Charring is a process where the light gases are burnt away from a heavy fuel or raw material, leaving a residue called "char". I am not aware of the Hebrew term used in industry in Israel, but the Academy of the Hebrew Language has specified in its environmental dictionary quite recently that both the process and the residue are called "Pikhum". This term can also be found at the website below.

The "carbon" part is self-implied by the Hebrew term "Pikhum",
no need to add another "Pakhman".

I would still add the "sheerit" part as just "Pikhum dakhus" does not sound right, and may cause confusion as to whether the process or the residue is implied.