Direct detection experiments aimed at uncovering the elusive nature of dark matter (DM) have made significant progress in probing ever lower cross-sections for DM-nucleon interactions. At the same time, an upper limit in the cross-section sensitivity region is present due to DM scattering in the Earth and atmosphere and as a result never reaching the detector. We investigate the impact of this effect for both spin-dependent and spin-independent interactions. In contrast to previous studies that assume a straight line path for DM scattering we employ a semi-analytic diffusion model that takes into account the impact of potentially large angle deviations prevalent for light DM masses. We find that for sufficiently low energy thresholds, this difference in modelling impacts the DM interaction cross-section sensitivity. This study evaluates the impact in the context of the QUEST-DMC experiment, which utilises surface-based detectors with superfluid Helium-3 bolometers to search for sub-GeV DM exploiting low energy threshold. At masses below 1 GeV/c^2 the deviation between the two frameworks becomes pronounced. The ceiling sensitivity limit for QUEST-DMC on spin-dependent DM-neutron cross-sections is ∼ 3 × 10^-24cm^2 using the diffusive framework and approximately doubles with the straight-line path DM scattering. Similarly, for spin-independent DM-nucleon cross-sections, the ceiling limit is ∼ 7.5 × 10^-27cm^2 under the diffusive framework and also increases about a factor of two with the straight-line path approximation, within the mass range of 0.025–5 GeV/c^2.

Abstract The focus of dark matter searches to date has been on Weakly Interacting Massive Particles (WIMPs) in the GeV/ $$c^2$$ c 2 -TeV/ $$c^2$$ c 2 mass range. The direct, indirect and collider searches in this mass range have been extensive but ultimately unsuccessful, providing a strong motivation for widening the search outside this range. Here we describe a new concept for a dark matter experiment, employing superfluid $$^3$$ 3 He as a detector for dark matter that is close to the mass of the proton, of order 1 GeV/ $$c^2$$ c 2 . The QUEST-DMC detector concept is based on quasiparticle detection in a bolometer cell by a nanomechanical resonator. In this paper we develop the energy measurement methodology and detector response model, simulate candidate dark matter signals and expected background interactions, and calculate the sensitivity of such a detector. We project that such a detector can reach sub-eV nuclear recoil energy threshold, opening up new windows on the parameter space of both spin-dependent and spin-independent interactions of light dark matter candidates.

We report the results of radioactivity assays and heat leak calculations for a range of common cryogenic materials, considered for use in the QUEST-DMC superfluid 3He dark matter detector. The bolometer, instrumented with nanomechanical resonators, will be sensitive to energy deposits from dark matter interactions. Events from radioactive decays and cosmic rays constitute a significant background and must be precisely modelled, using a combination of material screening and Monte Carlo simulations. However, the results presented here are of wider interest for experiments and quantum devices sensitive to minute heat leaks and spurious events, thus we present heat leak per unit mass or surface area for every material studied. This can inform material choices for other experiments, especially if underground operation is considered where the radiogenic backgrounds will dominate even at shallow depths.

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

The focus of dark matter searches to date has been on Weakly Interacting Massive Particles (WIMPs) in the GeV/$c^2$-TeV/$c^2$ mass range. The direct, indirect and collider searches in this mass range have been extensive but ultimately unsuccessful, providing a strong motivation for widening the search outside this range. Here we describe a new concept for a dark matter experiment, employing superfluid $^3$He as a detector for dark matter that is close to the mass of the proton, of order 1 GeV/$c^2$. The QUEST-DMC detector concept is based on quasiparticle detection in a bolometer cell by a nanomechanical resonator. In this paper we develop the energy measurement methodology and detector response model, simulate candidate dark matter signals and expected background interactions, and calculate the sensitivity of such a detector. We project that such a detector can reach sub-eV nuclear recoil energy threshold, opening up new windows on the parameter space of both spin-dependent and spin-independent interactions of light dark matter candidates.

