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ELECTROMAGNETIC SIMULATIONS OF HELICAL-BASED ION

ACCELERATION STRUCTURES*

Scott D. Nelson, George Caporaso, Alex Friedman, Brian R. Poole, Lawrence Livermore National

Laboratory (LLNL), Livermore, CA 94550, U.S.A., Richard Briggs, SAIC, Alamo, CA, 94507,

U.S.A., William Waldron, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, U.S.A.

Abstract

Helix structures have been proposed [1] for accelerating

low energy ion beams using MV/m fields in order to

increase the coupling efficiency of the pulsed power

system and to tailor the electromagnetic wave propagation

speed with the particle beam speed as the beam gains

energy.

Calculations presented here show the

electromagnetic field as it propagates along the helix

structure, field stresses around the helix structure (for

voltage breakdown determination), optimizations to the

helix and driving pulsed power waveform, and

simulations showing test particles interacting with the

simulated time varying fields.

INTRODUCTION

The helical structures are composed of wire wound

around an insulating hollow core. Inside the core is the

vacuum region for the ion beam. Outside the core is a

dielectric insulating material (e.g. oil, or a cast material)

which prevents breakdown between the helical windings

and the metallic outer cylinder (see Figure 1). In this

configuration, feeds penetrate through the outer cylinder

and directly drive the helix.

Figure 1: Early prototype of the helical acceleratin1]zMUlhu2/1tf2fbubTdl[UnhkV2u11U h1Mu1Mu]T"lk111[u1MUxhV2u1MM