Transcript ppt - Fusion Energy Research Program

LLNL Chambers Progress:
April-November 2002
presented by: Jeff Latkowski
contributors: D.T. Blackfield, T.K. Fowler, W. Meier,
D. Hewett, S. Reyes, and L. J. Perkins (LLNL)
D. Welch , T. Hughes and C. Mostrom (MRC)
W. Gekelmann and M. VanZeeland (UCLA)
T. Marshall et al. (INEEL)
High Average Power Laser Meeting
December 5-6, 2002
Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
LLNL chambers work
 Magnetic deflection
 Safety & environment
 Fast ignition
 Systems modeling
 Molecular dynamics simulations for graphite
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Magnetic deflection:
Why needed?
 Original SOMBRERO used 500 mTorr of
Xe gas and had relatively soft ion output
 Current understanding of target heating
during injection limits gas to 25-50 mTorr
 Energetic ions will reach chamber wall
and/or optics
1.6 MeV C
500 mTorr Xe
 Multiple “radiation damage” issues, but
exfoliation alone sufficient to cause serious
problems; could result in loss of ~2 mm/h
 Enhanced ion stopping in plasma; still likely
to be significant ion fluxes at chamber wall
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Burn a’s
50 mTorr Xe
Magnetic deflection:
General principles
1.
3.
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Initally, a hot, dense
plasma with unmagnetized
ions and magnetized
electrons.
Radial expansion continues
until the excluded
magnetic energy is roughly
equal to the expanding
plasma’s total kinetic
energy. This radius is
called the magnetic
confinement or “Bubble
Radius”.
2.
4.
The unmagnetized
ions pull electrons
across the magnetic
field by a strong
electric field,
producing an E X B
current that expels the
background
magnetic field.
The plasma continues
to diffuse down the
field lines and the
magnetic field relaxes
to its original state.
With a background plasma present this is modified, because the expanding ions are
neutralized by background electrons being pulled down field lines, possibly reducing
the laser-produced plasma’s diamagnetism and generating currents and waves.
Magnetic deflection: Analytic calculations
and review of past literature
 IFE chamber protection studied at LANL (1974-1980)
 Energy recovery in D-3He chamber at Kyushu University
(1991-1993)
 Experimental work at United Aircraft Research Laboratory
(1970); Pharos II & III Laser facility at NRL (1983-1990);
KI-1 facility in Novosibirsk (1987-2002); LLNL (1991)
 T.K. Fowler examined plasma expansion in a magnetic
field (Starfish, 1966); Provides estimates on bubble radius,
jet formation and chamber clearance time (May-June 2002)
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Magnetic deflection:
Current concept
B
Early time
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Late time
Magnetic deflection:
Current concept, (Cont’d.)
 E is plasma kinetic energy
 B0 is background magnetic field
Bubble radius:
1/ 3
 3m 0 E 

R b  
2 
 2B0 
 Assume high-yield direct-drive
target (400 MJ yield with ~110
MJ in ions)
 Allow mean bubble radius to
extend ~2/3 of the way to the
chamber wall (4.3 m), we
require:
– B0 = 0.9 T
– B0 = 0.6 T for flux conserving wall
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Magnetic deflection: Summary
of results from T.K. Fowler
Species
All
H
D
T
He
C
E (MJ)
112
1.85
37.1
42.7
28.7
1.56
Rb(m)
4.4
1.15
3.04
3.20
2.79
1.06
RMIN(m)
1.54
0.40
1.07
1.12
0.98
0.37
Rb = (6E/Bo2)1/3; RMIN = 0.35Rb; RMAX = 0.8Rb
RMAX(m)
3.5
0.88
2.44
2.55
2.23
0.88
RMAX assumes thin
shell compresses
field to 1.5Bo
RMIN uses special virial theorem and moment of inertia to
determine average radius accounting for plasma instability,
radiation, and snow-plowing of background gas
Ref. O’Neil and Fowler, Phys. Fluids. 9 (11) (1966) p. 2219
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Magnetic deflection: Summary
of Fowler results (Cont’d.)
