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Lepton scattering is an established ideal tool for studying inner structure of small particles such as nucleons as well as nuclei. As a future high energy nuclear physics project, an Electron-ion collider in China (EicC) has been proposed. It will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy-ion Accelerator Facility (HIAF) which is currently under construction, together with a new electron ring. The proposed collider will provide highly polarized electrons (with a polarization of ∼80%) and protons (with a polarization of ∼70%) with variable center of mass energies from 15 to 20 GeV and the luminosity of (2–3) × 1033 cm−2 · s−1. Polarized deuterons and Helium-3, as well as unpolarized ion beams from Carbon to Uranium, will be also available at the EicC. The main foci of the EicC will be precision measurements of the structure of the nucleon in the sea quark region, including 3D tomography of nucleon; the partonic structure of nuclei and the parton interaction with the nuclear environment; the exotic states, especially those with heavy flavor quark contents. In addition, issues fundamental to understanding the origin of mass could be addressed by measurements of heavy quarkonia near-threshold production at the EicC. In order to achieve the above-mentioned physics goals, a hermetical detector system will be constructed with cutting-edge technologies. This document is the result of collective contributions and valuable inputs from experts across the globe. The EicC physics program complements the ongoing scientific programs at the Jefferson Laboratory and the future EIC project in the United States. The success of this project will also advance both nuclear and particle physics as well as accelerator and detector technology in China. [ABSTRACT FROM AUTHOR]

The acceleration of high-current beam in Superconducting Radio Frequency (SRF) cavities is a challenging but essential for a variety of advanced accelerators. SRF cavities should be carefully designed to minimize the High Order Modes (HOM) power generated in the cavities by the beam current. The reduction of HOM power we demonstrate in a particular case can be quite large. This paper presents a method to systematically control the HOM resonance frequencies in the initial design phase to minimize the HOM power generation. This method is expected to be beneficial for the design of high SRF cavities addressing a variety of Energy Recovery Linac (ERL) applications. [ABSTRACT FROM AUTHOR]

Energy-recovery linacs (ERLs) are promising for advanced synchrotron light sources, high-power free electron lasers (FELs), high-brightness gamma-ray sources, and electron–ion colliders. To demonstrate the critical technology of ERL-based light sources, we have designed and constructed a test accelerator, the compact ERL (cERL). Using advanced technology that includes a photocathode direct current (DC) electron gun and two types of 1.3-GHz-frequency superconducting cavities, the cERL was designed to be capable of recirculating low emittance ( ≤ 1 mm ⋅ mrad) and high average-current ( ≥ 10 mA) electron beams while recovering the beam energy. During initial commissioning, the cERL demonstrated successful recirculation of high-quality beams with normalized transverse emittance of ∼ 0.14 mm ⋅ mrad and momentum spread of ∼ 1.2 × 10 −4 (rms) at a beam energy of 20 MeV and bunch charge below 100 fC. Energy recovery in the superconducting main linac was also demonstrated for high-average-current continuous-wave beams. These results constitute an important milestone toward realizing ERL-based light sources. [ABSTRACT FROM AUTHOR]

Realization of a short bunch beam by manipulating the longitudinal phase space distribution with a finite longitudinal dispersion following an off-crest acceleration is a widely used technique. The technique was applied in a compact test accelerator of an energy-recovery linac scheme for compressing the bunch length at the return loop. A diagnostic system utilizing coherent transition radiation was developed for the beam tuning and for estimating the bunch length. By scanning the beam parameters, we experimentally found the best condition for the bunch compression. The RMS bunch length of 250 ± 50 fs was obtained at a bunch charge of 2 pC. This result confirmed the design and the tuning procedure of the bunch compression operation for the future energy-recovery linac (ERL). [ABSTRACT FROM AUTHOR]

