Broadening of the Divertor Heat Flux Profile in High Confinement Tokamak Fusion Plasmas with Edge Pedestals Limited by Turbulence in DIII-D.

Multimachine empirical scaling predicts an extremely narrow heat exhaust layer in future high magnetic field tokamaks, producing high power densities that require mitigation. In the experiments presented, the width of this exhaust layer is nearly doubled using actuators to increase turbulent transport in the plasma edge. This is achieved in low collisionality, high confinement edge pedestals with their gradients limited by turbulent transport instead of large-scale, coherent instabilities. The exhaust heat flux profile width and divertor leg diffusive spreading both double as a high frequency band of turbulent fluctuations propagating in the electron diamagnetic direction doubles in amplitude. The results are quantitatively reproduced in electromagnetic XGC particle-in-cell simulations which show the heat flux carried by electrons emerges to broaden the heat flux profile, directly supported by Langmuir probe measurements.

Measuring the electron temperature and identifying plasma detachment using machine learning and spectroscopy.

A machine learning approach has been implemented to measure the electron temperature directly from the emission spectra of a tokamak plasma. This approach utilized a neural network (NN) trained on a dataset of 1865 time slices from operation of the DIII-D tokamak using extreme ultraviolet/vacuum ultraviolet emission spectroscopy matched with high-accuracy divertor Thomson scattering measurements of the electron temperature, Te. This NN is shown to be particularly good at predicting Te at low temperatures (Te < 10 eV) where the NN demonstrated a mean average error of less than 1 eV. Trained to detect plasma detachment in the tokamak divertor, a NN classifier was able to correctly identify detached states (Te < 5 eV) with a 99% accuracy (an F1 score of 0.96) at an acquisition rate 10× faster than the Thomson scattering measurement. The performance of the model is understood by examining a set of 4800 theoretical spectra generated using collisional radiative modeling that was also used to predict the performance of a low-cost spectrometer viewing nitrogen emission in the visible wavelengths. These results provide a proof-of-principle that low-cost spectrometers leveraged with machine learning can be used to boost the performance of more expensive diagnostics on fusion devices and be used independently as a fast and accurate Te measurement and detachment classifier.

Thomson scattering measurements on DIII-D using in-vessel laser mirrors and lenses to diagnose a new divertor location.

Translatable in-vessel mirrors have enabled the DIII-D Thomson scattering system to diagnose the divertor plasma in high triangularity shaped plasmas. Previous divertor Thomson scattering measurements in DIII-D were restricted to spatial locations along a Nd:YAG laser beam that was directed through a vertical port. This only allowed measurements to be made in low triangularity shaped plasmas. The new mirrors re-route the laser underneath floor tiles to a position of smaller major radius as necessary for high triangularity plasmas. New in-vessel collection optics transmit scattered light from regions inaccessible to external lenses. Damage to mirrors and high stray light levels are challenges that were overcome to successfully make these measurements. Through the careful use of baffles and light shields, stray light leakage into polychromator detector channels was reduced to negligible levels, allowing temperature measurements below 1 eV. The system is described and the initial results presented.

Tests of a full-scale ITER toroidal interferometer and polarimeter (TIP) prototype on the DIII-D tokamak (invited).

A full-scale ITER toroidal interferometer and polarimeter (TIP) prototype, including an active feedback alignment system, has been installed and tested on the DIII-D tokamak. In the TIP prototype, a two-color interferometry measurement of line-integrated density is carried out at 10.59 µm and 5.22 µm using a CO2 and quantum cascade laser, respectively, while a separate polarimetry measurement of the plasma-induced Faraday effect is made at 10.59 µm. The TIP prototype is equipped with a piezo tip/tilt stage active feedback alignment system that minimizes noise in the measurement and keeps the diagnostic aligned throughout DIII-D discharges. The measured phase resolution for the polarimeter and interferometer is 0.05° (100 Hz bandwidth) and 1.9° (1 kHz bandwidth), respectively. The corresponding line-integrated density resolution for the vibration-compensated interferometer is δnL = 1.5 × 1018 m-2, and the magnetic field-weighted line-integrated density from the polarimeter is δnBL = 1.5 × 1019 Tm-2. Both interferometer and polarimeter measurements during DIII-D discharges compare well with the expectations based on calculations using Thomson scattering measured density profiles and magnetic equilibrium reconstructions. Additionally, larger bandwidth interferometer measurements show that the diagnostic is a sensitive monitor of core density fluctuations with demonstrated measurements of Alfvén eigenmodes and tearing modes.

Upgraded divertor Thomson scattering system on DIII-D.

