atomic structure, radiation, collisions: what s in it for
TRANSCRIPT
YR, ICTP/IAEA School, 2019
Atomic structure, radiation, collisions:
whatβs in it for plasmas?..Yuri Ralchenko
National Institute of Standards and Technology
Gaithersburg, MD 20899, USA
YR, ICTP/IAEA School, 2019
plasma
t=0
The story of a photon
YR, ICTP/IAEA School, 2019
Questions to ask
β’ Why was the photon created?
β’ Who created the photon?
β’ What was the probability for the photon to be created?
β’ How does the plasma environment affect photon creation?
β’ How did the photon propagate in the plasma?
β’ What has changed when the photon was recorded?
β’ β¦β¦β¦β¦β¦
YR, ICTP/IAEA School, 2019
ΰ΅»Ξ¨π πβ², πβ², πβ², . . . Ξ Ϋ§Ξ¨π π, π, π, . . .
initial statefinal stateinteractionoperator
Most of the relevant physics is inside this matrix element
Why is atomic structure important for plasmas?
β’ Wavelengthsβ’ Energiesβ’ Transition probabilities (radiative and non-radiative)β’ Collisional cross sectionsβ’ β¦
YR, ICTP/IAEA School, 2019
A Few Textbooks on APPβ H.R. Griem
β Plasma Spectroscopy (1964)
β Principles of Plasma Spectroscopy (1997)
β R.D. Cowan
β Theory of Atomic Structure and Spectra (1981)
β V.P. Shevelko and L.A. Vainshtein
β Atomic Physics for Hot Plasmas (1993)
β D. Salzmann
β Atomic Physics in Hot Plasmas (1998)
β’ T. Fujimotoβ’ Plasma Spectroscopy (2004)
β’ H.-J. Kunzeβ’ Introduction to Plasma
Spectroscopy (2009)
β’ J. Bauche, C. Bauche-Arnoult, O. Peyrusseβ’ Atomic Properties in Hot
Plasmas (2015)
β’ Modern Methods in Collisional-Radiative Modeling of Plasmas (2016)β’ HKC, CJF, YR,β¦
YR, ICTP/IAEA School, 2019
Units
β’ Energyβ’ 1 Ry = 13.61 eV = 109 737 cm-1 (ionization energy of H)
β’ 1 eV = 8065.5447 cm-1
β’ Lengthβ’ a0 = 5.2910-9 cm = 0.529 Γ (radius of H atom)
β’ Area (cross section)β’ a0
2 = 8.8 10-17 cm2 (area of H atom)
β’ New SI (redefinition of base units): May 20 2019
http://physics.nist.gov/cuu/Units/
YR, ICTP/IAEA School, 2019
What kind of atomic data is of importance for spectroscopic diagnostics of plasmas?
β’ Wavelengths of spectral lines
β’ Line/level identifications
β’ Level energies
β’ Transition probabilities (radiative and non-radiative processes)
β’ Collisional cross sections and rate coefficients
β’ Spectral line shapes and widths
YR, ICTP/IAEA School, 2019
16-electron ion (S-like): how to describe its atomic structure?..
8
Averageatom
122836
1224344452
12283541
Superconfiguration
3s23p34s
3s23p3d24p
Configuration 5S
3S
3D
1D
3P
1P
LS term
3D1
3D2
3D3
Level
YR, ICTP/IAEA School, 2019
Hydrogen and H-like ions
Hydrogen atom H-like ion
Radius:
Energy:
1 R
y =
13
.61 e
V
ππ ~π2
π
πΈπ = βπππ π¦
π2
YR, ICTP/IAEA School, 2019
Each atomic state (wavefunction) is characterized by a set of quantum numbers
β’ Generally speaking, only two are exact for an isolated atom:β’ Total angular momentum J
β’ Parity = β1 Οπ ππ (but: weak interactions!)
β’ They are the consequences of conservation lawsβ’ Noether theorem (1915)
β’ Everything else (total L, total S,β¦) is not exact!
YR, ICTP/IAEA School, 2019
Complex atoms (non-relativistic)
π» = π»πππ + π»ππππβππ’ππ + π»ππππβππππ + π»π βπ + β¦
= β
π
1
2π»π2 β
π
π
ππ+
π>π
1
πππ+
π
1
2ππ ππ ππ β ππ + β¦
The SchrΓΆdinger equation for multi-electron atoms cannot be solved exactlyβ¦
π»Ξ¨ π1, π2, β¦ = πΈΞ¨ π1, π2, β¦
We know all important interactions:
YR, ICTP/IAEA School, 2019
Standard procedureβ’ Use central-field approximation to approximate the effects of the
Coulomb repulsion among the electrons:
β’ π» β π»0 = Οππ β
1
2π»π2 β
π
ππ+ π ππ
β’ Properly choose the potential V(r)
β’ Find configuration state functions Ξ¦ πΎππΏπ (accounting also for antisymmetry): n,l
β’ Assume that the atomic state function is a linear combination of CSFs: Ξ¨ πΎπΏπ = Οπ
π ππΞ¦ πΎππΏπ
β’ Solve Schrodinger equation for mixing coefficients:
β’ π» β πΈ απΌ ΖΈπ = 0, π»ππ = Ξ¦ πΎππΏπ π» Ξ¦ πΎππΏπ
β’ Include other effects (perturbation theory)β¦and live happily!
