81 research outputs found
STUDY ON EMITTANCE DILUTION IN THE JAERI-FEL ENERGY-RECOVERY TRANSPORT
Abstract An isochronous recirculating beam transport is under construction at the JAERI-FEL facility for energy-recovery experiments, where FEL output power over 2kW will be available. Since the FEL performance depends largely on the beam emittance, it is important to estimate emittance dilution along the recirculation. In the present paper, we study the emittance dilution in our recirculating transport, which is caused by higher-order aberrations, space charge force and coherent synchrotron radiation force
Opportunities for TeV Laser Acceleration
A set of ballpark parameters for laser, plasma, and accelerator technologies
that define for electron energies reaching as high as TeV are identified. These
ballpark parameters are carved out from the fundamental scaling laws that
govern laser acceleration, theoretically suggested and experimentally explored
over a wide range in the recent years. In the density regime on the order of
10^{16} cm^{-3}, the appropriate laser technology, we find, matches well with
that of a highly efficient high fluence LD driven Yb ceramic laser. Further,
the collective acceleration technique applies to compactify the beam stoppage
stage by adopting the beam-plasma wave deceleration, which contributes to
significantly enhance the stopping power and energy recovery capability of the
beam. Thus we find the confluence of the needed laser acceleration parameters
dictated by these scaling laws and the emerging laser technology. This may
herald a new technology in the ultrahigh energy frontier.Comment: 16 pages, 2 figures, 1 table, submitted to AIP Conference Proceeding
Compatible fossil fuel CO2 emissions in the CMIP6 earth system models' historical and shared socioeconomic pathway experiments of the twenty-first century
We present the compatible CO2 emissions from fossil fuel (FF) burning and industry, calculated from the historical and Shared Socioeconomic Pathway (SSP) experiments of nine Earth system models (ESMs) participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6). The multimodel mean FF emissions match the historical record well and are close to the data-based estimate of cumulative emissions (394 6 59 GtC vs 400 6 20 GtC, respectively). Only two models fall inside the observed uncertainty range; while two exceed the upper bound, five fall slightly below the lower bound, due primarily to the plateau in CO2 concentration in the 1940s. The ESMs' diagnosed FF emission rates are consistent with those generated by the integrated assessment models (IAMs) from which the SSPs' CO2 concentration pathways were constructed; the simpler IAMs' emissions lie within the ESMs' spread for seven of the eight SSP experiments, the other being only marginally lower, providing confidence in the relationship between the IAMs' FF emission rates and concentration pathways. The ESMs require fossil fuel emissions to reduce to zero and subsequently become negative in SSP1-1.9, SSP1-2.6, SSP4-3.4, and SSP5-3.4over. We also present the ocean and land carbon cycle responses of the ESMs in the historical and SSP scenarios. The models' ocean carbon cycle responses are in close agreement, but there is considerable spread in their land carbon cycle responses. Land-use and land-cover change emissions have a strong influence over the magnitude of diagnosed fossil fuel emissions, with the suggestion of an inverse relationship between the two. © 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses)
Effect of high dust amount on surface temperature during the Last Glacial Maximum: a modelling study using MIROC-ESM
The effect of aerosols is one of many uncertain factors in projections of
future climate. However, the behaviour of mineral dust aerosols (dust) can be
investigated within the context of past climate change. The Last Glacial
Maximum (LGM) is known to have had enhanced dust deposition in comparison
with the present, especially over polar regions. Using the Model for
Interdisciplinary Research on Climate Earth System Model (MIROC-ESM), we
conducted a standard LGM experiment following the protocol of the
Paleoclimate Modelling Intercomparison Project phase 3 and sensitivity
experiments. We imposed glaciogenic dust on the standard LGM experiment and
investigated the impacts of glaciogenic dust and non-glaciogenic dust
on the LGM climate. Global mean radiative perturbations by glaciogenic and
non-glaciogenic dust were both negative, consistent with previous studies.
