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/3-2 1 23rd IAEA Fusion Energy Conference, 11-16 October 21, Daejeon Convention Center, Korea
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
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.2.4.6.8 1 : the momentum diffusivity V conv : the convection velocity Other momentum sources / fluxes, for example, Residual stress (~ P i, T i,,,) NTorque (~ T i )
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. 15 1 5 =.3 i iii, iv.8.9 ii.2.4.6.8 1 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
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 = 6 4.26 4 2.57 V.82 t 2-2 NB 8 8.5 9 9.5 1 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 1 2 3 4 T i (kev) and V conv are used to calculate profiles. 5 calculated- -5-1 Data -15.2.4.6.8 1
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) -2-4 -6 3 2 1 ~.9 ~.9.5 1/e ~2 ms D 5.5 5.52 5.54 5.56 5.58 5.6 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.
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 ~.5-2 -3-4 H-L transition -5-5 -4-3 -2-1 ~.9 T i ~.5 (kev) Ion temperature (T i ) 5.5 5 4.5 4 H-L transition L-H transition.8 1 1.2 1.4 1.6 1.8 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?
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 ~.5-4 -8 RV conv / =-2.4-12 -12-8 -4 4 ~.8 M = m i n i r (1 5 m/s).4.2 -.2 -.4 +V conv m i n i.2.4.6.8 1 n e ~3. 1 19 m -3 n e ~1.8 1 19 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.
(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.2.4.6.8 1-5 4 3 2 1 H-mode P ABS =4.8 MW =6. MW =8.4 MW =1 MW -1-6 1 4-3 1 4 dp P i /dr i (Pa/m)
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 =1.5 1-7 m -1 s without res -4 res = k1 P i -6 res = k2 P i -8.2.4.6.8 1 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.
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 =1. 1-7 to 3. 1-7 m -1 s). H-mode, CO-NBI k =1. 1-7 m -1 s 15 1 5 Data res = k1 P i without res.2.4.6.8 1 L-mode k =1.8 1-7 m -1 s -2-4 -6-8 res = k1 P i Data res = k3 T i -1.2.4.6.8 1 We attempted to reproduce profiles using T i instead of P i. Tested in various plasmas (14 discharges) L- and H-mode, I p = 1. - 1.8 MA, B T = 2.5-3.8 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.
(iii) Parameter dependencies of edge- 12 n e (1 19 m -3 ) T (kev) 3 2 1 1 1-1 4 2 n e ~.9 T i T e ~.9 4 3 2 D 1 2 gas ~.9 ~.2 4 4.5 5 5.5 6 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.
n e (1 19 m -3 ) T i (kev) 3 2 1 1 1-1 4 2 linearly increases in the CO-direction with decreasing T i n e ~.9 T i 4 3 2 D 1 2 gas ~.9 1 T e ~.9 ~.2 4 4.5 5 5.5 6 Time (s) T e (kev) gas (Pa m 3 /s) T i (kev) 3 2 1 Relation between and T i (4.8-6. s) T i.7.8.9 1 CO CTR 13 edge L-H T i Here T i is defined as the T i gradient across the H-mode pedestal.
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.
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 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 ~3. 1 19 m -3 n e ~2.2 1 19 m -3 n e ~1.8 1 19 m -3 High n e Low n e -.1.2.4.6.8 1 Collisional torque (N/m 2 ).1 Low n e High n e -.1.2.4.6.8 1 Total torque (N/m 2 ) S NB coll +S jxb +S ion loss.1 remains constant (.62-.77 Nm) -.1.2.4.6.8 1 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.
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 ~3. 1 19 m -3 n e ~2.2 1 19 m -3 n e ~1.8 1 19 m -3 -.1.2.4.6.8 1 remains constant (.62-.77 Nm)
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 6 4 2-4 -8-12.2.4.6.8 1 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) 14 12 1 8 ITB region with ITB 6 w/o ITB 4.2.4.6.8 1 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.
(m 2 /s) V conv (m/s) i (m 2 /s) 1 1 1 1-1 2 1-1 -2 1 1 1 1-1 Momentum diffusivity ( ) and i decrease similarly in the ITB region w/o ITB with ITB ITB region w/o ITB with ITB i NC.2.4.6.8 1 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 ~ -13 19
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. 15 1 5 res = k P i ITB Correlation, V conv.2.4.6.8 1 L-H T i