Recent JET Experiments and Science IssuesJim Strachan

PPPL Students seminarFeb. 14, 2005

• JET is presently world’s largest tokamak, being ½ linear dimension of ITER and twice DIII-D.

• JET has produced the highest plasma current, largest fusion power, longest confinement time, and has Tritium and Be capability

• JET first operated in 1983, making many contributions• This talk will discuss some issues on:

– Size scaling– DT results– Divertor/wall material studies

• Some references:– J. Wesson “Tokamaks” Oxford Sci. Publ. (2004) general– G. Federici, et al, Nuclear Fusion 41, 1967 (2001) wall processes– J. Jacquinot, et al, Nuclear Fusion 39, 235 (1999) DT physics

D. Meade

NBI Shinethrough protection

Upper Dump plate

Inner wall cladding

Inner wall guard limiters

Mushrooms

Saddle coil protection

Saddle coil protection

BeBe

Outer poloidal limiters

LH + ICRH protection

KC1 coil covers

B&C tiles

Total main wall tiles = 4404

The JET plasma has a shape and relationship to its vacuum vessel which is similar to ITER, making the JET discharges an indication of ITER plasmas

JET plasmas haveachieved many of the scaled parametersneeded for ITER

J. Pamela

JET results extend scaling to conditions closest to ITER

J. Cordey

Confinement scales like:

I R n1/3 (a/P)1/2

J. Cordey

New regimes often tested at JET to understand size scaling

Confinement is complex: with interplay between pressure gradients, MHD, and transport irregularities

PTE DTE1 TTE DTE2

Largest machines have the performance to make it worth tritium

DT experiments study tritium technology, isotope and α particle effects

D. Meade

Time Evolution of JET DT pluses

Highest Fusion Power Highest Fusion EnergyITER prototype plasma

P. Lomas

10% of heating was attributed to alpha heating

P. Thomas

Large enough for ITER relevance if Ip ≥ 3MA & Pinp = 25-38 MW

Atop ~ 0.6 m2

Alimiters ~ 0.3-0.6 m2

Power density estimate:WELM

wall ~(0.5-1.0) WELMdiv

AELMwall ~ AELM

div

ELMwall ~ ELM

div ~ 200 - 500 s

WELM = 1MJ

Be-wall loads 9 – 39 MJm-2s-1/2

(melting ~ 16 MJm-2s-1/2)

One major effort is to mitigate ELMs and scale to ITER

G. Matthews

IAEA summary 2004

Objectives are to study:

• Material migration / lifetime

• Tritium retention / inventory control

• Damage due to transients / control

350 MJ

20 MJ

JET Wall Proposal: Option 1

Objectives

• Demonstrate low T retention

• Test de-tritiation techniques

• Study effect of Be on W erosion

• Study melt layer loss – wall + divertor ELMs and disruptions

• Refine control / mitigation techniques Limit disruption / ELM damage

• Operate without C - radiation

Demonstrate routine / safe operation of fully integrated ITER compatible scenarios at 3-5MA NBI power upgrade

350 MJ

20 MJ

JET Wall Proposal: option 2.

Discussion• JET being largest machine, and highest

performance, and closest to ITER: tests size scaling

• JET DT capability tests tritium technology, isotope effects, alpha particle effects, and trace tritium transport

• Similarity to ITER shape and relation to walls means JET tests power handling and wall material issues