2D ECEI OBSERVATION OF TEARING MODES IN KSTAR RMP EXPERIMENTS - - PowerPoint PPT Presentation

β–Ά
2d ecei observation of tearing modes in kstar rmp
SMART_READER_LITE
LIVE PREVIEW

2D ECEI OBSERVATION OF TEARING MODES IN KSTAR RMP EXPERIMENTS - - PowerPoint PPT Presentation

Dec 28, 2023 368 likes β€’611 views

2D ECEI OBSERVATION OF TEARING MODES IN KSTAR RMP EXPERIMENTS MINJUN J. CHOI * , G.S. YUN, J. LEE, W. LEE, H.K. PARK Center for Fusion POSTECH, POHANG, KOREA Plasma Diagnostics & Steady-State Operation C.W. DOMIER, N.C. LUHMANN, JR., UC

slide-1
SLIDE 1

2D ECEI OBSERVATION OF TEARING MODES IN KSTAR RMP EXPERIMENTS

MINJUN J. CHOI*, G.S. YUN, J. LEE, W. LEE, H.K. PARK

POSTECH, POHANG, KOREA

C.W. DOMIER, N.C. LUHMANN, JR.,

UC DAVIS, CALIFORNIA, U.S.A.

Y.M. JEON

NATIONAL FUSION RESEARCH INSTITUTE, DAEJEON, KOREA

* cmj0417@postech.edu Center for Fusion Plasma Diagnostics & Steady-State Operation

slide-2
SLIDE 2

2

MOTIVATION OF RESEARCH

In the 2011 KSTAR campaign, static π‘œ = 1 resonant magnetic perturbations (RMPs) have been applied to control the edge localized modes (ELMs) as well as to study error fields effects *. While the ELMs control experiments demonstrated that the π‘œ = 1 RMPs were effective to suppress or mitigate ELMs, unwanted effects of RMP have also been observed such as plasma locking and/or tearing mode, both of which could potentially lead to a confinement degradation or even disruption. We report three observations with the KSTAR ECEI system; (1) T

e fluctuation

  • f typical m/n=2/1 tearing mode, (2) 1/1 and 2/1 mode coupling, and (3)

tearing mode related transport event. Also, a method to estimate Ξ”β€² based on relatively calibrated ECEI data is introduced.

* Y.M. Jeon et. al., the 53rd Annual Meeting of the APS Division of Plasma Physics, Salt Lake City, USA (2011)

slide-3
SLIDE 3

3

KSTAR RESONANT MAGNETIC PERTURBATION (RMP)

Coils for magnetic perturbation fields

n=1

  • BR

+BR

Top-RMP Mid-RMP Bot-RMP Ip, BT

Figures are reprinted from *

* Y.M. Jeon et. al., Mini-workshop for NTM experiments on KSTAR, Pohang, Korea (2011)

slide-4
SLIDE 4

4

KSTAR ELECTRON CYCLOTRON EMISSION IMAGING SYSTEM

2 Γ— 24 Γ— 8 local electron cyclotron emission measurement*

𝑔

𝑓𝑑𝑓

𝑆 Heterodyne detector array (24) Large imaging

  • ptics

Heterodyne detector array (24)

Vertical resolution : ~1.4 cm/ch Radial resolution : ~1.5 cm/ch Time resolution : 0.5, 1, 2 us T

e resolution : 1 Γ—

1 𝑂𝑗𝑑 = πœπ‘‘ πœπ‘—π‘œπ‘’ = 2βˆ†π‘”

𝑀

Δ𝑔𝑗𝑔 ∼ 3%

* G.S. Yun et. al., RSI 81 (2010)

slide-5
SLIDE 5

5

TYPICAL m/n=2/1 TEARING MODE ON KSTAR (#6123)

1-D diagnostics and KSTAR ECEI system

Edge Localized Mode (ELM) is suppressed / mitigated by RMP After the turned-off static RMP, large amplitude oscillation is

  • bserved at Mirnov

coils, interferometer, and ECE signals Oscillations turned out to be the 2/1 tearing mode numbers from Mirnov coil and ECE/ECEI signals

