Space charge compensation studies of hydrogen ion beams in a drift section

Abstract

Demands of high intensity beams are increasing for material science and engineering applications. To control the high intensity beam dynamics, the nonlinear space charge forces, produced by the beam and the residual plasma at low energy, have to be carefully studied. Interactions between the beam and the residual gas tend to neutralize the beam space charge. The temporal and spatial evolutions of these interactions complicate the beam dynamics, even into a drift section. A 1.5D (xy for motion, r for space charge) PIC code, CARTAGO, has been written in order to simulate the beam dynamics in a low energy beam transport line including the space charge compensation effects. This paper relates the structure and the numerical methods used in the code and shows studies of the space charge compensation regime for H and H ÿ beams in a drift section.

Low energy beam transport system developments

“…[3,26,27] that demonstrated qualitative agreement with experiments [4], which exhibit more complex behavior of SCC with beam focusing to a small focusing waist. The usual location of the emittance scanner and other diagnostics between the solenoids is not very useful because most significant emittance growth arises in the beam focus at the entry to the RFQ.…”

“…If the axial symmetry of beam or secondary ion generation is broken, the peak of the ion distribution can be off axis, which can cause beam deflections and dipole oscillations. In more detailed simulations of SCC in MLEBT with secondary particle dynamics presented in [3,26,30], the SCC features discussed above were reproduced.…”

“…For high beam brightness preservation, a high density of heavy gases (~10 12 cm -3 for Kr) [4] is needed. For protons with energy 50 to 100 keV, the beam attenuation in the MLEBT is relative low (~5%) because cross sections for electron capture are relative low and the gas ionization cross sections is relative high [3,4,26,27]. However, for low energy positive ions for low emittance preservation, very high gas density is needed, which causes more significant beam attenuation because the ionization cross sections become very low [28] but electron capture cross sections are high.…”

“…Now this instability is a main limiting factor of beam performance in the Large Hadron Collider (LHC) in CERN, including some beam transfer lines and in many other accelerators and storage rings [23,25]. Simulations of SCC for protons and H -beams in MLEBT with secondary particle motion in the beams were conducted in [3,[25][26][27].…”

Emittance and proton fraction measurement in High current electron cyclotron resonance proton ion source

“…5 we can see that beam emittance/divergence has a lower value when the pressure is 2 Â 10 À 5 mbar, but the corresponding value of beam current in Fig. 6 is higher, so it can be concluded that at higher beam currents, the beam is more space charge compensated in the presence of high gas pressure (2 Â 10 À 5 mbar) into the beam line [19][20][21][22].…”