Development of a China test cryomodule for ILC

Research and development of a 1.3 GHz 9-cell cavity test cryomodule were carried out by a collaboration group between IHEP (Institute of High Energy Physics) and TIPC (Technical Institute of Physics and Chemistry) in China.The cryomodule is a "test model" for the ILC cryomodule,and a key component of a superconducting accelerator test unit which will be built in the near future,also can be used as a horizontal test facility for 1.3 GHz 9-cell cavities.This paper presents the development status of the cryomodule,including structure design,cryogenic flow diagram,thermal and mechanical simulations,heat load estimation and etc.     

Thermal simulation and analysis of the STF cryomodule

STF is a superconducting RF test facility constructed at the high energy accelerator research orga-nization of Japan (KEK), as a main part of a R&D project for the proposed International Linear Collider (ILC) in Asia. Thermal study of the STF 1.3 GHz 9-cell cavity cryomodule was carried out within a collaboration between China and Japan. Static and dynamic thermal behaviors of the STF cryomodule were simulated and analyzed with the FEM method, and some simulation results were compared with the available experimental data. This paper presents the details.     

Thermal simulation and analysis of the STF cryomodule

STF is a superconducting RF test facility constructed at the high energy accelerator research organization of Japan (KEK), as a main part of a R&;D project for the proposed International Linear Collider (ILC) in Asia. Thermal study of the STF 1.3 GHz 9-cell cavity cryomodule was carried out within a collaboration between China and Japan. Static and dynamic thermal behaviors of the STF cryomodule were simulated and analyzed with the FEM method, and some simulation results were compared with the available experimental data. This paper presents the details.     

A digital low-level radio-frequency system R&D for a 1.3 GHz nine-cell cavity

To test and verify the performance of the digital low-level radio-frequency (LLRF) and tuner system designed by the IHEP RF group, an experimental platform with a retired KEK 1.3 GHz nine-cell cavity is set up. A radio-frequency (RF) field is established successfully in the cavity and the frequency of the cavity is locked by the tuner in ±0.5° (about ±1.2 kHz) at room temperature. The digital LLRF system performs well in a five-hour experiment, and the results show that the system achieves field stability at amplitude <0.1% (peak to peak) and phase <0.1° (peak to peak). This index satisfies the requirements of the International Linear Collider (ILC), and this paper describes this closed-loop experiment of the LLRF system.     

Experimental study on SC RF cavities by using China large grain niobium for ILC

Large grain niobium has the potential of simplifying the production sequence and consequently reducing the cost of the superconducting RF cavities for ILC. To investigate the feasibility of fabrication and the possibility to achieve high gradient by large grain cavities, two 1.3GHz cavities were made of China large grain niobium and a series of vertical tests were carried out following several different surfaces treatment procedures. Two cavities have both reached the high gradient of more than 43MV/m repeatedly and the maximum accelerating field of 47.9MV/m has been achieved by China large grain niobium. This paper introduces the features of the fabrication and surface treatments on the large grain cavities and presents the preliminary results of the research.     

Flattop operation of the ILC accelerating cryomodule

A 500 GeV center-of-mass International Linear Collider (ILC), currently under R&D development, is foreseen as the next-generation high-energy physics (HEP) instrument [1]. The achievement of a 31.5 MV/m average operational accelerating gradient in a single cryomodule is a proof of principle for the ILC project. However, individual cavity performance may have a large spread in operating gradients, up to 20% of the nominal value [2, 3]. In case of cavities performing below the average, the design parameters could be achieved by tweaking the RF distribution accordingly. We present a simple theoretical analysis of the ILC cryomodule operation with a gradient spread. The difference in the gradients breaks the synchronism of a transient processes in each cavity and causes nonuniform acceleration along the bunch train. A proper solution was found to maintain flattop operation of the accelerating module. Finally, we perform numerical efficiency estimations for the proposed RF distribution scheme based on real data of the gradient spread of actual cavities. The text was submitted by the authors in English.     

Development of 1.3GHz high-T-c rf SQUID

A new high-T_c (HT_c) rf SQUID working at around 1.3GHz has been developed to avoid electromagnetic interference such as growing mobile communication jamming. This new system works in a frequency range from 1.23 to 1.42GHz (centred at 1.3GHz), which is not occupied by commercial communication. The sensor used in the 1.3GHz rf SQUID is made of a HT_c coplanar superconducting resonator and a large-area HT_c superconducting film concentrator. We have achieved in the 1.3GHz HT_c rf SQUID system a minimal flux noise of 2.5×10^{-5}Φ_0/\sqrt{Hz} and a magnetic field sensitivity of 38fT/\sqrt{Hz} in white noise range, respectively. The effective area of the concentrator fabricated on a 15×15mm^2 substrate is 1.35mm^2. It is shown that the 1.3GHz rf SQUID system has a high field sensitivity. Design and implementation of 1.3GHz HT_c rf SQUID offers a promising direction of rf SQUID development for higher working frequency ranges.     

