DOPPLER SPECTROSCOPY OF A BEAM IN THE CHANNEL OF A H- ION-SOURCE

It is shown that high-accuracy contact-free measurements of die diverg ence and emittance of an accelerated H- ion beam at the exit from the source can in principle be performed by passive Doppler spectroscopy o f a beam of excited hydrogen atoms produced by neutralization of the i ons with excitation on the residual gas in the source channel. The int ensity of the H-alpha-line radiation detected by the Doppler system is calculated, taking into account the principal processes leading to th e excitation and deexcitation of the 3s, 3p, and 3d levels of the hydr ogen atoms in the beam, for residual gas densities of the order of 10( -4)-10(-5) Torr in the source channel. The computed H-alpha-line inten sity was confirmed experimentally, making it possible to perform photo electronic detection of the spectral contour of the line in the curren t mode rather than the photon-counting mode. (C) 1998, American Instit ute of physics. [S1063-7842(98)00406-1].