In this work we investigate the effect of the bunch pattern in a linac on the Higher Order Mode (HOM) power generation. The future ERL-based electron–ion collider eRHIC at BNL is used as an illustrative example. This ERL has multiple high current Superconducting Radiofrequency (SRF) 5-cell cavities. The HOM power generated when a single bunch traverses the cavity is estimated by the corresponding loss factor. Multiple re-circulations through the Energy Recovery Linac (ERL) create a specific bunch pattern. In this case the loss factor can be different than the single bunch loss factor. HOM power can vary dramatically when the ERL bunch pattern changes. The HOM power generation can be surveyed in the time and frequency domains. We estimate the average HOM power in a 5-cell cavity with different ERL bunch patterns. [ABSTRACT FROM AUTHOR]

Next-generation synchrotron radiation sources, such as X-ray free-electron lasers, energy recovery linacs, and ultra-low-emittance storage rings, are catalyzing novel methods of biomolecular microcrystallography and solution scattering. These methods are described and future trends are predicted. Importantly, there is a growing realization that serial microcrystallography and certain cutting-edge solution scattering experiments can be performed at existing storage ring sources by utilizing new technology. In this sense, next-generation sources are serving two distinct functions, namely, provision of new capabilities that require the newer sources and inspiration of new methods that can be performed at existing sources. [ABSTRACT FROM AUTHOR]

We present the design study of an innovative scheme to generate high repetition rate (multi-MHz-class) THz radiation pulses by using an Energy Recovered Super Conducting Linac operating in Continuous Wave mode driving a Free-Electron Laser Oscillator. The FEL performance is illustrated for one and two color operation. Start-to-end simulations are presented to assess the capability of this scheme for typical values of wavelengths of interest in the 10– 50 μ m (6–30 THz) range. [ABSTRACT FROM AUTHOR]

Abstract: For a future synchrotron light source based on a linac, e.g. an X-ray free electron laser and an energy recovery linac (ERL), an injector is a key component to generate a high brightness electron beam. For the acceleration and transportation of the electron beam in the injector, the adjustment of beam orbit inside the cavity is important to avoid the deterioration of the beam quality due to the transverse electric field of it, which causes the transverse emittance growth. To adjust the beam orbit, an investigation of the electromagnetic center of the cavity is required in the beam operation. This paper shows a new method for measuring the electromagnetic center of the cavity, and describes an analytical model of emittance growth due to a combination of transverse electric field and orbit offset. The validation of the method was confirmed by the emittance measurement in the compact ERL (cERL) injector at KEK. [Copyright &y& Elsevier]

Abstract: Exploratory measurements of the Brookhaven Energy Recovery Linac (ERL) cavity at superconducting temperature produced a long list of high order modes (HOMs). The niobium 5-cell cavity is terminated at each end with HOM ferrite dampers that successfully reduce the Q-factors to levels required to avoid beam break up (BBU) instabilities. However, a number of un-damped resonances with Q≥106 were found at 4K and their mode identification forms the focus of this paper. The approach taken here consists of bead pulling on a copper (Cu) replica of the ERL cavity with dampers involving various network analyzer measurements. Several different S 21 transmission measurements are used, including those taken from the fundamental input coupler to the pick-up probe across the cavity, others between beam-position monitor probes in the beam tubes, and also between probes placed into the cells. The bead pull technique suitable for HOM identification with a metallic needle or dielectric bead is detailed. This paper presents the results for HOMs in the first two dipole bands, the un-damped modes in the first quadrupole band, and the identification of several high-Q modes beyond. [Copyright &y& Elsevier]

Abstract: Future particle accelerators will require continuous wave operation of SRF cavities capable of supporting high beam currents. An example of this is the Energy Recovery Linac (ERL) at Cornell University, a next generation light source designed to run high currents (100mA) with a high bunch repetition rate (1.3GHz). Obtaining the beam emittance necessary to meet design specification requires strong damping of higher-order modes that can lead to beam breakup. We discuss the optimization and verification of the accelerating cavity. Next we show that an ERL constructed from the optimized cavity geometry – including realistic shape errors – can support beam currents in excess of 300mA while still maintaining beam stability. A niobium prototype 7-cell cavity was fabricated and tested in a horizontal cryomodule. We show that the prototype cavity exceeds quality factor and gradient specifications of at 16.2MV/m at 1.8K by 50%, reaching . The prototype cavity also satisfies all design constraints and has a higher order mode spectrum consistent with the optimized shape geometry. At 1.6K, the cavity set a record for quality factor of a multicell cavity installed in a horizontal cryomodule reaching . [Copyright &y& Elsevier]

