Superconducting Accelerator Research Articles

Evaluation of the Parallel-Scheme Varistors as Energy-Extraction System for a Test Facility of Superconducting Accelerator Magnet

Evaluation of the Parallel-Scheme Varistors as Energy-Extraction System for a Test Facility of Superconducting Accelerator Magnet

Loss of insulation vacuum tests on an EuXFEL cryomodule

Many Free Electron Lasers (FEL) are nowadays based on linear superconducting accelerators (linacs). The typical layout of such a linac consists of a number of cryomodules (CMs) arranged in strings. Each cryogenic circuit in a string is protected by safety valves (SVs) in case of failure of the system or a catastrophic event. A typical worst-case scenario considers the venting of the insulation vacuum, causing a fast and uncontrolled warm up of the cryogenic circuits. Such venting can for example take place across a pump port belonging to a string. The amount of heat deposited on each circuit is a very important parameter to correctly size the safety devices.This paper describes the tests performed at DESY on an EuXFEL cryomodule to evaluate the heat input to the three cryogenic circuits of the CM while venting the insulation vacuum. Test results are given with a particular focus of their application to long strings.

Toward Practical Superconducting Accelerators for Machine Learning Using U-SFQ

Most popular superconducting circuits operate on information carried by ps-wide, μV-tall, single flux quantum (SFQ) pulses. These circuits can operate at frequencies of hundreds of GHz with orders of magnitude lower switching energy than complementary-metal-oxide-semiconductors (CMOS). However, under the stringent area constraints of modern superconductor technologies, fully-fledged, CMOS-inspired superconducting architectures cannot be fabricated at large scales. Unary SFQ (U-SFQ) is an alternative computing paradigm that can address these area constraints. In U-SFQ, information is mapped to a combination of streams of SFQ pulses and in the temporal domain. In this work, we extend U-SFQ to introduce novel building blocks such as a multiplier and an accumulator. These blocks reduce area and power consumption by 2\(\times\)and 4\(\times\)compared with previously proposed U-SFQ building blocks and yield at least 97% area savings compared with binary approaches. Using these multiplier and adder, we propose a U-SFQ Convolutional Neural Network (CNN) hardware accelerator capable of comparable peak performance with state-of-the-art superconducting binary approach (B-SFQ) in 32\(\times\)less area. CNNs can operate with 5–8 bits of resolution with no significant degradation in classification accuracy. For 5 bits of resolution, our proposed accelerator yields 5\(\times\)to 63\(\times\)better performance than CMOS and 15\(\times\)to 173\(\times\)better area efficiency than B-SFQ.

The MESA physics program

In the recent past, a comprehensive experimental program has been worked out at the Mainz Energy-Recovery Superconducting Accelerator, MESA, at the Institute of Nuclear Physics in Mainz. MESA is a high-intensity, low-energy electron accelerator presently under construction and will thereby provide great opportunities to perform a new generation of high-precision scattering experiments. The versatile MAGIX experiment will use MESA’s innovative energy recovery technique, with a science focus on the study of hadron structure and few-body systems, dark sector searches, and investigations into reactions pertinent to nuclear astrophysics. An external beam line will supply spin-polarized electrons to the P2 experiment, enabling the performance of sensitive tests of the Standard Model through parity-violating electron scattering. The DarkMESA beam dump experiment, situated behind P2, is dedicated to the search for light dark matter particles.

Magnetization in superconducting corrector magnets and impact on luminosity–calibration scans in the Large Hadron Collider

Superconducting accelerator magnets have a nonlinear dependence of field on current due to the magnetization associated with the iron or with persistent currents in the superconducting filaments. This also gives rise to hysteresis phenomena that create a dependence of the field on the powering history. Magnetization effects are of particular importance for luminosity–calibration scans in the Large Hadron Collider, during which a small number of Nb–Ti superconducting orbit correctors are excited at low field and with frequent flipping of the sign of the current ramp. This paper focuses on the analysis of special measurements carried out to estimate these nonlinear effects under the special cycling conditions used in these luminosity scans. For standard powering cycles, we evaluate the effect of the main magnetization loop; for complex operational schemes, magnetization-branch transitions occur that depend on the details of the current cycle. The modelling of these effects is not included in the magnetic field prediction software currently implemented in the LHC control system; here we present an approach to predict the transitions between the main magnetization branches. The final aim is to estimate the impact of magnetic hysteresis on the accuracy of luminosity-calibration scans.