YR, ICTP/IAEA School, 2019
Relativistic atomic structure: heavy and not so heavy ions
π»π·πΆ =
π
π πΆπ β ππ + πππ’π ππ + π½ππ2 +
π>π
1
πππ
π β‘ βππ΅ electron momentum operator
πΆ, π½ 4x4 Dirac matrices
Dirac-CoulombHamiltonian
π»ππ = β
π>π
πΌπ β πΌπ πππ ππππππ/π
πππ+ πΆπ β π΅π πΆπ β π΅π
πππ ππππππ/π β 1
πππ2 πππ/π
2
πππ’π π extended nuclear charge distribution
Transverse photons (magnetic interactions and retardation effects):
QED effects: self energy (SE), vacuum polarization (VP)
π»π·πΆπ΅+ππΈπ· = π»π·πΆ +π»ππ + π»ππΈ +π»ππ
YR, ICTP/IAEA School, 2019
Relativistic notations
s1/2 p1/2 p3/2 d3/2 d5/2 f5/2 f7/2
s p- p+ d- d+ f- f+
l 0 1 1 2 2 3 3
j Β½ Β½ 3/2 3/2 5/2 5/2 7/2
πΒ± β π = π Β± 1/2
YR, ICTP/IAEA School, 2019
Energy structure of an ion
Electrons are grouped into shells nl(K n=1, L n=2, M n=3,...)producing configurations (or even superconfigurations)
~Z2
~Z ~Z4
termslevels
electron-nucleusinteraction
electron-electroninteraction
spin-orbit(relativistic effects)
Every state is defined by a set ofquantum numbers which are mostlyapproximate
Continuum
Boundstates
YR, ICTP/IAEA School, 2019
Z-scaling of electron energies
πΈ0 = β1
π2
π» =
π
ππ2
2βπ
ππ+
π>π
1
πππ
New variables ππ = πππ , ππ = ππ/π lead to:
π» = π2
π
ππ2
2β1
ππ+ π
π>π
1
πππ= π2 π»0 + πβ1π
Kinetic+nuclear
electrons
π»π = πΈπ β π»0 + πβ1π π = πβ2πΈ π
πΈ = π2 πΈ0 + πβ1πΈ1 + πβ2πΈ2 +β―
Therefore, for high Z the energy structure looks more and more H-like!
YR, ICTP/IAEA School, 2019
Mg-like Al II: 3l3l'
Ionization potential
2p63s2
Grotrian diagram
YR, ICTP/IAEA School, 2019
Mg-like Sr XXVII: 3l3l'
Ionization potential
2p63s2
YR, ICTP/IAEA School, 2019
Importance of Zc
Spectroscopic charge: Zc= ion charge + 1 (H I, Ar XVβ¦)
This is the charge that is seen by the outermost (valence) electron
Isoelectronic sequences: ions with the same number of electronsβ’ Li I, Be II, B III,β¦
It is often useful to consider variation of atomic parameters along isoelectronic sequences
YR, ICTP/IAEA School, 2019
Spin-orbit interaction
Hydrogenic ion: πππ =π π¦ πΌ2 π4
π3 π π + 1/2 π + 1
Semi-theoretical Lande formula: πππ =π π¦ πΌ2 ππ
2 ΰ·¨π2
πβ3 π π + 1/2 π + 1
n*: effective n πΌ =π π¦ ππ
2
πβ2
ΰ·¨π: effective nuclear charge (for penetrating orbits) = Z-n for np orbitals
π» = β
π
1
2π»π2 β
π
π
ππ+
π>π
1
πππ+
π
1
2ππ ππ ππ β ππ + β¦
YR, ICTP/IAEA School, 2019
Types of coupling
β’ LS coupling: electron-electron Β» spin-orbitβ’ light elements
β’ jj coupling: spin-orbit Β» electron-electronβ’ heavy elements
β’ 2s2p: (2s1/2,2p1/2) or (2s,2p-)
β’ 3d5: ((3d-3)5/2,(3d+
2)2)3/2
β’ Intermediate coupling: neither is overwhelmingly strong
β’ Other types of couplings exist
πΏ = Τ¦π1 + Τ¦π2+. . . , Τ¦π = Τ¦π 1 + Τ¦π 2+. . . , Τ¦π½ = πΏ + Τ¦π
Τ¦π1 = Τ¦π1 + Τ¦π 1, Τ¦π2 = Τ¦π2 + Τ¦π 2, . . . Τ¦π½ = Τ¦π1 + Τ¦π2+. . .
YR, ICTP/IAEA School, 2019
sp
1P
3P
1P1
3P2
3P1
3P0
terms levels states
M
+1-1 0
0-1+1
-2
+2
electro-static
spin-orbit
magneticfield
+1-1 0
0
+G1
-G1
Configuration sp: LS coupling (LSJ)
YR, ICTP/IAEA School, 2019
sp
(1/2,3/2)
terms levels states
M
+1-1 0
0-1+1
-2
+2
spin-orbit
electro-static
magneticfield
+1-1
0
0
Configuration sp: jj coupling
(1/2,1/2)
(1/2,3/2)1
(1/2,3/2)2
(1/2,1/2)1
(1/2,1/2)0
YR, ICTP/IAEA School, 2019
From LS to jj: 1s2p in He-like ions
1P1
YR, ICTP/IAEA School, 2019
Spin-orbit interaction does depend on nuclear charge!
