RFQ Cooler SHIRaC developent

TL;DR

The paper details the development and experimental validation of the SHIRaC RFQ Cooler for high-emittance, high-current beams, achieving improved beam quality with reduced energy spread and emittance, and ensuring nuclear safety.

Contribution

It introduces a miniature RFQ at the exit to enhance beam quality, particularly energy spread reduction, and demonstrates successful beam transport with high efficiency.

Findings

Achieved a longitudinal energy spread close to 1 eV.

Reduced transverse emittance to less than 1.8 π.mm.mrad.

Transported over 95% of cooled beams to the HRS.

Abstract

The development of a new RFQ Cooler, named SHIRaC, was carried out to handle and cool typical SPIRAL 2 beams of large emittances (up to 80 {\pi}.mm.mrad) and high currents (up to 1 {\micro}A). SHIRaC is a part of SPIRAL 2 facility at GANIL laboratory in France. Its purposes are to enhance as much as possible the beam quality: transverse geometric emittance of less than 3 {\pi}.mm.mrad and a longitudinal energy spread close to 1 eV, and to transmit more than 60 % of ions. Numerical simulations and experimental studies have shown that the required beam quality can be reached only in the term of the emittance. The energy spread is very far from expected values. It is sensitive to the space charge and buffer gas diffusion and more importantly to the RF field derivative effect. The latter arises at the RFQ exit and increases with the following RF parameters: the frequency and the amplitude of the RF voltage applied to the RFQ electrodes. Studies allowing to enhance the cooled beam quality, mainly the energy spread reduction, are presented and discussed along this paper. They consist in implementing a miniature RFQ at the RFQ exit. Using the development of these studies, it becomes possible to enhance the cooled beam quality and to reach 1 eV of longitudinal energy spread and less than 1.8 {\pi}.mm.mrad of transverse geometric emittance for beam currents going up to 1 {\micro}A. The transport of the cooled beam from the exit of the extraction section towards a HRS has been done with an electrostatic quadrupole triplet. Simulations and first experimental tests showed that more than 95 % of cooled beams can reach the HRS. Finally, developments related to the nuclearization protection methods aimed to avoid the escape of any nuclear matter from the SHIRaC beamline are studied