Design of a compact superconducting accelerator for advanced heavy-ion therapy

Radiotherapy using energetic carbon beams from the Heavy Ion Medical Accelerator in Chiba (HIMAC) has been carried out at the National Institutes of Quantum Science and Technology (QST) since June 1994. Based on positive clinical results, carbon-ion radiotherapy was authorized as an Advanced Medical Technology by Japanese government from 2003 and it was subsequently approved for inclusion in the Japanese National Health Insurance system from 2016. For the widespread use of carbon-ion radiotherapy, design studies as well as related research and development projects were conducted to develop a compact accelerator facility from 2004. Based on these studies, five compact facilities were constructed in Japan. However, since the accelerators are large in size, construction of these facilities is currently limited to university hospitals or large medical centers, and hence development of a more compact accelerator is desired. To further promote widespread proliferation of heavy-ion facilities and concurrently to maximize the potential of heavy-ion therapy, a project to develop a compact superconducting accelerator, the Quantum Scalpel project, was proposed. The compact accelerator employs superconducting technology to reduce the footprint of the entire accelerator system and the accelerator can provide various therapeutic beams of helium, carbon, oxygen, and neon ions having the energy of 56-430 MeV/u to advanced heavy-ion therapy. In this article, we report the design of the compact superconducting accelerator for the advanced heavy-ion therapy and describe the progress of related research and development projects.

The MESA science program: dark matter and more

The Mainz Energy-recovery Superconducting Accelerator MESA will allow precise measurements in hadron and nuclear physics, as well as exciting opportunities in dark matter searches. Three experiments will be built around this new and unique facility: MAGIX, P2, and DarkMESA. In this contribution, the MESA science program will be presented, with focus on dark matter and new physics searches.

Onset of band structure in Ga70

Excited states in odd-odd $^{70}\mathrm{Ga}$ were studied using the $^{62}\mathrm{Ni}(^{14}\mathrm{C},\ensuremath{\alpha}pn)$ fusion-evaporation reaction performed at the John D. Fox Superconducting Accelerator Facility at Florida State University with a beam energy of 50 MeV. The depopulating $\ensuremath{\gamma}$ decays were measured in coincidence using a Compton-suppressed Ge array consisting of three clover detectors and seven single-crystal detectors. An investigation of these coincidences resulted in the addition of 16 new transitions in the $^{70}\mathrm{Ga}$ level scheme, including some which belong to the onset of a new positive-parity band structure likely based on the $\ensuremath{\pi}{g}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$ configuration. Spins and parities were assigned based on directional correlation of oriented nuclei ratios and linear polarization measurements. The excitation energies predicted by shell-model calculations using the JUN45 effective interaction compare favorably with the experimental ones for the positive-parity states, but are generally about 400--500 keV too low for the negative-parity states. Total Routhian surface calculations for the lowest positive-parity configuration with signature $\ensuremath{\alpha}=0$ predict significant triaxiality $(\ensuremath{\gamma}\ensuremath{\approx}\ensuremath{-}{20}^{\ensuremath{\circ}})$ with competing noncollective excitations developing at a spin $(J=8)$ that corresponds to the onset of the positive-parity band observed experimentally. The calculations for the lowest negative-parity states with $\ensuremath{\alpha}=0$ yielded surfaces that were qualitatively similar.

Superconducting niobium coating deposited using cold spray

New fabrication techniques associated with cost reduction is gaining attention in the field of superconducting (SC) accelerators. Owing to the low process temperature, cold spraying is a suitable technique to obtain SC cavities. In this work, superconducting properties of cold sprayed Niobium (Nb) is discussed and compared with other techniques. Critical temperature (Tc) for superconductivity of cold sprayed coatings were estimated to be ∼ 8.6 K as against 9.2 K for the same of bulk Nb. Residual Resistivity Ratio (RRR), critical fields (Hc1 and Hc2) were also compared. Cold spraying can be an alternate route to obtain Nb superconducting cavities.

