  A synthesis technology of endohedral fullerenes such as Fe@C60 has developed
with an electron cyclotron resonance (ECR) ion source. The production of N@C60
was reported. However, the yield was quite low, since most fullerene molecules
were broken in the ECR plasma. We have adopted gas-mixing techniques in order
to cool the plasma and then reduce fullerene dissociation. Mass spectra of ion
beams extracted from fullerene-He, Ar or Xe mixed plasmas were observed with a
Faraday cup. From the results, the He gas mixing technique is effective against
fullerene destruction.
