High Energy Neutral Beam Research Articles

Modelling of NBI shine-through in ITER non-nuclear phase to limit heat fluxes on first wall

The occurrence of localized high heat fluxes on the ITER first wall can limit the lifetime of plasma-facing components. This can be the case of excessive shine-through losses due to high-energy Neutral Beam Injection (NBI) in low density plasmas, as in the first operation phases of ITER. The use of ITER NBI will be therefore limited to densities that guarantee acceptable power fluxes on the first wall. In this work, we review the NBI shine-through issue in the ITER pre-fusion phases by numerical simulations, extending previous modelling assumptions and exploiting the IMAS modelling framework. The dependencies of shine-through on beam injection energy and plasma density profiles are discussed and a heuristic formula for shine-through fraction is proposed, fitting a large database of ad-hoc simulations. In particular the effect of NBI vertical tilt is properly taken into account by considering the effect of different plasma density profile shapes. Both on- and off-axis ITER H neutral beam injection are considered in the study. We show that increasing the density peaking, ITER NBI shine-through losses decrease, with magnitude depending on the beam vertical tilt. Two ionization codes, NEMO and BBNBI, are compared exploiting the standardized data input of the IMAS suite.

Thermodynamic analysis and heat transfer optimization of the CRAFT NNBI calorimeter

ABSTRACT In the process of neutral beam injection (NBI), the high-energy neutral beams, which are up to 31 MW/m2 and last for 3600 s in some cases, impinge on the calorimeter, which is a high-heat-flux component. Therefore, it is necessary to study the heat transfer performance of the calorimeter to ensure the testing and commissioning of NBI systems. First, the uniformity of the water mass flow distribution in each branch pipe of the calorimeter under five different flow configurations was studied. The results show that when two adjacent branches form a group of circuits, the uniformity of the mass flow distribution and the heat transfer capacity are better. Second, the influence of bending the middle of the pipe into several different buffer support structures on the deformation of the branch pipe was studied. Third, the heat transfer performance was compared between the optimized structure and the original circular pipe. Under the same water mass flow conditions, the maximum deformation of the optimized structure is reduced to 2.79 mm, and the maximum temperature is reduced by 30.31%, indicating effective improvement in the heat transfer performance and a reduction in deformation. Therefore, the optimized calorimeter can adapt to the future operational environment under a higher heat flux and long pulse. Finally, several groups of branch pipes were assessed to verify the feasibility of the design. This research can also provide theoretical and engineering support for the future design of calorimeters and other components under long-pulse and high-heat-flux operation.

First measurements of p11B fusion in a magnetically confined plasma

Proton-boron (p11B) fusion is an attractive potential energy source but technically challenging to implement. Developing techniques to realize its potential requires first developing the experimental capability to produce p11B fusion in the magnetically-confined, thermonuclear plasma environment. Here we report clear experimental measurements supported by simulation of p11B fusion with high-energy neutral beams and boron powder injection in a high-temperature fusion plasma (the Large Helical Device) that have resulted in diagnostically significant levels of alpha particle emission. The injection of boron powder into the plasma edge results in boron accumulation in the core. Three 2 MW, 160 kV hydrogen neutral beam injectors create a large population of well-confined, high -energy protons to react with the boron plasma. The fusion products, MeV alpha particles, are measured with a custom designed particle detector which gives a fusion rate in very good relative agreement with calculations of the global rate. This is the first such realization of p11B fusion in a magnetically confined plasma.

Interaction of high-energy neutral beams with Divertor Tokamak Test plasma

Interaction of high-energy neutral beams with Divertor Tokamak Test plasma

Upgrade of the neutral beam heating system on the TCV tokamak – second high energy neutral beam