WEST is an MA class superconducting, actively cooled, full tungsten (W) tokamak, designed to operate in long pulses up to 1000 s. In support of ITER operation and DEMO conceptual activities, key missions of WEST are: (i) qualification of high heat flux plasma-facing components in integrating both technological and physics aspects in relevant heat and particle exhaust conditions, particularly for the tungsten monoblocks foreseen in ITER divertor; (ii) integrated steady-state operation at high confinement, with a focus on power exhaust issues. During the phase 1 of operation (2017-2020), a set of actively cooled ITER-grade plasma facing unit prototypes was integrated into the inertially cooled W coated startup lower divertor. Up to 8.8 MW of RF power has been coupled to the plasma and divertor heat flux of up to 6 MW m(-2) were reached. Long pulse operation was started, using the upper actively cooled divertor, with a discharge of about 1 min achieved. This paper gives an overview of the results achieved in phase 1. Perspectives for phase 2, operating with the full capability of the device with the complete ITER-grade actively cooled lower divertor, are also described.

Introduction Although the average UK dose from medical ionising radiation is 0.44 mSv (PHE-CRCE-026, 2011), people with CF (pwCF) undergo many such investigations for the management of their disease. With improving survival their life-time exposure, a risk factor for the development of malignancy, may be important. We therefore monitored this radiation exposure in our adult CF center and wished to look for any trends over time. Methods We calculated the estimated effective dose (EED) of ionising radiation using standard reference values (HPA-CRCE-034, 2011; PHE-CRCE-013, 2010), and applied this to all procedures carried out in pwCF at our centre 2017–19, comparing it to that in 2010. Results There were 2,630 investigations in 327 pwCF 2017–19 and 693 in 253 in 2010 (mean [SD] yearly EED 1.49 ± 3.85 mSv, versus 1.66 ± 3.76 mSv respectively [p=0.56]): 217 pwCF in 2017–19 had an average yearly EED <0.44 mSv. A similar number of examinations were carried out in each time period (2.7 versus 2.8 per person), predominantly thoracic (76% versus 84%), of which most was CT imaging (89% versus 80% respectively). In 2017–19, EED was higher in those with chronic Pseudomonas aeruginosa infection (1.56 ± 3.90 mSV versus 1.27 ± 3.68 mSv; p<0.001), non-tuberculous mycobacterium (NTM) (1.52 ± 2.57 mSv versus 1.49 ± 4.05 mSv, p<0.001) and CF-related diabetes (1.56 ± 4.04 mSv versus 1.14±3.65 mSv; p<0.001). Thirteen pwCF (4%) had a yearly average EED of ≥10 mSv (16.33 m ± 13.07Sv in those 7 with malignancy). Conclusions Although radiation exposure remains high amongst pwCF, in keeping with other published reports (Plant et al), there was no upward trend in EED over time, and a similar number of procedures were performed per person. As expected, pwCF with more complications had higher radiation exposure, underlining the need to maintain vigilance for comorbidities in this complex chronic disease.

Remote experiment with WEST tokamak in CEA Cadarache from ITER Remote Experimentation Centre (REC) in Rokkasho had been successfully carried out under the agreement between the Government of Japan and the European Atomic Energy Community for the joint implementation of the Broader Approach (BA) activities in the field of fusion energy research. The WEST and the REC sites were connected with the international broadband network for science and education of SINET, GEANT and RENATER. Due to a long distance over 10,000 km of two sites, the latency was about 200 ms (round trip time) in total via the direct line between EU and Japan of SINET5. Based on the communication between local and remote participants, plasma discharges were successfully executed repeatedly according to the pulse schedule produced by remote Session Leader after the approval by Engineer in Charge on WEST site. Intershot analyses were successfully executed during the pulse interval on an analysis server prepared in Partners network in the WEST for external collaborator. Full function required for the remote experiments were successfully demonstrated in the large size tokamak facility, WEST. For remote participation of ITER, however, it is expected that the amount of experimental data and the number of remote participations will become very large. Distributed database system based on data replication using high-speed data transferring method and distributed computing resources in local and remote sites are proposed as a possible solution in ITER.