However, glaciogenic dust behaved differently in specific regions; e.g. it
resulted in less cooling over the polar regions. One of the major reasons for
reduced cooling is the ageing of snow or ice, which results in albedo
reduction via high dust deposition, especially near sources of high
glaciogenic dust emission. Although the net radiative perturbations in the
lee of high glaciogenic dust provenances are negative, warming by the ageing of
snow overcomes this radiative perturbation in the Northern Hemisphere. In
contrast, the radiative perturbation due to high dust loading in the
troposphere acts to warm the surface in areas surrounding Antarctica,
primarily via the longwave aerosolâcloud interaction of dust, and it is
likely the result of the greenhouse effect attributable to the enhanced cloud
fraction in the upper troposphere. Although our analysis focused mainly on
the results of experiments using the atmospheric part of the MIROC-ESM, we
also conducted full MIROC-ESM experiments for an initial examination of the
effect of glaciogenic dust on the oceanic general circulation module. A
long-term trend of enhanced warming was observed in the Northern Hemisphere
with increased glaciogenic dust; however, the level of warming around
Antarctica remained almost unchanged, even after extended coupling with the
ocean.</p
Twenty-first-century compatible co2 emissions and airborne fraction simulated by cmip5 earth system models under four representative concentration pathways
PublishedJournal ArticleThe carbon cycle is a crucial Earth system component affecting climate and atmospheric composition. The response of natural carbon uptake to CO2 and climate change will determine anthropogenic emissions compatible with a target CO2 pathway. For phase 5 of the Coupled Model Intercomparison Project (CMIP5), four future representative concentration pathways (RCPs) have been generated by integrated assessment models (IAMs) and used as scenarios by state-of-the-art climate models, enabling quantification of compatible carbon emissions for the four scenarios by complex, process-based models. Here, the authors present results from 15 such Earth system GCMs for future changes in land and ocean carbon storage and the implications for anthropogenic emissions. The results are consistent with the underlying scenarios but show substantial model spread. Uncertainty in land carbon uptake due to differences among models is comparable with the spread across scenarios. Model estimates of historical fossil-fuel emissions agree well with reconstructions, and future projections for representative concentration pathway 2.6 (RCP2.6) and RCP4.5 are consistent with the IAMs. For high-end scenarios (RCP6.0 and RCP8.5), GCMs simulate smaller compatible emissions than the IAMs, indicating a larger climate-carbon cycle feedback in the GCMs in these scenarios. For the RCP2.6 mitigation scenario, an average reduction of 50% in emissions by 2050 from 1990 levels is required but with very large model spread (14%-96%). The models also disagree on both the requirement for sustained negative emissions to achieve the RCP2.6 CO2 concentration and the success of this scenario to restrict global warming below 28C. All models agree that the future airborne fraction depends strongly on the emissions profile with higher airborne fraction for higher emissions scenarios. ©2013 American Meteorological Society.MOHC authors were supported by
the JointDECC/Defra MetOffice Hadley Centre Climate
Programme (GA01101), and work to performHadGEM2-
ES and MPI-ESM CMIP5 simulations was supported by
the EU-FP7 COMBINE project (Grant 226520). JS was
supported by the EU-FP7 CARBOCHANGE project
(Grant 284679). We acknowledge the World Climate
Research Programmeâs Working Group on Coupled
Modelling, which is responsible for CMIP, and we thank
the climate modeling groups (listed in Table 1 of this
paper) for producing and making available their model
output. For CMIP, the U.S. Department of Energyâs Program
for Climate Model Diagnosis and Intercomparison
provides coordinating support and led development of
software infrastructure in partnership with the Global
Organization for Earth System Science Portals. JT and
CR were supported by the Research Council of Norway
through the EarthClim (207711/E10) project
Neutron Halo Isomers in Stable Nuclei and their Possible Application for the Production of Low Energy, Pulsed, Polarized Neutron Beams of High Intensity and High Brilliance
We propose to search for neutron halo isomers populated via -capture
in stable nuclei with mass numbers of about A=140-180 or A=40-60, where the
or neutron shell model state reaches zero binding energy.
