Superconducting Accelerator Research Articles

The hydrogen migration in cryogenic tubes of superconductive accelerator with gas source

In superconductive linear accelerator, the performance and stability can be impacted by gas adsorbed on cryogenic surfaces adversely. The cryogenic devices usually work at 4.2 K or 1.9 K and are refrigerated by normal or super fluid liquid helium, respectively. The purpose of this paper is to study the character of gas migration in cryogenic tubes. Adsorption coefficient for hydrogen at 4.2 K is measured by experimental study. Then, a gas migration model is established based on the experimental results to depict the hydrogen migration process in cryogenic tubes. The experimental results and model analysis indicated that at cryogenic temperature (4.2 K), adsorption coefficient for hydrogen is very close to 1, which is several orders higher than the adsorption coefficient at room temperature, resulting in a unique pressure distribution pattern in cryogenic tubes when compared with the pressure distribution in room temperature tubes. At 4.2 K or 1.9 K, the gas migration process is obviously different from the process at room temperature and is significantly affected by the gas adsorption on the cryogenic surfaces. The model established in this article can be applied not only to hydrogen migration in cryogenic tubes but also to other gas migration in tubes with high adsorption coefficient.

Design of a cw, low-energy, high-power superconducting linac for environmental applications

The treatment of flue gases from power plants and municipal or industrial wastewater using electron beam irradiation technology has been successfully demonstrated in small-scale pilot plants. The beam energy requirement is rather modest, on the order of a few MeV, however the adoption of the technology at an industrial scale requires the availability of high beam power, of the order of 1 MW, in a cost effective way. In this article we present the design of a compact superconducting accelerator capable of delivering a cw electron beam with a current of 1 A and an energy of 1 MeV. The main components are an rf-gridded thermionic gun and a conduction cooled beta= 0.5 elliptical Nb3Sn cavity with dual coaxial power couplers. An engineering and cost analysis shows that the proposed design would result in a processing cost competitive with alternative treatment methods.

First heavy ion beam tests with a superconducting multigap CH cavity

Very compact accelerating-focusing structures, as well as short focusing periods, high accelerating gradients and short drift spaces are strongly required for superconducting (sc) accelerator sections operating at low and medium energies for continuous wave (cw) heavy ion beams. To keep the GSI-super heavy element (SHE) program competitive on a high level and even beyond, a standalone sc cw linac (Helmholtz linear accelerator) in combination with the GSI high charge state injector (HLI), upgraded for cw operation, is envisaged. Recently the first linac section (financed by Helmholtz Institute Mainz (HIM) and GSI) as a demonstration of the capability of 217 MHz multigap crossbar H-mode structures (CH) has been commissioned and extensively tested with heavy ion beam from the HLI. The demonstrator setup reached acceleration of heavy ions up to the design beam energy. The required acceleration gain was achieved with heavy ion beams even above the design mass to charge ratio at high beam intensity and full beam transmission. This paper presents systematic beam measurements with varying rf amplitudes and phases of the CH cavity, as well as phase space measurements for heavy ion beams with different mass to charge ratio. The worldwide first and successful beam test with a superconducting multigap CH cavity is a milestone of the R work of HIM and GSI in collaboration with IAP in preparation of the HELIAC project and other cw-ion beam applications.

A 2-D Finite-Element Model for Electrothermal Transients in Accelerator Magnets

Superconducting accelerator magnets require sophisticated monitoring and means of protection due to the large energy stored in the magnetic field. Numerical simulations play a crucial role in understanding transient phenomena occurring within the magnet, and can, therefore, help to prevent disruptive consequences. We present a 2-D FEM model for the simulation of electro-thermal transients occurring in superconducting accelerator magnets. The magnetoquasistatic problem is solved with a modified magnetic vector potential formulation, where the cable eddy currents are resolved in terms of their equivalent magnetization. The heat balance equation is then investigated, and the relevant heat sources are discussed. The model implements a two-port component interface and is resolved, as part of an electrical circuit, in a cooperative simulation scheme with a lumped-parameter network.

