What does the owner's manual or maintenance manual say? If the answer is not in the trouble shooting section of the manual; a phone number to the manufacturer is almost always in the manual. I recommend you call the manufacturer if the answer is not in their manual. Or you can get the manufacturer's phone number on line if not in the manual. Equipment manuals are also usually posted on line somewhere; in case you do not have a paper manual. The manufacturer will usually point you to where the information is on line if an expert is not available to talk with. Though talking with a manufacturer's rep who has run into this problem is usually first choice.

I do not fully understand the main purpose of adding a coil to HiPIMS plasma. Sputter-ejected atoms are highly ionized, depending on target materials, etc., and by controlling their energy with applying substrate bias, they can be guided toward the substrate.

If your purpose is attracting atoms/ions from target vicinity toward the substrate, I do doubt that coil will help. Adding a coil will help increasing the ionization of sputtered atoms in the bulk plasma by confining electrons, no significant impact on ions.