For 10 points, name this quantity, the radius over which charged particles will shield electric fields, a characteristic length from plasma physics.
For a single species, this quantity is equal to the square root of absolute temperature over 4-pi times the charge density squared. The Saha equation only holds for substances with large values of this quantity. This quantity also provides the upper cut-off for the value of the impact parameter. When this value is less than the particle radius, Smoluchowski's formula for calculating the (*) zeta potential is valid. For every value of this quantity, the amount of electric potential decreases by degree one-over-e. This value is cubed and multiplied by 4-pi times the electron number density in the dimensionless plasma parameter. For 10 points, name this quantity, the radius over which charged particles will shield electric fields, a characteristic length from plasma physics. 
For a single species, this quantity is equal to the square root of absolute temperature over 4-pi times the charge density squared.
Debye length [or Debye scale/parameter/number/radius or screening length] 