Computer-Automated Linac Diagnostics and Data Acquisition
Computer interactive diagnostics have been developed and tested for measuring RF Linac electron beam position and emittance. Electron beam position is measured with ferrite-loaded stripline monitors. The measured signals are processed by an APPLE-II computer, displayed and updated (at the Linac repetition rate) on a monitor. Data to determine emittance is collected by measuring electron beam spot size (using the wire scanner technique) as the focal strength of a quadrupole triplet is adjusted around the focus at the scanner. The emittance is calculated by the APPLE-II making a hyperbolic curve fit to these data.
Beam measurements on Argonne linac for collider injector design
The 20 MeV electron linac at Argonne produces 5 × 1010 electrons in a single bunch. This amount of charge per bunch is required for the proposed single pass collider at SLAC. For this reason the characteristics of the beam from this machine are of interest. The longitudinal charge distribution has been measured by a new technique. The technique is a variation on the deduction of bunch shape from a spectrum measurement. Under favorable conditions a resolution of about 1° of phase is possible, which is considerably better than can be achieved with streak cameras. The bunch length at 4.5 × 1010e− per bunch was measured to be 15° FWHM. The transverse emittance has also been measured using standard techniques. The emittance is 16 mm-mrad at 17. 2 MeV.
Non-Intercepting Monitor of Beam Current and Position
A compact monitor has been developed which measures beam current and beam position without intercepting or appreciably affecting the particle beam being measured. It is a broad band device which prevents the development of beam disturbing resonant modes. Although developed specifically for use on a short-pulse electron induction accelerator, it might be applied to other accelerator beams of pulsed or rf-bunched nature. The monitor consists of a resistive band inserted in the beam pipe wall with connections for reading the voltage across the band at each vertical and horizontal axis intercept. For pulsed or rf beams, return current equal in magnitude to the beam current flows on the beam pipe inside wall and through the resistive band. If the beam is centered, equal voltage appears on all four monitor connections. If the beam is off-center, the return currents are unsymmetrical and unequal voltages appear at the monitor connections. Beam current is proportional to the sum of all monitor voltages, while beam position is approximately proportional to the difference in voltage at opposing monitors. Tests and operating experience confirm its operation.