Simon S. Yu

Filamentation of a heavy-ion beam in a reactor vessel

A heavy‐ion beam driver for inertial confinement fusion is subject to filamentation instability over a broad range of beam and plasma background conditions. The case of a beam injected into a gas‐filled reactor vessel, where finite pulse length and propagation distance play an important role in limiting mode growth, is analyzed. The effects of transverse thermal spread, spherical convergence to the pellet, and finite magnetic decay rate of eddy currents are included in this treatment. It is concluded that a cold beam will be severly disrupted unless the product of magnetic plasma frequency and propagation time is not large compared with unity. If this condition is not met, mode growth may still be limited to about six e folds by adding transverse velocity spread such that the pulse tail is in a state of pinch equilibrium. However, this approach causes much of the pulse to be lost by thermal expansion.

Stacked insulator induction accelerator gaps

Stacked insulators, with alternating layers of insulating material and conducting film, have been shown to support high surface electrical field stresses. We have investigated the application of the stacked insulator technology to the design of induction accelerator modules for the Relativistic-Klystron Two-Beam Accelerator program. The RF properties of the accelerating gaps using stacked insulators, particularly the impedance at frequencies above the beam pipe cutoff frequency, are investigated. Low impedance is critical for Relativistic-Klystron Two-Beam Accelerator applications where a high current, bunched beam is transported through many accelerating gaps. An induction accelerator module designs using a stacked insulator is presented.

Design of a relativistic klystron two-beam accelerator prototype

We are designing an experiment to study physics, engineering, and costing issues of an extended Relativistic Klystron Two-Beam Accelerator (RK-TBA). The experiment is a prototype for an RK-TBA based microwave power source suitable for driving a 1 TeV linear collider. Major components of the experiment include a 2.5-MV, 1.5-kA electron source, a 11.4-GHz modulator, a bunch compressor, and a 8-m extraction section. The extraction section will be comprised of 4 traveling-wave output structures, each generating about 360 MW of RF power. Induction cells will be used in the extraction section to maintain the average beam energy at 5 MeV. Status of the design is presented.

Numerical Simulation of Secondary Electron Orbits near an Electron Beam Propagating in a Low Pressure Gas

A numerical simulation has been constructed to obtain a detailed, quantitative estimate of the electromagnetic fields generated in a recently-proposed collective accelerator scheme for electrons. The code treats the secondary electrons by particle simulation and the beam dynamics by a time-dependent envelope model. The simulation gives a fully relativistic description of secondary electrons moving in selfconsistent electromagnetic fields. The calculations are made using coordinates t, x, y, z for the electrons and t, ct-z, r for the axisymmetric electromagnetic fields and currents. Code results showing the axial electric field dependence on the configuration of the ultrashort U. V. laser pulse will be given.

RK-TBA studies at the RTA test facility

Construction of a prototype RF power source based on the RK-TBA concept, called the RTA, has commenced at the Lawrence Berkeley National Laboratory. This prototype will be used to study physics, engineering, and costing issues involved in the application of the RK-TBA concept to linear colliders. The status of the prototype is presented, specifically the 1-MV, 1.2-kA induction electron gun and the pulsed power system that are in assembly. The RTA program theoretical effort, in addition to supporting the development of the prototype, has been studying optimization parameters for the application of the RK-TBA concept to higher-energy linear colliders. An overview of this work is presented.

Relativistic-Klystron two-beam accelerator as a power source for future linear colliders

The technical challenge for making two-beam accelerators into realizable power sources for high-energy colliders lies in the creation of the drive beam and in its propagation over long distances through multiple extraction sections. This year we have been constructing a 1.2-kA, 1-MeV, induction gun for a prototype relativistic klystron two-beam accelerator (RK-TBA). The electron source will be a 8.9 cm diameter, thermionic, flat-surface cathode with a maximum shroud field stress of approximately 165 kV/cm. Additional design parameters for the injector include a pulse length of over 150-ns flat top (1% energy variation), and a normalized edge emittance of less than 300 pi-mm-mr. The prototype accelerator will be used to study, physics, engineering, and costing issues involved in the application of the RK-TBA concept to linear colliders. We have also been studying optimization parameters, such as frequency, for the application of the RK-TBA concept to multi-TeV linear colliders. As an rf power source the RK-TBA scales favorably up to frequencies around 35 GHz. An overview of this work with details of the design and performance of the prototype injector, beam line, and diagnostics will be presented.

Engineering systems designs for a recirculating heavy ion induction accelerator

Recirculating heavy-ion induction accelerators are being investigated as possible drivers for heavy ion fusion. Part of this investigation included the generation of conceptual design for a recirculator system. The authors describe the overall engineering conceptual design of this recirculator, including discussions of the dipole magnet system, the superconducting quadrupole system, and the beam acceleration system. Major engineering issues, evaluation of feasibility, and cost tradeoffs of the complete recirculator system are presented and discussed.<<ETX>>

Application of Dynamically Consistent Closures to Hydrodynamic Models of Beams

For applications to phenomena such as pinched beams in ion beam fusion or beams in dominant axial magnetic fields (ion sources, plasma lens etc.), in accelerators, dynamically consistent closure of hydrodynamical models is discussed within adiabatic assumptions mathematically analogous to that of Chew, Goldberger, and Lowl (abbrev. CGL) for magneto-hydrodynamics and that of Berman and Mark2 (abbrev. BM) for galactic dynamics. Numerical comparison with particle codes is discussed for pinched beams.

Dynamically consistent closure equations for hydrodynamic models of pinched beams

Abstract The closure of hydrodynamical models for pinched beams is discussed within adiabatic assumptions mathematically analogous to that of Chew, Goldberger and Low. A simplified drift-kinetic equation is derived which could be used for closure. In addition, some plasma regimes allow more simple closure in terms of adiabatic equations of state.