Reduction of edge-localized mode intensity using high-repetition-rate pellet injection in tokamak H-mode plasmas.

High repetition rate injection of deuterium pellets from the low-field side (LFS) of the DIII-D tokamak is shown to trigger high-frequency edge-localized modes (ELMs) at up to 12× the low natural ELM frequency in H-mode deuterium plasmas designed to match the ITER baseline configuration in shape, normalized beta, and input power just above the H-mode threshold. The pellet size, velocity, and injection location were chosen to limit penetration to the outer 10% of the plasma. The resulting perturbations to the plasma density and energy confinement time are thus minimal (<10%). The triggered ELMs occur at much lower normalized pedestal pressure than the natural ELMs, suggesting that the pellet injection excites a localized high-n instability. Triggered ELMs produce up to 12× lower energy and particle fluxes to the divertor, and result in a strong decrease in plasma core impurity density. These results show for the first time that shallow, LFS pellet injection can dramatically accelerate the ELM cycle and reduce ELM energy fluxes on plasma facing components, and is a viable technique for real-time control of ELMs in ITER.

A two photon absorption laser induced fluorescence diagnostic for fusion plasmas.

The quality of plasma produced in a magnetic confinement fusion device is influenced to a large extent by the neutral gas surrounding the plasma. The plasma is fueled by the ionization of neutrals, and charge exchange interactions between edge neutrals and plasma ions are a sink of energy and momentum. Here we describe a diagnostic capable of measuring the spatial distribution of neutral gas in a magnetically confined fusion plasma. A high intensity (5 MW/cm(2)), narrow bandwidth (0.1 cm(-1)) laser is injected into a hydrogen plasma to excite the Lyman ß transition via the simultaneous absorption of two 205 nm photons. The absorption rate, determined by measurement of subsequent Balmer α emission, is proportional to the number of particles with a given velocity. Calibration is performed in situ by filling the chamber to a known pressure of neutral krypton and exciting a transition close in wavelength to that used in hydrogen. We present details of the calibration procedure, including a technique for identifying saturation broadening, measurements of the neutral density profile in a hydrogen helicon plasma, and discuss the application of the diagnostic to plasmas in the DIII-D tokamak.

Charge exchange recombination detection of low-Z and medium-Z impurities in the extreme UV using a digital lock-in technique.

More sensitive detection of charge exchange recombination lines from low-Z elements, and first-time detection from the medium-Z elements nickel and copper, has been achieved in DIII-D plasmas with a digital lock-in technique. That portion of the extreme UV spectrum varying synchronously in time with the square-wave modulation of a high energy, neutral heating beam is extracted by forming a scalar product of a correlation function with the data record of each pixel in the linear array detector. The usual, dense array of collisionally excited, metallic lines from the tokamak plasma is strongly suppressed, leaving only a sparse spectrum of lines dominated by charge exchange recombination transitions from fully stripped, low-Z elements. In plasmas with high metal content, charge exchange recombination lines from the Li-like ions of nickel and copper have been positively identified.

Doppler coherence imaging and tomography of flows in tokamak plasmas (invited).

This article describes the results of spatial heterodyne Doppler "coherence imaging" of carbon ion flows in the divertor region of the DIII-D tokamak. Spatially encoded interferometric projections of doubly ionized carbon emission at 465 nm have been demodulated and tomographically inverted to obtain the spatial distribution of the carbon ion parallel flow and emissivity. The operating principles of the new instruments are described, and the link between measured properties and line integrals of the flow field are established. An iterative simultaneous arithmetic reconstruction procedure is applied to invert the interferometric phase shift projections, and the reconstructed parallel flow field amplitudes are found to be in reasonable agreement with UEDGE modeling.

Resonant pedestal pressure reduction induced by a thermal transport enhancement due to stochastic magnetic boundary layers in high temperature plasmas.

Good alignment of the magnetic field line pitch angle with the mode structure of an external resonant magnetic perturbation (RMP) field is shown to induce modulation of the pedestal electron pressure p(e) in high confinement high rotation plasmas at the DIII-D tokamak with a shape similar to ITER, the next step tokamak experiment. This is caused by an edge safety factor q95 resonant enhancement of the thermal transport, while in contrast, the RMP induced particle pump out does not show a significant resonance. The measured p(e) reduction correlates to an increase in the modeled stochastic layer width during pitch angle variations matching results from resistive low rotation plasmas at the TEXTOR tokamak. These findings suggest a field line pitch angle resonant formation of a stochastic magnetic edge layer as an explanation for the q95 resonant character of type-I edge localized mode suppression by RMPs.

