Symposium II: New Developments in Current Drive andCurrent Profile Control in Toroidal Systems
S203

Tokamak Operation without the Useof Center Solenoid CoilY. Takase
Graduate School of Frontier Sciences, The University of Tokyo
for the JT-60 Innovative Operations Group (University-JAERI Collaboration)

19th Annual Meeting of the Japan Society ofPlasma Science and Nuclear Fusion ResearchInuyama
26-29 November 2002

Externally driven advanced tokamak plasma
Improved confinement(transport barriers)
Transport

External heating
Equilibrium
Pressure profile
Current profile

Microinstability
Current drive
28pA08 O. Mitarai, et al.

Ip start-up and24MHD stability

High βTransformation to advanced tokamak
High confinement
High beta
High bootstrap fraction

Noninductive ramp-up

initial ramp-up

High self-driven
current fraction
Bootstrap current

6t (s)

810

Examples of CS-less Tokamak Reactors
Improved economic competitiveness may be realized by a CS-less design.

S. Nishio, et al., paper FT/P1-21, 19th Fusion Energy Conference, Lyon 2002.

JT-60U Coils and Heating/CD Systems
OH solenoid (F) current iskept at zero (no flux input)
EC/LH preionization as wellas the vertical field coil(VR)andthe triangularity
VRcoil (VT) are used for Ip
ramp-up
Full cross section divertor
configuration is used for Ip
ramp-up by LHCD
Inward shifted divertor
configuration is used for thehigh-power NB heatedadvanced tokamak phase
Normally flux and vertical field
can be controlled independentlyFlux and Bv Contributions fromVR and VT Coils
Flux @ R = 3.4 m∆Φ (Wb) = (30.1 + 88.1) ∆IVT (MA) + 257.6 ∆IVR (MA)VT in VT out

VR

In the present experiment
IVT = −7.3à +6.5 kA
IVR = 0.1 à +1.1 kA
Flux contribution from the inner VT coil is ~20% in these experiments
Vertical Field @ R= 3.4 m
Bv(T) = (−0.537 + 1.948) IVT (MA) + 8.720 IVR (MA)VT in VT out
VRComparison with OH Start-up
VT/VR coil start-up:
20% flux from VTin

OH coil start-up:
70% flux from OH+VTin

Magnetic Configuration Just Before
Ip Start-up“Field null” (minimum |Bp | region) is formed by VT coil (2 locations)“Field null” moves radially outward by VT and VR coil ramps

Configuration Evolution During
CS-less Ip Start-up
Ip ramp-up accomplished by EC/LH preionization and VT/VR coil ramps
Transition to divertor configuration (5) and further Ip ramp-up by LHCD
1 234512453

CS-less Formation of High-Performance
Plasma Demonstrated
Start-up andinitial ramp-up

Noninductive ramp-up

Transition to highperformance phase2002.06.21

Noninductive Ramp-up Efficiency(dWm/dt) / PNI = 3.6%
(dWm/dt − Pext) / PNI = 2.2% (40% contribution from PF coils)
where Wm = (Lext + Lint) Ip2 / 2 : total poloidal magnetic field energy
PNI = PLH + PEC : total noninductive input power
Pext : Poynting flux provided by PF coils

Advanced Tokamak Equilibrium andPressure and Current Density Profiles
Start NB heating when Ip becomes high enough for beam ion confinement
Deeply reversed shear configuration with “current hole” is formed
nCurrent hole and ITB already formed during LHCD ramp-up

Lext = 5.6 µH
Lint = 1.4 µH(li = 0.67)

Density and Temperature Profiles ofHigh-Performance Plasma
Reversed shear for r/a < 0.7
ITB + H-modeIp = 0.6MA
βp = 3.6
βN = 1.6
HH = 1.6
fBS > 90%li = 0.67
q95 = 13qmin = 5.6 @ r/a = 0.7

Y. Takase, et al.,J. Plasma Fusion Res.
(Rapid Communications)78, 719 (2002)

Stability Limited byn = 1 Kink-Ballooning ModeNo β collapse observed at βN = 1.6 in E41711
β collapse observed at βN = 1.7 in E41710
ERATO withprofiles fromE41711 @ 8.5s

Summary of CS-less Ramp-up
Inductive ramp-up by outer PF coils is effective
nnnn

Strong preionization by EC (fundamental) and/or LH is required for effective
Ip start-up with negative BvIp start-up by VR ramp alone is possible but less effective (~ 50 kA)
Formation of “field null” by VT coil is effective
Further improvement of start-up scenario is possible

Noninductive Ip ramp-up by LHCD (+ ECCD)
nDecouples ∆Φ and Bv from PF coils

w but ramp-up efficiency is not very high (a few %)n

Maintenance of 250 kA (but not further ramp-up) was possible by EC alone
w Ip ramp-up by EC alone should be possible but requires higher power

An integrated scenario with controlled Ip ramp-up, transformation toadvanced tokamak plasma, and controlled ramp-down is demonstrated:nITB + H-mode plasma with βp = 3.6, βN = 1.6, HH = 1.6, fBS > 90%

Remaining Issues
Inner VT coil provided 20% flux (VR and outer VT coils provide 80%)
→ Demonstrate a scenario that uses no turns on the inboard midplane(use inboard top/bottom coils)
Extension to higher Ip, higher βNApplication of CS-less operation to ST
Develop control algorithm that can react to β collapse, etc.