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(1)

F usion Reactor Technology I

(459.760, 3 Credits)

Prof. Dr. Yong-Su Na

(32-206, Tel. 880-7204)

(2)

Week 1. Magnetic Confinement/Fusion Reactor Energetics (Harms 8) Week 2. Tokamak Operation (I):

Basic Tokamak Plasma Parameters (Wood 1.2-3, Harms 9.2) Week 3. Tokamak Operation (II): H-mode

Week 4. Tokamak Operation (III): Advanced Operation Mode Week 7-8. Tokamak Operation Limits (I):

Plasma Instabilities (Kadomtsev 6, 7, Wood 6) Week 9-10. Tokamak Operation Limits (II):

Plasma Transport (Kadomtsev 8, 9, Wood 3, 4) Week 11. Heating and Current Drive (Kadomtsev 10) Week 12. Divertor and Plasma-Wall Interaction

Week 13-14. How to Build a Tokamak (Dendy 17 by T. N. Todd)

2

Contents

(3)

Week 1. Magnetic Confinement/Fusion Reactor Energetics (Harms 8) Week 2. Tokamak Operation (I):

Basic Tokamak Plasma Parameters (Wood 1.2-3, Harms 9.2) Week 3. Tokamak Operation (II): H-mode

Week 4. Tokamak Operation (III): Advanced Operation Mode Week 7-8. Tokamak Operation Limits (I):

Plasma Instabilities (Kadomtsev 6, 7, Wood 6) Week 9-10. Tokamak Operation Limits (II):

Plasma Transport (Kadomtsev 8, 9, Wood 3, 4) Week 11. Heating and Current Drive (Kadomtsev 10) Week 12. Divertor and Plasma-Wall Interaction

Week 13-14. How to Build a Tokamak (Dendy 17 by T. N. Todd)

3

Contents

(4)

Tokamak Operation Scenario

4

Current Ramp-up

High Power Phase

Plasma Quench Plasma

Initiation

JET pulse 69905 (BT = 3.1 T)

(5)

Tokamak Operation Scenario

5

JT-60U

(6)

H-mode

6

• 1982 IAEA F. Wagner et al. (ASDEX, Germany)

- Transition to H-mode: state with reduced turbulence at the plasma edge - Formation of an edge transport barrier: steep pressure gradient at the edge

(7)

H-mode

7

• 1982 IAEA F. Wagner et al. (ASDEX, Germany)

- Transition to H-mode: state with reduced turbulence at the plasma edge - Formation of an edge transport barrier: steep pressure gradient at the edge

t c

a

2 E

»

(8)

H-mode

8

• Established in stellarators as well

Wendelstein 7-AS

V. Erckmann et al, Physical Review Letters 70 2086 (1993)

(9)

H-mode

Hoover dam

9

• 1982 IAEA F. Wagner et al. (ASDEX, Germany)

- Transition to H-mode: state with reduced turbulence at the plasma edge - Formation of an edge transport barrier: steep pressure gradient at the edge

(10)

H-mode

Hoover dam

10

• 1982 IAEA F. Wagner et al. (ASDEX, Germany)

- Transition to H-mode: state with reduced turbulence at the plasma edge - Formation of an edge transport barrier: steep pressure gradient at the edge

(11)

11

• First H-mode Transition in KSTAR (November 8, 2010)

- B

0

= 2.0 T, Heating = 1.5 MW (NBI: 1.3 MW, ECH: 0.2 MW) After Boronization on November 7, 2010

H-mode

(12)

H-mode: How to?

12

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

• Advantage of the divertor configuration

- First contact with material surface at a distance from plasma boundary - Reducing the influx of ionized impurities into the interior of the plasma

by diverting them into an outer „SOL“

Strike point

(13)

Tokamak

13

(14)

H-mode: How to?

14

(15)

H-mode: How to?

15

• Role of wall condition

(16)

16

P

th

= 2.84M

-1

B

t0.82

n

200.58

R

1.0

a

0.81

H-mode: How to?

(17)

17

H-mode: How to?

J-W. Ahn, H.-S. Kim et al., “Confinement and ELM characteristics of H-mode plasmas in KSTAR”, Nucl.

Fusion 52 114001 (2012)

019 . 0 941 . 0 032 . 0 803 . 0 035 . 0 717 . 0

20

,

= 0 . 0488 ± 0 . 0028 n

±

B

±

S

±

P

thr scaling e T

Y. R. Martin et al., “Power requirement for accessing the H-mode in ITER”, J. Phys.: Conf. Ser. 123 012033 (2008)

(18)

H-mode: Why?

18

• 1982 IAEA F. Wagner et al. (ASDEX, Germany)

- Transition to H-mode: state with reduced turbulence at the plasma edge - Formation of an edge transport barrier: steep pressure gradient at the edge

(19)

H-mode: Why?

19

• 1982 IAEA F. Wagner et al. (ASDEX, Germany)

- Transition to H-mode: state with reduced turbulence at the plasma edge - Formation of an edge transport barrier: steep pressure gradient at the edge

Density fluctuations at r/a = 0.65

G.R. McKee, et al. Plasma Fusion Res. (2007)

(20)

20

H-mode: Why?

• 1982 IAEA F. Wagner et al. (ASDEX, Germany)

- Transition to H-mode: state with reduced turbulence at the plasma edge - Formation of an edge transport barrier: steep pressure gradient at the edge

(21)

H-mode: Why?