Injector linac stability requirements for high precision experiments at MESA

MESA is a recirculating superconducting accelerator under construction at Johannes Gutenberg-Universität Mainz. It will be used for high precision particle physics experiments in two different operation modes: external beam (EB) mode and energy recovery (ERL) mode. The operating beam current and energy in EB mode is 0.15 mA with polarized electrons at 155 MeV. In ERL mode an unpolarized beam of 1 mA at 105 MeV will be available. In a later construction stage of MESA the beam current in ERL-mode shall be upgraded to 10 mA. In order to achieve high beam stability and low energy spread in recirculating operation for external beam the acceleration in the main linac sections will be done on a certain phase with respect to the maximum of the accelerating field (off crest) while the return arcs provide longitudinal dispersion. On specific longitudinal working points this can result in a setting where any RF phase or magnitude jitters from main linac do not contribute to the resulting energy spread of the final beam at all. Then the resulting energy spread of the beam at the experiment is mostly determined by the beam properties provided by the injector linac. On the other hand the acceleration in ERL operation mode most likely needs to be done on crest of the accelerating field aiming for the highest efficiency in the energy recovering process albeit we are currently investigating different recirculation schemes for the ERL mode as well. Using on crest acceleration the achievable energy spread is determined by the longitudinal phase space properties behind the injector linac again but mostly by the bunch length of the beam injected to the main linac. Within this contribution we will investigate the requirements on the stability of the MESA injector linac MAMBO for achieving the experimental goals under both operating conditions.

Experience with Multi-Beam and Multi-Beamline FEL-Operation

DESY’s free-electron laser FLASH provides soft X-ray pulses for scientific users at wavelengths down to 4nm simultaneously in two undulator beamlines. They are driven by a common linear superconducting accelerator with a beam energy of up to 1.25 GeV. The superconducting technology allows the acceleration of electron bunch trains of several hundred bunches with a spacing of 1 microsecond or more and a repetition rate of 10 Hz. A fast kickerseptum system directs one part of the bunch train to FLASH1 and the other part to FLASH2 keeping the full 10 Hz repetition rate for both. The unique setup of FLASH allows independent FEL pulse parameters for both beamlines. In April 2016, simultaneous operation of FLASH1 and FLASH2 for external users started. This paper reports on our operating experience with this type of multi-beam, multi-beamline set-up.

Photon Beam Transport and Scientific Instruments at the European XFEL

European XFEL is a free-electron laser (FEL) user facility providing soft and hard X-ray FEL radiation to initially six scientific instruments. Starting user operation in fall 2017 European XFEL will provide new research opportunities to users from science domains as diverse as physics, chemistry, geo- and planetary sciences, materials sciences or biology. The unique feature of European XFEL is the provision of high average brilliance in the soft and hard X-ray regime, combined with the pulse properties of FEL radiation of extreme peak intensities, femtosecond pulse duration and high degree of coherence. The high average brilliance is achieved through acceleration of up to 27,000 electron bunches per second by the super-conducting electron accelerator. Enabling the usage of this high average brilliance in user experiments is one of the major instrumentation drivers for European XFEL. The radiation generated by three FEL sources is distributed via long beam transport systems to the experiment hall where the scientific instruments are located side-by-side. The X-ray beam transport systems have been optimized to maintain the unique features of the FEL radiation which will be monitored using build-in photon diagnostics. The six scientific instruments are optimized for specific applications using soft or hard X-ray techniques and include integrated lasers, dedicated sample environment, large area high frame rate detector(s) and computing systems capable of processing large quantities of data.

Cryogenics for high-energy particle accelerators: highlights from the first fifty years

Applied superconductivity has become a key technology for high-energy particle accelerators, allowing to reach higher beam energy while containing size, capital expenditure and operating costs. Large and powerful cryogenic systems are therefore ancillary to low-temperature superconducting accelerator devices – magnets and high-frequency cavities – distributed over multi-kilometre distances and operating generally close to the normal boiling point of helium, but also above 4.2 K in supercritical and down to below 2 K in superfluid. Additionally, low-temperature operation in accelerators may also be required by considerations of ultra-high vacuum, limited stored energy and beam stability. We discuss the rationale for cryogenics in high-energy particle accelerators, review its development over the past half-century and present its outlook in future large projects, with reference to the main engineering domains of cryostat design and heat loads, cooling schemes, efficient power refrigeration and cryogenic fluid management.

Instrumentation for localized superconducting cavity diagnostics

Superconducting accelerator cavities are now routinely operated at levels approaching the theoretical limit of niobium. To achieve these operating levels more information than is available from the RF excitation signal is required to characterize and determine fixes for the sources of performance limitations. This information is obtained using diagnostic techniques which complement the analysis of the RF signal. In this paper we describe the operation and select results from three of these diagnostic techniques: the use of large scale thermometer arrays, second sound wave defect location and high precision cavity imaging with the Kyoto camera.

