Overview of TFTR Li experiments

1
Overview of TFTR Li experiments

• Dennis K. Mansfield
• reported by Leonid E. Zakharov at
• ALPS/APEX meeting
• SNL Albuquerque NM
• Nov.13-17, 2000

2
Outline

• Lithium pellets and TFTR physics.
• DOLLOP
• Limiter H-mode.

3
Experimental Technique Lithium Introduced
onto Limiter by Injection of Pellets
Line Average Density
Li pellets introduced Li into the limiter. This
improved fusion performance during NB
injection. Improvement took several forms.
1.0
B
5.0- 6.0 T
t
0.8
I
2.0- 2.7 MA
p

-3
No Li in
cm
0.6
Plasma

During
14
10
NBI
0.4
0.2
NBI
Li PELLETS
0.0
0
2
4
6
8
Time (sec)
4
Li conditioning of the limiter improved energy
confinement over 1. ITER-89 P 2. TFTR
supershots 3. TFTR tritium isotope/enhancedsupersh
ots. More Li -gt More improvement.
t
Confinement Time -

E
0.4
0.3
Sec
0.2
0.1
ITER - 89P
0.0
0
10
20
30
40
Neutral Beam Power (MW)

D-T Discharges, R
2.52 m, I
gt 2.0 MA

p
p
5
Li conditioning improved overall DT fusion
power. TFTR record fusion power shot was designed
using precise Li conditioning. Use of less Li at
higher power was because of MHD high-beta
disruption limits in TFTR.
D-T Fusion Power
10
MW
5
Q 0.27
0
0
10
20
30
40
Neutral Beam Power (MW)

D-T Discharges, R
2.52 m, I
gt 2.0 MA

p
p
6

t
t
NBI Power
Confinement Time -

E
E
0.4
"Painted"
Supershots
0.3
(s)
0.2
E
t
20
0.1
MW
D, no Li
DT,
4 Pellets

0.0
0
0.7
0.3
0.5
5
10
15
20
0.1
Neutral Beam Power (MW)
Time (s)
7
t
t
NBI Power
Confinement Time -

E
E
Heavy Li conditioning led to reversal of
typical energy confinement drop with heating
power. Instead, with enough Li, energy
confinement rose with NB power. This suggests
formation of a transport barrier.
0.4
"Painted"
Supershots
0.3
(s)
0.2
E
t
20
0.1
MW
D, no Li
DT,
4 Pellets

0.0
0
0.7
0.3
0.5
5
10
15
20
0.1
Neutral Beam Power (MW)
Time (s)
8
All 3 factors of the fusion triple product were
enhanced by Li conditioning (involving only few
milligrams of Li)
Ion Temperature - T
(0)
i
50
T-only
40
with Li
30
keV
20
D-only
10
no Li
0

t
n
(0)
T
(0)
e
i
E
0.4
s keV
0.3
-3
sec
0.2
m
21
0.1
10
17 MW NBI
0.0
Time (Sec)
Time (Sec)
9
For at least 0.2 sec Li conditioning prevented a
rise in the edge density even at High NB
power. (This result led to the DOLLOP idea)
Confinement Time
H-Alpha Emission
0.4
1.0
T-only
with Li
0.3
D-only
Sec
A. U.
0.2
no Li
0.1
17 MW NBI
0.0
0.0
Edge line density
CII Emission
2.0
1.0
1.8
-2
cm
1.6
15
A. U.
1.4
10
1.2
1.0
Slope 0
0.8
0.0
0.0
0.7
0.0
0.7
Time (Sec)
Time (Sec)
10
Transport barrier in the core was obvious with Li
conditioning. Lower edge density decouples the
core rotation from the walls and resulted in
higher toroidal velocity. 83545 did not disrupt
being close to MHD limits.

DT Supershot 4 Pellets Painting
Electron Density
Pressure q (R)
7
6
4
6
5
3
-3
5
4
Magnetic
m
Pascals
4
Axis
19
3
2
3
5
10
2
10
2
1
1
1
0
0
0
Ion Temperature
Toroidal Velocity
8
50
40
-1
6
m s
30
keV
4
5
10
20
2
10
0
0
2.50
3.00
Major Radius
(m)
11
Li Tritium --- Large Rise in Te
After Neutral Beams
This shot 83545 maintained transport barrier
after termination of NB (and influx of cold
electrons). Dramatic rise and peaking in
electron temperature was discovered. About 15
of it was due to alpha heating. (not yet
published).

DT Supershot 4 Pellets Painting
MHD
-1
Instabilities
s
MW
18
10
Begin
End
Ramp
Beams
Down
16
.3
MW NBI
0.0
15
(a)
(b)
MHD
(a)
(keV)
e
T
(b)
DT
0
2.50
3.00
keV
R (m)
DD
12
A Brief Step-Down Experiment
Li Tritium vs Li Deuterium
Steady state enhanced electron temperature was
kept for several energy confinement times at
reduced NB power. Retro-heating was seen again
after NB phase.
Electron Density
Electron Temperature
7
13
DT
12
-3
11
DD
cm
10
Ramp Down
Ramp Down
13
keV
9
10
8
7
6
0
5
Neutrons
Beam Power
1
16
14
12
-1
10
Sec
Ramp Down
Ramp Down
MW
8
18
6
10
4
2
0
0
4.0
5.0
6.0
4.0
5.0
6.0
Time (Sec)
89402,403,387,385
13

DOLLOP Li Aerosol Controls Influxes and
Increases
Performance - Nonperturbing and Controllable
21
Total Electrons (10
)
1.0
No DOLLOP
YAG LASER
Laser
on
NBI
0
0
2
4
6
16
-1
Neutron Rate (10
s
)
2.5
Li Aerosol
Controlled
by Laser
18 MW
NBI
0
3.5
5.5
4.5
Molten
Time (s)
Lithium
14
DOLLOP Has Led to Enhanced and Sustained
Performance with No Harmful Effects
Three TFTR records were achieved (with NO
optimization of DOLLOP) Highest DD energy
confinement (no rollover) Highest Q DD Lowest
Zeff.
3.5
With DOLLOP
2 Pellets
-1
s
16
10
NO Li
LASER ON
0
Z
eff
NBI Power
4
20
Sawtooth
3
2
MW
10
Z 1.3
1
0
0
4.0
4.5
4.0
4.5
Time (s)
104017/104039
15
Zeff Profiles With and Without Li
Li flux to the plasma edge resulted in LOWER Zeff
both at the edge and in the plasma core.
7
6
5
83362
No Li
magnetic axis
4
eff
Z
3
2

With DOLLOP
1
Laser on
104039
0
2.5
2.7
2.9
3.1
3.3
2.3
Major Radius (m)
Zeff data determined spectroscopically and
displayed

at t 4.4 sec for discharges with identical
externally-
controlled parameters.
( R 2.52 m, I
2.3 MA, B
5.6 T, P
18 MW).
p
t
b
16
Lithium injection benefited both TFTR supershots
and limiter H-mode. Elms were delayed.
t
Confinement Time -
E
0.3
0.2
0.1
NBI
0.0
1.0
Start
H-Mode
0.5
Start
Elms
0.0
3.0
3.5
4.0