The TCV tokamak continues to leverage its unique shaping capabilities, flexible heating systems and modern control system to provide a stepladder approach for extrapolations of experimental results from different machines to ITER and DEMO. TCV's configurational flexibility has recently been enhanced by the installation of two heating neutral beams, new dual frequency gyrotrons, removable divertor gas baffles together with upgrades of its diagnostic infrastructure.Plasma regimes with high plasma pressure, a wider range of temperature ratios and significant fast-ion population are now attainable on TCV. A 1.3 MW/28 keV heating beam (NBI-1) has been operated on TCV from 2015 introducing the direct ion auxiliary heating. A second 1MW/50–60 keV high-energy neutral beam (NBI-2) has since been procured, manufactured and installed on TCV in July 2021. NBI-2 injected near anti-co-linearly to NBI-1 is designed to probe plasma physics issues of higher plasma density, fast ion plasma interactions with static and dynamic fields and plasma rotation. The higher NBI-2 energy greatly enhances the operational space for fast ion studies. NBI-2 commissioning is presently ongoing in parallel with TCV experiments using both NBIs.This paper summarises the experience with intensive use and improvements of the NBI-1, together with the status of NBI-2 commissioning.

Observation of significant Doppler shift in deuterium-deuterium neutron energy caused by neutral beam injection in the large helical device

The compact neutron emission spectrometer (CNES) having a tangential sightline was installed to observe a significant Doppler shift of the neutron energy due to the high-energy tangential neutral beam (NB) injections in the Large Helical Device (LHD) for understanding of the energy distribution of fast-ion. The CNES is based on a 1-inch diameter and 1-inch height EJ301 liquid scintillator coupled with a conventional 1-inch photomultiplier tube. The histogram of the integrated pulse signal (Qtotal) during different NBs heating phases measured by the CNES shows that the edge of Qtotal changes depending on NB directions. Using the simple derivative unfolding technique, the neutron energy spectra were unfolded from the measured Qtotal histogram. Peaks of the neutron energy shift to 2.0 MeV, 2.42 MeV, and 3.0 MeV according to the injection direction of NBs. The obtained neutron energy is almost consistent with the virgin deuterium-deuterium neutron energy evaluated by the simple two-body kinematics considering the sightline of CNES, NB injection angle, and NB injection energy.

RAMI evaluation of the beam source for the DEMO neutral beam injectors

Abstract DEMO is a first-of-a-kind DEMOnstration fusion power plant [1] , [2] and is intended to follow the ITER experimental reactor. The main goal of DEMO will be to demonstrate the possibility to produce electric energy for the grid from the fusion reaction early in the second half of the century. The injection of high energy neutral (1 MeV) particle beams is one of the main tools to heat the plasma up to fusion conditions, control the plasma burn phase and ramp the plasma down. Within the EUROfusion Framework a conceptual design of the Neutral Beam Injector (NBI) for the DEMO fusion reactor is currently being developed. Thereby, Reliability, Availability, Maintainability and Inspectability (RAMI) have to be taken into consideration for the conceptual design of the DEMO NBI, together with the exploitation of the currently available return of experience from the ITER NBIs. Comparing the failure risk of two different source concepts due to the considered failure modes has allowed for further design developments aiming at exploiting the advantages of the modular approach while minimizing its drawbacks.

KLEVER: An experiment to measure BR() at the CERN SPS

Precise measurements of the branching ratios for the flavor-changing neutral current decays can provide unique constraints on CKM unitarity and, potentially, evidence for new physics. It is important to measure both decay modes, and , since different new physics models affect the rates for each channel differently. The NA62 experiment at the CERN SPS will measure the BR for the charged channel to better than 20%. The BR for the neutral channel has never been measured. We are designing the KLEVER experiment to measure BR() to ∼20% using a high-energy neutral beam at the CERN SPS. The boost from the high-energy beam facilitates the rejection of background channels such as K L → π 0 π 0 by detection of the additional photons in the final state. On the other hand, the layout poses particular challenges for the design of the small-angle vetoes, which must reject photons from K L decays escaping through the beam exit amid an intense background from soft photons and neutrons in the beam. We present findings from our design studies, with an emphasis on the challenges faced and the potential sensitivity for the measurement of BR().

