The Bussard collection coil was a component of the Bussard unit. In a warp nacelle, this coil was located adjacent to the Bussard collector and there were at least two and probably more than two of these coils. The location of these coils was labeled on a schematic of the secondary hull of the USS Yamato in 2365. (TNG: "Contagion", "Disaster", okudagrams)

According to the Star Trek: The Next Generation Technical Manual, the main function of the coils was for generating magnetic fields, which compress collected gases. These gases were stored in holding tanks.
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