54621041
Kanthal Alloy Based S-Band Collinear Load R and D for Linear Accelerators
Collinear load is a substitute for waveguide load to miniaturize irradiation accelerators and make the system compact. The key technology is to design coaxial cavities coated inside with attenuating materials which will terminate the remnant power, meanwhile the operation frequency of 2856 MHz retains. For lossy materials such as Kanthal (25%Cr-5%Al-Fe) alloy, CST is used to simulate the effect of the coating on the load cavity properties like the operation frequency and attenuation. The frequency shifts caused by the coatings would be compensated by the strategy of cavity dimensions adjustment. Simulations revealed the compensation rules of the cavity inner radius b. Meanwhile the relationship between the attenuation and the coating area was also resolved. Based on a specified power allocation, a 15 kW collinear load consisting of six cavities at 2π/3 mode was designed with one-way attenuation of -18.8 dB. Two sets of prototype cavities have been manufactured and the experiment results are presented, compared with the CST simulations.
140119573
ELECTROMAGNETIC PARAMETERS STUDY OF MICROWAVE- ABSORBING MATERIAL FeSiAl FOR COLLINEAR LOAD OF LINAC*
Microwave-absorbing material is an essential part of LINAC collinear load. It is coated on the inner walls of several trailing accelerating cavities to transform the remnant microwave power into heat. Fe-85%Si-9.6%Al5.4% alloy, which reveals low outgassing rate and high attenuation, is selected for collinear load R&D. To measure the permittivity and permeability of FeSiAl at 2856 MHz, the coaxial transmission-reflection method is adopted. The system is firstly examined by testing the hollow coaxial fixture and comparing the results with the electromagnetic parameters of the air. Measurements of two PTFE rings show that the air gaps between the fixture and samples influence the test results seriously. CST is utilized to simulate the effects on the FeSiAl measurements. Eventually a scheme of molding the samples of FeSiAl powder mixed with paraffin to form a wax mold is proposed and the permittivity and permeability of FeSiAl are derived from the electromagnetic parameters equivalent formulas of mixed medium. INTRODUCTION In order to ensure LINAC running safely, the remnant microwave power has to be absorbed at the end of the accelerator tube. Waveguide load is regularly adopted, but the structures would make it difficult to miniaturize the LINAC. Collinear load is a new structure of LINAC load, which consists of several accelerating cavities coaxially extending the normal accelerating tube with efficient microwave-absorbing material coated on the inner walls. The remnant power is dissipated and transformed into heat, which is carried out through cavity walls by external cooling water. Without output coupler, the structure not only brings about simplification on focusing coils installation, but also makes the construction compact and the quality of beam current improved [1]. Absorbing material is an essential part of the collinear load and its absorbing capability depends on its electromagnetic parameters [2], which would be significant to the performance of the collinear load. There are two types of electromagnetic measurement methods for microwaveabsorbing materials: the network parameters method and the resonance cavity method. The resonance cavity method is fit for low loss materials, while the network parameter method is more suitable for higher loss materials. The latter consists of coaxial transmissionreflection method [3], free space method and so on. In this paper, coaxial transmission-reflection method is used to test the FeSiAl alloy which is an efficient absorbing material and prepared by Institute of Electronics, Chinese Academy of Sciences. THEORY OF TRANSMISSIONREFLECTION METHOD The transmission line is a reciprocal two-port network when the sample is a homogeneous, linear and isotropic medium. As shown in Fig. 1, the electromagnetic wave transmits and reflects back and forth in the medium. 1 R 2 (1 ) R T R 2 2 (1 ) R R T 3 2 4 (1 ) R R T 5 2 6 (1 ) R R T 7 2 8 (1 ) R R T 2 2 3 (1 ) R R T 8 2 9 (1 ) R R T 6 2 7 (1 ) R R T 4 2 5 (1 ) R R T 1 .... ..... .... .... 11 S 21 S Figure 1: The electromagnetic wave reflection and transmission in medium. Supposing that the reflection coefficient of the airmedium interface (A) is R, reflection coefficient of the medium-air interface (B) is -R and the transmission coefficient of the medium is T with the length of L, the complex number S11 of reflection sum in the A interface and S21 of transmission sum in the B interface will be
