1. 8th Meeting of the ITPA Confinement Database & Modeling Topical Group
on at Kyto university
H-mode power threshold in JFT-2M during with ferritic wall and boron coating
K. Tsuzuki JAERI

2. Contents Modification of JFT-2M High recycling steady H-mode
Installation of ferritic steel
Boron coating
High recycling steady H-mode
Threshold power for L-H transition
Effect of ferromagnetism and boron
BT dependence
Summary

3. Modification of JFT-2M(1) Installation of ferritic steel
Reduced activation ferritic steel is a leading candidate for structure material of DEMO reactor but ferromagnetic and easily oxidized.
Compatibility with high performance plasma is a critical issue.
Ferritic steel wall
Compatibility has been investigated in JFT-2M by installing ferritic wall inside vacuum vessel
Graphite tiles

4. Possible Magnetic effect of the ferritic wall
Ripple reduction
　　Ripple amplitude at plasma periphery
2.2% -->0.4% for optimum case
(2) Complex field
Higher harmonics is produced
(3) Error field
Miss-alignment and/or
inhomogeneous installation
(4) Wall stabilization

5. Modification of JFT-2M(2) boron coating
Boron coating with B(CH3)3 was first applied on JFT-2M in 2000.
Oxygen impurity : reduced
Hydrogen recycling : strong pumping
and fueling according to
wall condition

6. High Recycling Steady (HRS) H-mode
New H-mode was found after boronization
Enhancement of Da
Steady H-mode edge
ne/nGW > 0.4

7. Threshold power with/without ferritic wall
Pth was compared for standard configuration
BT = 1.3 T, Ip = 200 kA, q95 = 3.0
Partial ferritic
full ferritic
wo boron
690 kW
680 kW
with boron
440 kW
420 kW
Ferritic steel : No effect
Boron coating : Improvement

8. BT dependence of Pth
BT dependence of Pth was not well investigated in JFT-2M
Effect of the ferritic steel change
Permeability : 2 (2T) ~ 4 (0.8T)
Ripple : 1.5% (0.85T) ~ 0.5% (1.3 T)
JFT-2M

9. Other parameters BT was scanned from 0.85T to 1.9T
Ip is almost constant at 200 kA
q95 varied from 2 to 4.2
Low recycling conditions; not HRS but ELMy H-mode

10. BT dependence of Pth Pth obeys scaling law by 15 % for
0.85T < BT < 1.9T
J. Snipes, ITER H-mode Threshold Database Working Group, 7th H-mode Workshop, Oxford, 1999
2.84M-1*Bt0.82*n200.58*R*a0.81

11. Summary
Threshold power (Pth) for L-H transition has been investigated in JFT-2M after installation of ferritic steel and boron coating.
Pth is not changed by the installation of ferritic wall
Boron coating reduced Pth by ~250W
Toroidal field was scanned for wider range than previous data sets.
Ripple amplitude is also scanned from 0.4 % to 1.5 %
Permeability is also scanned from 2 to 4
Pth obeys conventional scaling law (B0.82) by 15 %