Development of 1.3GHz high-T-c rf SQUID

A new high-T_c (HT_c) rf SQUID working at around 1.3GHz has been developed to avoid electromagnetic interference such as growing mobile communication jamming. This new system works in a frequency range from 1.23 to 1.42GHz (centred at 1.3GHz), which is not occupied by commercial communication. The sensor used in the 1.3GHz rf SQUID is made of a HT_c coplanar superconducting resonator and a large-area HT_c superconducting film concentrator. We have achieved in the 1.3GHz HT_c rf SQUID system a minimal flux noise of 2.5×10^{-5}Φ_0/\sqrt{Hz} and a magnetic field sensitivity of 38fT/\sqrt{Hz} in white noise range, respectively. The effective area of the concentrator fabricated on a 15×15mm^2 substrate is 1.35mm^2. It is shown that the 1.3GHz rf SQUID system has a high field sensitivity. Design and implementation of 1.3GHz HT_c rf SQUID offers a promising direction of rf SQUID development for higher working frequency ranges.     

国际直线对撞机的参数选择

给出了确定直线对撞机参数的一般程序, 作为一个例子, 给出了超低束团电量时的参数表. 文章的主要目的是说明束流参数和对撞点以及阻尼环之间的相互制约关系. 对于17km的阻尼环, 它的能量被建议由5GeV升到7GeV. 然而,对于6km的阻尼环能量为5GeV是合理的.     

国际未来直线对撞机(ILC)阻尼环Lattice设计

为了使国际未来直线对撞机达到高的亮度, 对撞机的阻尼环必须要有很小的自然发射度. 同时, 阻尼环要有很大的接收度来接受来自正电子注入系统的大能散、大发射度的正电子束团. 对于磁聚焦结构的设计来说, 同时达到以上要求是一件很有挑战性的工作. 为了降低ILC阻尼环的造价采用修正的FODO结构设计了可以满足ILC要求的阻尼环备用Lattice, 并使四极磁铁的数量比起ILC阻尼环BCD设计减少了一半.     

Pair production of right-handed neutrinos in the left-right twin Higgs model at ILC and LHC

In the framework of the left-right twin Higgs model, we study pair production of the right-handed neutrinos at the International Linear Collider (ILC) and the CERN Large Hadron Collider (LHC). Our numerical results show that the production cross section of the process e+e→N N is at the level of several tens fb at the ILC. However, the resonance production cross section can be significantly enhanced to the order of pb. The pair production cross section for the right-handed neutrinos is the level of several h...     

Effects of machine errors on the ILC main linac

For a practical linac, the beam property is affected seriously by any machine imperfections. In this paper, the effects of several main errors in the ILC main linac, such as quadrupole misalignment, magnet strength error and cavity misalignment, were studied by a theoretical method. The tolerance for each error was also obtained. Comparison with the numerical simulation result is made and the agreement is quite good.     

Experimental study on SC RF cavities by using China large grain niobium for ILC

Large grain niobium has the potential of simplifying the production sequence and consequently reducing the cost of the superconducting RF cavities for ILC.To investigate the feasibility of fabrication and the possibility to achieve high gradient by large grain cavities,two 1.3 GHz cavities were made of China large grain niobium and a series of vertical tests were carried out following several different surfaces treatment procedures.Two cavities have both reached the high gradient of more than 43 MV/m repeatedly and the maximum accelerating field of 47.9 MV/m has been achieved by China large grain niobium.This paper introduces the features of the fabrication and surface treatments on the large grain cavities and presents the preliminary results of the research.     

Effects of machine errors on the ILC main linac

For a practical linac, the beam property is affected seriously by any machine imperfections. In this paper, the effects of several main errors in the ILC main linac, such as quadrupole misalignment, magnet strength error and cavity misalignment, were studied by a theoretical method. The tolerance for each error was also obtained. Comparison with the numerical simulation result is made and the agreement is quite good.     

SUSY-QCD Effects in Top Quark Pair Production in Association with a Gluon at the ILC

Given the null results of searches for new physics at the LHC, we investigate the one-loop effects SUSY QCD in the process e⁺e^-→ttg at the ILC in Minimal Supersymmetric Standard Model (MSSM). We find that the relative SUSY-QCD corrections to the cross section of e⁺e^-→ttg can maximally reach 6.5%(3.2%) at the ILC with √s=1000 GeV when m=313:4 GeV and m=500(1500) GeV.     