L-mode

slide-6
SLIDE 6

6

ECE images of 2/1 tearing mode of KSTAR

Plasma is rotating in laboratory frame, and so the fixed ECEI frames sweep the plasma in the plasma frame Clear phase inversion across πœ€π‘ˆ

𝑓 = 0,

normalized fluctuation amplitude is larger inside ECE images are made from normalized ECEI data against average values Given 𝑔

𝐹𝐷𝐹 ∼ n βˆ— 𝑔 𝑒𝑝𝑠, π‘œ = 1, and

𝑔

𝐹𝐷𝐹 = 1.3 kHz, plasma rotates with

𝑀𝑒𝑝𝑠 ∼ 18 km/s at 𝑆 = 2.17 m Fast visible bremsstrahlung images

  • btained from 2/1 tearing mode at

DIII-D* are shown for comparison White boxes are the virtual ECEI view

* Van Zeeland et. al., Nuclear Fusion 81 (2008)

slide-7
SLIDE 7

7

Find shaping parameters of the un-perturbed flux from ECE image Fit πœΊπ‘Όπ’‡ = 𝟏 contour with Inner separatrix position estimation with ECEI data only 𝑆 = 𝑆0 + 𝑠 cos(πœ„ + πœ€ sin πœ„) 𝑨 = 𝑨0 + πœ†π‘  sin πœ„ πœ€ = 0 Β± 0.1 πœ† = 1.0 Β± 0.1

πœ€π‘ˆ

𝑓/ π‘ˆ 𝑓 𝑒1 = 0

πœ€π‘ˆ

𝑓/ π‘ˆ 𝑓 𝑒1 = max

#5956

𝑛 = 2 tearing mode is observed at the both high and low field sides Separatrix position can be estimated by finding Ξ”π‘ˆ

𝑓 maximum position*

Assuming the flat temperature profile βŒ©π‘ˆ

𝑓βŒͺ𝑒1 = π‘‘π‘π‘œπ‘‘π‘’ inside the island, the inner Ξ”π‘ˆ 𝑓

maximum position is same with the inner Ξ”π‘ˆ

𝑓/βŒ©π‘ˆ 𝑓βŒͺ𝑒1 maximum position

* P.C. de Vries et. al., PPCF 39 (1997)

slide-8
SLIDE 8

8

Locked Mode field core ECE core ECE Spectrogram middle ECE Spectrogram

MODE LOCKING AND COUPLED MODES (#5951)

noise

When plasma is completely locked, no precursor is observed. Oscillation starts appear again in the RMP ramp-down phase core ECE spectrum : precursor oscillation of 𝑛/π‘œ = 1/1 sawtooth. The sawtooth crash

  • bservation shows π‘Ÿ = 1 surface at 𝑠 = 13 cm

middle ECE spectrum : T

e perturbation of

𝑛/π‘œ = 2/1 tearing mode. π‘Ÿ = 2 surface is found to be 𝑠 = 31 cm (phase inversion position) Both modes have n=1 and frequencies of

  • scillation are almost same

After the turned-off of RMP, vanishing of the RMP torque may increases core plasma rotation (white arrow). The stronger RMP in this shot compared to #6123 could explain further effect on plasma

slide-9
SLIDE 9

9

ECE images during the mode coupling

ECE measurements

  • f mode coupling on TEXTOR*

T

e perturbation

(a) w/o 𝑛 = 1 mode (b) w/ 𝑛 = 1 mode q=2

Phase of m=1 and m=2 modes are synchronized at the high field side where the flux surfaces are denser

* P.C. de Vries et. al., PPCF 39 (1997)

slide-10
SLIDE 10

10

BIG TRANSPORT EVENT WITH RMP FIELD (#6056)

Big transport events related to perturbation fields

𝑠 = βˆ’2.4 cm

  • 5.6
  • 8.6
  • 11.5
  • 14.4
  • 21.1
  • 23.6
  • 26.0
  • 28.4
  • 30.7
  • 32.9
  • 38.2

