in edge radiation, leading to the eventual radiative collapse of the plasma. Injecting a similar number of W particles into discharges with RMPs, either with or without ELMs, led to a measurable accumulation of core W but did not significantly impact the evolution of the discharge. These results indicate that RMPs are beneficial for controlling the buildup of impurities in the pedestal region of the plasma.

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Section: Evolution Of the Al Density Profilesupporting

confidence: 78%

Impurity transport in the pedestal of H-mode plasmas with resonant magnetic perturbations

Victor

Odstrčil

Paz-Soldan

et al. 2020

Plasma Phys. Control. Fusion

Self Cite

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“…However, the decay time of the Ar 16 + after each pulse is clearly longer in comparison to the ELMy phase after 6.8 s suggesting an increased Ar core confinement time under ELM-suppressed conditions and/or a reduced pumping efficiency. Recent helium exhaust experiments comparing RMP ELM-suppressed and non-perturbed ELM H-modes in DIII-D showed a better global exhaust of helium with RMPs [34]. A caveat of the present scenario regarding radiative power exhaust is the low density required for ELM suppression [31], which reduces the radiated power per Ar ion in the core and divertor and also leads to slow pumping, challenging active control.…”

Section: Ar Injection Into Resonant Magnetic Perturbation (Rmp) Elm-s...mentioning

confidence: 85%

Developments towards an ELM-free pedestal radiative cooling scenario using noble gas seeding in ASDEX Upgrade

et al. 2020

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Integrated edge-localized-mode (ELM)-free or small ELM scenarios for the demonstration fusion power plant (DEMO) are investigated in ASDEX Upgrade using argon seeding for radiative power removal mainly in the pedestal region. An important aspect is the modification of the electron pressure in the pedestal by the additional radiative power losses. Full ELM suppression could be achieved in a no-ELM H-mode scenario featuring an edge electromagnetic quasicoherent mode up to a heating power of 5 MW, where argon radiation allowed the extension of the heating power operational space. At higher powers up to 12 MW (reaching the beta limit), ELMs of reduced size prevail and detachment is obtained by the argon seeding. Control of the position of a radiating zone localized inside the X-point was found to be favorable compared to the control of the separatrix power for low P s e p / P h e a t . Integration of pedestal cooling with Ar and ELM suppression by resonant magnetic perturbations (RMP) allowed an increase of the core radiation and a partial recovery of normalized confinement to H98 = 1. This favorable behavior is finally limited by the loss of the RMP density pump-out effect, followed by an ELM-free H-mode phase and re-occurrence of ELMs. For an active tailoring of the pedestal pressure profile, precise knowledge of the radiation profile is required. Modeling of the argon radiation profile with the STRAHL code showed good agreement with bolometry only if charge exchange of neutral deuterium with argon ions was taken into account, highlighting the importance of the neutral density in the pedestal region. In view of best integration of a no-ELM scenario with divertor detachment and high heating power, the divertor compression and enrichment of argon and neon were compared using dynamic gas puff experiments. Argon shows more than a factor of 3 higher divertor enrichment compared to neon, but the absolute values decrease with higher neutral deuterium pressure.

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“…Impurity experiments using n = 3 RMP fields to suppress ELMs in ITER-shaped plasmas found a factor of 2-3 reduction in the effective helium particle confinement time compared to ELMy H-modes without RMP fields [53]. Measurements of neutral partial pressures in the pumping plenum from Penning gauges show the partial pressure of helium increases substantially more than that of deuterium during RMP ELM-suppression for a range of cases, in comparison with ELMy cases.…”

Section: Effect Of Rmp On Plasma Edgementioning

confidence: 95%

“…1 ITER Organization 2 General Atomics 3 Oak Ridge National Laboratory 4 National Institute for Fusion Science, Japan 5 Max-Planck Institute for Plasma Physics 6 Durham University 7 Lawrence Livermore National Laboratory 8 Princeton Plasma Physics Laboratory 9 University of Texas, Austin 24 Universita di Milano-Bicocca 25 Stony Brook University (SUNY) 26 University of Tennessee, Knoxville 27 Southwestern Institute of Physics, China 28 University of California, Irvine 29 University of Toronto 30 Auburn University 31 Palomar College 32 Kungliga Tekniska Hogskolan 33 Princeton University 34 Chambers University of Technology (Sweden) 35 Istituto di Fisica del Plasma CNR-EURATOM 36 United Kingdom Atomic Energy Authority (CCFE) 37 Oak Ridge Institute for Science Education 38 Aalto University 39 Korea National Fusion Research Center 40 Georgia Tech 41 Australian National University 42 Ulsan National Institute of Science and Technology 43 National Institutes for Quantum and Radiological Science, Japan 44 Harvard University 45 SLS2 Consulting 46 Far-Tech, Inc. 47 STI Optronics, Inc. 48 Tech-X Corporation 49 The College of William and Mary 50 General Atomics Temp 51 Qinzhou University 52 General Atomics (Retired) 53 University of Nice 54…”

Section: Affiliationsmentioning

confidence: 99%

DIII-D research towards establishing the scientific basis for future fusion reactors

Petty

2019

Nucl. Fusion

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DIII-D research is addressing critical challenges in preparation for ITER and the next generation of fusion devices through focusing on plasma physics fundamentals that underpin key fusion goals, understanding the interaction of disparate core and boundary plasma physics, and developing integrated scenarios for achieving high performance fusion regimes. Fundamental investigations into fusion energy science find that anomalous dissipation of runaway electrons (RE) that arise following a disruption is likely due to interactions with RE-driven kinetic instabilities, some of which have been directly observed, opening a new avenue for RE energy dissipation using naturally excited waves. Dimensionless parameter scaling of intrinsic rotation and gyrokinetic simulations give a predicted ITER rotation profile with significant turbulence stabilization. Coherence imaging spectroscopy confirms near sonic flow throughout the divertor towards the target, which may account for the convection-dominated parallel heat flux. Core-boundary integration studies show that the small angle slot divertor achieves detachment at lower density and extends plasma cooling across the divertor target plate, which is essential for controlling heat flux and erosion. The Super H-mode regime has been extended to high plasma current (2.0 MA) and density to achieve very high pedestal pressures (~30 kPa) and stored energy (3.2 MJ) with H 98y2 ≈ 1.6–2.4. In scenario work, the ITER baseline Q = 10 scenario with zero injected torque is found to have a fusion gain metric independent of current between q 95 = 2.8–3.7, and a lower limit of pedestal rotation for RMP ELM suppression has been found. In the wide pedestal QH-mode regime that exhibits improved performance and no ELMs, the start-up counter torque has been eliminated so that the entire discharge uses ≈0 injected torque and the operating space is more ITER-relevant. Finally, the high- (⩽3.8) hybrid scenario has been extended to the high-density levels necessary for radiating divertor operation, achieving ~40% divertor heat flux reduction using either argon or neon with P tot up to 15 MW.

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Enhanced helium exhaust during edge-localized mode suppression by resonant magnetic perturbations at DIII-D

Cited by 7 publications

References 22 publications

Impurity transport in the pedestal of H-mode plasmas with resonant magnetic perturbations

Impurity transport in the pedestal of H-mode plasmas with resonant magnetic perturbations

Developments towards an ELM-free pedestal radiative cooling scenario using noble gas seeding in ASDEX Upgrade

DIII-D research towards establishing the scientific basis for future fusion reactors

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