Search Results - (Author, Cooperation:D. A. Hammer)

2014-07-18

Nature Publishing Group (NPG)

0028-0836

1476-4687

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Animals ; Breast/cytology/metabolism/pathology ; Cell Line, Tumor ; Cell Proliferation ; Cell Survival ; Fibroblasts ; Glycocalyx/chemistry/*metabolism ; Glycoproteins/*metabolism ; Humans ; Immobilized Proteins/chemistry/metabolism ; Integrins/chemistry/*metabolism ; Mice ; Molecular Targeted Therapy ; Mucin-1/metabolism ; Neoplasm Metastasis/pathology ; Neoplasms/*metabolism/*pathology ; Neoplastic Cells, Circulating ; Protein Binding ; Receptors, Cell Surface

1089-7550

AIP Digital Archive

Physics

A novel intense source of 2.45 MeV neutrons is described. Exploratory experiments with deuterated polyethylene fibers in an x-pinch configuration have been performed using 370-kA, 80-ns current pulses. Up to 4.5×108 neutrons per pulse have been produced. Compared to a z pinch, an x pinch produced about the same number of neutrons for the same current, but the x-pinch neutron source may be 1 mm or less in diameter.

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1089-7550

AIP Digital Archive

Physics

We report results from experiments performed to measure and characterize the intense K-shell radiation from aluminum x-pinch plasmas at peak driving currents ranging from 280 kA to 1.0 MA. Single pulse aluminum K-shell (predominantly line radiation at 1.6–2 keV) x-ray yields ranged from 7.6 J at 290 kA to 240 J at 1.0 MA. In the range from 280 to 470 kA, the yield scales with current to the power of 3.6, whereas nonoptimized K-shell yields at 800 kA and 1.0 MA indicate a power of about 3 or higher.

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1089-7674

AIP Digital Archive

Physics

Bright, ∼1 μm x-ray sources (micropinches) produced within exploding wire X pinches are found to be near solid density and ∼1 keV electron temperature. For example, with a Ti X pinch, a 90 ps lifetime, 1.5–1.8 keV electron temperature, ∼1023/cm3 electron density plasma was observed. These plasma characteristics were determined using time-resolved x-ray spectra produced by 2- and 4-wire X pinches and collected by an x-ray streak camera with 〈10 ps time resolution. Together with a spherically bent mica crystal spectrograph, the streak camera recorded the 1–10 keV radiation emitted from X pinches made from different wire materials. Some spectra were dominated by continuum and others by line radiation. Spectral features varied on time scales ranging from 10 to 300 ps, depending on the wire material. Results are presented that demonstrate the necessity of time-resolved data for determining plasma conditions from micropinch x-ray spectra. © 2002 American Institute of Physics.

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1089-7674

AIP Digital Archive

Physics

Wire-array Z-pinch implosion experiments begin with wire heating, explosion, and plasma formation phases that are driven by an initial 50–100 ns, 0–1 kA/wire portion of the current pulse. This paper presents expansion rates for the dense, exploding wire cores for several wire materials under these conditions, with and without insulating coatings, and shows that these rates are related to the energy deposition prior to plasma formation around the wire. The most rapid and uniform expansion occurs for wires in which the initial energy deposition is a substantial fraction of the energy required to completely vaporize the wire. Conversely, wire materials with less energy deposition relative to the vaporization energy show complex internal structure and the slowest, most nonuniform expansion. This paper also presents calibrated radial density profiles for some Ag wire explosions, and structural details present in some wire explosions, such as foam-like appearance, stratified layers and gaps. © 2001 American Institute of Physics.

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1089-7674

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Physics

Substantial increases are reported in the expansion rates of exploding, dense wire cores under conditions simulating the prepulse phase of wire array z-pinch experiments [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] using wires with insulating coatings. The insulation apparently allows additional wire heating by delaying the formation of plasma around the wires. Once plasma is formed it terminates significant current flow in the residual wire cores. This effect is demonstrated for 25-μm diameter W and 25-μm diameter Ag wires. © 2000 American Institute of Physics.

