Positron sources are essential to the current and future lepton collider projects (ILC, CLIC, SuperKEKB, FCC-ee, etc.) with challenging critical requirements of high-beam intensity and low emittance necessary to achieve high luminosity. In the conventional positron-generation system, a possible scheme to increase the positron intensity is to increase the incident electron beam power (intensity and/or energy). However, the allowable heat load as well as the thermo-mechanical stresses in the target severely limit the allowable beam power of the incident electrons. The positron source community should consolidate the effort and explore different methods of positron production, both classical techniques and especially novel ones, primarily for future high-energy physics applications requiring orders of magnitude higher intensity than what was demonstrated up to now. The studies should be focused on different source types, targets, capture approaches including the existing limitations and potential for polarized positron production identifying the main axes for future R&D.
