Plasma Fueling and Implications for FIRE, ITER, ARIES

MJG:TTM, 3/01 Plasma Fueling Program 1

Plasma Fueling and Implications for FIRE, ITER, ARIES

M. J. Gouge

Oak Ridge National Laboratory

March 6, 2001

MJG:TTM 3/01 Plasma Fueling Program 2

Outline

• Fueling system functions

• Fueling program scope

• ITER and FIRE fueling

• Tritium systems

• Fueling efficiency (gas vs. pellets)

• DIII-D results (high field vs. low field, L-to-H mode…)

• Isotopic fueling

• Disruption mitigation technology and experiments on DIII-D


Fueling system functions

• to provide hydrogenic fuel to maintain the plasma density profile for the specified fusion power,

• to replace the deuterium-tritium (D-T) ions consumed in the fusion reaction,

• to establish a density gradient for plasma particle (especially helium ash) flow to the edge,

• to supply hydrogenic edge fueling for increased scrape off layer flow for optimum divertor operation,

• to inject impurity gases at lower flow rates for divertor plasma radiative cooling, wall conditioning, and for plasma discharge termination on demand.


Fueling program scope

• Gas fueling prototype for ITER

• Pellet fueling development• H, D, T, Ne, Ar, Xe cryogenic solid pellets

• Size from ~0.5 mm to 10 mm

• feed rates from single shot to 0.26 g/s (ITER)

• speeds from 100 to ~4000 m/s

• US-related plasma fueling experiments: • ORMAK, ISX, PDX, DIII, PLT, TEXT, PBX, TFTR, JET, TORE

SUPRA, DIII-D, GAMMA 10, LHD, MST (2001), NSTX (2002)

• Particle control and fueling physics; example: outside, inside and vertical launch on DIII-D

• Disruption mitigation and impurity fueling development

• Fueling system design for ITER and FIRE


Hydrogenic solids

• Have made hydrogenic pellets in sizes from ~0.5 to 10 mm

• Hydrogen properties:

Property H D T

density (g/cc) .09 .2 0.32

boiling pointat 1 atm (K)

20.4 23.7 25

triple point(K)

13.8 18.7 20.6

triple pointpressure (torr)

54 129 162

Shear Strength

0.000

0.200

0.400

0.600

0.800

1.000

1.200

4 6 8 10 12 14 16

T, K

, M

Pa

D2, Break-away dataT2, Break-away dataD2, Extrusion static equationD-T, Extrusion static equationT2, Extrusion static equationD2, Extrusion dynamicD-T, Extrusion dynamicT2, Extrusion dynamicH2, Viniar Bingham limiting strength


ITER fueling R&D results relevant to FIRE

• Gas fueling prototype testing– response time experiments for impurity

gas puffing into divertor

• Pellet fueling development– world’s largest cryogenic pellet ~ 10

mm

– first extrusions of tritium and DT

– record extrusion rate of 0.26 g/s (deuterium)

– pellet feed/rotor dynamics for centrifuge injector (with CEA)

– piston and screw (RF) extruder development

– high-field-side launch development


TPOP-II tritium extruder experiments

Highlights

• Demonstrated first extrusions of solid tritium at Tritium Systems Test Assembly Facility at LANL;

• Produced world’s largest pellets: 10 mm D, DT and T pellets (full scale for ITER);

• Processed over 40 grams of tritium through TPOP-II;

• Developed isotopic fueling concept to reduce ITER tritium throughputs and inventory.

Pure Tritium Extrusion Pure Tritium Pellet


FIRE fueling system

• Baseline is gas (mostly D) + pellets (DT to get 60% D/40%T in the core) – Magnetic field magnitude makes CT fueling difficult: ~2 MW just to

make up DT fusion losses.

• Use vertical or inside pellet launch– Vertical launch allows injection inside major radius at high pellet speeds

if the pellet injector is vertically oriented

– Inside launch fully leverages grad-B ablatant flow but will limit speeds to 100’s m/s with a pellet injector located at an arbitrary location (due to guidetube radius of curvature) with modest propellant gas requirements

– The optimum depends on pellet speed dependence of particle deposition for inside launch which is not quantified.


Double-screw extruder concept (ORNL STTR with Utron, Inc.)

