Normal-conducting Linac Research Articles

Installation and integrated testing of magnets for the ESS Linac

The European Spallation Source (ESS) linear accelerator is designed to accelerate a 62.5 mA, 2.86 ms, 14 Hz proton beam up to 2 GeV at the entrance of a rotating tungsten (W) target. Normal Conducting Linac (NCL) and Superconducting Linac (SCL) parts of the accelerator contain over 200 quadrupole, dipole and corrector magnets of different types and parameters for beam envelope and trajectory control. All magnets have been provided to ESS by in-kind collaborators and research institutes across Europe. Following the delivery of these components and their respective power converters to ESS, this proceeding presents the status of the installation together with the methodology and first obtained results from system local and integrated testing phase.

The Spallation Neutron Source Normal Conducting Linac RF System Design for the Proton Power Upgrade Project

The Spallation Neutron Source Normal Conducting Linac RF System Design for the Proton Power Upgrade Project

Thermally modified C-band acceleration unit for a high-repetition normal-conducting linac for free-electron lasers.

A high-repetition linear accelerator with multibeamline operation for X-rays allows users to perform multiple simultaneous experiments with an X-ray free-electron laser (XFEL) at lower actual cost per user while maintaining the availability of the laser. As the first step toward a higher pulse repetition rate (PRR), we developed radio frequency (RF) components at 5712 MHz and tested them for their feasibility at an RF PRR of 120 pulses per second (pps). To increase the RF PRR from the present value of 60 pps-at the SPring-8 Angstrom compact free-electron laser-to 120 pps, we re-examined the thermal designs of the present RF components for the XFEL. With the proposed design, the newly developed RF components worked well at 120 pps. The insulation-oil temperature in the high-voltage tank of the klystron modulator was below 70 °C, which is less than the operational temperature limit. At 5712 MHz, this is now the highest RF pulse repetition frequency yet to be achieved and represents a major step toward higher PRRs.

Lattice layout and linear optics for sharing superconducting linac

A superconducting (SC) linac is expected to lead to outstanding discoveries in various scientific fields because its beam current is a few orders of magnitude larger than in a normal-conducting linac. However, the widespread use of SC linac is limited by the high construction and operation costs. To resolve this problem, we propose a continuous wave (CW) operation of a SC linac shared by electron/positron beams for effective multi-purposes utilization. A high current positron/electron beam is required for high-energy physics projects such as linear collider and muon collider while high-current and high-quality electron beams is expected to realize the next generation X-ray light sources. As an example, we discuss the injector of the International Linear Collider, an X-ray free-electron laser and an energy-recovery linac light source. We found a feasible solution for the proposed multibeam operation despite the high-quality beam requirements and complicated opertion: control of mixed beams without pulsed magnets, lower beam loss and heat load in the cavity, high stability of beam energy, and operation at high average current.

Fermilab proton accelerator complex status and improvement plans

Fermilab carries out an extensive program of accelerator-based high energy particle physics research at the Intensity Frontier that relies on the operation of 8 GeV and 120 GeV proton beamlines for a number of fixed target experiments. Routine operation with a world-record 700 kW of average 120 GeV beam power on the neutrino target was achieved in 2017 as a result of the Proton Improvement Plan (PIP) upgrade. There are plans to further increase the power from 900–1000 kW. The next major upgrade of the FNAL accelerator complex, called PIP-II, is under development. It aims at 1.2 MW beam power on target at the start of the LBNF/DUNE experiment in the middle of the next decade and assumes replacement of the existing 40 years old 400 MeV normal-conducting Linac with a modern 800 MeV superconducting RF linear accelerator. There are several concepts to further double the beam power to [Formula: see text] 2.4 MW after replacement of the existing 8 GeV Booster synchrotron. In this review, we discuss current performance of the Fermilab proton accelerator complex, the upgrade plans for the next two decades and the accelerator R&D program to address cost and performance risks for these upgrades.

Dielectric assist accelerating structure

A higher-order ${\mathrm{TM}}_{02n}$ mode accelerating structure is proposed based on a novel concept of dielectric loaded rf cavities. This accelerating structure consists of ultralow-loss dielectric cylinders and disks with irises which are periodically arranged in a metallic enclosure. Unlike conventional dielectric loaded accelerating structures, most of the rf power is stored in the vacuum space near the beam axis, leading to a significant reduction of the wall loss, much lower than that of conventional normal-conducting linac structures. This allows us to realize an extremely high quality factor and a very high shunt impedance at room temperature. A simulation of a 5 cell prototype design with an existing alumina ceramic indicates an unloaded quality factor of the accelerating mode over 120 000 and a shunt impedance exceeding $650\text{ }\text{ }\mathrm{M}\mathrm{\ensuremath{\Omega}}/\mathrm{m}$ at room temperature.

Enabling cost-effective high-current burst-mode operation in superconducting accelerators

Superconducting (SC) accelerators are very efficient for CW or long-pulse operation, and normal conducting (NC) accelerators are cost effective for short-pulse operation. The addition of a short NC linac section to a SC linac can correct for the energy droop that occurs when pulsed high-current operation is required that exceeds the capability of the klystrons to replenish the cavity RF fields due to the long field fill-times of SC structures, or a requirement to support a broad range of beam currents results in variable beam loading. This paper describes the implementation of this technique to enable microseconds of high beam-current, 90mA or more, in a 12GeV SC long-pulse accelerator designed for the MaRIE 42-keV XFEL proposed for Los Alamos National Laboratory.

Normal conducting linac designs for low beam loading

To drive future X-ray FELs, normal-conducting linacs with a wide range of rf are being considered. In this paper, we present accelerator structure and high power rf system designs at three rf (2.856GHz, 5.712GHz and 11.424GHz) that are optimized for single bunch and multi-bunch linac operation with very low beam loading. General scaling laws for the main linac parameters are derived to serve as guidelines to optimize such linacs at other frequencies. The linac costs at the three rf are also discussed. High rf linacs are shown to provide compact, low cost and reasonably efficient drivers for X-ray FELs.