•The DIII-D neutral beam system continues to evolve to provide new capabilities.•Internal beamline components are being upgraded for higher power, longer pulse.•One beamline being rebuilt to provide ...off-axis co- or counter-injection.•New low voltage capability and more versatile controls being developed.•MACE device built to investigate ion source operational issues in helium.
As physics experiments on the DIII-D tokamak evolve to explore new regimes in fusion energy research, the capabilities of the Neutral Beam Injection (NBI) systems are being improved to help provide the necessary tools. Upgrades of beamline internal components and high voltage systems are currently being carried out to increase the injected power and pulse length. A new algorithm has been commissioned for feedback control that combines the variable beam energy (VBE) and variable beam perveance (VBP) capabilities. An extensive project is underway to modify a beamline for off-axis injection in either the co- or counter-plasma current direction. The MACE device (Miniature Arc Chamber Experiment) has recently been commissioned and is allowing investigation into the detrimental effects of operating ion sources in helium. Finally, exploration of the edge physics in tokamaks has benefited from a new capability to inject very low energy beams (15–20 kV). A description of these new capabilities and some results from experiments will be presented here.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Transmission electron microscopy with in situ ion irradiation has been used to examine the ion-beam-induced amorphisation of crystalline silicon under irradiation with light (He) and heavy (Xe) ions ...at room temperature. Analysis of the electron diffraction data reveal the heterogeneous amorphisation mechanism to be dominant in both cases. The differences in the amorphisation curves are discussed in terms of intra-cascade dynamic recovery, and the role of electronic and nuclear loss mechanisms.
Display omitted
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•A new control scheme for neutral beam operation has been implemented on DIII-D.•The new control allows for beam voltage to be changed in real time during a beam shot.•This variable beam energy (VBE) ...mode is controlled by the DIII-D plasma control system (PCS).•Additional control changes as part of the VBE operation have allowed for beam perveance sweeps in a single shot.•The new control maintains beamline safety and tracks energy efficiency.
In the DIII-D tokamak, one of the most powerful techniques to control the density, temperature and plasma rotation is by eight independently modulated neutral beam sources with a total power of 20MW. The rapid modulation requires a high degree of reproducibility and precise control of the ion source plasma and beam acceleration voltage. Recent changes have been made to the controls to provide a new capability to smoothly vary the beam current and beam voltage during a discharge, while maintaining the modulation capability.
The ion source plasma inside the arc chamber is controlled through feedback from the Langmuir probes measuring plasma density near the extraction end. To provide the new capability, the plasma control system (PCS) has been enabled to change the Langmuir probe set point and the beam voltage set point in real time. When the PCS varies the Langmuir set point, the plasma density is directly controlled in the arc chamber, thus changing the beam current (perveance) and power going into the tokamak. Alternately, the PCS can sweep the beam voltage set point by 20kV or more and adjust the Langmuir probe setting to match, keeping the perveance constant and beam divergence at a minimum. This changes the beam power and average neutral particle energy, which changes deposition in the tokamak plasma. The ion separating magnetic field must accurately match the beam voltage to protect the beam line. To do this, the magnet current control accurately tracks the beam voltage set point. These new capabilities allow continuous in-shot variation of neutral beam ion energy to complement the discontinuous “on or off” modulation method presently used to control average beam power and torque input.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We report the first direct experimental observation of the ablative Richtmyer-Meshkov instability. It manifests itself in oscillations of areal mass that occur during the shock transit time, which ...are caused by the "rocket effect" or dynamic overpressure characteristic of interaction between the laser absorption zone and the ablation front. With the 4-ns-long Nike KrF laser pulse and our novel diagnostic technique (monochromatic x-ray imaging coupled to a streak camera) we were able to register a peak and a valley of the areal-mass variation before the observed onset of the Rayleigh-Taylor growth.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
"Feedout" means the transfer of mass perturbations from the rear to the front surface of a driven target. When a planar shock wave breaks out at a rippled rear surface of the target, a lateral ...pressure gradient drives sonic waves in a rippled rarefaction wave propagating back to the front surface. This process redistributes mass in the volume of the target, forming the feedout-generated seed for ablative Rayleigh-Taylor (RT) instability. We report the first direct experimental observation of areal-mass oscillation associated with feedout, followed by the onset of exponential RT growth.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Internationally, chest radiography is the standard investigation for identifying rib fractures in suspected physical abuse in infants. Several small observation studies in children have found that ...chest CT can provide greater accuracy than radiography for fracture detection, potentially aiding medicolegal proceedings in abuse cases; however, to our knowledge, this greater accuracy has not been comprehensively evaluated. We aimed to determine differences in rib fracture detection rates between post-mortem chest radiographs and chest CT images, using forensic autopsy as the reference standard.
