KPS Meeting, ct. 22 25, Chonju RF Heating and Current Drive in the JT-6U Tokamak presented by T. Fujii Japan Atomic Energy Agency
Outline JT-6U 1. JT-6U Tokamak Device and its Objectives 2. LHRF Current Drive (1) Overview of the JT-6U LHRF system and its launchers (2) Performances of current profile control by LHCD 3. ECRF Heating and Current Drive (1) Development of the high power JT-6U ECRF system (2) Performances of local heating and current drive, especially for neoclassical tearing mode stabilization
JT-6U Objectives JT-6 Objectives JT-6U ITER Physics R&D Advanced Tokamak Concepts for ITER & DEMO ITER DEMO Reactor DEMO Reactor JT-6U NCT
JT-6U Device JT-6U Plasma Currents are generated inductively Major Radius 3.4m Minor Radius.9m Plasma Current 5MA Toroidal Field 4T
JT-6U Photo JT-6U
Inside Vacuum Vessel JT-6U
JT-6 Progress JT-6U High Performance High Efficiency Electron Heating Major Modification Year 85 86 87 88 89 9 91 92 93 94 95 96 97 98 99 1 2 3 4 W-shaped Div. Fusion Gain Q DT eq JT-6 ('85~) lower-x ('88~) JT-6U ('91~) Plasma sustainment Time High beta sustainment time 5s 1s Break Even 15s ('97~) 1.25(WR) 65s 24s Long Pulse Ion Temperature Fusion Product Bootstrap Current Fraction Fusion Product (full noninductive CD) 1.5 E21 m-3skev (WR) 5.2x1 8 [deg.] (WR) 1.5 E21 m-3skev (WR) 8% 9% full noninductive Normalized Beta in Steady-state Electron Temperature NNB injection power (>3keV) EC injection power (11GHz) 3x1 8 [deg.] (WR) 3.5 5.8MW(D) (WR) 3MW (WR)
Goal : Steady-state High Integrated Performance JT-6U compact & economically attractive steady-state tokamak reactor Advanced Tokamak Development n high power density = high pressure = high β sufficient burning efficiency plasma current D T α α particle heating high confinement improvement high fuel purity high density full noninductive CD external CD: NB& RF high bootstrap fraction heat / particle high radiation reduced diverter heat flux particle exhaust
How to Drive Plasma Current in Steady-State JT-6U Active Method Radio Frequency Wave produces electron flow Bootstrap Current Spontaneously Produced by Pressure Gradient electron(-) pressure profile Plasma Current ion(+) Plasma Neutral Beam produces ion flow Only with the active CD methods in a Reactor -> P CD for full current drive ~ 4 MW -> circulating power of 7 MW is required (if the active CD system efficiency =6%) This value is too large (out put of commercial reactor ~ 1 MWe) -> High bootstrap fraction (7-8%) is required = SSTR concept bootstrap current Fraction of bootstrap current is proportional to poloidal beta value β p totally hollow current profile Reversed Shear (RS) Plasma Advanced Tokamak Concept Plasma profile control, such as a current profile and a pressure profile, is necessary to achieve high integrated performance
RF Systems as Actuators for Profile Control High power radio-frequency (RF) systems has been used as actuator for plasma profile control via plasma heating and CD together with the neutral beam injection (NBI) system In particular, the RF systems are applied for sustaining high performance plasmas or suppression of MHD instabilities by control of the plasma current profile RF Heating and CD Systems 1) LHRF : 2 GHz, 4 MW / 2 Launchers (current drive) 2) ECRF : 11 GHz, 3 MW / 2 Antennas (local heating & current drive) 3) ICRF : 12 MHz, 6 MW into Plasmas Torus Hall P-NB (95 kev, 2 MW) #9, 1 P-NB #13, 14 #11, 12 P-NB T-NB T-NB (5 kev, 11 MW) N-NB (42 kev, 6 MW) N-NB LHRF (8x4 M.J.) (P11) JT-6U ECRF (P18) ICRF (P11, 12) ECRF LHRF (4x2 M.J.) P-NB (P17) (P18) JT-6U #1, 2 P-NB #3, 4 #5, 6 P-NB T-NB #7, 8 5 1 m Top view of heating an CD systems set in Torus Hall
