Speaker
Dr
Carine Giroud
(CCFE)
Description
Impurity seeding via injection of neon (Ne) or nitrogen (N) will be mandatory in ITER Q=10 reference scenario to reduce inter-ELM power load to the divertor within the engineering limits. The challenge is achieving the scenario requirement of $ H_{98(y,2)}$=1, $\beta_N $=1.8, $\frac{(n)}{n_{GW}}$=0.85, $\delta $=0.4, with a high radiative divertor. These conditions necessitate a high pedestal temperature which leads the pedestal to playing a key role in this challenging integration. Unravelling the mechanism that, in the absence of carbon in the plasma composition leads to a decrease in the pedestal temperature is critical in predicting the pedestal pressure in ITER. It is important to learn how to use the extrinsic impurity to optimise the pedestal temperature in high radiative scenarios. This paper aims at (1) reviewing our understanding of the effect of carbon (C), N and Ne-seeding on the pedestal pressure and temperature, (2) assessing whether the peeling ballooning stability limits the pedestal pressure, and (3) determining which instabilities are causing heat and particle transport.
In JET-ILW this limitation on the pedestal temperature is alleviated with the injection of nitrogen, or C in low and high-$\beta_N$ plasmas. Seeding Ne can result in opposite behaviour on the pedestal density depending on the collisionality $ \nu^*_e $ and $\beta_N $, but in all cases seeding Ne does not lead to an increase of temperature, unlike N or C. A detailed analysis of the differences in the electron and ion pedestal profiles in the high-$\beta_N$ plasmas indicate that the difference between C and Ne-seeding can be down to the value of collisionality $ \nu^*_e $ , but also the value of ExB shear considering the difference in $\bigtriangledown T_{i,\alpha_{max}}$ and $\bigtriangledown \Omega_{tor,\alpha_{max}}$ at the position of the maximum normalised pressure gradient. Similarly, seeding $CD_4$ in the low-$\beta_N $ plasmas increases $\bigtriangledown T_{i,\alpha_{max}}$ and $\bigtriangledown \Omega_{tor,\alpha_{max}}$. Detailed analysis with the GENE code will clarify which instability is at the origin of the difference in the pedestal temperature. The peeling ballooning stability has been assessed with MINERVA-DI code. The plasmas considered have the operational points (OP) of the high and low-$\beta_N $ plasmas within 20% of the stability boundary.
| Country or International Organization | United Kingdom |
|---|---|
| Paper Number | EX/3-4 |
Primary author
Dr
Carine Giroud
(CCFE)
Co-authors
Dr
Alex Chankin
(IPP Garching)
Dr
Alexander Huber
(Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik)
Dr
Anthony Field
(CCFE)
Dr
Balazs Tal
(Wigner research Institute)
Dr
Bartosz Lomanowski
(Aalto)
Dr
Christopher Bowman
(University of York)
Dr
Christos Stavrou
(Aalto)
Dr
Clive Challis
(Culham Centre for Fusion Energy)
Mr
Daniel Refy
(Wigner Research Centre for Physics)
Dr
David Hatch
(Institute for Fusion Studies, University of Texas at Austin)
Dr
David Moulton
(CCFE)
Dr
Domenico Frigione
(ENEA)
Dr
Ephrem Delabie
(Oak Ridge National Laboratory)
Dr
Ewa Belonohy
(CCFE)
Dr
Felix Parra
(Rudolf Peierls Centre for theoretical physics)
Dr
Fulvio Militello
(Culham Centre for Fusion Energy)
Dr
Istvan Pusztai
(Chalmers)
Dr
James Harrison
(CCFE)
Mr
James Simpson
(CCFE)
Mr
Jason Parisi
(Rudolf Peierls Centre for Theoretical Physics)
Dr
Jon Hillesheim
(Culham Centre for Fusion Energy)
Dr
Josep Maria Fontdecaba
(CIEMAT)
Dr
Michael Barnes
(Rudolf Peierls Centre for Theoretical Physics)
Dr
NOBUYUKI AIBA
(Japan Atomic Energy Agency)
Dr
Samuli Saarelma
(CCFE)
Dr
Sebastijan Brezinsek
(Forschungszentrum Jülich)
Dr
Sheena Menmuir
(CCFE)
Dr
Stanislas Pamela
(CCFE - UKAEA)
Mr
Stefan Buller
(Chalmers)
Dr
andy Meigs
(CCFE)
