Towards Zeptosecond-Scale Pulses from X-Ray Free-Electron Lasers

The short wavelength and high peak power of the present generation of free-electron lasers (FELs) opens the possibility of ultra-short pulses even surpassing the present (tens to hundreds of attoseconds) capabilities of other light sources - but only if x-ray FELs can be made to generate pulses consisting of just a few optical cycles. For hard x-ray operation (~0.1nm), this corresponds to durations of approximately a single attosecond, and below into the zeptosecond scale. This talk will describe a novel method to generate trains of few-cycle pulses, at GW peak powers, from existing x-ray FEL facilities by using a relatively short 'afterburner'. Such pulses would enhance research opportunity in atomic dynamics and push capability towards the investigation of electronic-nuclear and nuclear dynamics. The corresponding multi-colour spectral output, with a bandwidth envelope increased by up to two orders of magnitudes over SASE, also has potential applications.Comment: Submitted to 35th International Free Electron Laser Conference, New York, 201

Start-to-end modelling of a mode-locked optical klystron free electron laser amplifier

A free electron laser (FEL) in a mode-locked optical klystron (MLOK) configuration is modelled using start-to-end simulations that simulate realistic electron beam acceleration and transport before input into a full three-dimensional FEL simulation code. These simulations demonstrate that the MLOK scheme is compatible with the present generation of radiofrequency accelerator designs. A train of few-optical cycle pulses is predicted with peak powers similar to those of the equivalent conventional FEL amplifier. The role of electron beam energy modulation in these results is explained and the limitations of some simulation codes discussed. It is shown how seeding the FEL interaction using a High Harmonic seed laser can improve the coherence properties of the output

Superradiant evolution of radiation pulses in a free-electron laser

We demonstrate analytically and numerically superradiant spiking behavior in the leading and trailing regions of a radiation pulse propagating within a long electron pulse in a single-pass, high-gain free-electron laser (FED). A single superradiant spike is observed when the radiation pulse is shorter than a cooperation length Lc. We show this work may be relevant to the understanding of the spiking behavior in the FEL oscillator, and to possible spiking mechanisms in a perturbed steady-state amplifier

Start to end simulations of the ERL prototype at Daresbury Laboratory

Daresbury Laboratory is currently building an Energy Recovery Linac Prototype (ERLP) that will serve as a research and development facility for the study of beam dynamics and accelerator technology important to the design and construction of the proposed 4th Generation Light Source (4GLS) project. Two major objectives of the ERLP are the demonstration of energy recovery and of energy recovery from a beam disrupted by an FEL interaction as supplied by an infrared oscillator system. In this paper we present start-to-end simulations of the ERLP including such an FEL interaction. The beam dynamics in the highbrightness injector, which consists of a DC photocathode Gun and a superconducting booster, have been modelled using the particle tracking code ASTRA. After the booster the particles have been tracked with the code elegant. The 3D code GENESIS 1.3 was used to model the FEL interaction with the electron beam at 35 MeV. A brief summary of impedance and wakefield calculations for the whole machine is also given

Physical phenomena in containerless glass processing

Experiments were conducted on bubble migration in rotating liquid bodies contained in a sphere. Experiments were initiated on the migration of a drop in a slightly less dense continuous phase contained in a rotating sphere. A refined apparatus for the study of thermocapillar flow in a glass melt was built, and data were acquired on surface velocities in the melt. Similar data also were obtained from an ambient temperature fluid model. The data were analyzed and correlated with the aid of theory. Data were obtained on flow velocities in a pendant drop heated from above. The motion in this system was driven principally by thermocapillarity. An apparatus was designed for the study of volatilization from a glass melt

Transform-limited X-ray pulse generation from a high-brightness self-amplified spontaneous-emission free-electron laser

A method to achieve high-brightness self-amplified spontaneous emission (HB-SASE) in the free-electron laser (FEL) is described. The method uses repeated nonequal electron beam delays to delocalize the collective FEL interaction and break the radiation coherence length dependence on the FEL cooperation length. The method requires no external seeding or photon optics and so is applicable at any wavelength or repetition rate. It is demonstrated, using linear theory and numerical simulations, that the radiation coherence length can be increased by approximately 2 orders of magnitude over SASE with a corresponding increase in spectral brightness. Examples are shown of HB-SASE generating transform-limited FEL pulses in the soft x-ray and near transform-limited pulses in the hard x-ray. Such pulses may greatly benefit existing applications and may also open up new areas of scientific research