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1089-7674

AIP Digital Archive

Physics

The dynamics of the dense plasma near the cross point of an X pinch has been investigated using 1 ns x-ray backlighting images at different moments relative to the start of 100 ns [full width at half maximum (FWHM)] 200 kA current pulses. If the two metal wires are fine enough (e.g., 10 μm W or 17.5 μm Mo) to form a pinch at the cross point, accompanied by an x-ray burst, with the available current pulse, then the images show three stages of development: a radial explosion/expansion phase; an implosion during which a dense Z pinch of 200–300 μm length forms at the cross point together with plasma jets which move axially away from that point; and a breaking up of the Z pinch, coincident in time with one or two x-ray bursts, after which a 300 μm gap opens up. For W, the backlighter minimum sensitivity is 1017/cm2 areal density, and the dense Z pinch is estimated to have a volume density close to 1021/cm3. Shock waves appear to be expanding at about 50 μm/ns from the end points of the collapsing Z pinch, where the plasma was the most dense. © 1999 American Institute of Physics.

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1089-7674

AIP Digital Archive

Physics

X-ray backlighter images (radiographs) of current-induced explosions of 12.7–25 μm diam Al wires have been used to determine the expansion rate and internal structure of the dense wire cores. The current rises to 1–4.5 kA per wire in 350 ns, but voltage and current measurements show that the energy driving the explosion is deposited resistively during the first 40–50 ns, when the current is only a few hundred amperes per wire. A voltage collapse then occurs as a result of plasma formation around the wire, effectively terminating the energy deposition in the wire core. High-resolution radiographs obtained over the next 150–200 ns show the expanding wire cores to have significant axial stratification and foamlike structures with ∼10 μm scale lengths over most of the wire length before they disappear in the expansion process. The expansion rate of the portion of the wire cores that is dense enough to be detected by radiography is 1.4–2 μm/ns commencing approximately 25 ns after the moment of the voltage collapse. (The sensitivity limit is equivalent to 0.2 μm of solid density Al.) By 250 ns after the start of the current pulse, the detectable wire core diameter is 250 μm, but it contains only about 30% of the initial wire material. © 2000 American Institute of Physics.

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1089-7674

AIP Digital Archive

Physics

Experimental results are presented from studies of the dynamics of X-pinch plasmas, formed using two fine wires that cross and touch at a single point (in the form of an X) as the load of a high current pulser. High-resolution (sub-ns in time and 2–3 μm in space) x-ray radiographs of X pinches driven by current pulses that rise to 200–250 kA peak current in 40 ns show that ≤300 μm long Z pinches form in the region of the original wire cross-point a few ns prior to the first sub-ns intense x-ray bursts that are characteristic of an X pinch. The Z pinches implode to ≤10 μm diam and then appear to develop gaps in the radiographic images in one or two places, coincident in time with the x-ray burst(s). The emission spectra of the intense x-ray bursts from different wire materials indicate electron temperatures of 500–1300 eV and densities in excess of 1022/cm3. © 2001 American Institute of Physics.

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1089-7674

AIP Digital Archive

Physics

Calibrated density measurements have been obtained of the coronal plasmas around exploding 7.5–40 μm W wires carrying 15–120 kA per wire for 30–70 ns. X-ray radiographs of the exploding wire plasmas using 2.5–10 keV photons from a Mo wire X-pinch backlighter enabled measurements of areal densities of W ranging from 2×1017/cm2, equivalent to 0.03 μm of solid density W, to about 1019/cm2. The rapidly expanding (few mm/μs) coronal plasmas surrounding the slowly expanding (〈1 mm/μs) residual wire cores have areal densities up to about 2×1018/cm2. Single 7.5 μm wires tested with 100 kA had as much as 90% of the initial wire material in the coronal plasma. Coronal plasma W number densities were estimated to be up to a few times 1018/cm3, while core W densities as low as a few times 1020/cm3 were observed. With linear arrays of four (eight) 7.5 μm wires carrying 30 kA (15 kA)/wire, up to 35% (25%) of the initial W wire material was in the plasma around and between the wires at 46–48 ns after the current started. Preheating the wires to drive off adsorbed gases and hydrocarbons increased the W mass in the coronal plasma and made it more uniform then when wires were not preheated. © 1999 American Institute of Physics.

