Recent JET Experiments and Science Issues Jim Strachan PPPL Students seminar Feb. 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 Be 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 have achieved many of the scaled parameters needed for ITER J. Pamela

JET results extend scaling to conditions closest to ITER J. Cordey Confinement scales like: I R n 1/3 (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

PTEDTE1TTEDTE2 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 Energy ITER prototype plasma P. Lomas

10% of heating was attributed to alpha heating P. Thomas

 Large enough for ITER relevance if I p ≥ 3MA & P inp = MW A top ~ 0.6 m 2 A limiters ~ m 2 Power density estimate:   W ELM wall ~( )  W ELM div  A ELM wall ~ A ELM div   ELM wall ~  ELM div ~  s  W ELM = 1MJ Be-wall loads 9 – 39 MJm -2 s -1/2 (melting ~ 16 MJm -2 s -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