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 Program1
Plasma Fueling and Implications forFIRE, ITER, ARIES
M. J. Gouge
Oak Ridge National Laboratory
March 6, 2001
MJG:TTM 3/01 Plasma Fueling Program2
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
MJG:TTM 3/01 Plasma Fueling Program3
Fueling system functions
• to provide hydrogenic fuel to maintain the plasma densityprofile for the specified fusion power,
• to replace the deuterium-tritium (D-T) ions consumed inthe 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 offlayer flow for optimum divertor operation,
• to inject impurity gases at lower flow rates for divertorplasma radiative cooling, wall conditioning, and for plasmadischarge termination on demand.
MJG:TTM 3/01 Plasma Fueling Program4
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 andvertical launch on DIII-D
• Disruption mitigation and impurity fueling development
• Fueling system design for ITER and FIRE
MJG:TTM 3/01 Plasma Fueling Program5
Hydrogenic solids
• Have made hydrogenic pellets insizes 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 data
T2, Break-away data
D2, Extrusion static equation
D-T, Extrusion static equation
T2, Extrusion static equation
D2, Extrusion dynamic
D-T, Extrusion dynamic
T2, Extrusion dynamic
H2, Viniar Bingham limiting strength
MJG:TTM 3/01 Plasma Fueling Program6
ITER fueling R&D resultsrelevant 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 forcentrifuge injector (with CEA)
– piston and screw (RF) extruderdevelopment
– high-field-side launch development
Pure Tritium Extrusion
MJG:TTM 3/01 Plasma Fueling Program7
TPOP-II tritium extruder experiments
Highlights
• Demonstrated first extrusions of solidtritium at Tritium Systems TestAssembly Facility at LANL;
• Produced world’s largest pellets: 10mm D, DT and T pellets (full scale forITER);
• Processed over 40 grams of tritiumthrough TPOP-II;
• Developed isotopic fueling concept toreduce ITER tritium throughputs andinventory.
Pure Tritium Extrusion Pure Tritium Pellet
MJG:TTM 3/01 Plasma Fueling Program8
FIRE fueling system
• Baseline is gas (mostly D) + pellets (DT to get 60% D/40%T inthe 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 to100’s m/s with a pellet injector located at an arbitrary location (due toguidetube radius of curvature) with modest propellant gas requirements
– The optimum depends on pellet speed dependence of particle depositionfor inside launch which is not quantified.
MJG:TTM 3/01 Plasma Fueling Program9
Double-screw extruder concept(ORNL STTR with Utron, Inc.)
• Dual, opposed, counter-rotating screws
• Liquid helium is fed into the extruder atone end and flows through coolingchannels (alternative is G-M cryocooler)
• Deuterium is fed into the screw chamberand flows to the center of the extruder.
• As the liquid flows it freezes on theinner wall between the screw and theinner housing.
• As the screws rotate they scrape off thedeuterium and force the ice to the centerof the extruder were it is extruded outthe 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
MJG:TTM 3/01 Plasma Fueling Program10
Pellet launch paths into FIRE
• Pellet speed limited to about500 m/s for curved guidetubes.• Much higher speeds possiblefor vertical HFS launch
MJG:TTM 3/01 Plasma Fueling Program11
Preliminary FIRE fueling systemparameters
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
MJG:TTM 3/01 Plasma Fueling Program12
Efficiency of gas fueling much less thanpellet 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
MJG:TTM 3/01 Plasma Fueling Program13
0 0.2 0.4 0.6 0.8 1 1.2
Penetration Depth /a
0
20
40
60
80
100
Fu
eli
ng
Eff
icie
nc
y
(%
)
AUG L-modeAUG H-modeDIII-D H-modeTore Supra L-mode
Pellet fueling efficiency has a broad range
l Encouraging initial high field launch experiments on ASDEX-Ul implications for FIRE
l ongoing experiments on ASDEX-U, DIII-D, Tore Supra, JET, LHD
HFL AUG
LFL AUG
MJG:TTM 3/01 Plasma Fueling Program14
Multiple launch locations on DIII-D
MJG:TTM 3/01 Plasma Fueling Program15
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/s
t = 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/s
t = 1 ms
ne (
102
0 m
-3) DIII-D 98796 - measured ne
CalculatedPenetration
Four positions of pelletinjection guide tubesinstalled on DIII-D
MJG:TTM 3/01 Plasma Fueling Program16
Both vertical HFS and LFS pellet injection are consistent with anuutward major radius drift of pellet mass
• The net deposition profile measured by Thomson scattering 2-4 msafter pellet injection on DIII-D. V+1 HFS indicates drift towardmagnetic 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 ofVerticalPort
V+3 LFS H-mode - 4.5 MWvp = 200 m/s
ne (
101
9 m
-3)
V+3V+1
MJG:TTM 3/01 Plasma Fueling Program17
HFS pellet injection on DIII-Dyields deeper particle deposition than predicted
• The net deposition depth measured by Thomson scattering after pelletinjection on DIII-D is compared with the calculated pellet penetration depth.The high field side (inner wall and vertical injection) locations all showdeeper 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 (λ/a) Deposition Depth
LFS
HFS
Measu
red M
axi
mum
(λ
/a)
D
eposi
tion D
epth
MJG:TTM 3/01 Plasma Fueling Program18
ExB Polarization Drift Modelof 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 20keV 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-uniformtokamak field:
• The resulting E causes an ExB drift in themajor radius direction
Theoretical model for pellet radial drift predictsstrong inward drift for reactor
BBv �↔+
= ⊥� 3
||2
eB
WWB
PelletAblatant (Cloud)
B ∝ 1/R
MJG:TTM 3/01 Plasma Fueling Program19
Time (s)3.63.5 3.7 3.8 3.9
0
1
2
8
4
0
8
6
4
Upper Divertor
ne (
10
19
m-3
)D
(a.u
.)n
e (
10
19
m-3
)
ρ = 0.9
ρ = 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))
MJG:TTM 3/01 Plasma Fueling Program20
Possible vertical pellet injection test at JET
• Pipe-gun injector for vertical pellet injectionon JET
- Complements existing JET inner wall injection withhigh-speed vertical pellets.
