scholarly journals Validation of low-Z impurity transport theory using boron perturbation experiments at ASDEX Upgrade

2021 ◽  
Author(s):  
Rachael M McDermott ◽  
Clemente Angioni ◽  
Marco Cavedon ◽  
Athina Kappatou ◽  
Ralph Dux ◽  
...  
Keyword(s):  
Particle Flux ◽  
Transport Theory ◽  
Electron Cyclotron Resonance ◽  
Transport Coefficients ◽  
Electron Cyclotron Resonance Heating ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Density Profiles ◽  
Boron Particle ◽  
Impurity Transport

Abstract An experimental technique has been developed at ASDEX Upgrade (AUG) to separately identify the diffusive and convective components of the boron particle flux. Using this technique a database of B transport coefficients has been assembled that shows that the normalized ion temperature gradient (R/LTi) is the strongest organizing parameter for both the B diffusion and convection and large R/LTi is a necessary ingredient to obtain hollow B density profiles in AUG. This database also shows that large changes in the applied neutral beam injection (NBI) have a relatively small impact on impurity transport compared to similar changes in electron cyclotron resonance heating (ECRH). Even low levels of ECRH power dramatically increase both the diffusive and convective fluxes and lead to peaking of the impurity density profile. Comparisons to a combination of neoclassical and quasi-linear gyrokinetic simulations show good agreement in the measured and predicted diffusion coefficients. The outward convection measured in NBI dominated plasmas, however, is not well captured by the simulations, despite the inclusion of fast ions. In contrast, the convection is reasonably well reproduced for plasmas with flat or peaked boron density profiles. This dataset provides an excellent experimental validation of the non-monotonic, predicted, convective-particle-flux created by the combination of pure-pinch, thermo-diffusion, and roto-diffusion. In addition, this dataset demonstrates a non-monotonic dependence of the experimental particle diffusivity to ion heat conductivity (D/χi) in qualitative agreement with theoretical predictions.

Understanding core tungsten (W) transport and control in an improved high-performance fully non-inductive discharge on EAST

2021 ◽  
Author(s):  
Shengyu Shi ◽  
Jiale Chen ◽  
Clarisse Bourdelle ◽  
Xiang Jian ◽  
Tomas Odstrcil ◽  
...  
Keyword(s):  
Density Profile ◽  
Turbulent Diffusion ◽  
High Performance ◽  
Electron Cyclotron Resonance ◽  
Transport Coefficients ◽  
Linear Instability ◽  
Electron Cyclotron Resonance Heating ◽  
Plasma Parameters ◽  
Turbulent Diffusion Coefficient ◽  
Inductive Discharge

Abstract The behavior of heavy/high-Z impurity tungsten (W) in an improved high-performance fully non-inductive discharge on EAST with ITER-like divertor (ILD) is analyzed. It is found that W could be well controlled. The causes of no W accumulation are clarified by analyzing the background plasma parameters and modeling the W transport. It turns out that the electron temperature (T_e) and its gradient are usually high while the toroidal rotation and density peaking of the bulk plasma are small. In this condition, the modeled W turbulent diffusion coefficient is big enough to offset the total turbulent and neoclassical pinch, so that W density profile for zero particle flux will not be very peaked. Combining NEO and TGLF for the W transport coefficient and the impurity transport code STRAHL, not only the core W density profile is predicted but also the radiated information mainly produced by W in the experiment can be closely reconstructed. At last, the physics of controlling W accumulation by electron cyclotron resonance heating (ECRH) is illustrated considering the effects of changed T_e by ECRH on ionization balance and transport of W. It shows that the change of ionization and recombination balance by changed T_e is not enough to explain the experimental observation of W behavior, which should be attributed to the changed W transport. By comparing the W transport coefficients in two kinds of plasmas with different T_e profiles, it is shown that high T_e and its gradient play a key role to generate large turbulent diffusion through increasing the growth rate of linear instability so that W accumulation is prevented.