Design and mockup tests of the RING photo-neutralizer optical cavity for DEMO NBI

High energy Neutral Beam Injection (NBI) is one of the methods being considered to heat EU DEMO plasma. A major issue of present NBI systems is the limited efficiency of the gas neutralizer (for ITER NBI ˜55%), which impacts on the overall system efficiency. An attractive method, but still undemonstrated at full performance, is the photo-neutralization of the negative D-ion beam, with an expected neutralization efficiency for a full-scale DEMO NBI up to 90%.A possible scheme for photo-neutralization is named RING (Recirculation Injection by Nonlinear Gating) where a laser second harmonic is generated and trapped within a non-resonant optical cavity. A mockup of the optical cavity is being operated in Consorzio RFX with a low repetition rate Nd:YAG laser (f = 10 Hz, λ = 1064 nm) to study the feasibility of the RING concept and its potentiality for a full-scale NBI photo-neutralizer. The 2nd harmonic generation efficiency has been measured using a set of 3 Lithium Triborate (LBO) crystals in a disk configuration, confirming the non-linearity of the process with the total crystal thickness. Losses during the 2nd harmonic recirculation in the cavity have been quantified, and the number of 2nd harmonic roundtrips has been estimated with photodiode measurements in order to evaluate the optical cavity performance. Further improvements are considered to increase the optical cavity photon accumulation.

Simulation of Spectra Code (SOS) for ITER Active Beam Spectroscopy

The concept and structure of the Simulation of Spectra (SOS) code is described starting with an introduction to the physics background of the project and the development of a simulation tool enabling the modeling of charge-exchange recombination spectroscopy (CXRS) and associated passive background spectra observed in hot fusion plasmas. The generic structure of the code implies its general applicability to any fusion device, the development is indeed based on over two decades of spectroscopic observations and validation of derived plasma data. Four main types of active spectra are addressed in SOS. The first type represents thermal low-Z impurity ions and the associated spectral background. The second type of spectra represent slowing-down high energy ions created from either thermo-nuclear fusion reactions or ions from injected high energy neutral beams. Two other modules are dedicated to CXRS spectra representing bulk plasma ions (H+, D+, or T+) and beam emission spectroscopy (BES) or Motional Stark Effect (MSE) spectrum appearing in the same spectral range. The main part of the paper describes the physics background for the underlying emission processes: active and passive CXRS emission, continuum radiation, edge line emission, halo and plume effect, or finally the charge exchange (CX) cross-section effects on line shapes. The description is summarized by modeling the fast ions emissions, e.g., either of the α particles of the fusion reaction or of the beam ions itself.

Estimate of 3D power wall loads due to Neutral Beam Injection in EU DEMO ramp-up phase

Heating and current drive systems such as high energy Neutral Beam Injection (NBI) are being considered for pulsed EU DEMO (“DEMO1”) pre-conceptual design. Their aim is to provide auxiliary power, not only during flat-top, but also during transient phases (i.e. plasma current ramp-up and ramp-down).In this work, NBI fast particle power loads on DEMO1 first wall, due to shine-through and orbit losses, are calculated for the diverted plasma ramp-up phase. Numerical simulations are performed using BBNBI and ASCOT Monte Carlo codes. The simulations have been done using a complete 3D wall geometry, and implementing the latest DEMO NBI design, which foresees NBI at 800 keV particle energy. Location and power density of NBI-related power loads at different ramp-up time steps are evaluated and compared with the maximum tolerable heat flux taken from ITER case. Since NBI shine-through losses (dominant during low density phases) depend mainly on the beam energy, plasma density and volume, DEMO has a more favourable situation than ITER, enlarging NBI operational window. Using ITER criteria, DEMO NBI at full energy and power could be switched on during ramp-up at <ne> ~ 1.3 × 1019 m-3. This increases the appeal of neutral beam injectors as auxiliary power systems for DEMO.

Simulation of the beamline thermal measurements to derive particle beam parameters in the ITER neutral beam test facility.

Injection of high energy neutral beam particles will be used in the ITER experiment for plasma heating and current drive. In a ITER heating beam injector, a 40 MW electrostatically accelerated negative beam will be neutralised and filtered along the beamline, obtaining a nominal 16.5 MW neutral beam power to be injected in the tokamak plasma or intercepted during conditioning and commissioning. The beam will heat the actively cooled panels of the beamline components with up to 13 MW/m2 surface power density and 18 MW power. These extreme conditions require testing in a ITER full scale neutral beam test facility under construction in Padova where the temperature of the beamline components will be monitored by 610 embedded thermocouples for protection against critical conditions, for recognising beam conditioning, and for deriving beam parameters. Power density maps of the expected beam-component interactions are applied on a parametric non-linear finite element model to simulate fields of expected temperatures. Such thermal maps are analyzed to derive the beam parameters during operation: divergence of 3-7 mrad and misalignment of 0-3 mrad. The sensibility of the temperature measurements is discussed considering a minimum 10% fraction of the nominal beam power.