• Dual, opposed, counter-rotating screws

• Liquid helium is fed into the extruder at one end and flows through cooling channels (alternative is G-M cryocooler)

• Deuterium is fed into the screw chamber and flows to the center of the extruder.

• As the liquid flows it freezes on the inner wall between the screw and the inner housing.

• As the screws rotate they scrape off the deuterium and force the ice to the center of the extruder were it is extruded out the center hole to the feed tube.

ExtruderExtension

Extruder Center Section

Twin Screws

Drive Screw Extensions

Cooling In

Cooling out

LiquidFeed In

LiquidFeed In

Pellet Ice Out


Pellet launch paths into FIRE

• Pellet speed limited to about 500 m/s for curved guidetubes.• Much higher speeds possible for vertical HFS launch


Preliminary FIRE fueling system parameters

Parameter Gas Fueling System Pellet FuelingSystem

Remarks

Design fueling rate 200 torr-l/s for 20 s 200 torr-l/s for 20 s Torus pumping capacity is200 torr-l/s

Operational fuelrate

100-175 torr-l/s 100-25 torr-l/s Isotopic fueling

Normal fuelisotope

D (95-99%)T,H (5-1%)

T (40-99 %)D(60-1%)

D-rich in edge, T-rich incore

Impurity fuel rate 25 torr-l/s TBD(prefer gas for

impurity injection)

25 torr-l/s reduces DT fuelrate due to fixed pumping

capacityImpurity species Ne, Ar, N2, other? TBD TBDRapid shutdown

systemMassive gas puff~106 torr-liter/s

“killer” pellet orliquid D jet

For disruption/VDEmitigation

Pellet sizes (cyl.diameter)

N/A 3, 4, 4 mm 3 mm for density rampup, 4mm for flat-top


Efficiency of gas fueling much less than pellet fueling

Device Gas Fuelling

Efficiency

(%)

Pellet

Fuelling

Efficiency

(%)

Remarks

ASDEX 20 30-100 high density

PDX 10-15 high density

Tore Supra 1 30-100 ergodic divertor

for gas fuelling

JET 2-10 20-90 active divertor

JT-60

JT-60U

TFTR 15 low density DT

ASDEX-U 8-40

DIII-D 10 40-100 active divertor


0 0.2 0.4 0.6 0.8 1 1.2

Penetration Depth /a

0

20

40

60

80

100

Fu

elin

g E

ffic

ien

cy

(%

)

AUG L-modeAUG H-modeDIII-D H-modeTore Supra L-mode

Pellet fueling efficiency has a broad range

Encouraging initial high field launch experiments on ASDEX-U implications for FIRE ongoing experiments on ASDEX-U, DIII-D, Tore Supra, JET, LHD

HFL AUG

LFL AUG


Multiple launch locations on DIII-D


High Field Side (HFS 45°) Pellet Injection on DIII-DYields Deeper Particle Deposition than LFS Injection

• Net deposition is much deeper for the lower velocity HFS 45° pellets.

• The pellets were injected into the same discharge under the same conditions (ELMing H-mode, 4.5 MW NBI, Te(0) = 3 keV).

• L. R. Baylor, P. Gohil et al., Physics of Plasmas, page 1878 (2000)

2.7 mm Pellets - HFS 45° vs LFS

HFS 45°vp = 118 m/st = 5 ms

0.0

0.5

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

LFS vp = 586 m/st = 1 ms

ne (

102

0 m

-3) DIII-D 98796 - measured ne

Calculated Penetration

Four positions of pellet injection guide tubes installed on DIII-D


Both vertical HFS and LFS pellet injection are consistent with an uutward major radius drift of pellet mass

• The net deposition profile measured by Thomson scattering 2-4 ms after pellet injection on DIII-D. V+1 HFS indicates drift toward magnetic axis while V+3 LFS suggests drift away from axis.

2.7mm Pellet - Vertical HFS vs Vertical LFS

V+1 HFS H-mode - 6.5 MWvp = 417 m/s

0.0

5

10

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Radius of Vertical Port

V+3 LFS H-mode - 4.5 MWvp = 200 m/s

ne (

101

9 m

-3)

V+3V+1


HFS pellet injection on DIII-Dyields deeper particle deposition than predicted

• The net deposition depth measured by Thomson scattering after pellet injection on DIII-D is compared with the calculated pellet penetration depth. The high field side (inner wall and vertical injection) locations all show deeper than expected depth of the deposition of the pellet mass.