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1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A new laser-driven atomic-probe-beam diagnostic (LAD) is proposed for local, time-resolved measurements of electric field and ion dynamics in the accelerating gap of intense ion beam diodes. LAD adds new features to previous Stark-shift diagnostics which have been progressively developed in several laboratories, from passive observation of Stark effect on ion species or fast (charge-exchanged) neutrals present naturally in diodes, to active Stark atomic spectroscopy (ASAS) in which selected probe atoms were injected into the gap and excited to suitable states by resonant laser radiation. The LAD scheme is a further enhancement of ASAS in which the probe atoms are also used as a local (laser-ionized) ion source at an instant of time. Analysis of the ion energy and angular distribution after leaving the gap enables measurement, at the chosen ionization location in the gap, of both electrostatic potential and the development of ion divergence. Calculations show that all of these quantities can be measured with sub-mm and ns resolution. Using lithium or sodium probe atoms, fields from 0.1 to 10 MV/cm can be measured. © 2000 American Institute of Physics.

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1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Virtually all practical applications for intense ion beams require that the beam pulses be generated at high repetition rates. This paper reports the development of the first high pulse rate, long-lived ion beam diode. It is a magnetically insulated diode which has produced ∼75 keV proton and carbon beam pulses of 1.0–2.5 A/cm2 and 100 ns duration at up to 90 Hz in four pulse bursts. It has also produced 125 keV, 5 A/cm2 Ar beams at a steady 1 pulse per 30 s for over 1000 pulses between failures in many runs. This diode employs a magnetically confined anode plasma ion source, and the high repetition rate pulsed power systems are based upon saturable magnetic switching. © 1995 American Institute of Physics.

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1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A new type of shearing interferometer using an air wedge is described. This interferometer is based on a beam splitter constructed using two 90-degree prisms. A small air gap, which varies in spacing from top-to-bottom, separates the second prism from the first and forms the air wedge. The single incident laser beam is focused near the gap, and the two primary reflections from the long sides of each prism form the two coherent virtual sources necessary for interferometry. The shift between the two images of the object at the detector, as well as the orientation and frequency of the fringes, can be independently adjusted by altering the air gap thickness and angle, as well as the position of the laser focus in the gap. This interferometry scheme is inexpensive and easily aligned, and has been successfully and reliably used in exploding wire experiments. © 2001 American Institute of Physics.

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1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Using an X pinch as a source of radiation for point-projection radiography, it is possible to project a high-resolution (1–10 μm) shadow image of dense plasma or test objects onto x-ray-sensitive film. The emission characteristics of X pinches composed of a wide variety of materials have been studied using several diagnostics. The pulse duration and shape of the x-ray bursts were measured in the 1.5–6 keV band using fast diamond PCDs and an x-ray streak camera with sweep speeds as fast as 10 ns for the full sweep (3.5 cm). To investigate the line and continuum radiation emitted by the X pinches, a convex spectrograph using a mica or KAP crystal, and a spectrograph based on a spherically bent mica crystal were used. Summarizing the data, including radiography results, wires known to have slower expansion rates and high boiling temperatures (NiCr, Ti, Nb, Mo, Pd, Ta, W, and Pt) appeared to yield the smallest x-ray source sizes, i.e., gave the best spatial resolution in radiographs and provided subnanosecond time resolution. All of these materials yield intense continuum radiation with energy up to 6 keV, and the highest resolution images are achieved using only the continuum radiation from the X pinch. © 2001 American Institute of Physics.

