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Fourth generation light sources based on high gain free electron lasers require production, acceleration and transport up to the undulator entrance of high brightness (low emittance, high peak current) electron bunches. Wake field effects in accelerating sections and in magnetic bunch compressors typically contribute to emittance degradation, and hence the design of the injector and its operation constitute the leading edge for high quality beam production and for the success of the future light sources. RF and DC guns, cathode materials, laser pulse shaping and sub-picosecond synchronization systems are evolving toward a mature technology to produce high quality and stable beams. Nevertheless, reduction of thermal emittance, damping of emittance oscillations and bunch compression are still the main issues and challenges for injector designs. With the advent of energy recovery linacs, superconducting RF guns have been also considered in many new projects as a possible electron source operating in CW mode. An overview of recent advancements and future perspectives of high performance electron injectors are presented in this article.

Direct current accelerators form the basis of many front-line industrial processes. They have many advantages that have kept them at the forefront of technology for many decades, such as a small and easily managed environmental footprint. In this article, the basic principles of the different subsystems (ion and electron sources, high voltage generation, control, etc.) are overviewed. Some well-known (ion implantation and polymer processing) and lesser-known (electron beam lithography and particle-induced X-ray aerosol mapping) applications are reviewed.

We suggest starting an accelerator physics project called the Mainz Energy-recovering Superconducting Accelerator (MESA) as an extension to the experimental facilities at the institute for nuclear physics. MESA may allow us to introduce an innovative internal target regime based on the ERL principle. A second mode of operation will be to use an external polarized electron beam for parity violating experiments. Furthermore, MESA could also allow us to establish a CW source of polarized positrons.

Since 2000, an inverted source of polarized electrons has been operated routinely at the electron stretcher accelerator ELSA, providing a pulsed beam with a current of 100 mA and a polarization of about 80 %. One micro-second long pulses with 100 nC charge are produced in space-charge limitation by irradiating a strained-layer superlattice photocathode (8 mm in diameter) with laser light from a flash lamp pumped Ti:Sapphire laser.

Part of the future hadron physics programme requires significantly higher beam intensity, which can be supplied by enlarging the emission area or by improving the quantum efficiency (QE). Both will significantly influence the beam parameters and the optics of the transfer line. Numerical simulations of the space-charge dominated beam transport show that a quasi lossless transport to the linear accelerator is achievable using the existing setup of magnets. Dedicated beam diagnostics like wire scanners and fluorescence monitors will allow an in situ optimization of the optics and the transfer efficiency.

Fourth generation light sources based on high gain free electron lasers require production, acceleration and transport up to the undulator entrance of high brightness (low emittance, high peak current) electron bunches. Wake field effects in accelerating sections and in magnetic bunch compressors typically contribute to emittance degradation, and hence the design of the injector and its operation constitute the leading edge for high quality beam production and for the success of the future light sources. RF and DC guns, cathode materials, laser pulse shaping and sub-picosecond synchronization systems are evolving toward a mature technology to produce high quality and stable beams. Nevertheless, reduction of thermal emittance, damping of emittance oscillations and bunch compression are still the main issues and challenges for injector designs. With the advent of energy recovery linacs, superconducting RF guns have been also considered in many new projects as a possible electron source operating in CW mode. An overview of recent advancements and future perspectives of high performance electron injectors are presented in this article.

Direct current accelerators form the basis of many front-line industrial processes. They have many advantages that have kept them at the forefront of technology for many decades, such as a small and easily managed environmental footprint. In this article, the basic principles of the different subsystems (ion and electron sources, high voltage generation, control, etc.) are overviewed. Some well-known (ion implantation and polymer processing) and lesser-known (electron beam lithography and particle-induced X-ray aerosol mapping) applications are reviewed.