Superconducting Linear Accelerator Research Articles

The CeBrA demonstrator for particle-[formula omitted] coincidence experiments at the FSU Super-Enge Split-Pole Spectrograph

We report on a highly selective experimental setup for particle-γ coincidence experiments at the Super-Enge Split-Pole Spectrograph (SE-SPS) of the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University (FSU) using fast CeBr3 scintillators for γ-ray detection. Specifically, we report on the results of characterization tests for the first five CeBr3 scintillation detectors of the CeBr3 Array (CeBrA) with respect to energy resolution and timing characteristics. We also present results from the first particle-γ coincidence experiments successfully performed with the CeBrA demonstrator and the FSU SE-SPS. We show that with the new setup, γ-decay branching ratios and particle-γ angular correlations can be measured very selectively using narrow excitation energy gates, which are possible thanks to the excellent particle energy resolution of the SE-SPS. In addition, we highlight that nuclear level lifetimes in the nanoseconds regime can be determined by measuring the time difference between particle detection with the SE-SPS focal-plane scintillator and γ-ray detection with the fast CeBrA detectors. Selective excitation energy gates with the SE-SPS exclude any feeding contributions to these lifetimes.

Multiparticle-hole excitations in nuclei near N = Z = 20: $$^{41}$$K

This experimental study of high-spin structure near \(N = Z = 20\) nuclei was focused on \(^{41}\)K, but will also mention three newly observed \(\gamma \) transitions in \(^{41}\)Ca observed in the same reaction. High-spin states were populated using the \(^{26}\)Mg(\(^{18}\)O, \(p2n\gamma \))\(^{41}\)K and \(^{26}\)Mg(\(^{18}\)O, \(3n\gamma \))\(^{41}\)Ca reactions. The experiment was carried out at an incident beam energy of 50 MeV at the Florida State University (FSU) John D. Fox Superconducting Linear Accelerator Laboratory and used the FSU high-purity germanium detector array. The \(^{41}\)K level scheme was extended to 12325 keV, possibly with J\(^{\pi }\) = 25/2\(^-\) or 27/2\(^+\), by means of 25 new transitions and that of \(^{41}\)Ca to 9916 keV. Linear polarization and a measure of angular distribution results are also reported and used to provide information on the spins and parities of several states in the \(^{41}\)K level scheme. The results have been compared to the spsdpf cross-shell FSU shell model interaction calculations. The theoretical results from configurations involving no or one additional nucleon promoted from the sd to the fp shell agree relatively well with the energies of known states, while those that involve multi-particle excitations paint an interesting and complex picture of interplay between single-particle excitations, collective pairing, and deformation. This presents an interesting challenge for future theory.

CBETA: First Multipass Superconducting Linear Accelerator with Energy Recovery.

Energy recovery has been achieved in a multipass linear accelerator, demonstrating a technology for more compact particle accelerators operating at higher currents and reduced energy consumption. Energy delivered to the beam during the first four passes through the accelerating structure was recovered during four subsequent decelerating passes. High-energy efficiency was achieved by the use of superconducting accelerating cavities and permanent magnets. The fixed-field alternating-gradient optical system used for the return loop successfully transported electron bunches of 42, 78, 114, and 150MeV in a common vacuum chamber. This new kind of accelerator, an eight-pass energy recovery linac, has the potential to accelerate much higher current than existing linear accelerators while maintaining small beam dimensions and consuming much less energy per electron.

European XFEL Superconducting Cryomodules Characterization Toward Modules Acceptance and Future LLRF Operation

This paper describes some achievements of the low-level radio frequency (LLRF) tests performed to evaluate the superconducting cryomodules in preparation of their installation in the European X-ray Free Electron Laser (XFEL) accelerator. The software developed to characterize the cryomodules tested at the Accelerator Module Test Facility (AMTF) will be presented. The purpose of these tests is to evaluate some of the key parameters of the eight Tera Electronvolt Superconducting Linear Accelerator cavities, housed in every cryomodule. These parameters include: cavity quench gradients, cavity fundamental resonant modes, performance of the slow and fast frequency tuners, and characteristics of the input power coupler. These results impact the final decision on the cryomodule acceptance and its installation inside the linear accelerator (linac). In this approach, the MicroTCA.4-based LLRF system is used to control and assess the cryomodule performance. Middle layer servers are developed to verify the tests initial conditions, carry the test, and log the results in a dedicated database. The tests results provide a basis for the cryomodule validation, but also serve as a reference useful during the commissioning and operating phase of the accelerator.

