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Atomic and Molecular Ion Merged-Beams Experiments with Atomic H
C. C. Havener Oak Ridge National Laboratory
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Merged-Beam CollaboratorsI.N. Draganić, ORNL/NASA
X. DeFay, K. Morgan, D. Wulf, D. McCammon, University of Wisconsin, Madison
D. G. Seely, Albion CollegeV. M. Andrianarijaona, S. L. Romano, C. I. Guillen, A. K. Vassantachart,
Pacific Union CollegeM. Fogle, Auburn University
A. Galindo-Uribarri, F. Salces Carcoba, D. J. Nader,ORNL, Universidad Veracruzana, Universidad Autonoma de San Luis
Potosi, MexicoTheory Support
D. Schultz and P. Krstic, ORNL
P. C. Stancil, University of Georgia, Athens
Research supported by the U.S Department of Energy Office of Fusion Energy Sciences and the Office of Basic Energy Sciences under contract DE-AC05-00OR22725 with UT-Battelle, LLC and .
the NASA Solar & Heliospheric Physics Program NNH07ZDA001N. 2
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Outline• Introduction/Motivation Charge Transfer Experiments • Merged-beams technique• CT with atomic highly charged ions • CT with molecular ions• State-selective measurements
• Motivation• Current progress
• Summary/Future
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Motivation
CT is important process in magnetic fusion, ion-source development, astrophysics, plasma processing, lighting, ..
Ion-atom merged-beams experiment is unique and provides independently absolute benchmark measurements from keV/u down to near thermal energies.
Interplay between theory/experiment provides foundation for our quantum mechanical understanding of low-energy interactions between atomic/molecular species
Xq+(n,l) + H X(q-1)+ + H+
e Low Energy Charge Transfer
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Low Energy Charge Transfer
CT in magnetic fusion
Inside TFTR
Plasma diagnostics,modeling charge state balance,
and divertor design
CT in astrophysics
“Cats Eye” Planetary Nebulae
Ionization structure, line emission, thermal structure
present and future NASA flightmissions require more accurate
atomic data
Funding: US DOE Basic Energy Sciences, Fusion Energy Sciences, NASA
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CT with Solar Wind
Xq++ A → X(q-1)+*(nl) + A+ ;
Charge exchange with the Solar wind
Xq+→ HCI of C, N, O …
A → H, He, C… or H2, H2O, CO, …
NASA
6
Mars (Chandra)
X-ray emission from CT of Solar Wind with planetary atmospheres
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0.01 0.1 1 10 100 10000
50
100
Energy (eV/u)
Cros
s Se
ctio
n (1
0-16 c
m2 )
C4+
N4+
Si4+
Ne4+
molecular orbitals
Intermediate/Low energySi4+ + HTheory
Si4+ + DExperiment
isotope effect
Xq+
qr
2
42 H D
Enhancements
ORNL Merged-Beams Charge Transfer DataXq+ + H(D) -> X(q-1)+ + H+(D+)
High energy
scaling laws atomic orbitals
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Low Energy CT Behavior
For stronger dipole interaction -> shape resonances are wider, enhancements should appear at higher energies
N3+ + H Theory
Rittby et al., J. Phys. B: 84
“Orbiting”resonances
4
2
2)(
rqrV
Xq+
H
Li H 36He2+ + Li
Landau-Zener estimates:Xq+ + H Stancil & Zygelman PRL 95
Ion E thresholdN4+ 8 eV/uCl7+ 17 eV/uTi22+ 1400 eV/u
Gioum. & Stev. J. Chem. Phys. 58
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Why Merged Beams ?Gas Cell Technique
9
Gas CellXq+
Low Collision Energy LimitAtomic H Target Difficult
Target Density High“Relative” cross sections
Thermal collision energyAtomic H Target
Target Density LowAbsolute Measurements
Merged-Beams Technique𝜋 𝑔𝑎𝑠 3𝑥 1013𝑐𝑚2
𝜋𝑏𝑒𝑎𝑚−𝑏𝑒𝑎𝑚 108𝑐𝑚2
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Merged-Beams Technique
20 meV/amu 5 keV/amu
Wide range of interaction energies
cos(21
21
2
2
1
1
mmEE
mE
mEErel
m1 v1
m2 v2
VcmLarge angular collection in CM
cm increases with Vcm
lab cm
cm increases toward lower collision energies
Good resolution even at lowest energies
Center-of-Mass FrameEcm = 25 meV (25 meV)
ED = 7.0 keV (6 eV)ESi
4+ = 98 keV (37 eV) cm = 0.1 (0.1)
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ion-atom merged-beams apparatus
cross section measurements independently absolute
FLvII
vvR
r
eq21
212
measurements technically difficult• # of beam-beam collisions in merge path is small (max I)
