low dimensional edge-localised- modes dynamics in jet tokamak edge-localised-modes characterization...
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Low dimensional Edge-localised- modes dynamics in JET tokamak
Edge-localised-modes characterization through data analysis
Francisco A. CalderonUniversity of Warwick
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Outline
1. Brief introduction to fusion• High confinement and instabilities: ELMs
2. What is needed for? ITER … DEMO
3. Description and results
4. Further work
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Brief introduction to Fusion
Controlled thermonuclear fusion reactions
Inertial confinement
Magnetically confined plasma
Tokamak
Stellerator
Section 1
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High confinement: ELMs
First saw H-mode: ASDEX (1982)1
H-mode is accompanied by many instabilities [1-3].
ELMs are more easily found in “divertor” geometry.
They are a nonlinear bursting instability occurring in the edge of plasma.
1 Asdex-Upgrade tokamak
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Why do we need to study ELMs?
Challenge
ITER, DEMO
Human Well-Being
Section 2
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ITER
• Is a Tokamak• Lab for burning plasma• Prove DEMO feasibility• Been built in:
• Caradache, Les Bouches du Rhône, southern France.
• Further info: www.iter.org • Check for ITER newsletter!
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Work andResults
Section 3
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Experimental data
Analysis Da time trace (Lyman 656.3nm)
• Highly nonlinear• Reduced number – few hundred per shot• Low frequency (ELM type I)
Time series analysis
• We found useful to use a new time series as defined by Schreiber et al. (2000) for spiky events in time series
Greenhough (2003) states: “…[Need for] thresholding to define and quantify the
individual ELM burts.”
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• Use time ocurrence(see figure) as new time series {tn}.
• We define the inter-ELM time interval as [6]: dt n= t n – t n-1.• Construct delay plots.• Make PDF of the inter- ELMs time intervals.
Analysis
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Delay plots
• Are not a phase space reconstruction as we used here
• Example: single pendulum, with a period .p
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Threshold scheme
There are a few ELMs per time series, and they ranges from 67 - 196.
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Gas puffing rate
Reproduced from Calderon et al. (2013) [9]
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First set with lower gas puffing rate
Reproduced from Ref. [9]
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Second set with higher gas puffing rate
The population in the sharp peak increases with the gas puffing rate. Reproduced from Ref. [9]
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Conclusions
> Long-duration (~5s) quasi-stationary JET plasmas reveal significant variations in the ELMing process or processes along with the variations of the control parameter G— the gas puffing rate.
> ELM population in each plasma enables us to characterize the dynamics, which is found to be low dimensional.
> Demonstrating and quantifying the effectiveness of ELM control and mitigation techniques will be assisted by characterizing the measured sequences of inter-ELM time intervals in this way.
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Further Work
• Webster et al. (2013)has recently found signs of Resonant behaviour in JET plasmas.
- We see this as Stripes on Delay plots- Are ELMs couplingwith Coils?
Section 4
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Why is this been seen now?
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The End
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References• [1] A Loarte et al., Plasma Phys. Control. Fusion 45, 1549 (2003)• [2] K Kamiya et al., Plasma Phys. Control. Fusion 49, S43 (2007)• [3] R J Hawryluk et al., Nucl. Fusion 49, 065012 (2009)• [4] www.iter.org Retrieved 15th june 2013.• [5] J Greenhough, S C Chapman, R O Dendy, and D J Ward, Plasma Phys. Control. Fusion 45, 747 (2003)• [6] T Schreiber and A Schimdt Physica D 142 346–382, (2000) . • [7] A Degeling, Y Martin, P E Bak, J B Lister, and X Llobet, Plasma• Phys. Control. Fusion 43, 1671 (2001)• [8] Webster et al. “Time-resonant tokamak plasma edge instabilities?” (2013), In press.• [9] F A Calderon, R O Dendy, S C Chapman, A J Webster, B Alper et al., Phys. Plasmas 20, 042306 (2013)