E. D. Fredrickson, D. Darrow,

N. N. Gorelenkov, S. Medley, J. Menard, L. Roquemore

45th Annual Meeting of Division of Plasma PhysicsAmerican Physical Society

October 27 – 31, 2003Albuquerque, New Mexico

MHD-induced Fast Ion Losses on NSTX

Supported by

Columbia UComp-X

General AtomicsINEL

Johns Hopkins ULANLLLNL

LodestarMIT

Nova PhotonicsNYU

ORNLPPPL

PSISNL

UC DavisUC Irvine

UCLAUCSD

U MarylandU New Mexico

U RochesterU Washington

U WisconsinCulham Sci Ctr

Hiroshima UHIST

Kyushu Tokai UNiigata U

Tsukuba UU Tokyo

JAERIIoffe Inst

TRINITIKBSI

KAISTENEA, Frascati

CEA, CadaracheIPP, Jülich

IPP, GarchingU Quebec

Will fast ion driven instabilities be important in the NSST, CTF?

• Fast ion instabilities important for fusion reactors;– Fast ion losses raise ignition threshold, first wall damage

– Potentially beneficial (alpha-channeling)?

• ST's, with intrinsic low field, are particularly susceptible to fast ion driven instabilities.–  Vfast ion / Valfvén>1; fast ion energy available to drive modes

– fi/aplasma; sets mode structure scale, fast ion transport

– Also affected by q and density profiles, thermal ion/electron .

• Need to understand instability drive, loss mechanisms.– Result important for conventional aspect ratio reactors (ITER).

10

100

1000

0.1 0.2 0.3TIME (s)

FR

EQ

UE

NC

Y (

kHz)

“fishbones”

TAE

CAE/GAE

108170

A broad spectra of kinetic instabilities are seen on NSTX

“mostly harmless”

Usually do not result in large fast ion losses.

However, in some cases…

Gorelenkov - GI2.001, Taylor - QP1.048, Fu - QP1.122

Neutron rate drops, D bursts imply fast ion loss in some shots

• Neutrons are beam-target; drops mean fast ion loss– S nfi

• D bursts probably due to fast ions hitting wall or divertor plates– Can be confused with ELMs

• In L-mode, sometimes correlated with D drops.

• Loss also seen in iFLIP, redistribution in NPA.

H-alpha (a.u.)

Plasma Current (MW)

Pnbi (MW)

0.8

0.4

0.0

1.0

0.01.0

0.06

0

-6

shot 108530

4

00.2 0.30.0 0.1 0.4

TIME (s)0.20 0.25 0.30

Neutrons (1014/s)

Mirnov Coil (a.u.)

TAE bursts responsible for most of fast ion loss here

• Neutron drops ≈ 10-15 %.• Period is ≈ 10 ms.• In steady-state, predicted

reduction in fast ion beta of 40 %.

• TAE have strong bursting character with multiple modes present.

• Fishbones have small neutron drops

black n=1 red n=2 green n=3 blue n=4 yellow n=5

FR

EQ

UE

NC

Y (

kHz)

200

150

100

50

0

108530

fTAE= VA(0)/4qR0 + n “frot”

0.20 0.300.22 0.24 0.26 0.28

1.0

0.0

Neutrons (1014/s)

TIME (s)

Large fast ion losses also with " fishbones”

• Up to 20% drops in the neutron rate, with f.b. periods of ≈ 10 ms; steady-state reduction in fast ion population of ≈50%.

• Why do some fishbones cause neutron drops, others no drop?

• Even no-drop f.b.'s affect CAE.• Do CAE trigger f.b.’s?• Correlation of (large) fishbones

with H-mode transitions?

Ip = 0.8 MA, Pb = 3.4 MW, tor = 16%)

CAE (0.5-1.2MHz)

FR

EQ

UE

NC

Y (

kHz)

TIME (s)0.15 0.20 0.25 0.30 0.35

1.41.0

0.00.4

(x10

14/s

)

0.80.6

0.0

0.40.2

D-alpha

150

100

50

0

“TAE”

“Fishbone”

108170

Neutron Rate

3

2

1

050

0

fishbone (10-90 kHz)

(mG

)(G

)

Strong frequency chirping correlated

with fast ion loss

• In this case, multiple modes also seem to co-exist.

• Lack of neutron drop may mean loss of lower energy ions; but not according to NPA.

• It would be very nice to have good internal data.

S. Medley - NPAIp = 0.8 MA, Pb = 6 MW, tor = 18%)

0.3 0.35 0.40 0.45

0

20

40

60

80109022

TIME (s)

5

04

2

032

10

5

0

n = 1 n = 2 n = 3 n = 4

FR

EQ

UE

NC

Y (

kHz)

SN

PA

(10

5 /s)

(10

13/s

)(G

)

NEUTRON RATE

ED = 50 keV

ED = 10 keV

5 - 50 kHz, 0.45 - 1.2 MHz (x100)

TAE, f.b. and CAE/GAE interact

• TAE bursts precede fishbones.

• TAE-induced fast-ion losses don't affect CAE.

• Fishbone-induced bursts cause drops in CAE amplitude, small effect on neutron rate.

H-alpha (a.u.)

