How To Achieve High Ion Generation?

Increase emission points and increase voltage.

Nano size emitters will help,if you have enough of them.

Still,no guarantee you will reach your target.

..."About 3 X 10^22 air molecules in a cubic meter. A mole of any gas takes up 22.4 cubic meters, and contains 6.023 X 10 ^23 molecules. Divide the latter by the former to get molecules per cubic liter. For an exact answer, adjust for temperature and pressure, and use the values corrected to STP.Jul 31, 2017"...

https://www.quora.com/How-many-air-molecules-are-present-in-a-cubic-meter-of-air

What is it exactly that you are trying to do?

My aim is to make a plasma conductor in which plasma is made from electric field.

My aim is to conduct 8amps so for that i need atleast 5x10^20 ion pairs.

..." the unit of electric charge is amp seconds (ampsec, which is also called “coulomb”); its symbol is Q. One ampsec is the charge of 6.25×10¹⁸electrons or protons (ions). An amp is 6.25×10¹⁸ electrons/sec. Force is expressed in grams (technically gramweights)."...

https://www.alphalabinc.com/electrostatic-formulas/

..."You can do that by connecting a charge pump like a Van de Graaff generator or a Wimshurst machine to a large capacitor such as Leyden jar.

If you really do mean Amperes, then you can discharge the capacitor and release the charge in a short high-ampere burst. "...

https://forum.allaboutcircuits.com/threads/electrostatic-current.20153/

I think you're a factor of 1000 out there. A gram-mole contains 6.023 X 10²³ molecules. A kg-mole contains 6.023 X 10²⁶ molecules.

Air has density (at NTP) 1.29 kg/m³. Molecular weight ~ 29. So number of molecules in 1 m³ = 1.29/29*6.023 X 10²⁶ ~ 2.7*10²⁵.

So this density of negative ions should be doable....?

https://scienceline.ucsb.edu/getkey.php?key=274

I was just commenting on your post, but 2.7*10²⁵ molecules/m³ = 2.7*10¹⁹ molecules/cm³, so 5*10²⁰ ions/cm³ looks highly unlikely, more so if the plasma is hot. I've not heard of making a plasma from an electric field, as the OP says.

What if the temperature was close to absolute 0 ?

That's likely isn't it? Happens all the time

https://rdreview.jaea.go.jp/review_en/2008/3_6.html