Abstract: We report measurements of photon and neutron radiation levels observed while transmitting a 0.43MW electron beam through millimeter-sized apertures and during beam-off, but accelerating gradient RF-on, operation. These measurements were conducted at the Free-Electron Laser (FEL) facility of the Jefferson National Accelerator Laboratory (JLab) using a 100mev electron beam from an energy-recovery linear accelerator. The beam was directed successively through 6mm, 4mm, and 2mm diameter apertures of length 127mm in aluminum at a maximum current of 4.3mA (430kW beam power). This study was conducted to characterize radiation levels for experiments that need to operate in this environment, such as the proposed DarkLight Experiment. We find that sustained transmission of a 430kW continuous-wave (CW) beam through a 2mm aperture is feasible with manageable beam-related backgrounds. We also find that during beam-off, RF-on operation, multipactoring inside the niobium cavities of the accelerator cryomodules is the primary source of ambient radiation when the machine is tuned for 130mev operation. [Copyright &y& Elsevier]

Abstract: The Energy Recovery Linac (ERL) is one of the candidates for the next generation light sources, which is based on the 1.3GHz superconducting radio frequency (SRF) linear accelerator. The ERL can produce high brilliance synchrotron radiation and a short pulse beam. We investigated the beam dynamics in the compact-Energy Recovery Linac (c-ERL) with a beam energy of 35MeV, which is a prototype of the 5GeV ERL at KEK. One of the main goals of our studies on the c-ERL is the emittance compensation in the merger section to achieve an emittance smaller than 1.0mmmrad. In the case of the early commissioning phase, the injector system produces electron bunches of 5MeV with a repetition rate of 1.3GHz. The compensation of the emittance growth due to the space charge effect was investigated in order to achieve a small emittance at the exit of the merger. We discuss the results of a method to compensate the emittance growth which is based on beam envelope matching between the betatron function and the linear dispersion induced by the space charge force. We investigated the space charge effect when the beam energy in the superconducting RF section was changed. The effect of space charge in the arc section was also investigated. It is shown that the space charge effect in the c-ERL is an important source of distortion of the optics function. In this paper, we show the results on the analysis of the effect of space charge in the compact-ERL at KEK which has a low-energy beam. [Copyright &y& Elsevier]

Abstract: We present a novel modular magnetic system that can introduce a large and continuously variable path length difference without simultaneous variation of the longitudinal dispersion. This is achieved by using a combination of an electrically adjustable magnetic chicane and a mechanically adjustable focusing chicane. We describe how such a system may be made either isochronous or with a given longitudinal dispersion, and show that the nonlinear terms in such a system are relatively small. [Copyright &y& Elsevier]

The development of ways to increase the intensity of extreme ultraviolet (EUV) light sources for future EUV lithography is important to realize high throughput fine patterning. The energy-recovery linac (ERL) free-electron laser (FEL), which is an accelerator based light source, is a candidate for this. We clarify the design concept of the ERL-FEL for EUV light sources for future lithography, delivery systems of the FEL light to multiscanners, and future development items of the accelerator technologies and a possibility of the beyond EUV. [ABSTRACT FROM AUTHOR]

We expand upon the idea of using γ-rays for nuclear photofission of 238U at the giant dipole resonance to generate rare neutron-reach nuclei. The SPIRAL II project proposes the employment of 10-20-MeV Bremsstrahlung γ-rays generated by a 45-MeV electron beam /http://ganinfo.in2p3.fr/research/developments/ spiral2/ index.html/. In this paper, we explore the possibility of using a Compton γ-ray source for such a process. The Collider Accelerator Department at Brookhaven National Laboratory is developing high-current (up to 1 A), high-brightness (down to 1-mm · mrad normalized emittance), and high-energy energy-recovery linacs (up to 20-GeV electron beam energy for eRHIC). These electron beams are perfectly suited for generating photon beams with tremendous average power, approaching the megawatt level. The range of photon's energy extends from subelectronvolts from free-electron lasers to 10 GeV from the Compton process. In this paper, we focus on a γ-ray source for producing rare isotopes. [ABSTRACT FROM AUTHOR]