 Worse case jetting (at 0.9 T) would contain <14% of total
ion energy
 Chamber clearing could be an issue:
– If orbital bounce motions keep loss cone full, plasma recompression
must be ~5.6 before chamber clearing time falls to 0.1 s
– If ion collisions are needed to fill the loss cone:
• tclear ~ 10 tii ; tii = 1016T3/2 / n; n = 1019(Rb/R)3 during recompression
• T < 150 keV for tclear = 0.1 s (requires thermalization and some
entrainment of Xe plasma, which is formed by prompt x-rays)
– Raising field reduces need for recompression and thermalization due
to smaller mirror ratio
 Still worried about charge exchange – needs to be more
carefully addressed
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Magnetic deflection: Significant effort has
gone into continual development of LSP
 3D PIC calculations with 30-cm-radius plasma at very high
(uniform) density  conditions severely stressed the code
 Switch to 2D calculations resulted in numerical
instabilities produced by transition of electrons from a
fluid to kinetic description
 Switch to a 2D description with kinetic ions and fluid
electrons produced a more stable code, but resulted in
energy losses (fictional plasma cooling)
 LSP has now been configured (by MRC) to allow for fluid
and kinetic ions as well as electrons
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Magnetic deflection: Brief discussion
of numerical issues with LSP
 LSP has never operated with such dense, hot plasmas in
meter-scale geometries
 Presence of magnetic field is not the cause of numerical
problem
 Use of implicit solver can lead to lack of energy
conservation
 Need to resolve plasma skin depth at plasma/vacuum
interface results in “too small” cell sizes and too many
particles (plasma skin depth ~ 0.01 cm)
 Kinetic electrons require too short a time step  cDt < re
 Dt < 210-4 ns; wpeDt < 1  Dt < 2.510-4 ns
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Magnetic deflection: 2D x vs. y LSP plasma
simulation rchamber = 3.5 m; Bo = 0.8 T, (Cont’d.)
H+ only
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Magnetic deflection: 2D x vs. y LSP plasma
simulation rchamber = 3.5 m; Bo = 0.8 T
All
species
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Magnetic deflection: 2D x vs. y LSP plasma
simulation rchamber = 3.5 m; Bo = 0.8 T
Cat’s Eye
Nebula
(NGC 6543)
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Magnetic deflection: Energy loss with kinetic
ions 2D x vs. y (rchamber = 3.5 m; Bo = 0.8 T)
Field Energy
Total Energy
Energy loss
reduced with
fluid treatment
for ions; valid?
D+ Energy
Time (ns)
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H+ Energy
Time (ns)
2D r vs. z Lsp plasma simulation
rchamber = 3.5 m ; Bo = 0.8 T
All species
Electrons
D+
H+
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Magnetic deflection: Plasma expansion
experiments at LAPDU
Parameters
LAPDU = Large Plasma
Device Upgrade
http://plasma.physics.ucla.edu/bapsf
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n = 1-4  1012 cm-3
B = 0.5-4 kG
Plasma Radius = 25 cm
Plasma Length = 17 m
Magnetic deflection: Laser plasma
experiments on LAPDU
 Spectra Physics Nd-Yag Quanta Ray Pro Laser; 1.06 mm;
1.8 J ( 1.5 J); tpulse < 8 ns; 0.5 – 1.0 Hz
 Target diameter of 0.5mm  1011W/cm2
