elm control by rmp is foreseen in iter to suppress or reduce size of elm energy loss

Alberto Loarte- NSTX Research Forum 2009 1st - 3rd December 2009

ELM control by RMP is foreseen in ITER to suppress or reduce size of ELM energy loss Application of RMP affects edge magnetic field structure and power/particle fluxes between

ELMs and at ELMs ELM control in ITER required for large range of plasma conditions not only flat top of 15 MA

scenario dependences on plasma parameters of effects on power/particle fluxes required to determine compatibility with other scenario requirements :

acceptable stationary power fluxes, erosion, etc. Understanding of effects influences application of scheme in ITER (perturbation rotation…)

Effects of ELM control with RMP on Edge Power/Particle Fluxes between ELMs and at ELMs (I)

4 6 8 10 12 14 160

5

10

15

20

WE

LM (

MJ)

Ip (MA)

Unmitigated ELMs q95

= 45/Ip(MA)

Required Controlled ELMs

ITER ELM control requirements

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

400 440 480 520 560 600 640 680 720

p

time, s

Ip = 15 MA

Ip = 10 MA

A. Kavin


Application of RMP coils affects both magnitude and spatial distribution of power/particle fluxes at the plasma edge between ELMs and at ELMs

Spreading of steady power and particle fluxes & lower of separatrix fluxes but

• Possible loss of high recycling regime and high divertor radiation (qdiv/qmp ~ ¼)

• Large power fluxes away from separatrix

• High stationary fluxes in “unexpected” areas • possible large erosion on toroidally asymmetric deposition regions (lower redeposition)

“Sharing” of ELM power flux on various flux bundles

Reduced requirements for WELM in controlled ELMs by increased of AdivELM

Larger ELM fluxes on divertor wall and baffles

Effects of ELM control with RMP on Edge Power/Particle Fluxes between ELMs and at ELMs (II)

T. Evans and O. Schmidt

10 Mwm-2

5 Mwm-2


Experimental plan

Plasma conditions for with high Padd for good H-mode and large pedestal plasma with Ip as high as possible (compatible with q95 ~ 5-6)

1. Establish q95 = 3 low <ne> H-mode plasma and apply best aligned RMP coil current distribution to achieve DIII-D criterion. Scan RMP coil magnitude around this value Total : 4-6 shots

2. Misalign RMP coil spectrum by q95 = 0.5 and increase RMP coil current to match Chirikov criterion. Scan RMP coil magnitude around this value Total 4-6 shots

3. Perform density scan in 3-4 discharges for q95 = 3 H-mode plasma with optimum RMP coil distribution and repeat at higher or lower power level Total 8-10 shots

4. Establish q95 = 5-6 low <ne> H-mode plasma with same current as in 1. and repeat study in 1 Total : 4-6 shots (If not possible to keep same Ip then use

Ip to vary q95)

Effects of ELM control with RMP on Edge Power/Particle Fluxes between ELMs and at ELMs (III)


ITER will be equipped with in-vessel coils for vertical stability control which provide fast feedback on vertical plasma position

If compatible with requirements for VS, the plasma in ITER could be jogged to reduce ELM size to acceptable levels (estimated frequency 20-40 Hz)

Vertical plasma jogging demonstrated successfully in various tokamaks (TCV, AUG, JET, NSTX, … but physics of ELM triggering unclear (shape deformation, edge current, ?)

requirements for ITER difficult to specify (magnitude and speed of jog) Experiment in NSTX proposed to address this issue and to get some empirical guidance for

assessing viability of method in ITER

Physics processes leading to ELM triggering by Vertical Jogs and extrapolation to ITER (I)

VS coils


Experimental plan

Plasma conditions for successful ELM control “demonstrated” at 45 Hz (~1.0 MA)

1. Perform density scan (3-4 shots) at fixed power with fixed jog amplitude (assessment of jedge effect)

2. Perform a jog amplitude scan at two densities (3-4 discharges)

3. If 2 shows effect repeat 1,2 at high input powers to see Tped dependence (3-4) shots

4. Establish Ip = 0.6 MA plasma to change ratio of jedge/Ip and allow larger jog. Repeat experiments in 1 and 2. (4-8 shots)

Effects of ELM control with RMP on Edge Power/Particle Fluxes between ELMs and at ELMs (II)

elm control by rmp is foreseen in iter to suppress or reduce size of elm energy loss

Documents