LHRF Current Drive
Outline of the JT-6U LHRF System Frequency 1.74-2.2 GHz Output at Klys. 1 MW Power into Plasma 4 MW Pulse duration 1 s 16 High Power Klystrons 2 Multi-Junction Launchers JT-6U Torus Hall P11 Launcher 8 x 4 M.J. (upper port) 8 x 4 W/G Lines (length ~ 1 m) #1 #2 #3 Amp. Room II Klystrons.6 MW x 1 s #8 P18 Launcher 4 x 2 M.J. (equatorial port) Dummy Loads #4 JT-6U 4 x 2 W/G Lines (length ~ 1 m) #8 Phase Shifter Amp. Room I
High Directivity Launcher Needed for Efficient LHCD JT-6U LHRF CD efficiency η CD r (directivity) if the power spectrum is relatively sharp A multi-junction launcher has higher directivity than the conventional one, however, it requires low reflection of < 1% (or good coupling) for power injection into plasmas Plasma Multi-Junction (M.J.) Launcher High Directivity.8 -.95 φ M + φ φ M + 2φ φ M + 3φ φ 2φ 3φ º φ M 2 φ M Kly. 1 Kly. 2 Kly. 3-5 Power Spectrum from a Launcher Conventional Type of Launcher Plasma P(N // ) (a. u.) driving opposite currents -4-3 Low Directivity.5 -.7 φ 1 φ 2 φ 3 φ 4-2 -1 sharp and lowered N // => more efficient CD.6.4.2 not access. N // 1 2 3 Kly. 1 Kly. 2 Kly. 3 Kly. 4 B T Geometrical Phase Shifters built in B T φ = φ i - φ i+1 Array of waveguides
Development of Multi-Junction Launchers for JT-6U 8 x 4 Multi-Junction Launcher 8-column x 4-row modules P (N // ) (a.u.) Jacket for bundling 5 46 3 subwaveguides in a column (including phase shifter) N 2 gas cooling pipe CFC guard limiter standard w/g Wide Control of N // Spectrum 1.8.6.4.2 12º 2.2 GHz Directivity ~.9 18º 2 GHz φ M = 24º 1.74 GHz N // =.4 4 x 4 Multi-Junction Launcher For high power injection and simplified waveguide lines bellows 4-column x 4-row modules 65 P (N // ) (a.u.) 79 1.8.6.4.2 2 GHz φ M = - 6º 12 subwaveguides in a column (including phase shifter) CFC guard limiter 3º 18º P JT-6U standard w/g oversized taper w/g Fairly Sharp N // Directivity ~.95 N =.2 // 1 1.5 2 2.5 3 N // 1 1.5 2 2.5 3 N //
Full-CD by Combined LHRF and N-NB in RS Plasmas JT-6U P NB (MW) 1 P LH 4 (MW).4 V.2 l (V) -.2 T e,i (kev) E37964,.9MA, 2.5T, deuterium N-NB P-NB LHRF 4 2 T e Ti 5.5 6. 6.5 7. 7.5 time (s) LHCD (2 GHz) + N-NBCD (E b ~ 36keV) => V l ~V, βn ~ 2.2, βp ~ 2.1, T e ~ T i, q 95 = 6.9 2 1 βn n e (1 19 m -3 ) T e,i (kev) V l (V).4.2 -.2 4 2 4 2 6.85-7.5s MSE analysis T e T i 7.24s 7.24s ITB 6.15s foot.5 1 ρ full non-inductive CD T e, T i and n e ITBs expand
q j/q Profile Modification by External Current Drivers N-NBCD (+ P-NB) increases j => lower q however in ρ <.3, 8 6 4 2 q is still high N-NBCD LHCD.6 Inner region ρ =.4 q 6 6.5 7 7.5 time (s) 7 5 3 7.24s 6.15s.5 1 ρ Outer region LHCD j LH at just outside q-min expands ρ q-min => ITB expansion ρfoot The results are demonstrated with high f BS (62%)..8.7 6.15s.6.7 ρq-min JT-6U 7.24s
Development of Real-time Control of q(r) JT-6U Real-time evaluation of q(r) with MSE Change CD location by LHW phase difference φ MSE LH ρ CD q MSE φ ρ ref q ref q MSE 5 4 3 2 E43167,t=12.s real-time calc. 1 eq. reconstruction.2.4.6.8 1 ρ