20-30 uA ions, up to 1 uA H, D
• a two-beam modulation technique separates signal (Hz) from backgrounds (kHz)backgrounds from H stripping, ion photons and knock-ons
• ultra-high vacuum minimizes backgrounds
Xq+
H-
-H
CHANNEL ELECTRON MULTIPLIER
H+
H0
X
Xq+
(q-1)+
CW Nd: YAG LASER
DEFLECTORS
NEUTRAL BEAM DETECTOR
FARADAY CUP
35 cm
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Upgraded Multicharged Ion Research Facility (MIRF)
e-ion merged beams
ion-surface
ion-atom merged beams
Cap
rice
0-2
5 kV
“floa
ting
bea
mlin
e”
COLTRIMS
grazing-surface
Perm
Mag
net
ECR
20-2
70 k
V
e-ion crossed beams
molecular-ion trap
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Ion-atom merged-beams
Permanent Magnet ECR Source Ar 8+ 510 uA; 11+ 90 ua Xe 20+ 52 uA; 30+ 1 uAO 1-3+ 700 uA;7+ 90uA
HV Platform (2-20-270 kV)
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Merged-Beams with Atomic Ions
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Intense Highly Charged Ions Extraction from ECR
40 60 80 100 120 140 160 180 2000
5
10
15
20
25
30
35
4014N6+
16O7+18O8+
He2+ He+
18O8+
O7+
O6+
O5+
O4+
O3+
O2+O1+H+
Analyzing magnet current (A)
Beam
Inte
nsity
(e
)
18O8+
on 11-09-09P
SHF=300W
Uext=18.5 kVIbeam=0.72 ASlits 6 x 6 mm2
Oxygen-Helium Ion Beam Spectrum
68 69 70
0.0
0.2
0.4
0.6
0.8
1.0
16
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ORNL Merged-Beam Measurements
Rejoub et al. PRA 2004
Havener et al. PRA 2005
insufficient angular collectionR. Mawhorter DAMOP 2004
Ne is injected in magnetic fusion devices as a diagnostic and to mitigate disruptions
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• Direct measurement [Havener et al., 2009] of isotope effect due to ion induced dipole attraction for Si4+ + H,D; N2+ + H,D
Langevin estimates
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PRL 2007
Xq+
H D @ E=100 eV/amuRmin(H)=.65 a.u.Rmin(D)=.4 a.u.
Low Energy Access to Rmin
K-vacancy productionPeterson et al. PRL 76
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0.1 1 100.01
0.1
1
10
100
Present Measurement Fite 62 Nutt 78 Gilbody 78 Krstic 04 Liu 03 Janev, IAEA (1995) Barnett, ORNL (1990) Harel 96
C
ross
Sec
tion
(10-1
6 cm
2 )
Energy (keV/u)
He2+ + H
Merged-Beams Measurements
Extend measurements to lower energies with HV platformHavener et al., PRA 2005
HC-MOCC
HSCC
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VcmLarge angular collection in CM
lab cm
cm increases toward lower collision energies
He2+ + H -> He+ + H+
Havener et al., PRA 2005
(HeH)2+
Merged-Beams Technique cont’d
2005 apparatus
2.5 deg. lab
Present apparatus 3.5 deg. lab
2005 apparatus
2.5 deg. lab
Present apparatus 3.5 deg. lab
21
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22
C5+ + H
Draganic et al., PRA 83, 022711, (2011)
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23
State-selective calculations for C5+ + H using ORNL total cross sections…Nolte, Stancil, et al., PRA 2012
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24Unpublished
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100 10000
10
20
30
40
50
60
70
80 present measurements HSCC AOCC 03 AOCC 84 MOCC-KL MOCC-SGB Meyer et al. 85
O8+ + H -> O7+ + H+
Cro
ss s
ectio
n (1
0-1
6 c
m2 )
Energy (eV/u)
Factor of two discrepancy between previous measurement [Meyer et al., 1985] and
predictions of state-of-the-art hyperspherical close coupling theory [Lee et
al., 2004]
25Need state-selective to resolve differences between theory/experiment !
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Merged-Beams with Molecular Ions
26
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14.5 GHz ECR Ion SourceIntense Molecular Ion Beams
enriched D2 injection4.2 x 10-6 Torr
16.4 kV extraction3 W microwave power
Draganic et al., NIM A 640 (2011) 1
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Low Energy Charge Transfer
H + D2+ (v,j)i H+ + D2 (v,j)f
H+ + D + D
present measurements with D2+
e
H + H2+
H+ + H2
Hb+ + (Ha-Hc)
Hc+ + (Hb-Ha)
H+ + H + H
(1)
(2)
(3a)
(3b)
Ha + (Hb-Hc)+
low energy CT involves dynamically coupled electronic, vibrational, and rotational degrees of freedom
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previous status experiment/theory
Important for Interstellar cloud chemistry; H2+ + H2 -> H3
+; H2
+ + H destruction mechanism?
