Studies of dual-harmonic acceleration at CSNS-Ⅱ

The Rapid Cycling Synchrotron （RCS） of the China Spallation Neutron Source （CSNS） complex is designed to provide 1.56×10^13 protons per pulse （ppp） during the initial stage, and it is upgradeable to 3.12× 10^13 ppp during the second stage and 6.24× 10^13 ppp during the ultimate stage. The high beam intensity in the RCS requires alleviation of space charge effects to reduce beam losses, which is key in such high beam power accelerators. With higher intensities in the upgrading phases, a dual-harmonic RF system is planned to produce flat-topped bunches that are useful to reduce the space charge effects. We have studied different schemes to apply the dual-harmonic acceleration in CSNS-Ⅱ, and have calculated the main parameters of the RF svstems, which are presented in this Darter.

Design and commissioning of a wideband RF system for CSNS-Ⅱ rapid-cycling synchrotron

The China Spallation Neutron Source(CSNS) upgrade project(CSNS-Ⅱ) aims to enhance the beam power from 100 to 500 kW. A dual-harmonic accelerating method has been adopted to alleviate the stronger space-charge effect in rapid-cycling synchrotrons owing to the increased beam intensity. To satisfy the requirements of dual-harmonic acceleration, a new radiofrequency(RF) system based on a magnetic alloy-loaded cavity is proposed. This paper presents design considerations and experimental results regarding the performance evaluation of the proposed RF system through high-power tests and beam commissioning. The test results demonstrate that the RF system satisfies the desired specifications and affords significant benefits for CSNS-Ⅱ.

Nanoparticle assembly enabled by EHD-printed monolayers

Augmenting existing devices and structures at the nanoscale with unique functionalities is an exciting prospect.So is the ability to eventually enable at the nanoscale,a version of rapid prototyping via additive nanomanufacturing.Achieving this requires a step-up in manufacturing for industrial use of these devices through fast,inexpensive prototyping with nanoscale precision.In this paper,we combine two very promising techniques—self-assembly and printing—to achieve additively nanomanufactured structures.We start by showing that monolayers can drive the assembly of nanoparticles into pre-defined patterns with single-particle resolution;then crucially we demonstrate for the first time that molecular monolayers can be printed using electrohydrodynamic(EHD)-jet printing.The functionality and resolution of such printed monolayers then drives the self-assembly of nanoparticles,demonstrating the integration of EHD with self-assembly.This shows that such process combinations can lead towards more integrated process flows in nanomanufacturing.Furthermore,in-process metrology is a key requirement for any large-scale nanomanufacturing,and we show that Dual-Harmonic Kelvin Probe Microscopy provides a robust metrology technique to characterising these patterned structures through the convolution of geometrical and environmental constraints.These represent a first step toward combining different additive nanomanufacturing techniques and metrology techniques that could in future provide additively nanomanufactured devices and structures.

Longitudinal beam dynamic design of 500 kW beam power upgrade for CSNS-II RCS

Purpose The accelerator of the China Spallation Neutron Source(CSNS)consists of an 80 MeV H-linac and a 1.6 GeV rapid cycling synchrotron(RCS).The design beam power is 100 kW,which has been reached.In the upgrade project(CSNS-II),the beam power will be upgraded to 500 kW by increasing the linac energy to 300 MeV and adding a dual harmonic RF system in the RCS.In order to alleviate space charge effect and improve beam quality,the longitudinal beam dynamic of CSNS-II RCS dual harmonic RF system has been studied.Methods According to the longitudinal beam dynamic characteristics of CSNS-II RCS at different acceleration stages,the longitudinal emittance,bunching factor,momentumfilling factor and bunch length are studied and optimized in this paper.Results and conclusions The optimized bunching factor is greatly improved,and the tune spread caused by space charge effect is greatly reduced in CSNS-II.With the suppressed space charge effects,the beam loss can be well controlled in CSNS-II RCS.

Optimizing the RF cavity parameters at CSNS-II with Particle Swarm Optimization

Objective This study is aimed at optimizing the parameters of a dual-harmonic RF systemwhich will be used in CSNS-II to have a larger bunching factor and less particle losing to decrease the space charge effect.Methods By studying the synchrotron equation of motion in a double RF system,some features of the bunch are quantized.The normalized bucket area should be constant,the injection condition should be satisfied,and larger bunching factor is preferred during the cycle period.With these ideas,three objective functions are proposed.Particle swarm optimization(PSO)method is employed to search the optimal solution.Results There is less particle loss in the simulation with the optimized parameters.The growth rate of the transverse emittance is smaller after the optimization.The bunch can keep a larger bunching factor which is very useful to decrease the space charge force.Conclusion The parameters of the dual-harmonic RF system are optimized with swarm optimization method.This study provides a general method to optimize the similar system,especially for an accelerator.