The InjectorⅡ, one of the two parallel injectors of the high-current superconducting proton driver linac for the China Accelerator-Driven System (C-ADS) project, is being designed and constructed by the Institute of Modern Physics. At present, the design work for the injector is almost finished. End-to-end simulation has been carried out using the TRACK multiparticle simulation code to check the match between each acceleration section and the performance of the injector as a whole. Moreover, multiparticle simulations with all kinds of errors and misalignments have been performed to define the requirements of each device. The simulation results indicate that the lattice design is robust. In this paper, the results of end-to-end simulation and error simulation with a 3-D field map are presented.
The taper-shaped superconducting quarter wave resonators with frequency of 80.5 MHz,β of 0.041and 0.085 have been pre-researched.The radio frequency(RF) design of the cavities has been completed,and the structural design is also an important aspect which will be discussed in the following.The frequency shift caused by the etching efects of the surface treatment,the helium bath pressure and the Lorentz force,and the mechanical modes caused by the microphonic excitation have been analyzed.The results show that the frequency variation from the Lorentz force is not serious and stifening rings are explored aimed at decreasing the deformation brought by the helium pressure and microphonic excitation.
A superconducting quarter-wave resonator (QWR) of frequency=162.5 MHz and β=0.085 (β =v/c) has been designed at Peking University. The multipacting (MP) simulation and analysis for the QWR with CST Particle Studio has been performed. The simulation results reveal that there is no sign of MP with its normal operating accelerating gradients in the range of 6-8 MV/m. The accelerating gradient range that may incur MP is from about 1.4 to 3.2 MV/m, and the places where MP may be encountered are mainly located at the top part of the QWR. So the effect of different top geometries on MP has also been studied in depth. Our results show that an inward convex round roof is better than other round roofs, and plane roofs have an advantage over round roofs on the suppression of MP in general. While considering the optimization of its electromagnetic (EM) design, our initial designed model is also acceptable.
A 162.5 MHz four-vane radio frequency quadruple(RFQ) accelerator has been developed at the Institute of Modern Physics(IMP) for Injector II of the China ADS linac. The RFQ will operate in continuous wave mode at 100 k W. For the designed 10 mA beam, the additional RF power dissipation will induce a very large reflection of power. A water-temperature controlling system will be used to reduce the power reflection by tuning the frequency of the RFQ. The tuning capability of the water temperature is studied under different configurations of cooling water.Simulations and experiment are compared in this paper. The experimental results agree well with simulation using ANSYS. This can be used as a reference to tune the RFQ in beam commissioning.
In this paper, we present the RF simulation, the fabrication and the normal RF test of a six-cell copper model cross bar H mode(CH) cavity. The CH cavity was researched and developed at the Institute of Modern Physics for Injector II of the superconducting linac of the accelerator driven system of China, operating at a frequency 162.5MHz, β=0.065. The deep drawing and electron beam welding were employed to fabricate this cavity, which would be used to develop the superconducting CH cavity in the future. The results of the normal RF test agree with the simulation of the electromagnetic properties, such as the electric field distribution on the cavity axis, frequency and Q factor.
For the application of high intensity continuous wave(CW) proton beam acceleration, a new superconducting accelerating structure for extremely low β protons working in TE210 mode has been proposed at Peking University. The cavity consists of eight electrodes and eight accelerating gaps. The cavity's longitudinal length is368.5 mm, and its transverse dimension is 416 mm. The RF frequency is 162.5 MHz, and the designed proton input energy is 200 ke V. A peak field optimization has been performed for the lower surface field. The accelerating gaps are adjusted by phase sweeping based on KONUS beam dynamics. The first four gaps are operated at negative synchronous RF phase to provide longitudinal focusing. The subsequent gaps are 0?sections which can minimize the transverse defocusing effect. Solenoids are placed outside the cavity to provide transverse focusing. Numerical calculation shows that the transverse defocusing of the KONUS phase is about three times smaller than that of the conventional negative synchronous RF phase. The beam dynamics of a 10 m A CW proton beam is simulated by the Trace Win code. The simulation results show that the beam's transverse size is under effective control, while the increase in the longitudinal direction is slightly large. Both the Trace Win simulation and the numerical calculation show that the cavity has a relatively high effective accelerating gradient of 2.6 MV/m. On the whole, our results show that this new accelerating structure may be a possible candidate for superconducting operation at such a low energy range.
The cross bar H mode (CH) cavity is suitable to accelerate the low energy and medium energy proton. Theoperating mode in the CH cavity is H210. Compared with other low-beta superconducting cavities, the CH cavitywith multi-cell structure has high real acceleration gradient. In superconducting CH cavity, the cross bar is helpfulto rigidize the cavity mechanically. Since the year of 2011, IMP have involved into the research of superconductingCH cavity for the ADS project[1]. There are three CH cavity have been fabricated, one copper model CH cavityand two niobium superconducting CH cavity[2].
