Management of dust in fusion devices
ReNeW Research Needs Workshop
Theme III: Taming the Plasma Material Interface,
UCLA, March 2-6, 2009
Charles. H. Skinner
Princeton Plasma Physics Laboratory
Presented by R. Maingi
Outline:
1.
Dust production
2.
Dust hazards
3.
Dust monitoring
4.
Dust removal
5.
R&D needs
Supported by US DoE DE-AC02-76CH03073
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
1 /16
Dust production
Dust in fusion devices is produced by :
1. Thermal overload of plasma facing
surfaces.
a) Brittle destruction of carbon
surfaces (‘shrapnel’).
b) Melt layer loss (aerosol) from metal
surfaces.
c) Disintegration of codeposited layers
2. Chemical agglomeration of sputtered Cn
clusters.
3. Debris from in-vessel activities.
Tungsten droplet tracks in QSPA ELM simulator at Troitsk,
1.6 MJ/m2 first pulse.
Zhitlukhin et al., J. Nucl. Mater., 363-365, 301 (2007)
Increase in duty cycle and plasma stored
energy in next-step long pulse devices will
cause huge scale-up in dust produced.
Up to 400 µm codeposit expected from
10 days of ITER operations.
Thermal and mechanical stability uncertain.
C. H. Skinner
0.1 mm
Iron spheres from TEXTOR-94 with the large
sphere showing a regular surface texture
J Winter, Plasma Phys. Control. Fusion, 40 (1998) 1201
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
2 /16
Dust hazards:
1. Public safety
Dust particles may be radioactive
from tritium or activated metals,
toxic and /or chemically reactive
with steam or air.
•
Tritiated dust is respirable
•
Radiation dose depends on
residence time in body.
In-vitro dissolution rate of
tritiated dust from TFTR
measured in simulated lung fluid.
Only 8% of carbon tritide was
dissolved after 110 days !
Low solubility means tritium will
remain for long time increasing
radiation dose to lung.
•
•
•
TEM microphotograph of tritiated dust particles from TFTR.
The count mean diameter is 1.23 µm.
1.00
Tritium
Retentionactivity
of Tritium
•
Sample #1
Sample #2
Fitted curve for retention
0.98
0.96
0.94
0.92
0.90
0
Data needed on BeT dust to determine
allowable occupational exposure !
C. H. Skinner
20
40
60
80
100
120
140
Duration of Dissolution (day)
Cheng et al., Fus. Technol., 41 (2002) 867
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
3 /16
Tritiated dust levitation by
beta induced static charge
•
Radioactive decay of tritium via beta
emission leaves a positive charge on a
dust particle.
•
Tritiated particles could be uniquely
more mobile than other dust.
•
Movie of tritiated dust from TFTR-->
•
A release of radioactive dust in an
accident would have major
consequences.
•
To assure public safety the
mobilisable dust inventory of ITER
will be maintained below 670 kg.
Fus. Sci. Technol., 45 (2004) 11
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
4 /16
Dust hazards
2. Hot dust - Vac. Vessel protection
•
Dust on hot surfaces will produce H2 with
air ingress and can react with air.
•
–
Hot = > 600°C for C, > 400 C for Be and W.
–
H limited to 2.5 Kg in ITER.
Need to avoid overpressure events that
could rupture the vacuum vessel and
ITER Design Basis Accidents
include potential for:
• H2 explosion
• Dust explosion triggered by
H2 ignition.
• Pure dust explosion
jeopardize its primary safety function:
confinement of dust and tritium.
•
Quantities of hot dust that could produce
2.5 Kg of H in steam reaction during ITER
accident are 6 kg of Be, C, and W dust, or,
if carbon is not present, 11 kg of Be and
77 kg of W dust.
•
Reliable detection of dust at this level is
problematic.
S. Ciattaglia IAEA RCM meeting Vienna Dec 2008.
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
5 /16
Dust hazards
3. Plasma Contamination
•
A third limit on dust is related to
potential transport of tungsten dust
to the plasma core. Tungsten is a very
efficient radiator and the core
tungsten concentration needs to be in
the 10-5 range or below to sustain a
burning plasma.
•
Ambipolar effects charge up tokamak
dust and ion drag then leads to core
contamination.
Simulated profiles of
neutral carbon density
(Pigarov/Krasheninnikov DUSTT code)
•
However the relation between core
tungsten and surface tungsten dust is
not known at present.
(A. Pigarov et al., Phys. Plasmas
12 (2005) 122508, PSI-17)
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
6 /16
Dust hazards:
4. Plasma operations first mirror survivability
ITER divertor
Image from
disruption
simulator
•
Dust accumulation can ‘blind’
the first diagnostic mirrors
•
Optical diagnostics necessary
for machine operation.
•
Mirror lifetime not clear
•
Cleaning techniques unproven
Diagnostic mirrors in divertor dome
Divertor target plate will be eroded
~1 cm at strike point over 3 year lifetime.
Material will go somewhere !
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
7 /16
Potential dust monitoring
techniques:
ITER strategy:
•
Monitor erosion
Viewing System.
with
ITER In-vessel
viewing system
head
In-Vessel
– Conservative assumption that
100% of erosion products turn
into
dust
(JT60, Tore Supra measure ~
10%)
New systems proposed:
•
Dedicated laser erosion monitors
for divertor
•
Local dust detectors based on
capacitance manometer.
– Needs adaption and hardening
to tokamak environment and
nuclear environment.