A design to extend the unique divertor Thomson scattering system on DIII-D to allow measurements of electron temperature and density in high triangularity plasmas is presented. Access to this region is selectable on a shot-by-shot basis by redirecting the laser beam of the existing divertor Thomson system inboard - beneath the lower floor using a moveable, high-damage threshold, in-vacuum mirror - and then redirecting again vertically. The currently measured divertor region remains available with this mirror retracted. Scattered light is collected from viewchords near the divertor floor using in-vacuum, high temperature optical elements and relayed through the port window, before being coupled into optical fiber bundles. At higher elevations from the floor, measurements are made by dynamically re-focusing the existing divertor system collection optics. Nd:YAG laser timing, analysis of the scattered light spectrum via polychromators, data acquisition, and calibration are all handled by existing systems or methods of the current multi-pulse Thomson scattering system. Existing filtered polychromators with 7 spectral channels are employed to provide maximum measurement breadth (Te in the range of 0.5 eV-2 keV, ne in the range of 5 × 1018-1 × 1021 m3) for both low Te in detachment and high Te measurement up beyond the separatrix.

Field reversed configuration confinement enhancement through edge biasing and neutral beam injection.

Field reversed configurations (FRCs) with high confinement are obtained in the C-2 device by combining plasma gun edge biasing and neutral beam injection. The plasma gun creates an inward radial electric field that counters the usual FRC spin-up. The n = 2 rotational instability is stabilized without applying quadrupole magnetic fields. The FRCs are nearly axisymmetric, which enables fast ion confinement. The plasma gun also produces E × B shear in the FRC edge layer, which may explain the observed improved particle transport. The FRC confinement times are improved by factors 2 to 4, and the plasma lifetimes are extended from 1 to up to 4 ms.

Differences in zinc status and the leptin axis in anorexic and recovered adolescents and young adults: a pilot study.

BACKGROUND: Evidence from animal studies suggests that leptin metabolism is associated with zinc (Zn) status. However, research investigating this relationship in adolescents and young adults with anorexia nervosa (AN) is scarce; the present study aims to fill that gap. METHODS: Serum concentrations of leptin, the soluble leptin receptor (sOB-R) and the free leptin index (FLI) were obtained in healthy control subjects (n=19), acutely ill individuals (n=14) and recovered patients with AN (n=15). Serum Zn concentrations noted in previous research data were also incorporated for all groups. RESULTS: Leptin, FLI and Zn concentrations were higher in recovered subjects with AN when compared with acutely ill AN patients. Remitted patients showed higher sOB-R concentrations but no difference in FLI compared with the control group. Leptin and FLI were lower in the acutely ill patients compared with the control subjects, who showed no differences in Zn concentrations. Zn concentrations were not correlated with leptin, sOB-R or FLI concentrations in any of the three investigated subgroups. CONCLUSIONS: The present investigation does not entirely support an association between Zn, Leptin and FLI concentrations in subjects with AN, possibly due to limited statistical power. Further research and replication of the present findings related to the interaction between leptin and Zn is warranted. However, with respect to serum leptin levels the data of the present investigation indicate that acutely ill and remitted patients with AN differ as regards serum leptin concentrations and FLI, which is in line with previous research.

Randomized controlled trial of ultrasonic dissection versus standard surgical technique in open left hemicolectomy or total gastrectomy.

BACKGROUND: Ultrasonic dissection devices have been designed for use in open surgery but it is not certain how they compare with standard surgical techniques. METHODS: This was a multicentre randomized controlled trial comparing ultrasonic dissection with the traditional surgical technique for haemostasis and dissection during left hemicolectomy and total gastrectomy. The primary endpoint was duration of operation; secondary endpoints were blood loss and other intraoperative parameters, and patient outcomes. Performance of the two techniques was rated by surgeons and assistants on a ten-point Likert scale. RESULTS: The analysis included 100 patients in the ultrasonic and 101 in the conventional dissection group. Patient demographics, and clinical and tumour-related parameters were similar in the two groups. There was no significant difference in duration of operation (mean 170 and 178 min in ultrasonic and conventional groups respectively; P = 0·405). Nor were there significant differences in intraoperative blood loss (median 350 and 400 ml respectively; P = 0·882), other intraoperative parameters, oncological or functional outcome. The ultrasonic dissector device was rated one point higher than conventional techniques by the surgeons. CONCLUSION: Use of the ultrasonic dissector in open total gastrectomy and hemicolectomy had no impact on the overall operating time or other endpoints studied. Surgeons preferred the ultrasonic device for dissection.

