Tomi Tuohimaa

Phase-contrast x-ray imaging with a liquid-metal-jet-anode microfocus source

Phase-contrast methods increase contrast, detail, and selectivity in x-ray imaging. Present compact x-ray sources do not provide the necessary spatial coherence with sufficient power to allow the laboratory-scale high-resolution phase-contrast imaging with adequate exposure times. In this letter, the authors demonstrate phase-contrast imaging with few-micron detail employing a compact ∼6.5μm spot liquid-metal-jet-anode high-brightness microfocus source. The 40W source is operated at more than ten times higher electron-beam power density than present microfocus sources and is shown to provide sufficient spatial coherence as well as scalability to high power, thereby enabling the application of phase-contrast x-ray imaging with short exposure times in clinics and laboratories.

A 9 keV electron-impact liquid-gallium-jet x-ray source

We demonstrate a high-brightness compact 9 keV electron-impact microfocus x-ray source based on a liquid-gallium-jet anode. A approximately 30 W, 50 kV electron gun is focused onto the approximately 20 ms, 30 mum diameter liquid-gallium-jet anode to produce an approximately 10 microm full width at half maximum x-ray spot. The peak spectral brightness is >2 x 10(10) photons(s mm(2) mrad(2)x0.1% BW). Calculation and experiments show potential for increasing this brightness by approximately three orders of magnitude, making the source suitable for laboratory-scale x-ray crystallography and hard x-ray microscopy.

Single-optical-element soft-x-ray interferometry with a laser-plasma x-ray source

We report on a compact interferometer for the water-window soft-x-ray range that is suitable for operation with laser-plasma sources. The interferometer consists of a single diffractive optical element that focuses impinging x rays to two focal spots. The light from these two secondary sources forms the interference pattern. The interferometer was operated with a liquid-nitrogen jet laser-plasma source at lambda=2.88 nm. Scalar wave-field propagation was used to simulate the interference pattern, showing good correspondence between theoretical and experimental results. The diffractive optical element can simultaneously be used as an imaging optic, and we demonstrate soft-x-ray microscopy with interferometric contrast enhancement of a phase object.

Force generation in small ensembles of Brownian motors

The motility of certain gram-negative bacteria is mediated by retraction of type IV pili surface filaments, which are essential for infectivity. The retraction is powered by a strong molecular motor protein, PilT, producing very high forces that can exceed 150 pN. The molecular details of the motor mechanism are still largely unknown, while other features have been identified, such as the ring-shaped protein structure of the PilT motor. The surprisingly high forces generated by the PilT system motivate a model investigation of the generation of large forces in molecular motors. We propose a simple model, involving a small ensemble of motor subunits interacting through the deformations on a circular backbone with finite stiffness. The model describes the motor subunits in terms of diffusing particles in an asymmetric, time-dependent binding potential (flashing ratchet potential), roughly corresponding to the ATP hydrolysis cycle. We compute force-velocity relations in a subset of the parameter space and explore how the maximum force (stall force) is determined by stiffness, binding strength, ensemble size, and degree of asymmetry. We identify two qualitatively different regimes of operation depending on the relation between ensemble size and asymmetry. In the transition between these two regimes, the stall force depends nonlinearly on the number of motor subunits. Compared to its constituents without interactions, we find higher efficiency and qualitatively different force-velocity relations. The model captures several of the qualitative features obtained in experiments on pilus retraction forces, such as roughly constant velocity at low applied forces and insensitivity in the stall force to changes in the ATP concentration.

Stability and debris in high-brightness liquid-metal-jet-anode microfocus x-ray sources

We investigate the x-ray spot stability and the debris emission in liquid-metal-jet anode electron-impact x-ray sources operating in the 10-100 W microfocus regime. The x-ray spot size is 15-23 mu ...

Liquid-metal-jet x-ray tube technology and tomography applications

The power and brightness of electron-impact micro-focus X-ray sources have long been limited by thermal damage in the anode. Here we describe a novel X-ray microfocus source based on a new anode concept, the liquid-metal-jet anode (MetalJet). The regenerative nature of this anode allows for significantly higher e-beam power density than on conventional anodes, resulting in this source generating significantly higher brightness than other X-ray tubes in the microfocus regime (~5-50 μm). We describe the fundamental properties of the technology and will review the current status specifically in terms of spot size, stability, lifetime, flux, acceleration voltage and brightness.

Laboratory x-ray micro imaging: Sources, optics, systems and applications

We summarize the recent progress in laboratory-scale soft and hard x-ray micro imaging in Stockholm. Our soft x-ray work is based on liquid-jet laser-plasma sources which are combined with diffractive and multilayer optics to form laboratory x-ray microscopes. In the hard x-ray regime the imaging is based on a liquid-metal-jet electron-impact source which provides the necessary coherence to allow phase-contrast imaging with high fidelity.

A microfocus x-ray source based on a nonmetal liquid-jet anode

We demonstrate stable operation of a nonmetallic anode in an electron-impact x-ray source. A high-brightness electron beam is focused on a ∼70m∕s speed, ∼10μm diameter methanol jet producing stable x-ray emission with peak spectral brightness at ∼5.4×105photons∕(s×μm2×sr×0.1%BW). The jet is fully evaporated in the interaction point. The shape of a simulated spectrum using Monte Carlo methods shows good agreement with experimental data, and the theoretical brightness values give an upper limit for the achievable x-ray emission from jets with very high velocities. Using this anode concept, all compounds and elements found in liquid form are potentially usable for x-ray generation.

Status of the liquid-metal-jet-anode electron-impact x-ray source

We have demonstrated a new electron-impact hard-x-ray source based on a liquid-metal-jet anode in a proof-of-principle experiment. Initial calculations show that this new anode concept potentially allows a >100x increase in source brightness compared to todays compact hard-x-ray sources. In this paper we report on the scale up of the system to medium electron-beam power resulting in a brightness comparable to current state-of-the-art sources. The upgraded system combines a ~20-μm diameter liquid-tin jet operating at ~60 m/s with a 50 kV, 600 W electron beam focused to ~150 μm FWHM. We describe the properties of the current system, experimental results, as well as a brief discussion of key issues for future high-power scaling.

High-intensity electron beam for liquid-metal-jet anode hard x-ray generation

We report on our progress towards the experimental realization of a liquid-metal-jet-anode x-ray source with high brightness. We have previously shown that this electron-impact source has potential for very high x-ray brightness by combining small-spot high-flux operation of the electron beam with high-speed operation of the regenerative liquid-metal-jet anode. In the present paper we review the system and describe theoretical calculations for improving the 50 kV, 600 W electron-beam focussing to ~30 μm spot size. With such a system the power density on the liquid-metal-jet would be ~400 kW/mm2, i.e., more than an order of magnitude higher than the power density on a state-of-the-art rotating anode.