Paper  Title  Page 

WPAT049  The Penetrability of a Thin Metallic Film Inside the RF Field  3073 


Funding: Under contract with the U.S. Department of Energy, Contract Number DEAC0298CH10886. Thin metallic film was widely applied in varies area. Especially, recently we are planning to apply it in a "Secondary emission enhanced photoinjector," of which a diamond cathode is coated with a golden film or so on its back to serve as a current path. The thickness of the film is originally considered to be in the order of 10 nm, which is much less than the skin depth, say 1/200. Since it is so thin, that intuitively the RF filed is penetrable. However, we found it is not true. The film will block most of the field. This paper addresses theoretic analysis as well as the experimental results. All demonstrated that the penetrability of a thin film is very poor. Consequently, most of the RF current will flow on the thin film causing a serous heating problem. 

MPPT027  ThreeDimensional Design of a NonAxisymmetric Periodic Permanent Magnet Focusing System  1964 


Funding: Work supported by the MIT Deshpande Center for Technological Innovation, the U.S. Department of Energy, HighEnergy Physics Division, Grant No. DEFG0295ER40919, and the Air Force Office of Scientific Research, Grant No. F496200310230. A threedimensional (3D) design is presented of a nonaxisymmetric periodic permanent magnet focusing system which will be used to focus a largeaspectratio, ellipseshaped, spacechargedominated electron beam. In this design, an analytic theory is used to specify the magnetic profile for beam transport. The OPERA3D code is used to compute and optimize a realizable magnet system. Results of the magnetic design are verified by twodimensional particleincell and threedimensional trajectory simulations of beam propagation using PFB2D and OMNITRAK, respectively. Results of fabrication tolerance studies are discussed. 

TPAE022  Analytical and Numerical Calculations of TwoDimensional Dielectric Photonic Band Gap Structures and Cavities for Laser Acceleration  1793 


Funding: Research supported in part by Department of Energy, Office of High Energy Physics, Grant No. DEFG0295ER40919 and in part by Department of Defense, Joint Technology Office, under a subcontract with University of Arizona. Dielectric photonic band gap (PBG) structures have many promising applications in laser acceleration. For these applications, accurate determination of fundamental and high order band gaps is critical. We present the results of our recent work on analytical calculations of twodimensional (2D) PBG structures in rectangular geometry. We compare the analytical results with computer simulation results from the MIT Photonic Band Gap Structure Simulator (PBGSS) code, and discuss the convergence of the computer simulation results to the analytical results. Using the accurate analytical results, we design a modeselective 2D dielectric cylindrical PBG cavity with the first global band gap in the frequency range of 8.8812 THz to 9.2654 THz. In this frequency range, the TM01like mode is shown to be well confined. 

TPAT002  ThreeDimensional Simulation of LargeAspectRatio EllipseShaped ChargedParticle Beam Propagation  823 


Funding: U.S. Department of Energy: Grant No. DEFG0295ER40919, Grant No. DEFG0201ER54662, Air Force Office of Scientific Research: Grant No. F496200310230, and the MIT Deshpande Center for Technological Innovation. The threedimensional trajectory code, OMNITRAK, is used to simulate a spacechargedominated beam of largeaspectratio elliptic crosssection propagating in a nonaxisymmetric periodic permanent magnet focusing field. The simulation results confirm theoretical predictions in the paraxial limit. A realistic magnetic field profile is applied, and the beam sensitivity to magnet nonlinearities and misalignments is studied. The imagecharge effect of conductor walls is examined for a variety of beam tunnel sizes and geometries. 

TPAT003  ColdFluid Equilibrium of a LargeAspectRatio EllipseShaped ChargedParticle Beam in a NonAxisymmetric Periodic Permanent Magnet Focusing Field  853 


Funding: U.S. DOE, Grant: No. DEFG0295ER40919,Grant No. DEFG0201ER54662, Air Force Office of Scientific Research, Grant No. F496200310230, and the MIT Deshpande Center for Technological Innovation. A new class of equilibrium is discovered for a largeaspectratio ellipseshaped chargedparticle beam in a nonaxisymmetric periodic permanent magnet focusing field. A paraxial coldfluid model is employed to derive the equilibrium flow properties and generalized envelope equations with negligibly small emittance. A periodic beam equilibrium solution is obtained numerically from the generalized envelope equations. It is shown that the beam edges are well confined in both transverse directions, and that the equilibrium beam exhibits a smallangle periodic wobble as it propagates. A twodimensional particleincell (PIC) code, PFB2D, is used to verify the theoretical predictions in the paraxial limit, and to establish validity under nonparaxial situations and the influence of the conductor walls of the beam tunnel. 

WPAP057  ThreeDimensional Theory and Simulation of an EllipseShaped ChargedParticle Beam Gun  3372 


Funding: U.S. DOE: Grant No. DEFG0295ER40919, Grant No. DEFG0201ER54662, Air Force Office of Scientific Research: Grant No. F496200310230, and the MIT Deshpande Center for Technological Innovation. A threedimensional (3D) theory of nonrelativistic, laminar, spacechargelimited, ellipseshaped, chargedparticle beam formation has been developed recently (Bhatt and Chen, PR:STAB, submitted Dec. 2004), whereby charged particles (electrons or ions) are accelerated across a diode by a static voltage differential and focused transversely by Piercetype external electrodes placed along analytically specified surfaces. The treatment is extended to consider the perturbative effects of anode hole lensing, thermal isolation of the emitter, finiteness and nonuniformities of beamforming electrodes, and an initial thermal spread. Analytic and semianalytic results are presented along with 3D simulations utilizing the 3D trajectory code, OMNITRAK. Considerations with regard to beam matching into a periodic magnetic focusing lattice are discussed. 

FPAT030  Parametric Studies of ImageCharge Effects in SmallAperture AlternatingGradient Focusing Systems  2128 


Funding: The U.S. Department of Energy, Office of HighEnergy Physics, Grant No. DEFG0295ER40919, Office of Fusion Energy Science, Grant No. DEFG0201ER54662, and in part by Air Force Office of Scientific Research, Grant No. F496200310230.
Image charges have important effects on an intense chargedparticle beam propagating through an alternatinggradient (AG) focusing channel with a small circular aperture. This is especially true with regard to chaotic particle motion, halo formation, and beam loss.* In this paper, we examine the dependence of these effects on system parameters such as the filling factor of the AG focusing field, the vacuum phase advance, the beam perveance, and the ratio of the beam size to the aperture. We calculate the percentage of beam loss to the conductor wall as a function of propagating distance and aperture, and compare theoretical results with simulation results from the particleincell (PIC) code PFB2D.
*Zhou, Qian and Chen, Phys. Plasmas 10, 4203 (2003). 