61 research outputs found
Effect of nano-scale surface roughness on transverse energy spread from GaAs photocathodes
High quantum yield, low transverse energy spread and prompt response time
make GaAs activated to negative electron affnity, an ideal candidate for a
photocathode in high brightness photoinjectors. Even after decades of
investigation, the exact mechanism of electron emission from GaAs is not well
understood. We show that a nanoscale surface roughness can affect the
transverse electron spread from GaAs by nearly an order of magnitude and
explain the seemingly controversial experimental results obtained so far. This
model can also explain the measured dependence of transverse energy spread on
the wavelength of incident light.Comment: 3pages, 3figure
Comparison of DC and SRF Photoemission Guns For High Brightness High Average Current Beam Production
A comparison of the two most prominent electron sources of high average
current high brightness electron beams, DC and superconducting RF photoemission
guns, is carried out using a large-scale multivariate genetic optimizer
interfaced with space charge simulation codes. The gun geometry for each case
is varied concurrently with laser pulse shape and parameters of the downstream
beamline elements of the photoinjector to obtain minimum emittance as a
function of bunch charge. Realistic constraints are imposed on maximum field
values for the two gun types. The SRF and DC gun emittances and beam envelopes
are compared for various values of photocathode thermal emittance. The
performance of the two systems is found to be largely comparable provided low
intrinsic emittance photocathodes can be employed
Detection and clearing of trapped ions in the high current Cornell photoinjector
We have recently performed experiments to test the effectiveness of three
ion-clearing strategies in the Cornell high intensity photoinjector: DC
clearing electrodes, bunch gaps, and beam shaking. The photoinjector reaches a
new regime of linac beam parameters where high CW beam currents lead to ion
trapping. Therefore ion mitigation strategies must be evaluated for this
machine and other similar future high current linacs. We have developed several
techniques to directly measure the residual trapped ions. Our two primary
indicators of successful clearing are the amount of ion current removed by a DC
clearing electrode, and the absence of bremsstrahlung radiation generated by
beam-ion interactions. Measurements were taken for an electron beam with an
energy of 5 MeV and CW beam currents in the range of 1-20 mA. Several
theoretical models have been developed to explain our data. Using them, we are
able to estimate the clearing electrode voltage required for maximum ion
clearing, the creation and clearing rates of the ions while employing bunch
gaps, and the sinusoidal shaking frequency necessary for clearing via beam
shaking. In all cases, we achieve a maximum ion clearing of at least 70 percent
or higher, and in some cases our data is consistent with full ion clearing
Thermal emittance measurements of a cesium potassium antimonide photocathode
Thermal emittance measurements of a CsK2Sb photocathode at several laser
wavelengths are presented. The emittance is obtained with a solenoid scan
technique using a high voltage dc photoemission gun. The thermal emittance is
0.56+/-0.03 mm-mrad/mm(rms) at 532 nm wavelength. The results are compared with
a simple photoemission model and found to be in a good agreement.Comment: APL 201
Specifics of Developing Professional Thinking in Law Students
The article examines the essence, role and significance of professional thinking within lawyers’ professional development, making a special emphasis on the specifics of evolving law students’ professional thinking. The research purpose is a theoretical and empirical study of the developmental specifics of law students’ professional thinking. Besides, there is a focus on the structure and features of lawyers’ professional thinking as a special professionally important quality. The authors conduct a comprehensive analysis of the developmental specifics of law students’ professional thinking, propose their own definition of this concept and consider its structure and structural components. The analysis of relevant literature contributed to studying the validity of the chosen topic. The article also reflects the methodology of research and its algorithm that include conducting a complex psychological and pedagogical experiment, assessing the declared parameters and fulfilling the statistical analysis of the results based on methods such as variance analysis, correlation analysis using Marsch’s I coefficient, Friedman’s R coefficient and Kruskal – Wallis H-criterion. The research base was the International Law Institute (Moscow, Russia). The experimental and control groups of subjects were formed, numbering 60 people representative in gender, etc. The results of the study demonstrate the effectiveness of combining trainings, special courses and the evolvement of formal-logical reasoning within the development of law students’ professional thinking
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