Transcript No Slide Title

IFE Chamber Dynamics
Presented by
Mark S. Tillack
contributors:
ESLI
F. Najmabadi, A. R. Raffray, S. S. & Bindhu Harilal,
D. Blair, A. Gaeris, S. Krasheninnikov (UCSD),
C. Olson, T. Renk (SNLA), T. Knowles (ESLI), D. Haynes (UWisc),
J. P. Sharpe (INEEL), J. Latkowski, D. Blackfield (LLNL)
DOE Budget Planning Meeting
Germantown, MD
March 12, 2002
Background
• Following target explosions, several distinct stages of
chamber response occur:
1. Prompt transport of energy through and
deposition into materials (ns-ms)
2. Radiation fireball & shock propagation,
mass ejection from walls (1-100 ms)
3. Afterglow plasma & transport processes (1-100 ms)
4. Liquid wall dynamics (ms-s)
5. Long-term changes in materials (days-months)
neutrons &
gammas
• A better understanding of chamber physics is needed
in order to make progress on key IFE technology issues:
8 Wall protection
8 Chamber clearing for target and driver injection
• This presentation focuses on the underlying science of
IFE chambers in a generic sense (i.e., without ties to a
specific chamber design concept), using results from OFES
IFE Technology, DP-HAPL and ARIES-IFE programs
x-rays
ions
Outline
1. Surface modification from pulsed ion flux
2. Fireball dynamics in a gas-protected chamber
3. Plume ejection dynamics
4. Aerosol and dust generation and transport
5. Magnetic diversion of expanding plasma
6. Ion stopping by beam-plasma instabilities
Details of target emissions have a strong
impact on chamber and wall responses
NRL Direct-Drive Target
1 mm CH +300 Å Au
.195 cm
.169 cm
.150 cm
CH Foam + DT
DT Fuel
DT Vapor
0.3 mg/cc
CH foam
 = 20 mg/cc
Energy
Split
Direct Drive
Target (MJ)
High Yield
DD Target
2.14 (1%)
6.07 (1%)
115 (25%)
109 (71%)
279 (70%)
316 (69%)
Ions
43 (28%)
112 (28%)
26.5 (6%)
Total
154
397
458
X-rays
Neutrons
X-ray spectra
LLNL/LBNL HIF Target
Indirect Drive
Target (MJ)
Time-of-flight spreading allows significant
thermal penetration during energy deposition
NRL direct drive target spectrum (154 MJ)
Ion power at chamber wall (R=6.5 m)
100 ns
Photon and ion attenuation in C and W slabs
11
Energy deposition (J/m3)
1x10
1x1010
Debris ions, C
Fast ions, W
1x109
Photons, W
1x108
Fast ions, C
Photons, C
1x107
Debris ions,W
6
1x10
1x10 -8
1x10 -7
1x10 -6
1x10 -5
1x10 -4
1x10 -3
Penetration depth (m)
1x10 -2
(1 ms~1 mm thermal penetration depth)
Modeling and simulation experiments are being used
to improve our understanding of chamber dynamics
Facilities:
Modeling tools:
Pulsed ion sources (e.g., RHEPP)
Rad/hydro (LASNEX, BUCKY)
Pulsed x-ray sources (e.g., Z)
Surface responses (SRIM, Ablator)
Pulsed e-beam facilities (DTRA)
Mass ejection and recondensation
Lasers:
1–2 J materials response,
laser propagation
diagnostic development
100–200 J rep-rated chamber dynamics
1–2 kJ IRE (integrated effects)
Gasdynamics (CFDSTARS)
Ignited targets (ETF)
Ion transport (LSP)
Atomic physics
1. Surface modification from pulsed ion flux
Ion exposure experiments are being performed
at the RHEPP pulsed ion source
• 0.5 MeV ions C+, H+
– Range ~ 1 mm
• 150-300 ns pulse
– Thermal penetration ~ microns
• 10 J/cm2 fluence
– Similar to IFE
• Repeating
Magnetically confined
Anode Plasma
– 1000 shots max
IFE Materials Test Matrix:
° W alloys
° C-graphite, Ceramic fiber composites
° Innovative architectures
e.g., fiber flocked, functionally graded,
nano-engineered
° Flibe
Severe carbon erosion and roughening are
observed above 2–3 J/cm2