 Targets are 0.5 – 0.75”  1.0’ long rods of Al, C, or Ba
 NAl ~ 21015; Vo|| ~ 1.5107cm/s; Vo+ ~ 1107cm/s
 ~0.75 J coupled to target; EAl ions ~3-4keV; Ee~10-20eV;
some fast electrons with E < 100 eV; Zeff ~ 2
 1.4 cm (0.4T) < RbAl < 26 cm (0.005T)
 5.3 cm (0.4T) < RhAl < 424 cm (0.005T)
 0.26 (0.4T) > ebAl > 0.06 (0.05T)
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Magnetic deflection: IFE-relevant
experiments on LAPDU
 Key parameter:
‒ eb = Rh / Rb
‒ For IFE  7.9 cm / 429 cm = .018
Rb = (3moEo/2Bo2)1/3
Rh = Vo / wci
 With Al target, LAPDU can achieve 0.26 < eb < 0.06; Key
is that value is <<1
 Previous work has investigated bubble radius vs. magnetic
field strength, including effects from low-density plasmas
 We would like to explore the effects of higher background
plasma densities and the rate of expansion along the
magnetic axis
 Would use experiments to (1) investigate IFE-relevant
parameter space, and (2) benchmark LSP models
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Magnetic deflection: LAPDU data
on bubble radius vs. magnetic field
At the time of peak
diamagnetism, the laser
plasma is O(1013cm-3)
For IFE chamber:
‒ Background plasma could
be >1015 cm-3
‒ At stagnation, density in
plasma bubble <1013 cm-3
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5
4
Bubble Radius (cm)
There appears to be little
difference with a
background plasma of
1012 cm-3
3
2
1
0
400
600
800
1000
1200
Applied Magnetic Field (G)
1400
1600
The high ratio of the background to
bubble plasma densities (>102) in the IFE
case suggests that we need to investigate
higher background plasma densities
Magnetic deflection: Additional
calculations and analyses are planned
 2D calculations, although slow, will be the focus of our
LSP work
 3D calculations deferred until new platform becomes
available (MCR has 2300 CPUs and 4600 GB memory)
 Will be moving to non-uniform cases; should aid
chamber clearing
 IFE-relevant plasma expansion data will be collected at
LAPDU:
– Rate of plasma leakage along magnetic field axis (chamber
clearing)
– Rb vs. B0 for higher background plasma densities
– Non-uniform fields to be studied
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Reaction Rate (mg/m2-s)
S&E: INEEL’s FSP responded to concerns
about graphite reaction rate data
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NB31 Tests: 525-1000 °C,
100 sccm of 21% O/Ar mix
S&E: With the new data, an excursion in
SOMBRERO is much less of a concern
Temperature (˚C)
 Excellent example of how
process is supposed to
work:
– Analysis identifies issue
– Capabilities improved to
confirm result
– Experiment conducted
using newly available
material
– New analysis performed to
address issue
Time (hours)
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S&E: Scaled SOMBRERO accident dose
results for average weather
Site boundary dose (mSv)
Contributor
Basecase
10% gas
10% gas/ no
oxidation / no T
release
First wall
0.5
0.5
0
Blanket
1.2
1.2
0
Li2O
0
0
0
HTO
7.8
7.8
0
Xe
47
4.7
4.7
Xe*
2.4
0.24
0.24
Kr
1.1
0.11
0.11
Total w/ Xe
56
14
4.7
Total w/ Xe*
12
9.7
0.24
Total w/ Kr
11
9.6
0.11
* Xe scrubbed to remove Cs, I isotopes
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Without oxidation,
SOMBRERO has
good chance of
meeting 10 mSv
goal—even for
conservative
weather.