Optics and Thermomechanical Analysis of the Accelerator for the DEMO Neutral Beam Injector

The injection of high energy neutral beams is one of the main tools to heat the DEMO plasma up to fusion conditions. A conceptual design of the neutral beam injector (NBI) for the DEMO fusion reactor is currently being developed by Consorzio RFX in collaboration with other European research institutes. High injector efficiency and RAMI, which are fundamental requirements for the success of DEMO, have been taken into special consideration for the DEMO NBI. A novel design of the beam source for the DEMO NBI is being developed featuring multiple subsources, following a modular design concept, capable of increasing the reliability and availability of the DEMO NBI. A full comprehensive model of the extraction/acceleration system has been developed, able to estimate all the main physics and engineering aspects (beam optics, coextracted and stripped electrons, heating power deposited on the grids, working temperature of the grids, and related stress and deformations) in a self-consistent way. This paper describes the results obtained applying the full comprehensive model to the present design of the extraction/acceleration system.

Compact acceleration of energetic neutral atoms using high intensity laser-solid interaction

Recent advances in high-intensity laser-produced plasmas have demonstrated their potential as compact charge particle accelerators. Unlike conventional accelerators, transient quasi-static charge separation acceleration fields in laser produced plasmas are highly localized and orders of magnitude larger. Manipulating these ion accelerators, to convert the fast ions to neutral atoms with little change in momentum, transform these to a bright source of MeV atoms. The emittance of the neutral atom beam would be similar to that expected for an ion beam. Since intense laser-produced plasmas have been demonstrated to produce high-brightness-low-emittance beams, it is possible to envisage generation of high-flux, low-emittance, high energy neutral atom beams in length scales of less than a millimeter. Here, we show a scheme where more than 80% of the fast ions are reduced to energetic neutral atoms and demonstrate the feasibility of a high energy neutral atom accelerator that could significantly impact applications in neutral atom lithography and diagnostics.

Prospects for an experiment to measure at the CERN SPS

Precise measurements of the branching ratios for the decays can provide unique constraints on CKM unitarity and, potentially, evidence for new physics. It is important to measure both decay modes, and , since different new physics models affect the rates for each channel differently. We are investigating the feasibility of performing a measurement of using a high-energy secondary neutral beam at the CERN SPS in a successor experiment to NA62. The planned experiment would reuse some of the NA62 infrastructure, including possibly the NA48 liquid-krypton calorimeter. The mean momentum of mesons decaying in the fiducial volume is 70 GeV; the decay products are boosted forward, so that less demanding performance is required from the large-angle photon veto detectors. On the other hand, the layout poses particular challenges for the design of the small-angle vetoes, which must reject photons from decays escaping through the beam pipe amidst an intense background from soft photons and neutrons in the beam. We present some preliminary conclusions from our feasibility studies, summarizing the design challenges faced and the sensitivity obtainable for the measurement of .

Conceptual design of the beam source for the DEMO Neutral Beam Injectors

DEMO (DEMOnstration Fusion Power Plant) is a proposed nuclear fusion power plant that is intended to follow the ITER experimental reactor. The main goal of DEMO will be to demonstrate the possibility to produce electric energy from the fusion reaction. The injection of high energy neutral beams is one of the main tools to heat the plasma up to fusion conditions. A conceptual design of the Neutral Beam Injector (NBI) for the DEMO fusion reactor, is currently being developed by Consorzio RFX in collaboration with other European research institutes. High efficiency and low recirculating power, which are fundamental requirements for the success of DEMO, have been taken into special consideration for the DEMO NBI. Moreover, particular attention has been paid to the issues related to reliability, availability, maintainability and inspectability. A conceptual design of the beam source for the DEMO NBI is here presented featuring 20 sub-sources (two adjacent columns of 10 sub-sources each), following a modular design concept, with each sub-source featuring its radio frequency driver, capable of increasing the reliability and availability of the DEMO NBI. Copper grids with increasing size of the apertures have been adopted in the accelerator, with three main layouts of the apertures (circular apertures, slotted apertures and frame-like apertures for each sub-source). This design, permitting to significantly decrease the stripping losses in the accelerator without spoiling the beam optics, has been investigated with a self-consistent model able to study at the same time the magnetic field, the electrostatic field and the trajectory of the negative ions. Moreover, the status on the R&D carried out in Europe on the ion sources is presented.