Simultaneous acceleration of two kinds of ion beams in the RISP

The Rare Isotope Science Project (RISP) is a research complex consisting of a heavy-ion accelerator, which contains a front-end system, a super-conducting linear accelerator, an isotope separator online (ISOL) system, and an in-flight system. The original purpose of the post-linear-accelerator (post-linac) section was to accelerate either a stable driver beam derived from an electron cyclotron resonance ion source, or an unstable rare-isotope beam from an ISOL system. The post-linac lattice has now been redesigned using a novel and improved acceleration concept that allows the simultaneous acceleration of both a stable driver beam and a radioisotope beam. To achieve this, the post-linac lattice is set for a mass-to-charge ratio (A/q) that is the average of the two beams. The performance of this simultaneous two-beam acceleration is here assessed using two ion beams: \(^{58}{\mathbf{Ni}}^{8+}\) and \(^{132}{} {\mathbf{Sn}}^{20+}\). A beam dynamics simulation was performed using the TRACK and TraceWin codes. The resultant beam dynamics for the new RISP post-linac lattice design are examined. We also estimate the effects of machine errors and their correction on the post-linac lattice.

Overview of ten-year operation of the superconducting linear accelerator at the Spallation Neutron Source

The Spallation Neutron Source (SNS) has acquired extensive operational experience of a pulsed proton superconducting linear accelerator (SCL) as a user facility. Numerous lessons have been learned in its first 10 years operation to achieve a stable and reliable operation of the SCL. In this paper, an overview of the SNS SCL design, qualification of superconducting radio frequency (SRF) cavities and ancillary subsystems, an overview of the SNS cryogenic system, the SCL operation including SCL output energy history and downtime statistics, performance stability of the SRF cavities, efforts for SRF cavity performance recovery and improvement at the SNS, and maintenance activities for cryomodules are introduced.

Performance of cryocoolers in a High Temperature Superconducting ECR ion source (HTS-ECR) and its application for the High Current Injector Programme at IUAC, New Delhi

At the Inter University Accelerator Centre, a high current injector programme (HCI) is being developed as an alternate injector to the superconducting linear accelerator (SC-LINAC). For this purpose, a high temperature superconducting ECR ion source, PKDELIS, based on Gifford McMahon cryocoolers was designed, installed and commissioned in the Low Energy Beam Transport section of the high current injector. The ion source will inject multiply charged ions having A/q ∼ 6 for further acceleration into the downstream RFQ and DTL accelerators before final injection into the superconducting linear accelerator. The details of the design, and experimental results of the ion source together with performance of the cryocoolers are presented in this paper.

Mirror symmetric optics design for charge-stripping section in Rare Isotope Science Project

The main aim of the Rare Isotope Science Project is to construct a high power heavy-ion accelerator based on the superconducting linear accelerator (SCL). The heavy ion accelerator is a key research facility that will allow ground-breaking research into numerous facets of basic science, such as nuclear physics, astrophysics, atomic physics, life science, medicine and material science. The machine will provide a beam power of 400kW with a 238U79+ beam of 8pμA and 200MeV/u. One of the critical components in the SCL is the charge stripper between the two segments, SCL1 and SCL2, of the SCL. The charge stripper removes electrons from the ion beams to enhance the acceleration efficiency in the subsequent SCL2. To improve the efficiency of acceleration and power in SCL2, the optimal energy of stripped ions in a solid carbon foil stripper was estimated using the code LISE++. The thickness of the solid carbon foil was 300μg/m2. The charge stripping efficiency of the solid carbon stripper in the present study was approximately 87%. For charge selection from the ions produced by the solid carbon stripper, a dispersive section is needed down-stream of the foil. The designed optics for the dispersive section is based on the mirror-symmetric optics to minimize the effect of high-order aberrations.

