China Accelerator Driven Sub-critical System Research Articles

Research on the newest GaN-Based solid-state power amplifier for CiADS project

Institute of Modern Physics (IMP), Chinese Academy of Sciences is the first domestic institute to widely apply solid-state power amplifier (SSPA) to linear accelerator project from China Accelerator Driven Sub-critical System (C-ADS) project started since 2011. Until now, SSPA design has already been considered for two large-scale scientific facilities in Guangdong Province of southeast China: China initiative Accelerator Driven System (CiADS) and High Intensity Heavy-ion Accelerator Facility (HIAF). The SSPA was developed rapidly due to the reliable technologies of LDMOS-based (laterally diffused metal oxide semiconductor) power amplifiers.With the maturation of GaN (Gallium Nitride) technology, GaN-based amplifiers have been studied in the field of accelerators since 2020. Last year, IMP made new progress with GaN SSPA, measuring power modules at three fundamental frequency points of 162.5 MHz, 325 MHz, and 650 MHz. The first 50 kW rack with GaN SSPA was measured at 650 MHz in IMP, and its modules offer huge advantages of 40% output power and 8% efficiency compared to the newest LDMOS at the same frequency, which holds a fascination for our project.Until the beginning of 2023, the prototype power modules on three frequency points were completed and tested. This paper will detail the design development of GaN technology and its technical characteristics.

一种用于C-ADS 低能束流传输线束流强度控制的新型可调限束光阑

A novel adjustable aperture is developed for the low energy beam transport line (LEBT) of the China Accelerator Driven Subcritical System (C-ADS). Two relatively rotating mirror-symmetry cores are adopted for the adjustable aperture to scrape unwanted outer particles, improve the beam quality and reduce the beam losses, and most of all, realize continuously tunable beam current and meet the requirement of round beam. The results of simulation and test show that the unwanted outer particles can be cut away and the beam current can be adjusted continuously online within the range of 0 to 10 mA. This device provides a convenient beam tuning method for the proton linear accelerator, which can satisfy the stable and reliable online operation of C-ADS linear accelerator.

Commissioning of China ADS demo Linac and baseline design of CiADS project

China Accelerator Driven Subcritical System (C-ADS) program was launched in China in 2011. In the first five-year phase, a 25 MeV demo linac has been successfully built to demonstrate the key technologies of the driven linac. Beam commissioning activities have been carried out to study the high-power beam physics. Followed by the previous phase, China Initiative Accelerator Driven Subcritical System (CiADS) is approved contain a superconducting proton linac with 500 MeV and 5 mA. In this paper, the commissioning results of the demo linac and the beam dynamics design of CiADS linac based on commissioning experiences are presented.

Development of a low beta half-wave superconducting cavity and its improvement from mechanical point of view

A 162.5 MHz superconducting half-wave cavity with an optimizing beta of 0.10 (HWR010) has been developed for China Accelerator Driven Sub-Critical System (CADS) Project at Institute of Modern Physics (IMP), Chinese Academy of Sciences. In this paper, the detailed development of the HWR010 cavity will be presented, and will mainly focus on the mechanical design and the corresponding test results. A new stiffening strategy is proposed for the cavity. Compared to the original scheme of the stiffening design for the cavity, the simulation results of the frequency shift for the cavity adopted the new stiffening strategy show that the cavity has much lower frequency sensitivity coefficient (df/dp) and Lorentz force detuning coefficient (KL), and good mechanical stability.