Plasma Current (MW)

Pnbi (MW)

0.8

0.4

0.0

1.0

0.01.0

0.0

shot 108530

4

00.2 0.30.0 0.1 0.4

TIME (s)0.20 0.25 0.30

Neutrons (1014/s)

~rm

s(B

)

103

102

101

103

102

101

100

102

101

100

10-1CAE 500 - 1500 kHz

TAE 70 - 150 kHz

f.b. 10- 40 kHz

Ip = 0.65 MA, Pb = 3.6 MW, tor = 10%)

"Not your typical fishbones…"

• Retain strong frequency chirping and periodic bursting character.

• Toroidal mode numbers up to n=5 have been seen.

• Often with q(0) > 1 and m >1• Onset frequency well above

precession drift frequency.– Probably bounce resonance*

– May be relevant for ITER…

0.1 0.2 0.3

0

50

100

150108794

TIME (s)

FR

EQ

UE

NC

Y (

kHz)

2

1

0

Neutron Rate (x1013/s)

black n=1 red n=2 green n=3 blue n=4 yellow n=5

*Fredrickson, Chen, White, Nucl. Fusion

(Ip =1.0 MA, Pb = 1.7 MW, tor = 11%)

Summary

• "Collective" fast ion losses seen on NSTX– "fishbone" induced losses of up to 20% and new

fishbone physics– TAE induced losses of 10-15% per burst– Coupled TAE/fishbone induced losses

• Losses are significant, either because they may:– Raising ignition threshold– Increase first wall power loading

• Need physics basis to extrapolate to NSST or ITER

Bounce-resonance, as well as

precession, can drive f.b.’s

• For effective drive, need large average bounce angle…

• …and bounce frequency in reasonable range.

• For most conventional, beam heated tokamaks, this is not the case.

• However, ITER may be a different story.

Bou

nce

Ang

le

0

1

2

3

0 20 40 60 800

20

40

60

80

Energy (keV)

Fre

quen

cy (

kHz)

mode frequency range

108794_0.145

Principal diagnostics of mode structure are

Mirnov arrays, soft x-ray cameras

• Mirnov coils have limited poloidal coverage; plasma-coil separation varies significantly.

• Soft x-ray data dependent on plasma conditions; H-modes are bad. 2.01.00.0

0.0

2.0

-2.0

1.0

1.0

MAJOR RADIUS (m)

ELE

VA

TIO

N (

m)

108794_0.15s

Mirnov Coils

Mode amplitude typically largest near core, data limited.

• Data acquisition rate ≈ 200 kHz.

• Horizontally viewing camera.

• High frequency f.b.s also seen; much weaker.

• No obvious phase inversion; no island?

• Signal low near edge.Soft x-ray data from JHU cameras.

108794(a) (b)

0 200 400

0

-10

-20

-30

-40

-50

-60

0.140 0.145 0.150

TIME (s)

‘MIN

OR

RA

DIU

S’ (

cm)

Chord Integrated soft x-ray

(a.u.)

3

0

-3Gau

ss B~

(c)

Fishbones appear to be strongly ballooning?

• Interpretation a little tricky due to varying plasma-coil separation.

• Outboard poloidal wavelength reasonably long.

• Inboard wavelength irrelevant?

360

270

180

90

0

0 90 180 270 360

POLOIDAL ANGLE

RE

LAT

IVE

PH

AS

E

108794_0.145

0.8

0.6

0.4

0.2

0.0

AM

PLI

TU

DE

(G

)

TAE/fishbones synergistic?

150

100

50

0

0.20 0.22 0.24 0.26

1.5

1.0

0.5

0.0

109022F

RE

QU

EN

CY

(kH

z)S

(10

14/s

)

TIME (s)

(b) Neutron Emission

TAE (n = 1, 2, 3, 4)

5 - 50 kHz 70 - 110 kHz

10.0

1.0

0.1

0.01

Brm

s(G

)(a) Mirnov Spectrum

(c)

• Correlation of f.b. and TAE bursts suggests coupling.

• Attribution of cause of fast ion losses difficult to make.

• TAE bursts cause initial, fast drop, fishbones later, slower drop.

• Neutron drops related to loss of fastest ions; slower ions may also be lost.

“Small” losses can add up

• Fast ion population is modeled as constant source and exponential decay, S(t) = S0(1-et/).

• 20% drops every 18 ms with s ≈ 36 ms means average drop of 30%.

• Lots swept under rug, but coincidently the prediction is pretty good… (tor = 16%)

TIME (s)0.0 0.2 0.4 0.6 0.8

0

2

4

6

80

1

2

3

4

5

Pbe

am (

MW

)N

EU

TR

ON

RA

TE

(10

14/s

) 108736z01

TRANSP

Measured

30% reduction

Many modes are present simultaneously during losses

• Largest amplitude (on Mirnov) at lower n, but higher m’s should have faster fall-off from plasma edge.

0 100 20050 150 250

n=2 n=3n=4

n=5

0.4

0.2

0.0

Am

plitu

de (

a.u.

)

108530_0.2847s

Frequency (kHz)

n=6

Fast ion loss parameters

• Vfast ion / VAlfvén;

– How much, if any, of energy in fast ion distribution available to drive waves.

– Fusion ’s are all at full energy, only fraction of beam power at full energy.

• fi/aplasma;

– Measure of mode structure, effectiveness at causing fast ion losses.

• But high q-profile may ameliorate,

MHD-induced Fast Ion Losses on NSTX

E. D. Fredrickson, D. Darrow N. N. Gorelenkov,

S. Medley, J. Menard, L. Roquemore

Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543

45th Annual Meeting of APS-DPPAlbuquerque, New Mexico

Oct. 27-31, 2003