Low dimensional Edge-localised- modes dynamics in JET tokamak

Edge-localised-modes characterization through data analysis

Francisco A. CalderonUniversity of Warwick

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

Brief introduction to Fusion

Controlled thermonuclear fusion reactions

Inertial confinement

Magnetically confined plasma

Tokamak

Stellerator

Section 1

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

Why do we need to study ELMs?

Challenge

ITER, DEMO

Human Well-Being

Section 2

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!

Work andResults

Section 3

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.”

• 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

Delay plots

• Are not a phase space reconstruction as we used here

• Example: single pendulum, with a period .p

Threshold scheme

There are a few ELMs per time series, and they ranges from 67 - 196.

Gas puffing rate

Reproduced from Calderon et al. (2013) [9]

First set with lower gas puffing rate

Reproduced from Ref. [9]

Second set with higher gas puffing rate

The population in the sharp peak increases with the gas puffing rate. Reproduced from Ref. [9]

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.

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

Why is this been seen now?

The End

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)