q profile control was demonstrated JT-6U φ was controlled q(r) approached to the reference, and was sustained for 3s n e =.5x1 19 m -3 η CD ~1x1 19 A/W/m -2 q(r) control in high f BS and/or β N plasmas is a next target
ECRF Heating and Current Drive
Necessity of High Power ECRF System JT-6U B [arb.] Ip [MA] β N B [arb.] 2 1 3 2 1.3.2.1 Performance was degraded by NTMs in High βp H-mode plasmas E29442 n=2(m=3) n=1(m=2) Ip=1.5, B t =3.7T, q 95 =3.9 5 6 7 8 9 time[s] 4 2 PNB [MW] Plasma performance at high β N was limited by MHD instabilities, especially neoclassical tearing modes (NTM), which appear locally in plasma middle region The NTM can be suppressed by driving currents only at its location A multi-mw ECRF system was needed, which can converge the ECRF beam on a spot of ~ 1 cm in diameter at plasma center and can scan it from plasma center to the edge
Outline of Developed JT-6U ECRF System JT-6U Frequency 11 GHz Power at gyrotrons 4 MW Power into Plasma 3 MW Pulse Duration 5 s Transmission Mode HE 11 Transmission Length ~ 6 m / line Transmission Efficiency 7-8 % Pressure in Lines 1-4 - 1-3 Pa Antenna B Antenna A Torus Windows MOU #1 Gyrotrons (1MW each) #4 Main Power Supplies (6 kv, 65 A each) #2 Pumping #3 JT-6U Transmission Lines (31.75 mm Corrugated Waveguides, 9 Bends/line) Waveguide Acceleration Dummy Load Power Supplies (1 kv,.3 A each)
Expansion of the Gyrotron Operation Region Output of the JT-6U gyrotron can be increased with the beam current I C 1 MW (designed) at I C ~ 55 A to 1.2 MW at I C ~ 6 A by suppressing parasitic oscillation and adjusting the anode voltage JT-6U The anode voltage controller is also useful for power modulation and extension of the pulse duration since it can control the gyrotron oscillation JT-6U Control System Local Control (sequencer) Timing Generator Functional Generator Controller Heater Controller Gyrotron H Main P/S DC Generator AC DC 18 kv / 6 kv, 65 A 4.45 MVA IGBT Switch 1 kv, 1 A Body P/S 1kV, 3mA Acceleration P/S Optical Signal Heater P/S Anode Voltage Controller -6 kv K -2 kv A 25 kv B kv C Electron Beam DC Break RF Power I C
Development of ECRF beam Scanning Antenna Poloidal ECRF Beam Scan Antenna A : from center to edge Antenna B : from center to the predicted NTM position (r ~.6) (limited by the port space) By both preprogram and feed-back control Antenna B With beam scan speed of 15 deg/s (fast mode) and Top View of JT-6U 5 deg/s (high resolution mode : resolution.4 deg) Side View of the Antenna A Antenna A 2 Ip ±2 Simple and reliable mechanical driving P17 P18 Antenna A Converging Mirror Antenna B JT-6U Steering Mirror Rotating Mirror Servo motor * Servo Motor Driven Steering Plane Mirror Steering Mirror
Progress of Injected Energy into Plasmas JT-6U Injected energy was increased from 1 MJ to 15 MJ in long pulse operation of the gyrotron by the preprogrammed anode voltage and heater input controllers P in ~ 1 MW, 15 s (15 MJ) : Combined Injection with three gyrotrons P in ~.35 MW, 45 s (15 MJ) : Series Injection with automatic succession control Injected Energy (MJ) 2 15 1 5 '2 '3 '4 Tentative Objective 18MJ (.6MW,3s) E44264 ~3MW ~1MW ~.35MW 3.2 3 E44264 I p (MA) V l (V) Plasma Stored Energy (a. u.) Injected EC Power (a.u.) #3 #1 #4 #2 1 1 2 3 4 Pulse Duration (s) 5 1 2 3 4 5 6 Time (s)