21

Theoretical physics

(22)

H-mode: Why?

22

Theoretical physics

Experimental physics

(23)

Basic Tokamak Variables

• Safety factor q = number of toroidal orbits per poloidal orbit

23

q-profile

3

0 0.5 0.95

Normalised radius 1

5

2

Advanced scenario Baseline scenario

q

95

4 Hybrid scenario

Magnetic field lines Magnetic flux surfaces

(24)

q-profiles

0 1 2 3 4 5

0 0.5 1

r/a

ELMy H-mode

Tokamak Operation Modes

24

(25)

Conventional Operation Mode – H-mode

25

plasma radiusa

plasma pressure

0

core

pedestal

plasma radiusa

plasma pressure

0

core

pedestal

• Naturally peaked current profile

• Mild pressure gradient with steep edge pedestal

• Monotonic q-profile

• Positive magnetic shear

(26)

q

0

< 1: Sawtooth instability, periodic flattening of the pressure in the core Stability of H-mode plasmas related safety factor profile: q(r)

H-mode: Limitations

0 1 2 3 4 5

0.5 1

r/a

H-mode, q-profile

q = 1

0

(27)

Sawtooth

27

time (s)

0 2 4 6 8

8 6 1 10 1

Ip(MA)

PNBI (MW) PRF (MW)

WMHD(MJ)

Nel x1.1019

Ti(keV) Te (keV)

pulse 20438

- nonlinear low-n internal mode - internal (minor) disruption - enhanced energy transport

in the plasma centre

(28)

q

0

< 1: Sawtooth instability, periodic flattening of the pressure in the core Stability of H-mode plasmas related safety factor profile: q(r)

q = 3/2 and q = 2:

Neoclassical Tearing Modes (NTMs):

• limit the achievable β ≡ 2µ

0

p/B

2

• degrade confinement (+ disruptions)

• often triggered by sawteeth.

H-mode: Limitations

0 1 2 3 4 5

0.5 1

r/a

H-mode, q-profile

q = 1

0

q = 3/2

q = 2

• ITER work point is chosen

conservatively: b

N

£1.8 !

(29)

Neoclassical Tearing Mode (NTM)

29

ASDEX Upgrade

f

b f

b aB

I

N t(%)=

(30)

Neoclassical Tearing Mode (NTM)

30

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

p

(31)

Neoclassical Tearing Mode (NTM)

31

0.4 0.8 1.2

Pressure(kPa)

6620

Temperature(keV)

Radius (m) 0.7

0.6 0.5 0.4 0.3 0.2 0.1 0.8 0.6 0.4 0.2 0

EFIT q=2 surface magnetic estimate

12cm inboard 2/1 island

• Pressure flattening across magnetic islands due to large transport

coefficients along magnetic field lines

(32)

Neoclassical Tearing Mode (NTM)

32

(33)

q

0

< 1: Sawtooth instability, periodic flattening of the pressure in the core Stability of H-mode plasmas related safety factor profile: q(r)

q = 3/2 and q = 2:

Neoclassical Tearing Modes (NTMs):

• limit the achievable β ≡ 2µ

0

p/B

2

• degrade confinement (+ disruptions)

• often triggered by sawteeth.

H-mode: Limitations

0 1 2 3 4 5

0.5 1

r/a

H-mode, q-profile

q = 1

0

q = 3/2

q = 2

• ITER work point is chosen conservatively: b

N

£1.8 !

K. Miyamoto, “Controlled Fusion and Plasma Physics” Taylor & Francis (2007)

(34)

q

0

< 1: Sawtooth instability, periodic flattening of the pressure in the core Stability of H-mode plasmas related safety factor profile: q(r)

q = 3/2 and q = 2:

Neoclassical Tearing Modes (NTMs):

• limit the achievable β ≡ 2µ

0

p/B

2

• degrade confinement (+ disruptions)

• often triggered by sawteeth.

H-mode: Limitations

0 1 2 3 4 5

0.5 1

r/a

H-mode, q-profile

q = 1

0

q = 3/2

q = 2

• ITER work point is chosen conservatively: b

N

£1.8 !

q

95

1/I

p

) = 3: Safe operation at max. I

P

Periodic collapses of

the ETB (ELMs)

q

95

=3

(35)

35

Edge Localised Mode (ELM)

• Example of sawteeth and ELMs

JET, Pulse 52022

(36)

36

Edge Localised Mode

Disruption

Edge Localised Mode (ELM)

(37)

37

Edge Localised Mode (ELM)

(38)

t(s)

t(s)

Power Supply Limit

Inherent drawback of Tokamak!

Faraday‘s law

ds dt B

v d

S

× -

= ò

H-mode: Limitation

38

Plasma Current

PF Coil Flux [Wb]

[MA]

(39)

Faraday‘s law

ds dt B

v d

S

× -

= ò

H-mode: Limitation

39

I

C

B

T

B

P

I

P

I

OH

dt

dI

C

By

induction

I

P

= I

OH

+

INI

Standard inductive operation

steady state scenario: producing continuous fusion power in a tokamak reactor.

I

P

= 0 + I

NI

Non-inductive operation

(40)

40

References

- E. Joffrin, “Advanced tokamak scenario developments for the next step”, 34th EPS Conference, Warsaw 2007

- A. C. C. Sips, Seminars

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