JET Trace Research Articles

SS433's Jet Trace from ALMA Imaging and Global Jet Watch Spectroscopy: Evidence for Post-launch Particle Acceleration

Abstract We present a comparison of Doppler-shifted Hα line emission observed by the Global Jet Watch from freshly launched jet ejecta at the nucleus of the Galactic microquasar SS433 with subsequent Atacama Large Millimeter/submillimeter Array (ALMA) imaging at mm-wavelengths of the same jet ejecta. There is a remarkable similarity between the transversely resolved synchrotron emission and the prediction of the jet trace from optical spectroscopy: this is an a priori prediction and not an a posteriori fit, confirming the ballistic nature of the jet propagation. The mm-wavelength of the ALMA polarimetry is sufficiently short that the Faraday rotation is negligible and therefore that the observed -vector directions are accurately orthogonal to the projected local magnetic field. Close to the nucleus, the -field vectors are perpendicular to the direction of propagation. Further out from the nucleus, the -field vectors that are coincident with the jet instead become parallel to the ridge line; this occurs at a distance where the jet bolides are expected to expand into one another. X-ray variability has also been observed at this location; this has a natural explanation if shocks from the expanding and colliding bolides cause particle acceleration. In regions distinctly separate from the jet ridge line, the fractional polarization approaches the theoretical maximum for synchrotron emission.

Neutron spectroscopy measurements of tritium beam transport at JET

A detailed description of the 14 MeV neutron emission in plasmas heated by neutral beam injection has been carried out by coupling Monte Carlo calculations of the neutron emission spectrum with TRANSP modelling of the beam ion energy distributions. The model is used to study tritium beam injection experiments of the JET trace tritium campaign for internal transport barrier (ITB) and H-mode discharges. For ITB discharges, the measured neutron emission spectrum is well described by modelling using as input the beam ion distribution calculated with TRANSP. For H mode discharges the neutron spectrum can be reproduced only if high energy tritons are lost from the plasma, suggesting the possible role of low frequency tearing modes on the beam ions. The presented results are of relevance for tritium beam transport studies in trace tritium experiments and, more generally, for deuterium and tritium transport studies in high power experiments using neutron emission spectroscopy.

Interaction of shock wave with subsonic heated layer

The problem of attenuation of an incident shock wave on the passage through a heated layer of finite thickness has been considered by numerical methods. Three possible regimes of interaction of the incident shock wave with the heated layer are revealed. It is shown that a significant decrease in intensity of the incident shock wave is caused by its interaction with a heated subsonic jet trace.

Film cooling performance of converging slot-hole rows on a gas turbine blade

Experimental tests have been performed to investigate the film cooling performance of converging slot-hole (console) rows on the turbine blade. Film cooling effectiveness of each single hole row is measured under three momentum flux ratios based on the wide-band liquid crystal technique. Measurements of the cooling effectiveness with all the hole rows open are also carried out under two coolant–mainstream flux ratios. Film cooling effectiveness of cylindrical hole rows on the same blade model is measured as a comparison. The results reveal that the trace of jets from both consoles and cylindrical holes is converging on the suction surface and expanding on the pressure surface by the influence of the passage vortex, while the influence of passage vortex on the jets from consoles is weaker. The film coverage area and the film cooling effectiveness of single/multiple console row(s) are much larger than those of single/multiple cylindrical hole row(s). When the console row is discrete and the diffusion angle of the console is not very large, the adjacent jets cannot connect immediately after ejecting out of the holes and the cooling effectiveness in the region between adjacent holes is relatively lower. On the pressure surface, the film cooling effectiveness of console rows increases notably with the increasing of momentum flux ratio or coolant–mainstream flux ratio. But on the suction side, the increase in cooling effectiveness is not very notable for console row film cooling as the coolant flux increases. Moreover, for the film cooling of single console row at the gill region of the suction surface, the jets could lift off from the blade surface because of the convex geometry of the suction surface.

