Transcript ICPP 2000: Results from Helical Axis Stellarators

H-1 Heliac: Parameters
3 period heliac: 1992
Major radius
1m
Minor radius
0.1-0.2m
Vacuum chamber 33m2
Aspect ratio
5+
Magnetic Field
1 Tesla (0.2 DC)
Heating Power
0.2(0.4)MW GHz ECH
0.3MW 6-25MHz ICH
Parameters:
n
T

achieved / expected
3e18/1e19
~100eV(Ti)/0.5-1keV(Te)
0.1/0.5%
H-1 Heliac: Parameters
Complex geometry requires
minimum 2D diagnostic
3 period heliac: 1992
Major radius
1m
Minor radius
0.1-0.2m
Vacuum chamber 33m2
Aspect ratio
5+
Magnetic Field
1 Tesla (0.2 DC)
Heating Power
0.2(0.4)MW GHz ECH
0.3MW 6-25MHz ICH
Parameters:
n
T

achieved / expected
3e18/1e19
~100eV(Ti)/0.5-1keV(Te)
0.1/0.5%
Cross-section of the magnet structure showing a 3x11 channel tomographic diagnostic
Plasma production and heating:
resonant and non-resonant RF
• Non-resonant heating is flexible
in B0, works better at low fields.
• Resonant heating is much more
successful at high fields.
<ne> 1018m-3
helicon/frame antenna
3.5
Helicon wave (non resonant) heating
3
Ion cyclotron resonant heating:
Hydrogen, and
Minority H in He
2.5
argon
2
H:He
Update with
helium, Tesla
1.5
1
H
0.5
0
0
1000
2000
3000
4000
Magnetic Field (T)
5000
6000
7000
CH On axis
=w
w=w
wCh
on
axis
8000
2D electron density tomography
Helical axis  non-circular  need true 2D
H density profile evolution (0.5T rf)
Raw chordal data
coherent drift mode in
argon, 0.08T
Tomographically inverted data
rotation
Ion Temperature
Camera
Intensity
temperature
radius
Hollow Ti at low B0
0
10
20
time (ms)
30
Confinement transitions in H-1
“Pressure” (Is) profile
evolution during transition
Parameter space map,  ~ 1.4
PRF (kW)
transition
I si (mA)
(a)
6
5
4
3
2
Modulation
inversion
B0(T)
1
•many features in common with
large machines
0
0
30
0.5
r/a
20
1
10
0
t (ms)
•associated with edge shear in Er
•easily reproduced and
investigated
Bulk Rotation Impeded
ExB and ion bulk rotation velocity in high
confinement mode: magnetic structure causes
viscous damping of rotation
V_pol
(cm/s)
2E+6
Radial force balance
(x10)
Er =
0E+0
15
20
25
r(cm)
(cm)
VExB
LCFS
(cm)
-6E+6
0
0
Vp, Vt << VExB ~ 1/(neB) dPi/dr
-2E+6
-4E+6
1
Pi  V p Bt  Vt B p
zen
Mass (ion) flow velocities
much smaller than
corresponding VExB