Porous plug gas injection systems for studies of hydrocarbon dissociation and transport in the DIII-D tokamak.

A probe has been designed, constructed, and successfully used to inject methane into the DIII-D lower divertor in a manner imitating natural release by chemical erosion. This porous plug injector (PPI) probe consists of a self-contained gas reservoir with an integrated pressure gauge and a 3 cm diameter porous surface through which gas is injected into the lower divertor of the tokamak. The probe is positioned flush with the divertor target surface by means of the divertor materials evaluation system. Two gas delivery systems were developed: in the first, gas flow is regulated by a remotely controlled microvalve and in the second by a fixed micro-orifice flow restrictor. Because of the large area of the porous surface through which gas is admitted, the injected hydrocarbon molecules see a local carbon surface (>90% carbon) similar to that seen by hydrocarbons being emitted by chemical sputtering from surrounding carbon tiles. The distributed gas source also reduces the disturbance to the local plasma while providing sufficient signal for spectroscopic detection. In situ spectroscopic measurements with the PPI in DIII-D allow the direct calibration of response for measured plasma conditions from a known influx of gas.

Measurements of spatial line emission profiles in the main scrape-off layer of the DIII-D tokamak.

A video camera system is described as that measures the spatial distribution of visible line emission emitted from the main scrape-off layer (SOL) of plasmas in the DIII-D tokamak. A wide-angle lens installed on an equatorial port and an in-vessel mirror, which intercepts part of the lens' view, provide simultaneous tangential views of the SOL on the low-field and high-field sides of the plasma's equatorial plane. Tomographic reconstruction techniques are used to calculate the two-dimensional (2D) poloidal profiles from the raw data, and one-dimensional (1D) poloidal profiles simulating chordal views of other optical diagnostics from the 2D profiles. The 2D profiles can be compared with SOL plasma simulations; the 1D profiles with measurements from spectroscopic diagnostics. Sample results are presented, which elucidate carbon transport in plasmas with toroidally uniform injection of methane and argon transport in disruption mitigation experiments with massive gas jet injection.

Dust measurements in tokamaks (invited).

Dust production and accumulation present potential safety and operational issues for the ITER. Dust diagnostics can be divided into two groups: diagnostics of dust on surfaces and diagnostics of dust in plasma. Diagnostics from both groups are employed in contemporary tokamaks; new diagnostics suitable for ITER are also being developed and tested. Dust accumulation in ITER is likely to occur in hidden areas, e.g., between tiles and under divertor baffles. A novel electrostatic dust detector for monitoring dust in these regions has been developed and tested at PPPL. In the DIII-D tokamak dust diagnostics include Mie scattering from Nd:YAG lasers, visible imaging, and spectroscopy. Laser scattering is able to resolve particles between 0.16 and 1.6 microm in diameter; using these data the total dust content in the edge plasmas and trends in the dust production rates within this size range have been established. Individual dust particles are observed by visible imaging using fast framing cameras, detecting dust particles of a few microns in diameter and larger. Dust velocities and trajectories can be determined in two-dimension with a single camera or three-dimension using multiple cameras, but determination of particle size is challenging. In order to calibrate diagnostics and benchmark dust dynamics modeling, precharacterized carbon dust has been injected into the lower divertor of DIII-D. Injected dust is seen by cameras, and spectroscopic diagnostics observe an increase in carbon line (CI, CII, C(2) dimer) and thermal continuum emissions from the injected dust. The latter observation can be used in the design of novel dust survey diagnostics.

Filterscopes: spectral line monitors for long-pulse plasma devices.