The New York Bight Jet: Climatology and Dynamical Evolution

Abstract This paper describes the southerly New York Bight (NYB) jet (11–17 m s−1) that develops primarily during the warm season just above the surface offshore (east) of the northern New Jersey coast and south of Long Island (the NYB). Observations from two offshore buoys are used to develop a 9-yr climatology of 134 jet events from 1997 to 2006. There is a seasonal maximum (2.5 events per month) during June and July, with a skew toward the spring months. The wind directions for the jet trace out a nearly elliptical orbit for the 24-h period around the time of jet maximum at ~2300 UTC [1900 eastern daylight time (EDT)] on average. Composites reveal that the NYB jet occurs on days with southwesterly synoptic flow, and the jet is part of a larger-scale (200–300 km) wind enhancement offshore of the mid-Atlantic and northeast U.S. coasts during the early evening hours. High-resolution observations (surface mesonet, aircraft soundings, and a terminal Doppler weather radar) and Weather Research and Forecasting (WRF) model simulations down to 1.33-km grid spacing are used to diagnose the evolution of the NYB jet on 2 June 2007. The NYB jet at ~150 m MSL occurs within the sloping marine inversion near the coast. Low-level trajectories illustrate low-level diffluence and weak subsidence within the jet. A WRF momentum budget highlights the evolving pressure gradient and accelerations during jet formation. The maximum jet winds occur 1–2 h after the peak meridional pressure gradient is established through a geostrophic adjustment process. Sensitivity experiments show that jet occurrence is dependent on diurnal heating and that the concave bend in the southern New Jersey coast limits the southern extent of the jet.

A novel method for trace tritium transport studies

A new method combining a free-form solution for the neutron emissivity and the ratio method (Bonheure et al 2006 Nucl. Fusion 46 725–40) is applied to the investigation of tritium particle transport in JET plasmas. The 2D neutron emissivity is calculated using the minimum Fisher regularization method (MFR) (Anton et al 1996 Plasma Phys. Control. Fusion 38 1849, Mlynar et al 2003 Plasma Phys. Control. Fusion 45 169). This method is being developed and studied alongside other methods at JET. The 2D neutron emissivity was significantly improved compared with the first MFR results by constraining the emissivity along the magnetic flux surfaces. 1D profiles suitable for transport analysis are then obtained by subsequent poloidal integration.In methods on which previous JET publications are based (Stork et al 2005 Nucl. Fusion 45 S181, JET Team (prepared by Zastrow) 1999 Nucl. Fusion 39 1891, Zastrow et al 2004 Plasma Phys. Control. Fusion 46 B255, Adams et al 1993 Nucl. Instrum. Methods A 329 277, Jarvis et al 1997 Fusion Eng. Des. 34–35 59, Jarvis et al 1994 Plasma Phys. Control. Fusion 36 219), the 14.07 MeV D–T neutron line integrals measurements were simulated and the transport coefficients varied until good fits were obtained. In this novel approach, direct knowledge of tritium concentration or the fuel ratio nT/nD is obtained using all available neutron profile information, e.g both 2.45 MeV D–D neutron profiles and 14.07 MeV D–T neutron profiles (Bonheure et al 2006 Nucl.Fusion 46 725–40). Tritium particle transport coefficients are then determined using a linear regression from the dynamic response of the tritium concentration nT/nD profile.The temporal and spatial evolution of tritium particle concentration was studied for a set of JET discharges with tritium gas puffs from the JET trace tritium experiments. Local tritium transport coefficients were derived from the particle flux equation Γ = −D∇nT + VnT, where D is the particle diffusivity and V the convection velocity.Tritium transport in the plasma core approaches the neoclassical level in some cases. For the set of plasmas analysed and within the uncertainty, tritium particle confinement follows the ITER IPB98(y,2) particle scaling confinement.

