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IOS-2.2 Ramp-down from q 95 =3 Topic Group: Integrated Operation Scenarios

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IOS-2.2 Ramp-down from q 95 =3 Topic Group: Integrated Operation Scenarios Spokes person: G. Sips (JET) Key persons: G. Sips (JET), S. Wolfe (C-Mod), G. Jackson (DIII-D), W. Suttrop (AUG) Devices: JET, C-Mod, DIII-D, AUG Outline and aims:

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slide1

IOS-2.2Ramp-down from q95=3

  • Topic Group: Integrated Operation Scenarios
  • Spokes person: G. Sips (JET)
  • Key persons: G. Sips (JET), S. Wolfe (C-Mod), G. Jackson (DIII-D), W. Suttrop (AUG)
  • Devices: JET, C-Mod, DIII-D, AUG
  • Outline and aims:
  • Demonstrate ramp-down from an ITER base-line plasma (at q95=3, with similar shape).
  • Starting ramp down from both H- and L-mode (to simulate fault condition). Demonstration how to stay within (k, li,q95) stability envelope of ITER. Develop shape control for vertical stability, fixed divertor strike points with increasing top gap (MHD-TG).
  • Document merits/demerits of staying (as long as) in H mode or L mode during the ramp-down.
  • Also document heating requirements during ramp down.
slide2

IOS-2.2: Results so far….

  • JET: Investigated “controlled” and “emergency” ramp-down (22 pulses in 2008)
  • Effect of Ip ramp rate from 0.07MA/s (slow) to 0.5MA/s (emergency).
  • Ohmic ramp down (H-mode in f/t or not) gives plasma profile peaking up to li~1.8
  • Heating: See viewgraphs….
  • DIII-D: Detailed experiments, matching proposed scenario for ITER.
  • C-Mod: Dedicated experiments in 2008, varying the Ip ramp down rate (5 pulses)
  • AUG: Many parasitic data are available, although NOT many discharges at q95~3
  • To be done: More detailed modelling of these discharges
slide3

JET: H-mode ramp-down

li(3)

15MW

Padd

Vloop

Ip

5x1019m-3

<ne>

Da

slide4

JET: H-mode ramp-down

li(3)

15MW

Padd

Vloop

Ip

5x1019m-3

<ne>

Da

slide5

DIII-D results, 2009

See T. Luce talk tomorrow, April 1st

slide6

C-Mod: Current ramp down experiments

Ramp down in divertor shape with kappa reduction (1.8  1.4)

1.32MA

0.98MA

0.61MA

0.26MA

2MA/s

1.14 s

1.34 s

1.54 s

1.72 s

time (s)

slide7

1.4

Ip [MA]

1.0

k~1.8

k

0.6

k

k1.4

k1.4

0.2

2.0

1.6

li(3)

1.2

0.8

IOH [kA]

24

10%

20

16

12

1.0

1.2

1.4

1.6

1.8

2.0

Time (s)‏

C-Mod: Current ramp down experiments

  • Elongation reduced from 1.8 to 1.4 to keep plasma vertically stable. Current ramp down keeping ~1.8 has VDE.
  • For ohmic or L-mode discharges, fast decay (dIp/dt ~ 4MA/s) or standard decay (dIp/dt ~ 2MA/s) li(3) > 1.5.
  • 1MA/s ramp down keeps li(3) < 1.2 However, this ramp down requires ~10% increase in central OH current.
slide8

ASDEX Upgrade: Ramp down phase

  • Shopping list for ASDEX-Upgrade:
  • Design a scenario for ITER: Avoidance of high li for termination phase.
  • Control of plasma shape and vertical stability with PF coils saturated. (central solenoid).
  • Conditioning effects of the current decay.
  • Simulate the (sudden) termination of the burn and H to L transition.

ASDEX Upgrade (2008/2009, no dedicated pulses):

Collect the data already available.

slide9

IOS-2.2: Ramp down experiments in 2009

  • Aims: Dedicated experiments !!!
  • Experiments
  • JET: Further dedicated experiments in deuterium, hydrogen and helium.
  • DIII-D: Matching ITER proposals for ramp-down
  • C-Mod: Some more (parasitic) experiments planned at high Ip.
  • AUG: Experiments are proposed….
  • Modelling:
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