Substantial progress is being made
with fast ignition experiments
 Fuel assembly: experiments on Omega and Z, modeling/design for NIF concept
 Heating/transport:
‒ Planar experiments have elucidated transport physics
‒ Cone appears to concentrate and facilitate energy
transport
‒ Proton heating identified as possible alternative
‒ Optimistic results from ILE Osaka cone target
experiment: 1000 increase in D-D neutron yield,
heating to 1 keV, 30% efficient
Laser
Electrons
 Improvements in laser technology
‒ Advanced front ends allowing higher fidelity ignitor pulses
‒ Damage resistant compressor gratings that are scalable to larger (~1m) size
‒ Petawatt ignitor additions compatible with existing facilities (Omega, Z, NIF)
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FI poses new challenges for laser final
optics layout and protection
 Compression beam requirements similar to hot spot ignition
(but may not require uniform illumination)
 However, petawatt ignitor beams require development of high
energy, short-pulse compatible gratings and focusing optics
 Need to develop an appropriate solution for FI final optics
layout: number of beams, size, stand-off distance
Critical issues that need to be addressed:
-
potential for directional target output (for cone-focused design)
cone-focused design would have x-ray and debris output rivaling indirect-drive designs
optics damage threshold for high intensity laser
optimum stand off-distance compatible with spot size requirement
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New data on laser damage of multilayer
dielectric optics provides optimism for FI
20000
Damage fluence
~5 J/cm2 for 20 ps
pulse
10
Fused Silica
Surface Damage
15000
10000
5
5 kJ HEPW
5000
Beam Line Energy (Joules)
Damage Fluence (J/cm^2)
15
MLD mirrors are being
developed for HEPW
(better LIDT, h, wavefront,
and scalable to IFE)
B
Gold Grating Damage
0
0
0.1
A
1
10
100
Pulse Duration (ps)
(A) 2000 LULI: MLD grating was 2 better than gold gratings for 0.5 ps pulse
(B) Recent LULI: Intermediate dispersion gratings with low field
enhancement (~1.2) [from GA] are encouraging for >3 J/cm2 operation
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Cone focusing may be able to ease
spot size requirements
 Sentoku observed focusing of ignitor
beam due to reflection from oblique cone
surface (about factor of 4 for 60º cone)
 Could relax the spot size requirement
from 30 mm to >300 mm
 This would make FI final optic survival
easier by increasing the stand-off distance
Need to measure and model the concentration
of electron energy for laser radiation
obliquely incident at relativistic intensities on
the inner surface of the cone
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Summary & future work
 Magnetic deflection effort to be split between calculations and
experiment (fielded on LAPDU):
– 2D expansions with LSP; LSP benchmarking (energy losses)
– LSP modeling of LAPDU experiments
– LAPDU experiments – Rb vs. B0 and nplasma; axial leakage rate
 S&E work to continue as-needed; perform additional
shielding calculations when non-uniform magnet
configurations are available
 FI work will focus on development of a integrated
beam/chamber layout
 MDS work is focused on prediction of thermal conductivity
vs. dose and tritium retention for graphite
 Systems modeling moving from DPSSL to chamber scaling
work
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Chambers Phase I Goals
Chamber Wall Temperature (deg C)
1. Develop a viable first wall concept for a fusion power plant.
2. Produce a viable “point design” for a fusion power plant
3000
3000
Surface
1 micron
5 microns
10 microns
100 microns
2600
2200
1800
Surface temperature
2500
2000
1600
1500
1200
154 MJ Target
Tungsten wall @ 6.5 m radius
No gas in chamber
600
400 MJ Target
Graphite wall @ 8.25 m radius
25 mTorr Xe in chamber
1000
500
200
0
2
4
6
time (msec)
Long term material issues are
being resolved.
Example- Ion exposures on RHEPP
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8
10
0
2
4
6
time (msec)
8
10
UCSD
Wisconsin
SNL
ORNL
LLNL
UCSD
LLNL chambers: 3-year plan
 Increase options/flexibility by developing magnetically protected
chamber concept to protect against ion radiation damage:
–
–
–
–
Complete modeling for uniform-field configuration (FY03)
Field IFE-relevant experiments on LAPDU (FY03)
Propose additional experiments, if needed
Develop magnetic deflection point design, if warranted
 Scope unique aspects and feasibility of fast ignition for IFE:
– Produce a self-consistent beam/chamber layout for an FI-IFE power plant
(FY03)
– Continue to work with FI community to provide input on FI-IFE power
plants
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LLNL chambers: 3-year plan, (Cont’d.)
