Engineering topics

Ko, K

Publications and source records attributed to Ko, K.

6 records

DOE OSTI2012

3D simulations of multipacting in the 56 MHz SRF cavity

The 56 MHz SRF Quarter-Wave Resonator (QWR) is designed for RHIC as a storage cavity to improve the collider performance. 2D multipacting simulation has been done for the cavity alone. Ripples were added to the outer body of the cavity for multipacting suppression based on the simulation findings. During operation, there will be four higher order mode (HOM) couplers. All of these components will be exposed to high RF fields. In this paper we compare 2D and 3D codes simulation results for multipacting in the cavity. We also report 3D simulation results for multipacting simulation at the couplers.

43 PARTICLE ACCELERATORS↗

DOE OSTI2011

Coupled Magnetic Cycloids in Multiferroic TbMnO3 and Eu3/4Y1/4MnO3

Based on the detailed Mn L{sub 2,3}-edge x-ray resonant scattering results, we report a new complexity in the magnetic order of multiferroic orthomangnites, which has been considered as the simple A-type cycloid order inducing ferroelectricity. The Dzyaloshinskii-Moriya interaction involved in the orthorhombic distortion brings on F-type canting from the A type, and the ordering type becomes the off-phase synchronized bc cycloid in TbMnO{sub 3} or the tilted antiphase ab cycloid in Eu{sub 3/4}Y{sub 1/4}MnO{sub 3}. The F-type canting is responsible for the magnetic field-driven multiferroicity to weak ferromagnetism transition.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2011

Fragile Magnetic Ground State in Half-Doped LaSr(2)Mn(2)O(7)

We investigated the orbital and antiferromagnetic ordering behaviors of the half-doped bilayer manganite La{sub 2-2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} (x {approx_equal} 0.5) by using Mn L{sub 2,3}-edge resonant soft x-ray scattering. Resonant soft x-ray scattering reveals the CE-type orbital order below T{sub oo} {approx_equal} 220 K, which shows partial melting behavior below T{sub m} {approx_equal}65 K. We also found coexistence CE- and A-type antiferromagnetic orders. Both orders involve the CE-type orbital order with nearly the same orbital character and are coupled with each other. These results manifest that the ground state with the CE-type antiferromagnetic order is easily susceptible to destabilization into the A-type one even with a small fluctuation of the doping level, as suggested by the extremely narrow magnetic phase boundaries at x {approx_equal} x {yields} 0.5 {+-} 0.005.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2011

Parallel Computation of Integrated Electromagnetic, Thermal and Structural Effects for Accelerator Cavities

The successful operation of accelerator cavities has to satisfy both rf and mechanical requirements. It is highly desirable that electromagnetic, thermal and structural effects such as cavity wall heating and Lorentz force detuning in superconducting rf cavities can be addressed in an integrated analysis. Based on the SLAC parallel finite-element code infrastructure for electromagnetic modeling, a novel multi-physics analysis tool has been developed to include additional thermal and mechanical effects. The parallel computation enables virtual prototyping of accelerator cavities on computers, which would substantially reduce the cost and time of a design cycle. The multi-physics tool is applied to the LCLS rf gun for electromagnetic, thermal and structural analyses.

43 PARTICLE ACCELERATORS↗

DOE OSTI2011

Dark Current Simulation for Linear Collider Accelerator Structures

The dynamics of field-emitted electrons in the traveling wave fields of a constant gradient (tapered) disk-loaded waveguide is followed numerically. Previous simulations have been limited to constant impedance (uniform) structures for sake of simplicity since only the fields in a unit cell is needed. Using a finite element field solver on a parallel computer, the fields in the tapered structure can now be readily generated. We will obtain the characteristics of the dark current emitted from both structure types and compare the two results with and without the effect of secondary electrons. The NLC and JLC detuned structures are considered to study if dark current may pose a problem for high gradient acceleration in the next generation of Linear Colliders.

43 PARTICLE ACCELERATORS↗

DOE OSTI2011

Numerical Verification of the Power Transfer and Wakefield Coupling in the Clic Two-Beam Accelerator

The Compact Linear Collider (CLIC) provides a path to a multi-TeV accelerator to explore the energy frontier of High Energy Physics. Its two-beam accelerator (TBA) concept envisions complex 3D structures, which must be modeled to high accuracy so that simulation results can be directly used to prepare CAD drawings for machining. The required simulations include not only the fundamental mode properties of the accelerating structures but also the Power Extraction and Transfer Structure (PETS), as well as the coupling between the two systems. Time-domain simulations will be performed to understand pulse formation, wakefield damping, fundamental power transfer and wakefield coupling in these structures. Applying SLAC's parallel finite element code suite, these large-scale problems will be solved on some of the largest supercomputers available. The results will help to identify potential issues and provide new insights on the design, leading to further improvements on the novel two-beam accelerator scheme.

43 PARTICLE ACCELERATORS↗