Abstract: Applying tomographic techniques to study the longitudinal phase space of the electron beam in future energy recovery linacs presents a challenge as it requires nondestructive diagnostics and the manipulations of the phase space are restricted by the energy recovery. The different methods of tomographic reconstruction and previous experiments at the BNL DUV-FEL facility are presented. Different schemes to utilize tomography for an ERL are proposed, including non-destructive transverse and longitudinal beam profile measurements and the necessary phase space transformations to generate the tomographic projections. [Copyright &y& Elsevier]

Abstract: The primary power consumption of large linear accelerators can be significantly lowered by means of superconducting RF technologies. Nevertheless, superconducting RF cavities dissipate energy at low temperatures, and large cryogenic plants have to be operated for the cryogenic supply. In particular, cryogenic plants for future superconducting Energy Recovery Linacs (ERLs) will require primary power in the order of some mega watts. Because of the fundamental laws of thermodynamics, the efficiencies of the cryogenic plants decrease with decreasing operation temperature. At the same time, the dynamic heat losses of high-Q 0 superconducting cavities decrease strongly with temperature. In order to minimize the primary power consumption at stable operating conditions of the cavities, the cryogenic operating conditions, and in particular the operation temperature, have to be optimized. With the focus on helium II cooling, some aspects of cryogenic efficiencies at low temperatures and the consequences for the layout of cryogenic systems are discussed. As an example, options for the cryogenic layout of the European XFEL-Linac including some ERL upgrade options are presented. [Copyright &y& Elsevier]

Abstract: Advanced accelerators as well as 4th generation light sources require extremely precise timing distribution. Energy recovery linacs, for example, require precise timing of the electron bunches reentering the linac in order to minimize the disturbance of the RF amplitude and phase to evade resonant effects on the subsequent accelerated bunch. The timing distribution system has to maintain femtosecond precision over lengths ranging from several hundred meters to a few kilometers. We discuss potential optical master oscillators with exceptionally low timing jitter that can be used for ultra-precise timing distribution in such facilities. A promising approach is the use of a mode-locked laser that generates pulses with an ultra-stable repetition rate, distributed through fiber links. A good candidate is a mode-locked Erbium-doped fiber laser, featuring very low high-frequency noise in comparison to presently available microwave sources. Laser systems locked to atomic references are discussed, which may eventually enable synchronization of independent lasers in the facility with potentially few-femtosecond precision as well as pump–probe measurements with attosecond time resolution. [Copyright &y& Elsevier]

Abstract: The proceedings of Working Group 4 of the 2005 Energy Recovery Linac (ERL) workshop are summarized. Working Group 4 dealt with the challenging topic of beam diagnostics for ERL machines. Energy Recovery Linacs represent a challenge for beam diagnostics from several perspectives; invasive versus non-invasive diagnostics, longitudinal and transverse beam diagnostics, overall machine timing/synchronization and machine protection. Beam diagnostics for an ERL can benefit strongly from the experience at third generation light sources, recirculating linacs and presently operating ERLs. During the workshop there were presentations from all these communities, representing a large range of experience in beam diagnostics. A brief summary Working Group 4 discussion is presented in this paper. [Copyright &y& Elsevier]

Abstract: We summarize the proceedings of Working Group 1 of the 2005 Energy Recovery Linac (ERL) Workshop. The subject of this working group, the electron gun and injector design, is arguably the most critical part of the ERL as it determines the ultimate performance of this type of accelerators. Working Group 1 dealt with a variety of subjects: The technology of DC, normal-conducting RF and superconducting RF guns; beam dynamics in the gun and injector; the cathode and laser package; modeling and computational issues; magnetized beams and polarization. A short overview of these issues covered in the Working Group is presented in this paper. [Copyright &y& Elsevier]

