Atomic and Molecular Ion Merged-Beams Experiments with Atomic H

C. C. Havener Oak Ridge National Laboratory

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

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

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

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

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

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

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

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

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)

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

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

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)

Merged-Beams with Atomic Ions

15

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

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

• Direct measurement [Havener et al., 2009] of isotope effect due to ion induced dipole attraction for Si4+ + H,D; N2+ + H,D

Langevin estimates

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

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

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

22

C5+ + H

Draganic et al., PRA 83, 022711, (2011)

23

State-selective calculations for C5+ + H using ORNL total cross sections…Nolte, Stancil, et al., PRA 2012

24Unpublished

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 !

Merged-Beams with Molecular Ions

26

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

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

previous status experiment/theory

Important for Interstellar cloud chemistry; H2+ + H2 -> H3

+; H2

+ + H destruction mechanism?

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

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

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

PRA 84, 062716 (2011)

State-selective charge transfer

34

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

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

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

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

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

O8+ + KrORNL Measurements

Stancil et al., priv.

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

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

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

44

X-ray Spectra Research groupOak Ridge, TN, 2012.

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