New Applications for Linear Electron Accelerators*

Electron linacs in the 100 MeV to 25 GeV energy range have by now been in operation for periods ranging from one year to over 20 years. In 1951 the Mark III accelerator at Stanford became the first electron linac to exceed an energy of 100 MeV. Since then significant increases in maximum electron energy have been made by the h'Iark III (reaching an energy of 1 GeV in 1960) and SLAC (exceeding 20 GeV in 19G7). In the energy range between 100 and 600 MeV, emphasis has more recently been on the development of linacs with high intensity and duty cycle; for example, the NBS, Saclay and h’fIT accelerators. Because linacs approaching present limits of duty cycle and energy have been in operation for a number of years, most of the “easy” physics experiments have by now been carried out with these accelerators. Major increases in linac energy and ‘duty cycle would make possible a new generation of such experiments,, However, current worldwide trends in accelerator funding have reduced the chances for achieving major improvements in linac performance by straightforward increases in either length or rf power. Instead, more indirect and less costly schemes, such as recirculation or SLED 22 , will most probably be the means for achieving major performance gains. Superconducting linacs, of course, offer the possibility of greatly improving linac duty cycle and energy resolution. Even in the case of a superconducting l.inac, recirculation may be the best path toward attaining energies of interest for mediumand high-energy physics. .