Sprite Light in a Bottle URSI Meeting Boulder, CO January 5, 2004

1
Sprite Light in a BottleURSI MeetingBoulder,
COJanuary 5, 2004

• Earle Williams, MIT, Cambridge, MA
• Michael Valente, East Coast Induction, Brockton,
  MA
• Robert Golka, Golka Associates, Brockton, MA

2
A Small Tube
3
Current Density in Glow Discharge Tubes

• Investigator Current
  Density J
• 
  (Amperes/m2)
• DC Current
• Herz (1895)
  2-15
• Wilson (1902)
  0.3-3
• Townsend (1915)
  3
• Günther-Schulze (1924)
  4.2
• Günther-Schulze (1927)
  35-70
• Found and Langmuir (1931) 1.5
• Capacitive Discharge
• Naudé (1932) 1-2
  x 104
• Elmore (1974) 7
  x 104
• Goto et al (2003) 8
  x 103
• This study
  .004 to 40

4
The Large Discharge Tube
5
Replacement of Lower Electrode
6
Air Pressure vs. Altitude
7
Absolute Spectral Units

• PR-650 Colorimeter provides spectral radiance L?
• in absolute units (watts/m2/sr/nm)
• Rayleighs (megaphotons/cm2/sec)
• 4? (sr/unit sphere) BW (nm)
  L?(watts/m2/sr/nm)
• hc/? (joule/photon) (104 cm2/m2)(106photons/
  megaphoton)
• (2.39 x 1011) L?

8
Spectral Comparison
9
Radiance vs. Input Power
10
Striations in Positive Column
(P 70 mT) (J 0.12 A/m2)
11
Constricted Discharge at Higher Pressure
(1.2 TORR) (6.6 A/m2)
12
Radiance vs. Current Density
13
Conductivity vs. Radiance
14
Column Sprites
J (A/m2) 10-2 A/m2 3 x 10-3
A/m2 10-3 A/m2
Elizabeth Gerken
15
Carrot Sprite
J (A/m2) 10-2 A/m2 3 x 10-3 A/m2 10-3
A/m2
Elizabeth Gerken
16
Large and Energetic Sprite
Elizabeth Gerken
17
Sub-Structure of Sprite
J (A/m2) 10-2 A/m2 3 x 10-3 A/m2 10-3 A/m2
Elizabeth Gerken
18
Langmuirs Plasma Frequency
19
Conclusions

• Sprite spectra are reasonably well replicated in
  an air-filled glow discharge tube, with dominant
  N21PG emission (red light)
• The power dissipation per unit volume for a 1
  Megarayleigh sprite is inferred to be 1 watt/m3
• The current density in a 1 Megarayleigh sprite
  streamer is inferred to be 10-2 A/m2, with
  radiance proportional to current density
• The electrical conductivity of a 1 Megarayleigh
  sprite at 65-70 km altitude is inferred to be 3
  x 10-5 mho/m, with conductivity proportional to
  radiance