Heating and Current Drive Scenarios in a Tokamak

1
Heating and Current Drive Scenarios in a Tokamak

• Yong-Su Na
• Seoul National University

Korean Fusion Plasma Summer School 2009
2
Contents

• 1. What is Tokamak? Why Heating and Current
  Drive?
• 2. Heating and Current Drive in a Tokamak
• 3. Tokamak Operation Scenario
• 4. H-mode Scenario
• 5. Reversed Shear Scenario
• 6. Hybrid Scenario

3
Contents

• 1. What is Tokamak? Why Heating and Current
  Drive?
• 2. Heating and Current Drive in a Tokamak
• 3. Tokamak Operation Scenario
• 4. H-mode Scenario
• 5. Reversed Shear Scenario
• 6. Hybrid Scenario

4
To build a sun on earth
5
Magnetic confinement

• Imitation of the Sun on Earth

magnetic field
vessel wall
plasma pressure
plasmapressure
Plasma on earthmuch, much smaller tiny mass!
Equilibrium in the sun
6
Magnetic confinement
Magnetic field
ion
7
Tokamak
Magnetic field
ion
8
Tokamak
Donut-shaped vacuum vessel
9
Tokamak
R0
a
Plasma needs to be confined R0 1.8 m, a 0.5 m
in KSTAR
10
Tokamak
Toroidal Field (TF) coil
Applying toroidal magnetic field 3.5 T in KSTAR
11
Tokamak
Toroidal Field (TF) coil
Magnetic field of earth?
0.5 Gauss 0.00005 T
12
Tokamak
ion
electron
Applying toroidal magnetic field 3.5 T in KSTAR
13
Tokamak
14
Tokamak
ion
- - - electron
15
Tokamak
ion
Electric field, E
- - - electron
16
Tokamak
ion
ExB drift
Electric field, E
- - - electron
ExB drift
17
Tokamak
ion
ExB drift
Electric field, E
- - - electron
ExB drift
Poloidal magnetic field required
Then, how to?
Tokamak .VS. Stellarator
Plasma current ? Tokamak
18
Tokamak
Central Solenoid (CS)
Transformer
19
Tokamak
Central Solenoid (CS)
Faradays law
Transformer
20
Tokamak
Central Solenoid (CS)
Plasma
Faradays law
Transformer
21
Tokamak
Central Solenoid (CS)
Plasma
Faradays law
Poloidal field
Pulsed Operation!
22
Pulsed Operation Current Drive
Plasma Current
MA
t(s)
PF Coil Flux
Power Supply Limit
Wb
t(s)
Pulsed Operation!
23
Tokamak
Adding vertical field coils (PF)
current
current
coil
coil
24
Tokamak
X
PF coils
?
X
current
current
Force
X
X
?
coil
coil
X
Plasma shaping by PF coils
25
Tokamak

• The plasma shape can be modified by PF coil
  currents.

26
Tokamak
27
Tokamak
Adding vertical field coils (PF)
Plasma shaping by PF coils
28
Tokamak
Invented by Tamm and Sakharov in 1952
Toroidalnaja kamera magnitnaja katushka (Toroidal
chamber magnetic coil)
29
Tokamak
Invented by Tamm and Sakharov in 1952
Cutaway of the Toroidal Chamber in
Artsimovitch's Paper Research on Controlled
Nuclear Fusion in the USSR
Toroidalnaja kamera magnitnaja katushka (Toroidal
chamber magnetic coil)
30
Tokamak
JET (Joint European Torus) R03m, a0.9m,
1983-today
31
Tokamak
JET (Joint European Torus) R03m, a0.9m,
1983-today
32
Tokamak
KSTAR (Korea Superconducting Tokamak Advanced
Research) R01.8m, a0.5m, 2008
33
Fusion Reaction
34
Fusion Reactor Requirements
What is required to light a fire in a stove?

