Development steps of the LEBT Chopper
D. Rifuggiato, A. Caruso, F. Consoli, G. Gallo, E. Zappalà and M. Di Giacomo
The slow chopper of the Low Energy Beam Transport-line (LEBT), is the device used in the Spiral 2 driver to rapidly cut the beam when required. This device also participates (in combination with the RFQ) to change the beam intensity during the commissioning and tuning phases of the accelerator and to the match beam structure when rotating targets are used. Its design and manufacture constitute one of the work-packages of the accelerator RF systems.
INFN-LNS (Catania, Italy) and GANIL (Caen, France) have collaborated to the design of this component, and INFN LNS, in the framework of the European SPIRAL2 Preparatory Phase project, is in charge of manufacturing and test of a full scale prototype.
The Slow Chopper first developments focused on field maps simulation, electrode geometry design, electrical power design, prototyping and tests in an existing vacuum chamber. The design approach was focused mainly on the reliability and decrease of the maintenance time, both being very important issues in high power accelerators. For the power and high voltage parts, standard commercial devices were chosen, that are easy to check and to replace in case of failure. These devices were successfully tested at INFN-LNS late in 2008.
A protection system based on a pick-up antenna was developed in 2009 to check the high voltage presence and to produce an alarm in case of faulty operation of the device.
The standard GANIL high voltage power supply interface was finally chosen to let the device communicate with the machine computer control.
The latest development steps will check the radiation hardness of the main components and the behaviour on a real beam. Spare units of the HV power supply and of the fast HV switch are going to be irradiated and checked at the IFIN-HH, in Romania, while a new vacuum chamber is being prepared at SARAF, Israel, to host the electrodes for a test on their high intensity beam. The present preliminary prototype is a quite complete system (power electronics and electrodes) to be available for beam tests. This test will show whether more detailed electrostatic and beam dynamics simulations still have to be performed to optimize the electrode shape.