THE VARIABLE CURRENT GUN - THE PARAMETER TESTS AND THE RESULTS OF THEFIRST ELECTRON COOLING EXPERIMENTS AT LEAR

The electron cooling time (or equivalently the cooling force) is inver sely proportional to the electron beam current I-b, aimed to cool hot low-energy ions [1-3]. On the other hand, highly cooled ions tend to b ecome unstable. This implies that once the ion beam upper density limi t is attained, the electron current intensity has to be reduced to a l evel which prevents the ion beam instability and maintains low emittan ces. An adiabatic-type gun [4-6] has been constructed, which provides low-temperature electrons of large, but variable densities. The electr on current density is adjusted through the voltage control, U-g, of a so-called grid electrode. Its main drawback is the storage of secondar y electrons when the grid potential is larger than the anode potential , thus inducing a reduction of the nominal electron current intensity. A detailed analysis of the storage process is presented, and the way to cure this drawback is explained. Finally, experimental results are given.