Indirect determination of the astrophysical S factor for the Li6 ( p,γ)Be7 reaction using the asymptotic normalization coefficient method

Background: The Li 6 ( p , γ ) Be 7 cross section influences a variety of astrophysical scenarios, including big-bang and stellar nucleosynthesis. In recent years, conflicting results of direct measurements have been published, reporting contradictory low-energy trends. Purpose: To shed light on the contradiction between the existing data sets, the reaction was studied using the asymptotic normalization coefficient (ANC) technique which was up-to-now never used for this reaction. Methods: To derive the ANC, the Li 6 ( He 3 , d ) Be 7 transfer reaction, studied at the Department of Physics and Astronomy of the University of Catania and at the John. D. Fox Superconducting Accelerator Laboratory at Florida State University, was re-analyzed, focusing on the proton transfer mechanism [the α transfer process is discussed by Kiss et al. [Phys. Lett. B 807, 135606 (2020)]. The energy of the He 3 beam impinging on a Li 6 target was E lab = 3 MeV and E lab = 5 MeV. The yield of the emitted deuterons was measured with high precision by using silicon Δ E - E telescopes. Results: From the DWBA analysis of the angular distributions of the emitted deuterons populating the ground ( E * = 0.0 MeV; 3 2 − ) and the first excited ( E * = 0.429 MeV ; 1 2 − ) states of Be 7 , the ANCs for the Li 6 + p → Be 7 system were deduced. Furthermore, the recently measured Li 6 ( p , γ ) Be 7 reaction cross sections [Piatti , Phys. Rev. C 102, 052802 (2020)] were also analyzed within this theoretical framework. Excellent agreement was found between ANC values derived indirectly and those determined from the direct data, which strengthens the conclusion of the present work. The astrophysical S factor—at energies characterizing the Sun—for the Li 6 ( p , γ ) Be 7 reaction was calculated using the weighted mean of the experimentally derived ANC values. Conclusions: The result of the present comprehensive study supports the extrapolation of Piatti [Phys. Rev. C 102, 052802 (2020)], Dong [J. Phys. G Nucl. Partic. 44, 045201 (2017)], and Gnech and Marcucci [Nucl. Phys. A 987, 1 (2019)], and thus disfavors the conclusions drawn by He [Phys. Lett. B 725, 287 (2013)] and Xu [Nucl. Phys. A 918, 61 (2013)].

Coherent Smith-Purcell radiation for minimally invasive bunch length measurement at the subpicosecond time scale

We have designed a tool to measure the bunch length of an electron beam in a minimally invasive way by means of coherent Smith-Purcell radiation (SPR). The technique has been employed successfully at a test apparatus for the Mainz Energy-recovery Superconducting Accelerator MESA, demonstrating it is possible to determine the bunch length while losing less than 0.6% of the electron beam. The impact of the space charge on the bunch length can be reduced while tuning the longitudinal bunch preparation system during a live measurement at beam currents up to 1 mA. Doing so, RMS bunch lengths of $70\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ can be achieved in a typical operating mode of the low-energy beam transport system of MESA. In addition to the bunch length measurements, typical properties of the generated SPR are demonstrated.

Simulation study of the long range wakefield induced multi-bunch instability in the China X-ray free electron laser

A 1.3GHz superconducting accelerator (SC) which can generate 32 bunches (0.2nC/bunch) with an interval of 2.3ns has been designed for the China free electron laser (CXFEL), the effects of the long range wakefield in the superconducting cavities are analyzed in this paper. In our simulation results, the fundamental mode of the longitudinal wakefield (beam loading) may result in an energy droop of 844eV/cavity to the bunch train, and may also disturb the bunch compression process by altering the energy chirp. The effects of the transverse wakefield are studied by injecting all bunches with an initial position error of 200µm, and also by applying a random misalignment of σΔx,y=100µm (in Gaussian distribution) to the cavities and the focusing quadrupoles, then the trajectory of the bunch train is corrected with horizontal and vertical correctors. In both cases the transverse wakefield induced bunch to bunch variation are negligible, whereas the misalignment may result in emittance degradation to all bunches.