These halo nuclei can be produced for the first time with new -beams of
high intensity and small band width ( 0.1%) achievable via Compton
back-scattering off brilliant electron beams thus offering a promising
perspective to selectively populate these isomers with small separation
energies of 1 eV to a few keV. Similar to single-neutron halo states for very
light, extremely neutron-rich, radioactive nuclei
\cite{hansen95,tanihata96,aumann00}, the low neutron separation energy and
short-range nuclear force allows the neutron to tunnel far out into free space
much beyond the nuclear core radius. This results in prolonged half lives of
the isomers for the -decay back to the ground state in the 100
ps-s range. Similar to the treatment of photodisintegration of the
deuteron, the neutron release from the neutron halo isomer via a second,
low-energy, intense photon beam has a known much larger cross section with a
typical energy threshold behavior. In the second step, the neutrons can be
released as a low-energy, pulsed, polarized neutron beam of high intensity and
high brilliance, possibly being much superior to presently existing beams from
reactors or spallation neutron sources.Comment: accepted for publication in Applied Physics
Impact of bioenergy crop expansion on climateâcarbon cycle feedbacks in overshoot scenarios
Stringent mitigation pathways frame the deployment of second-generation bioenergy crops combined with carbon capture and storage (CCS) to generate negative CO2 emissions. This bioenergy with CCS (BECCS) technology facilitates the achievement of the long-term temperature goal of the Paris Agreement. Here, we use five state-of-the-art Earth system models (ESMs) to explore the consequences of large-scale BECCS deployment on the climateâcarbon cycle feedbacks under the CMIP6 SSP5-3.4-OS overshoot scenario keeping in mind that all these models use generic crop vegetation to simulate BECCS. First, we evaluate the land cover representation by ESMs and highlight the inconsistencies that emerge during translation of the data from integrated assessment models (IAMs) that are used to develop the scenario. Second, we evaluate the land-use change (LUC) emissions of ESMs against bookkeeping models. Finally, we show that an extensive cropland expansion for BECCS causes ecosystem carbon loss that drives the acceleration of carbon turnover and affects the CO2 fertilization effect- and climate-change-driven land carbon uptake. Over the 2000â2100 period, the LUC for BECCS leads to an offset of the CO2 fertilization effect-driven carbon uptake by 12.2â% and amplifies the climate-change-driven carbon loss by 14.6â%. A human choice on land area allocation for energy crops should take into account not only the potential amount of the bioenergy yield but also the LUC emissions, and the associated loss of future potential change in the carbon uptake. The dependency of the land carbon uptake on LUC is strong in the SSP5-3.4-OS scenario, but it also affects other Shared Socioeconomic Pathway (SSP) scenarios and should be taken into account by the IAM teams. Future studies should further investigate the trade-offs between the carbon gains from the bioenergy yield and losses from the reduced CO2 fertilization effect-driven carbon uptake where BECCS is applied
Production of Medical Radioisotopes with High Specific Activity in Photonuclear Reactions with Beams of High Intensity and Large Brilliance
We study the production of radioisotopes for nuclear medicine in
photonuclear reactions or ()
photoexcitation reactions with high flux [()/s], small
diameter m and small band width () beams produced by Compton back-scattering of laser
light from relativistic brilliant electron beams. We compare them to (ion,np) reactions with (ion=p,d,) from particle accelerators like
cyclotrons and (n,) or (n,f) reactions from nuclear reactors. For
photonuclear reactions with a narrow beam the energy deposition in the
target can be managed by using a stack of thin target foils or wires, hence
avoiding direct stopping of the Compton and pair electrons (positrons).
isomer production via specially selected cascades
allows to produce high specific activity in multiple excitations, where no
back-pumping of the isomer to the ground state occurs. We discuss in detail
many specific radioisotopes for diagnostics and therapy applications.
