Beam Injection Energy Research Articles

Divertor Tokamak Test: Impact of NBI shine-through and beam-plasma interaction on Divertor Tokamak Test facility

IntroductionIn this work, we aim to explore numerically the behavior of beam energetic particles in the Divertor Tokamak Test (DTT), a superconductive device equipped with a Neutral Beam Injection (NBI) system capable of injecting neutrals up to 510 keV.MethodWe explore beam ionization and beam slowing down for different DTT plasma scenarios. Numerical simulations are performed using the ASCOT suite of codes, including a wide-range scan of plasma density and beam injection energy. For different plasma conditions, we estimate shine-through losses, including the heat fluxes on the first wall thanks to dedicated particle tracing simulations. Orbits of newly-born fast ions are characterized by means of the constant of motion phase space, showing how trapped energetic particles’ population and prompt losses change with plasma density and NBI energy.Results and discussionSlowing down simulations show that NBI injection at 510 keV is well coupled to DTT plasmas. DTT NBI will be one of the sources of auxiliary ion heating, with an absorbed power ratio of up to ∼50% depending on plasma and beam parameters. At low plasma densities, energetic particle confinement is less efficient, and NBI power and/or energy reduction is expected.

COSMONAUT: A COmpact spectrometer for measurements of neutrons at the ASDEX upgrade tokamak.

A COmpact Spectrometer for Measurements Of Neutrons at the ASDEX Upgrade Tokamak (COSMONAUT) has been developed for spectroscopy measurements of the 2.45MeV neutron emission from deuterium plasmas at the ASDEX Upgrade. The instrument is based on a CLYC-7 inorganic scintillator, whereby the detection of fusion neutrons occurs via their interaction with 35Cl nuclei in the detector crystal, leading to a peak in the detector response function and providing excellent neutron/gamma-ray discrimination capabilities. The diagnostics is installed along a radial line of sight and makes use of a digital system to record time resolved data for the whole duration of the discharge. Measurements in ASDEX Upgrade plasmas with neutral beam injection have been carried out and are successfully interpreted using state-of-the-art modeling codes. Next step applications of the diagnostics are in experiments aimed at generating energetic particles by ion cyclotron resonance heating schemes. In these scenarios, COSMONAUT will provide unique information on the acceleration of deuterons beyond the beam injection energy and on their confinement, for comparison with modeling.

Accelerated particle beams in a 3D simulation of the quiet Sun

Context. Charged particles are constantly accelerated to non-thermal energies by the reconnecting magnetic field in the solar atmosphere. Our understanding of the interactions between the accelerated particles and their environment can benefit considerably from three-dimensional atmospheric simulations that account for non-thermal particle beam generation and propagation. In a previous publication, we presented the first results from such a simulation, which considers quiet Sun conditions. However, the original treatment of beam propagation ignores potentially important phenomena such as the magnetic gradient forces associated with a converging or diverging magnetic field. Aims. Here we present a more general beam propagation model incorporating magnetic gradient forces, the return current, acceleration by the ambient electric field, corrected collision rates due to the ambient temperature, and collisions with heavier elements than hydrogen and the free electrons they contribute. Neglecting collisional velocity randomisation makes the model sufficiently lightweight to simulate millions of beams. We investigate how each new physical effect in the model changes the non-thermal energy transport in a realistic three-dimensional atmosphere. Methods. We applied the method of characteristics to the steady-state continuity equation for electron flux to derive ordinary differential equations for the mean evolution of energy, pitch angle, and flux with distance. For each beam, we solved these numerically for a range of initial energies to obtain the evolving flux spectrum, from which we computed the energy deposited into the ambient plasma. Results. Magnetic gradient forces significantly influence the spatial distribution of deposited beam energy. The magnetic field converges strongly with depth in the corona above loop footpoints. This convergence leads to a small coronal peak in deposited energy followed by a heavy dip caused by the onset of magnetic mirroring. Magnetically reflected electrons carry away 5 to 10% of the injected beam energy on average. The remaining electrons are relatively energetic and produce a peak in deposited energy below the transition region a few hundred kilometres deeper than they would in a uniform magnetic field. A diverging magnetic field at the beginning of the trajectory, which is common in the simulation, enhances the subsequent impact of magnetic mirroring. The other new physical effects do not qualitatively alter the picture of non-thermal energy transport for the atmospheric conditions under consideration.