Ip [MA] Te()[keV] T e () ~ 23 kev was achieved by EC waves 1.5 3 2 1 E41651 Te() ECCD analysis Ip=.6MA.5 PEC=2.9MW 1 4 5 6 7 TIME(s) Vl [V].5 n e [1 19 /m 3 ] JT-6U Objective is to analyze EC driven current in a high-t e regime. Resonance location of ECH/ECCD was optimized to achieve high-t e for long enough for ECCD analysis Te [kev] 25 2 15 1 5 E41651 t=5.7 ECE Thomson CL ECH.6MW ECCD 2.3MW T e () = 23 kev for.8 s On-axis ECCD efficiency η CD increased with T e and reached 4.2 x 1 18 m -2 A W -1.2.4.6.8 1 ρ
Real-time NTM Feedback Stabilization System JT-6U NTM stabilization is required for sustaining high beta plasmas Mode location can be changed in time Real-time NTM FB stabilization Complete NTM stabilization was demonstrated using the real-time NTM FB stabilization system in JT-6U Z[m] 1 fec Steerable mirror EC ECE M-shaped amplitude profile -1 ECE 2 3 4 R[m] Rs Real-time calculation of plasma shape with a given q-profile [%] 5 4 3 2 1 3.5 Rs at step 1 δt e /T e Local min.: island center 3.6 3.7 R [m] 3.8 EC Steerable mirror Calculation: 1ms Mirror scan: Rdep/ t~1cm/s Rough estimation Fine tuning EC mirror steering
Complete Stabilization of m/n=3/2 NTM with Real-time Feedback Control System JT-6U PNB[MW] B [arb.] βn Channel number Angle [degree] 3 E41666 1 n=2 (m=3) 1.8 1.5 1.3 8 6 43 44 CH at ~ Te min Mirror angle Ip=1.5MA, Bt=3.7T, q95=3.9 EC(~3MW) 1.67 Reference 6 7 8 9 1 11 time[s] Te[keV] ~ Te/Te.2.15.1.5 -.5.4.2 E41666 Increment of T e at 9ms after ECW injection 7.52s(6.84kHz) CH1 CH6 Center CH12 3.5 3.6 3.7 3.8 R [m] β N increased by the stabilization, and even after the EC turn-off Confinement improvement: HH 98y2 : 1. 1.1
B / f [arb.] [arb.] [MW].8.6.4.2 3 2 1 1 E4165 B Effective NTM Suppression Control Late injection PNB β N =1.4 Real-time FB on PEC(1.5MW) n=2 (m=3) 5 6 7 8 9 1 11 time[s] Early injection Late injection 1 2 3 PEC [MW] Early injection is effective Injection timing [arb.] [MW] 3 2 1 1 Effectiveness of NTM suppression Injection location E41693 B Early injection PNB PEC(1.7MW) JT-6U Real-time FB off n=2 (m=3) 5 6 7 8 9 1 11 time[s] B / f [arb.].5.4.3.2.1 Early injection Island center 4 units 3 units 2 units.45.5.55.6.65 ρ EC Center injection is effective Suppression control can be effectively made for saving EC power by using early and island-center injection.
1. LHRF Current Drive Summary Efficient LHCD (η CD = 1.5-3.5 x 1 19 m -2 A W -1 ) was performed with the multi-junction launchers having high directivity as well as with plasma shaping and constant-gap control and additional gas puffing Full non-inductive CD was attained in RS plasmas by combined LHCD and NBCD, where LHCD drove currents at just outside q-min Real-time current profile (exactly q profile) control was demonstrated by LHCD together with multi-channel MSE measurements 2. ECRF Heating and Current Drive JT-6U The high power (3 MW into plasmas) ECRF system was developed for local heating and CD, which can converge the ECRF beam on a spot of ~1 cm in diameter and can scan it from plasma core to periphery High electron temperature of T e () ~ 23 kev was achieved by 3 MW on-axis heating, and ECCD efficiency increased with T e up to 4.2 x 1 18 m -2 A W -1 NTM stabilization was demonstrated with the real-time feedback control system and it was found that key points to effective suppression of NTM instabilities were injection timing and injection location