ITC-12/APFA’01
Ceratopia Toki, Toki
11-14, Dec. 2001

Global Particle Balance of Long Duration
Discharges on TRIAM-1M
Mizuki SAKAMOTO and the TRIAM Group
Advanced Fusion Research Center,Research Institute for Applied Mechanics,
Kyushu University,

TRIAM Group: S. Itoh, K. Hanada, K. Nakamura, H. Zushi, M. Sakamoto, E. Jotaki,
M. Hasegawa, S. Kawasaki, H. Nakashima, A. Iyomasa

Contents¾ Introduction¾Wall pumping rates oflow and high density discharges¾ Static and dynamic properties of wall recycling¾ Global particle balance ofthe ultra-long discharge (τD ~ 3 hours)¾ SummaryIntroduction
TRIAM, Advanced Fusion Research Center

LHe ReservoirTankCS
CoilValve
Unit

PlasmaPF Coils

Superconducting
TF CoilPumping duct

Bird’s-eye view of TRIAM-1M

Major radius

0.84 mMinor radius

0.12 mToroidal field

8 T (Steady State)

TF coils : Nb3Sn (superconductor)
PF coils : Cu (normal conductor)
Plasma facing components: High Z
vacuum vessel : stainless steel
Limiter: Molybdenum
Divertor: Molybdenum
Without low Z material and coating

Progress of long tokamak operation
TRIAM, Advanced Fusion Research Center

2.45 GHz LHCD, Limiter configuration

3h 10min
In TRIAM-1M, the study and development of the long pulse
operation have actively been carried out.
Particle control is one of key issues for long pulse operation.

Particle balance inside the vacuum vessel （I）
TRIAM, Advanced Fusion Research Center

WallPellet
Recycling

PlasmaPumping

Wall pumping
Fueling

Particles supplied inthe vacuum vessel

External pump
Wall pumping
This depends on theplasma condition.

Particle balance inside the vacuum vessel （II）
TRIAM, Advanced Fusion Research CenterIn the vacuum vessel

dNp / dt + dN0 / dt = Γfuel – Γpump – ΓwallΓabsorb

Γwall = Γabsorb - ΓreleasereflectionΓreleaseΓfuel : fueling rateΓpump : pumping rateΓwall : net wall pumping rate

WallPositive : Sink
Negative : Source
Γwall = 0 looks like wall saturation

Comparison of Γwall between low and high density discharges
TRIAM, Advanced Fusion Research Center

8.2 GHz LHCD, ~ 0.8 x 1019 m-3

51.2
Wall saturation

41.0

~7min
pump3

Wall pump again

Wall Pumping

1by pump unit

000.6gWallsaturation

20.820)Wall saturation

Σ S ( 10Γdt （1020 atoms）

2.45 GHz LHCD, ~ 0.1 x 1019 m-3

10 20 30 40 50 60 70 80

Time (min)70 min

The wall repeats the process ofbeing saturated and refreshed.
Ref: M.Sakamoto et al., NF 42 (in press)

0.4
0.2
0.0
0

5

10

1520Time(sec)25303533 sec

Γwall = Γfuel - Γpump

Comparison of Γwall between low and high density discharges
TRIAM, Advanced Fusion Research Center

8.2 GHz LHCD, ~ 0.8 x 1019 m-3

51.2
Wall saturation

41.0~7minpump

3Wall pump againWall Pumping

1by pump unit

000.6gWallsaturation

20.820)Wall saturation

Σ S ( 10Γdt （1020 atoms）

2.45 GHz LHCD, ~ 0.1 x 1019 m-3

10 20 30 40 50 60 70 80

Time (min)

0.4
0.2
0.0
05

101520253035Time(sec)Γwall ~ 1.5×1016 atoms m-2 s-1

Γwall ~ 4×1017 atoms m-2 s-1

Γwall of high density discharge is ~ 30 times higher than that of low density discharge.

Γwall seems to depend on the particle flux to the wall.
TRIAM, Advanced Fusion Research Center

CX neutral flux

Diffused flux
Limiter surface

Wall surface

10017(10eT

1n2.45GHz LHCD
2.45
GHz LHCD

1051041031020.105101520

SOL（8.2GHz） 〜 Te

SOL

（8.2GHz） ＞ １０ nee

2.45GHzLHCD

10101234E (keV)

z (mm)e

Horizontal Port

8.2GHzLHCD

1-5SOLeSOL

10CX Flux (a.u.)

-3m )

(eV)

10•n6100

8.28.2GHzGHzLHCD
LHCD

•T

10SOL

（2.45GHz）

SOL（2.45GHz）

The difference of wall pumping rates between
low and high density plasmas seems to be causedby the difference of the total amount of thediffused flux and/or the CX neutral flux with theenergy of < ~0.7 keV.