Landeformula
πππ =π π¦ πΌ2 ππ
2 ΰ·¨π2
πβ3 π π + 1/2 π + 1
YR, ICTP/IAEA School, 2019
Na-like doublet: from neutral to HCI
D1
D2
5890 Γ
5896 Γ
0.1%
Fraunhofer absorption linesin the solar spectrum
D1: 3s1/2 β 3p1/2
D2: 3s1/2 β 3p3/2
YR, ICTP/IAEA School, 2019
D1
D2
5890 Γ
5896 Γ
0.1%3p3/2
3p1/2
Na-like doublet: from neutral to HCI
YR, ICTP/IAEA School, 2019
Sodium Atom (Na0+)
Sodium-like Tungsten (W63+)
Little Ions With a Big Charge
11 electrons
YR, ICTP/IAEA School, 2019
D-doublet in Na-like W, Hf, Ta, and Au
J.D. Gillaspy et al,
Phys. Rev. A 80,
010501 (2009)
YR, ICTP/IAEA School, 2019
State mixing in intermediate coupling
expansion coefficients
He-like Na9+: 1s2p 3P1
= 0.999 3P + 0.032 1PHe-like Fe24+: 1s2p 3P
1= 0.960 3P + 0.281 1P
He-like Mo40+: 1s2p 3P1
= 0.874 3P + 0.486 1P
Ξ¨ π, π, π, . . .= πΌ β Ξ¨1 π, π, π, . . . + π½ β Ξ¨2 π, π, π, . . . + πΎ β Ξ¨3 π, π, π, . . . +. . .
Very, VERY important for radiative transitions!!!
YR, ICTP/IAEA School, 2019
Hundβs rules (equivalent electrons, LS)β’ Largest S has the lowest
energy
β’ Largest L with the same Shas the lowest energy
β’ For atoms with less-than half-filled shells, lowest Jhas lowest energy
C I
O I
YR, ICTP/IAEA School, 2019
SuperconfigurationsMotivation: for very complex atoms (ions) not only the number of levels isoverwhelmingly large, but also the number of configurations
Example: 1s22s22p53s1s22s22p53p1s22s22p53d1s22s2p63s1s22s2p63p1s22s2p63d
(1s)2(2s2p)7(3s3p3d)1 β‘ (1)2(2)7(3)1
different nβs
BUT: (1s)2(2s2p)7(3s3p3d4s4p4d4f)1
Instead of producing millions or billions of lines, SCs are used to calculate Super Transition Arrays
Statistical methods
See J. Bauche et alβs book (2015)
YR, ICTP/IAEA School, 2019
Superconfigurations vs.detailed level accounting
Ga: photoabsorptioncross section
Iglesias et al (1995)
YR, ICTP/IAEA School, 2019
Ionization potentialsβ’ IPs are directly connected with ionization
distributions in plasmas
β’ Most often are determined from Rydberg series
1 10 10010
100
1000
10000
Ioniz
atio
n p
ote
ntia
l (e
V)
Spectroscopic charge, Zsp=z+1
IP
A + B*Zc + C*Z2c
Ne-like ions: 1s22s22p6
experiment
int/ext
theory
YR, ICTP/IAEA School, 2019
Ionization potentials of W ions
Closed-shell ions exist for wideranges of plasma temperatures
π2π π¦ = 74505 ππ
πΌ π73+ = 80756 ππ
YR, ICTP/IAEA School, 2019
Ionization potential: constant?..
β’ IP is a function of plasma conditions
β’ High-lying states are no longer bound due to interactions with neighboring atoms, ions, and electrons
β’ Orbit radius in H I: where is n=300,000?
