A collector for a linear beam has a segmented ceramic collector core that permits sustained operation at high temperatures and power densities. The collector provides efficient heat transfer from the while reducing stresses on collector components caused by thermal cycling and comprises a heat sink having a cavity providing interior vacuum walls for the collector a segmented ceramic insulator disposed inside the cavity, and an electrode disposed inside and against the insulator. The insulator comprises sectors separated from one another by gaps, and may be notched in its outer surface for high-voltage stand-off from the sink. The electrode is preferably not brazed/soldered to the insulator. A stage of the electrode may be probeless and comprise a depression. A molybdenum-fabricated heat sink and stage assembly utilizes an insulator constructed from beryllium oxide, aluminum nitride, or alumina; alternatively, a copper assembly, uses an aluminum nitride insulator.