Oxygen and nitrogen cycling in the northeast Pacific – Simulations and observations at Station Papa in 2003/2004

A long-term air-sea exchange mooring has been maintained in the North Pacific near Ocean Station Papa (OSP, 145W, 50N) since September 2002 as part of the Canadian Surface Ocean Lower Atmosphere Study (C-SOLAS). The mooring provides a new long-term data set for gas measurements. In addition to Conductivity, Temperature and Depth (CTD) recorders at two depths, the mooring is equipped with ProOceanus Gas Tension Devices (GTDs) measuring the total gas pressure at four different depths, two oxygen sensors, two fluorometers for chlorophyll estimates, and an upward-looking 200 kHz echo-sounder for bubble measurements. Chlorophyll data have been added using SeaWiFS imagery and occasional bottle casts. Data collected from June 2003 to June 2004 are compared with simulations from a 1-D coupled atmosphere-ocean-biogeochemical model. The coupled model consists of an atmospheric Single Column Model (SCM), based on the CCCma AGCM (Canadian Centre for Climate Modelling and Analysis-Atmospheric General Circulation Model), the General Ocean Turbulence Model (GOTM) and a 7-component ecosystem model embedded in GOTM. The ecosystem model also includes oxygen, nitrogen, carbon, and silica cycling. The study focuses on simulated and observed N2 and O2 variability. The comparison of these gases allows for separation of physical and biological processes; which can then be evaluated in more detail with the aid of model simulations. The model also tests different parameterizations for saturation and gas exchange, including a formulation for gas injection via bubbles, which affects gas concentrations within the whole mixed layer. For most of the time the model shows good agreement with observations. However, in summer 2003 the observations reveal a strong oxygen and chlorophyll event, which is not reproduced in the standard model run. A weaker signal is seen in May 2004. OSP is a High Nutrient Low Chlorophyll (HNLC) region, limited by the micronutrient iron. Increases in usually low chlorophyll values occur occasionally due to natural iron enrichment (dust deposition, eddy transport, below surface layer transport). Although limitations of 1-D modeling become apparent here, an assumed input of iron in the model explains the differences between simulated and observed oxygen and chlorophyll maxima. The model provides information on the strength and duration of potential iron contribution. No obvious dust events or eddy traverses to supply iron were recorded during this time period. An alternative explanation is entrainment from deeper waters, where occasional iron enrichment is known to occur due to off-shelf transport via eddies or recirculation from the Alaskan shelf

Entry Dispersion Analysis for the Stardust Comet Sample Return Capsule

Stardust will be the first mission to return samples from beyond the Earth-Moon system. The sample return capsule, which is passively controlled during the fastest Earth entry ever, will land by parachute in Utah. The present study analyzes the entry, descent, and landing of the returning sample capsule. The effects of two aerodynamic instabilities are revealed (one in the high altitude free molecular regime and the other in the transonic/subsonic flow regime). These instabilities could lead to unacceptably large excursions in the angle-of-attack near peak heating and main parachute deployment, respectively. To reduce the excursions resulting from the high altitude instability, the entry spin rate of the capsule is increased. To stabilize the excursions from the transonic/subsonic instability, a drogue chute with deployment triggered by an accelerometer and timer is added prior to main parachute deployment. A Monte Carlo dispersion analysis of the modified entry (from which the impact of off-nominal conditions during the entry is ascertained) shows that the capsule attitude excursions near peak heating and drogue chute deployment are within Stardust program limits. Additionally, the size of the resulting 3-sigma landing ellipse is 83.5 km in downrange by 29.2 km in crossrange, which is within the Utah Test and Training Range boundaries

Designing, building, measuring, and testing a constant equivalent fall height terrain park jump

Previous work has presented both a theoretical foundation for designing terrain park jumps that control landing impact and computer software to accomplish this task. US ski resorts have been reluctant to adopt this more engineered approach to jump design, in part due to questions of feasibility. The present study demonstrates this feasibility. It describes the design, construction, measurement, and experimental testing of such a jump. It improves on the previous efforts with more complete instrumentation, a larger range of jump distances, and a new method for combining jumper- and board-mounted accelerometer data to estimate equivalent fall height, a measure of impact severity. It unequivocally demonstrates the efficacy of the engineering design approach, namely that it is possible and practical to design and build free style terrain park jumps with landing surface shapes that control for landing impact as predicted by the theory