Superconducting RFQs

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Hardware Commissioning of the Refurbished ALPI Linac at INFN-LNL to Serve as SPES Exotic Beam Accelerator

Abstract The ALPI linac at INFN-LNL was substantially refurbished in 2018, especially in view of its use as secondary accelerator for exotic species in the framework of the SPES project. In particular: 10 magnetic triplets were replaced with higher gradient ones; two cryomodules with quarter wave resonator were moved from the PIAVE injector to ALPI, so as to make them available both for exotic and stable beams; the cryogenic plant was renovated; the whole linac, its injector and its beam lines were eventually realigned via LASER tracking (LT). The expected outcome of the refurbishment project is a larger beam transmission (crucial for the efficient transport of the unavoidably low current exotic beams) and improved overall reliability so as to further extend the lifetime of an already 25 years old machine. The hardware commissioning of this new configuration will be reported

Experience with the ALPI linac resonators

Abstract The medium β section of the linac accelerator ALPI [G. Fortuna et al., Nucl. Instr. and Meth. A 328 (1993) 236] is now in operation: beams of 32 S, 37 Cl, 58 Ni, 76 Ge, 81 Br were accelerated for nuclear physics experiments in the first half of 1995. The medium β section of ALPI includes 12 cryostats containing four accelerating quarter-wave resonators each ( β = 0.11, f = 160 MHz). Two similar resonators are installed in a buncher cryostat and two in a rebuncher unit. Accelerating fields around 2.5 MV/m are available. The experience in cavity preparation, installation, conditioning and operation is described

Integration of RFQ beam coolers and solenoidal magnetic fields

Electromagnetic traps are a flexible and powerful method of controlling particle beams, possibly of exotic nuclei, with cooling (of energy spread and transverse oscillations) provided by collisions with light gases as in the Radio Frequency Quadrupole Cooler (RFQC). A RFQC prototype can be placed inside the existing Eltrap solenoid, capable of providing a magnetic flux density component Bz up to 0.2 T, where z is the solenoid axis. Confinement in the transverse plane is provided both by Bz and the rf voltage Vrf (up to 1 kV at few MHz). Transport is provided by a static electric field Ez (order of 100 V/m), while gas collisions (say He at 1 Pa, to be maintained by differential pumping) provide cooling or heating depending on Vrf. The beamline design and the major parameters Vrf, Bz (which affect the beam transmission optimization) are here reported, with a brief description of the experimental setup

Helium Gas Evacuation in Superconducting RFQ Structure

The PIAVE injector for the Legnaro Accelerator complex is an accelerating machine made of superconducting resonators. One of them, the superconducting RFQ, needs to be cooled by the helium bath on the whole outer surfaces. In particular the region of the electrode tips and the lower vertical electrode are involved in RF power dissipation and can have a trapped volume of liquid. During the operation the liquid evaporates and the produced gas needs to be evacuated, in order to cool the structure properly. The problem of gas production and evacuation from a trapped volume of liquid helium has been studied and solved. Studies of the possible evacuation systems and experimental apparatus are presente

Construction of superconducting RFQs at INFN-LNL

The tests on the stainless steel prototype for one of the two superconducting RFQs (SRFQs) for PIAVE (SRFQ2), the being built heavy ion injector for the Legnaro booster, were completed in summer 1998, while the construction of the first niobium resonator started in February 1998 and is expected to be completed by April 1999. The structure, resonating at 80 MHz, is 0.8 m long and 0.76 m in diameter. All technological aspects connected with the construction of the SRFQs, and the corresponding tests on the stainless steel model, are reviewed: development of the parts, assembly sequence, electron beam welding (EBW) steps, rough and fine adjustment of the resonant frequency, bead-pull measurements, characterization of the mechanical vibration modes, frequency change due to cooling down and chemical etching tests. The updated development of SRFQ1 is briefly reviewed