100
Mechanically polished Poco graphite exposed to 75 pulses of
70% C/30% H beam at average dose of 5.5 J/cm2
Ablation Step
Ra (treated)
(microns)
10
Ra (untreated)
1
Step measurement accuracy ~ 0. 4 µm reached below ~ 3 J/cm2
0.1
0
1
2
3
4
5
6
Ion Beam Fluence (J/cm2)
Profilometer scan across interface:
~ 20 micron step (0.27 µm/pulse)
Ra (original) = 0.23 microns
Ra (treated) = 3.6 microns
ESLI engineered wall exhibits much less net erosion
 Each pulse is spread over 15x more area
 The ablated material may redeposit on the nearby fibers:
recycling
 Thermal penetration into vertical fibers may be providing
effective cooling on this time scale
Specimen fractured to reveal interior
IBEST (Ion Beam Surface Treatment) uses
intense ion beams to melt and modify surfaces
Melt
Region
Cooling by
Thermal
Diffusion
IONS
• 500-750 keV N+ ions
• Range ~ 2–10 mm
• 109 K/s cooling rate due to
thermal diffusion
• 2–8 J/cm2 fluence to melt
Ion
Range
Tribometer wear tracks in Pt-Ti cosputtered layer
without and with surface treatment (2000 wear cycles)
T. Renk et al., “Improvement of surface properties by modification and
alloying with high-power ion beams,” Phys. Plasmas 5(5), May 1998.
2. Fireball dynamics in a gas-protected chamber
The dominant threat for the indirect-drive target
is from soft x-rays created by debris ions
Simulating the protection of a dry first wall with a buffer gas requires:
•
•
Radiative hydrodynamics (BUCKY)
EOS/opacity data from the coronal to the collisional regimes (IONMIX)
X-ray energy percentiles
X-ray Attenuation Lengths (NIST)
90%
80%
70%
1.E+01
HIB (115MJ xrays)
DD laser
(2.7MJ)
60%
50%
40%
30%
20%
1.E+00
Attenuation length (cm)
Fraction of total x-ray energy below
100%
1.E-01
C
1.E-02
1.E-03
1.E-04
1.E-05
1.E-06
10%
0%
1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03
Photon Energy (keV)
Nearly half of the 115MJ of prompt x-ray energy
comes in the form of sub-keV photons
1.E-07
0.01
0.1
1
10
100
Energy (keV)
This would be deposited in the first micron of the wall
effectively instantaneously, causing the graphite to sublimate
at a rate incompatible with rep-rated reactor concepts.
For the HIB target in a 4.5m radius graphite chamber,
1 Torr of Xe is sufficient to prevent first wall sublimation
•
•
The simulation proceeds by instantly
depositing the prompt target x-rays
through the gas and the wall.
The ions from the target then traverse the
ionized gas, depositing their energy
through a stopping power formalism,
while the gas dynamics are tracked using
1d Lagrangian radiative-hydrodynamics.
Gas
Wall
X-ray
energy
(MJ)
Ion energy
(MJ)
105
19
10
6 (knockons only)
HIB target output energy deposited in the
gas and wall of a 4.5m radius graphite
walled chamber filled with 960mTorr of
Xe starting at 1000C.
Ion temperature (eV) contours from BUCKY simulation
Fireball forms
from captured
x-ray and ion
energy
Fireball propagates
and slowly re-radiates
energy, allowing wall to
conduct energy away
from surface, avoiding
sublimation
3. Plume ejection dynamics
Processes present in IFE mass ejection and
transport are analogous to laser micromachining
• Energy absorption in surface
• Prompt thermal response of surface
• Liquid hydrodynamics
• Evaporation
• Unsteady gas dynamics
(including chamber environment)
• Radiation transport
• Condensation
• Laser-plume interaction
Table-top experiments with extensive diagnostics
are being developed to explore chamber responses