The role of BT-dependent flows on W accumulation at the edge of the confined plasma

2021 ◽  
Author(s):  
Shawn Angelo Zamperini ◽  
J.H. Nichols ◽  
Peter C. Stangeby ◽  
David Donovan ◽  
Jonah David Duran ◽  
...  
Keyword(s):  
Experimental Evidence ◽  
Background Plasma ◽  
Ion Temperature ◽  
Plasma Flows ◽  
Ion Temperature Gradient ◽  
Deposition Patterns ◽  
Metal Rings ◽  
Impurity Transport ◽  
Radial Diffusion Coefficient

Abstract Near-separatrix impurity accumulation between the crown and the outer midplane of tokamaks is a common feature in results from codes such as SOLPS-ITER and DIVIMP; however, experimental evidence of accumulation has only recently been obtained and is reported here. The codes find that the poloidal distribution of impurity ions in the scrape-off layer (SOL) depends primarily on toroidal field (BT)-dependent parallel flow patterns of the background plasma and the parallel ion temperature gradient (∇||Tion) force. Experimentally, Mach probes used in L-mode plasmas with favorable (for H-mode access) BT measure fast (M~0.3-0.5) inner-target-directed (ITD) background plasma flows at the crown of single-null discharges. This study reports a set of DIVIMP simulations for two similar H-mode discharges from the DIII-D W Metal Rings Campaign differing primarily in BT-direction to assess the effect that fast ITD flows have on the distribution of W ions in the SOL. It is found that for imposed ITD flows of M = 0.3, W ions that otherwise accumulate due to the ∇||Tion-force are largely flushed out. It is also found that doubling the radial diffusion coefficient from 0.3 to 0.6 m2/s prevents accumulation due to rapid cross-field transport into the far-SOL, where background plasma flows drain W ions to the divertors. Far-SOL W distributions from DIVIMP are then used to specify input to the impurity transport code 3DLIM, which is used to interpretively model collector probe deposition patterns measured in the “wall-SOL.” It is demonstrated that the deposition patterns are consistent with the DIVIMP predictions of near-SOL accumulation for the unfavorable-BT direction, and little/no accumulation for the favorable-BT direction. The wall-SOL collector probes have thus provided the first experimental evidence, albeit indirect, of near-SOL W accumulation – finding it occurs for the unfavorable-BT direction only. For the favorable-BT direction, fast flows can largely prevent accumulation from occurring.

Properties of ion temperature gradient and trapped electron modes in tokamak plasmas with inverted density profiles

2017 ◽  
Vol 24 (12) ◽  
pp. 122501 ◽  
Author(s):  
Huarong Du ◽  
Hogun Jhang ◽  
T. S. Hahm ◽  
J. Q. Dong ◽  
Z. X. Wang
Keyword(s):  
Temperature Gradient ◽  
Tokamak Plasmas ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Density Profiles ◽  
Trapped Electron

Collisionless trapped-electron-mode turbulence and transport in fluid descriptions

2007 ◽  
Vol 73 (5) ◽  
pp. 731-740 ◽  
Author(s):  
H. NORDMAN ◽  
P. STRAND ◽  
X. GARBET
Keyword(s):  
Fluid Transport ◽  
Fluid Model ◽  
Transport Coefficients ◽  
Ion Temperature ◽  
Plasma Parameters ◽  
Ion Temperature Gradient ◽  
Electron Mode ◽  
Mode Tem ◽  
Gyrokinetic Simulations ◽  
Trapped Electron

AbstractA study of particle and electron heat transport in tokamaks due to trapped-electron-mode (TEM) turbulence is presented. The study is based on the Weiland fluid model for ion-temperature-gradient (ITG) modes and TEMs, complemented and compared with a trapped electron fluid treatment which retains contributions from the weakly trapped electrons. The dependence of the fluid transport coefficients on magnetic shear and other plasma parameters is discussed and compared with results obtained from nonlinear gyrokinetic simulations. Inward (pinch) flows of particles and heat, previously reported for the coupled ITG–TEM system, are also found in the TEM dominated regime.

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