Abstract: For energy recovery linacs, excellent damping of higher-order modes (HOMs) in superconducting cavities is required for preventing beam breakup. As a promising method for this purpose, we propose to damp the HOMs using a radial transmission line attached to the sides of the cavity. The HOM powers are dissipated in RF absorbers while an accelerating field is rejected with a choke filter. An initial design of this radial-line HOM damper was carried out with simulations. Then, we measured the damping of HOMs by means of this method using a model cavity of the TESLA type. Investigations on a single-cell cavity showed a promising performance of HOM damping. [Copyright &y& Elsevier]

Abstract: Energy recovery linacs (ERLs) are potential candidates for the high power and high brightness electron beams sources. The main advantages of ERL are that electron beam is generated at relatively low energy, injected and accelerated to the operational energy in a linac, and after the use is decelerated in the same linac down to injection energy, and, finally, dumped. A merging system, i.e. a system merging together high energy and low energy beams, is an intrinsic part of any ERL loop. One of the challenges for generating high charge, high brightness electron beams in an ERL is development of a merging system. In this paper, we discuss merger system currently employed or planned to use for ERL as discuss their advantages and shortcomings. We also discuss analytical approach showing a way towards an optimal merger. [Copyright &y& Elsevier]

Abstract: A conceptual design for a test accelerator based on an energy recovery scheme is under way in developing a next generation light source at KEK. A high bright electron beam will be delivered from the test accelerator with a maximum energy of 200MeV using 1.3GHz superconducting accelerating cavities installed in two cryomodules. It is of great importance to design a pre-injector that can generate an electron beam with exceptionally high brightness and low emittances. A new simulation code is being developed to simulate the beam dynamics of the electron beam and to optimize the beam characteristics at the pre-injector. The simulation code describes semi-analytically the two-dimensional (transverse and longitudinal) beam dynamics of the electron beam based on a well-known envelope equation taking into account the space charge effect. The purpose of this code is not to rigorously simulate the particle dynamics, as is done by the particle tracking code “Parmela”, but rather to quickly optimize the design parameters of the accelerator components and beam characteristics themselves. This code has been validated by comparison with the results obtained from the “Parmela” code using the pre-injector design parameters. In this report, the development and some numerical results obtained from this new simulation code are presented in detail. [Copyright &y& Elsevier]

Abstract: The design, fabrication and commissioning of a 703.75MHz SRF photoinjector with a retractable multi-alkali photocathode designed to deliver 0.5A average current at 100% duty factor is the present undertaking of the electron cooling group in the Collider Accelerator Division of Brookhaven National Labs. This photoinjector represents the state of the art in photoinjector technology, orders of magnitude beyond the presently available technology, and should be commissioned by 2007. The R&D effort presently underway, and the focus of this paper, will address the numerous technological challenges that must be met for this project to succeed. These include the novel physics design of the cavity, the challenges of inserting and operating a multi-alkali photocathode in the photoinjector at these high average currents, and the design and installation of a laser system capable of delivering the required 10s of watts of laser power needed to make this photoinjector operational. [Copyright &y& Elsevier]

Abstract: Recent advances in superconducting radio-frequency (RF) technology and a better understanding of RF photoinjector design optimization make it possible to propose a specific design for a superconducting RF gun that can simultaneously produce both ultra-high peak brightness and high average current. Such a device is a critical component of next generation X-ray sources, such as self-amplified spontaneous emission free-electron lasers (SASE FEL) and energy recovery linac-based systems. The design presented in this paper is scaled from the present state-of-the-art normal conducting RF photoinjector that has been studied in the context of the linac coherent light source and SPARC SASE FEL injection schemes. Issues specific to the superconducing RF photoinjector, such as accelerating gradient limit, RF cavity and cryostat design, and compatibility with magnetic focusing and laser excitation of a photocathode are discussed. [Copyright &y& Elsevier]