Modeling and experiments are being
performed for both liquid and solid surfaces
Electron Density [cm-3]
0.15 Torr
1.E+19
Electron density of Si ablation plume
measured by Stark broadening
at 390 nm, 1e9 W/cm2
1.E+18
1.E+17
10
100
Time [ns]
1000
100 Torr
Expansion velocity
= 4.5e6 cm/s (300 eV)
10000
4. Aerosol and dust generation and transport
Aerosol and dust generation and transport are
important for both chamber clearing and safety
 
n    nv    Dn    cn  n
t
t
Convective Diffusion
and Transport
growth,
homo
 
 
 n t growth ,  n t
hetero
coag
Particle Growth Rates
Growth Rate Models:
Nova dust
Homogeneous Nucleation (Becker-Doring model)
 t
n
growth,
homo
2 
 dcrit
Psat 2 2m 1/ 2 S2
 # 1 
 Vcrit ,  3 3 
   

exp
 kT     l

m s m 
 3kT 

Condensation Growth
#
n growth,  I

 V  , 


n

t he tero
t
 V 
 V 
m 3s
 


1 

m 3 

dcrit 
t V   2
4m
3
, and Vcrit   6 dcrit
l kT ln S
 6
1/ 3
S  K Psat Dd p
kT
m 3 
Vmol F,  
 s 
Coagulation
 t
n
coag
V