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.

Design of a 250 MeV linac injector system for the Southern Advanced Photon Source

The Southern Advanced Photon Source (SAPS) is a 4th generation storage ring based light source under design started several years ago, which is planned to be constructed at Guangdong province at China. The equilibrium emittance of the storage ring(SR) will be below 100 pm.rad and the beam energy is determined to be 3.5 GeV. Over the past two years, the nominal current of the SR was increased from 200 to 500 mA, requiring the injector system to provide more bunch charge. Additionally, the injection beam energy for the booster has been increased from 150 to 250 MeV, which means two more accelerating cavities have to been added. This paper presents an update of the linac injector. And also a beam transfer line from linac to booster is presented.

Assessments of the performance of neutral beam injection on the spherical tokamak EXL-50

The numerical simulation of the neutral beam injection (NBI) heating in the spherical tokamak EXL-50 has been performed in order to offer a guideline for the practicable engineering design. A series of parameter scans on injected beam energy, plasma density, electron temperature, plasma current and injection direction have been performed with the NBI heating analysis code NUBEAM. The simulation results show that the injected beam energy should be matched with the plasma density to avoid the excessive shine-through loss. For the scenario with central plasma density of 3.0 × 1019 m−3, the 20 keV beam injection has a power absorption rate about 77%, while for the 50 keV beam injection, only 57% injected power has been absorbed by plasma. When the central plasma density increases to 5.0 × 1019 m−3, a power absorption rate more than 70% can be obtained even for the 50 keV beam injection. As the increase in the electron temperature, the injected power is more likely to heat ions while the total absorbed power by plasma roughly remains stable. The increased plasma current leads to the stronger poloidal magnetic field. A qualitative elucidation on the fast ion trajectory has been given to reveal that the orbit loss has been remarkably suppressed by the enhanced poloidal magnetic field. In addition, a comparison of power absorption rate in the co-current and counter-current injection cases has been carried out, which suggests that counter-current injection leads to more orbit loss and hence less power absorption rate.

Electron cyclotron resonance charge breeder plasma parameters from the modeling of 1+ beam stopping

As a part of SPIRAL1 upgrade, several experiments were carried out to understand the transport of $1+$ (monocharged) ion beam through the SP1 ECR charge breeder ion source and to investigate the physical processes involved in charge breeding. Ion beam transport simulations were performed to reproduce the trends of the experimental results (charge breeding efficiency versus $1+$ beam injection energy $\mathrm{\ensuremath{\Delta}}\mathrm{V}$) by transporting the $1+$ beam through a potential map that reflects the presence of the ECR (electron cyclotron resonance) plasma. The role of Coulomb collisions in the capture of $1+$ beam leads to a necessary detailed analysis for an accurate description of the charge breeding process. This was done by using a full six-dimensional (6D) phase space Monte Carlo charge breeding (MCBC) code. MCBC models Coulomb collisions of the injected $1+$ beam in an ECR plasma and atomic processes (ionization and charge exchange). A simplified background ECR plasma model is implemented in the code to reproduce the trends of three different experiments (interaction of ${\mathrm{Na}}^{1+}$ with He plasma, ${\mathrm{K}}^{1+}$ with He plasma and ${\mathrm{K}}^{1+}$ with ${\mathrm{O}}_{2}$ plasma). The model is able to reproduce the low charge state ($1+$ and $2+$) experimental trends by tuning each plasma parameter (plasma density, plasma ion temperature and electron temperature) independently. The estimated plasma parameters obtained from each case are presented and their contribution in charge breeding process are discussed.

Validation of the imaging neutral particle analyzer in nearly MHD quiescent plasmas using injected beam ions on DIII-D

The imaging neutral particle analyzer (INPA) is a scintillator-based diagnostic that provides energy and radially resolved measurements of confined fast ions. To verify operation, understanding and modeling of the diagnostic performance, distributions of deuterium beam ions in low density, nearly MHD-quiescent plasmas are measured on the DIII-D tokamak using the INPA. The distribution is altered by changing the pitch-angle scattering rate with electron cyclotron heating (ECH). Experimental images are mostly reproduced with simulation of core fast ions charge exchanging with injected beam and edge cold neutrals in classical cases. Image comparisons between the experiment and simulation show agreement with less than 25% discrepancies near the beam injection energy of 50 keV. Other strong passive signals, observed in a localized region on the image, are suggested to come from charge exchange between cold neutrals and fast ions around the plasma boundary.