YR, ICTP/IAEA School, 2019
-4 -3 -2 -1 0 1 2 3 4-15
-10
-5
0
Energ
y (
eV
)
X
n=1
n=2
n=3n=4
β1
π
continuum
Isolated atom
YR, ICTP/IAEA School, 2019
-4 -3 -2 -1 0 1 2 3 4-15
-10
-5
0
Energ
y (
eV
)
X
unbound
QM tunneling
Ionizationpotential
depression
Stewart-Pyatt: βπΌ β 2.2 β 10β7π§
ππ1 +
ππ
ππ
3 2/3
βππ
ππ
2(eV)
YR, ICTP/IAEA School, 2019
Atomic Structure Methods and Codesβ Coulomb approximation (Bates-Damgaard)
β Thomas-Fermi (SUPERSTRUCTURE, AUTOSTRUCTURE)
β Single-configuration Hartree-Fock (self-consistent field)
β Cowanβs code (LANL)
β Model potential (including relativistic)
β HULLAC, FAC
β Multiconfiguration non-relativistic HF (http://nlte.nist.gov/MCHF)
β Multiconfiguration Dirac-(Hartree)-Fock (MCDF or MCDHF)
β GRASP2K (http://nlte.nist.gov/MCHF)
β Desclauxβs code
β Various perturbation theory methods (MBPT, RMBPT)
β B-splines
http://plasma-gate.weizmann.ac.il/directories/free-software/
YR, ICTP/IAEA School, 2019
Atomic Structure & Spectra Databases
β’ (Reasonably) Extensive list β’ http://plasma-gate.weizmann.ac.il/directories/databases/
β’ Evaluated and recommended dataβ’ NIST Atomic Spectra Database http://physics.nist.gov/asd
β’ Level energies, ionization potentials, spectral lines, transition probabilities
β’ Other data collectionsβ’ VALD (Sweden)β’ SPECTR-W3 (Russia)β’ CAMDB (China)β’ CHIANTI (USA/UK/β¦)β’ Kurucz databases (USA)β’ GENIE (IAEA)β’ β¦
YR, ICTP/IAEA School, 2019
Now to radiative processesβ¦
YR, ICTP/IAEA School, 2019
Three major sources of photons
β’ Free-free transitions (bremsstrahlung)β’ Az+ + e β Az+ + e + hΞ½
β’ Free-bound transitions (radiative recombination)β’ Az+ + e β A(z-1)+ + hΞ½
β’ Bound-bound transitionsβ’ Aj
z+ β Aiz+ + hΞ½
Ener
gy
Continuum
Bound states
A
B
C
Ionizationenergy
YR, ICTP/IAEA School, 2019
βBremsstrahlung (free-free)
β’ Calculation is straightforward for Maxwellian electrons off bare nuclei of Z:
β’ Total power loss
β’ Multicomponent plasma:
+
E1
E2
( )( )
( )
,1
33
322
2/1
2
3
0e
ffT
hc
e
eZ
ff TGeT
RyZNN
Ryace
β
=
= β
3
2/1
2451051.4cmsr
WNN
Ry
TZ ez
eff
Dominant at longer wavelengths
( ) ( )
===
zi
i
zi
zi
i
zi
zi
i
zi
e
eff
ff
eff
ff
Nz
NzNz
NzHz
,
,
2
,
21;
Maximum emission at eVT
nm
e
620max =
YR, ICTP/IAEA School, 2019
Bremsstrahlung (contβd)
π π ππ = π π ππ π =2ππ
π
( )( )
( )
,33
642/1
2
3
0e
ffT
e
eZ
ff TGeT
RyZNN
c
Ryace
β
=
ππππ
πΈ β π΄πβπΈππ
YR, ICTP/IAEA School, 2019
Spectral Line Intensity
Einstein coefficient ortransition probability (s-1)
Upper state density (cm-3)
Photon energy (erg)Energy emitted due to a specifictransition from a unit volumeper unit time
(almost) purelyatomic parametersstrongly depends
on plasma conditions ijijjij EANI =
YR, ICTP/IAEA School, 2019
BB Radiative transitions
β Classical rate of loss of energy: dE/dt ~ |a|2, and decay rate ~ |r|2 for harmonic oscillator
β Quantum treatment:
β eikr = 1+ikr+β¦ 1 (electric dipole or E1 = allowed)
β Velocity form:
β Length form:
i
rki
f ea
if
if r
must be equal foran exact wavefunction(good test!)
YR, ICTP/IAEA School, 2019
Why would a STATIONARY excited state of the atomic Hamiltonian not live forever but rather experience a radiative decay to a lower state?..
QUESTION:
YR, ICTP/IAEA School, 2019
S, f, and A (1)
β’ Line strength β’ Symmetric w/r to initial-final
β’ Oscillator strength (absorption or emission)β’ gjfij = gifji (gj = 2Jj+1); dimensionless
β’ Typical values for strong lines: ~ 0.1-1
j
iijji SjriS ==
2
SRy
E
gf
i
ij
=
3
1
YR, ICTP/IAEA School, 2019
S, f, and A (2)
β’ Transition probability (or Einstein coefficient)
β’ Typical values for neutrals: ~108-109 s-1
j
i
( ) ][103.4 127 β= sfeVEg
gA ij
j
iji
ijijijjiji BgBgBc
hA == ,
22
3