• Fuel D, T
• Amount/density
• Heat insulation
• Ignition temperature

35
Contents

• 1. What is Tokamak? Why Heating and Current
  Drive?
• 2. Heating and Current Drive in a Tokamak
• 3. Tokamak Operation Scenario
• 4. H-mode Scenario
• 5. Reversed Shear Scenario
• 6. Hybrid Scenario

36
Heating and Current Drive
37
Ohmic Heating
Electric blanket
38
Ohmic Heating
F
Ip
Vp
ICS
http//en.wikibooks.org/w/index.php?titleFileTra
nsformer.svgfiletimestamp20070330220406
39
Neutral Beam Injection
Autobahn in Germany 259 Car Crash
40
Neutral Beam Injection
NBI
Plasma
Neutral beam
Andy Warhol
http//www.nasa.gov/mission_pages/galex/20070815/f
.html
41
Neutral Beam Injection
Injection of a beam of neutral fuel atoms (H, D,
T) at high energies (Eb gt 50 keV)
? Ionisation in the plasma
? Beam particles confined
? Collisional slowing down
Eb 120 keV and 1 MeV for KSTAR and ITER,
respectively
42
Electromagnetic Waves
Tuning fork
Resonance
43
Electromagnetic Waves
Tacoma Narrows Bridge (1940. 11. 4)
44
Electromagnetic Waves
Microwave oven
http//cafe.naver.com/nadobaker.cafe?iframe_url/A
rticleRead.nhn3Farticleid82
http//blog.naver.com/rlhyuny27?RedirectLoglogNo
30029307561
45
Electromagnetic Waves
Resonance zone
Excitation of plasma wave (frequency w) near
plasma edge
? wave transports power into the plasma center
Antenna
? absorption near resonance, e.g. ? ? ?c , i.e.
conversion of wave energy into kinetic energy of
resonant particles
? Resonant particles thermalise
R
46
Electromagnetic Waves
Resonance zone
Antenna
KSTAR first plasma
R
47
Contents

• 1. What is Tokamak? Why Heating and Current
  Drive?
• 2. Heating and Current Drive in a Tokamak
• 3. Tokamak Operation Scenario
• 4. H-mode Scenario
• 5. Reversed Shear Scenario
• 6. Hybrid Scenario

48
Tokamak Operation Scenario
JET pulse 69905 (BT3.1T)
Plasma initiation
Plasma quench
49
Contents

• 1. What is Tokamak? Why Heating and Current
  Drive?
• 2. Heating and Current Drive in a Tokamak
• 3. Tokamak Operation Scenario
• 4. H-mode Scenario
• 5. Reversed Shear Scenario
• 6. Hybrid Scenario

50
H-mode

• 1982 IAEA F. Wagner et al. (ASDEX)

51
H-mode

• 1982 IAEA F. Wagner et al. (ASDEX)

52
Energy Confinement Time
Temperature
Time
53
Energy Confinement Time
Temperature
Time
tE

• tE is a measure of how fast the plasma looses
  its energy.
• The loss rate is smallest, tE largest if the
  fusion plasma is big and well insulated.

54
H-mode

• 1982 IAEA F. Wagner et al. (ASDEX)

Hoover dam
55
H-mode

• 1982 IAEA F. Wagner et al. (ASDEX)

Hoover dam
56
H-mode How to? (I)

• Separation of plasma from wall by a limiter and
  a divertor

Strike point
57
Tokamak
58
Tokamak
59
H-mode How to? (II)
Pth 2.84M-1Bt0.82n200.58R1.0a0.81
60
H-mode Why?

• 1982 IAEA F. Wagner et al. (ASDEX)

61
Turbulence Stabilisation
62
H-mode Why?
Theoretical physics
63
H-mode Why?
Theoretical physics
Experimental physics
64
Safety Factor, q

• Safety factor q number of toroidal orbits per
  poloidal orbit

65
Tokamak Operation Scenario
q-profiles
5
4
3
2
1
ELMy H-mode
0
0
0.5
1
r/a
66
H-mode Limitations
Stability of H-mode plasmas related safety factor
profile q(r)
q0 lt 1 Sawtooth instability, periodic
flattening of the pressure in the core
H-mode, q-profile
5
4
3
2
q 1
1
0
0.5
1
0
r/a
67
Sawtooth
ASDEX Upgrade pulse 20438
1
Ip (MA)
PNBI (MW)
10
PRF (MW)
WMHD (MJ)
1
6
Nel x1.1019
8
Ti (keV)
Te (keV)
0
2
4
6
8
time (s)
68
H-mode Limitations
Stability of H-mode plasmas related safety factor
profile q(r)
q0 lt 1 Sawtooth instability, periodic
flattening of the pressure in the core
H-mode, q-profile
5
4

• q 3/2 and q 2
• Neoclassical Tearing Modes (NTMs)
• limit the achievable ß 2µ0p/B2
• degrade confinement ( disruptions)
• often triggered by sawteeth.

