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Li, Z.

Paper Title Page
MOP104 Parallel 3D Finite Element Particle-In-Cell Code for High-Fidelity RF Gun Simulations 317
  • A.E. Candel, A.C. Kabel, K. Ko, L. Lee, Z. Li, C. Limborg-Deprey, C.-K. Ng, G.L. Schussman, R. Uplenchwar
    SLAC, Menlo Park, California

Funding: Work supported by DOE contract DE-AC02-76SF00515.
SLAC's Advanced Computations Department (ACD) has developed the first high-performance parallel Finite Element 3D Particle-In-Cell code, Pic3P, for simulations of rf guns and other space-charge dominated beam-cavity interactions. As opposed to standard beam transport codes, which are based on the electrostatic approximation, Pic3P solves the complete set of Maxwell-Lorentz equations and thus includes space charge, retardation and wakefield effects from first principles. Pic3P uses advanced Finite Element methods with unstructured meshes, higher-order basis functions and quadratic surface approximation. A novel scheme for causal adaptive refinement reduces computational resource requirements by orders of magnitude. Pic3P is optimized for large-scale parallel processing and allows simulations of realistic 3D particle distributions with unprecedented accuracy, aiding the design and operation of the next-generation of accelerator facilities. Applications to the Linac Coherent Light Source (LCLS) rf gun are presented.

THP038 A New SRF Cavity Shape with Minimized Surface Electric and Magnetic Fields for the ILC 867
  • Z. Li, C. Adolphsen
    SLAC, Menlo Park, California

Funding: Work supported by DOE contract DE-AC02-76SF00515.
The TESLA-shape cavity has been chosen as the baseline design for the 1.3 GHz SCRF linacs of the International Linear Collider. However, there is ongoing research to develop new cavity shapes that will support higher gradients and hence lower the machine cost. The critical magnetic flux (Bc) of the niobium, which is approximately 180 mT, ultimately limits the gradient achievable in a superconducting cavity. Thus far, the new designs have focused on minimizing the peak surface magnetic field (Bs) for a given on-axis gradient, while relaxing the requirement on the peak surface electric field (Es). For example, the Low Loss (LL) design reduces Bs by more than 10% relative to the baseline design, which should allow a gradient of up to 50 MV/m with a 20% reduction in cryogenics loss. However, Es is about 15% higher in this case, which enhances field emission that in practice is one of the main impediments to achieving the Bc-limited gradient. In this paper, we will present an optimized cavity shape that reduces both Bs and Es, and thus should have a better chance of reaching higher gradients. The design of HOM couplers for wakefield damping in this cavity will also be presented.


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THP039 SRF Cavity Imperfection Studies Using Advanced Shape Uncertainty Quantification Tools 870
  • V. Akcelik, K. Ko, L. Lee, Z. Li, C.-K. Ng, L. Xiao
    SLAC, Menlo Park, California

Funding: Work supported by DOE contract DE-AC02-76SF00515.
The shape deviation of a SRF cavity from the design shape may result in significant impact on cavity performance and wakefields that could lead to unexpected effects in beam dynamics. Yet, most of these deviations are unknown in the final cavity installation because of the complicated process of assembly and tuning. It is desirable to be able to uncover such distortions using measurable rf quantities. With these data, the cavity performance can be analyzed and realistic tolerance criteria may be implemented in the cavity design and manufacture for quality assurance. To perform such analyses, SLAC has developed advanced Shape Determination Tools, under the SciDAC support for high performance computing, that recover the real cavity shape by solving an inverse problem. These tools have been successfully applied to analyze shape distortions to many SRF cavities, and identified the cause of unexpected cavity behaviors. The capabilities and applications of these tools will be presented.

THP023 Crab Cavities for Linear Colliders 830
  • G. Burt, P.K. Ambattu, R.G. Carter, A.C. Dexter, M.I. Tahir
    Cockcroft Institute, Lancaster University, Lancaster
  • C. Adolphsen, Z. Li, A. Seryi, L. Xiao
    SLAC, Menlo Park, California
  • C.D. Beard, D.M. Dykes, P. Goudket, A. Kalinin, L. Ma, P.A. McIntosh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • L. Bellantoni, B. Chase, M. Church, T.N. Khabiboulline
    Fermilab, Batavia
  • R.M. Jones
    UMAN, Manchester
  • A. Latina, D. Schulte
    CERN, Geneva

Crab cavities have been proposed for a wide number of accelerators and interest in crab cavities has recently increased after the successful operation of a pair of crab cavities in KEK-B. In particular crab cavities are required for both the ILC and CLIC linear colliders for bunch alignment. Consideration of bunch structure and size constraints favours a 3.9 GHz superconducting, multi-cell cavity as the ILC solution, whilst bunch structure and beam-loading considerations suggest an X-band copper travelling wave structure for CLIC. These two cavity solutions are very different in design but share complex design issues. Phase stabilisation, beam loading, wakefields and mode damping are special issues for these crab cavities. Requirements and potential design solutions will be discussed for both colliders.