Non-intercepting diagnostics for intense, strongly focused heavy ion beam

In order to compare the results of HEDP/WDM experiments with simulations, it is important to know beam parameters at the target. As high level of energy deposition would destroy any material1 in a single shot, nonintercepting methods have to be used for beam diagnostics. The longitudinal paramters – total number of particles and beam intensity profile – are recorded in every short with current transformers. At HHT, measurement of transverse beam profile at the focal plane is usually done by recording beam induced fluorescence of argon gas with two perpendicular, fast gated and intensified CCD-cameras. Due to hydrodynamic expansion of the heated gas during the irradiation, the observed beam profile may be blurred out. As an alternative non-intercepting beam diagnostic method, a capacitive pickup probe has been developed and successfully tested at the HHT experimental area. The probe has four equal knob capacitor plates in a cylindrical geometry, as shown in Figure 1. With this probe, the position of the beam position and its transverse aspect ratio at the focal plane can be precisely determined by calculating the dipole and quadrupole moments of the charge distribution induced by the ion beam on the probe plates. The signal difference from two opposite plates is proportional to the beam displacement ∆x (Eq. (1)), whereas the so-called ”quadrupole moment”2 q is given by Eq.(2):