  Nonlinear cascade of low-frequency Alfvenic fluctuations (AFs) is regarded as
one candidate of the energy sources to heat plasma during the non-adiabatic
expansion of interplanetary coronal mass ejections (ICMEs). However, AFs inside
ICMEs were seldom reported in the literature. In this study, we investigate AFs
inside ICMEs using observations from Voyager 2 between 1 and 6 au. It is found
that AFs with high degree of Alfvenicity frequently occurred inside ICMEs, for
almost all the identified ICMEs (30 out of 33 ICMEs), and 12.6% of ICME time
interval. As ICMEs expand and move outward, the percentage of AF duration
decays linearly in general. The occurrence rate of AFs inside ICMEs is much
less than that in ambient solar wind, especially within 4 au. AFs inside ICMEs
are more frequently presented in the center and at the boundaries of ICMEs. In
addition, the proton temperature inside ICME has a similar distribution. These
findings suggest significant contribution of AFs on local plasma heating inside
ICMEs.