Lifetime: j=1/Ξ£iAji
H I: 4.7e8 (1-2)5.6e7 (1-3)
He I: 1.8e9 (1s2-1s2p)5.7e8 (1s2-1s3p)
YR, ICTP/IAEA School, 2019
Selection rules and Z-scaling
Fundamental law: parity and J do not change
Before:
After:
jj JP
phiphi JJPP
+
Exact selection rules:Pj = - Pi
|J| β€ 1, 0 β 0 (Jj+Ji1)
Pph = -1Jph(E1) = 1
Approximate selection rules (for LS coupling):S = 0, |L| β€ 1, 0 β 0
Intercombination transitions: S β 02s2 1S0 β 2s2p 3P1
YR, ICTP/IAEA School, 2019
Selection rules and Z-scaling
β’n β 0β’ r Z-1 S Z-2
β’ E Z2 f Z0
β’A Z4
β’n = 0β’ r Z-1 S Z-2
β’ E Z f Z-1
β’A Z
ijji SjriS ==2
YR, ICTP/IAEA School, 2019
Some useful info
β’ βLeftβ is stronger than βrightββ’ f(l = -1) > f(l = +1)
β’ He Iβ’ f(1s2p 1P1 β 1s3s 1S0) = 0.049
β’ f(1s2p 1P1 β 1s3d 1D2) = 0.71
β’ Level groupingβ’ Average over initial states
β’ Sum over final states
β’ Example: from levels to terms
β’ Any physical parameter
sp
d
p
j
i
A
B
=
i
j
j
j
ijj
BAg
g
YR, ICTP/IAEA School, 2019
Principal quantum number n
β’ n-dependence for f:
β’ n-dependence for A
β’ Total radiative rate from a specific n
( )
( )
( )3
2
12
3
2
5
1
3
2
2
2
1
21
1
245.033
41
1111
33
32
nnnf
nnnf
nnnnnnf
=
ββ
β
( )2/9
410106.1
n
ZnAZ
( )3
2
12
1
nnnA
YR, ICTP/IAEA School, 2019
Mixing effects
He-like Na9+: 1s2p 3P1
= 0.999 3P + 0.032 1PHe-like Fe24+: 1s2p 3P
1= 0.960 3P + 0.281 1P
He-like Mo40+: 1s2p 3P1
= 0.874 3P + 0.486 1P
Z 1s2 1S0 - 1s2p 1P1 1s2 1S0 - 1s2p 3P1
2 1.8(9) 1.8(2)
11 1.3(13) 1.4(10)
26 4.6(14) 4.4(13)
42 2.6(15) 9.0(14)
54 6.7(15) 3.0(15)
74 2.2(16) 1.2(16)
YR, ICTP/IAEA School, 2019
Quick estimates of A
( ) ][103.4 127 β= sfeVEg
gA ij
j
iji
Calculate A(Fe24+ 1s2 1S0 - 1s2p 1P1) if f(O6+ 1s2 1S0 - 1s2p 1P1) = 0.7
NIST ASD: 4.6Β·1014 s-1 (<10%)
YR, ICTP/IAEA School, 2019
Forbidden transitions (high multipoles)
β’ QED: En, Mn (n=1, 2,β¦)
β’ E1/M1 dipole, E2/M2 quadrupole, E3/M3 octupole,β¦
β’ Selection rulesβ’ PjPi
β’ +1 for M1, E2, M3,β¦β’ -1 for E1, M2, E3,β¦
β’ Jph(En/Mn) = n
β’ M3 and E3 were measured!
β’ Magnetic dipole (M1)β’ Stronger within the same
configuration/term
β’ A Z6 or stronger
β’ Same parity, |J| β€ 1, Jj+Ji1
β’ Electric quadrupole (E2)β’ Stronger between
configurations/terms
β’ A Z6 or stronger
β’ Same parity, |J| β€ 2, Jj+Ji2
Generally weakβ¦
YR, ICTP/IAEA School, 2019
Aurora borealis
YR, ICTP/IAEA School, 2019
Forbidden transitions: auroras
O I 2p4
3P
1D
1S E2: 5577 Γ M1: 6300 Γ M1: 6364 Γ
Wavelength Transition A(s-1)
2958 1S0-3P2 E2: 2.42(-4)
2972 1S0-3P1 M1: 7.54(-2)
5577 1S0-1D2 E2: 1.26(+0)
6300 1D2-3P2 M1: 5.63(-3)
6300 1D2-3P2 E2: 2.11(-5)
6364 1D2-3P1 M1: 1.82(-3)
6364 1D2-3P1 E2: 3.39(-6)
6392 1D2-3P0 E2: 8.60(-7)
YR, ICTP/IAEA School, 2019
Scaling in Ne-like ions
JΓΆnsson et al, 2011
YR, ICTP/IAEA School, 2019
Forbidden transitions: highly-charged W
W52+
W52+
W52+
W51+
W53+
W53+
W51+
Practically all strong lines are due to M1 transitionswithin 3dn ground configurations
EBIT spectrum: EB = 5500 eV
A ~ 104-106 s-1
YR, ICTP/IAEA School, 2019
He-like Ar Levels and Lines
1s2 1S0
1s2s 1S0
1s2p 1P1
1s2s 3S1
1s2p 3P0
1s2p 3P1
1s2p 3P2
W
X
YZ
E1
2E1
Line He0 Ar16+ Fe25+ Kr34+
W 1.8(9) 1.1(14) 4.6(14) 1.5(15)
Y 1.8(2) 1.8(12) 4.4(13) 3.9(14)
X 3.3(-1) 3.1(8) 6.5(9) 9.3(10)
Z 1.3(-4) 4.8(6) 2.1(8) 5.8(9)
YR, ICTP/IAEA School, 2019
Z-scaling of Aβs
β’ W[E1]: A(1s2 1S0 β 1s2p 1P1) Z4
β’ ΞJ = 1, P1*P2 = -1, ΞS = 0
β’ Y[E1]: A(1s2 1S0 β 1s2p 3P1)β’ ΞJ = 1, P1*P2 = -1, ΞS = 1
β’ Z10 for low Z
β’ Z8 for large Z
β’ Z4 for very large Z
β’ X[M2]: A(1s2 1S0 β 1s2p 3P2) Z8
β’ ΞJ = 2, P1*P2 = -1, ΞS = 1
β’ Z[M1]: A(1s2 1S0 β 1s2s 3S1) Z10
β’ ΞJ = 1, P1*P2 = -1, ΞS = 1
YR, ICTP/IAEA School, 2019
j
i
t ~ 1/A
Why are the forbidden lines sensitive to density?
