Core and edge toroidal rotation study in JT-60U

Transcription

1 Core and edge toroidal rotation study in JT-6U Japan Atomic Energy Agency M. Yoshida, Y. Sakamoto, M. Honda, Y. Kamada, H. Takenaga, N. Oyama, H. Urano, and the JT-6 team JT-6U EXC/ rd IAEA Fusion Energy Conference, October 21, Daejeon Convention Center, Korea

2 Contents 2 1. Motivation 2. Objectives 3. Experimental results i. Relation between core and edge rotation ii. Core-rotation with intrinsic rotation iii. Parameter dependency of edge-rotation iv. Momentum transport inside ITB 4. Summary

3 Motivation 3 It is essential to understand the physical mechanisms determining rotation profile from the core to the edge regions in order to control plasma performance. Toroidal rotation velocity ( ) profiles are determined by various factors. 1 m i n i t = M + S NB coll + S j B + S ion loss +? M = m i n i r Collsional torque 15 + V conv m i n i +? Momentum transport 5 jxb torque prompt fast ion loss : the momentum diffusivity V conv : the convection velocity Other momentum sources / fluxes, for example, Residual stress (~ P i, T i,,,) NTorque (~ T i )

4 Objectives 4 To understand the factors affecting profile from the core to the edge region, we investigate i. Relation between core and edge rotations, ii. Core-rotation with intrinsic rotation, and iii. Parameter dependency of the edge-rotation in H-mode plasmas. iv. Momentum transport properties in an ITB plasma =.3 i iii, iv.8.9 ii In this talk, the plasma areas of focus are as follows: i. core and edge relation: ~.3-.8 ii. core rotation: <.7 iii. edge rotation: ~.8-.9 iv. ITB: <.7

5 Approach: Momentum transport study in JT-6U 5 Momentum diffusivity ( ) and convection velocity (V conv ) are evaluated using transient transport analysis with modulated PERP-NBs. 6 = V.82 t 2-2 NB Time (s) NB Power (MW) Momentum balance eq. m i n i t = M + S M = m i n i r + V conv m i n i We refer to some scalings of and V conv that were given at the last IAEA meeting. V conv (m/s), (m 2 /s) 2-2 V conv T i (kev) and V conv are used to calculate profiles. 5 calculated Data

6 Core- is affected by edge-, and varies with the transport timescale at L-H transition 6 Impact of the edge- upon the core- during L-H and H-L transitions T i (kev) ~.9 ~.9.5 1/e ~2 ms D Time (s) At L-H and H-L transitions, the edge- changes rapidly at first, followed by gradual changes in the core-. 1/e ~2 ms after the L-H transition This timescale can be almost explained by a transport timescale using and V conv. T i at the edge region slowly varies.

7 behavior differs from T i behavior in its profile stiffness Relation between the core- and the edge- at L-H and H-L transitions 7 Toroidal rotation velocity ( ) L-H transition -1 ~ H-L transition ~.9 T i ~.5 (kev) Ion temperature (T i ) H-L transition L-H transition T i ~.9 (kev) First, the edge- varies while the core- remains constant, and then the core- varies with the edge-. On the other hand, T i in the core and edge regions varies nearly simultaneously. What are the characteristics of the profile?

8 Correlation between the core- and edge- has been identified in steady-state plasmas Parametric scans of n e, P NB, and magnetic field ripple have been performed in H-mode plasmas with small torque input (BAL-NBI). 8 Steady-state 4 ~ RV conv / = ~.8 M = m i n i r (1 5 m/s) V conv m i n i n e ~ m -3 n e ~ m -3 A linear correlation between the core- and edge- is observed in H- mode plasmas, where the pressure gradient ( P i ) is small. The structure in ~.5-.8 is not characterized by the profile stiffness but determined by the momentum transport equation using and V conv from transient transport analysis.

9 (ii) Core-rotation with intrinsic rotation 9 As reported at the last IAEA meeting: profiles are not reproduced solely by and V conv with a large P i. Intrinsic rotation increases with increasing P i. This relationship does not strongly depend on. (m/s) with a large P i calculation using and V conv -4-8 Data H-mode P ABS =4.8 MW =6. MW =8.4 MW =1 MW dp P i /dr i (Pa/m)

10 profiles with a large P i have been reproduced by incorporating a residual stress term We propose res = k P i as a turbulent residual stress term, (assuming k is a radial constant) based on the experimental results: Intrinsic rotation increases with increasing P i, The tendency remains almost the same over a wide range of, and a thought: is adopted as the turbulent state of a plasma. 1 (m/s) H-mode, BAL-NBI -2 k1 = m -1 s without res -4 res = k1 P i -6 res = k2 P i Momentum balance eq. m i n i t = M + S M = m i n i r + V conv m i n i + res We calculate the profile with res = k1 P i and compare them to measured profile. When we use res = k2 P i (no ), the profile is not reproduced.

