Observation of self-generated flows in tokamak plasmas with lower-hybrid-driven current.

In Alcator C-Mod discharges lower hybrid waves have been shown to induce a countercurrent change in toroidal rotation of up to 60 km/s in the central region of the plasma (r/a approximately <0.4). This modification of the toroidal rotation profile develops on a time scale comparable to the current redistribution time (approximately 100 ms) but longer than the energy and momentum confinement times (approximately 20 ms). A comparison of the co- and countercurrent injected waves indicates that current drive (as opposed to heating) is responsible for the rotation profile modifications. Furthermore, the changes in central rotation velocity induced by lower hybrid current drive (LHCD) are well correlated with changes in normalized internal inductance. The application of LHCD has been shown to generate sheared rotation profiles and a negative increment in the radial electric field profile consistent with a fast electron pinch.

Spatially resolved high resolution x-ray spectroscopy for magnetically confined fusion plasmas (invited).

The use of high resolution x-ray crystal spectrometers to diagnose fusion plasmas has been limited by the poor spatial localization associated with chord integrated measurements. Taking advantage of a new x-ray imaging spectrometer concept [M. Bitter et al., Rev. Sci. Instrum. 75, 3660 (2004)], and improvements in x-ray detector technology [Ch. Broennimann et al., J. Synchrotron Radiat. 13, 120 (2006)], a spatially resolving high resolution x-ray spectrometer has been built and installed on the Alcator C-Mod tokamak. This instrument utilizes a spherically bent quartz crystal and a set of two dimensional x-ray detectors arranged in the Johann configuration [H. H. Johann, Z. Phys. 69, 185 (1931)] to image the entire plasma cross section with a spatial resolution of about 1 cm. The spectrometer was designed to measure line emission from H-like and He-like argon in the wavelength range 3.7 and 4.0 A with a resolving power of approximately 10,000 at frame rates up to 200 Hz. Using spectral tomographic techniques [I. Condrea, Phys. Plasmas 11, 2427 (2004)] the line integrated spectra can be inverted to infer profiles of impurity emissivity, velocity, and temperature. From these quantities it is then possible to calculate impurity density and electron temperature profiles. An overview of the instrument, analysis techniques, and example profiles are presented.

A spatially resolving x-ray crystal spectrometer for measurement of ion-temperature and rotation-velocity profiles on the Alcator C-Mod tokamak.

A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra (lambda/d lambda>6000) of He-like and H-like Ar K alpha lines with good spatial (approximately 1 cm) and temporal (approximately 10 ms) resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic inversion enables inference of local line emissivity, ion temperature (T(i)), and toroidal plasma rotation velocity (upsilon(phi)) from the line Doppler widths and shifts. The data analysis techniques, T(i) and upsilon(phi) profiles, analysis of fusion-neutron background, and predictions of performance on other tokamaks, including ITER, will be presented.

Wide-angle point-to-point x-ray imaging with almost arbitrarily large angles of incidence.

The paper describes a new scheme for wide-angle point-to-point x-ray imaging with almost arbitrarily large angles of incidence by a matched pair of spherically bent crystals to eliminate the astigmatism, which is a well-known imaging error of spherical mirrors. In addition to x rays, the scheme should be applicable to a very broad spectrum of the electromagnetic radiation, including microwaves, infrared and visible light, as well as UV and extreme UV radiation, if the crystals are replaced with appropriate spherical reflectors. The scheme may also be applicable to the imaging with ultrasound.

Observation of ion-cyclotron-frequency mode-conversion flow drive in tokamak plasmas.

Strong toroidal flow (Vphi) and poloidal flow (Vtheta) have been observed in D-3He plasmas with ion cyclotron range of frequencies (ICRF) mode-conversion (MC) heating on the Alcator C-Mod tokamak. The toroidal flow scales with the rf power Prf (up to 30 km/s per MW), and is significantly larger than that in ICRF minority heated plasmas at the same rf power or stored energy. The central Vphi responds to Prf faster than the outer regions, and the Vphi(r) profile is broadly peaked for r/a < or =0.5. Localized (0.3 < or = r/a < or =0.5) Vtheta appears when Prf > or =1.5 MW and increases with power (up to 0.7 km/s per MW). The experimental evidence together with numerical wave modeling suggests a local flow drive source due to the interaction between the MC ion cyclotron wave and 3He ions.

Genomic organization and regulation of the vav proto-oncogene.

Vav and vav2 are members of the dbl family of guanine nucleotide exchange factors (GEF) for the rho/rac family of GTP binding proteins. Vav is expressed primarily in hematopoietic cells, while vav2 has a wider tissue distribution. The genomic structure of the human vav proto-oncogene was studied by identifying and sequencing all 27 exons of the gene from overlapping P1 and cosmid clones. The gene spans a 77-kb region on chromosome 19. In contrast, the coding region of vav2 is distributed over 30 exons spanning 227-kb. The overall organization of the exons which encode both proteins was found to be similar. In humans, alternative splicing of exons 6, 16 and 28 generated at least two distinct vav2 mRNA species. Several differences from the original vav cDNA sequence were noted. The most important difference was the identification of amino acid 718 as isoleucine, rather than threonine. This change warrants the reclassification of the vav SH2 domain as a type 3 SH2, instead of a type 2 SH2 as originally proposed by Songyang et al. (Mol. Cell. Biol. 14 (1994) 2777-2785). A series of vav promoter deletions were constructed using the enhanced green fluorescent protein (EGFP) as a reporter gene. A 23-bp segment that included a potential CBF/AML-1 binding site was found to be essential for EGFP expression in U937 cells. The same constructs were not active in HeLa cells, which do not express vav. A potential c-myb DNA binding site within the vav promoter was not required for EGFP expression.

Systemic candidiasis and endophthalmitis in neurosurgical patients. Report of three cases.

Three cases of systemic candidiasis in neurosurgical patients are presented. Two of the three patients also had endophthalmitis. All of the cases were treated with broad-spectrum antibiotics and glucocorticoids prior to the appearance of candidiasis. The authors stress the high susceptibility of neurosurgical patients to opportunistic infections of this type.