Frontiers Research 2012

8/2/2019 Frontiers Research 2012

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Extremes:violent events close up

Nigel C Woolsey

York Plasma InstituteDepartment of Physics

[email protected]

Cassiopeia A, in X-rays at 300 yrsNASA/CXC/SAO


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Outline

High power lasers

Laser-plasma physics

Fusion (inertial confinement fusion, ICF)

Laboratory astrophysics


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Collaborations & funding

My students and post docs

Ozgur, Rachel and Rob

United Kingdom

Central Laser Facility, Culham Centre for Fusion, Oxford

France Ecole Polytechnique, CEA, lObservatoire de Paris

Japan

Osaka University (ILE & Graduate School)

USA

Livermore (LLNL), Rochester (LLE), Princeton


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These are big,National Ignition Facilityoccupies space of 3 football pitches

Part 1

High energy, high power lasers


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Expensive and massive

NIF has 192 beams and delivers 0.5 PW


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The 192 beams go to a 10 metre target chamber

This is the best option for laser fusion


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The oscillator(start here with nJs)

Stretch in time


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Nd:Glass lasers

These lasers operate at a wavelength of 1.53 m(photon energy ~1eV)

For many applications the laser wavelength is converted

to the UV a process called harmonic conversion

3rd harmonic gives 1.053 m/3 = 0.351 m

This increases the plasma density (by factor 10) at whichthe laser is absorbed

It increases the intensity (by factor 10) at whichresonance absorption dominates


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Use lasers to createscaled dynamicalsystems (e.g. shocks)

Laser-plasma physics

Part 2


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What happens

Laser first hits a solid Electrons absorb photons until energies exceed the

work function (called multi-photon absorption)

Occurs at intensities of ~109 W/cm2(note mixed units)

These electrons then collide with ions efficientlyabsorbing laser energy (called collisional absorption orinverse bremsstrahlung)

Occurs at intensities up to 1016 W/cm2

Above 1016 W/cm2 resonance (or collisionless)absorption dominates


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Use lasers to deposit lots of energyinto small volumes

Initial laser ablation from solid surface

Main part of laser pulse interacts with plasma plume,

absorbed up to a critical density

Critical density = density at which plasma frequencyequals laser frequency

Laser

0

2

e

epe

m

enlaser

laser

c

2

3

2laser

21

cm

m

1022

22

4

laser

ecrit

e

cmn


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Intensity

Pressure from momentum balance, p = momentum flux

Apply Newtons 2nd law: P = F/Area

Laser

Pressure generated by a modest laser

1 mm

Shockedor

ramped

Mbar201121

mI21MbarP

3232

14abl

2Wcm10s)(10cm)(0.05

J10

timeareaspot

EnergyI 1492

3

0

12g10azgA

FP

z

= 2.7 gcm-3

z = 50 m

2 1012 Pa


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What is inertial confinement fusion?

Part 3


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D + T collide, tunnel, fuse and release energy

Neutron carries away bulk of the energy (14.1MeV)

3.5 MeV particle is important for ignition and burn

Energy released from fusion is captured in a blanket &

used to heat a steam turbine

Use deuterium and tritium isotopes of H

Q = 17.6 MeV


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particle ignition and burn

The conditions (e.g. temperatures) needed are demanding.

So heat a small part of the DT to produce fusion and then

the particle to ignite and burn the rest


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The density-radius product (rho-r)

Need to re-use of boot strap the particles

The particles released by DT reaction reabsorbed in

hot region if rho-r > 0.3g/cm

2

(~ the particle range)

In solid density (0.22 g/cm3) this requires cms of DT

This is a lot. Risky! And Uncontrolled.


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The controlledICF approach ..

Take a small (1 mg) of DT,contain and freeze this aspherical capsule

Frozen DT (18 K) density is0.22 g/cm3

The next step is to compress thisx1000 solid density

At x1000 solid density heat a

central region to form a hot spot


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Lasers compress the capsule

Reach 1000x solid density

The trick is to do this with a laser, keeping the DT cool,and using the hot spot particles to heat the material

Lasers Compression IgnitionAcceleration

1. 2. 3. 4.


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Use deuterium and tritium isotopes of H

The isotopes of hydrogen collide, fuse and releaseenergy

This all occurs very quickly

Fusion lasts around 10 ps


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Problems

Rayleigh-Taylor fluid instability

This problem is solved by ensuring extremely uniform capsulesand laser focal spots

Electron preheat The laser generates high-energy electrons via resonance

absorption, and plasma instabilities

Solved (in part) by using short wavelength, UV, lasers

These are major & interesting challenges today

In a power plant the process needs repeating 5 to 10x a

second


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What is laboratory astrophysics?

supernova remnant isan example of shock

Credit: NASA

Part 4


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Plasma physics is important to

Cosmic microwave background Large scale structure

Reionisation epoch

Gravitational collapse

Primordial magnetic field Galactic formation

Stellar evolution

Nuclear reactions

Relativistic processes Cosmic rays

Jets

Gamma Ray Bursters

It is possible to addresssome aspects of these

in the laboratory

Shocks & remnants of asupernova explosion


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Interstellar medium

The local interstellar medium (ISM) composition is typical

Energy density of all components ~ 1 eV/cm3

Supernovae and supernova remnants

drive cosmic rays and grow magnetic fields

What can experiment tell us?

Component Energy density Pressure (J/m3)

Stellar radiation 0.7 eV/cm3 1.1 10-13 Pa

Cosmic microwave 0.4 eV/cm3

6.4 10-14

PaTurbulent motion 0.5 eV/cm3 8.0 10-14 Pa

Cosmic rays 1.6 eV/cm3 2.6 10-13 Pa

Magnetic field 1.5 eV/cm3 2.4 10-13 Pa


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The typical supernova remnant

Launches 1 solar mass

10,000 km/s

1044 J

Pressure

pressure: 10-7 Pa

1000 yrs old

30 light-yrs across

Into the ISM

1 particle / cm3

few G B field

Astronomy Picture of the Day4th June, 2008

blue x-rayyellowish optical

red radio


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It can be done!