Photonuclear reactions with beams allow to produce certain
radioisotopes, e.g. Sc, Ti, Cu, Pd, Sn,
Er, Pt or Ac, with higher specific activity and/or
more economically than with classical methods. This will open the way for
completely new clinical applications of radioisotopes. For example Pt
could be used to verify the patient's response to chemotherapy with platinum
compounds before a complete treatment is performed. Also innovative isotopes
like Sc, Cu and Ac could be produced for the first time
in sufficient quantities for large-scale application in targeted radionuclide
therapy.Comment: submitted to Appl. Phys.
Changes in soil organic carbon storage predicted by Earth system models during the 21st century
Soil is currently thought to be a sink for carbon; however, the response of
this sink to increasing levels of atmospheric carbon dioxide and climate
change is uncertain. In this study, we analyzed soil organic carbon (SOC)
changes from 11 Earth system models (ESMs) contributing simulations to the
Coupled Model Intercomparison Project Phase 5 (CMIP5). We used a reduced
complexity model based on temperature and moisture sensitivities to analyze
the drivers of SOC change for the historical and high radiative forcing (RCP
8.5) scenarios between 1850 and 2100. ESM estimates of SOC changed over the
21st century (2090â2099 minus 1997â2006) ranging from a loss of 72 Pg C to
a gain of 253 Pg C with a multi-model mean gain of 65 Pg C. Many ESMs
simulated large changes in high-latitude SOC that ranged from losses of
37 Pg C to gains of 146 Pg C with a multi-model mean gain of 39 Pg C
across tundra and boreal biomes. All ESMs showed cumulative increases in
global NPP (11 to 59%) and decreases in SOC turnover times (15 to
28%) over the 21st century. Most of the model-to-model variation in SOC
change was explained by initial SOC stocks combined with the relative changes
in soil inputs and decomposition rates (R2 = 0.89, p < 0.01). Between
models, increases in decomposition rate were well explained by a combination
of initial decomposition rate, ESM-specific Q10-factors, and changes in
soil temperature (R2 = 0.80, p < 0.01). All SOC changes depended on
sustained increases in NPP with global change (primarily driven by increasing
CO2). Many ESMs simulated large accumulations of SOC in high-latitude
biomes that are not consistent with empirical studies. Most ESMs poorly
represented permafrost dynamics and omitted potential constraints on SOC
storage, such as priming effects, nutrient availability, mineral surface
stabilization, and aggregate formation. Future models that represent these
constraints are likely to estimate smaller increases in SOC storage over the
21st century
Regionally aggregated, stitched and deâdrifted CMIPâclimate data, processed with netCDFâSCM v2.0.0
The world's most complex climate models are currently running a range of experiments as part of the Sixth Coupled Model Intercomparison Project (CMIP6). Added to the output from the Fifth Coupled Model Intercomparison Project (CMIP5), the total data volume will be in the order of 20PB. Here, we present a dataset of annual, monthly, global, hemispheric and land/ocean means derived from a selection of experiments of key interest to climate data analysts and reduced complexity climate modellers. The derived dataset is a key part of validating, calibrating and developing reduced complexity climate models against the behaviour of more physically complete models. In addition to its use for reduced complexity climate modellers, we aim to make our data accessible to other research communities. We facilitate this in a number of ways. Firstly, given the focus on annual, monthly, global, hemispheric and land/ocean mean quantities, our dataset is orders of magnitude smaller than the source data and hence does not require specialized âbig dataâ expertise. Secondly, again because of its smaller size, we are able to offer our dataset in a text-based format, greatly reducing the computational expertise required to work with CMIP output. Thirdly, we enable data provenance and integrity control by tracking all source metadata and providing tools which check whether a dataset has been retracted, that is identified as erroneous. The resulting dataset is updated as new CMIP6 results become available and we provide a stable access point to allow automated downloads. Along with our accompanying website (cmip6.science.unimelb.edu.au), we believe this dataset provides a unique community resource, as well as allowing non-specialists to access CMIP data in a new, user-friendly way
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