When a B-2 takes off, does it use some device to ionise the airflow in front it?
I have never heard of an ionization device being used on an aircraft, but when I searched Google for "Northrop B-2 ionization", I actually found a reference for this:


  Microwave frequencies emitted along the leading edge would readily ionize the approaching air and allow the B-2's high-voltage electric field to discharge a greater flux of positive ions. With increased ion currents, the B-2 would be able to generate a greater ion sheath space charge at a given velocity and thereby increase the electrogravitic and electrostatic thrust propelling the craft.


This quote is from the book Secrets of Antigravity Propulsion: Tesla, UFOs, and Classified Aerospace Technology by Paul A. LaViolette, which sounds a lot like pseudo-science and conspiracy theories. This page says about the author:


  In addition, Paul LaViolette has developed a new theory of gravity that replaces the deeply flawed theory of general relativity.  Predicted from subquantum kinetics, it accounts for the electrogravitic coupling phenomenon discovered by Townsend Brown and may explain the advanced aerospace propulsion technology utilized in the B-2 bomber.


Putting the conspiracy theories aside, how much energy would be needed to ionize the air in front of an aircraft? It requires 14.5eV to ionize a single nitrogen atom (main component in air) and air has an average molar density of 28.97 g/mol resulting in a required energy per gram of air of

$$ E = \frac{14.5 \, \mathrm{eV} \times N_A}{28.97 \, \mathrm{g}/\mathrm{mol}} \approx 3.014 \times 10^{23} \, \mathrm{eV}/\mathrm{g} \approx 48.3 \, \mathrm{kJ}/\mathrm{g} $$

For comparison, jet fuel has an energy density of around 43kJ/g. So you need to burn about the same mass of jet fuel as air passes over the wings in order to ionize it. It goes without saying that this is not done on the B-2, nor any other aircraft.