3
q 2
2
q 3/2
q 1
1
0
0.5
1
0

• ITER work point is chosenconservatively bN ?1.8
  !

r/a
69
Neoclassical Tearing Mode (NTM)
ASDEX Upgrade
70
Neoclassical Tearing Mode (NTM)

• Pressure flattening across magnetic islands due
  to large transport coefficients along
  magnetic field lines

71
Neoclassical Tearing Mode (NTM)
72
Neoclassical Tearing Mode (NTM)
NTM stabilisation with ITER relevant broad
deposition in ASDEX Upgrade
Feedback controlled Deposition in DIII-D

• Demonstration of individual elements as well as
  integrated feedback

73
NTM Stabilisation by ECCD

• JT-60U

74
Contents

• 1. What is Tokamak? Why Heating and Current
  Drive?
• 2. Heating and Current Drive in a Tokamak
• 3. Tokamak Operation Scenario
• 4. H-mode Scenario
• 5. Reversed Shear Scenario
• 6. Hybrid Scenario

75
Inductive Current Drive
Pulsed Operation!
76
Reversed Shear Scenario
Plasma Current
MA
SoF
Ip2MA
ECH Heating
SoB
?N2.0
(?N1.8)
NBI(8MW) ICRH(6MW) Heating
t(s)
40
44
64
68
PF Coil Flux
Flux-linkage V-s
Wb
(5.5)
(6.0)
30
40
t(s)
70
(-5.7)
(-6.1)
77
Tokamak Operation Scenario
q-profiles
5
strong
4
Reversed shear
3
weak
2
1
ELMy H-mode

• Good confinement
• Poor stability

0
0
0.5
1
r/a
78
Tokamak Operation Scenario
q-profiles
5
strong
4
Reversed shear
3
weak
2
1
ELMy H-mode

• Good confinement
• Poor stability
• Only weak RS plasmas are stable
• but they require a delicate active
  control

0
0
0.5
1
r/a
79
Reversed Shear Scenario
High bootstrap current!

• Higher pressure gradient region in the core with
  steep edge pedestal

• Hollow current profile

• Reversed q-profile

• With negative magnetic shear

80
Bootstrap Current
B
R
81
Bootstrap Current

• But more faster particles on orbits nearer the
  core (green cf blue) lead to a net banana
  current
• this is transferred to a helical bootstrap
  current via collisions

82
Reversed Shear Scenario
H-mode Reversed shear
mode
83
Reversed Shear Scenario
Internal Transport Barrier (ITB)
H-mode ETB
84
Reversed Shear Scenario
Internal Transport Barrier (ITB)
H-mode ETB
85
Turbulence Stabilisation

• Turbulence stabilisation

Z
Z
ITB
Temperature profile
R
R
Contour lines of electric potential.
Contour lines of electric potential.
86
Reversed Shear Scenario
Non-monotonic current profile Turbulence
suppression High pressure gradients
Large bootstrap current Non-inductive current
drive
87
Reversed Shear Scenario
q95 5
Technique used since mid 1990s
Ip
III Performance at stable q(r)
II Create ITB
time
I Reverse q(r)
I Heat during current rise, external current
drive (reverse q). II Increase heating power to
stabilise turbulence (ITB).Improve plasma
confinement, try to increase pressure (bN) III
Keep going ITER non-inductive regime(ITER
9MA, 50 external current drive (73MW), 50
bootstrap fraction)
88
Reversed Shear Scenario
I Form q(r), II create ITB, III But discharge
terminates (unstable)
Fukuda T and the JT-60U team 2002 Plasma Phys.
Control. Fusion 44 B39B52
89
Reversed Shear Scenario

• Formation of an ITB at low ne,with 15 MW NBI
  powerTi gt Te, high rotation shear
• ITBs are relatively short lived,only few tE
• Good, transient performanceH893, bN 3
• ITB not compatible with H-mode edge barrier and
  large ELMs

