Dynamics of the IFMIF very high-intensity beam

AbstractFor the purpose of material studies for future nuclear fusion reactors, the IFMIF deuteron beams present a simultaneouscombination of unprecedentedly high intensity (2×125 mA CW), power (2×5 MW) and space charge. Specialconsiderations and new concepts have been developed in order to overcome these challenges. The global strategy forbeam dynamics design of the 40 MeV IFMIF accelerators is presented, stressing on the control of micro-losses, and thepossibility of online fine tuning. Start-to-end simulations without and with errors are presented for the prototypeaccelerator. Considerations about conflicts between halo and emittance minimization are then discussed in this veryhigh space charge context.Keywords: Beam dynamics; High-intensity beams; Linear accelerators; Space charge 1. INTRODUCTIONSet in the Fusion Broader Approach agreement betweenEurope and Japan, IFMIF (International Fusion MaterialsIrradiation Facility) will be the world’s most intense neutronsource dedicated to studymaterials covering internal walls ofthe future fusion reactors. It will include two identical linearaccelerators accelerating 2×125 mA of CW deuteron beamsto the energy of 40 MeV, resulting in a total beam power of2×5 MW (Mosnier et al., 2010). The two beam lines mustconverge on a liquid lithium target to produce the requiredneutron flux, with a rectangular and uniform footprint.In a first phase currently in progress, a full scale prototypeaccelerator up to 9 MeV – 1.1 MW is being studied and con-structedinEurope,tobeinstalledinJapan.ForthisprototypecalledLIPAc(LinearIFMIFPrototypeAccelerator),thefinalbeam must be properly expanded toward a beam dump. Inthis paper, the global parameters of IFMIF are compared tothose of other high-power accelerators. This reveals the sim-ultaneous combination of unprecedented characteristicsto beachieved. The induced challenges in beam dynamics designare pointed out, and the strategies to overcome them are out-lined. Obtained results are shown and discussed, with afocus on LIPAc start-to-end simulations results. Finally, theconflicts between beam halo and emittance minimizationsare addressed, and possibleways for improvement discussed.This work has been briefly approached in short papers(Nghiem et al., 2011a; Chauvin et al., 2011; Simeoni Jret al., 2011). It is here gathered, updated and furthermoredeveloped to form a coherent and complete topic.2. ISSUESThe general layout of the IFMIF accelerators is given inFig. 1 where beam energy and power are pointed out alongthe beam line. Due to the very high CW beam intensity re-quired,theD