external user perspective burning plasmas s j rose ... · 500Å naf/fe. sampled bathed in radiation...

External user perspectiveBurning plasmas

S J RoseImperial College London

Overview

Potential for experimental measurement of microphysics processes in a burning plasma

• Kinetic processes

• Survival of bound electronic structure - spectroscopy

Applications of the output from a burning plasma

• Photoionised plasmas


Kinetic processes

Many aspects of the microphysics of burning plasmas have not been tested experimentally

α

n

radiationInelastic collisions

Inelastic collisions

Inelastic collisionsem+nuclear

nuclear reactions

bremmsstrahlung/scattering

thermalnon-thermal

free electrons

DT ions




α

n




nuclear reactions


thermalnon-thermal

free electrons

DT ions



For Te < 32keV


α

n




nuclear reactions


thermalnon-thermal

free electrons

DT ions



For Te > 32keV

Heating of 2keV, 300gcm-3 plasma (D,T and electrons) with 3.6MeV alpha particles

n α = 0.125nD

α heats electrons

α heats ions

Sherlock and Rose, HEDP (2008)

T energy distribution at 14psec

Sherlock and Rose, HEDP (2008)

α

n




nuclear reactions


thermalnon-thermal

free electrons

DT ions



Possibility exists of driving non-thermal aspect to fusion

Brueckner and Brysk, J Plasma Phys (1973)Brueckner, Brysk and Janda J Plasma Phys (1974)


Survival of bound electronic structure - spectroscopy

Introduction of bound electrons perturbs kinetics and allows spectroscopic diagnostic possibilities

α

n




nuclear reactions


thermalnon-thermal

free electrons

DT, X ions



bound electrons

ion collisional excitation photoexcitation / potoionisation

ion collisional excitation

Radiation intensity for DT,25keV, 500gcm-3, ρr=2.5gcm-2

1 10 100 10001021

1022

1023

1024

1025in

tens

ity (e

rg/c

m2 /s

/keV

/ste

r)

photon energy (keV)

Compton scattering not included Compton scattering included

High-Z-doped DT implosion

• High-Z dopant (Kr) needed to retain bound electrons at high Te

• High density gives a large depression of the continuum (only Kr n=1 and 2 survive).

• High temperature leads to non-LTE populations.

• Populations come into a steady-state in 100fsec.

Time-dependence of ionisation of Kr in DTTe=25keV, ρ=500gcm-3

1 10 10010-2

10-1

100

101

LTE non-LTE

n=1

n=2

n=1

shel

l pop

ulat

ion

time (fsec)

Distribution of ionisation of Kr in D0.49995T0.49995Kr0.0001Te=25keV, ρ=500gcm-3, ρr=2.5gcm-2

33 34 35 360.0

0.1

0.2

0.3

0.4

0.5

Li-like He-like H-like fullystripped

no escape factor, no radiation field escape factor, no scattering, no radiation field escape factor, scattering, no radiation field no escape factor, Comptonised bremsstrahlung field

popu

latio

n fra

ctio

n

ionisation stage

Emission from D0.49995T0.49995Kr0.0001Te=25keV, ρ=500gcm-3, ρr=2.5gcm-2

1 10 100 10001021

1022

1023

1024

1025

no line contribution line contribution total

inte

nsity

(erg

/cm

2 /s/k

eV/s

t)

photon energy (keV)

Applications of the output from a burning plasma

Photoionised plasmas

Accretion-powered objects

Photoionised plasmas (radiation-dominated plasmas) scale with the ionisation parameter ξ=4πF/ne

Tarter, Tucker and Salpeter, ApJ, 156, 943,(1969)Tarter and Salpeter, ApJ, 156, 953 (1969)

EXO 0748-676

Low mass X-ray binary

ξ=30 ergcms-1

NGC 4593

Seyfert galaxy

ξ=300 ergcms-1

Spectral interpretationneeds reliable models

Photoionised plasma experiments have only reached ξ=20ergcms-1

Foord, Heeter, van Hoof, Thoe, Bailey, Cuneo, Chung, Liedahl, Fournier, Chandler, Jonauskas, Kisielius, Mix, Ramsbottom, Springer, Keenan, Rose and Goldstein, Phys Rev Letts, (2004)

collapsed Z-pinchpinhole camera

flux and spectral measurements

absorptionspectrum

emissionspectrum

1000Å CH

500Å NaF/Fe

sampled bathed in radiation frompinch over 4πα steradians

13 14 15 16 17 18 190.0

0.2

0.4

0.6

0.8

1.0

fract

ion

Z*

experiment NIMP with radiation field CLOUDY with radiation field NIMP without radiation field

Much higher ξ values could be obtained by using radiation output from a burning capsule on NIF, allowing access to most extreme astrophysical photoionised plasma conditions.

Photoionised experiments using radiation output from NIF capsule

Much higher ξ values could be obtained by using radiation output from a burning capsule on NIF, allowing access to most extreme astrophysical photoionised plasma conditions.(see: Fujioka et al, arXiv:0909.0315v1)

Conclusions

• Operation of the NIF target depends critically on microphysics of burn (connected to the transport properties). No experiments to measure kinetics in the burning phase, although some experiments have measured rates in cooler phase.

• Kinetic modelling of ion distributions shows no effect from fast alphas. However other studies show 10-20% effect which include large-angle scattering, nuclear interactions and neutron scattering kinetically. Possibility of measuring non-thermal aspect to burn?

• High-Z spectroscopy of doped plasma may be able to diagnose conditions through usual spectroscopic techniques.

• High photon output could be used to drive photoionised plasma experiment with ξ~100 ergcms-1.

external user perspective burning plasmas s j rose ... · 500Å naf/fe. sampled bathed in radiation...

Documents