A photomultiplier (PMT)-based diagnostic system for monitoring spectral lines along multiple viewchords, named the "Filterscope" [R. J. Colchin et al., Rev. Sci. Instrum. 74, 2068 (2003)], is currently in use at the DIII-D, NSTX, and CDX-U fusion plasma devices in the US, and has been installed at the KSTAR device in Korea. This diagnostic has recently been upgraded for application to long-pulse devices, such as KSTAR, EAST in China, and the future ITER in France. A new data acquisition system, employing the PXI instrumentation platform with an embedded Windows microprocessor controller, can simultaneously record up to 72 channels at 100 kHz sampling rates for plasma periods lasting up to 20 min. Based on the average signal level during an adjustable time interval (100 ms in the present DIII-D implementation), the controller digitally adjusts PMT dynode voltage throughout the course of a discharge, thereby maintaining the output signals at a level where they are neither saturated nor dominated by digitizer noise. The new system's ability to accommodate large variations in source strength, discharge to discharge and within a single discharge, has proved particularly valuable during DIII-D operations, since changes between top, bottom, and double-null divertor magnetic configurations lead to large temporal variations in signal brightness.

Outcome in the real-world of coronary high-risk intervention with drug-eluting stents (ORCHID) -- a single-center study comparing Cypher sirolimus-eluting with Taxus paclitaxel-eluting stents.

OBJECTIVE: We present real world experience from a single center registry comparing the 6-month outcome of percutaneous coronary intervention (PCI) in unselected high-risk individuals using either sirolimus-eluting (SES) or paclitaxel-eluting stents (PES). METHODS/RESULTS: We compared clinical outcome at 6 months follow-up in two cohorts of 156 consecutive patients (total n = 312) who underwent SES (June 2002-February 2003) and PES (march 2003-July 2003) implantation. The primary endpoint was a composite of major adverse cardiac events (MACE). Baseline clinical characteristics were well matched. The 6-month target vessel revascularization (TVR) rates were 1.9% (SES) and 2.6% (PES) and MACE rates were similar in the two groups (SES 4.5% vs. PES 3.2%, P = NS). In the PES group, intervention for multivessel disease, bifurcation lesions and in small vessels was more common, and for in-stent restenosis less common, reflecting the impact of drug eluting stents on indications for PCI. The incidence of sub-acute stent thrombosis, related to inadequate antiplatelet therapy in 3 of the 6 cases, was 0.95% with no difference between the two groups. CONCLUSION: This study confirms the safety and efficacy of SES and PES in unselected high risk patients undergoing PCI. Clinical outcomes of both stents are equivalent at 6 months with low rates of MACE and TVR. These data provide important complementary information to forthcoming randomized studies.

A novel polymorphism of the gene encoding furin, a TGF-beta1 activator, and the influence on cardiac allograft vasculopathy formation.

BACKGROUND: Coronary vasculopathy (CV) is an important determinant of survival following cardiac transplantation. We have previously shown that G915C polymorphism of the Transforming Growth Factor-beta1 (TGF-beta1) gene strongly influences CV development. Furin is a proprotein convertase enzyme important in TGF-beta1 activation. We investigated for polymorphism within the promoter region of the gene for furin (fur). Allelic variation of the fur gene, in conjunction with TGF-beta1 polymorphism, was subsequently related to the development of CV. METHODS AND RESULTS: The fur gene promoter region (position -1199 to +39) was analysed by SSCP and sequencing. A C/T single nucleotide substitution polymorphism at position -231* was identified. Using PCR the fur and TGFB1 genotypes were identified in 115 cardiac transplant recipients. CV was diagnosed at routine surveillance post-transplant coronary angiography. Fur polymorphism had no influence on vasculopathy development; median time to diagnosis, *C/C homozygotes, 2.27 years (2.10-4.32), *C/T heterozygotes 2.97 years (2.09-4.24), *T/T homozygotes 2.65 years (2.33-4.08), (P=0.95). Allelic variation did not influence Kaplan Meier actuarial analysis of disease onset (P=0.54). Ninety-three percent of recipients were high TGF-beta1 producers. We used fur polymorphism to substratify patients with the +915*G/G TGFB1 (high producing) allele. Fur polymorphism did not influence CV development within this TGF-beta1 high producer cohort, when analysed by time to first diagnosis and Kaplan Meier testing. CONCLUSIONS: We have described a novel polymorphism at position -231* in the gene encoding furin. The fur -231* single nucleotide polymorphism in isolation, or in conjunction with TGFB1 polymorphism, is not useful as a genetic risk marker for cardiac transplant associated coronary vasculopathy.

Donor and recipient-transforming growth factor-beta 1 polymorphism and cardiac transplant-related coronary artery disease.