Preliminary design and simulation of a 162.5 MHz high-intensity proton RFQ for an accelerator driven system

A new procedure for the design and simulation of a Radio Frequency Quadrupole (RFQ) accelerator has been developed at the Argonne National Laboratory. This procedure is integrated with the beam dynamics design code DESRFQ and the simulation code TRACK, which are based on three-dimensional field calculations and the particle-in-cell mode beam dynamics simulations. This procedure has been applied to the development of a 162.5 MHz CW RFQ which is capable of delivering a 10 mA proton beam for the Accelerator Driven System (ADS) of the CAS. The simulation results show that this RFQ structure is characterized by the stable values of the beam acceleration efficiency for both the zero current beam and space charge dominated beam. For an average beam current of 10 mA, there is no transverse rms emittance growth, the longitudinal rms emittance at the exit of RFQ is low enough and there is no halo formation. The beam accelerated in the RFQ could be accepted easily and smoothly by the following super-conducting linear accelerator.

Research and Development Program on Accelerator Driven Subcritical System in JAEA

For a dedicated transmutation system, Japan Atomic Energy Agency (JAEA) has been proceeding with the research and development on an accelerator-driven subcritical system (ADS). The ADS proposed by JAEA is a lead-bismuth eutectic (LBE) cooled fast subcritical core with 800 MWth. JAEA has started a comprehensive research and development (R&D) program since the fiscal year of 2002 to acquire knowledge and elemental technology that are necessary for the validation of engineering feasibility of the ADS. In this paper, the outline and the results in the first three-year stage of the program are reported. Items of R&D were concentrated on three technical areas peculiar to the ADS: (1) a superconducting linear accelerator (SC-LINAC), (2) the LBE as spallation target and core coolant, and (3) a subcritical core design and reactor physics of the ADS. For R&D on the accelerator, a prototype cryomodule was built and its good performance in electric field was examined. For R&D on the LBE, various technical data for material corrosion, thermal-hydraulics and radioactive impurity were obtained by loop tests and reactor irradiation. For R&D on the subcritical core, engineering feasibility for the LBE cooled tank-type ADS was discussed using thermal-hydraulic and structural analysis not only in normal operation but also in transient situations. Reactor physics experiments for subcritical monitoring and physics parameters of the ADS were also performed at critical assemblies.

Research and Development Program on Accelerator Driven Subcritical System in JAEA

For a dedicated transmutation system, Japan Atomic Energy Agency (JAEA) has been proceeding with the research and development on an accelerator-driven subcritical system (ADS). The ADS proposed by JAEA is a lead-bismuth eutectic (LBE) cooled fast subcritical core with 800 MWth. JAEA has started a comprehensive research and development (R&D) program since the fiscal year of 2002 to acquire knowledge and elemental technology that are necessary for the validation of engineering feasibility of the ADS. In this paper, the outline and the results in the first three-year stage of the program are reported. Items of R&D were concentrated on three technical areas peculiar to the ADS: (1) a superconducting linear accelerator (SC-LINAC), (2) the LBE as spallation target and core coolant, and (3) a subcritical core design and reactor physics of the ADS. For R&D on the accelerator, a prototype cryomodule was built and its good performance in electric field was examined. For R&D on the LBE, various technical data for material corrosion, thermal-hydraulics and radioactive impurity were obtained by loop tests and reactor irradiation. For R&D on the subcritical core, engineering feasibility for the LBE cooled tank-type ADS was discussed using thermal-hydraulic and structural analysis not only in normal operation but also in transient situations. Reactor physics experiments for subcritical monitoring and physics parameters of the ADS were also performed at critical assemblies.

