The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of ...polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19 MeV/c, limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.
Electroless nickel plating is an established industrial process that provides a robust and relatively low-cost coating suitable for transporting and storing ultracold neutrons (UCN). Using roughness ...measurements and UCN-storage experiments we characterized UCN guides made from polished aluminum or stainless-steel tubes plated by several vendors.
All electroless nickel platings were similarly suited for UCN storage with an average loss probability per wall bounce of 2.8 ⋅ 10-4 to 4.1 ⋅ 10-4 for energies between 90neV and 190neV, or a ratio of imaginary to real Fermi potential η of 1.7 ⋅ 10-4 to 3.3 ⋅ 10-4. Measurements at different elevations indicate that the energy dependence of UCN losses is well described by the imaginary Fermi potential. Some special considerations are required to avoid an increase in surface roughness during the plating process and hence a reduction in UCN transmission. Increased roughness had only a minor impact on storage properties.
Based on these findings we chose a vendor to plate the UCN-production vessel that will contain the superfluid-helium converter for the new TRIUMF UltraCold Advanced Neutron (TUCAN) source, achieving acceptable UCN-storage properties with η=3.5(5)⋅10-4.
A beamline for fundamental neutron physics at TRIUMF Ahmed, S.; Andalib, T.; Barnes, M.J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2019, Letnik:
927
Journal Article
Recenzirano
Odprti dostop
This article describes the new primary proton beamline 1U at TRIUMF. The purpose of this beamline is to produce ultracold neutrons (UCN) for fundamental-physics experiments. It delivers up to 40µA of ...480MeV protons from the TRIUMF cyclotron to a tungsten spallation target and uses a fast kicker to share the beam between the Center for Molecular and Materials Science and UCN. The beamline has been successfully commissioned and operated with a beam current up to 10µA, facilitating first large-scale UCN production in Canada.
.
A
6
Li-glass-based scintillation detector developed for the TRIUMF neutron electric dipole moment experiment was characterized using the ultra-cold neutron source at the Paul Scherrer Institute ...(PSI). The data acquisition system for this detector was demonstrated to perform well at rejecting backgrounds. An estimate of the absolute efficiency of background rejection of
99
.
7
±
0
.
1
% is made. For variable ultra-cold neutron rate (varying from < 1 kHz to approx. 100 kHz per channel) and background rate seen at the Paul Scherrer Institute, we estimate that the absolute detector efficiency is
89
.
7
-
1
.
9
+
1
.
3
%. Finally a comparison with a commercial Cascade detector was performed for a specific setup at the West-2 beamline of the ultra-cold neutron source at PSI.
Two K2CsSb photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure ∼10−11Torr . These photocathodes were evaluated ...using a dc high voltage photogun biased at voltages up to 200 kV, and illuminated with laser light at wavelengths 440 or 532 nm, to generate dc electron beams at currents up to 20 mA. Some conditions produced exceptionally large photocathode charge lifetimes, without measurable quantum efficiency decay, even from the center of the photocathode where operation using GaAs photocathodes is precluded due to ion bombardment. Under other conditions the charge lifetime was poor due to extensive ion bombardment under severely degraded vacuum conditions, and as a result of localized heating via the laser beam. Following beam delivery, the photocathodes were evaluated using a scanning electron microscope to determine surface morphology.
A precise measurement of the neutron decay β asymmetry A₀ has been carried out using polarized ultracold neutrons from the pulsed spallation ultracold neutron source at the Los Alamos Neutron Science ...Center. Combining data obtained in 2008 and 2009, we report A₀ = -0.119 66±0.000 89{-0.001 40}{+0.001 23}, from which we determine the ratio of the axial-vector to vector weak coupling of the nucleon g{A}/g{V}=-1.275 90{-0.004 45}{+0.004 09}.
Compact noninvasive electron bunch-length monitor Roberts, B.; Mammei, R. R.; Poelker, M. ...
Physical review special topics. Accelerators and beams,
12/2012, Letnik:
15, Številka:
12
Journal Article
Recenzirano
Odprti dostop
A compact rf cavity was constructed that simultaneously resonates at many harmonic modes when excited by a repetitive bunched electron beam passing through its bore. The excitation of these modes ...provides a Fourier description of the temporal characteristics of the bunch train. The cavity was used to noninvasively characterize electron bunches produced from thin and thick GaAs photocathodes inside a DC high voltage photogun illuminated with 37 ps (full width half maximum, FWHM) laser pulses at repetition rates near 1500 MHz, at average beam current from 5 to 500μA , and at beam energy from 75 to 195 keV. The cavity bunch-length monitor could detect electron bunches as short as 57 ps (FWHM) when connected directly to a sampling oscilloscope, and could clearly distinguish bunches with varying degrees of space-charge induced growth and with different tail signatures. Efforts are under way to detect shorter bunches by designing cavities with increased bandwidth. This demonstration lends credibility to the idea that these cavities could also be used for other applications, including bunching and shaping, when driven with external rf.
The Nab experiment will measure the ratio of the weak axial-vector and vector coupling constants
λ
=
g
A
/
g
V
with precision
δ
λ
/
λ
∼ 3 × 10
− 4
and search for a Fierz term
b
F
at a level Δ
b
F
< ...10
− 3
. The Nab detection system uses thick, large area, segmented silicon detectors to very precisely determine the decay proton’s time of flight and the decay electron’s energy in coincidence and reconstruct the correlation between the antineutrino and electron momenta. Excellent understanding of systematic effects affecting timing and energy reconstruction using this detection system are required. To explore these effects, a series of ex situ studies have been undertaken, including a search for a Fierz term at a less sensitive level of Δ
b
F
< 10
− 2
in the beta decay of
45
Ca using the UCNA spectrometer.
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