BACKGROUND: Transforming growth factor-beta1 (TGF-beta1) has been implicated in the pathogenesis of coronary vasculopathy following cardiac transplantation. The TGFB1 gene contains polymorphisms at positions +915* (Arg25Pro) and +869* (Leu10Pro) which may influence TGF-beta1 expression. We investigated the relationship between the development of coronary vasculopathy and the prevalence of these alleles in a cardiac transplant population. METHODS: Vasculopathy was diagnosed at routine surveillance post-transplant coronary angiography. Using sequence-specific polymerase chain reaction we identified the TGFB1 +915* and +869* genotypes in 147 cardiac transplant recipients and 134 cardiac donors. RESULTS: TGFB1 +915*C allele carriers (low producers) made up 10.5% of the recipient population but were significantly less likely to develop coronary vasculopathy (P=0.03). Median time to diagnosis was 6.0 years (3.9-8.72) in +915*C allele carriers compared to 2.75 years (2.10-4.22) in *G/G homozygotes (p=0.002). Pre- and 1 year post-transplant clinical variables were equivalent between the two groups. Multivariate analysis identified the recipient +915*G/G genotype (hazard ratio 2.96 (95% CI, 1.09-9.98); p=0.039), donor age (hazard ratio 1.05 (95% CI, 1.02-1.09); p=0.008) and number of acute rejection episodes of ISHLT grade 3 or greater in the first year (hazard ratio 1.12 (95% CI, 1.01-1.23); p=0.03) as significant predictors of vasculopathy. The recipient TGFB1 +869*, and both alleles in the donor, had no influence on vasculopathy development. CONCLUSIONS: Recipient TGFB1 +915* genotype influences the development of cardiac transplant-related coronary vasculopathy. This gives an important insight to the pathophysiology of the disease. On the contrary, donor TGFB1 +915* and TGFB1 +869* polymorphisms do not appear to be important and cannot be used as genetic risk factors.

Rare case of heart failure caused by compression of the left atrium by a thoracic aortic aneurysm.

A 61 year old patient was found to have an aneurysm extending from the aortic root to the suprarenal region. He underwent first stage surgery with aortic root and arch replacement, prosthetic aortic valve replacement, and coronary artery bypass grafting. Four weeks later, he presented with breathlessness and signs of heart failure and pleural effusion. Computed tomography showed that the left atrium was compressed between the aortic aneurysm posteriorly and the left ventricle and sternum anteriorly. Obstruction of the superior vena cava, bronchus, oesophagus, and rarely right atrium by an aortic aneurysm has been described before but presentation with left atrial compression has not been reported.

Influence of interleukin-10 polymorphism on the development of coronary vasculopathy following cardiac transplantation.

BACKGROUND: Interleukin-10 (IL-10), an important anti-inflammatory cytokine has been implicated in the pathogenesis of acute rejection and long term graft tolerance. Polymorphism in the IL-10 promoter at positions -1082, -819 and -592, correlates with IL-10 production. Haplotype inheritance of these alleles determines whether individuals are high, intermediate, or low producers of IL-10. We investigated the effect of this polymorphism on the development of cardiac transplant vasculopathy (CV). METHODS: CV was defined at routine surveillance coronary angiography as any abnormality in 1 or more epicardial vessels. Recipient and donor DNA was amplified by PCR using primers to the 3 allele sites. After identifying the phenotype by electrophoresis, freedom from CV was analysed by Kaplan-Meier and the log rank test. RESULTS: One hundred and forty eight recipients and 135 donors were studied. High, intermediate and low producers made up 26.4, 47.3 and 26.3% of recipients and 35.6, 48.2 and 16.2% of donors (P=0.42). No significant differences were noted between the phenotype groups. The recipient and donor genotypes, when considered in isolation, had no effect on the freedom from CV; recipients: P=0.85; donors: P=0.52. When the recipient and donor genotypes were combined for an individual patient the freedom from CV was again unaffected; high producing IL-10 allele in donor or recipient: P=0.76, low producing IL-10 allele in donor or recipient: P=0.51. Increasing donor age and acute rejection episodes and the presence of a high producing TGF-beta1 phenotype were independent risk factors for CV. CONCLUSIONS: Polymorphism of the IL-10 promoter region fails to predict the development of CV and cannot be used as a genetic risk marker. This may be due to the effects of immunosuppressive treatment.

Slow L-H transitions in DIII-D plasmas.