Role of recycling in JET trace tritium transport experiments

JET experiments with transient puffed injection of low tritium levels were carried out with the goal of using measured time- and space-dependent neutron emission to determine the scaling of particle transport in the core for ITB, ELMy H-mode and hybrid scenarios. Several attempts to find core τp scaling based on the same dataset have reached contradictory conclusions: core particle diffusivity inversely proportional to density, scaling proportional to density, and scaling independent of collisionality (density independence). The analyses have also varied the assumed boundary conditions. In all three cases, ELM-averaged transport was analyzed. To see what can be learned about resolution of such differences through possible systematic SOL effects on particle transport scaling, using the available edge/SOL data for these core particle transport experiments, we analyze representative cases from the JET trace T experimental database. The pulses considered cover a range in average core electron density, with approximately constant tritium puffing rates. The study is motivated by the realization that, although these experiments were not designed for such a purpose, similar future ‘trace T’ experiments could better characterize the SOL, and thus its influence of on particle transport in the edge/pedestal region (0.8<ρ<1) since important elements of the tritium pathway are measured: the external T2 gas puff rate (Γpuffmax), and, from the neutron analysis, the influx to the plasma core region at ρ=0.8 (ΓT+in,max) and the efflux from the core (ΓT+out,max). Systematic effects on edge/pedestal particle transport scaling in puffing experiments are found to depend on the status of saturation in the near-inlet region, on the details of ELM-induced particle expulsion from both core and SOL, and on the degree of near-wall T enrichment.

Modeling of neutron emission spectroscopy in JET discharges with fast tritons from (T)D ion cyclotron heating

The measurement of fast ion populations is one of the diagnostic capabilities provided by neutron emission spectroscopy (NES). NES measurements were carried out during JET trace tritium campaign with the magnetic proton recoil neutron spectrometer. A favorable plasma scenario is (T)D where the resulting 14 MeV neutron yield is dominated by suprathermal emission from energetic tritons accelerated by radio frequency at their fundamental cyclotron frequency. Information on the triton distribution function has been derived from NES data with a simple model based on two components referred to as bulk (B) and high energy (HE). The HE component is based on strongly anisotropic tritium distribution that can be used for routine best-fit analysis to provide tail temperature values (THE). This article addresses to what extent the THE values are model dependent by comparing the model above with a two-temperature (bi-) Maxwellian model featuring parallel and perpendicular temperatures. The bi-Maxwellian model is strongly anisotropic and frequently used for radio frequency theory.

Expanding the operating space of ICRF on JET with a view to ITER**This paper is an expanded version of the material originally presented at the 20th IAEA Fusion Energy Conference, Vilamoura, Portugal, 1–6 November 2004 (Fusion Energy 2004, Vienna: IAEA), CD-ROM file EX/P4-26.

This paper reports on ITER-relevant ion cyclotron resonance frequency (ICRF) physics investigated on JET in 2003 and early 2004. Minority heating of helium three in hydrogen plasmas—(3He)H—was systematically explored by varying the 3He concentration and the toroidal phasing of the antenna arrays. The best heating performance (a maximum electron temperature of 6.2 keV with 5 MW of ICRF power) was obtained with a preferential wave launch in the direction of the plasma current. A clear experimental demonstration was made of the sharp and reproducible transition to the mode conversion heating regime when the 3He concentration increased above ∼2%. In the latter regime the best heating performance (a maximum electron temperature of 8 keV with 5 MW of ICRF power) was achieved with dipole array phasing, i.e. a symmetric antenna power spectrum. Minority heating of deuterium in hydrogen plasmas—(D)H—was also investigated but was found inaccessible because this scenario is too sensitive to impurity ions with Z/A = 1/2 such as C6+, small amounts of which directly lead into the mode conversion regime. Minority heating of up to 3% of tritium in deuterium plasmas was systematically investigated during the JET trace tritium experimental campaign (TTE). This required operating JET at its highest possible magnetic field (3.9 to 4 T) and the ICRF system at its lowest frequency (23 MHz). The interest of this scenario for ICRF heating at these low concentrations and its efficiency at boosting the suprathermal neutron yield were confirmed, and the measured neutron and gammay ray spectra permit interesting comparisons with advanced ICRF code simulations. Investigations of finite Larmor radius effects on the RF-induced high-energy tails during second harmonic (ω = 2ωc) heating of a hydrogen minority in D plasmas clearly demonstrated a strong decrease in the RF diffusion coefficient at proton energies ∼ 1 MeV, in agreement with theoretical expectations. Fast wave heating and current drive experiments in deuterium plasmas showed effective direct electron heating with dipole phasing of the antennas, but only small changes of the central plasma current density were observed with the directive phasings, in particular at low single pass damping. New investigations of the heating efficiency of ICRF antennas confirmed its strong dependence on the parallel wavenumber spectrum. Advances in topics of a more technological nature are also summarized: ELM studies using fast RF measurements, the successful experimental demonstration of a new ELM-tolerant antenna matching scheme and technical enhancements planned on the JET ICRF system for 2006, they being equally strongly driven by the preparation for ITER.