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Franck-Condon distribution [Amitay et al. PRA 1999]
vi
0 1 2 3 4 5 6 7 8
% 9 16 18.5 15.5 12 9.5 6 4.5 3
Andrianarijaona et al., ICPEAC Proc. 2009
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CO+ + HMOCC with IOSA approximation
vibrational state-to-state calculations for CO+ + H
by C.Y. Lin, P.C. Stancil, et al. PRA (2007)
Havener et al., AIP Conf. Proc. 1336, (2011) pp 101
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calculations for CO+ + H by C.Y. Lin, P.C. Stancil, et al.
PRA (2007)orientation-angle dependence
CO+ + H
Havener et al., AIP Conf. Proc. 1336, (2011) pp 101
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PRA 84, 062716 (2011)
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State-selective charge transfer
34
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Si4+ + D -> Si3+(3d) + D+ ; Q=11.7 eV -> Si3+(4s) + D+ ; Q=7.5 eV
Wu & Havener, J. Phys. B 1997
Q of reaction in CM amplified in lab frame
Center-of-Mass (CM)
Lab FrameD+ Signal
35
Vcm
lab cmQ
Amplification of Q in lab frame
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XX--ray Emission Studies using Mergedray Emission Studies using Merged--BeamsBeams
Sounding rocket XSounding rocket X-- ray Calorimeterray Calorimeter(McCammon, (McCammon, ApJApJ 2002)2002)
Sounding rocket observed soft X-ray background 36 1 mm2 microcalorimeter5 – 12 eV, 60 mK operation
1 uA C6+; 1 uA H 20 cm-2 beam-beam overlap
1 cm interaction length 10-15 cm2 cross section 10% geometrical efficiency 20% filter transmission 4 Hz Signal
Proposed WorkSingle capture,
total and X-ray emissionBare and H-like ions + He.g., C, N, O ions
C6+ + H; X-ray emission
Holy Grail,X-ray emission with H
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n
2
5
3
1
4
s p d f
C6+ + He -> C5+ (n=5, l?)
X-ray Calorimeter, McCammon, J Low Temp Phys 151, 715 (2008)
First Experiment with Gas Cell
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Ionization potential H 13.6 eVHe 24.6 eVH2 15.4 eV
Kr 14 eV
Gas Cell Results
Measurements taken from 1.5 kV to 60 kVMust model cascade process
for comparison with l distribution
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C6+ + He
C6+ + Kr
R3 n=3->1/n=2->1R4 n=4->1/n=2->1
R3
R4
R3
R4
Karchenko, priv comm
C6+ + H
Karchenko, priv comm
Morgan et al., proceedings CAARI 2012
R3
R4
R4
R3
Karchenko,priv comm, data used for Solar Wind Simulatioin
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O8+ + KrORNL Measurements
Stancil et al., priv.
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X-ray Emission from Merged-Beams
Sig/Background = .01
Sig + Bkgrd with H and C6+ beam (1 hr)Bkrd C6+ beam only (1 hour)
Design new chopping scheme
10 sec
Background from CT with 5 x 10-9 Torr H2 and H20
C6+ + H2Calorimeter not UHV
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C-
H3+
Laser Upgrade820 nm, 1.51 eV
(C- 1.262 affinity)
Cs sputterion source
H beams can be replaced by C beams to enable synthesis of simple hydrocarbons in merged beams where initial/final states can be manipulated and observed
Future Molecular Ion Studies
C
H3+
H2
CH2+
H
Reactions to study:H+ + C -> CH+
H3+ + C -> H2 + CH+
-> H + CH2+
CH+
C
42
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Summary
• Intense beams from the ECR ion source enable molecular ion CT measurements with H from keV/u to meV/u corresponding to collision times from “frozen” vibrational and rotational states to collisions where rotational and vibrational states important
• D2+ + H , CO+ + H, O2
+ + H measurements are compared to vibrational state-to-state calculations.
CT with atomic ions
CT with molecular ions
• CT measurements with atomic ions and H from keV/u to meV/u continue to benchmark AOCC, MOCC theory and explore trajectory/isotope effects effects at low energies. CT with bare and H-like ions surprisingly still lack low energy data & theory
• State- selective measurements with X-ray calorimeter are needed to further benchmark theory. Gas cell measurements simulate H but better signal/background needed for merged-beam measurements with H.
43
• Modify XQ calorimeter to increase sig/noise to allow merged-beams measurements with H
• Future measurements of proton transfer will have reduced backgrounds and explore hydrocarbon synthesis
Future Directions
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44
X-ray Spectra Research groupOak Ridge, TN, 2012.
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0.01 0.1 1 10 100 10000
20
40
60
80
100
120
140
160
180
200
Energy (eV/u)
Cros
s Se
ctio
n (1
0-16 c
m2 )
ORNL Merged-Beams Charge Transfer DataSi4+ + D -> Si3+ + D+
~ q x 10-15 cm2
(Phaneuf 83)
scaling
D
Trajectory effects
Si4+ + H TheoryGargaud (87)
Si4+ + D ExpPieksma (96)
isotope effect
Xq+
qr
2
42H
vPc /11
Pieksma et al. PRA 96
Stancil & Zygleman PRL 95Havener et al., ICPEAC 91