2.7mm Pellets

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

LFSV+1HFS 45HFS mid

MagneticAxis

Edge Calculated Maximum (/a) Deposition Depth

LFS

HFS

Mea

sure

d M

a xim

um

(/ a

)

Dep

osi ti

on D

ept h


ExB Polarization Drift Model of Pellet Mass Deposition (Rozhansky, Parks)

• Drift R is a strong function of local Te (Parks et al. Physics of Plasmas, p. 1968 (2000)):

– For ITER-FEAT with Te(0) of 20 keV and rp = 6mm, the drift R is

~2m, all the way to the axis.

-+

+

-

R

E

ExB

HFS LFS

• Polarization of the pellet cloud occurs from B and curvature drift in the non-uniform tokamak field:

• The resulting E causes an ExB drift in the major radius direction

Theoretical model for pellet radial drift predicts strong inward drift for reactor

BBv

3

||2

eB

WWB

PelletAblatant (Cloud)

B 1/R


Time (s)3.63.5 3.7 3.8 3.9

0

1

2

8

4

0

8

6

4

Upper Divertor

n e (

1019

m-3)

D(

a.u

.)n e

(10

19 m

-3)

= 0.9

= 0.1

HFS Pellet

ELMs

DIII-D 100162

• HFS pellet induces H-mode transition that is maintained

• H-mode power threshold reduced by 2.4MW (up to 33%) usingpellet injection

L-to-H Mode transition triggered by single D pellet(P. Gohil et al., Phys. Rev. Lett., p. 644, (2001))


Possible vertical pellet injection test at JET

Pipe-gun injector for vertical pellet injection on JET

- Complements existing JET inner wall injection with high-speed vertical pellets.

- Simple “pellet injector in a suitcase” for flexible installation. 1-4 pellets.

- Self contained cryorefrigerator for simple operation.

- For characterization of pellet drift physics in a large device.

IW

IW*

V


Isotopic Fueling: • minimize tritium introduced into torus • but maintain Pfusion (fuel rates shown typical of reactor)

Tritium-rich pellet ~ 50 Pa-m3/s

Deuterium gas ~ 150 Pa-m3/s

75 % D / 25 % T gas ~ 200 Pa-m3/s

60 % D / 40 % Tin core plasma


Isotopic fueling model results are promising

Figure 2

Normalized Pellet Penetration

Tri

tium

Fra

cti

on

0.00

0.10

0.20

0.30

0.40

0.50

0.10 0.20 0.30 0.40 0.50

ft(0)

ft(a)

Divertor Pumping, 1.00 bar-l/sPellets (90% T), 0.27 bar-l/sGas (100% D), 0.75 bar-l/s

Figure 1

D Gas (bar-l/s)

Trit

ium

Fra

ctio

n

0.00

0.20

0.40

0.60

0.80

1.00

0.60 0.70 0.80 0.90

ft(0)

ft(a)

Divertor Pumping, 1.00 bar-l/s

Pellets (90% T)

Gas (100% D)

• Isotopic fueling provides a radial gradient in the T and D densities.

• The magnitude of the effect depends on the separation of the two fueling sources.

• In-vessel tritium throughputs and wall inventories can be reduced by about a factor of two or more.

• This can ease requirements on the tritium breeding ratio.

• M. J. Gouge et al., Fusion Technology, 28, p. 1644, (1995)


Fueling technology for mitigating disruptions and VDEs

• Massive gas puff into DIII-D (T. C. Jernigan et al.)• Peak halo currents were reduced up to about 50% by the massive He and D

puffing. • Toroidal spatial nonuniformity was also reduced by the He puffs.

• Ne, Ar and methane pellets into DIII-D(Todd Evans et al.) • Peak halo current amplitudes are reduced by up to 50% in triggered VDEs

with both neon and argon killer pellets.

• Halo current toroidal peaking factors are reduced from 3 to 1.1 for these discharges.

• Cryogenic liquid jet modeling (Paul Parks, GA et al.) and development (P. W. Fisher, ORNL)

• Low Z impurity pellets (e.g. LiD) may be option if no runaway electron issue


Disruption mitigation systems by a massive gas puff

T. Jernigan ORNL

• Conceived as a “quick and dirty” test of a simple mitigation technique to overcome potential runaway electron problems with impurity pellets in ITER class devices

• Uses existing hardware developed for pellet injector program at ORNL

• Model for gas penetration assumes that the sufficient density can be obtained in the gas puff to shield the interior from plasma electrons thus allowing deep, rapid penetration of the neutrals.