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1089-7623

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Physics

Electrical Engineering, Measurement and Control Technology

The fine metal wire x-pinch is a compact source of soft-x-ray emission. Under certain conditions, x rays in the 3–7 keV range are emitted in 〈1 ns bursts from source regions that are 〈10 μm in size. The small size and high intensity of these 3–7 keV sources makes the x-pinch useful as a point source for x-ray backlighting. This capability has been demonstrated by using an x-pinch to produce radiographic images of separate x-pinches and z-pinches. © 1995 American Institute of Physics.

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1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A plasma source based on an inductive breakdown of a supersonic gas puff is described. The source was developed to provide an anode plasma for an annular, extraction geometry, magnetically insulated ion diode. In this source, plasmas with densities of 1013 cm−3 were generated and accelerated to velocities of 20–30 cm/μs; plasma fluxes of 10–40 A/cm2 were obtained. Operating the source under the diode insulating field effect, plasma fluxes above 100 A/cm2 were observed. When the plasma source was used in conjunction with a magnetically insulated diode gap, intense ion beams with proton fluxes of more than 100 A/cm2, energies of 100 keV, and beam pulses longer than 1 μs were extracted.

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1077-3118

AIP Digital Archive

Physics

A novel soft x-ray source for submicron resolution lithography is described. Exploratory experiments with the x-pinch dense plasma radiation source have been performed using a 500 kA, 40 ns pulsed power generator. About 33 J of magnesium K-shell radiation (1.3–1.5 keV) and 10 J of aluminum K-shell radiation (1.6–1.7 keV) have been produced in a source approximately 0.5 mm or less in diameter during a single pulse. The yield increased rapidly with current, implying the possibility of exposing a resist at a distance of 40 cm using a〈750 kA pulser in as few as ten pulses.

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1077-3118

AIP Digital Archive

Physics

The electrostatic potential profile in the accelerating gap in a plasma-prefilled magnetically insulated intense pulsed ion beam diode has been determined using laser-induced fluorescence spectroscopy. Results for a 300–400 kV planar diode are presented, both with and without an electron emitting vane protruding from the cathode. In both cases, a 5–6 mm accelerating gap forms in the 1012–1013/cm3 plasma in a few nanoseconds. The experimental potential profiles are not consistent with electrons confined to a sheath near the cathode. Rather, electrons are required throughout the gap to explain the observations.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A weakly diamagnetic rotating proton beam propagating at about four times the Alfvén speed along a magnetized hydrogen plasma column generated magnetosonic waves when the beam rise time was less than about three radial Alfvén transit times. The waves were collisionally damped and the damping increased as the induced cross-field plasma current became stronger. Our beam and plasma conditions suggest that the damping is due to an enhanced collision frequency resulting from a modified two-stream instability.

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1089-7550

AIP Digital Archive

Physics

A recently developed high pulse rate intense ion beam diode has been exploited to measure the relative density profile of electrons in the ion diode's acceleration gap as a function of time. This diode was magnetically insulated and it produced 100 keV Ar+ beams at up to 4 A/cm2 using an active anode plasma ion source. The diode also had a backfill of 10−2 Torr of He that was collisionally excited by energetic electrons in the acceleration gap. When the excited He atoms radiatively decayed, the emitted light was measured and used to deduce the relative electron density profile with space and time resolution. The profile was peaked toward the center of the gap and dropped off significantly toward both the anode and the cathode. The absence of electron density near the physical cathode is evidence for magnetic field profile modification from the diamagnetic drift of the electrons in the diode. With a macroscopic electric field of order 100 kV/cm, the electron current takes many tens of nanoseconds, from the moment the cathode begins to emit, to reach the Child–Langmuir current. The extent to which this limit is exceeded depends strongly on the profile of the insulating magnetic field and appears to be dominated by the dynamics of the electron flow in the diode gap. In contrast, the delay between when electrons are first observed in the gap spectroscopically and when the ion beam is first formed is independent of the magnetic field profile. This delay is about the time that it takes an argon ion to transit the acceleration gap, suggesting that ion inertia is the rate limiting factor. © 1998 American Institute of Physics.

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