Contents¾ Introduction¾Wall pumping rates oflow and high density discharge¾ Static and dynamic properties of wall recycling¾ Global particle balance of
the ultra-long discharge (τD ~ 3 hours)¾ SummaryEffective particle confinement timein the static condition
Recycling Coefficient

TRIAM, Advanced Fusion Research Center
1.00

Particle balance equation inside the plasmadNe / dt = ηΓgas + R Ne / τp - Ne / τp0.99

Recycling coefficient increases
with time and approaches to 1.
0.980102030405060Time(sec)

Effective particle confinement time15

τp* (sec)#71859

τ1050*p=τp(1 − R)τp* : 1~10 sec
010203040Time (sec)5060τp* in the dynamic condition
puffV(V)TRIAM, Advanced Fusion Research Center
1008060
40200Gas puff was carried out
at intervals of 5 s.

Decay time of ne is only ~ 0.2 s.

Comparison of τp* between in thestatic and the dynamic conditions
TRIAM, Advanced Fusion Research Center

Static condition

Dynamic condition

150.5#71859#7751810τp* (sec)τp* (sec)

0.4

50.3
0.2
0.1

0010203040Time (sec)50

60

0.0010203040

50

Time (sec)This suggests that the wall pumping rate is enhancedby the additional gas puff.

60

Another example for the static anddynamic conditions
TRIAM, Advanced Fusion Research Center

WallGate valve close

PlasmaPumping

Recycling

Fueling

Particles in the vacuum vessel(1) are ionized,(2) stay as neutrals,(3) are wall-pumped,(4) are evacuated by the pump unit.

Experiment on stopping thepumping and the fueling during
the long duration discharge.

Pumping and fueling termination during the discharge
TRIAM, Advanced Fusion Research Centergate valve close

Recycling coefficient = 1

Plasma current (kA)

The pumping and the fuelingare stopped at t~ 33 sec.

Electron density (1018 m-3)

After stopping the pumping
and the fueling, recycling
coefficient must be unity.

Hα line intensity (a.u.)
10

Vpiezo for feedback (V)Additional gas puff is carriedout at 50, 54.5, 61, 68 sec.

Vpiezo for puff (V)0204060

Time (sec)

80

100

Wall pumping is enhanced by the additional gas-puff
TRIAM, Advanced Fusion Research Center

Static condition
Dynamic condition

Decay time
~ a few sec.

Decay time
~ a few 100 ms.
0.5#7751815p0.4τp* (sec)τ * (sec)#7 1859~4 sec

1050

0.3
0.2
0.1
0.0

0

1020

30

40

T im e (sec)50

60010203040

Time (sec)5060

Contents¾ Introduction¾Wall pumping rates of
low and high density discharge¾ Static and dynamic properties of wall recycling¾ Global particle balance ofthe ultra-long discharge (τD ~ 3 hours)¾ SummaryParticle balance in 3 hours discharge
TRIAM, Advanced Fusion Research Center

Plasma current

Hα line intensity

Wall saturation

Until t ~ 30 min, the Hα line intensity followed the reference
level indicated by the chain line. After that, it increased
spontaneously and no particle control until the end of thedischarge. From the viewpoint of the global particle balance,
it looks like wall saturation.

1003.0(a.u.)
HαIτ ~ 0.24 s
2.6

60

2.4

40

2.2

20

2.0
900.0900.5

901.0

901.5

Time (sec)t ~ 15 min
Time (min)3h 10min0902.080

2.8

τ ~ 0.33 s
2.660

2.4

40

2.2

20

2.0
1350.01350.51351.01351.5Time (sec)t ~ 23 min

01352.0

Vpuff

OV line intensity

80

2.8

Vpuff

Neutral pressure#76675IHα (a.u.)gas puff100

3.0#76675Global particle behavior during the 3 hours discharge
TRIAM, Advanced Fusion Research CenterΓwall > 0 (sink)Tlimiter : < 5min
Tchamber : 30~60 min

Supplied gas
250

Pumping by the external
pump unit

Temperature (oC)Γdt （1020 atoms）

Γwall < 0 (source)

Hydrogen atoms pumped by the wall
were released from the wall until the endof the discharge.

Limiter
200
150

VacuumvesselBellows

100
Divertor

500050100

150200time (min)

250

300

Estimation of absorption rate from the comparison
between before and after the plasma termination
Γdt （1020 atoms）

TRIAM, Advanced Fusion Research Center

Just after the plasma termination8

Γabsorb

During discharge

6After discharge

4reflection

Γrelease

2Wall00

Γwall ~1234
5Time (hour)

2.4 x 1016 atoms m-2 s-1

67PreliminaryΓabsorb = Γwall - Γwall
beforeorder of >1018

afterSummary
The study of the global particle balance has been carried out in the longdischarge of the superconducting tokamak TRIAM-1M.
¾ The wall pumping rate depends on the particle fluxes, i.e. diffused flux and
CX neutral flux (E<0.7keV).
¾ The wall recycling properties in the static and dynamic conditions are quite
different. The wall pumping is enhanced by the additional gas puff.
The
difference of the effective particle confinement time between static and dynamicconditions is more than one order of magnitude.

τp* : 1~10 sec in the static condition

τp* : ~0.2 sec in the dynamic condition¾ 3 hours discharges ware achieved. Around t~30min, the wall seems to besaturated from a viewpoint of global particle balance. One candidate is increasein hydrogen release from the main chamber due to the temperature increase.