Energy composition of high-energy neutral beams on the COMPASS tokamak

Abstract The COMPASS tokamak is equipped with two identical neutral beam injectors (NBI) for additional plasma heating. They provide a beam of deuterium atoms with a power of up to ~(2 × 300) kW. We show that the neutral beam is not monoenergetic but contains several energy components. An accurate knowledge of the neutral beam power in each individual energy component is essential for a detailed description of the beam- -plasma interaction and better understanding of the NBI heating processes in the COMPASS tokamak. This paper describes the determination of individual energy components in the neutral beam from intensities of the Doppler-shifted Dα lines, which are measured by a high-resolution spectrometer viewing the neutral beam-line at the exit of NBI. Furthermore, the divergence of beamlets escaping single aperture of the last accelerating grid is deduced from the width of the Doppler-shifted lines. Recently, one of the NBI systems was modified by the removal of the Faraday copper shield from the ion source. The comparison of the beam composition and the beamlet divergence before and after this modification is also presented.

Characteristics of flows of energetic atoms reflected from metal targets during ion bombardment

Particle number and energy reflection coefficients for energetic neutralized gas ions (Ar and O atoms) backscattered from metal targets during ion bombardment have been calculated using TRIM code. The energy distributions of reflected atoms are computed, too, and their dependence on the primary ion energy and the angle of ion incidence is determined. The obtained data confirm the possibility of employing energetic atoms reflection for generation of high energy neutral beams and point out to take this phenomenon into account under analysis of the ion technology for coating deposition.

A new deflection technique applied to an existing scheme of electrostatic accelerator for high energy neutral beam injection in fusion reactor devices.

A scheme of a neutral beam injector (NBI), based on electrostatic acceleration and magneto-static deflection of negative ions, is proposed and analyzed in terms of feasibility and performance. The scheme is based on the deflection of a high energy (2 MeV) and high current (some tens of amperes) negative ion beam by a large magnetic deflector placed between the Beam Source (BS) and the neutralizer. This scheme has the potential of solving two key issues, which at present limit the applicability of a NBI to a fusion reactor: the maximum achievable acceleration voltage and the direct exposure of the BS to the flux of neutrons and radiation coming from the fusion reactor. In order to solve these two issues, a magnetic deflector is proposed to screen the BS from direct exposure to radiation and neutrons so that the voltage insulation between the electrostatic accelerator and the grounded vessel can be enhanced by using compressed SF6 instead of vacuum so that the negative ions can be accelerated at energies higher than 1 MeV. By solving the beam transport with different magnetic deflector properties, an optimum scheme has been found which is shown to be effective to guarantee both the steering effect and the beam aiming.

Negative hydrogen ion production in a helicon plasma source

In order to develop very high energy (&amp;gt;1 MeV) neutral beam injection systems for applications, such as plasma heating in fusion devices, it is necessary first to develop high throughput negative ion sources. For the ITER reference source, this will be realised using caesiated inductively coupled plasma devices, containing either hydrogen or deuterium discharges, operated with high rf input powers (up to 90 kW per driver). It has been suggested that due to their high power coupling efficiency, helicon devices may be able to reduce power requirements and potentially obviate the need for caesiation due to the high plasma densities achievable. Here, we present measurements of negative ion densities in a hydrogen discharge produced by a helicon device, with externally applied DC magnetic fields ranging from 0 to 8.5 mT at 5 and 10 mTorr fill pressures. These measurements were taken in the magnetised plasma interaction experiment at the Australian National University and were performed using the probe-based laser photodetachment technique, modified for the use in the afterglow of the plasma discharge. A peak in the electron density is observed at ∼3 mT and is correlated with changes in the rf power transfer efficiency. With increasing magnetic field, an increase in the negative ion fraction from 0.04 to 0.10 and negative ion densities from 8 × 1014 m−3 to 7 × 1015 m−3 is observed. It is also shown that the negative ion densities can be increased by a factor of 8 with the application of an external DC magnetic field.