Studies of X-ray burst reactions with radioactive ion beams from RESOLUT

Reactions on certain proton-rich, radioactive nuclei have been shown to have a significant influence on X-ray bursts. We provide an overview of two recent measurements of important X-ray burst reactions using in-flight radioactive ion beams from the RESOLUT facility at the J. D. Fox Superconducting Accelerator Laboratory at Florida State University. The 17 F(d,n) 18 Ne reaction was measured, and Asymptotic Normalization Coefficients were extracted for bound states in 18 Ne that determine the direct-capture cross section dominating the 17 F(p, γ ) 18 Ne reaction rate for T≲ 0.45 GK. Unbound resonant states were also studied, and the single-particle strength for the 4.523-MeV (3 + ) state was found to be consistent with previous results. The 19 Ne(d,n) 20 Na proton transfer reaction was used to study resonances in the 19 Ne(p, γ ) 20 Na reaction. The most important 2.65-MeV state in 20 Na was observed to decay by proton emission to both the ground and first-excited states in 19 Ne, providing strong evidence for a 3 + spin assignment and indicating that proton capture on the thermally-populated first-excited state in 19 Ne is an important contributor to the 19 Ne(p, γ ) 20 Na reaction rate.

Design and Experimental Study of a Model Magnet for Spiral-Sector FFAG Accelerators

A project to develop fundamental technologies for accelerator magnets using high- $T_{c}$ superconductors is currently underway. In this project, conceptual design studies of fixed-field alternating gradient (FFAG) accelerators for carbon cancer therapy and for accelerator-driven subcritical reactors have been carried out. To establish technologies for cryocooler-cooled high- $T_{c}$ superconducting (HTS) accelerator magnets wound with coated conductors, a downscaled model magnet system for a spiral-sector FFAG accelerator has been developed. A model magnet consisting of multiple coils with complicated shapes, including a negative-bend part or a 3-D bent part, was designed to demonstrate the generation of an asymmetrical magnetic field on the midplane of the magnet bore. One issue is how to wind coils for the accelerator magnets by using tape-shaped coated conductors, which have anisotropic bending flexibility between the flatwise and edgewise directions. Another issue is the effects of the characteristic features of the coated conductors on the accuracy of the magnetic field. The field precision of coils wound with coated conductors is considered to be influenced by the dimensional accuracy of the YBCO tapes and coils, as well as the magnetization of the HTS layer. This paper describes the design and fabrication of YBa2Cu3Ox coils for the model magnet, as well as disturbance factors of the field of the HTS magnet and the effect of dimensional variations of the YBCO coil on the magnetic field.

Performance of Conduction Cooled Splittable Superconducting Magnet Package for Linear Accelerators

New linear superconducting accelerators need superconducting magnet packages installed inside SCRF cryomodules to focus and steer electron or proton beams. A superconducting magnet package was designed and built as a collaborative effort of FNAL and KEK. The magnet package includes one quadrupole and two dipole windings. It has a splittable in the vertical plane configuration and features for conduction cooling. The magnet was successfully tested at room temperature, in a liquid He bath, and in a conduction cooling experiment. This paper describes the design and test results, including magnet cooling, training, and magnetic measurements by rotational coils. The effects of superconductor and iron yoke magnetization, hysteresis, and fringe fields are discussed.

Optimization of Distributed Data Processing System for NICA BM@N Experiment by Using Simulation

Superconducting accelerator complex NICA is now in a developing stage at the Joint Institute for Nuclear Research11Russian Federation, Moscow region, Dubna (JINR). The development of the NICA computing complex is carried out at the JINR's Laboratory of Information Technologies (LIT) with the aim to process, analyze, store experimental data and simulate its sophisticated design and evolution. NICA includes the BM@N experiment first run of which is planned to be performed in 2017. Therefore, it is necessary to develop a computing system for distributed data storing and processing for the experiment. The simulation program SyMSim is used to choose a proper architecture of the BM@N computing system infrastructure. SyMSim facilitates making a decision regarding a required equipment. The paper presents the results obtained by simulating a process of receiving and processing data from the BM@N experiment involving a model of the computing complex.

