Confinement Degradation of Energetic Ions due to Alfvén Eigenmodes in JT-60U Negative-Ion

-Based Neutral Beam Injection Plasmas

M. Ishikawa, M. Takechi , K. Shinohara, G. Matsunaga, Y. Kusama, V.A. Krasilnikov1, Yu. Kashuck1, M. Isobe2, T. Nishitani, A. Morioka, M. Sasao3, M. Baba3, JT-60 team

JAEA (Japan), 1 TRINITI (Russia), 2 NIFS (Japan), 3 Tohoku Univ. (Japan)

Presented by Masao Ishikawa (JAEA)

21th IAEA FEC‘06.10.16th ~ 21th, Chengdu, China

E X / 6 - 2

- Introduction

• Background

• Previous results (large h) and issues of Alfvén eigenemodes study in JT-60U

- Alfvén eigenmodes experiments in weak shear plasmas

• Alfvén eigenmodes in weak shear plasma (moderate h)

• Investigation of confinement degradation of energetic ions

- Summary

Table of Contents

Burning plasmas are self-sustained by alpha-particle heating

AEs induce the enhanced transport of alpha-particles from the core region

- A performance of a burning plasma could be degraded

- First walls could be damaged by lost alpha-particles

Understanding of the alpha particle transport in the presence of AEs is the important research issues for ITER

However, a high alpha particle pressure gradient could destabilize Alfvén eigenmodes (AEs)

TAEモードの励起

高速α 粒子

ねじれアルヴェン波

核融合プラズマ 高速α 粒子の損失

Burning plasma Loss of α-particle

Excitation of AE

Fast α-particle

Shear Alfvén wave

Background

In weak shear plasma with large h

• Bursting AEs called Abrupt Large amplitude Events (ALEs)

In JT-60U, AE experiments have been performed utilizing Co-injected Negative-ion-based Neutral Beam (NNB)

(ENNB : 340 ~ 400keV, PNNB :3 ~ 5MW) in several kinds of magnetic shear plasma under combination with PNBs

JT-60U

Previous results and issuesof AE studies in JT-60U

time scale : < msamplitude : large

In weak shear plasma with moderate h

time scale : 100ms ~ 1 samplitude : moderate

Investigation energetic ion behavior

ALE

(h : energetic ion beta)

We did not investigate energetic ion behavior

redistribution of energetic ions due to resonant interaction with AEs M. Ishikawa, 20th. IAEA FEC in Portugal

New simulation resultG. Vlad, TH/P6-4 Fri, (this Conf.)

To investigate energetic ion behavior in the presence of AEs

Diagnostics for investigationof energetic ion transport

Neutron ProfileMonitor

Energy distribution of neutral particles has information on energy distribution of energetic ions

JT-60U

T-NBI

N-NBI

P-NBI

P-NBI

P-NBI

P-NBI

P-NBI

T-NBIP-1

P-9P-10

P-13

P-14

P-16P-17 P-18

P-8

P-7

P-5

P-4

P-2

Neutral ParticleAnalyzer (NDD)

Neutron emission profile measurement

CX neutral particle measurement

radial profile energy distribution

Beam -Thermal neutron is dominant component of the total neutron rate

0

0.2

0.4

0.6

0.8

5 5.5 6 6.5 7 7.5 8

am

plit

ud

e (

a.u

.)

time (s)

1

1.5

2

qm

in

100

20

40

60

80

Fre

qu

en

cy

(k

Hz)

0

24

PN

NB (

MW

)AEs in Weak Shear Plasma (moderate h)

E46078 1.0MA/1.7T, ENNB~390 (keV) n =1 modes with up-frequency sweeping are observed and its frequency saturates.

(A) (B)

(A)

(B)

Energetic ion confinement with AE can be investigated by compared with that in the later NNB injection phase

Only weak AEs are observed

RSAE is global AEs localized near the zero magnetic shear region.

weak AEs

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.2 0.4 0.6 0.8 1

w/w

A

r/a

qmn~ 1.5

transition

(2)2 > qmn > 1.5

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.2 0.4 0.6 0.8 1

w/w

A

r/a

RSAE

(1)

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.2 0.4 0.6 0.8 1

w/w

A

r/a

qmn< 1.5

qmn= 1.4

TAE

(3)

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.2 0.4 0.6 0.8 1

w/w

A

r/a

qmn= 1.2(4)

(1) (2) (3)

(4) 0

1

2

3

4

0 0.2 0.4 0.6 0.8 1

(%)

r/a

classical b

Confinement degradation of energetic ions due to n = 1 AEs

E46078 1.0MA/1.7T To investigate energetic ion confinement, the total neutron rate (Sn) is calculated with the OFMC code

• Confinement of energetic ions is classical(B)(A)

02.5

5

(MW

)

PN

NB

100

20

40

60

80

Fre

qu

en

cy

(k

Hz)

0

0.4

0.8

am

plit

ud

e(a

. u.)

0

0.5

1

1.5

2

2.5

3

3.5

5 5.5 6 6.5 7 7.5 8

rate

(1

015

n/s

)N

eu

tro

n e

mis

sio

n measurement

time (s)

00.05

0.10.15

0.20.25

5 5.5 6 6.5 7 7.5 8

S

n/S

n

time (s)

calculation Sn

Energetic ion transport ?0

0.05

0.1

0.15

0.2

0.25

0.3

0 0.2 0.4 0.6 0.8 1

red

uct

ion

rat

e

amplitude (a.u.)