1
   V*,V  V *n(V*)n(V  V*)dV *    V,V *n(V)n(V*)dV *
20
0
where the coagulation kernel is given by
 V,V *  2 D D *d p  d *p Fcoag
Opportunities and challenges for IFE research on
aerosol and dust generation and transport
• Computational improvements to solve stiff integro-differential transport equations
• Plasma effects on dust growth and transport mechanisms (e.g., dusty plasmas)
• In-situ particle diagnostics for determining fundamental mechanisms of nucleation
•
and growth in fusion, space, and industrial plasma environments
Development of nanoparticle generation systems for industrial and medical uses
10
36
2500 K
3500 K
10
2000 K
Button 1 data
3000 K
10 34
1500 K
10 32
10 30
1
10 28
1000 K
10 26
1500 K
10 24
2000 K
10
22
2500 K
10
20
(dashed curves)
(solid curves)
SIRENS simulator vs. TopGun model
1
0.1
3000 K
10 18
3500 K
10 16
typical value for a
bubble chamber
10 14
1
10
Saturation Ratio
0.01
100
Particle Distribution (frac/ln(µm))
10
38
Critical Radius (nm)
HMG Nucleation Rate (#/m 3/s)
Formation Rate and Size of Pb droplets in an IFE System
0.8
Region I Predicted
0.6
Cu plasma
5.2 kJ, 120 ms
450 mg particulate
70% melt blowoff
0.4
0.2
0
0.1
1
Particle Diameter (µm)
10
J.P. Sharpe, B.D. Merrill, D.A. Petti, "Modeling of Particulate Production in the SIRENS
Plasma Disruption Simulator," J. Nuclear Materials, vol.290-293, 1128-1133 (2001).
5. Magnetic diversion of expanding plasma
Magnetic deflection is being studied for
protection of the first wall against ions
Three configurations are currently
under consideration:
– Uniform field
– Mirror arrangement
– Cusp arrangement
Cusp configuration is
simply a mirror with the
field reversed in one of
the coils.
L. A. Booth and T. G. Frank, “Commercial Applications of
Inertial Confinement Fusion,” LA-6838-MS, May 1977.
Uniform field
configuration would
require more magnets
but lower (~2 T) fields.
PIC simulations have been initiated using
LSP code (MRC) developed for HIF
• Ions only in these two movies
• Field strength ~8 T, 14 m diameter coils
• Red particles are DT (mass=2.5, charge=1) at 250 keV; blue particles
are alphas at 1 MeV; Total plasma energy is 113 MJ
Mirror
Cusp
Inclusion of electrons is computationally
very challenging, but necessary
QuickTime™ and a
PNG decompressor
are needed to see this picture.
•
•
QuickTime™ and a
PNG decompressor
are needed to see this picture.
Red particles are DT (mass=2.5, charge=1) at 250 keV; green particles are alphas,
blue particles are electrons
Key issues include stability, collisions, charge exchange, Bremsstrahlung & synchotron
radiation, cost of magnets & shielding, recirculating power for magnet cooling
6. Ion stopping by beam-plasma instabilities
Residual plasma persists longer than the dwell time
Chamber gas/plasma temperature
stops falling below ~1 eV
˜ few eV) ~
t rad (T 
T
3
1
~ 10 s  f
L(T )npl
LZ(T)e (watts cm 3 )
for Lrad(t)~10–25 W-cm3
Be
Boron
Carbon
Neon
Argon
10-25
10-26
10-27
10-28
Recombination becomes
ineffective below npl~1019/m3
1
10
Te (eV)
100
Characteristic plasma recombination time, trec
T / np l
1018 mĞ3
1019 mĞ3
1020 mĞ3
0.2 eV
~ 0.1 s
~ 3x10Ğ3 s
~ 10Ğ4 s
0.6 eV
~ 1s
~ 0.1 s
~ 2x10Ğ3 s
1.2 eV
~ 3s
~ 0.4 s
~ 10Ğ2 s
1000
Impact of residual plasma on ion stopping
• For reasonable chamber gas density the impact of binary collisions on stopping of
energetic (~ 1 MeV) ions is small
(e.g., for H on Xe at 10 mTorr, dE/dx=87 MeV-cm2/g = 0.05 MeV/m)
• However, collective effects of the interactions of the beam of energetic ions with
residual plasma can significantly alter the population of energetic ions
 i be am ~  pi ni be am / n pl 
1/ 3
• Total number of fast ions per pellet,
ni-fast~1020 m–3, results in average ion
beam density ni-beam~1016 m–3
• During pellet explosion the electron temperature of residual plasma can be quickly
heated up by electron heat conduction, so
that the electron temperature of residual
plasma exceeds the ion temperature.
Impact of residual plasma on ion stopping
• For ni-beam~1016 m–3 and, npl~1018 m–3, we find i-beam~108 s–1
• Assuming the effective collision frequency of the beam with residual plasma
is of the order of i-beam , we find a crude estimate of stopping distance of fast
ions caused by collective effects, Li-beam:
Li be am ~
Vi  be am
 i be am
~ 10 cm  R
• Further study of the impact of collective
effects on fast ion stopping is needed:
– a more accurate description of the evolution of
residual plasma parameters
– a more detailed evaluation of collective
interactions of fast components (both electron and
ion) with the background gas/plasma
• Free expansion into an ambient plasma is also
a subject of astrophysical interest
D. S. Spicer, R. W. Clark and S. P. Maran, “A model of the pre-Sedov expansion phase of supernova remnantambient plasma coupling and x-ray emission from SN1987A,” The Astrophysical Journal 356 (1990) 549.
Closing Remarks
• IFE chamber dynamics encompasses a wide
variety of phenomena with numerous
opportunities for fundamental scientific
investigations
• A better understanding of IFE chamber
dynamics is needed in order to make progress
toward an IFE power plant
• IFE chamber dynamics shares many features in
common with MFE and non-fusion sciences
• A multi-institutional program of theory,
modeling and experiments is being developed
through a combination of DP & OFES support