Impurity and α-particle transport in the W7-X using Charge Exchange Recombination Spectroscopy: An overview.

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Motivation

P. Valson*a,b, M. Beurskensa, O. Forda, A. Langenberga and R.J.E JaspersbaMax-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, D-17491 Greifswald

bEindhoven University of Technology, De Rondom 70, 5612 AP Eindhoven*pranay.valson@ipp.mpg.de

Transport in Tokamaks Vs. Stellarators

References[1] T. Klinger et al., 13th SOFE, San Francisco, (2013) :7.[2] P. Helander et al., Plasma Physics and Controlled Fusion 54, (2012) 124009.[3] P. Helander et al., Transactions of Fusion Science and Technology 54, 56, ( 2012) 61:133–141,

1. To determine if transport in the W7-X follows from neoclassical theory for stellarators, if not what causes this deviation.2. To estimate the effects of (low Z) impurities, especially α-particles on density profiles and overall transport.3. To explore the performance of CXRS and other diagnostics to evaluate such questions in the W7-X environment.

Primary research objectives

Classical diffusion

Banana Diffusion

Plateau Diffusion

Helium Transport & CXR Spectroscopy

Confinement Quality in Stellarators (εeff & Z)

1. W7-X (heliac) is an optimized disruption free, quasi-steadystate device with no inductive current drive requirement.

2. Particles and impurities are confined within helicalmagnetic wells in a quasi-axisymmetric configuration.

3. Ambipolar electric field resulting from varyingcollisionality (and diffusivities) leads to an inward flux ofimpurities causing high radiative losses.

4. Neoclassical transport is higher than for tokamaks and hasvarying regimes when compared.

5. α–particle confinement time is to be detrimental as itsdensity and retention period is critical in a fusion device.

6. Impurity and particle transport is to be analyzed usingcharge exchange recombination and other diagnostics.

7. The contribution of anomalous transport in the W7-X is tobe studied resulting in global transport.

1. W7-X Major device components[1] magnetic flux surface for the W7-X

2. Modular SC coils and outer magnetic flux surface for the W7-X[2]

3. Neoclassical collisionality (showing Diffusion Vs. collisionality) regimes for tokamaks[3]

4. ‘Mono-energetic’ diffusion coefficient versus collisionality using GSRAKE for W7-X and a tokamak of similar aspect ratio[2]

5. Neoclassical confinement quality parameter εeffversus minor radius in various stellarators[2]

6. Basic Drift wave mechanism leading to anomalous transport[4]

Ion diffusion Electron

diffusion

e E

7. The plasma operating contours (POPCON) in theneτE Vs. T - plane for different values of ρ[6]

D-T reaction by products lead for an equation burn control parameter ‘ρ’ to determine helium confinement quality.

Ionized impurities gain electron charge via charge exchange.1. Line intensity – ni2. Emitted line broadening – Ti3. Line shifting – v║,v╧

[4] Kendl, A, European Journal of Physics 29.5 (2008): 911.[5] H. Maassberg et al., Plasma Physics and Controlled Fusion 41, (1999) 1135.[6] Jakobs, M. et al., Nuclear Fusion 54.12 (2014): 122005.

8. W7-X NBI active CXRS system with schematic

P-S Diffusion (18 – 31 times Dc)

The “Joint Doctoral Programme in Nuclear Fusion Science and Engineering” –FUSION-DC, is acknowledged by the first author for supporting this study.

[5]Neoclassical particle flux equation for aspecies ‘α’ where Lij are transportcoefficients, solved to obtain transport ofspecies in a magnetic flux surface.