1. Atomic and Molecular Ion Merged-Beams
Experiments with Atomic H
C. C. Havener
Oak Ridge National Laboratory
2. Merged-Beam Collaborators
I.N. Draganić, ORNL/NASA
X. DeFay, K. Morgan, D. Wulf, D. McCammon,
University of Wisconsin, Madison
D. G. Seely, Albion College
V. M. Andrianarijaona, S. L. Romano, C. I. Guillen, A. K. Vassantachart,
Pacific Union College
M. Fogle, Auburn University
A. Galindo-Uribarri, F. Salces Carcoba, D. J. Nader,
ORNL, Universidad Veracruzana, Universidad Autonoma de San Luis
Potosi, Mexico
Theory 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
3. 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
3
4. 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
5. 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 flight
missions require more accurate
atomic data
Funding: US DOE Basic Energy Sciences,
Fusion Energy Sciences, NASA
6. CT with Solar Wind
X
q+
+ 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
7. 0.01 0.1 1 10 100 1000
0
50
100
Energy (eV/u)
CrossSection(10
-16
cm
2
)
C
4+
N
4+
Si
4+
Ne
4+
molecular orbitals
Intermediate/Low energy
Si4+ + H
Theory
Si4+ + D
Experiment
isotope effect
Xq+
q
r
2
4
2
H D
Enhancements
ORNL Merged-Beams Charge Transfer Data
Xq+ + H(D) -> X(q-1)+ + H+(D+)
High energy
scaling laws
atomic orbitals
8. 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
)(
r
q
rV
Xq+
H
Li H 36
He2+ + Li
Landau-Zener estimates:
Xq+ + H Stancil & Zygelman PRL 95
Ion E threshold
N4+ 8 eV/u
Cl7+ 17 eV/u
Ti22+ 1400 eV/u
Gioum. & Stev. J. Chem. Phys. 58
9. Why Merged Beams ?
Gas Cell Technique
9
Gas Cell
Xq+
Low Collision Energy Limit
Atomic H Target Difficult
Target Density High
“Relative” cross sections
Thermal collision energy
Atomic H Target
Target Density Low
Absolute Measurements
Merged-Beams Technique
𝜋 𝑔𝑎𝑠 ~3 𝑥 10^13 𝑐𝑚2
𝜋 𝑏𝑒𝑎𝑚 − 𝑏𝑒𝑎𝑚 ~ 10^8 𝑐𝑚2
10. Merged-Beams Technique
20 meV/amu 5 keV/amu
Wide range of interaction energies
cos(
21
21
2
2
1
1
mm
EE
m
E
m
E
Erel
m1 v1
m2 v2
Vcm
Large 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 Frame
Ecm = 25 meV (25 meV)
ED = 7.0 keV (6 eV)
ESi
4+ = 98 keV (37 eV)
cm = 0.1 (0.1)
11. ion-atom merged-beams apparatus
cross section measurements independently absolute
FLvII
vvR
r
eq
21
21
2
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
X
q+
H
-
-
H
CHANNEL ELECTRON
MULTIPLIER
H
+
H
0
X
X
q+
(q-1)+
CW Nd: YAG
LASER
DEFLECTORS
NEUTRAL BEAM
DETECTOR
FARADAY
CUP
35 cm
16. Intense Highly Charged Ions Extraction from ECR
40 60 80 100 120 140 160 180 200
0
5
10
15
20
25
30
35
40
14
N
6+
16
O
7+
18
O
8+
He
2+
He
+
18
O
8+
O
7+
O
6+
O
5+
O
4+
O
3+
O
2+
O
1+
H
+
Analyzing magnet current (A)
BeamIntensity(e)
18
O
8+
on 11-09-09
PSHF
=300W
Uext
=18.5 kV
Ibeam
=0.72 A
Slits 6 x 6 mm
2
Oxygen-Helium Ion Beam Spectrum
68 69 70
0.0
0.2
0.4
0.6
0.8
1.0
16
17. ORNL Merged-Beam
Measurements
Rejoub et al. PRA 2004
Havener et al. PRA 2005
insufficient angular collection
R. Mawhorter DAMOP 2004
Ne is injected in magnetic fusion devices
as a diagnostic and to mitigate disruptions
18. • Direct measurement [Havener et al., 2009] of isotope effect due to ion induced
dipole attraction for Si4+ + H,D; N2+ + H,D
Langevin estimates
19. PRL 2007
Xq+
H D @ E=100 eV/amu
Rmin(H)=.65 a.u.
Rmin(D)=.4 a.u.
Low Energy Access to Rmin
K-vacancy production
Peterson et al. PRL 76
20. 0.1 1 10
0.01
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
CrossSection(10
-16
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
21. Vcm
Large 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
25. 100 1000
0
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 -> O
7+
+ H+
Crosssection(10
-16
cm
2
)
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]
25
Need state-selective to resolve differences between theory/experiment !
27. 14.5 GHz ECR Ion Source
Intense Molecular Ion Beams
enriched D2 injection
4.2 x 10-6 Torr
16.4 kV extraction
3 W microwave power
Draganic et al.,
NIM A 640 (2011) 1
28. 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
30. 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
31. CO+ + H
MOCC 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
32. 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
35. 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
cm
Q
Amplification of Q in lab frame
36. 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 Work
Single capture,
total and X-ray emission
Bare and H-like ions + H
e.g., C, N, O ions
C6+ + H; X-ray emission
Holy Grail,
X-ray emission with H
37. 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
38. Ionization potential
H 13.6 eV
He 24.6 eV
H2 15.4 eV
Kr 14 eV
Gas Cell Results
Measurements taken from 1.5 kV to 60 kV
Must model cascade process
for comparison with l distribution
39. C6+ + He
C6+ + Kr
R3 n=3->1/n=2->1
R4 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
41. 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+ + H2
Calorimeter not UHV
42. C-
H3
+
Laser Upgrade
820 nm, 1.51 eV
(C- 1.262 affinity)
Cs sputter
ion 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
43. 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