YR, ICTP/IAEA School, 2019
Radiative Recombination
AZ+ + e β A(Z-1) + hh = E + I
E
I
Semiclassical Kramers cross section: ( ) 2
0
3
5
4
33
64a
IE
Ry
n
ZEKr
+=
Quantummechanical cross section: ( ) ( ) ( )EGEE bf
nKrph =
Cross section Z-scaling:
22
1
ZZ
h
(inverse of photoionization)
YR, ICTP/IAEA School, 2019
FF+BF at Alcator C-mod: 1 eV, H
Edge: n=1
n=2
n=3
Lumma et al (1997)
YR, ICTP/IAEA School, 2019
Collisions in plasmas
β’ More than one particle: collisions!
β’ Elastic, inelastic
projectile_density[1/cm3] *velocity[cm/s] *effective_area[cm2]
Number of collisions per unit time:
v
Equilibrium plasma: Te = TA
π£ππ£π΄
=π
ππ
Electrons are much faster!
[1/s]
YR, ICTP/IAEA School, 2019
Collision (excitation)
e
ΞE
ΞE
.
..
Continuum
Atom
Main binary quantity: cross section (E) [cm2]
Effective area for a particular process
Process rate in plasmas:
π [π β1] = π πv β‘ π ΰΆ±
πΈπππ
πΈπππ₯
π πΈ β v β π πΈ ππΈ
π πΈ = ΰΆ± π πΈ, π, π2
πΞ©
rate coefficient
f is the scattering amplitude
Physics is here!
YR, ICTP/IAEA School, 2019
Basic Parameters
β Cross sections are probabilities
β Classically:
β Typical values for atomic cross sections
β a0 ~ 5Β·10-9 cm a02 ~ 10-16 cm2
β Collision strength Ξ© (dimensionless, on the order of unity):
β Ratio of cross section to the de Broglie wavelength squared
β Symmetric w/r to initial and final states
π ΞπΈ, πΈ = ΰΆ±
0
β
π ΞπΈ, πΈ, π β 2ππππ
πππ πΈ = ππ02π π¦
πππΈΞ©ππ πΈ
Ο
v
YR, ICTP/IAEA School, 2019
Direct and inverse
β’ Quantum mechanics tells us that characteristics of direct and inverse processes are related
excitation
deexcitation
Ξ©ππ πΈ + ΞπΈ = Ξ©ππ πΈ
i
j
ππ πΈ + ΞπΈ πππ₯π πΈ + ΞπΈ = πππΈπππ₯π πΈ
ΞE is the excitation threshold
ππ ππ£ ππ₯π = ππ ππ£ ππ₯π β πβΞπΈ/π
Klein-Rosseland formula:
Milne formula for photoionization/photorecombination: βπ = πΈ + πΌπ
ππ§ππβ βπ =2ππ2
β2π2ππ§+1πππ πΈπ΄ + βπ β π΄+ + π
π΄ π + π β π΄ π + π Rates:
YR, ICTP/IAEA School, 2019
Types of transitions for excitation
β Optically(dipole)-allowed
β PΒ·P' = -1 (different parity)
β |βl| = 1
β βS = 0
β (Eββ) ~ ln(E)/E
β Optically(dipole)-forbidden
β βS = 0
β (Eββ) ~ 1/E
β Spin-forbidden (EXCHANGE! Coulomb does not change spinβ¦)
β βS β 0
β (Eββ) ~ 1/E3
Examples in He I:
1s2 1S β 1s2p 1P
1s2p 3P β 1s4d 3D
1s2s 1S β 1s3s 1S
1s2s 3S β 1s4d 3D
1s2 1S β 1s2p 3P
1s2p 3P β 1s4d 1D
YR, ICTP/IAEA School, 2019
Order of cross sectionsβ General order
β optically allowed > optically forbidden > spin forbidden
β OA: long-distance, similar to E1 radiative transitions
β The larger Ξl, the smaller cross section
Li-like ions: 2s β 2p excitation
Excitation cross sections for ions are NOTzero at the threshold
+e-
YR, ICTP/IAEA School, 2019
From cross sections to rates
vπ = ΰΆ±
πΈπππ
πΈπππ₯
v β π πΈ β π πΈ ππΈπππ₯π€ 8
πππ3
1/2
ΰΆ±
ΞπΈ
β
πΈ β π πΈ β πβπΈ/πππΈ
For (E) = A/E: π£π βπβ
ΞπΈπ
π
Rate coefficients for an arbitrary energy distribution function
Often only threshold is important:
πΎ ππ =1
ππΰΆ±Ξ© πΈ exp β
πΈ
ππππΈ
π ππ ππ
=8
ππππ
1/2ππ0
2
πππ π¦ β πΎππ ππ
Effective collision strength:
YR, ICTP/IAEA School, 2019
van Regemorter-Seaton-Bethe formula
β Optically-allowed excitationsGaunt factor
oscillatorstrength
Xβ‘E/ΞEijπππ πΈ = ππ0
28π
3
π π¦
ΞπΈππ
2π π
ππππ
π β β : π π β3
2πln π π πΈ β