55951342
STUDY ON FREQUENCY CHANGE BY 3D RECONSTRUCTION OF DEFORMED CAVITIES OF LINAC COLLINEAR LOAD*
Collinear load, consisted of several coaxial cavities, is a substitute for traditional waveguide-type load to absorb the remnant power of the LINAC and makes the accelerating structure compact and small-size. The power loss on the cavities of collinear load brings thermal deformation which affects their resonant frequency deeply. In this paper, a new approach of 3D reconstruction of the thermal deformed cavities is utilized to evaluate the accurate influence on frequency change caused by non-uniform deformation and water cooling strategies of collinear absorbing load are studied. Then the thermal behavior of a six-cavity collinear load, which is coated with Kanthal alloy and FeSiAl alloy and used on a 2856MHz, 2π/3 mode respectively, is researched. The results show that the collinear load with Kanthal alloy can only absorb up to 10kW, while with FeSiAl alloy it can dissipate 15kW when the water flow controlled within 3.0kg/s for energy saving.
119280465
Characterizing Temporal Structure of the Relativistic Electron Bunch
Using proper beam energy chirp and the undulator detuning effect, we propose a modified optical replica synthesizer scheme to characterize the temporal structure of a relativistic electron bunch, which predicts a 100-fs temporal resolution in numerical simulation. The proof of principle experiment demonstrates a peak current of 9 A and a slice energy spread of about 0.5 keV for the uncompressed electron beam of the Shanghai Deep UV Free Electron Laser Facility.
122959126
Shear viscosity of a multi-component hadronic system
The shear viscosity and entropy density s of a hadron gas with zero baryon number density are calculated using the Chapman-Enskog and virial expansion approaches, respectively. Interactions are included via the K-matrix parametrization of cross sections preserving the unitarity of the S-matrix. In the four component mixture ( K N ), a total of 57 resonances up to 2 GeV mass are included. Interactions forming resonances reduce the magnitude of and increase s, both eects serving to progressively reduce =s as the temperature nears the QCD phase transition temperature.
116133157
Quadrupole magnets measurement
A rotating coil setup is designed for quadrupole magnet measurement at the Accelerator Test Facility (ATF); Hall probe measurement was also performed for one of each type of quadrupole magnet. Both mechanical and magnetic properties of the quadrupole magnets were measured, the results are reported here. 5 refs., 12 figs., 12 tabs.
122022031
Concentration of Non-maximally Entangled States via Entanglement Swapping in Cavity QED
Using the highly detuned interaction between Λ-type three-level atoms and coherent optical fields in cavity QED, we can create a maximally entangled state between an atom and a cavity mode from a non-maximally entangled atomic state and a non-maximally entangled coherent state via entanglement swapping. The averaged output entanglement of the scheme is the product of the initial two non-maximal entanglements rather than the sum of them. The impact made by the spontaneous emission from the atomic excited levels has been canceled here, which makes the current protocol more feasible.
15279605
Matter in extremis: Ultrarelativistic nuclear collisions at RHIC
We review the physics of nuclear matter at high energy density and the experimental search for the Quark-Gluon Plasma at the Relativistic Heavy Ion Collider (RHIC). The data obtained in the first three years of the RHIC physics program provide several lines of evidence that a novel state of matter has been created in the most violent, head-on collisions of Au nuclei at √ s = 200 GeV. Jet quenching and global measurements show that the initial energy density of the strongly interacting medium generated in the collision is about two orders of magnitude larger than that of cold nuclear matter, well above the critical density for the deconfinement phase transition predicted by lattice QCD. The observed collective flow patterns imply that the system thermalizes early in its evolution, with the dynamics of its expansion consistent with ideal hydrodynamic flow based on a Quark-Gluon Plasma equation of state.