Long term renovation inside KSTAR vacuum vessel toward steady state operation

Transcription

1 IAEA SSO Long term renovation inside KSTAR vacuum vessel toward steady state operation Jong-Gu Kwak, S.W. Jung, S.G. Kim, J.H. Kim, D.R. Lee K-DEMO On behalf of KSTAR team NFRI, Korea KSTAR ITER

2 Near term(~2021) focusing the heating upgrade Priority : NBI(12 MW, 2019), ECH(6MW, 2020), RF(Innovated, 2022) I-5, Hahn, Access to long-pulse high-beta operation regime in KSTAR O-8: Chung, Formation of the internal transport barrier in KSTAR I-8, Oh, Status of the high performance and long pulse operation in KSTAR and exploring the issues in ITER and K-DEMO Source Power Advanced CD R&D 0.5MW betan=2 1 MW 5.5 MW 2 MW LHCD 8.5 MW betan=3 2 MW 16 MW 8.5 MW 12 MW betan=4 20 MW 6 MW MW 8 MW LHCD/Helicon/ Vertical ECH 2 MW ECH 105/140 GHz NBI-1 ICRF Steady State, High beta, 100 sec High beta, 100 sec Steady State, High beta It is expected that the long pulse operation is possible by 2021 using conventional methods But more efficient and reliable CD resources and diverter solution for high heat flux are required for fusion reactor beyond KSTAR - 2 -

3 OUTLINE Motivation (renovation) inside the vacuum vessel Ripple, controllability, confinement of energetic particle Additional advantages of upgrade What to do and work schedule Summary - 3 -

4 Aiming for diverter physics 1 Diverter physics study for DEMO Present KSTAR diverter is a very old design - Double null with flat type (no dome, open diverter) - It shows MARFE at high density operation even though cryopump operation - It is not compatible with the steady state long pulse operation - PFC bonding for long pulse operation is needed. Lower single null configuration with W shape diverter Many options are considered including innovative concept - Super-X, SAD or snow-flake configurations Changing of plasma facing material to tungsten Diagnostics for diverter(bolometer, impurity, H-alpha ) Urgent need for modification of in-vessel structure for SSO Basic idea is to push out the present stabilizer to the wall and use the lower single null configuration with full utilizing the upper port as heating and diagnostics - 4 -

5 Aiming for Advanced CD with diverter physics 1 Upper or off mid-plane launcher of ECCD, LHCD, and Helicon offer high efficiency CD for DEMO Top launching of EC wave A large Doppler shift is beneficial because waves will interact with higher energy electrons, which are less collisional and provide larger ECCD. Doppler shift is increased by ray trajectories with Large k// (strong toroidal component of aiming) Nearly vertical trajectories, so that the resonance is approached slowly Rant=1.62m Top launching of LH wave ω = l γ + k v 2 v = 1 ω2 c 2 v t l v + 2n ω 2 c v 2 t l 2 2 (1 + n ω2 v 2 v t v t l 2 2) 2 v t Cold resonance Garofalo et al.,,2nd IAEA DEMO Programme Workshop(2013) LaBombard et al., NF, 55(5), 2015 Top or off mid-plane launcher of RF is the highest priority - 5 -

6 Additional advantages Size scaling of tokamak - Increase of confinement time(~1.3x) and plasma volume (~ 1.8x) R : a : Flexible aspect ratio(3-3.6) experiments - Enhancing confinement of energetic particle Easy plasma shape control - Plasma to coil gap is closer than present Full usage of upper vertical port NB Heating upgrade with higher beam accelerating voltage KSTAR-U - 6 -

7 Modification of components inside VV Research aiming for diverter physics - Modification of the lower diverter - Modification of PFC to tungsten - Adding new coils Access for top LHCD/ECCD launcher - Removing the upper diverter plate - pushing passive plate and in-vessel control coils to outer radius TF ripple reducing(optimization) - Ferritic steel attaching to VV Shinohara et al., NF 47(8)

