Ultrafast Laser-Induced Melting of Long-Range Magnetic Order in Multiferroic TbMnO3

We performed ultrafast time-resolved near-infrared pump, resonant soft X-ray diffraction probe measurements to investigate the coupling between the photoexcited electronic system and the spin cycloid magnetic order in multiferroic TbMnO3 at low temperatures. We observe melting of the long range antiferromagnetic order at low excitation fluences with a decay time constant of 22.3 +- 1.1 ps, which is much slower than the ~1 ps melting times previously observed in other systems. To explain the data we propose a simple model of the melting process where the pump laser pulse directly excites the electronic system, which then leads to an increase in the effective temperature of the spin system via a slower relaxation mechanism. Despite this apparent increase in the effective spin temperature, we do not observe changes in the wavevector q of the antiferromagnetic spin order that would typically correlate with an increase in temperature under equilibrium conditions. We suggest that this behavior results from the extremely low magnon group velocity that hinders a change in the spin-spiral wavevector on these time scales.Comment: 9 pages, 4 figure

Analysis of the technical capabilities of DOE sites for disposal of residuals from the treatment of mixed low-level waste

The US Department of Energy (DOE) has stored or expects to generate over the next five years more than 130,000 m{sup 3} of mixed low-level waste (MLLW). Before disposal, MLLW is usually treated to comply with the land disposal restrictions of the Resource Conservation and Recovery Act. Depending on the type of treatment, the original volume of MLLW and the radionuclide concentrations in the waste streams may change. These changes must be taken into account in determining the necessary disposal capacity at a site. Treatment may remove the characteristic in some waste that caused it to be classified as mixed. Treatment of some waste may, by reduction of the mass, increase the concentrations of some transuranic radionuclides sufficiently so that it becomes transuranic waste. In this report, the DOE MLLW streams were analyzed to determine after-treatment volumes and radionuclide concentrations. The waste streams were reclassified as residual MLLW or low-level or transuranic waste resulting from treatment. The volume analysis indicated that about 89,000 m{sup 3} of waste will require disposal as residual MLLW. Fifteen DOE sites were then evaluated to determine their capabilities for hosting disposal facilities for some or all of the residual MLLW. Waste streams associated with about 90% of the total residual MLLW volume are likely to present no significant issues for disposal and require little additional analysis. Future studies should focus on the remaining waste streams that are potentially problematic by examining site-specific waste acceptance criteria, alternative treatment processes, alternative waste forms for disposal, and pending changes in regulatory requirements

Ultrafast Pump / Probe Diffraction and Spectroscopy Experiments with FEL Radiation: Setup Development from the Soft to the Hard X-rays with the Aim of Studying Chemical Processes,

We developed a multipurpose vacuum chamber which function is to be used in the pump/probe diffraction / scattering and spectroscopy experiments with free electron laser (FEL) radiation. By using a liquid jet setup to deliver the sample into the chamber it is possible to overcome the difficulties coming from the fact that a single shot of the FEL radiation is sufficient to induce irreversible damage to the sample. The refreshment of the sample allows for the experiments with the repetition rate of up to the MHz regime. The liquid jet nozzle size will be in the sub-micrometer range. This multipurpose chamber is in particular suited for chemistry and biochemistry experiments in solution

ANDECS: A Computation Environment for Control Applications of Optimization

Control Applications of Optimization can be seen under the perspective of mathematical control synthesis and under the perspective of engineering control design

Spatial and temporal pre-alignment of an X-ray split-and-delay unit by laser light interferometry

We present a novel experimental setup for performing a precise pre-alignment of a hard X-ray split-and-delay unit based on low coherence light interferometry and high-precision penta-prisms. A split-and-delay unit is a sophisticated perfect crystal-optics device that splits an incoming X-ray pulse into two sub-pulses and generates a controlled time-delay between them. While the availability of a split-and-delay system will make ultrafast time-correlation and X-ray pump-probe experiments possible at free-electron lasers, its alignment process can be very tedious and time-consuming due to its complex construction. By implementing our experimental setup at beamline P10 of PETRA III, we were able to reduce the time of alignment to less than 3 h. We also propose an alternate method for finding the zero-time delay crossing without the use of X-rays or pulsed laser sources. The successful demonstration of this method brings prospect for operating the split-and-delay systems under alignment-time-critical environments such as X-ray free electron laser facilities

Sliding-Induced Decoupling and Charge Transfer between the Coexisting Q1 and Q2 Charge Density Waves in NbSe3

International audienceUsing high-resolution x-ray scattering in the presence of an applied current, we report evidence for a dynamical decoupling between the two NbSe3 charge-density waves (CDWs), Q1 (TC1 = 145 K) and Q2 (TC2 = 59 K), coexisting below TC2. Simultaneous and oppositely directed shifts of the relevant CDW superlattice spots develop above a threshold current which we identify as the depinning threshold IC1 for the more strongly pinned upper CDW Q1 (IC1~10IC2). In contrast with shifts induced by current conversion processes, the present effect is not current polarized and is not limited to the current-contact regions. We propose a model which explains this instability through a sliding-induced charge transfer between the two electronic reservoirs corresponding to the Q1 and Q2 CDWs