Beam distribution reconstruction simulation for electron beam probe

An electron beam probe (EBP) is a detector which makes use of a low-intensity and low-energy electron beam to measure the transverse profile, bunch shape, beam neutralization and beam wake field of an intense beam with small dimensions. While it can be applied to many aspects, we limit our analysis to beam distribution reconstruction. This kind of detector is almost non-interceptive for all of the beam and does not disturb the machine environment. In this paper, we present the theoretical aspects behind this technique for beam distribution measurement and some simulation results of the detector involved. First, a method to obtain a parallel electron beam is introduced and a simulation code is developed. An EBP as a profile monitor for dense beams is then simulated using the fast scan method for various target beam profiles, including KV distribution, waterbag distribution, parabolic distribution, Gaussian distribution and halo distribution. Profile reconstruction from the deflected electron beam trajectory is implemented and compared with the actual profile, and the expected agreement is achieved. Furthermore, as well as fast scan, a slow scan, i.e. step-by-step scan, is considered, which lowers the requirement for hardware, i.e. Radio Frequency deflector. We calculate the three-dimensional electric field of a Gaussian distribution and simulate the electron motion in this field. In addition, a fast scan along the target beam direction and slow scan across the beam are also presented, and can provide a measurement of longitudinal distribution as well as transverse profile simultaneously. As an example, simulation results for the China Accelerator Driven Sub-critical System (CADS) and High Intensity Heavy Ion Accelerator Facility (HIAF) are given. Finally, a potential system design for an EBP is described.

Development of fundamental power coupler for C-ADS superconducting elliptical cavities**Supported by China ADS Project (XDA03020000) and National Natural Science Foundation of China (11475203)

5-cell elliptical cavities have been selected for the main linac of the China Accelerator Driven sub-critical System (C-ADS) in the medium energy section. According to the design, each cavity should be driven with radio frequency (RF) energy up to 150 kW by a fundamental power coupler (FPC). As the cavities work with high quality factor and high accelerating gradient, the coupler should keep the cavity from contamination in the assembly procedure. To fulfil the requirements, a single-window coaxial type coupler was designed with the capabilities of handling high RF power, class 10 clean room assembly, and heat load control. This paper presents the coupler design and gives details of RF design, heat load optimization and thermal analysis as well as multipacting simulations. In addition, a primary high power test has been performed and is described in this paper.

The mechanical design and fabrication of 162.5 MHz buncher for China accelerator driven sub-critical system injector II

Abstract A buncher is one of the main pieces of equipment in the medium energy beam transport line (MEBT) for China accelerator driven sub-critical system (C-ADS) Injector II. To focus the beam longitudinally and match the beam for the acceptance of the superconducting linac section, two room temperature quarter wave resonator (QWR) bunchers with frequency of 162.5 MHz have been designed as parts of the MEBT. According to the beam transmission matching of the MEBT and the geometric parameters requirements of bunchers, the unique mechanical structure and the main processing technology of buncher cavities and their couplers and tuners are described in this paper. The fabrication of bunchers and their parts have been completed and tested at high power, the test results agree well with the design requirements. These bunchers work well for about two years in Institute of Modern Physics, Chinese Academy of Sciences.

Measurement of the transfer function for a spoke cavity of C-ADS Injector I**Supported by Proton Linac accelerator I of China Accelerator Driven Sub-critical System (Y12C32W129)

The spoke cavities mounted in the China Accelerator Driven sub-critical System (C-ADS) have high quality factor (Q) and very small bandwidth, making them very sensitive to mechanical perturbations, whether external or self-induced. The transfer function is used to characterize the response of the cavity eigenfrequency to the perturbations. This paper describes a method to measure the transfer function of a spoke cavity. The measured Lorentz transfer function shows there are 206 Hz and 311 Hz mechanical eigenmodes excited by Lorentz force in the cavity of C-ADS, and the measured piezo fast tuner transfer function shows there are 12 mechanical eigenmodes from 0 to 500 Hz. According to these results, some effective measures have been taken to weaken the influence of helium pressure fluctuation, avoid mechanical resonances and improve the reliability of the RF system.

A Compact Superconducting Solenoid for China-ADS Injector II

A compact solenoid for the China Accelerator Driven Subcritical System (China-ADS) injector II has been developed. It includes a focusing solenoid and two steering dipoles. The magnet is compact with an entire length of 160 mm, including the helium vessel and the side flanges. Nonlinear optimization method was used to meet the requirement of focusing strength and stray field with minimized solenoid volume. The steering dipoles are placed inside the solenoid to reduce the magnet size. The structural analysis, quench protection design, and fabrication and test results are presented in this paper.

