Since then, induction LINAC have been abondoned for this wavelength field, because it seemed very difficult to obtain the required electron beam qualities. On the other hand, new technologies, using photoinjectors (Los Alamos) or grid modulated electrostatic electron guns (TRW), minimizes space charge effects and thus allow lows emittances. For example, the photocathode at the High Brightness Accelerator Facility (HIBAF, at Los Alamos National Laboratory) is in the wall of the first RF cavity; owing to the very high electric field (26 MV/m), electrons become very quickly relativistic: space charge effects become negligible. Table 1 indicates emittances and energy dispersions of some FELs, given at the 12th FEL International Conference held in PARIS from Sept. 17 to 21, 1990. This is a major improvement, since characteristics of RF Linacs were about en=150 it mm mrad and AE/E = 1% previously. RF linacs with superconductivity cavities (TRW) should give better performance: • AE/E=0.1% thanks to high electric field stability; • lower emittance, thanks to a higher electric field and a better absorption of High Order Modes (HOM). Moreover, RF Linacs with superconducting cavities have major advantages for our applications:
RkJQdWJsaXNoZXIy MTU5NjU0Mg==