A synchronous beam sweeper for heavy ions

The Argonne Tandem Linac Accelerator System (ATLAS) facility provides a wide range of accelerated heavy ions from the periodic table. Frequently, the beam delivery rate of 12 MHz is too fast for the type of experiment on line. Reaction by-products from a target bombardment may have a decay interval much longer than the dead time between beam bunches. To prevent data from being corrupted by incoming ions a beam sweeper was developed which synchronously eliminates selected beam bunches to suit experimental needs. As the sweeper is broadband (DC to 4 MHz), beam delivery rate can be instantaneously changed. Ion beam bunches are selectively kicked out by an electrostatic dipole electrode pulsed to 2 kVDC. The system has been used for almost three years with several hundred hours of operating time logged to date. Beam bunch delivery rates of 6 MHz down to 25 kHz have been provided. Since this is a nonresonant system, any beam delivery rate from 6 MHz down to zero can be set. In addition, burst modes have been used where beam is supplied in 12-MHz bursts and then shut down for a period of time set by the user.<>