Optimization of solenoid based low energy beam transport line for high current H⁺beams

Abstract

A 20 MeV, 30 mA CW proton linac is being developed at BARC, Mumbai. This linac will consist of an ECR ion source followed by a Radio Frequency Quadrupole (RFQ) and Drift tube Linac (DTL). The low energy beam transport (LEBT) line is used to match the beam from the ion source to the RFQ with minimum beam loss and increase in emittance. The LEBT is also used to eliminate the unwanted ions like H + 2 and H + 3 from entering the RFQ. In addition, space charge compensation is required for transportation of such high beam currents. All this requires careful design and optimization. Detailed beam dynamics simulations have been done to optimize the design of the LEBT using the Particle-in-cell code TRACEWIN. We find that with careful optimization it is possible to transport a 30 mA CW proton beam through the LEBT with 100% transmission and minimal emittance blow up, while at the same time suppressing unwanted species H + 2 and H + 3 to less than 3.3% of the total beam current.

Higher order mode beams mitigate halos in high intensity proton linacs

“…We first show how a HOMB can be generated in the LEBT of a HIPL. Figure 1 shows a schematic of the beamline transporting beam from a 50 keV, 30 mA proton ion source, through a LEBT to the RFQ; the parameters were chosen in conformity with the requirements of the ADRS system being studied and designed at our center [29]. The LEBT comprises two magnetic solenoids with drift spaces before, in-between and after the solenoids.…”

Design of a high-current low-energy beam transport line for an intense D-T/D-D neutron generator

“…Focusing of low-energy beam using an electric field is more effective than using a magnetic field; however, in an electrostatic LEBT, the beam is completely unneutralized and results in high-current beam filamentation in phase space and, eventually, in significant emittance growth. In addition, the electrostatic LEBT is sensitive to beam losses which might result in high-voltage breakdowns [10][11][12]. Electrostatic lenses result in larger beam emittance growth when compared to magnetostatic lenses of the same focal length, and the magnetostatic LEBTs are usually adopted [10][11][12].…”

“…In addition, the electrostatic LEBT is sensitive to beam losses which might result in high-voltage breakdowns [10][11][12]. Electrostatic lenses result in larger beam emittance growth when compared to magnetostatic lenses of the same focal length, and the magnetostatic LEBTs are usually adopted [10][11][12]. However, in the case of an intense neutron generator, the design of high-current LEBT line is based on both electrostatic and magnetostatic focusing.…”

“…The transport of high-current low-energy beam is critical because the beam is space charge dominated [12]. These space charge forces arise due to the Coulombic repulsion between the beam ions; these are highly nonlinear and cause expansion of beam envelope and increase in emittance growth.…”

“…These ions can be removed by placing some apertures at a suitable location. The aperture allows the D þ beam to pass through the column but reduces a significant amount of D þ 2 and D þ 3 ions [12,14]. The position and size of the apertures were simulated using the TRACK code.…”