Apparatus for use with a vessel used to generate plasma are provided. One apparatus includes a first comb structure configured to partially wrap around a circumference of the vessel. The first comb structure has a first end and a second end, and a first separation is defined between the first end and the second end. The first comb structure defines a first plurality of fingers oriented perpendicular to the circumference of the vessel. The first comb structure is configured to be connected to a first end of a radio frequency (RF) coil. Also provided is a second comb structure configured to partially wrap around the circumference of the vessel. The second comb structure has a first end and a second end. A second separation is defined between the first end and the second end the second comb structure. The second comb structure defines a second plurality of fingers oriented perpendicular to the circumference of the vessel. The second comb structure is configured to be connected to a second end of the RF coil. Further, ends of the first plurality of fingers and ends of the second plurality of fingers are configured to face each other and maintain a third separation.