Ultimate energy recovery from spent relativistic electron beam in energy recovery linear accelerators

Energy recovery linear accelerators (ERLs) rely upon single-axis superconducting radio frequency (SRF) cavities to be an efficient source of relativistic electrons for high energy and nuclear physics. SRF cavities are also considered relevant for next-generation photon factories and radio-isotope production facilities. The ultimate energy recovery capability for the accelerator would be the ability to operate with a sufficiently spent beam and decrease the energy of the beam before the beam dump to a value lower than the beam injection energy. This is especially important for high current accelerators, where the beam injection energy could be as high as several MeV, and systems where partial beam loss can be expected. The efficient operation of energy recovery in linear accelerators is adversely affected by the typical degradation of the beam quality and current loss. This hinders the application of the ERLs in research and industry, and enabling the use of spent (partially lost current), degraded beams should broaden their application. We suggest that the use of the asymmetric operating mode observed in the dual-axis asymmetric cavities will enable such ultimate capabilities. We discuss the advantages of the application of fields of different amplitude along the cavity accelerating and decelerating axes and demonstrate that the fields can be tuned separately in each axis of the dual-axis cavity. The design of such a cavity and ways to optimize the energy recovery of a spent electron beam by tuning the dual-axis asymmetric SRF cavity are discussed.

Efficient THz radiation source from spoof surface plasmons modes on a dielectric-filled metallic grating by electron beam

Abstract Spoof surface plasmons(SSP) is attractive to develop efficient THz radiation source owing to its strong localized electric field. In this work, a THz radiation source based on SSP modes on a layered metal-dielectric plasmonic metamaterial is proposed and investigated. The dispersion characteristics of SSP modes on the structure are solved analytically and numerically. Besides, the propagation of SSP mode which is tuned by the filled dielectric is also demonstrated. Following the studies, THz radiation source which is induced by injected electron beam in the system is studied by a FDTD simulation method. The outputs of THz source based on the interaction between SSP mode and electron beam with various kinds of filled dielectric are given and compared with the same injected beam energy. It is shown that maximum power is decreased in the structure compared with no dielectric situation and the frequency spectrum is lowered. The presented studies about the excitation of SSP modes by electron beam on the structure may provide a good candidate of enhanced and tunable THz radiation source.

Energy-and-pitch-angle-resolved escaping beam ion measurements by Faraday-cup-based fast-ion loss detector in Wendelstein 7-X

With the objective of understanding the energetic-particle loss mechanism in three-dimensional plasmas, a Faraday-cup-based fast-ion loss detector (FILD) was developed and installed in OP1.2b in Wendelstein 7-X (W7-X) as a collaboration between the National Institute for Fusion Science and Max-Planck-Institute for Plasma Physics. The FILD, which consists of double apertures and thin aluminum foils, was based on a magnetic spectrometer using the magnetic field of the fusion device. The double aperture limits the thermal ion, but allows the energetic ion to enter the FILD box. The thin aluminum foils serve as the ion collector. Orbit-following calculations were performed in order to find a suitable position for the FILD. The results indicated that barely co- and counter-going transit ions reached the FILD position mounted on the multi-purpose manipulator installed on W7-X. Moreover, because the injection angle of neutral beams injector installed on W7-X was relatively perpendicular, the target range of pitch angle was set to from 91 degrees to 150 degrees. An energy-and-pitch-angle map was created using a grid calculation code in order to decide on the position/size of aperture and aluminum foil. The grid calculation code indicates the position where the energetic ion would strike on the aluminum foil. Here, the map was used as the basis for designing an aluminum foil pattern with two energies and four pitch angle ranges. Also, note that the lower energy range was designed so that it accommodates a neutral beam injection energy of 55 kV. Measurements of beam ion losses were performed in neutral beam (NB) blip experiments, where concurrent increases and decreases of barely co-going transit beam ion losses due to NB injections were observed. Furthermore, this study validated that the FILD installed on a midplane manipulator probe is capable of probing a range of radii spanning 1.0–1.5 cm, over which the beam ion loss current would vary significantly.