 Provide safety & environmental assessments:
– Assess importance of uncertainties in activation cross sections (FY03)
– Support laser-IFE community, as needed
 Investigate fundamental nature of radiation damage for materials of
interest for laser-IFE chambers:
– Produce a scaling law for graphite conductivity as a function of defect
concentration (FY03)
– Study neutron irradiation effects in tungsten or other alternate wall
materials
 Develop integrated systems modeling capability to support overall
laser-IFE program & future design efforts:
– Develop scaling relationships for candidate laser-IFE chambers (FY03)
– Work with laser-IFE community to improve models for drivers and other
power plant systems
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BACK-UP SLIDES
&
ADDITIONAL INFORMATION
Plasma expansion experiments at LAPDU
Parameters
n=1- 4 X 1012 cm-3
Te~5 eV, Ti~1 eV
B=.5 - 4 kG
Plasma Radius = 25 cm
Plasma Length = 17 m
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Plasma expansion experiments in LAPDU
The experiment proceeds as follows:
1) The probe is positioned at some point on a predetermined data acquisition plane using a
computer controlled stepper motor system,
2) Plasma is pulsed on and allowed to reach a steady state,
3) 0.5 ms before the laser is fired data acquisition begins and continues for 0.32 ms,
4) Laser fires,
5) Steps 2-4 are repeated for 5 shots at 1 Hz,
6) Target is rotated and/or translated,
7) Entire process is repeated at a new
probe location.
Data planes were taken both parallel and
perpendicular to the background magnetic
field.
Perpendicular planes were 25cm X 20cm
with .5cm interpoint spacing
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2D Observation of the diamagnetic cavity
Diamagnetic cavity is clearly visible as well as
enhancement of background field on leading edge
of expanding plasma.
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XY plane of data taken
on green line shown
above. ~ 1.5cm down Bo
from laser impact.
LAPD Upgrade: Available Diagnostics and
Infrastructure
 Over 450 Access ports
 Computer Controlled Parameters and Data Acquisition
 Data Acquisition: 20 channels @ 2GHz, add’l LF
channels
 Microwave Interferometers/ Reflectometers
 Laser Induced Fluorescence
 State of the Art Data Analysis and Visualization
 Bay: 100’ X 30’, ceiling height 15’,overhead crane
 Laser Clean Room: 20’ X 15’,(space for 4 lasers)
 Cooling water: 4.5+ Megawatt
 Electrical Power available : 4.5 MW
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Plasma expansion experiments at LAPD
(con’t)
 Number of particles in a Debye sphere nl D3 (variable
from 102 to106)
 Magnetization parameter w pe/W e (variable from
310-2 - 5104)
 Ratio of plasma kinetic energy density to magnetic energy
density b (variable from 10-7 to > 2)
 Ratio of Alfvén speed to electron thermal velocity vA/ve
(variable from .1 - 10)
 Number of axial Alfvén wavelengths (.5 - 10)
 ne ~51012 cm-3 ; Te = 10-20 eV
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Characteristics of the
laser produced plasma
Laser Beam
Background
Magnetic Field
1.5kG
.2ms
.6ms
No B
2 cm
10 ns gated imager
time series of lpp
expansion across
background magnetic
field
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1.0ms
1.4ms
1.8ms
Laser Plasma
Elpp ~ 50% laser energy = 0.75 J
Number of particles ~ 2  1015
Vperp-expansion ~ 1.4-2  107 cm/s, Vparllel-expansion ~ 1.0  107 cm/s
2.2ms
Results of plasma expansion experiments in
LAPDU
1) Bubble scaling has been verified
2) Ambipolar electric field has been observed
3) Background plasma has not been observed to effect laser-plasma diamagnetism
4) Laser-plasma diamagnetism has been observed in 2-D
5) Laser-plasma has been observed to generate current structures in the background
plasma, the magnitude of which are proportional to the background density.
6) Later time lpp expansion induces current sheets in the background plasma
7) The generated current structures radiate Alfven waves
8) For the conditions used, approximately 0.5% of the laser-produced plasma’s
kinetic energy goes into Alfvén waves.
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