980 research outputs found
Analytic 1D approximation of the divertor broadening S in the divertor region for conductive heat transport
Outer target heat fluxes and power decay length scaling in L-mode plasmas at JET and AUG
Change of the scrape-off layer power width with the toroidal B-field direction in ASDEX Upgrade
Numerical Investigation of Impurity Seeded Radiation Enhancement in the Divertor region with Magnetic Perturbations in ASDEX Upgrade
Density dependence of SOL power width in ASDEX upgrade L-Mode
AbstractUnderstanding the heat transport in the scrape-off layer (SOL) and the divertor region is essential for the design of large fusion devices such as ITER and DEMO. Current scalings for the power fall-off length λq in H-Mode [1] are available only for the outer divertor target at low densities with low recycling divertor conditions. For the divertor power spreading S only an empirical scaling for ASDEX Upgrade L-Mode is available based on global plasma parameters [2]. Modelling using SOLPS shows a dependence of S on the divertor electron temperature [3]. A more detailed analysis of the heat transport forming λq and S is presented for ASDEX Upgrade L-Mode discharges in hydrogen (H), deuterium (D) and helium (He). For low densities the power fall-off length λq,o on the outer divertor target in H and D is described by the same parametric dependencies as the H-Mode scaling [1] but with a larger absolute size of the power fall-off length in L-Mode.The divertor power spreading S is studied using the local divertor measurements of the target electron temperature Te,tar and density ne,tar. It is found that the competition of the diffusive transport parallel and perpendicular to the magnetic field forming SâÏâ„/Ïâ„ is dominated by the temperature dependence of parallel electron conduction. For high divertor temperatures the ion gyro radius has a significant contribution to S, resulting in a minimum of S at âŒ30âeV.A recent study [4] with an open divertor configuration found an asymmetry of the power fall-off length between inner and outer target with a smaller power fall-off length λq,i on the inner divertor target. Measurements with a closed divertor configuration find a similar asymmetry for low recycling divertor conditions. It is found, in the experiment, that the in/out asymmetry λq,i/λq,o is strongly increasing with increasing density. Most notably the heat flux density at the inner divertor target is reducing with increasing λq,i whilst the total power onto each divertor target stays constant. It is found that λq,o exhibits no significant density dependence for hydrogen and deuterium but increases with about the square root of the electron density for helium. The difference between H,D and He could be due to the different recycling behaviour in the divertor. These findings may help current modelling attempts to parametrize the density dependence of the widening of the power channel and thus allow for detailed comparison to both divertor effects like recycling or increased upstream SOL cross field transport
ELM divertor peak energy fluence scaling to ITER with data from JET, MAST and ASDEX upgrade
A newly established scaling of the ELM energy fluence using dedicated data sets from JET operation with CFC & ILW plasma facing components (PFCs), ASDEX Upgrade (AUG) operation with both CFC and full-W PFCs and MAST with CFC walls has been generated. The scaling reveals an approximately linear depen- dence of the peak ELM energy with the pedestal top electron pressure and with the minor radius; a square root dependence is seen on the relative ELM loss energy. The result of this scaling gives a range in parallel peak ELM energy fluence of 10â30 MJm â2 for ITER Q = 10 operation and 2.5â7.5 MJm â2 for in- termediate ITER operation at 7.5 MA and 2.65 T. These latter numbers are calculated using a numerical regression ( Δ II = 0 . 28 MJ m 2 n 0 . 75 e T 1 e E 0 . 5 ELM R 1 geo ). A simple model for ELM induced thermal load is introduced, resulting in an expression for the ELM energy fluence of Δ II âŒ= 6 Ïp e R geo q edge . The relative ELM loss energy in the data is between 2â10% and the ELM energy fluence varies within a range of 10 0.5 âŒ3 con- sistently for each individual device. The so far analysed power load database for ELM mitigation experi- ments from JET-EFCC and Kicks, MAST-RMP and AUG-RMP operation are found to be consistent with both the scaling and the introduced model, ie not showing a further reduction with respect to their pedestal pressure. The extrapolated ELM energy fluencies are compared to material limits in ITER and found to be of concern.RCUK Energy Programme P012450/1EURATOM 63305
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