Discrete Alfvén eigenmodes in HL-2A tokamak

Basing on HL-2A tokamak, applying a magnetohydrodynamic (MHD) simulate codes, we study the characteristics of discrete Alfven eigenmodes ( α TAEs, α is a measure of plasma pressure gradient) in the power deposition region of lower hybrid wave auxiliary heating scheme. We explore the distribution of α TAE upon varied different plasma profiles. Employing gyrokinetic-MHD hybrid simulate codes, we investigate α TAE kinetically excited by energetic particles produced by neutral beam injection. Furthermore, we study physical characteristics of α TAE destabilized by energy particles in the lower hybrid wave power deposition region. In addition, we find that there exist α TAEs in HL-2A tokamak with relatively small α values. Besides, the α TAEs are mainly distributed in the reversal magnetic shear region. There are the abundant α TAEs in the lower hybrid wave power deposition region, where the amount of lower hybrid wave power deposition is greater. Moreover, with different plasma profiles, abundant α TAEs are found in the different region in the directions of the small radius of the HL-2A tokamak. With the increase of the neutral beam injection energy, the multiple branches of α TAEs are developed kinetically into unstable modes, which may potentially affect the plasma confinement of tokamak.

Design features and commissioning of pulse arc plasma source and power supply system for the VEST neutral beam injection system

A short-pulse, high-power filament arc ion source is developed for the neutral beam injection (NBI) system of the Versatile Experiment Spherical Torus (VEST) device. The 0.6-MW NBI system is designed to deliver positive hydrogen ion beams at 20 keV for a pulse length >10 ms. In addition, the power supply system for the VEST NBI system is designed to change the beam injection energy during the pulse under VEST's initial target plasma parameters to increase beam–plasma coupling efficiency. To satisfy these requirements, a large-area, high-power arc plasma source with a pulse power system based on a Marx generator utilizing high-energy capacitors and a solid-state switching system is developed and successfully commissioned. In this paper, design features of the plasma source and the power supply system for the VEST NBI system is described and the arc plasma discharge characteristics are presented.

CEPC booster design study

In September 2012, Chinese scientists proposed a Circular Electron Positron Collider (CEPC) in China at 240 GeV center-of-mass energy for Higgs studies. The booster provides 120 GeV electron and positron beams to the CEPC collider for top-up injection at 0.1 Hz. The design of the full energy booster ring of the CEPC is a challenge. The ejected beam energy is 120 GeV and the injected beam energy is 6 GeV. In this paper we describe two alternative schemes, the wiggler bend scheme and the normal bend scheme. For the wiggler bend scheme, we propose to operate the booster ring as a large wiggler at low energy and as a normal ring at high energy to avoid the problem of very low dipole magnet fields. For the normal bend scheme, we implement the orbit correction to correct the earth field.

Development of pulse power supply system based on Marx generator for the arc ion source of the VEST NBI

A short-pulse and high power supply system is developed for the pulse arc ion source of the neutral beam injector (NBI) of the Versatile Experiment Spherical Torus (VEST). The NBI system, with the maximum ion beam power of 20keV, 0.8MW and pulse length of 10ms, was designed for the auxiliary plasma heating and current drive source. However, the beam injection energy needs to be lower than 20keV under the initial target plasma parameters of VEST due to the beam-plasma coupling efficiency. For this reason, modulation of the beam energy in pulse duration is important to increase efficiency of the VEST NBI system. To satisfy these requirements, a pulse power system based on Marx generator is developed by utilizing high-energy capacitors and a solid-state switching system for the ion beam extraction and arc power supply. In addition, a battery-based power supply system is developed for the filament heating power supply which is highly cost-effective. In this paper, circuit structure and features of the power supply system of the ion source for the VEST NBI is described and the results of the discharges test are presented.