- Simple “pellet injector in a suitcase” for flexibleinstallation. 1-4 pellets.
- Self contained cryorefrigerator for simple operation.
- For characterization of pellet drift physics in a largedevice.
IW
IW*
V
MJG:TTM 3/01 Plasma Fueling Program21
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
MJG:TTM 3/01 Plasma Fueling Program22
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)
Tri
tiu
m F
ractio
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/sPellets (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 twofueling sources.
• In-vessel tritium throughputs and wall inventories can be reduced byabout 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)
MJG:TTM 3/01 Plasma Fueling Program23
Fueling technology for mitigatingdisruptions 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 thesedischarges.
• Cryogenic liquid jet modeling (Paul Parks, GA et al.) anddevelopment (P. W. Fisher, ORNL)
• Low Z impurity pellets (e.g. LiD) may be option if norunaway electron issue
MJG:TTM 3/01 Plasma Fueling Program24
Disruption mitigation systems by a massive gas puff
T. Jernigan ORNL
• Conceived as a “quick and dirty” test of a simple mitigation techniqueto overcome potential runaway electron problems with impurity pelletsin ITER class devices
• Uses existing hardware developed for pellet injector program at ORNL
• Model for gas penetration assumes that the sufficient density can beobtained in the gas puff to shield the interior from plasma electronsthus allowing deep, rapid penetration of the neutrals.
• Very successful in preliminary tests on DIII-D in mitigating verticaldisplacement event (VDE) discharges with no runaway electrons usinghelium
• Recently results extended to deuterium gas
MJG:TTM 3/01 Plasma Fueling Program25
Objectives of massive gas puff
• Mitigate disruption forces and heat flux to the first wall aseffectively as impurity pellets using electromagneticradiation to dissipate the plasma energy
• Eliminate runaway electron generation by using low-Z (D2
or He) and high density (1015 cm-3)
MJG:TTM 3/01 Plasma Fueling Program26
High PressureReservoir (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"
MJG:TTM 3/01 Plasma Fueling Program27
DIII-D with Massive Gas Puff ValveFlux Surfaces for Shot 95195 at 1.700 s
MJG:TTM 3/01 Plasma Fueling Program28
Plasma ionizes ~50% of input gas before the thermal collapse
ne
(cm
-3)
t (s)
Calculated Rise200,000 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 of3.2 torr in 1200 liter volume whichimplies the flow = 400,000 torr-liters/s
Slope of density rise matches flow of200,000 torr-liter/s until thermalcollapse (fully ionized helium)
MJG:TTM 3/01 Plasma Fueling Program29
Plasma
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 QuenchNote 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
MJG:TTM 3/01 Plasma Fueling Program30
Plasma 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
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 QuenchNote 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
MJG:TTM 3/01 Plasma Fueling Program31
Mitigation with massive gas puff
• Halo currents: both magnitude and toroidal peaking factor reduced byfactor of 2 which means a factor of 4 reduction in peak forces to thefirst wall
• Radiated power: virtually all the energy (both thermal and magnetic) isdissipated as radiation
• Power to divertor: could not be measured due to high radiation levelsin infrared
• Still have not been able to use Thomson scattering to determine densityprofiles during the density rise - density measured by multiple chordfar-infrared interferometers.
MJG:TTM 3/01 Plasma Fueling Program32
Disruption mitigation conclusions
• Mitigation by massive gas puff test in DIII-D with heliumand 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 thusreducing the source for runaway electrons
– Density rise is uniform across plasma cross-section lending supportto the self–shielding model thus enabling deep penetration of the gas
– Simple, reliable implementation
– Strong candidate for next step devices
MJG:TTM 3/01 Plasma Fueling Program33
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 deuteriumdisruption 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 usedto 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
MJG:TTM 3/01 Plasma Fueling Program34
Conclusions
• Innovation and R&D in plasma fueling systems continues topositively 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 advancedtokamaks while having credible mitigation scheme for disruptions orfast plasma shutdown