ECE signals

slide-11
SLIDE 11

11

2-D Te dynamics observed in ECE images

Note that strong static RMP is applied (bβ€”d) crescent shape decrease (inside) and increase (outside) around typical π‘Ÿ = 2 region. It may be due to T

e flattening of tearing mode

(e) core part moves upward, and small heat transport occurs (fβ€”h) heat channel is formed at the midplane, and large signal decrease

  • f core and increase of edge are
  • bserved

(e) (fβ€”h)

slide-12
SLIDE 12

12

Ξ”β€² ESTIMATION WITH RELATIVELY CALIBRATED ECEI DATA

Ren’s tearing mode flux model*

equilibrium flux TM perturbed flux constant flux condition

1 2 𝑦2 1 + πœ—1𝑦 + π‘₯ 4

2

1 + πœ—2𝑦 cos π‘›πœ„ = 𝑧 Ο΅1 ≑ πΆπœ„

β€²β€²(𝑠 𝑑)/3πΆπœ„ β€² (𝑠 𝑑)

Ο΅2 ≑

1 𝛽± + 1 𝑠𝑑 and w 4 2

≑

𝑠𝑑𝐢𝑠 π‘›πΆπœ„

β€²

* C. Ren et. al., Physics of Plasma 5 (1998)

slide-13
SLIDE 13

13

Application to 2-D system (#6123) relative calibration : assuming (1) flat Te profile inside the island and (2) axis symmetry of average Te profile

𝑠

projection using the shaping parameters

𝑠’

πœ€π‘ˆ

𝑓/ π‘ˆ 𝑓 = 0

πœ€π‘ˆ

𝑓/ π‘ˆ 𝑓 = max

π‘ˆπΉπ·πΉ(𝑠′) 𝑒 = π‘ˆ0(𝑠)

slide-14
SLIDE 14

14

Measure the Te contour and find fitting parameters Uncertainty is considered to be large and not able to quantize the error at this moment. Measurement error can be improved by increasing channel resolution

1 2 𝑦2 1 + πœ—1𝑦 + π‘₯ 4

2

1 + πœ—2𝑦 cos π‘›πœ„ = 𝑧

π‘₯ ∼ 3.0, πœ—1 ∼ 0.082, 𝛽+ ∼ βˆ’1.22, and π›½βˆ’ ∼ βˆ’0.58. Therefore, Ξ”β€² ∼ 0.90 Note that tearing mode in this plasma survives for a longer time after the turned-off of RMP, which is contrast to the case of #5951.

slide-15
SLIDE 15

15

SUMMARY

2-D Te perturbation due to 2/1 mode tearing mode clear phase inversion in 2-D space larger fluctuation amplitude inside rational surface than outside estimation of un-perturbed fluxes surface shape Coupling between 1/1 and 2/1 mode mode locking (rotation speed changes) and synchronization of mode phases at high field side n=1 RMP related big transport event sudden temperature (and density) drop over large radial range Application of 2-D ECE diagnostics to estimate πš¬β€²

slide-16
SLIDE 16

16

BACKUP

normalized ECE data with values of O-point

slide-17
SLIDE 17

17

BACKUP

3/2 tearing mode (#6304)

1/4 (1/6) toroidal (poloidal) turn (20 ms later)

slide-18
SLIDE 18

18

TM Poster : study crash more, Mirnov coil data mode spectra analysis, 3/2 mode and also 2/1 mode onset study what happens tracking island position with ECE data EFIT data manage : q, B data

slide-19
SLIDE 19

19

inside inside

slide-20
SLIDE 20

20

upper channels show increase and lower

  • decrease. the core seems

to be deformed ? tearing mode ? whole this area show a little decrease can’t find any localized heat channel in this case whole this area show significant increase

slide-21
SLIDE 21

21

large increase almost unchanged less decrease small increase inner the inner, the steeper increase of signal. there is the region where the signal does not change much (channel 1,2,3 in HFS) HFS LFS

slide-22
SLIDE 22

22

HFS LFS channels of HFS 2,1 and LFS 8,7 show decrease and channels of LFS 6β€”2 show increase decrease increase no change

slide-23
SLIDE 23

23