In this retrospective diagnostic accuracy study, we searched the Great Ormond Street Hospital (London, UK) radiology information system for all children aged 0–16 years who had a post-mortem skeletal survey (ie, full-body radiography), CT, and full autopsy between Jan 1, 2012, and Jan 1, 2017, for a purpose of death investigation. Cases were excluded if the imaging was done for a reason other than a forensic investigation or if image quality was suboptimal. Radiologists were recruited as reporters on a voluntary basis via membership databases from international radiology and post-mortem imaging societies with no specific inclusion or exclusion criteria. Reporters were sent a set of chest radiographs on a password protected and encrypted USB flash drive or via a secure filesharing website and independently reported on the presence of rib fractures, fracture location, and the confidence level of their interpretation. They were masked to the clinical information of the images. 1 month later, the same reporters were sent CTs for the same cases in a random order and asked to report on the same features. The primary objective was to compare the accuracy of detection of rib fractures by use of post-mortem chest radiographs and CTs, with autopsy data as reference standard. Accuracy was assessed by comparison of diagnostic statistics, calculated using random-intercept multilevel logistic models with reporter and patient included as cross-classified random-effects.
25 cases of children (aged 1 month to 7 years), with 136 rib fractures at autopsy with paired post-mortem chest radiographs and CTs, were selected for analysis. 38 radiologists were recruited as reporters from 23 international centres; 12 (32%) were consultants, median experience of 14·5 years (range 6–27), and 26 (68%) were registrars, median experience of 4 years (range 2–9). Across all radiologists, three times as many rib fractures were correctly detected by use of chest CTs compared with chest radiography (sensitivity 44·9% 95% CI 31·7–58·9 vs 13·5% 8·1–21·5; difference 31·4% 23·3–37·8; p<0·001). Sensitivity for detection on the correct rib was higher by use of CT than by use of radiography (62·4% 95% CI 44·9–77·1 vs 23·1% 12·9–37·8; difference 39·3% 31·9–42·2; p<0·001), as was diagnosis of a patient with any rib fracture or fractures (81·5% 75·8–86·0 vs 64·7% 57·3–71·4; difference 16·7% 11·5–22·2; p<0·001). Radiologist confidence was higher when using CT images than radiographs (highest confidence rating given on 3317 63·6% of 5218 fractures for CT vs 1518 46·6% of 3303 on radiographs) and was a predictor for accurate fracture detection.
Chest CT provides greater accuracy than conventional chest radiography for post-mortem rib fracture detection, irrespective of radiologist experience or fracture location, although both methods detected a substantial number of false positives. The diagnostic accuracy of CT should be studied further in live children ideally in a multicentre trial to assess the applicability of our results.
Great Ormond Street Children's Charity, Medical Research Council, Royal College of Radiologists, Research Councils UK, National Institute for Health Research.
: Background/Aims: Resolution of liver fibrosis is possible but the identity of the matrix metalloproteinases (MMPs) which degrade the accumulated collagens is uncertain. We examined MMP‐2 and MMP‐14 ...expression in established and resolving fibrosis to assess their role in resolution of liver fibrosis.
Methods: MMP and tissue inhibitor of metalloproteinase (TIMP)‐2 expression in liver extracts was examined by ribonuclease protection assay, Western blotting and gelatin zymography. MMP activity was examined by 14C gelatin degradation.
Results: In human cirrhotic liver, MMP‐14 mRNA was increased to 230–330% of normal liver expression. Both 63 kDa proenzyme and 60 kDa activated form were present. Cirrhotic livers had 270–320% of normal liver expression of MMP‐2 protein with 20–25% being the 62 Da activated form. Protein and mRNA for MMP‐2 and MMP‐14 progressively increased during 8 weeks of CCl4 treatment in rats. Between 3 and 7 days of resolution from CCl4 liver fibrosis, MMP‐2 and MMP‐14 persisted at elevated levels. Gelatinolytic activity in liver homogenates peaked at 7 days of recovery, being 140% above that in livers at peak fibrosis.
Conclusions: Increased expression and activation of MMP‐2 and ‐14 occurs even under conditions of elevated TIMPs during liver fibrogenesis. During liver fibrosis resolution, as TIMP expression decays, the persistence of MMP‐2 and MMP‐14 may permit collagen degradation.
Full text
Available for:
BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
On the DIII-D National Fusion Facility tokamak plasma diagnostics continue to improve and experiments increase in complexity. Hence the utility of dynamic control of the beam energy (and therefore ...also the injected torque, ion heating fraction, etc.) has become apparent. Here we report on upgrades that have been incorporated into the DIII-D Plasma Control System (PCS) and Neutral Beam Injection (NBI) systems in order to allow the beam acceleration voltage (Vaccel) to be varied continuously in a ≤20 kV range during a shot for the first time, generating new capabilities such as smooth plasma transitions and controllable interactions with Alfvén waves.
Full text
Available for:
BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
We used transmission electron microscopy with in situ ion irradiation to examine the ion-beam-induced amorphisation of crystalline silicon under irradiation with light (He) and heavy (Xe) ions at ...room temperature. Analysis of the electron diffraction data reveal the heterogeneous amorphisation mechanism to be dominant in both cases. Moreover, for the differences in the amorphisation curves are discussed in terms of intra-cascade dynamic recovery, and the role of electronic and nuclear loss mechanisms.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
PDF