11 profiles are reproduced using the proposed formula res = k P i for various plasmas 11 We also adopt res = k1 P i for various plasmas. We set the value of k1 at each discharge. The value of k1 varies within the factor of three ( k1 = to m -1 s). H-mode, CO-NBI k = m -1 s Data res = k1 P i without res L-mode k = m -1 s res = k1 P i Data res = k3 T i We attempted to reproduce profiles using T i instead of P i. Tested in various plasmas (14 discharges) L- and H-mode, I p = MA, B T = T, P ABS = 6-11 MW, N = 1-1.6, : CO, CTR The best fit is obtained with res = k1 P i for this range of plasmas.

12 (iii) Parameter dependencies of edge- 12 n e (1 19 m -3 ) T (kev) n e ~.9 T i T e ~ D 1 2 gas ~.9 ~ Time (s) gas (Pa m 3 /s) H-mode plasma (BAL-NBI) The edge-n e rises with increasing gas puff rate. At that point, T i and T e at the edge region decrease with increasing n e. Edge- increases in the CO-direction after n e increases. Core- also increases in the CO-direction following a time delay.

13 n e (1 19 m -3 ) T i (kev) linearly increases in the CO-direction with decreasing T i n e ~.9 T i D 1 2 gas ~.9 1 T e ~.9 ~ Time (s) T e (kev) gas (Pa m 3 /s) T i (kev) Relation between and T i ( s) T i CO CTR 13 edge L-H T i Here T i is defined as the T i gradient across the H-mode pedestal.

14 CTR-rotation increases with increasing T i 14 Many possible factors may account for the change in the edge-. m i n i t m = i n i V t r + V conv m i n i + res + S NB coll + S j B + S ion loss + S NTV? In order to minimize the effects of S NB coll, S jxb, S ion loss and, V conv, we performed a n e scan with small torque input (BAL-NBI) at a constant magnetic field ripple ( B~1%), P RP ~.9 MW, I p =1.2 MA and P ABS ~6 MW.

15 CTR-rotation increases with increasing T i 15 Many possible factors may account for the change in the edge-. m i n i t m = i n i V t r + V conv m i n i + res + S NB coll + S j B + S ion loss + S NTV? In order to minimize the effects of S NB coll, S jxb, S ion loss and, V conv, we performed a n e scan with small torque input (BAL-NBI) at a constant magnetic field ripple ( B~1%), P RP ~.9 MW, I p =1.2 MA and P ABS ~6 MW. Steady-state ~.9 ~.9 P i does not vary largely This result is different from findings in the core region. One difference in the condition is the magnetic field ripple ( B): B~.15% at ~.3; B~1% at ~.9.

16 16 Total external torque input remains almost constant even if n e varies jxb is calculated at low and high n e with the OFMC code. THC/P4-1, Wed. p.m. M. Honda jxb torque (N/m 2 ).1 n e ~ m -3 n e ~ m -3 n e ~ m -3 High n e Low n e Collisional torque (N/m 2 ).1 Low n e High n e Total torque (N/m 2 ) S NB coll +S jxb +S ion loss.1 remains constant ( Nm) jxb torque in the edge region, which is due mainly to the ripple loss of fast ions, remains almost constant. Although jxb torque in the core region decreases with increasing n e, this change is cancelled by a change in collisional torque.

17 Other momentum sources / fluxes, which increase with T i, also exist in the edge region 17 m i n i t BAL-NBI, I p, P ABS constant m = i n i + V conv m i n i + res? r + S NB coll + S j B + S ion loss + S NTV? ~.9 ~.9 not varied enough to induce intrinsic rotation Total torque (N/m 2 ).1 n e ~ m -3 n e ~ m -3 n e ~ m remains constant ( Nm)

18 18 (iv) Momentum transport inside ITB: Transient transport analysis has been performed Positive shear L-mode plasmas T i (kev) (1 5 m/s) 1 w/o ITB 8 with ITB I p =1. MA, B T =3.8 T P ABS = 8.5 MW (with ITB) P ABS = 6.8 MW (w/o ITB) Phase delay of modulated part of Phase delay (degree) ITB region with ITB 6 w/o ITB a large phase delay We use the off-axis PERP-NBs with marginal power for modulation (~11% of the total input power). The modulated parts of T i and n e amounts to only ~2% and ~1%, respectively. These effects on transport and intrinsic rotation are negligible.

19 (m 2 /s) V conv (m/s) i (m 2 /s) Momentum diffusivity ( ) and i decrease similarly in the ITB region w/o ITB with ITB ITB region w/o ITB with ITB i NC Reduction of inside an ITB has been observed. Convection velocity (V conv ) does not change significantly in the ITB region. In the ITB region ~.3-.4 w/o ITB with ITB / i ~.6 ~ 1 RV conv / ~ -4 ~

20 Summary 2 Relation between the core- and edge- in H-mode plasmas (BAL-NBI) At a L-H transition, the core- varies with a transport timescale after a rapid change in the edge-. In steady state; a linear correlation between the core- and edge- is observed in H-mode plasmas with a small P i structure is determined by and V conv. Core-rotation with the intrinsic rotation profiles with a large P i have been reproduced by incorporating res = k P i over a wide range of plasma conditions. Edge-rotation properties CTR- increases with increasing T i. Momentum transport properties in an ITB plasma and i decrease similarly in the ITB region res = k P i ITB Correlation, V conv L-H T i