Development of a nine spatial point, multipulse Thomson scattering diagnostic.

A Thomson scattering diagnostic has been developed for the C-2 field-reversed configuration device. Based on a multipulse ruby laser, the system measures the electron temperature at nine spatial points. These points are chosen from 22 selectable positions covering r≈1-41 cm. Twin collection lenses couple the scattered photons to nine optical fiber pairs. Extra fiber lengths delay the signals from different spatial points relative to each other, allowing up to three points to be analyzed by a single polychromator. The polychromator, using compact photomultipliers as detectors, has six spectral channels covering the range of 685-725 nm and is able to estimate electron temperatures of ≈10-200 eV. The photomultiplier output signals are recorded by digital storage oscilloscopes integrated with the main MDSplus database, with temperature and error estimates generated automatically at the conclusion of each plasma discharge.

Dynamic formation of a hot field reversed configuration with improved confinement by supersonic merging of two colliding high-ß compact toroids.

A hot stable field-reversed configuration (FRC) has been produced in the C-2 experiment by colliding and merging two high-ß plasmoids preformed by the dynamic version of field-reversed θ-pinch technology. The merging process exhibits the highest poloidal flux amplification obtained in a magnetic confinement system (over tenfold increase). Most of the kinetic energy is converted into thermal energy with total temperature (T{i}+T{e}) exceeding 0.5 keV. The final FRC state exhibits a record FRC lifetime with flux confinement approaching classical values. These findings should have significant implications for fusion research and the physics of magnetic reconnection.

Sentinel lymph node biopsy for melanoma: controversy despite widespread agreement.

Although sentinel lymph node (SLN) biopsy for melanoma has been adopted throughout the United States and abroad as a standard method of determining the pathologic status of the regional lymph nodes, some controversy still exists regarding the validity and utility of this procedure. SLN biopsy is a minimally invasive procedure, performed on an outpatient basis at the time of wide local excision of the melanoma, with little morbidity. Numerous studies have documented the accuracy of this procedure for identifying nodal metastases. There are four major reasons to perform SLN biopsy. First, SLN biopsy improves the accuracy of staging and provides valuable prognostic information for patients and physicians to guide subsequent treatment decisions. Second, SLN biopsy facilitates early therapeutic lymph node dissection for those patients with nodal metastases. Third, SLN biopsy identifies patients who are candidates for adjuvant therapy with interferon alfa-2b. Fourth, SLN biopsy identifies homogeneous patient populations for entry onto clinical trials of novel adjuvant therapy agents. Overall, the benefit of accurate nodal staging obtained by SLN biopsy far outweighs the risks and has important implications for patient management.

Cutaneous lymphatic drainage in patients with grossly involved nodal basins.

BACKGROUND: The development of lymphatic mapping techniques has facilitated the identification of the sentinel lymph node (SLN), the first node in the regional basin into which cutaneous lymphatics flow from a particular skin area. Previous studies have shown that SLN histology reflects the histology of the entire basin, because melanoma metastases progress in an orderly fashion, involving the SLN before higher nodes in the basin become involved with metastatic disease. It is uncertain whether these orderly cutaneous lymphatic flow patterns are maintained in grossly involved basins. Lymphatic mapping was performed in a population of melanoma patients with clinically palpable lymphadenopathy to address this question. We aimed to determine whether the presence of gross nodal disease in the basin alters lymphatic flow into that basin so that lymphatic mapping techniques are not applicable, and, in patients referred with a grossly involved basin, whether preoperative lymphoscintigraphy should be performed to identify other regional basins at risk for metastases. METHODS: Eight patients presented with grossly palpable disease in the regional basin and underwent preoperative lymphoscintigraphy. All patients with palpable disease and all basins indicated by lymphoscintigraphy to be at risk were dissected. Three patients presented with clinically palpable nodes at the time of diagnosis, and five developed nodal disease on clinical follow-up after undergoing initial wide local excision only. A total of 10 basins in the eight patients were dissected. Of these, eight of the basins had grossly palpable regional nodal disease, and the other two basins were identified by preoperative lymphoscintigraphy as being at risk for metastases. The SLN was identified with intraoperative mapping, harvested, and submitted to pathology. Complete therapeutic lymph node dissections were performed following the SLN harvest in the basins with grossly palpable disease. SLN biopsy alone was performed in the two basins that did not have clinically palpable adenopathy but showed cutaneous lymphatic flow from the scintigram. RESULTS: Sixteen SLNs were harvested from these eight basins with grossly palpable disease, and 14 (87.5%) contained tumor. In each case, one of the SLNs was the grossly palpable node, and in six of the basins (75%) it was the only site of melanoma metastases. An additional 190 higher level, non-SLNs were removed, 32 (16.8%) of which contained microscopic foci of metastatic melanoma (P = .015). The null hypothesis that melanoma nodal metastasis is a random event is rejected. Two patients with trunk melanoma primary sites were identified to have other basins at risk for metastatic disease on lymphoscintigraphy. SLN biopsies were performed in these two patients, and one had microscopic nodal disease in the SLN. CONCLUSIONS: These data support the fact that cutaneous lymphatic drainage patterns are maintained in patients with grossly involved basins, thus buttressing the idea that the SLN is the node most likely to develop metastatic disease. Gross disease in the basin does not significantly alter cutaneous lymphatic flow into the regional basin, as the sentinel lymph node identified under these circumstances is the same as with the grossly involved node. Preoperative lymphoscintigraphy in patients who present with grossly involved nodes in one basin may identify other regional basins with micrometastatic disease and deserves further study in this setting.