Numerical Simulation of Microchannel Deformation in Enhanced Insulation for Nb–Ti Superconducting Accelerator Magnets

A new insulation scheme for the Nb-Ti superconducting magnets to better extract heat from the coil was proposed in 2007, and several experiments were done to validate this novel concept, including the construction of a large aperture quadrupole. An essential parameter of this scheme is the size of the microchannels provided by a new topology of the insulation wrapping, allowing a direct helium path from the helium bath to the strands. The main question is whether these channels are still open under the large pressures induced during assembly and by electromagnetic forces. In this paper, one shows that a thermal model of the insulation scheme can be used to interpret the experimental data. The model suggests that the microchannels are significantly reduced with respect to their nominal values but are still well open. To validate this result, a finite-element model of the insulation and strands under pressure is done, and the behavior of this complex topology is estimated. The mechanical model confirms that the microchannels are open even under pressures of 100 MPa, with a cross-sectional reduction on the order of 50%. A parametric analysis of the microchannel deformation versus pressure is carried out, showing a good agreement with the experiments.

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.

Fiber Bragg Grating Cryosensors for Superconducting Accelerator Magnets

The design, fabrication, and tests of the new generation of superconducting magnets for the High Luminosity upgrade of the Large Hadron Collider (HL-LHC) require the support of an adequate sensing technology able to assure the integrity of the strain-sensitive and brittle superconducting cables through the whole service life of the magnet: assembly up to 150 MPa, cool down to 1.9 K, and powering up to about 16 kA. A precise temperature monitoring is also needed, in order to guarantee the safe working condition of the superconducting cables in the power transmission lines (SC-Link) designed to feed the magnet over long distance. Fiber Bragg Grating-based temperature and strain monitoring systems have been implemented in the first SC-Link prototype and in two subscale dipole magnets and tested in the cryogenic test facility at CERN, at 30 K, 77 K, and 1.9 K.

Reduction of helium loss from a superconducting accelerating cavity during initial cool-down and cryostat exchange by pre-cooling the re-condensing cryostat

A Zero-Boil-Off (ZBO) cryostat is designed to realize a compact, stand-alone cryogenic system for the AIST superconducting accelerator (SCA). Under normal operation there is no evaporative helium loss from the cryomodule and therefore operating costs associated with the supply of liquid helium can be eliminated. The only significant loss of helium from the module occurs during the initial cavity cool-down procedure or when the re-condensing cryostat is replaced. It takes about 3h to cool down the cryostat head from room temperature (300K) to 4K. During this time around 100L of liquid helium is lost due to evaporation. By pre-cooling the cryostat inside a low heat load vacuum tube before transfer to the cryomodule, this evaporative loss could be essentially eliminated, significantly reducing the volume of liquid helium required for the initial cryomodule cool-down. The pre-cooling system also provides an efficient method to test the cryostat prior to use.

Study on the selection of BLM detector for C-ADS Injector II

The injector of C-ADS (Chinese Accelerator Driven Sub-critical System) project is a high current, fully super-conducting proton accelerator. Meanwhile, a BLM system is indispensable for this facility, especially in low energy segments. This paper presents some basic simulations for 10 MeV proton by Monte Carlo program FLUKA, as well as the distributions on different secondary particles in three aspects: angular, energy spectrum, and current. These results are beneficial to selecting the detector type and its location and determining its dynamic range matching different requirements for both fast and slow beam loss. Furthermore, in this paper the major impact of the background is also analyzed, such as superconducting cavity X radiation and radiation caused by material activation. This work is meaningful in BLM system research.

超伝導加速管用ハーフセル形状測定装置の開発 第4章 セルの測定実験

超伝導加速管用ハーフセル形状測定装置の開発 第4章 セルの測定実験

Design of N-type feedthrough for HOM coupler for cERL injector cavity

The injector cryomodule for the compact energy recovery linac (cERL) is under development at KEK. The cryomodule with 3L-band 2-cell cavities was built in June 2012. A prototype 2-cell cavity and three other 2-cell cavities with five higher-order-mode (HOM) couplers for actual operation were fabricated in May 2011. The vertical tests of these cavities were carried out after standard surface preparation at the KEK Superconducting accelerator Test Facility (KEK-STF) from October 2010 to March 2012. Radio-frequency feedthroughs with high thermal conductivity for the HOM coupler were also developed to achieve 12.5MV/m CW operation in the cryomodule. A Kyocera NR-type connector was modified to connect to this target. The results of vertical tests of the 2-cell cavities to measure their feedthrough performance will be reported in this paper.