In parallel to the direct contribution to the procurement phase of ITER and Broader Approach, CEA has initiated research & development programmes, accompanied by experiments together with a significant modelling effort, aimed at ensuring robust operation, plasma performance, as well as mitigating the risks of the procurement phase. This overview reports the latest progress in both fusion science and technology including many areas, namely the mitigation of superconducting magnet quenches, disruption-generated runaway electrons, edge-localized modes (ELMs), the development of imaging surveillance, and heating and current drive systems for steady-state operation. The WEST (W Environment for Steady-state Tokamaks) project, turning Tore Supra into an actively cooled W-divertor platform open to the ITER partners and industries, is presented.

he National Ignition Facility (NIF) is the world's most energetic laser, having demonstrated in excess of 1.9MJ @351nm with Inertial Confinement Fusion pulse-shapes in July, 2012. First commissioned with 192 operational beamlines in March, 2009, NIF has since transitioned to routine operation for stockpile stewardship, inertial confinement fusion research, and basic high energy density science.The NIF design includes component placement and beam alignment tolerances to preclude laser beam clipping on components within the laser chain, indeed lengthy studies and analyses, including various statistical approaches, were done in the design phase as early as 1996. The margin between the available optical aperture and the beam was established to ensure, given beam centering variations and component placement errors, that we would achieve a confidence level such that even low-level clipping, which causes downstream modulation damage, would occur at an acceptably or even vanishingly low rate.With the completion of NIF and nearly 4 years of operational experience, it became apparent that we could increase the beam size to more optimally fill the available aperture, and gain an additional 5% to 10% or more energy and power delivered to targets. It was also shown that additional energy could be recovered by removing approximately 70% of our beam 'corner blockers' originally installed in May 2010 to prevent target-chamber 1 mu m counterpropagating light from leaking back through the extinction minimums at the corners of vacuum-loaded square optics. Subsequent analyses showed that only one and in some cases two of the corner blockers were really needed. Increasing the beam size was a challenging endeavor, however, as it fundamentally meant recommissioning the entire NIF laser chain to tailor all 192 beams to their specific available aperture, individual beam rotation (for the NIF square beam), beam centering offsets, change-out of the 48 front-end aperture (relay-plane "0"), and removal of 48 Laser Mirror #2 line replaceable units for corner-blocker removal. Some of this commissioning, such as tailoring beam sizes to their specific available aperture, had not been performed during the original commissioning. Furthermore, achieving this required precise diagnostics and rapid analysis of massive quantities of images and data in order to direct the changes and feed-back the achieved results. Completed on June 1, 2012, the beam area was increased by 7.5%, and was a significant contributing factor in NIF transitioning from a 1.6MJ laser to its present 1.9MJ capability

The National Ignition Facility (NIF) is the world's largest optical instrument, comprising 192 37 cm square beams, each generating up to 9.6 kJ of 351 nm laser light in a 20 ns beam precisely tailored in time and spectrum. The Facility houses a massive (10 m diameter) target chamber within which the beams converge onto an ∼1 cm size target for the purpose of creating the conditions needed for deuterium/tritium nuclear fusion in a laboratory setting. A formidable challenge was building NIF to the precise requirements for beam propagation, commissioning the beam lines, and engineering systems to reliably and safely align 192 beams within the confines of a multihour shot cycle. Designing the facility to minimize drift and vibration, placing the optical components in their design locations, commissioning beam alignment, and performing precise system alignment are the key alignment accomplishments over the decade of work described herein. The design and positioning phases placed more than 3000 large (2.5 m×2 m×1 m) line-replaceable optics assemblies to within ±1 mm of design requirement. The commissioning and alignment phases validated clear apertures (no clipping) for all beam lines, and demonstrated automated laser alignment within 10 min and alignment to target chamber center within 44 min. Pointing validation system shots to flat gold-plated x-ray emitting targets showed NIF met its design requirement of ±50 μm rms beam pointing to target chamber. Finally, this paper describes the major alignment challenges faced by the NIF Project from inception to present, and how these challenges were met and solved by the NIF design and commissioning teams.

The National Ignition Facility in Livermore, California, completed it's commissioning milestone on March 10, 2009 when it fired all 192 beams at a combined energy of 1.1 MJ at 351nm. Subsequently, a target shot series from August through December of 2009 culminated in scale ignition target design experiments up to 1.2 MJ in the National Ignition Campaign. Preparations are underway through the first half of of 2010 leading to DT ignition and gain experiments in the fall of 2010 into 2011. The top level requirement for beam pointing to target of 50μm rms is the culmination of 15 years of engineering design of a stable facility, commissioning of precision alignment, and precise shot operations controls. Key design documents which guided this project were published in the mid 1990's, driving systems designs. Precision Survey methods were used throughout construction, commissioning and operations for precision placement. Rigorous commissioning processes were used to ensure and validate placement and alignment throughout commissioning and in present day operations. Accurate and rapid system alignment during operations is accomplished by an impressive controls system to align and validate alignment readiness, assuring machine safety and productive experiments.