Abstract: Energy recovery linacs (ERL) have significant potential uses in high energy physics and nuclear physics. We describe some of the potential applications which are under development by our laboratories in this area, and the technology issues that are associated with these applications. The applications that we discuss are electron cooling of high-energy hadron beams and electron–nucleon colliders. The common issues for some of these applications are high currents of polarized electrons, high-charge and high-current electron beams and the associated issues of high-order modes. The advantages of ERLs for these applications are numerous and will be outlined in the text. It is worth noting that some of these advantages are the high brightness of the ERL beams and their relative immunity to beam–beam disturbances. [Copyright &y& Elsevier]

Dilution of the electron beam emittance through a return arc is one of the critical problems in the design of an energy-recovery linac for a high-power FEL and synchrotron light sources. This study reports that the emittance dilution can be compensated by matching a beam envelope to the CSR-induced dispersion. In linear regime, this optimized design of an achromatic cell is obtained from a simple matrix calculation. [Copyright &y& Elsevier]

We propose a full-DC injector for an energy-recovery linac. The injector is based on a 2 MeV DC accelerator that is commercially available (Dynamitron type), combined with a photo cathode. A bunched beam from the DC accelerator is merged with a recirculating beam and injected into a superconducting buncher-booster, which accelerates the beam up to ∼20 MeV. The buncher-booster is operated in partial energy-recovery mode, in which we can reduce the capacity of the RF generators to 10 kW even for a high-average current operation, 100 mA. We present results of beam dynamics simulation and RF system optimization. [Copyright &y& Elsevier]

The first lasing near wavelength 140 μm was achieved in April 2003 on a high-power free electron laser (FEL) constructed at the Siberian Center for Photochemical Research. In this paper, we briefly describe the design of FEL driven by an accelerator–recuperator. Characteristics of the electron beam and terahertz laser radiation, obtained at the first experiments, are also presented in the paper. [Copyright &y& Elsevier]

Mini-pole (short period) in-vacuo superconducting undulators, a vert5ical-winding racetrack coil structure, a horizontal-winding racetrack coil structure and a staggered array structure, were studied for use in the X-ray source in a 1.5 GeV or a medium-energy 3 GeV storage ring. The magnetic arrays are all installed in the ultra-high vacuum environment, required for passing electron beams. In a periodic length of 15 mm and a gap of 5 mm, field strengths of 1.5 T, 1.5 T and 0.7 T can be generated in the three different structures, respectively. Additionally, the staggered undulator with variable-period length or a translator structure with different periodic length can yield various deflection parameters k, by driving a longitudinal solenoid field of 0.8 T. Accordingly, this study addresses the magnet structure of and mechanism of the magnet, and the advantages and disadvantages of the structures of these undulators. The spectral characteristics and the magnetic field features of these undulators are also studied. [ABSTRACT FROM AUTHOR]

4GLS is a novel low-energy light source proposed as a complementary facility to the DIAMOND X-ray project for the UK, and could probably replace the present SRS at Daresbury in about 6 years time. This facility will use a combination of three separate FELs, undulators and bending magnets to provide a unique source of high-brightness continuous and pulsed radiation from the IR to XUV (∼100 eV). Here, we give a brief description of the proposed FELs in the IR and VUV followed by a pre-design parameter study of the more technically challenging XUV high-gain FEL. The electron beam source for this FEL is a 600 MeV superconducting energy recovery linac with peak currents of a few kA, normalised rms emittance ∼3π mm mrad and rms energy spread ∼5×10−4. Computer simulations using the 3-D FEL code GENESIS 1.3 are used to investigate a feasible undulator and beam focussing scheme, allowing estimates for achievable radiation power and saturation length to be made. [Copyright &y& Elsevier]

An energy-recovery linac for a high-power FEL has been developed at Japan Atomic Energy Research Institute, and a research program towards a 10 kW FEL is in progress. Since FEL interaction introduces large energy spread in the electron beam, special attention should be paid to both transverse and longitudinal phase space manipulation through the return-arc and the deceleration path. We present beam dynamics simulations coupled with a 1D FEL code, and discuss the limitation of FEL extraction efficiency determined by phase space acceptance of the return path. [Copyright &y& Elsevier]