Numerical simulation codes are basic tools for designing Free Electron Lasers (FELs). This paper describes a numerical method for the time-dependent, three-dimensional simulation of the free electron laser (FEL) using a rectangular waveguide within overmoded configuration when the radiation wavelength is much shorter than the waveguide cut-off wavelength. Instead of developing a new code, the GENESIS simulation code is modified for our purpose. This method presented here can be used for extending the capacity of GENESIS to cover this special configuration. The major modification is to apply the metal boundary conditions on the field equations in a limited rectangular region and the full Cartesian mesh using the Alternating Direction Implicit (ADI) integration scheme to solve the field equation remains adopted.
The preliminary research work of Hefei Advanced Light
Facility (HALF), a fourth generation diffraction limit storage ring,
is in progress. Two 499.8 MHz superconducting cavities may be used
in the HALF RF system. RF power will be feed into each cavity
through a coaxial fundamental power coupler (FPC). Thermal design of
the coupler is very important because of the large power losses on
the coupler will cause overheating. Accurate and fast thermal
analysis is a challenge in the thermal design. In this paper, two
thermal analysis methods for evaluating the cooling effect of the
coupler were compared. Computational Fluid Dynamics (CFD) code is
used to perform thermal-fluid coupled analysis for the coupler in
the first method, which is quite accurate but time-consuming. In the
second method, average convective heat transfer coefficient
calculated by correlation equations based on experimental results is
used to evaluate the heat transfer between the fluid and the cooling
pipe wall. The calculation time of the first method is about four
times that of the second method. The simulation results of the two
methods are consistent well at high flow rate, especially for
turbulent flow. Therefore, the second method was used to perform
thermal simulation under different cooling conditions and RF power
levels. The influence of thermal radiation on the heat load to the
cryogenic environment was also given in this paper. Simulation
results show that thermal radiation has a slight impact on the heat
load. When the copper emissivity equal to 0.02, the total static and
dynamic heat load to 4.5 K are 0.833 W and 2.614 W at the power
level of 200 kW, and the heat load to 4.5 K cryogenic environment
caused by thermal radiation is 0.065 W.
Mesoscopic conductance fluctuations are a ubiquitous signature of phase-coherent transport in small conductors, exhibiting universal character independent of system details. In this Letter, however, we demonstrate a pronounced breakdown of this universality, due to the interplay of local and remote phenomena in transport. Our experiments are performed in a graphene-based interaction-detection geometry, in which an artificial magnetic texture is induced in the graphene layer by covering a portion of it with a micromagnet. When probing conduction at some distance from this region, the strong influence of remote factors is manifested through the appearance of giant conductance fluctuations, with amplitude much larger than e 2 =h. This violation of one of the fundamental tenets of mesoscopic physics dramatically demonstrates how local considerations can be overwhelmed by remote signatures in phasecoherent conductors.
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