6.51 β 10β14
ΞπΈ ππ 2
ln( π)
ππππ ππβ2
βRecommendedβ Gaunt factors:
π Ξπ = 0, π = 0.33 β0.3
π+0.08
π2ln π
π Ξπ β 0, π =3
2πβ0.18
πln π
Atoms:
π Ξπ = 0, π = 1 β1
π0.7 +
1
π0.6 +
3
2πln π
π Ξπ β 0, π = 0.2 π < 2 ,3
2πln π πππ π β₯ 2
Ions:
YR, ICTP/IAEA School, 2019
Scaling of Excitations
πππ πΈ βπ
ΞπΈππ2
β’ n-scalingβ’ n=1
β’ f~n, E~n-3, ~ n7, ~ n4
β’ Into high n
β’ f~n-3, E~n0, ~ n-3
β’ Z-scalingβ’ n=0
β’ f~Z-1, E~Z, ~ Z-3, <Οv> ~ Z-2
β’ nβ 0
β’ f~Z0, E~Z2, ~ Z-4, <Οv> ~ Z-3
YR, ICTP/IAEA School, 2019
Direct and Exchange (contβd)
1s2
1s2p
2s2
2s2p
Ne IX
Ne VII
He-like ion Be-like ion
YR, ICTP/IAEA School, 2019
Ionization cross sections
Z
Lotz formula:
ππππ π, πΈ = 2.76 ππ02π π¦2
πΌπ
ln πΈ/πΌππΈ
= 2.76 ππ02π4
π4ln π
π
Same theoretical methods as for excitation: Born, Coulomb-Born, DW, CC, CCC, RMPSβ¦
π΄ + π β π΄+ + π + π
YR, ICTP/IAEA School, 2019
3-Body Recombination
π΄ + π β π΄+ + π + π
3-body rate coefficient πΌπ+1 ππ from ionization rate coefficient ππ ππ :
πΌπ+1 ππ =1
2
ππ§ππ§+1
2πβ2
ππππ
3/2
ππ₯ππΈπ§ππ
ππ ππ
Rates from rate coefficients: ππππ ππ but ππ2πΌπ+1 ππ
Likes high-n states; πΌ ππ ~1/ππ9/2
YR, ICTP/IAEA School, 2019
Collisional Methods and Codesβ Plane-wave Born (first order perturbation)
β Coulomb-Born (better for HCI)
β Distorted-wave methods
β Close-coupling (CC) methods
β Convergent CC (CCC)
β R-matrix (with pseudostates, etc.)
β B-splines R-matrix
β Time-Dependent CC
β β¦
β Relativistic versions are available
YR, ICTP/IAEA School, 2019
Heavy-particle collisions
In thermal plasmas electrons are always more important for excitations than heavy particlesException: closely-spaced levels (e.g., 2s and 2p in H-like ions)
Neutral beams: E ~ 100-500 keV heavy particle collisions are of highest importance
Charge exchange H + Az+ H+ + A(z-1)+(n) β’ Very large cross sections > 10-15 cm2; π π ~π β 10β15 ππ2
β’ High excited states populated: π ~ π0.77
β’ Higher l values are preferentially populated but it depends on collision energy and n
Ionization cross sections
YR, ICTP/IAEA School, 2019
Neutral beam in ITER: H+W64+
Classical Trajectory Monte Carlo (CTMC): two variations
D.R.Schultz and YR, to be published
π π ~π β 10β15 ππ2 = π. π β ππβππ ππ2 π ~ π0.77 β ππ
YR, ICTP/IAEA School, 2019
Autoionization
1s2 1s2l 2l2lβ
IP~ ΒΎ IP
Energy of 2l2lβ
βE
βE
A** β A+ + e
π΄π =2π
βπ π» π
2; 1013-1014 s-1
YR, ICTP/IAEA School, 2019
Resonances in excitation
e e e
Direct excitation Intermediate states Intermediate AI states(coupled channels!)
YR, ICTP/IAEA School, 2019
Excitation-Autoionization
3s23p63d104s2 Xe24+: Pindzola et al, 20113p63d Ti3+: van Zoest et al, 2004
IP
When EA is important:β’ few electrons on the outermost shellβ’ Mid-Z multielectron ionsβ’ β¦but less important for higher Z (rad!)
EA in ionization cross sections isnot required for detailed modelingwith AI states!
YR, ICTP/IAEA School, 2019
Resonances in photoionization
A. Pradhan
Fe III
3d5(6S)ns 7S + hΞ½-> 3d5 6S
3d5(6S)ns 7S + hΞ½-> 3d44p(4Po)ns 7Po
-> 3d5 6S
YR, ICTP/IAEA School, 2019
Selection rules
β’ Examples of AI states: 1s2s2, 1s22pnl (high n)
β’ Same old rule: before = after
β’ A** βA* + lβ’ Exact: Pj = Pi; J = 0β’ Approximate (LS coupling): S = 0, L = 0
β’ 2p2 3P β 1s + p: parity/L violation (for LS)!
