A nozzle valve having a programmable opening time has been realized and tested. Its working principle differs from those used before in similar devices. In a preliminary version, the valve has been shown to be able to deliver gas pulses having a rise time of about 45 &mgr;s and a variable time length from 250 &mgr;s (FWHM) to continuum. It can also be operated as a beam chopper with frequency in the range 0–270 Hz and a variable duty factor. The valve does not generate either rf disturbances or appreciable current spikes in the ground network. It is a simple construction device and does not require a critical setup.