Design and development of RF structures for Linac4

A Cell-Coupled Drift Tube Linac (CCDTL) accelerating structure at 352 MHz has been adopted for the energy range 40 to 90 MeV of Linac4, the new 160 MeV injector linac for the CERN accelerator complex. With regard to a conventional DTL in this energy range this structure presents the advantages of lower construction cost and easier access, cooling and alignment of the focusing quadrupoles placed between tanks. A full-scale high-power prototype representing 1/3 of a complete module has been designed and built at CERN. It is fed by a waveguide input coupler of novel conception. This paper summarizes the main mechanical features of the prototype and reports the RF tuning procedure and the results of high-power RF testing.

1993

The Superconducting Super Collider (SSC) Linear Accelerator (Linac) produces a 600-MeV, 35-ps, H-beam at a lo-Hz repetition rate. The beam is accelerated by a series of RF cavities. These consist of a Radio Frequency Quadrupole (RFQ), two bunchers. and four Drift Tube Linac (DTL) tanks at 427.617 MHz, and two bunchers, nine side-coupled Linac modules, and an energy compressor at 1282.851 MHz. The RFQ amplifier and the lowfrequency buncher cavity amplifiers use gridded tubes, while the other cavities use klystron amplifier systems. The RF control system consists of a reference line and cavity feedback and feedforward loops for each amplifier. The RF amplifier system for each of these accelerator cavities is described, and the current status of each system is presented.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

The energy upgrade of the SPARC_LAB photo-injector at LNF-INFN (Frascati, Italy) has been originally conceived replacing one low gradient (13 MV/m) 3 m long SLAC type S-band traveling wave (TW) section with two 1.4 m long C-band accelerating sections. Due to the higher gradients reached by such structures, a higher energy beam can be obtained within the same accelerator footprint length. The use of C-band structures for electron acceleration has been adopted in a few FEL linacs in the world, among others, the Japanese Free Electron Laser at SPring-8 and the SwissFEL at Paul Scherrer Institute (PSI). The C-band sections are traveling wave, constant impedance structures with symmetric input and output axial couplers. Their design has been optimized for the operation with a SLED RF pulse compressor. In this paper we briefly review their design criteria and we focus on the construction, tuning, low and high-power RF tests. We also illustrate the design and realization of the dedicated low level RF system that has been done in collaboration with PSI in the framework of the EU TIARA project. Preliminary experimental results appear to confirm the operation of such structures with accelerating gradients larger than 35 MV/m.

2011

Linac4 is employing three types of accelerating structures after the RFQ: a Drift Tube Linac (DTL), a Cell- Coupled DTL (CCDTL), and a Pi-Mode Structure (PIMS) to accelerate the beam up to 160 MeV at 352.2MHz. The structures are designed for a peak power of approximately 1 MW per power coupler, which is transported via rectangular waveguides from the klystron

… of EPAC 2006, …, 2006

The TOP Linac (Oncological Therapy with Protons), under development by ENEA and ISS is a sequence of three pulsed (5 microseconds, 300 Hz) linear accelerators: a 7 MeV, 425 MHz RFQ+DTL (AccSys Model PL-7), a 7-65 MeV, 2998 MHz Side Coupled Drift Tube Linac (SCDTL) and a 65-200 MeV, variable energy 2998 MHz Side Coupled Linac (SCL). The first SCDTL module structure, composed by 9 DTL tanks coupled by 8 side cavities, has been built. Low power RF measurements have shown good field uniformity and stability along the axis. The structure has been tested with a 1 -4 MW power RF. Results of low and high power tests are reported and discussed.

Journal of the Korean Physical Society, 2009

A conventional 20-MeV drift tube linac (DTL) for the Proton Engineering Frontier Project (PEFP) has been developed as part of the low-energy section of the 100-MeV proton accelerator. The 20-MeV DTL consists of four tanks, and the RF power generated by a klystron is coupled to the DTL tanks through RF power couplers. By introducing analytical and numerical methods to correlate the coupling coefficient with the coupling hole size in a dumbbell shaped iris coupler, we optimized the coupling coefficient to minimize the required power. The results from the two approaches are in excellent agreement with each other and with the experimental measurements. The coupling coefficient is shown to be proportional to the third power of the coupling hole diameter.

2018

We illustrate the RF design of the X-band linac for the upgrade of the SPARC_LAB facility at INFN-LNF (EuPRAXIA@SPARC_LAB). The structures are travelling wave (TW) cavities, working on the 2π/3 mode, fed by klystrons with pulse compressor systems. The tapering of the cells along the structure and the cell profiles have been optimized to maximize the effective shunt impedance keeping under control the maximum value of the modified Poynting vector, while the couplers have been designed to have a symmetric feeding and a reduced pulsed heating. In the paper we also present the RF power distribution layout of the accelerating module and a preliminary mechanical design.

HHH- …, 2009

Linac4 is the new 160 MeV, 40 mA Haccelerator which will be the source of particles for all proton accelerators at CERN from 2013. Its construction has started in 2008, as part of a programme for the progressive replacement or upgrade of the LHC injectors during the next decade. Linac4 will initially inject into the PS Booster and at a later stage into a 4 GeV Superconducting Proton Linac (SPL), which could ultimately be upgraded to high duty cycle operation. For this reason accelerating structures, RF infrastructure and shielding of Linac4 are dimensioned for higher duty cycle from the initial phase.

Project-X, a multi-MW proton source, is under develop-ment at Fermilab. It enables a Long Baseline Neutrino Ex-periment via a new beam line pointed to DUSEL in Lead, South Dakota, and a broad suite of rare decay experiments. The initial acceleration is provided by a 3-GeV 1-mA CW superconducting linac. In a second stage, about 5% of the H − beam is accelerated up to 8 GeV in a 1.3 GHz SRF pulsed linac and injected into the Recycler/Main Injector complex. In order to mitigate problems with stripping foil heating during injection, higher current pulses are acceler-ated in the CW linac in conjunction with the 1 mA beam which is separated and further accelerated in the pulsed linac. The optimal current in the pulsed linac is discussed as well as the constraints that led to its selection. A con-ceptual design which covers optics and RF stability anal-ysis is presented. Finally, the need for HOM damping is discussed.

2006

A conventional 20-MeV drift tube linac (DTL) for the Proton Engineering Frontier Project (PEFP) has been developed as part of the low-energy section of the 100-MeV proton accelerator. The 20-MeV DTL consists of four tanks, and the RF power generated by a klystron is coupled to the DTL tanks through RF power couplers. By introducing analytical and numerical methods to correlate the coupling coecient with the coupling hole size in a dumbbell shaped iris coupler, we optimized the coupling coecient to minimize the required power. The results from the two approaches are in excellent agreement with each other and with the experimental measurements. The coupling coecient is shown to be proportional to the third power of the coupling hole diameter.