Three-dimensional nonlinear transverse beam dynamics of a radio-frequency quadrupole: comparison of PARMTEQ with an exact image-charge calculation

Abstract

voltage, current and phase shlft. From these measurements the series equivalent discnarae resistance, Rd, has been caizulated. T%eu~--, shows that Rd can be dilideC irito t r v o I?' components, the plasma body r -e s i s t a n c e , R and the sheath rzsistance, R, (corresponding to ion acceleration), where H-=Vp/I ( V p is the plasma body voltage) and 5; and R S are fairly constant over a wide range o f I. two components: the power dissicated in the plasma body and the power dissipated in accelerating ions in the rf sheaths. In this form the total discharge power is:lhe t-atio of the power dissipated In ion acceleration in the. rf sheaths to the total power dissipated ir. t 5 e discharge have been determined using both techniques and compared graphically. The details of the analysis techniques and the comparison of the resuits using these techniques will be presented. AbstractA small section of a Radiofrequency Quadrupole accelerator has been analyzed using both a full three-dimensional beam dynamics code and a more conventional beam dynamics analysis ,approach represented by the code PARMTEQ. Transverse beam-dynamics effects are compared as they were predicted by both approaches. The difference between the approaches is shown as a function of beam current. For beam currents in excess of 100 mA our results would indicate that space-charge/ image-charge effects must be treated with detailed calculations. Previous analyses of the stimulated Raxnan forward scattering( SRFS) and the relativistic Inodulational instability (RXII) of light waves have treated these instabilities separately. In a rarefied plasma. however. they are closely-linked branches of the .came instability. The results of a unified analysis of SRFS and R l I I n-ill be desribed and their consequences for beat-wave particle acceleration will he discussed briefly. 5P2-3 N u m e r i c a l S i m u l a t i o n of t h e Mirrortron*We have recently begun investigation of a novel accelerator concept, the Mirrortron', using the 2 1/2 D cylindrical PIC code GYMNOS. The Mirrortron takes advantage of large transient potentials generated in a mirror cell in order to accelerate and focus an ion beam. We are concerned with the behavior of the chamber plasma as an external coil produces a substantial change in the local axial magnetic field. We investigate how these changes produce both accelerating and focusing electrostatic fields. In addition, effects produced by the propagation of a finite-length space-charge dominated ion beam during the pulse will be considered. At present GYMNOS is electro-and magnetostatic; consideration of magnetoinductive effects will occur with the implementation of a Darwin field model. 1.