β’ BUT: (2p2 3P2 ) = (2p2 3P2 ) + (2p2 1D2) + β¦β’ and (2p2 3P0 ) = (2p2 3P0 ) + (2p2 1S0) + β¦β’ YET: Aa(2p2 3P1) is much smallerβ¦
YR, ICTP/IAEA School, 2019
2p2 autoionization probabilities
Level Ne8+ Fe24+
3P0 2.2(10) 3.7(12)3P1 3.1(8) 1.9(10)3P2 6.2(11) 1.1(14)1D2 2.7(14) 2.3(14)1S0 1.4(13) 3.2(13)
YR, ICTP/IAEA School, 2019
Radiative recombination
Continuum
Bound states
π΄ π+1 + + π β π΄π+ + βπ
Ion recombined
YR, ICTP/IAEA School, 2019
DR step 1: dielectronic capture
Continuum
Bound states
Resonant process!
π΄ π+1 + + π β π΄π+ββ
YR, ICTP/IAEA School, 2019
Continuum
Bound states
π΄ π+1 + + π β π΄π+ββ β π΄ π+1 + + π
Dielectronic capture + autoionization= no recombination
DC and AI aredirect and inverse
YR, ICTP/IAEA School, 2019
DR step 2: radiative stabilization
Continuum
Bound states
π΄ π+1 + + π β π΄π+ββ β π΄π+β + βπ
Stabilizing transition:Mostly x-rays
YR, ICTP/IAEA School, 2019
Dielectronic Recombination
A++e β A** β A++eDC AI
A*+h
Example: Ξn=0 for Fe XX 2s22p3
2s22p3 4S3/2 + e β 2s2p4(4P5/2)nl2s22p3 4S3/2 + e β 2s2p4(4P5/2)nl2s22p3 4S3/2 + e β 2s2p4(4P5/2)nl
RS
Savin et al, 2004
n β₯ 7
YR, ICTP/IAEA School, 2019
Examples of dielectronic recombination & resonances
A. Burgess, ApJ 139, 776 (1964)
This work solved the ionization balance problem for solar corona
He+ + e
Ar at NSTX, Bitter et al (2004)
Dielectronic satellites areimportant for plasma diagnostics
(e.g., He- and Li-like ions)
BUT: DR for high-Z multi-electron ionsis barely known!
YR, ICTP/IAEA School, 2019
Connection between DC and EXC
βE
βE
βE
βE
βE
βE
βE
βE
?
YR, ICTP/IAEA School, 2019
Connection between DC and EXC
βE
βE
DC can be treated asan under-threshold excitationand DC cross sections can bederived by extrapolation ofthe excitation cross sections
YR, ICTP/IAEA School, 2019
Inner-shell dielectronicresonances in HCI
πΎ2πΏ8ππ + π β πΎ2πΏ7πππππβ²πβ²
~Yb40+
YR, ICTP/IAEA School, 2019
Experiment
LMnLNn
5
67
4
5
6
Theory
1s22s22p63s23pm3dk + e β 1s22s22p53s23pm3dk+1nl
1s22s22p63s23pm3dk + e β 1s22s22p53s23pm3dk4lnl'
1s22s22p63s23pm3dk + e β 1s22s2p53s23pm3dk+1nl
YR, ICTP/IAEA School, 2019
He-like lines and satellites
O.Marchuk et al, J Phys B 40, 4403 (2007)
YR, ICTP/IAEA School, 2019
Energy levels in He-like Ar
β’ Ground state: 1s2 1S0
β’ Two subsystems of termsβ’ Singlets 1snl 1L, J=l (example 1s3d 1D2)
β’ Triplets 1snl 3L, J=l-1,l,l+1 (example 1s2p 3P0,1,2)
β’ Radiative transitions within each subsystem are strong, between systems depend on Z
YR, ICTP/IAEA School, 2019
He-like Ar Levels and Lines
1s2 1S0
1s2s 1S0
1s2p 1P1
1s2s 3S1
1s2p 3P0
1s2p 3P1
1s2p 3P2
W
X
YZ
E1
2E1
Line He0 Ar16+ Fe25+ Kr34+
W 1.8(9) 1.1(14) 4.6(14) 1.5(15)
Y 1.8(2) 1.8(12) 4.4(13) 3.9(14)
X 3.3(-1) 3.1(8) 6.5(9) 9.3(10)
Z 1.3(-4) 4.8(6) 2.1(8) 5.8(9)
YR, ICTP/IAEA School, 2019
Z-scaling of Aβs
β’ W[E1]: A(1s2 1S0 β 1s2p 1P1) Z4
β’ Y[E1]: A(1s2 1S0 β 1s2p 3P1) β’ Z10 for low Z
β’ Z8 for large Z
β’ Z4 for very large Z
β’ X[M2]: A(1s2 1S0 β 1s2p 3P2) Z8
β’ Z[M1]: A(1s2 1S0 β 1s2s 3S1) Z10
YR, ICTP/IAEA School, 2019
1s2lnl satellites
β’ 1l2l2lββ’ 1s2s2: 2S1/2
β’ 1s2s2p:β’ 1s2s2p(1P) 2P1/2,3/2
β’ 1s2s2p(3P) 2P1/2,3/2; 4P1/2,3/2,5/2
β’ 1s2p2
β’ 1s2p2(1D) 2D3/2,5/2
β’ 1s2p2(3P) 2P1/2,3/2; 4P1/2,3/2,5/2
β’ 1s2p2(1S) 2S1/2
β’ 1s2lnlββ’ Closer and closer to Wβ’ Only 1s2l3l can be reliably resolvedβ’ Contribute to W line profile
1s2+π β 1π 2π2πβ²