Snapshot scaling is based on ideal MHD (Ryutov et al.)

Create collisionless shocks in the laboratory

Quantity SNR Laser

Distance 3x1016

m 5x10-3

m

Time 100 yrs 500 ps

Density 1 cm-3 1018 cm-3

Speed 109

cm/s 108

cm/s

Magnetic 10-10

T 20 T

Woolsey et al., Phys Plasmas 8, 2439 (2001)

labSNR

labb

cSNR

labSNR

labc

bSNR

labSNR

c

b

a

a

BB

vv

rr

=

=

=


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G Gre ori et al. Nature481, 480-483 2012 doi:10.1038/nature10747

Experimental set-up showing the laser beams anddiagnostics configuration.


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Plasma Jets

Plasma jets will be discussed by Chris Gregory on Friday

Gregory, et al, Phys Plasmas (2010); ApJ (2008); PPCF (2008)

Waugh et al, Astrophys. Space Sci. (2009)

2 mm

Shadowgraph and self emission taken

at the same time (85 ns) for the sameshot

Jets in 100mb He:+3, +4,+5 ns

Top: phasemapsBottom: electron maps


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Why lab astro

Good science that complements observations &numerical simulations

Detail of shocks and plasma conditions that are superiorto astrophysical observations

Repeatable, controllable

Access conditions that are inaccessible to numericalsimulation

study extended spatial and temporal scales

Once scaled, can study additional non-scalable physics

non-linear, multi-scale physics

There are limitations too


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Plasma temperatures and densities

RELATIVISTIC PLASMAS

QUANTUMPLASMAS

CLASSICALPLASMAS

stronglycoupledplasmas

Pulsar

MFE

IFESolar

Corona

Dis-

chargeIono-sphere

SolarWind

Magneto-sphere

Non-neutral

Thermal

processing

Lightning

White

Dwarfs

Electrons inMetals

SolarInterior

kBT=mc2

EF=e2n1/3

10

6

104

102

100

10-2

10-4

Tempe

rature(eV)

1 1010

1020

1030

Density (cm-3)

uLHRe

uLPe H

m

H

mD

uLRe

R

H

r

uLPe

Astronomical systems are large, LH is huge

Flow speeds, uare also large

Use magneto-hydrodynamics

small viscosities, resistivities and diffusivities


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Conclude

The science possible with high energy, high power laseris diverse weve looked at:

Fusion: addressing the energy need

Astrophysics: advancing fundamental knowledge

Both rely on advances in

Plasma physics

Laser technology Computational modelling

They use very similar tools by pursuing one we pursue

the other


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Thank you


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Suggested papers

Lab astro

Gregori et al. Nature 481, 480 (2012)

H-S Park et al. High Energy Density Physics 8, 38e45 (2012)

Kuramitsu et al. Phys. Rev. Lett. 106, 175002 (2011)

Woolsey et al. Plasma Phys. Control. Fusion 46, B397-B405 (2004)

ICF

Dunne et al. Nature Physics 2, 2 (2006)

Pasley and Stephens, Phys. Plasmas 14, 054501, (2007) Ribeyre et al Plasma Phys. Control. Fusion 50 025007 (2008 )

Green et al. Phys. Rev. Lett. 100, 015003 (2008)

Woolsey et al. Phys. Rev. E 53, 6396, (1996)


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Latest updates (Nov 2011)

Presented at the annual plasma meeting in USA

http://pop.aip.org/53rd_meeting

Astrophysical jets (tutorial)

http://pop.aip.org/polopoly_fs/1.2688788!/menu/standard/file/FR1Stone.pdf

http://www.sciencemag.org/content/284/5419/1488

Inertial confinement fusion

http://pop.aip.org/polopoly_fs/1.2688123!/menu/standard/file/BI3Glenzer.pdf

LIFE (https://life.llnl.gov/), HiPER (http://www.hiper-laser.org/)
http://pop.aip.org/53rd_meetinghttp://pop.aip.org/polopoly_fs/1.2688788!/menu/standard/file/FR1Stone.pdfhttp://pop.aip.org/polopoly_fs/1.2688788!/menu/standard/file/FR1Stone.pdfhttp://www.sciencemag.org/content/284/5419/1488http://pop.aip.org/polopoly_fs/1.2688123!/menu/standard/file/BI3Glenzer.pdfhttp://pop.aip.org/polopoly_fs/1.2688123!/menu/standard/file/BI3Glenzer.pdfhttps://life.llnl.gov/https://life.llnl.gov/https://life.llnl.gov/http://pop.aip.org/polopoly_fs/1.2688123!/menu/standard/file/BI3Glenzer.pdfhttp://pop.aip.org/polopoly_fs/1.2688123!/menu/standard/file/BI3Glenzer.pdfhttp://pop.aip.org/polopoly_fs/1.2688123!/menu/standard/file/BI3Glenzer.pdfhttp://www.sciencemag.org/content/284/5419/1488http://www.sciencemag.org/content/284/5419/1488http://pop.aip.org/polopoly_fs/1.2688788!/menu/standard/file/FR1Stone.pdfhttp://pop.aip.org/polopoly_fs/1.2688788!/menu/standard/file/FR1Stone.pdfhttp://pop.aip.org/polopoly_fs/1.2688788!/menu/standard/file/FR1Stone.pdfhttp://pop.aip.org/53rd_meeting

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Frontiers Research 2012