C. Neri ENEA, Frascati
Electrostatic
dust detector
100 µm
dia. of
human
hair
500
µm
C.H. Skinner J. Nucl. Mater., 376 (2008) 29–32
Converted
capacitance
manometer
GF Counsell et al, Rev. Sci. Instrum. 77 (2006) 093501
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
8 /16
.
•
Dust monitoring is not enough.
0.6
0.4
0.2
0 V/2 V
dis tance
0 V/2 V
0
1000
V/2 V 0 V/2 V
600
-0.2
800
0
400
Plasma
operation
will
not
be
permitted if dust inventory exceeds
safety limits.
0.8
200
•
Fusion power reactor cannot have
high (~ 90%) availability without
remote dust removal.
1
0
•
1.2
electric field
Potential dust removal
technology 1.
Traveling electrostatic wave: potential
gradient is created by three different
voltages on the three electrodes.
Electrostatic dust conveyor a possibility:
•
5 g/min (air) 1 g/min (vac) dust
transported (even vertically) in
travelling electrostatic wave by
JAERI/Mitusubishi during ITER EDA.
•
Potential for large improvement with
modern macroelectronics technology.
C. H. Skinner
Y Oda et al., “Development of dust removal system
for fusion reactor” J. Fus. Energy 16 (1997) 231
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
9 /16
Dust removal 2.
•
Nanotechnology and large area displays are
a rapidly evolving area.
•
Propose to apply advances in
macroelectronics to develop electrostatic
dust transporter
•
Mosaic of these devices could cover VV
floor
•
Use low activation substrate e.g. SiO2
Demonstration of a flexible E-Ink display
on a transistor backplane made at
Princeton University on steel foil.
[Y. Chen, K. Denis, P. Kazlas, P. Drzaic, SID 2001
Technical Digest, Paper P-12.2]
C. H. Skinner
Before and after images of a dust shield
prototype on a metal plate.
From “Dust Particle Removal by Electrostatic and
Dielectrophoretic Forces with Applications to NASA
Exploration Missions”
C.I. Calle et al ESA Proc. Annual Meeting on
Electrostatics 2008.
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
10 /16
R&D needed:
Developing and validating dust inventory
diagnostics to nuclear safety standards
•
Estimation of dust production rates.
•
Quantification of fraction of erosion that becomes dust.
Tokamak + ELM/disruption simulator data needed.
•
Adaption of local dust diagnostics to tokamak environment
•
Adaption of local dust diagnostics to nuclear environment.
•
Validation of erosion measurements in realistic reactor geometry.
•
Qualification of dust measurement techniques and uncertainties
(for nuclear regulators).
•
Dedicated large-scale mockup facility with tile castellations, hidden
areas… dedicated to studying dust behavior, mobilisation factors,
measurement and removal.
•
…..
Acknowledge ITER dust task force lead by S. Ciattaglia
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
11 /16
R&D needed: Management of hot dust
•
Estimation of hot dust inventories.
•
R&D on diagnostics on dust on hot surfaces.
– Direct measurement seems difficult.
– Chuyanov proposal to measure reactivity by small calibrated
injection of steam.
– Development and validation of 3D models of dust-H explosion
•
Engineering measures to overpressure of vessel:
– Design requirement to limit maximum air entering the VV- needs
feasibility analysis.
– Injection of an inert gas into the VV in accident situations needs model validation to establish time scale for mixing and
engineering optimization
•
Crosscheck safety/plasma physics and design codes
–
•
(timing of transients could/should be different, e.g. temperature of dust could be below the
self-sustaining reaction temperature limit).
…..
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
12 /16
R&D needed:
Managing plasma contamination issues
•
Benchmarking of models on dust transport with calibrated dust
injection experiments.
•
Benchmarking of melt layer aerosol transport codes in disruption
simulators and tokamaks.
•
Deriving limits on tolerable surface dust in different locations.
•
Developing countermeasures to mitigate contamination.
•
…
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
13 /16
R&D needed:
Developing countermeasures to clean dusty
diagnostic mirrors remotely
•
Helium puff ?
•
Vibration ?
•
Laser cleaning ?
•
…
•
related to general issue of
survival of first mirror in
tokamak environment potential erosion of and
deposition on mirror.
C. H. Skinner
“Self Cleaning Sensor Unit
A key element of minimizing dust is preventing it from clinging
to the front surface of the imaging sensor. To combat against
this, the EOS 40D features a Canon-designed Self Cleaning
Sensor Unit. The low-pass filter at the front of the sensor
shakes off dust automatically with ultrasonic vibrations,
removing dust from the sensor assembly.”
http://www.usa.canon.com/consumer/controller?act=ModelInfo
Act&fcategoryid=139&modelid=15653#ModelFeaturesAct
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
14 /16
R&D needed:
Means to remove dust remotely without impacting tokamak availability
• Electrostatic
dust
conveyor ?
Mars Rover Spirit after a dust storm.
• ….
Will fusion reactor interior end up looking like this ?
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
15 /16
Final points:
• Issues such as dust are not an problem for contemporary
tokamaks but are potential show-stoppers for fusion
reactors !
• Environment needed that can foster and fund
creative solutions to these issues.
• Development path needed from lab experiments, small
scale simulators to next-step devices.
• A next-step long-pulse, flexible, high power, hot wall
machine with relevant first-wall materials and appropriate
access and flexibility would be ideal to validate the most
promising candidates for dust monitoring and removal.
• Work should be coordinated with ITER R&D and ITPA.
C. H. Skinner
ReNeW Research Needs Workshop Theme III: Taming the Plasma Material Interface, UCLA, March 2-6, 2009
16 /16