8 TF ripple reducing w/o ferritic steel - Ripple ~ 0.8% at r=2.6m (N.B. 0.1% at 2.2m) - Ten times increase at new plasma boundary - Energetic ptl loss from should be avoided Ferritic steel attached inside VV - Ferritic steel is attached on the vessel between the ports - Candidate material : F82H, ARRA - Ripple is reduced to less than 0.5% at boundary - 8 -

9 Enhancing controllability of plasma shaping Plasma control depends on geometrical factor as well as PS. Coil 4 Coil 5 Coil 3 Coil 2 Coil 1 Coil 0 Pnt 2 Pnt 3 Pnt 1 Pnt 0 Coil 6 Coil 0 Coil 1 Coil 11 Coil 10 Pnt 4 Pnt 5 Pnt 7 Pnt 6 Coil 7 Coil 9 Coil 8 Control points: 8 points(30, 75, 120, 150, 210, 240, 285, 330 ) from magnetic axis KSTAR equilibrium #17209: 1 MA, 2.5 T Upgraded KSTAR equilibrium: 1 MA, 3.0 T Only geometric effect is considered: C rel ij = M ij ψ i where i: control point indices and j: coil indices

10 Controllability enhances more than twice KSTAR equilibrium #17209: 1 MA, 2.5 T Upgraded KSTAR equilibrium: 1 MA, 3.0 T Only geometric effect is considered: C rel ij = M ij ψ i Coil 4 Coil 5 Coil 3 Coil 2 Coil 1 Coil 0 Pnt 2 Pnt 3 Pnt 1 Pnt 0 Coil 6 Coil 0 Coil 1 Coil 11 Coil 10 Pnt 4 Pnt 5 Pnt 7 Pnt 6 Coil 7 Coil 9 Coil

11 Energetic particle confinements Fusion reactor should consider alpha particle confinement - Demo needs MeV level accelerating voltage neutral beams with the negative ion source. - Feasibility study at KSTAR by using 200 kev beams is planned - Beam loss of neutral beam is checked Note that present goal of positive ion source(100 kev /2MW/300s) shows also very harsh conditions - failure during long pulse operation (Peak power density at beam dump and electron backstream plate )

12 Beam loss calculation for 100/200 kev beams NBI1-B NBI1-A NBI1-C NBI1-A NBI1-B NBI1-C Lost 3T 1MA RX RX RX T 1MA 200keV RX keV kev beam loss is not decreased with the plasma size - but shows dependency on the triangularity(x-point position) 200 kev beam loss is also increased with the plasma size Incident particle number : 150,000 More study is needed by varying plasma profile and beam positions

13 Aspect for top launching feasibility Heavy LH/helicon launcher at top - PAM power density : 500 kw/24*17(400)cm 2 - Area of an upper vertical port : ~ 500 cm 2 - Weight of 500 kw module is about 150 kg weight of helicon - PAM power density is 20% higher than active grill type Unabsorbed EC Beam power damage - very narrow window with resonant layer - size of reflecting mirror : 12 cm - beam divergence : 1.2 degree Fig. 3 Fig. 4 θ = 180, = 192 θ = 13 mirror

14 Work to do and work schedule Calculation of ripple, stability, confinement, energetic ptl loss Diagnostic view angle readjustment Rearrangement of internal structure - Diverter, IVCC, NB armor and ELM coil etc. Rearrangement of ports (RF antenna, diagnostic) Schedule for target ~ Conceptual design : 1 y - Engineering design : 1-2 y - Manufacturing : 1 y - Disassemble/assemble : 1 y - Starting time :

15 Summary Long term upgrade plan of KSTAR vacuum vessel structure is suggested for studying new diverter concepts and advanced CD. - The space between the present passive stabilizer position and outer vessel wall is to be used. - Calculation of TF ripple is done with ferritic steel. - Controllability of plasma shaping is enhanced more than 2 times than present configuration. For operation start at 2021, beginning of the conceptual study shall be started in Calculation of stability, confinement, etc. for new diverter configuration is urgently needed - Feasibility study of top/off axis RF launching also has to be preceded

16 Your comments and guidance is very much appreciated