ILC正电子源靶接触热传导冷却技术的初步研究

国际直线对撞机（ILC）正电子靶沉积的热功率将超过20 kW,传统的冷却方式已无法满足要求。美国Argonne国家实验室提出了摩擦接触热传导冷却的方法。根据Argonne实验室的研究方案,设计了一种旋转摩擦接触冷却的简化装置,根据热传导理论,结合ANSYS软件模拟了旋转冷却过程中的温度分布,理论上验证了方法的可行性。按照模拟的参数和结果,进行了摩擦接触热传导冷却实验,通过实验结果和数据分析证实了,低温区（20℃~50℃）有良好的冷却效应,初步验证了摩擦接触热传导冷却方案的有效性。A new scheme that cooling international Linear Collider (ILC) positron source target by touching thermal conduction (TTC) is presented by Argonne National Laboratory (ANL).Recent results of simulation for cooling the iron targets with 300 and 450 W heat reservoir by ANSYS and experiment of cooling the iron target with 300 and 450 W friction heat reservoir at Institute of Modern Physics (IMP),Chinese Academy of Sciences (CAS),have proved that the TTC has good cooling effect in low temperature zone (20℃~50℃),and preliminarily verified the feasibility of TTC for cooling the ILC positron source target.     

HOMs simulation and measurement results of IHEP02 cavity

In accelerator RF cavities, there exists not only the fundamental mode which is used to accelerate the beam, but also higher order modes(HOMs). The higher order modes excited by the beam can seriously affect beam quality, especially for the higher R/Q modes. 1.3 GHz low-loss 9-cell superconducting cavity as a candidate for ILC high gradient cavity, the properties of higher order mode has not been studied carefully. IHEP based on existing low loss cavity, designed and developed a large grain size 1.3 GHz low-loss 9-cell superconducting cavity(IHEP02cavity). The higher order mode coupler of IHEP02 used TESLA coupler's design. As a result of the limitation of the mechanical design, the distance between higher order mode coupler and end cell is larger than TESLA cavity.This paper reports on measured results of higher order modes in the IHEP02 1.3 GHz low-loss 9-cell superconducting cavity. Using different methods, Q e of the dangerous modes passbands have been obtained. The results are compared with TESLA cavity results. R/Q of the first three passbands have also been obtained by simulation and compared with the results of the TESLA cavity.     

First samples of Ti and Nb tubes explosion welding joint with stainless steel for ILC 1.8 K cryomodule

The world first samples of Ti and Nb tubes joint with stainless steel ones by an explosion welding by the JINR-VNIIEF-FNAL-INFN cooperation were manufactured in the frame of ILC R&D programe. An applying methods of relaxation of residual tensions (after explosion and electron beam welding), macro- and microanalyses of welding seam and cryogenic tests of the samples produced manifest the achievement of high mechanic strength (≈250 MPa/share) of welding seam, solidity and leak absence on 10^?10 l atm/s level at 1.8 K. The explosion welding technology and methods introducing to industrial manufacturing of the 4-th generation of cryomodule of TESLA TYPE DESIGN can exclude the Ti—communications, connect the Nb—cavity with stainless steel vessel and reduce significantly the accelerator cost.     

Associated Production of a Photon with Dark Matter Pair at the ILC within the Littlest Higgs Model with T-parity

Within the context of the Littlest Higgs model with T -parity, the heavy photon (AH) is supposed to be an ideal dark matter (DM) candidate. One direct proof of validity of the model is to produce the heavy photon at collider. In this paper, we investigate the associated production of a photon with heavy photon pair at the planned international e+e- linear collider (ILC),i.e., e+e-→ AHAHγ and show the distributions of the transverse momenta of the photon. The numerical results indicate that the heavy photon production rate could reach several fb at the low mass parameter space and the characteristic signal is a single high energetic photon and missing energy, carried by the heavy photons. All in all, it can be a good chance to observe the heavy photon via this process with the high yearly luminosity of the ILC.     

The Effects of Simplest Little Higgs Model on the Spin Correlations in the Top Quark Pair Production at the LHC and ILC

In the simplest little Higgs model (SLH),we study the spin correlations in the top quark pair production at the LHC and ILC.We find that the SLH always suppresses the t spin correlations compared to the SM values.At the LHC,the suppression can be over 10% for mZ′ 750 GeV.The SLH prediction value is outside the 1σ range of the experimental data from ATLAS,and within 1σ range of the experimental data from CMS.At the ILC,the SLH can sizably suppress the t spin correlation for mZ′approaching the center-of-mass energy √s.For example,the maximal suppression can reach-22.5%,-14.5%,and-9.5% for √s=500 GeV,800 GeV,and 1000 GeV,respectively.Therefore,the t spin correlation at the ILC can be a sensitive probe for the SLH.