Beam emittance control by changing injection painting area in a pulse-to-pulse mode in the 3-GeV rapid cycling synchrotron of Japan Proton Accelerator Research Complex

The 3-GeV rapid cycling synchrotron (RCS) of Japan Proton Accelerator Research Complex (J-PARC) simultaneously delivers high intensity beam to the Material and Life Science Experimental Facility (MLF) as well as to the main ring (MR) at a repetition rate of 25 Hz. The RCS is designed for a beam power of 1 MW. RCS has to meet not only the need of power upgrade but also the specific requirement of each downstream facility. One of the issues, especially for high intensity operation, is to maintain two different transverse sizes of the extracted beam for MLF and MR; namely, a wider beam for MLF in order to reduce damage on the neutron production target but reversely a narrower one for the MR in order to ensure a permissible beam loss in the beam transport line of 3-GeV to MR and also in the MR. We proposed pulse-to-pulse direct control of the transverse painting area during the RCS beam injection process in order to get an extracted beam profile as desired. In addition to two existing dc septum magnets used for fixing injected beam trajectory for MLF beam, two additional dipoles named pulse steering magnets are designed for that purpose in order to control injected beam trajectory for a smaller painting area for the MR. The magnets are already installed in the injection beam transport line and successfully commissioned well in advance before they will be put in normal operation in 2014 for the 400 MeV injected beam energy upgraded from that of the present 181 MeV. Their parameters are found to be consistent to those expected in the corresponding numerical simulations. A trial one cycle user operation run for a painting area of $100\ensuremath{\pi}\text{ }\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$ for the MR switching from the MLF painting area of $150\ensuremath{\pi}\text{ }\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$ has also been successfully carried out. The extracted beam profile for the MR is measured to be sufficiently narrower as compared to that for the MLF, consistent with numerical simulation successfully demonstrating validity of the present principle.

Quantitative monitoring of the stripper foil degradation in the 3-GeV rapid cycling synchrotron of the Japan proton accelerator research complex

A hybrid-type boron doped carbon stripper foil of 200 μg/cm2 is used for the present H− injection beam energy of 181 MeV in the 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC). A stripper foil has a certain lifetime and usually lifetime goes shorter for high power operation. Foil degradation such as foil thinning and pinhole formation caused by the radiation might be a signal of the foil breaking. As a result, one can avoid sudden foil breaking by an efficient monitoring of the foil degradation. We have succeeded measuring even a little change of the stripper foil thickness during user operation of the RCS. It is the main motivation of the present study. A single foil was irradiated with a total of 2.7 × 1021 particles (injected H− itself) during 4 months continuous operation of the RCS but we did not observe any indication of the foil degradation.

Fast-ion deuterium alpha spectroscopic observations of the effects of fishbones in the Mega-Ampere Spherical Tokamak

Using the recently installed fast-ion deuterium alpha (FIDA) spectrometer, the effects of low-frequency (20–50 kHz) chirping energetic particle modes with toroidal mode number n ⩾ 1 on the neutral beam injection-driven fast-ion population in Mega-Ampere Spherical Tokamak (MAST) plasmas are considered. Results from the FIDA diagnostic are presented and discussed in the light of the present theoretical understanding of these modes, known as fishbones, in plasmas with reversed shear. Measurements of the fast-ion population reveal strong redistribution of fast ions in both real and velocity space as a result of the fishbones. Time-resolved measurements throughout the evolution of a fishbone show radial redistribution of fast ions with energies up to 95% of the primary beam injection energy. Correlations between changes in the FIDA signal and the peak time derivative of the magnetic field perturbation are observed in a limited range of operating scenarios. The transient reduction in signal caused by a fishbone may in some cases reach 50% of the signal intensity before mode onset.

Combination of fast-ion diagnostics in velocity-space tomographies

Fast-ion Dα (FIDA) and collective Thomson scattering (CTS) diagnostics provide indirect measurements of fast-ion velocity distribution functions in magnetically confined plasmas. Here we present the first prescription for velocity-space tomographic inversion of CTS and FIDA measurements that can use CTS and FIDA measurements together and that takes uncertainties in such measurements into account. Our prescription is general and could be applied to other diagnostics. We demonstrate tomographic reconstructions of an ASDEX Upgrade beam ion velocity distribution function. First, we compute synthetic measurements from two CTS views and two FIDA views using a TRANSP/NUBEAM simulation, and then we compute joint tomographic inversions in velocity-space from these. The overall shape of the 2D velocity distribution function and the location of the maxima at full and half beam injection energy are well reproduced in velocity-space tomographic inversions, if the noise level in the measurements is below 10%. Our results suggest that 2D fast-ion velocity distribution functions can be directly inferred from fast-ion measurements and their uncertainties, even if the measurements are taken with different diagnostic methods.

Large Hadron Collider (LHC).

Keywords large hadron collider, LHC, supersymmetry, Higgs boson, CERN, string theory, dark matter, dark energy