On alpha particle effects in tokamaks with a current hole

During operation with so-called advanced scenarios in a tokamak, current holes, characterized by a virtually current-free central region, often develop. They might also be difficult to avoid, at least transiently, in reactor plasmas. This paper is focused on how the presence of a current hole affects quantities related to fusion born alpha particles. In particular, the anisotropy in the fast ion pressure, the current they generate and the profile of the power they transfer to the thermal plasma via collisions. Possible implications for the confinement of the alpha particles and the performance of the plasma are discussed. Furthermore, the results of a comparison between simulations and gamma-ray data from recent JET trace tritium experiments with current holes are presented.

Overview of transport, fast particle and heating and current drive physics using tritium in JET plasmas

Results are presented from the JET Trace Tritium Experimental (TTE) campaign using minority tritium (T) plasmas (nT/nD < 3%). Thermal tritium particle transport coefficients (DT, vT) are found to exceed neo-classical values in all regimes, except in ELMy H-modes at high densities and in the region of internal transport barriers (ITBs) in reversed shear plasmas. In ELMy H-mode dimensionless parameter scans, at q95 ∼ 2.8 and triangularity δ = 0.2, the T particle transport scales in a gyro-Bohm manner in the inner plasma (r/a < 0.4), whilst the outer plasma particle transport scaling is more Bohm-like. Dimensionless parameter scans show contrasting behaviour for the trace particle confinement (increases with collisionality, ν* and β) and bulk energy confinement (decreases with ν* and is independent of β). In an extended ELMy H-mode data set, with ρ*, ν*, β and q varied but with neo-classical tearing modes (NTMs) either absent or limited to weak, benign core modes (4/3 or above), the multiparameter fit to the normalized diffusion coefficient in the outer plasma (0.65 < r/a < 0.8) gives DT/Bϕ ∼ ρ*2.46ν*−0.23β−1.01q2.03. In hybrid scenarios (qmin ∼ 1, low positive shear, no sawteeth), the T particle confinement is found to scale with increasing triangularity and plasma current. Comparing regimes (ELMy H-mode, ITB plasma and hybrid scenarios) in the outer plasma region, a correlation of high values of DT with high values of vT is seen. The normalized diffusion coefficients for the hybrid and ITB scenarios do not fit the scaling derived for ELMy H-modes. The normalized tritium diffusion scales with normalized poloidal Larmor radius in a manner close to gyro-Bohm , with an added inverse β dependence. The effects of ELMs, sawteeth and NTMs on the T particle transport are described. Fast-ion confinement in current-hole (CH) plasmas was tested in TTE by tritium neutral beam injection into JET CH plasmas. γ-rays from the reactions of fusion alpha and beryllium impurities (9Be(α, nγ)12C) characterized the fast fusion-alpha population evolution. The γ-decay times are consistent with classical alpha plus parent fast triton slowing down times (τTs + ταs) for high plasma currents (Ip > 2 MA) and monotonic q-profiles. In CH discharges the γ-ray emission decay times are much lower than classical (τTs+ταs), indicating alpha confinement degradation, due to the orbit losses and particle orbit drift predicted by a 3-D Fokker–Planck numerical code and modelled using TRANSP.