The features of high intensity beam dynamics in low energy super-conducting linear accelerator

The super-conducting linear accelerator is considered as a candidate for the high intensity beam acceleration in low energy region from 2–5 MeV and up to 50–100 MeV. The conventional room temperature linear accelerator was struck off the list of effective accelerators for this purpose, because of the high power RF and the appropriate cooling systems are needed to produce high gradient with duty factor near to 100%. The super-conducting linear accelerator has a number of advantages in comparison with room temperature accelerators. However, due to RF requirements the geometry of super-conductive cavity has to be simplified as much as possible. Also cavities belonging to one family should have identical geometry. Therefore in such accelerators the longitudinal and transverse dynamics of high intense beam are more complicated. In this paper, we consider 3D beam dynamics together with space charge effect. The latter is investigated in the system without synchronism, when focusing and defocusing factors in longitudinal and transverse planes are the time dependent functions.

Beam dynamics in super-conducting linear accelerator: Problems and solutions

The linac based on SC cavities has special features. Due to specific requirements the SC cavity is desirable to have a constant geometry of the accelerating cells with limited family number of cavities. All cavities are divided into modules, and each module is housed into one cryostat. First of all, such geometry of cavity leads to a non-synchronism. Secondly, the inter-cryostat drift space parametrically perturbs the longitudinal motion. In this article, we study the non-linear resonant effects due to the inter-cryostat drift space, using the separatrix formalism for a super-conducting linear accelerator [Yu. Senichev, A. Bogdanov, R. Maier, Phys. Rev. ST AB 6 (2003) 124001]. Methods to avoid or to compensate the resonant effect are also presented. We consider 3D beam dynamics together with space charge effects. The final lattice meets to all physical requirements.

Achievement of [formula omitted] in the superconducting nine-cell cavities for TESLA

The Tera Electronvolt Superconducting Linear Accelerator (TESLA) is the only linear electron–positron collider project based on superconductor technology for particle acceleration. In the first stage with 500 GeV center-of-mass energy an accelerating field of 23.4 MV/ m is needed in the superconducting niobium cavities which are operated at a temperature of 2 K and a quality factor Q 0 of 10 10. This performance has been reliably achieved in the cavities of the TESLA Test Facility (TTF) accelerator. The upgrade of TESLA to 800 GeV requires accelerating gradients of 35 MV/ m . Using an improved cavity treatment by electrolytic polishing, it has been possible to raise the gradient to 35– 43 MV/ m in single cell resonators. Here we report on the successful transfer of the electropolishing technique to multi-cell cavities. Presently 4 nine-cell cavities have achieved 35 MV/ m at Q 0⩾5×10 9, and a fifth cavity could be excited to 39 MV/ m . In two high-power tests it could be verified that EP-cavities preserve their excellent performance after welding into the helium cryostat and assembly of the high-power coupler. One cavity has been operated for 1100 h at the TESLA-800 gradient of 35 MV/ m and 57 h at 36 MV/ m without loss in performance.

Numerical simulation of two-phase Helium II stratified flow in cryogenic units of TESLA

Numerical simulation has been carried out for two-phase Helium II stratified flow in 12 horizontal or declining cryogenic units each with a length of about 2.5 Km for the proposed 500 GeV TESLA (TeV Superconducting Linear Accelerator). The simulation predicts the He II level, the vapor mass flow rate in the two-phase tube, and the pressure profile through the gas return pipe of all units as well. Based on the numerical results the flow pattern and the stability of He II/vapor two-phase flow are discussed.

Magnet and superconductor development for a high power SMES based power modulator

A superconducting magnetic energy storage (SMES) based power modulator is being developed by the Forschungszentrum Karlsruhe for the proposed TESLA (TeV Superconducting Linear Accelerator) project, under development at the Research Centre DESY, Hamburg. Given the high power (25 MW), high dB/dt (above 50 T/s) pulses required for this application, a cored Rutherford cable with copper oxide insulated strands of mixed matrix NbTi conductor was chosen, to minimize AC losses. The modulator magnet will utilize a structure to provide good cooling of the liquid helium cooled conductor. Optimization of the magnet system with respect to stray magnetic field and costs has led us to choose two solenoids in antiparallel orientation. A test solenoid was constructed and tested, to measure conductor performance and AC losses. The current distribution in the individual strands of the cable was measured at different current ramp rates, through the use of low resistance shunts. Results of these tests and calculations are presented, along with details of the full sized magnets for the modulator.