Lymphatic mapping and sentinel node biopsy in the management of high-risk melanoma.

We review sentinel lymph node biopsy in patients with high-risk melanoma. This method of selective lymphadenectomy provides valuable staging information about the regional lymphatics without the need of prophylactic complete lymph node dissection. Only patients with micrometastases are candidates for complete lymph node dissection. This avoids, in nearly 85% of patients, the morbidity of the more extensive procedure. In addition, sentinel lymph node-positive patients may qualify for adjuvant therapy protocols. Whether this surgical approach ultimately results in a survival advantage awaits the results of a National Cancer Institute-sponsored national multicenter trial.

Results of complete lymph node dissection in 83 melanoma patients with positive sentinel nodes.

BACKGROUND: The technique of sentinel lymph node (SLN) biopsy for melanoma provides accurate staging information because the histology of the SLN reflects the histology of the entire basin, particularly when the SLN is negative. METHODS: We combined two mapping techniques, one using vital blue dye and the other using radiolymphoscintigraphy with a hand-held gamma Neoprobe, to identify the SLN in 600 consecutive patients with stage I-II melanoma. The SLNs were examined using conventional histopathology and immunohistochemistry for S-100. RESULTS: Eighty-three (13.9%) patients had micrometastatic disease in the SLNs. Thirty percent of patients with primary melanomas greater than 4.0 mm in thickness had positive SLNs, followed by 48 of 267 (18%) of patients with tumors between 1.5 mm and 4 mm, and 12 of 169 (7%) of those with lesions between 1.0 mm and 1.5 mm. No patient with a tumor less than 0.76 mm in thickness had a positive SLN. Sixty-four of the 83 SLN-positive patients consented to undergo complete lymph node dissection (CLND), and five of 64 (7.8%) of the CLNDs were positive. All patients with positive CLNDs had tumor thicknesses greater than 3.0 mm. CONCLUSIONS: The rate of SLN-positive patients increases with increasing thickness of the melanoma. SLN-positive patients with primary lesions less than 1.5 mm in thickness may have disease confined to the SLN, thus rendering higher-level nodes free of disease, and may not require a CLND.

Radioguided surgery for the ultrastaging of the patient with melanoma.

PURPOSE: Lymphatic mapping techniques have changed the standard of surgical care for the malignant melanoma population and are being investigated to improve the staging and decrease the morbidity of patients with all types of cancer. This study aimed to describe a combination of techniques and the use of multiple disciplines for accurately staging and treating patients with melanoma. MATERIALS AND METHODS: Over a 4-year period, 595 patients were studied using a protocol consisting of preoperative lymphoscintigraphy using filtered technetium sulfur colloid to define all regional basins at risk for metastatic disease, and intraoperative lymphatic mapping with a vital blue dye and radiocolloid to identify the node in the basin most at risk for metastases (the sentinel lymph node). Detailed pathological exam (serial sectioning, immunohistochemical staining, reverse transcriptase polymerase chain reaction [RT-PCR] analysis) of the sentinel lymph node was used to stage the melanoma patient. RESULTS: A combination of blue dye and radiocolloid intraoperative mapping resulted in a 98% success rate for the identification of the sentinel lymph node. Routine pathological examination identified 73.8% of the metastases. The remainder were detected with serial sectioning (7.8%) and immunohistochemical staining (18.4%). RT-PCR analysis based on a tyrosinase probe has upstaged 47% of the histologic sentinel lymph node-negative population. CONCLUSION: Lymphatic mapping technology provides accurate staging of the melanoma patient, at lower costs for the health care system and a lower morbidity for the patient.