ITER relevant developments in neutron diagnostics during the JET Trace Tritium campaign

During the JET Trace Tritium campaign a few new neutron diagnostic systems were deployed under different plasma scenarios to provide information on the total neutron emission and its spatial and energy distribution. The 14MeV neutron yield was measured with a chemical vapour deposited (CVD) diamond detector. Comparison with the JET 14MeV monitors (Si diodes) illustrates the good performance of the CVD device. Key information on the tritium transport and the behaviour of fast particles in the plasma was obtained from the spatially and temporally measurements of neutron emission from the upgraded neutron profile cameras which also provide an independent measure of the total neutron yield. Spatial asymmetries in the neutron emission were observed which is evidence for the influence of fast particles on the plasma. With regard to the energy distribution of the neutron emission, a spectrometer based on a liquid organic scintillator with n-γ pulse shape discrimination (PSD) features was installed. The results demonstrate that such system can operate in real fusion experiments as compact broadband neutron (1.5 MeV < E n <20MeV) spectrometer with high energy resolution. A fast transient recorder has been successfully applied for digital pulse shape discrimination (DPSD) of neutron and gamma events acquired with an organic scintillator at high count rate operation (MHz range). The experience gained at JET indicates that these neutron measurement systems are suitable for large fusion devices such as JET-EP and ITER where fusion neutron diagnostics will play an increasingly important role.

Technical and Scientific Aspects of the JET Trace-Tritium Experimental Campaign

The JET Trace Tritium (TTE) programme marked the first use of tritium in experiments under the managerial control of UKAEA, which operates the JET Facility on behalf of EFDA. The introduction of tritium into the plasma by gas fuelling and neutral beam injection, even in trace quantities, required the mobilisation of gram-quantities of tritium gas from the Active Gas Handling System (AGHS) product storage units into the supply lines connected to the torus gas valve and the neutral beam injectors. All systems for DT gas handling, recovery and reprocessing were therefore recommissioned and operating procedures re-established, involving extensive operations staff training. The validation of Key Safety Related Equipment (KSRE) is described with reference to specific examples. The differences between requirements for TTE and full DT operations are shown to be relatively small. The scientific motivation for TTE, such as the possibility to obtain high-quality measurements in key areas such as fuel-ion transport and fast ion dynamics, is described, and the re-establishment and development of JET’s 14MeV neutron diagnostic capability for TTE and future DT campaigns are outlined. Some scientific highlights from the TTE campaign are presented.

Radio Variability of the Galactic X-ray Binaries with Relativistic Jets

Variable non-thermal radio emission from Galactic X-ray binaries is a trace of relativistic jets, created near accretion disks. The spectral characteristics of a lot of radio flares in the X-ray binaries with jets (RJXB) is discussed in this report. We carried out several long daily monitoring programs with the RATAN-600 radio telescope of the sources: SS433, Cyg X-3, LSI +61°303, GRS 1915+10 and some others.Many flaring RJXB show, exponential and power laws of flare decay. Moreover, these different laws could be present in one or several flares and commonly flare decays are faster at a higher frequency. The decay law seems to change because of geometric form of the conical hollow jets. The synchrotron and inverse Compton losses could explain general frequency dependences in flare evolution.

Radio emission of galactic X-ray binaries with relativistic jets

Abstract Variable non-thermal radio emission from Galactic X-ray binaries is a trace of relativistic jets, created near accretion disks. The spectral characteristics of many radio flares in X-ray binaries with jets (RJXB) is discussed in this report. We carried out several long daily monitoring programs with the RATAN-600 radio telescope of the sources: SS433, Cyg X-3, LSI+61°303, GRS 1915+10, and some others. We also reviewed some data from the GBI monitoring program at two frequencies and hard X-ray BATSE (20–100 keV) and soft X-ray RTXE (2–12 keV) ASM data. We confirmed that flaring radio emission of Cyg X-3 correlated with hard and anticorrelated with soft X-ray emission during the strong flare (> 3 Jy) in May 1997. During two orbital periods we investigated radio light curves of the remarkable X-binary LSI +61°303. Two flaring events near the phase 0.6 of the 26.5–day orbital period have been detected for the first time at four frequencies simultaneously. Powerful flaring events of SS433 were detecte...