Design and beam dynamics studies of low energy beam transport for MEHIPA

Low Energy High Intensity Proton Accelerator (LEHIPA), the initial stage of India’s Accelerator Driven Subcritical System (ADSS) program has been commissioned to the design energy of 20 MeV at BARC, Mumbai. The subsequent stage, the Medium Energy High Intensity Proton Accelerator (MEHIPA), a 325 MHz, 40 MeV, 10 mA proton accelerator, will be constructed at BARC, Vizag. This accelerator will have an Electron Cyclotron Resonance Ion Source (ECR-IS) producing 30 keV proton beam, which will be transported, matched, and focused into the first accelerating structure—the Radio Frequency Quadrupole (RFQ)—through a Low Energy Beam Transport (LEBT) channel. The transmission efficiency and beam quality through the linac depend on the input beam parameters, with significant sensitivity at low energies where space charge effects dominate. Beam quality degradation originating in these low-energy sections can lead to the formation of beam halos and beam emittance growth at higher energies. Thus, detailed studies are necessary to optimize the matching between the ion source and the RFQ to minimize emittance growth, suppress halo formation, and reduce beam losses down the line in the linac. Based on the operational experience of LEHIPA LEBT and evolving LEBT design concepts worldwide, the MEHIPA LEBT design has been improvised on many fronts. A compact three-solenoid-based LEBT design is proposed, optimized for a 30 keV proton beam with a realistic emittance of approximately 0.3π mm.mrad. The design incorporates the option of a bending magnet for species selection. Detailed beam dynamics simulations of the proposed LEBT are carried out using the particle-in-cell (PIC) code TraceWin, examining the effect of varying input beam parameters, such as Courant-Snyder parameters, root mean square (rms) emittance, beam distributions, magnet misalignment and beam currents. The impact of different levels of space charge compensation on beam transport has also been analysed to ensure optimal performance.