Beam dynamics redesign of ifmif-eveda rfq for a larger input beam acceptance

Status and future developments of the Linear IFMIF Prototype Accelerator (LIPAc)

For the purpose of material studies for future nuclear fusion reactors, the IFMIF deuteron beams present a simultaneous combination of unprecedentedly high intensity (2 × 125 mA CW), power (2 × 5 MW) and space charge. Special considerations and new concepts have been developed in order to overcome these challenges. The global strategy for beam dynamics design of the 40 MeV IFMIF accelerators is presented, stressing on the control of micro-losses, and the possibility of online fine tuning. Start-to-end simulations without and with errors are presented for the prototype accelerator. Considerations about conflicts between halo and emittance minimization are then discussed in this very high space charge context.

/pdf/dynamics-of-the-ifmif-very-high-intensity-beam-51x45kcm2u.pdf

Dynamics of the IFMIF very high-intensity beam

Fusion materials research is a worldwide endeavor as old as the parallel one working toward the long term stable confinement of ignited plasma. In a fusion reactor, the preservation of the required minimum thermomechanical properties of the in-vessel components exposed to the severe irradiation and heat flux conditions is an indispensable factor for safe operation; it is also an essential goal for the economic viability of fusion. Energy from fusion power will be extracted from the 14 MeV neutron freed as a product of the deuterium–tritium fusion reactions; thus, this kinetic energy must be absorbed and efficiently evacuated and electricity eventually generated by the conventional methods of a thermal power plant. Worldwide technological efforts to understand the degradation of materials exposed to 14 MeV neutron fluxes >1018 m−2s−1, as expected in future fusion power plants, have been intense over the last four decades. Existing neutron sources can reach suitable dpa (“displacement-per-atom”, the figure of merit to assess materials degradation from being exposed to neutron irradiation), but the differences in the neutron spectrum of fission reactors and spallation sources do not allow one to unravel the physics and to anticipate the degradation of materials exposed to fusion neutrons. Fusion irradiation conditions can be achieved through Li (d, xn) nuclear reactions with suitable deuteron beam current and energy, and an adequate flowing lithium screen. This idea triggered in the late 1970s at Los Alamos National Laboratory (LANL) a campaign working toward the feasibility of continuous wave (CW) high current linacs framed by the Fusion Materials Irradiation Test (FMIT) project. These efforts continued with the Low Energy Demonstrating Accelerator (LEDA) (a validating prototype of the canceled Accelerator Production of Tritium (APT) project), which was proposed in 2002 to the fusion community as a 6.7MeV, 100mA CW beam injector for a Li (d, xn) source to bridge with the International Fusion Materials Irradiation Facility (IFMIF) under discussion at the time. Worldwide technological efforts are maturing soundly and the time for a fusion-relevant neutron source has arrived according to world fusion roadmaps; if decisions are taken we could count the next decade with a powerful source of 14 MeV neutrons thanks to the expected significant results of the Engineering Validation and Engineering Design Activity (EVEDA) phase of the IFMIF project. The accelerator know-how has matured in all possible aspects since the times of FMIT conception in the 1970s; today, operating 125 mA deuteron beam at 40 MeV in CW with high availabilities seems feasible thanks to the understanding of the beam halo physics and the three main technological breakthroughs in accelerator technology: (1) the ECR ion source for light ions developed at Chalk River Laboratories in the early 1990s, (2) the RFQ operation of H+ in CW with 100 mA demonstrated by LEDA in LANL in the late 1990s, and (3) the growing maturity of superconducting resonators for light hadrons and low β beams achieved in recent years.

Accelerators for Fusion Materials Testing

MYRRHA is designed as an accelerator driven system (ADS) for transmutation of long-lived radioactive waste. The challenge of the linac development is the very high reliability of the accelerator to limit the thermal stress inside the reactor. With the concept of parallel redundancy the injector will supply a cw proton beam with 4 mA and 17 MeV to the main linac. The new MYRRHA injector layout consists of a very robust beam dynamics design with low emittance growth rates. Sufficient drift space provides plenty room for diagnostic elements and increases the mountability. Behind a 4-Rod-RFQ and a pair of two-gap QWR rebunchers at 1.5 MeV the protons are matched into the CH cavity section. A focussing triplet between the rebunchers ensures an ideal transversal matching into the doublet lattice. Each of the 7 room temperature (RT) CH structures has a constant phase profile and does not exceed thermal losses of 29 kW/m. The transition to the 5 superconducting (SC) CH cavities with constant beta profile is at 5.9 MeV. For a safe operation of the niobium resonators the electric and magnetic peak fields are defined below 25 MV/m and 57 mT respectively.

R&D of the 17 MeV MYRRHA Injector

The relevance of classical parameters like beam emittance and envelope used to describe a particle beam is questioned in case of a high intensity accelerator. In the presence of strong space charge effects that affect the beam differently following its density, the much less dense halo part behaves differently from the much denser core part. A method for precisely determining the core-halo limit is proposed, that allows characterizing the halo and the core independently. Results in 1D case are given and discussed. Expected developments extending the method to 2D, 4D, or 6D phase spaces are examined.

/pdf/core-halo-issues-for-a-very-high-intensity-beam-o3upza3sgx.pdf

Core-halo issues for a 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

Dynamics of the IFMIF Very High-intensity Beam

The MYRRHA project, a flexible spectrum neutron irradiation facility, is designed according to the Accelerator Driven System (ADS) reactor concept. The MYRRHA driver consists of a high power superconducting proton linac. A prototype of the front end injector is being built up into a test platform conceived to experimentally address its design issues. Currently, the ECR proton source has been industrially procured. LPSC Grenoble designed the subsequent Low Energy Beam Transport (LEBT) section. Right before the RFQ, a short section hosts an electrostatic beam chopper producing carefully controlled beam interruptions. In this paper the status of the LEBT design with the associated beam instrumentation is reviewed. Future experimental plans including LEBT beam characterization and optimization of the beam transmission are presented.

/pdf/design-progress-of-the-myrrha-low-energy-beam-line-2prrbxdbk7.pdf

Design progress of the myrrha low energy beam line

The EVEDA (Engineering Validation and Engineering Design Activities) phase of the IFMIF (International Fusion Materials Irradiation Facility) project consists in building, testing and operating a 125 mA/9 MeV prototype accelerator in Rokkasho-Mura (Japan). Because of high beam intensity and power, the different sections of the accelerator (injector, RFQ, MEBT, Superconducting Radio-Frequency linac and HEBT) have been optimized with the twofold objective of minimizing losses along the machine and keeping a good beam quality. Extensive start-to-end multi-particles simulations have been performed to validate the prototype accelerator design. A Monte Carlo error analysis has been carried out to study the effects of misalignments and field variations. In this paper, the results of theses beam dynamics simulations, in terms of beam emittance, halo formation and beam losses, are presented.

Start-to-end beam dynamics simulations for the prototype accelerator of the ifmif/eveda project

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