IFMIF, the European–Japanese efforts under the Broader Approach agreement towards a Li(d,xn) neutron source: Current status and future options

The necessity of a neutron source for fusion materials research was identified already in the 70s. Though neutrons induced degradation present similarities on a mechanistic approach, thresholds energies for crucial transmutations are typically above fission neutrons spectrum. The generation of He via 56Fe (n,α) 53Cr in future fusion reactors with around 12 appm/dpa will lead to swelling and structural materials embrittlement. Existing neutron sources, namely fission reactors or spallation sources lead to different degradation, attempts for extrapolation are unsuccessful given the absence of experimental observations in the operational ranges of a fusion reactor. Neutrons with a broad peak at 14 MeV can be generated with Li(d,xn) reactions; the technological efforts that started with FMIT in the early 80s have finally matured with the success of IFMIF/EVEDA under the Broader Approach Agreement. The status today of five technological challenges, perceived in the past as most critical, are addressed. These are: 1. the feasibility of IFMIF accelerators, 2. the long term stability of lithium flow at IFMIF nominal conditions, 3. the potential instabilities in the lithium screen induced by the 2 × 5 MW impacting deuteron beam, 4. the uniformity of temperature in the specimens during irradiation, and 5. the validity of data provided with small specimens. Other ideas for fusion material testing have been considered, but they possibly are either not technologically feasible if fixed targets are considered or would require the results of a Li(d,xn) facility to be reliably designed. In addition, today we know beyond reasonable doubt that the cost of IFMIF, consistently estimated throughout decades, is marginal compared with the cost of a fusion reactor. The less ambitious DEMO reactor performance being considered correlates with a lower need of fusion neutrons flux; thus IFMIF with its two accelerators is possibly not needed since with only one accelerator as the European DONES or the Japanese A-FNS propose, the present needs > 10 dpa/fpy would be fulfilled. World fusion roadmaps stipulate a fusion relevant neutron source by the middle of next decade, the success of IFMIF/EVEDA phase is materializing this four decades old dream

Status of the RFQ linac installation and conditioning of the Linear IFMIF Prototype Accelerator

Abstract The Radio Frequency Quadrupole (RFQ) linac and 1.6 MW RF power system of the Linear IFMIF Prototype Accelerator (LIPAc) facility in the International Fusion Energy Research Center (IFERC) in Rokkasho (Japan) has been installed and conditioned. During the assembly and tuning process, the RFQ cavity was protected with a temporary tent from the potential deterioration of performance caused by dust. The vacuum in the cavity was improved through the 100 °C baking process of the cavity. The high power test of the 175 MHz RF systems up to 200 kW in CW for each of the eight RF chains was performed for checking its stable output reproducibility in Japan, before connecting 9–3/16 inch coaxial transmission lines from the RF chains to the RF input couplers of the cavity. It was confirmed that the eight RF chains provided the balanced RF power to the single RFQ cavity in-phase using a feedback loop and a synchronization system. The peak power in the cavity achieved 150 kW in the pulsed mode, which corresponds approximately to the required electric field to accelerate proton beam. Such RF conditioning process is ongoing to achieve 600 kW approximately required for deuteron beam commissioning planned in 2018

The vacuum chamber in the interaction region of particle colliders : a historical study and developments implemented in the LHCb experiment at CERN

El colisionador de protenes actualmente en construcción en el CERN llamado LHC (Large Hadron Collider) se convertirá en el más potente acelerador jamas construido con una energía por protón de 7 TeV. Se prevé que esta en operación en 2007. Constará de 4 grandes experimentos uno de los cuales, LHCb, se dedicará a la investigación de la violación CP. Los requerimientos de la cámara de vacío de los experimentos en colisionadores de partículas son muy especiales. La presente tesis doctoral, en una primera parte, hace un análisis histórico de la evolución en los diseños desde el nacimiento de los colisionadores a principios de los 70 describiendo dichos criterios pormenorizadamente. En una segunda parte, se describe la implementación de los mismos en el diseño de la cámara de vacío del experimento LCHb, explicando los desarrollos realizados. La camara de vacío que se instalara tiene una forma biconica (25 y 10 mrad) de 12 m de berilio de 1 a 2.4mm de espesor, constará de compensadores metálicos de aluminio, bridas de ultra-alto vacio de aluminio específicamente diseñadas y una ventana esférica de 850 mm de diámetro fabricada en alumnio. La radiación de fondo generada por el presente diseño se reduce en un factor 5 con respecto a la cámara de vacío inicialmente considerada

An assessment of the evaporation and condensation phenomena of lithium during the operation of a Li(d,xn) fusion relevant neutron source