Study of medium beta elliptical cavities for CADS*Supported by National Natural Science Foundation of China (91426303)

The China Accelerator-Driven Sub-critical System (CADS) is a high intensity proton facility to dispose of nuclear waste and generate electric power. CADS is based on a 1.5 GeV, 10 mA CW superconducting (SC) linac as a driver. The high energy section of the linac is composed of two families of SC elliptical cavities which are designed with geometrical beta 0.63 and 0.82. In this paper, the 650 MHz β=0.63 SC elliptical cavity is studied, including cavity optimization, multipacting, high order modes (HOMs) and generator RF power calculation.

A computational investigation on radiation damage and activation of structural material for C-ADS

The C-ADS (China Accelerator-Driven Subcritical System) project, which aims at transmuting high-level radiotoxic waste (HLW) and power generation, is now in the research and development stage. In this paper, a simplified ADS model is set up based on the IAEA Th-ADS benchmark calculation model, then the radiation damage as well as the residual radioactivity of the structural material are estimated using the Monte Carlo simulation method. The peak displacement production rate, gas productions, activity and residual dose rate of the structural components like beam window and outer casing of subcritical reactor core are calculated. The calculation methods and the corresponding results provide the basic reference for making reasonable predictions for the lifetime and maintenance operations of the structural material of C-ADS.

Full period superconducting section physics design for injector II of China-ADS

The China Accelerator Driven Subcritical System (China-ADS) project, which is a strategic plan and aims to design and build an ADS demonstration facility, has been proposed and launched actively in China. Injector II as one of the parallel injectors of China-ADS, and is prompted by the Institute of Modern Physics (IMP). In this paper, a new scheme with full period lattice structure for the SC section is proposed. In the new scheme, there are sixteen periods, with one superconducting solenoid and one superconducting cavity included in each period. All of the elements are contained in four cryomodules. The dreadful influence of the mismatch caused by period structural change can be avoided, and the beam quality is favorable. In addition, this new scheme has certain advantages in reducing the project's difficulty and construction risk. The details of the design and beam dynamic simulation for the full period lattice structure are given in this paper.

Multi-physics analysis of the RFQ for Injector Scheme II of C-ADS driver linac

A 162.5 MHz, 2.1 MeV radio frequency quadruples (RFQ) structure is being designed for the Injector Scheme II of the China Accelerator Driven Sub-critical System (C-ADS) linac. The RFQ will operate in continuous wave (CW) mode as required. For the CW normal conducting machine, the heat management will be one of the most important issues, since the temperature fluctuation may cause cavity deformation and lead to the resonant frequency shift. Therefore a detailed multi-physics analysis is necessary to ensure that the cavity can stably work at the required power level. The multi-physics analysis process includes RF electromagnetic analysis, thermal analysis, mechanical analysis, and this process will be iterated for several cycles until a satisfactory solution can be found. As one of the widely accepted measures, the cooling water system is used for frequency fine tunning, so the tunning capability of the cooling water system is also studied under different conditions. The results indicate that with the cooling water system, both the temperature rise and the frequency shift can be controlled at an acceptable level.

China ADS sub-critical experimental assembly—Venus-1 and preliminary experiment

China’s accelerator-driven sub-critical system (ADS) sub-critical experimental assembly—Venus-1 and the preliminary experiment is presented. The core of Venus-1 is a coupled one of a fast neutron zone and a thermal neutron zone. The fast neutron zone is at the centre of the core and formed by natural uranium fuel. A fast neutron spectrum field can be produced in the fast neutron zone and used for the transmutation of minor actinides (MAs). The thermal neutron zone surrounds the fast neutron zone and is formed by low-enriched uranium fuel. It is a fission zone. An epithermal neutron zone between the fast neutron zone and the thermal neutron zone can be established for the transmutation of longlived fission products (LLFP). On July 18, 2005, the first fuel element was loaded into the Venus-1 sub-critical assembly and some preliminary experiments about the sub-critical neutronics were performed. The Venus-1 can be driven by an Am-Be source or other steady neutron source (Cf-252, D-D reaction and D-T reaction) to study the effect of the external neutron source with different energies or a D-T pulsed neutron source on the dynamic characteristics.