The main results of the Tore Supra experimental programme in the years 2007–2008 are reported. They document significant progress achieved in the domain of steady-state tokamak research, as well as in more general issues relevant for ITER and for fusion physics research. Three areas are covered: ITER relevant technology developments and tests in a real machine environment, tokamak operational issues for high power and long pulses, and fusion plasma physics. Results presented in this paper include test and validation of a new, load-resilient concept of ion cycotron resonance heating antenna and of an inspection robot operated under ultra-high vacuum and high temperature conditions; an extensive experimental campaign (5 h of plasma) aiming at deuterium inventory and carbon migration studies; real-time control of sawteeth by electron cyclotron current drive in the presence of fast ion tails; ECRH-assisted plasma start-up studies; dimensionless scalings of transport and turbulence; transport experiments using active perturbation methods; resistive and fast-particle driven MHD studies. The potential role of Tore Supra in the worldwide fusion programme before the start of ITER operation is also discussed.

The potassium dihydrogen phosphate (KDP) crystals present in the final optics assembly at the National Ignition Facility (NIF) are used for conversion of an infrared laser light beam into an ultraviolet beam. The conversion is highest for a certain incident angle, the alignment of which is determined from the position of the backreflection beam, which exhibits a distinct characteristic shape. When a phase-plate device is introduced before the final assembly to increase the uniformity of the beam, the backreflection pattern changes drastically. The algorithm that is best for tracking the special-shaped beam is no longer suitable for tracking the phase-modified beam. We discuss our detection schemes for both situations. In particular, we demonstrate how the algorithm senses the modified beam by using a newly proposed criterion of correlation peak pedestal area and executes an alternate algorithm in real time without operator intervention. This new algorithm continuously tracks the beam pattern to guarantee reliable and repeatable sensing. Results from simulation and real-world implementation of the algorithm at the NIF facility are presented.

An algorithm for determining the position of the KDP back-reflection image was developed. It was compared to a centroid-based algorithm. While the algorithm based on centroiding exhibited a radial standard deviation of 9 pixels, the newly proposed algorithm based on classical matched filtering (CMF) and a Gaussian fit to correlation peak provided a radial standard deviation of less than 1 pixel. The speed of the peak detection was improved from an average of 5.5 seconds for Gaussian fit to 0.022 seconds by using a polynomial fit. The performance was enhanced even further by utilizing a composite amplitude modulated phase only filter; producing a radial standard deviation of 0.27 pixels. The proposed technique was evaluated on 900+ images with varying degrees of noise and image amplitude as well as real National Ignition Facility (NIF) images.

A wavefront control system will be employed on NIF to correct beam aberrations that otherwise would limit the minimum target focal spot size. For most applications, NIF requires a focal spot that is a few times the diffraction limit. Sources of aberrations that must be corrected include prompt pump-induced distortions in the laser slabs, thermal distortions in the laser slabs from previous shots, manufacturing figure errors in the optics, beam off-axis effects, gas density variations, and gravity, mounting, and coating-induced optic distortions.

The National Ignition Facility (NIF) laser will use a 192- beam multi-pass architecture capable of delivering several MJ of UV energy in temporal phase formats varying from sub- ns square to 20 ns precisely-defined high-contrast shapes. Each beam wavefront will be subjected to effects of optics inhomogeneities, figuring errors, mounting distortions, prompt and slow thermal effects from flashlamps, driven and passive air-path turbulence, and gravity-driven deformations. A 39-actuator intra-cavity deformable mirror, controlled by data from a 77-lenslet Hartman sensor will be used to correct these wavefront aberrations and thus to assure that stringent farfield spot requirements are met. We have developed numerical models for the expected distortions, the operation of the adaptive optics systems, and the anticipated effects on beam propagation, component damage, frequency conversion, and target-plane energy distribution. These models have been extensively validated against data from LLNL's Beamlet, and Amplab lasers. We review the expected beam wavefront aberrations and their potential for adverse effects on the laser performance, describe our model of the corrective system operation, and display our predictions for corrected-beam operation of the NIF laser.