Intelliquench: An Adaptive Machine Learning System for Detection of Superconducting Magnet Quenches

In superconducting magnets, the irreversible transition of a portion of the conductor to resistive state is called a “quench.” Having large stored energy, magnets can be damaged by quenches due to localized heating, high voltage, or large force transients. Unfortunately, current quench protection systems can only detect a quench after it happens, and mitigating risks in Low Temperature Superconducting (LTS) accelerator magnets often requires fast response (down to ms). Additionally, protection of High Temperature Superconducting (HTS) magnets is still suffering from prohibitively slow quench detection. In this study, we lay the groundwork for a quench prediction system using an auto-encoder fully-connected deep neural network. After dynamically trained with data features extracted from acoustic sensors around the magnet, the system detects anomalous events seconds before the quench in most of our data. While the exact nature of the events is under investigation, we show that the system can “forecast” a quench before it happens under magnet training conditions through a randomized experiment. This opens up the way of integrated data processing, potentially leading to faster and better diagnostics and detection of magnet quenches.

Beam parameter stabilization for the P2 experiment at MESA

The P2 Experiment at MESA (Mainz Energy-recovering Superconducting Accelerator) will measure the weak mixing angle via electron proton scattering at 155MeV. The expected measured parity violation asymmetry will be about 40ppb. This requires a high precision beam diagnostic and control system in order to minimize asymmetries that derive from helicity correlated fluctuations of the beam parameters. A control system for position and angle has been installed and tested at MAMI (Mainz Microtron) and the P2 precision requirements for determining the asymmetry and controlling the transverse beam parameters have been met.

KEK Center for Applied Superconducting Accelerator (CASA) and Applied Superconducting Accelerator Consortium

KEK Center for Applied Superconducting Accelerator (CASA) and Applied Superconducting Accelerator Consortium

Polish Input to Beam Dynamic Research for a Superconductive Linear Accelerator in the Early Neutron Source Project

Polish Input to Beam Dynamic Research for a Superconductive Linear Accelerator in the Early Neutron Source Project

Stand-alone accelerator system based on SRF quarter-wave resonators

Superconducting accelerators are large and complex systems requiring a central refrigerator and distributed transfer systems to supply 2-4 K liquid helium. Stand-alone, cryocooler-based systems are of interest both to scientific facilities and for industrial applications, as they do not require large cryogenic infrastructure and trained specialists for operation. Presented here is our approach to the challenge of using low-power commercially avail-able cryocoolers to operate niobium superconducting resonators at 4.4 K with high accelerating voltages and several watts of heating. Engineering and design results from RadiaBeam Systems, collaborating with Argonne National Laboratory, for a stand-alone liquid-cooled cryomodule with 10 Watts of 4.4 K cooling capacity housing a 72.75 MHz quarter-wave resonator operating at 2 MV for synchronous ions travelling at 7.7% of speed of light will be discussed.

Collimation of target induced halo following MAGIX at MESA

The Mainz Energy-recovering Superconducting Accelerator (MESA) will be an electron accelerator allowing operation in energy-recovery linac (ERL) mode. It provides the opportunity to operate scattering experiments at energies of ~ 100 MeV with thin gas-targets. The MESA Internal Gas Target Experiment (MAGIX) aims to operate windowless jet targets and different gases up to Xenon to search for possible dark photon interactions, to precisely measure the magnetic proton radius and astrophysical S-factors. Investigations on the impact of the target on beam dynamics and beam losses are required for machine safety and to examine limits to ERL operation. The goal of this work is to understand target induced halo in the different experimental setups, track halo particles through downstream sections to examine beam losses and include a suitable collimation system and shielding into the accelerator layout to protect the machine from direct and indirect damage through beam losses and radiation. The present status of the investigations is presented.

Low-energy beam transport system for MESA

An important part of the new accelerator MESA (Mainz Energy-recovering Superconducting Accelerator) is the low-energy beam transport system connecting the 100 keV electron source with the injector. The present setup includes the chopper and bunching system. The devices are of highest importance in order to achieve sufficient bunch compression, particularly at higher bunch charges and currents. With the circularly deflecting cavity of the chopper system it is possible to measure the longitudinal profile of the bunches upstream of the buncher, whereas downstream the longitudinal size will be measured by Smith-Purcell radiation. Based on experimental results obtained from this setup, we will discuss the beam parameters and compare them with simulations of the beamline.

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.