Electron interactions with CO2

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Electron interactions with CO2
U. S. Department of Energy National Energy
Technology Laboratory May 30, 2008

• Bob Merlino
• Department of Physics and Astronomy
• The University of Iowa
• Iowa City, IA

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Electron impact ionization
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Electron attachment to CO2

• CO2 cannot permanently
• bind an electron, so that
• is metastable, with
• lifetimes in the microsec to
• millisec range, decaying
• back to CO2 by auto-
• detachment
• the electron attachmentprobability is enhanced
  if CO2 is in an excited vibrational state

attach. cross section (10-18 cm2)
electron energy (eV)
Y. Itikawa, J. Phys. Chem. Ref. Data, 31,749, 2002
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Devices at the University of Iowa Plasma
Laboratory

• 2 Q machines with magnetic fields up to 0.5 T
• 6 cm diam. by 2 m length, variable B profile
• 6 cm diam. by 1 m length, which can also operate
  in the presence of micron sized dust particles
• A glow discharge, dusty plasma / multidipole
  device, 60 cm diam. x 90 cm length
• A multidipole/inductively coupled plasma
  device, 84 cm diam. x 130 cm length (The UI
  physics dept.has agreed to provide this device.)

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Q machine / Discharge plasma

• This device can be operated either with a
  thermal, surface ionizationplasma source (QM)
  which produces either as K or Cs plasma, or asa
  discharge device using He, Ar, Ne, Xe, N2, by
  removing the hot plate and biasing the filament
  negatively.
• In the Q mode the electrons are relatively cold
  with Te 0.2 eV
• In the discharge mode there are thermal electrons
  with Te 2 5 eV and with a population of
  energetic electrons with Ee 30 100 V.

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IOWA Q-3
IOWA Q-2
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Hot filament multidipole plasma source
GAS
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Inductively coupled plasma source
TURBOMOLECULAR PUMP
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Formation of

• The presence of
• is confirmed by observing
• the spectrum of ion cyclotron waves in the plasma
• is a metastable negative ion

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Mass spectrometer measurements
2 ion plasma K / Cs
K / SF6 plasma
VOLTS