90
Reversed Shear Scenario
(R01.7m. ,a0.6m. )

• Less RS
• HH98(y,2) 1.37
• ßN 2.62
• q95 5
• Weak ITBs

Wade, Nucl. Fusion 43 (2003) 634646
91
Sustainment of Non-monotonic Current Profile

• Plasma current diffusion into the core from the
  edge

Current and pressure profile control !
92
Reversed Shear Scenario

• Current density profile control at ASDEX Upgrade

93
RT Current and Pressure Profile Control

• Simultaneous control of distributed magnetic and
  kinetic paramters
• Dedicated experiments to identify controller
  coefficients

• Modulation combinations of actuators (NBI, LH,
  ICRH) to infer the coefficients of the state
  space model of the slow loop.
• Two control loops, 4 actuators (NBI, LH, ICRH,
  PF)

94
RT Current and Pressure Profile Control

• JT60-U Real time qmin control with MSE
  diagnostics and LHCD

jOH or jBS change

• Transport reduction at t12.4 s
• Time delay in response of qmin

MSE LH
95
Contents

• 1. What is Tokamak? Why Heating and Current
  Drive?
• 2. Heating and Current Drive in a Tokamak
• 3. Tokamak Operation Scenario
• 4. H-mode Scenario
• 5. Reversed Shear Scenario
• 6. Hybrid Scenario

96
Tokamak Operation Scenario
q-profiles
5
strong
4
Reversed shear
3
weak
2
Hybrid

• Good confinement together with high
  stability
• w/o active control

1
ELMy H-mode

• Good confinement
• Poor stability
• Only weak RS plasmas are stable
• but they require a delicate active
  control

0
0
0.5
1
r/a
97
Tokamak Operation Scenario
98
Hybrid Scenario
Ip
q953.3-4.5
II Timing, heating, MHD
III Perf. at stable q(r)
time
I Form q(r)
I Obtain low magnetic shear in the centre q0 gt
1 II Timing and amount of the heating are
important. MHD behaviour (no sawteeth, but
fishbones and/or small NTMs). H-mode, but no
confinement transients (ITBs). III Mild MHD
events to obtain stable q(r).Ultimate goal
H89bN gt 6 stationary, 50 non-inductive drive.
99
Hybrid Scenario
17870
Ip (MA)
Da
PNBI (MW)
4xli
bN
H98(y,2)
1.0
H98(y,2)
ltnegt/nGW
ltnegt/nGW

• H98(y,2) 1.4
• ßN 2.8
• fBS 34
• fNB 31

0.0
1.0
Even n
0.0
Odd n
-1.0
0
2
4
6
8
Time (s)
100
Hybrid Scenario
101
Reversed Shear Scenario
HH98(y,2)bN/q952
HH98(y,2)bN/q952
0.4
0.4
q953
0.3
0.3
q95 5
Performance
Performance
ITER reference (Q10)
0.2
0.2
ITER advanced (Q5)
0.1
0.1
q95? 7
0
0
65
0
10
20
30
40
Bootstrap fraction
duration/tE
Distinct groups of results, best ones just fine
for Q5. Transient for q95 ? 4, ITER target for
q95 5 only.
102
Hybrid Scenario
HH98(y,2)bN/q952
HH98(y,2)bN/q952
AUG DIII-D JT-60U JET Tore Supra
AUG DIII-D JT-60U JET Tore Supra
0.4
0.4
q953
0.3
0.3
ITER reference (Q10)
q95 5
Performance
Performance
0.2
0.2
(Q5)
0.1
0.1
q95? 7
0
0
0
20
40
60
80
40
Bootstrap fraction
duration/tE
Similar results from all machines, Qgt10 possible
(ignition?). 2x ITER target at q953, or long
pulse (2000s) at q954-4.5.
103
Identity Experiments
Plasma shapes used in JET compared to ASDEX
Upgrade
JET
d ? 0.44
d ? 0.20
AUG
104
Identity Experiments
AUG 17870 (2.1T)
JET 58323 (1.7T)
Ip (MA)
q95
Pnbi (MW)
H98 (y,2)
Ti0 (keV)
bN
Small MHD modes
105
Summary

• 1. What is Tokamak? Why Heating and Current
  Drive?
• 2. Heating and Current Drive in a Tokamak
• 3. Tokamak Operation Scenario
• 4. H-mode Scenario
• 5. Reversed Shear Scenario
• 6. Hybrid Scenario