• Very successful in preliminary tests on DIII-D in mitigating vertical displacement event (VDE) discharges with no runaway electrons using helium

• Recently results extended to deuterium gas


Objectives of massive gas puff

• Mitigate disruption forces and heat flux to the first wall as effectively as impurity pellets using electromagnetic radiation to dissipate the plasma energy

• Eliminate runaway electron generation by using low-Z (D2 or He) and high density (1015 cm-3)


High Pressure Reservoir (300 ml @ 7 MPa)

Fast Valve (Pellet Injector Propellant Valve)

Ballast Volume

Gate Valve

DIII-D Port 15R+1

Pressure Transducer

6 inch diameter Tube 3/4 inch diameter Tube

16.5" 18.4"


DIII-D with Massive Gas Puff Valve Flux Surfaces for Shot 95195 at 1.700 s


Plasma ionizes ~50% of input gas before the thermal collapse

n e(c

m-3

)t (s)

Calculated Rise 200,000 Torr liter/s

Vertical Chord (V1)

Horizontal Chord (R0)

96764

5.500 5.505 5.510 5.515 5.5200

1

2

3

4

Massive Gas Valve Drive Current

92796

5.500 5.505 5.510 5.515 5.520-2

-1

0

1

2

Massive Gas Valve Pressure Transducer Signal

92796

t (s)

A. U

.A

. U.

t (s)

9 ms wide pulse gives pressure rise of 3.2 torr in 1200 liter volume which implies the flow = 400,000 torr-liters/s

Slope of density rise matches flow of 200,000 torr-liter/s until thermal collapse (fully ionized helium)


Plasma Current

96757

Line Density R0 Chord96757

-5.00•10 5

1.25•10 5

7.50•10 5

1.37•10 6

2.00•10 6

-5.0•10

0.0

5.0•10

1.0•10

1.5•10

13

13

14

14

0

2•10

4•10

6•10

8•10

14

14

14

14

1.700 1.710 1.720 1.730

1.700 1.710 1.720 1.730

1.700 1.710 1.720 1.730

1.700 1.710 1.720 1.7300.00

0.25

0.50

0.75

1.00

Soft Xray Signal (Sum)96757

-1.4

-0.7

0.0

0.7

1.4

1.0 1.7 2.4

t=1.7070 sI= 1.46 MA

96757Line Density V2 Chord

t=1.7160 s t=1.7170 s

-1.4

-0.7

0.0

0.7

1.4

1.0 1.7 2.4 1.0 1.7 2.4 1.0 1.7 2.4 1.0 1.7 2.4 1.0 1.7 2.4

1.0 1.7 2.4

I= 1.51 MA I= 1.53 MAt=1.7180 sI= 1.46 MA

t=1.7190 sI= 1.35 MA

t=1.7200 sI= 0.99 MA

t=1.7210 sI= 0.48 MA

t=1.7220 sI= 0.20 MA

t=1.7230 sI= 0.08 MA

1.0 1.7 2.41.0 1.7 2.4

Triggered Vertical Displacement Event Disruption with no Mitigation

Motion During Current Quench Note that the current decay begins after the plasma has moved about half way down in the vacuum chamber.

Plasma Current Quench

V2 Chord

R0 Chord

t=1.7130 sI= 1.43 MA

t=1.7140 sI= 1.43 MA

t=1.7150 sI= 1.45 MA

t=1.7160 sI= 1.51 MA

1.0 1.7 2.4 1.0 1.7 2.4 1.0 1.7 2.4 1.0 1.7 2.4-1.4

-0.7

0.0

0.7

1.4

Plasma Motion During Plasma Thermal Collapse . Note that the plasma is moves noticably downward during the plasma thermal decay.