The transition from the low to the high mode of plasma confinement ( L-H transition) is studied in the DIII-D by an experimental technique which allows an arbitrarily slow transition. During an initial transition, periodic turbulent instability bursts are observed near the separatrix which inhibit the full transition. These bursts are damped by self-generated shear flows, and a predator-prey-type relationship is shown to give a good description of the data. As the neutral-beam power is raised, the oscillations change to type III edge localized modes. Another transition then leads to a quiet H mode.

Tumour necrosis factor alpha gene polymorphism: a predisposing factor to non-ischaemic myocardial dysfunction?

BACKGROUND: Tumour necrosis factor alpha (TNF alpha) is implicated in the pathophysiology of heart failure. Plasma TNF alpha is raised in patients with myocardial dysfunction in proportion to the symptoms. OBJECTIVE: To determine whether this genetic variant is over represented in heart transplant recipients. PATIENTS: 175 heart transplant recipients and a control group of 212 healthy volunteers were studied. The reason for transplantation was severe symptomatic myocardial dysfunction in all cases. METHODS: The TNF alpha genotype was determined by polymerase chain reaction and gel electrophoresis. The populations were compared for their fit to Hardy-Weinberg equilibrium by calculating the expected frequencies of each genotype and comparing them to the observed values. A chi(2) test was used to determine the significance of the difference between the observed and expected values. RESULTS: No differences were found in the frequency of the TNF2 allele between all heart transplant recipients taken together (54/175, 31%) and healthy volunteers (58/212, 27%). A higher proportion of TNF2 allele carriers was present in cardiac recipients with a pretransplant diagnosis of viral mediated or idiopathic heart failure than in those with ischaemic myocardial dysfunction (26/69 (37.7%) v 28/106 (26.4%), p = 0.03). PATIENTS with a non-ischaemic aetiology had a higher prevalence of TNF2 than healthy volunteers (26/69 (37.7%) v 58/212 (27%), p = 0.05). CONCLUSIONS: The TNF2 allele is overrepresented in patients with end stage non-ischaemic myocardial dysfunction. This may represent a genetic predisposition in a small subset of patients who could respond favourably to anti-TNF alpha treatment.

Influence of tumor necrosis factor-alpha gene-308 polymorphism on the development of coronary vasculopathy after cardiac transplantation.

BACKGROUND: Tumor necrosis factor-alpha (TNF-alpha) has been implicated in cardiovascular disease. Polymorphism of the TNF-alpha gene promoter region (position -308) influences an individual's production of TNF-alpha. This affects susceptibility to acute rejection after cardiac transplantation. Because the highest serum levels of TNF-alpha have been found in recipients with cardiac transplant vasculopathy and because TNF-alpha blockade can prevent the disease in rabbits, we investigated the effect of TNF-alpha promoter polymorphism on the development of vasculopathy in human cardiac allograft recipients. METHODS: Using sequence-specific primers to the TNF-alpha gene and polymerase chain reaction, the genotypes of 147 cardiac transplant recipients and 134 heart donors were identified. An association was sought between the presence of high-producing (A homozygotes, GA heterozygotes) or low-producing (G homozygotes) TNF-alpha genotype and the development of coronary vasculopathy, diagnosed by routine surveillance coronary angiography. RESULTS: We found that 31.9% of recipients and 27.0% of donors were high TNF-alpha producers. The presence of the high-producing TNF-alpha allele led to an earlier diagnosis of vasculopathy; 3.42 years (+/- 91.3 days) vs 3.84 years (+/- 76.3 days) for high- and low-producing cardiac graft recipients, respectively; 3.52 years (+/- 87.3 days) vs 3.78 years (+/- 77.4 days) for high- and low-producing donor grafts, respectively. However, neither of these differences were significant. By Kaplan Meier actuarial analysis and log-rank test, TNF-alpha polymorphism had no effect on the freedom from vasculopathy when considering either recipient (p = 0.99) or donor (p = 0.86) TNF-alpha genotype. Multivariate analysis identified increasing donor age and the number of acute rejection episodes of International Society for Heart and Lung Transplantation grade 3 or greater as independent risk factors for vasculopathy in both the recipient and donor cohorts. CONCLUSIONS: Polymorphism at position -308 in the promoter region of the TNF-alpha gene fails to predict the development of cardiac transplant-related vasculopathy and cannot be used as a genetic risk marker. This may be because of the effects of immunosuppressive treatment.