Reduction rate in Sn increases when mode amplitude increases

Sn

/Sn

(B) with only weak AEs

(A) with clear AEsMeasured Sn is smaller than calculated one

Time evolution of measured Sn agrees with calculated Sn

~ Classical confinement

Confinement degradationSn/Sn ~ 25 %

0

2

4

6

8

10 MeasurementTOPICS

(101

3 m

-2s-1

)N

eutr

on fl

ux

0.40.60.8

11.21.41.61.8

2

0 0.2 0.4 0.6 0.8 1Mea

s./T

OP

ICS

r/a0.40.60.8

11.21.41.61.8

2

0 0.2 0.4 0.6 0.8 1Mea

s./T

OP

ICS

r/a

02468

101214 Measurement

TOPICS

(101

3 m

-2s-1

)N

eutr

on fl

ux

(A) with AEs (t=6.4s) (B) with weak AEs (t=7.8s)

0

2

4

6

8

10

5 5.5 6 6.5 7 7.5 8ne

utr

on

co

un

ts (

10

13 m

-2s

-1)

time (s)

-- r/a ~ 0.19 -- r/a ~ 0.32 -- r/a ~ 0.46 -- r/a ~ 0.56 -- r/a ~ 0.73 -- r/a ~ 0.84

NNB NNB

20

40

60

80

100

Fre

qu

ency

(kH

z)

Energetic ion transport from the core region due to AEs

Calculated line integrated neutron profile with a transport code (TOPICS) is compared with the measurement.

(A) (B)

Plasma configuration and sight lines

Energetic ion transport from the core region of the plasma

To investigate energetic ion transport, neutron emission profile was measured

0.4

0.5

0.6

0.7

0.8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

t = 5.9s

Me

as.

/TO

PIC

S

r/a

t = 6.1s

0

2

4

6

8

10

5 5.5 6 6.5 7 7.5 8ne

utr

on

co

un

ts (

10

13 m

-2s

-1)

time (s)

-- r/a ~ 0.19 -- r/a ~ 0.32 -- r/a ~ 0.46 -- r/a ~ 0.56 -- r/a ~ 0.73 -- r/a ~ 0.84

NNB NNB

20

40

60

80

100

Fre

qu

ency

(kH

z)

The second channel signal increases rapidly

Local transport of energetic ions in the center region

qmin and q = 1.5 surface (TAE gap) both lie around r/a < 0.3

The innermost channel signal does not increase

Local transport of energetic ionsin the transition phase

In transition phase,

qmin=1.5

Resonant energy range => 140 ~ 280 keV

10

100

1000 with AEs (t=5.9 - 6.2s)

w/o AEs (t=7.4 - 7.7s)

Cou

nts

(a.u

.)

ENNB

(a)

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200 250 300 350 400

F/F

energy (keV)

(b)

Neutral particle fluxes in limited energy range (50 ~ 300 keV) are enhanced.

Peak fraction of enhanced neutral particle flux is ~ 200 keV.

[ Resonance condition with the mode ]

N= (f / fc) q - nq + m = integer f = mode frequency (60 - 70 kHz) q = safety factor ( 1.4 - 1.6) n, m = toroidal, poloidal mode number Fc = troidal transition frequency of energetic ions

( R. B. White et.al. Phys. Fluids 26 (1983) 2958 )

Fre

qu

enc

y (k

Hz) 100

50

0

5.5 6.0 7.06.55.0 8.06.5time (s)

Changes in the energy distribution suggest the resonant interaction between energetic ions and modes

Resonant interaction with AEs and eneregetic ions

summary

Confinement degradation of energetic ions are quantitatively observed.

Changes in neutral particle flux suggest the resonant interaction between energetic ions and modes.

• total neutron emission rate• neutron emission profile• charge exchange neutral particle flux

Neutron emission profile measurements indicate energetic ion transport from core region to outer region and local transport in the core region in the transition phase.

( time scale : 100ms ~ 1s, amplitude : moderate )

in weak shear plasma with moderate h

• AEs with frequency sweeping

Energetic ion behavior is investigated with

0

1

2

3

4total neutron

Neu

tron

rat

e(1

015 s

-1)

0

1

2

3 neutral particleflux E>20 keV

4 4.5 5 5.5 6 6.5 7

Neu

tral

par

ticle

flux

(104

s-1

)

Time (s)

Fre

quen

cy (

kHz)

180

100

120

140

160

N N B

Change in neutral particle flux suggests energetic ion transport from core to outer region

Neutral particle flux change after neutron emission rate changed Time lag (t) ~ 100 ms time scale of transport and /or slowing downEnergetic ions are neutralized through

charge exchange reactions with D0 or C5+ in outer region of the plasma

t

energetic ion transport from core region to outer region

1.5

2

2.5

3

3.5

5400 5500 5600 5700 5800 5900 6000

(b) 20 - 100 keV

1.5

2

2.5(a) 100 - 500 keV

Neu

tral

par

ticle

flux

(a.

u.)

~ 50 ms

time (ms)