Plasma Thermal Collapse


Plasma Current 96764

1.700 1.710 1.720 1.730-1•10

0

1•10

2•10

3•10

6

6

6

6

Line Density R0 Chord96764

1.700 1.710 1.720 1.730

-5.00•10

1.25•10

7.50•10

1.37•10

2.00•10

14

14

14

15

15

Line Density V1 Chord96764

1.700 1.710 1.720 1.730

1•10

0

5•1015

16

Soft Xray Signal (Sum)96764

1.700 1.710 1.720 1.730-0.100

0.075

0.250

0.425

0.600

t=1.7070 sI= 1.44 MA

t=1.7072 sI= 1.42 MA

t=1.7074 sI= 1.46 MA

t=1.7076 sI= 1.40 MA

t=1.7078 sI= 1.39 MA

t=1.7080 sI= 1.45 MA

-1.4

-0.7

0.0

0.7

1.4

1.0 1.7 2.4R(m)

1.0 1.7 2.4R(m)

1.0 1.7 2.4R(m)

t=1.7080 sI= 1.45 MA

t=1.7090 sI= 1.60 MA

t=1.7100 sI= 1.38 MA

t=1.7110 sI= 1.14 MA

t=1.7120 sI= 0.90 MA

t=1.7130 sI= 0.62 MA

t=1.7140 sI= 0.43 MA

t=1.7150 sI= 0.31 MA

t=1.7160 sI= 0.18 MA

t=1.7170 sI= 0.15 MA

t=1.7180 sI= 0.04 MA

1.0 1.7 2.4R(m)

1.0 1.7 2.4R(m)

1.0 1.7 2.4R(m)

1.0 1.7 2.4R(m)

1.0 1.7 2.4R(m)

1.0 1.7 2.4R(m)

1.0 1.7 2.4R(m)

1.0 1.7 2.4R(m)

Approximate Gas Puff Width

1.0 1.7 2.4 1.0 1.7 2.4 1.0 1.7 2.4 1.0 1.7 2.4 1.0 1.7 2.4 1.0 1.7 2.4-1.4

-0.7

0.0

0.7

1.4

Motion During Current Quench Note that the current decay and plasma motion begin after the plasma is cold.

Plasma Motion During Thermal Collapse Note that the plasma has not moved and remains virtually motionless during the rapid thermal energy decay caused by the gas puff.

Triggered Vertical Displacement Event Disruption Mitigated with Massive Gas Puff

V1 Chord

R0 Chord

Plasma Current Quench

Plasma Thermal Collapse


Mitigation with massive gas puff

• Halo currents: both magnitude and toroidal peaking factor reduced by factor of 2 which means a factor of 4 reduction in peak forces to the first wall

• Radiated power: virtually all the energy (both thermal and magnetic) is dissipated as radiation

• Power to divertor: could not be measured due to high radiation levels in infrared

• Still have not been able to use Thomson scattering to determine density profiles during the density rise - density measured by multiple chord far-infrared interferometers.


Disruption mitigation conclusions

• Mitigation by massive gas puff test in DIII-D with helium and deuterium gas– Rapid penetration of density

– Rapid energy collapse

– Mitigation as effective as medium-Z pellets

– No runaway electrons

– Deuterium just as effective as helium

– Extra electrons from helium not required for penetration thus reducing the source for runaway electrons

– Density rise is uniform across plasma cross-section lending support to the self–shielding model thus enabling deep penetration of the gas

– Simple, reliable implementation

– Strong candidate for next step devices


Liquid jets for disruption controlstatus: March 2001

Shown below is a water jet produced using a nozzle that is being considered for use in a liquid deuterium disruption control device for DIII-D. The liquid core of the jet is clouded by mist that surrounds the jet.

This water jet with the same Reynolds number and Weber number as the proposed cryogenic jet is being used to develop the system. The first phase of the work injected jets into air; this jet is traveling into a vacuum.

18002000Jet L/D

3.7E67.6E6Weber No.

8.2E51.2E6Reynolds No.

Achieved to DateDIII-D GoalParameter

5 ms after burst disk rupture


Conclusions

• Innovation and R&D in plasma fueling systems continues to positively impact future MFE devices– high-field-side launch: increased fueling efficiency, profile peaking

for approach to ignition and high-Q burn

– pellet-triggered L-H mode: required power threshold reduced ~ 30%

– isotopic DT fueling: reduced tritium throughput, wall inventories

– disruption mitigation: exploit performance base of advanced tokamaks while having credible mitigation scheme for disruptions or fast plasma shutdown

Documents

Plasma Fueling and Implications for FIRE, ITER, ARIES