The flowing lithium target of a Li(d,xn) fusion relevant neutron source must evacuate the deuteron beam power and generate in a stable manner a flux of neutrons with a broad peak at 14 MeV capable to cause similar phenomena as would undergo the structural materials of plasma facing components of a DEMO like reactors. Whereas the physics of the beam-target interaction are understood and the stability of the lithium screen flowing at the nominal conditions of IFMIF (25 mm thick screen with +/-1 mm surface amplitudes flowing at 15 m/s and 523 K) has been demonstrated, a conclusive assessment of the evaporation and condensation of lithium during operation was missing. First attempts to determine evaporation rates started by Hertz in 1882 and have since been subject of continuous efforts driven by its practical importance; however intense surface evaporation is essentially a non-equilibrium process with its inherent theoretical difficulties. Hertz-Knudsen-Langmuir (HKL) equation with Schrage’s ‘accommodation factor’ η = 1.66 provide excellent agreement with experiments for weak evaporation under certain conditions, which are present during a Li(d,xn) facility operation. An assessment of the impact under the known operational conditions for IFMIF (574 K and 10-3 Pa on the free surface), with the sticking probability of 1 inherent to a hot lithium gas contained in room temperature steel walls, is carried out. An explanation of the main physical concepts to adequately place needed assumptions is included

Experimental Study on Cavitation of a Liquid Lithium Jet for International Fusion Materials Irradiation Facility

A liquid Li jet flowing at 15 m/s under a high vacuum of 10 3Pa is intended to serve as a beam target (Li target) in the planned International Fusion Materials Irradiation Facility(IFMIF). The engineering validation and engineering design activities (EVEDA) for the IFMIF are being implemented under the broader approach (BA) agreement. As a major activity of the Li target facility, the EVEDA Li test loop (ELTL) was constructed by the Japan Atomic Energy Agency. A stable Li target under the IFMIF conditions (Li temperature:523.15 K, velocity: 15 m/s, and vacuum pressure: 10 3 Pa) was demonstrated using ELTL. This study focuses on a cavitationlike acoustic noise detected in a downstream conduit where the Li target flowed under vacuum conditions. This noise was investigatedusing acoustic-emission (AE) sensors installed at eight locations via acoustic wave guides. The sound intensity of the acoustic noise was examined against the cavitation number of the Li target. In addition, two types of frequency analysis, namely, fast Fourier transform (FFT) and continuous wavelet transform (CWT), were performed to characterize the acoustic noise. Owing to the acoustic noise’s intermittency, high frequency, and the dependence on cavitation number, we conclude that this acoustic noise is generated when cavitation bubbles collapse and/or the structural material of the pipe is cracked because of the collapse of cavitation bubbles (cavitation pitting). The location of the cavitationwas fundamental for presuming the mechanism. In this study, the propagation ofacoustic waves among AE sensors placed at three locations was used to localize the cavitation and a method to determine the location of cavitation was formulated. As a result, we found that cavitation occurred only in a narrow area where the Li target impinged on the downstream conduit; therefore, we concluded that this cavitation was induced by the impingement. The design of the downstream conduit of the IFMIF Li target facility should be tackled in future based on information obtained in this study

Radiation safety study for the beam commissioning of IFMIF/EVEDA LIPAc RFQ in Rokkasho

The construction of the Linear IFMIF Prototype Accelerator (LIPAc) is in progress at Rokkasho, Japan. The important milestone of the project is to commission the necessary components, namely RFQ, MEBT and diagnostics, to accelerate the proton beam up to 2.5 MeV or the deuteron beam up to 5.0 MeV in pulsed mode with a low duty cycle of 0.1%. The detailed radiation safety analysis has been conducted for the beam commissioning with the consideration of the specific radiation source conditions and the building configuration. As a result, it turned out that the dose rate expected outside the accelerator vault during deuteron beam operation at 5 MeV is mostly dominated by the neutron streaming effect through three major penetration sectors, i.e. HVAC ducts, water pipe holes and underground pits, while it is negligibly small during the proton beam operation at 2.5 MeV. It was confirmed that the dose rate expected does not exceed the legal limit for the controlled area boundary and no serious radiological issues exist in the beam commissioning planned

Beam Diagnostics of the LIPAC Injector With a Focus on the Algorithm Developed for Emittance Data Analysis of High Background Including Species Fraction Calculation

International audienceTo prove the feasibility of the IFMIF accelerators concept, the EVEDA phase will commission in Japan the LIPAC accelerator, which will deliver a 125 mA/9 MeV CW deuteron beam. LEDA already managed 100 mA in CW at 6.7 MeV in 2000. The different subsystems of LIPAC have been designed and constructed mainly by European labs with the injector developed by CEA-Saclay. This injector must deliver a 140 mA/100 keV CW deuteron beam at 99% D⁺ ratio, which is produced by a 2.45 GHz ECR ion source. The low energy beam transport line is based on a dual solenoid focusing system to transport the beam and to match it into the RFQ. The normalized RMS target emittance at the RFQ entrance is targeted to be within 0.25π mm·mrad. This article describes the diagnostics installed in the LEBT to measure beam parameters such as intensity, profile, emittance, species fraction and degree of space charge compensation. The article also focuses on the algorithm developed to analyze emittance data of high background from an Allison scanner. Species fractions (D⁺, D2+, D3+) using mass separation technique were also calculated with the Allison scanner installed between the two solenoids in a first stage