the usage of the continuous Electron Beam Accelerator
Facility (CEBAF) on the department of power's Jefferson Lab, a team of
researchers has, for the first time, demonstrated a new approach for producing
polarized positrons. The method could allow new studies in advanced substances
and gives a new street for generating polarized positron beams for a proposed
worldwide Linear Collider and an estimated Electron-Ion Collider.
Jefferson Lab Injector Scientist Joe Grames says the concept
for the approach grew out of the numerous advances that have been made in
expertise and controlling the electron beams used for research in CEBAF.
"we've lots of enjoy right here at Jefferson Lab in
operating a global-leading electron accelerator," Grames stated.
"we're continuously enhancing the electron beam for the experiments,
pushing the bounds of what we are able to get the electrons to do."
The CEBAF accelerator gathers up unfastened electrons, units
the electrons to spinning like tops, packs them complete of extra power
("accelerating" the particles to up to 12 billion electron-volts),
and directs them along a tightly managed course into experimental targets.
Grames and his colleagues would like to take that finesse a step further and
rework CEBAF's nicely-managed polarized electron beams into well-controlled
beams of polarized positrons to offer researchers at Jefferson Lab an extra
probe of nuclear be counted. They named the undertaking the Polarized Electrons
for Polarized Positrons test, or PEPPo.
Positrons are the anti-particles of electrons. wherein the
electron has a terrible fee, the positron has a fine one. producing positrons
which can be spinning inside the same route, just like the electrons in CEBAF,
may be very challenging. earlier than PEPPo, researchers had efficaciously
controlled to coax polarized positrons into life using very excessive-power
electron beams and complicated technologies. The PEPPo method, however, places
a brand new twist on things.
"From the beginning, our purpose changed into to show
that we ought to use the polarized electron beam we produce every day at CEBAF
to create the positrons. but we desired to do that the use of a low-strength
and small-footprint electron beam, so that a college or enterprise may
additionally benefit from our evidence of precept," Grames explained.
The PEPPo system turned into positioned within the CEBAF
accelerator's injector, that is the part of the accelerator that generates
electrons. The machine consists especially of small magnets for managing the
particle beams, objectives for transforming them, and detectors for measuring
the debris.
In it, a brand new beam of electrons from CEBAF is directed
right into a slice of tungsten. The electrons rapidly slow down as they bypass
via the tungsten atoms, giving off gamma rays. those gamma rays then have
interaction with different atoms inside the tungsten target to provide
lower-power pairs of positrons and electrons. during the procedure, the
polarization of the authentic electron beam is handed alongside. The
researchers use a magnet to siphon the positrons far from the alternative
debris and direct them into a detector system that measures their energy and
polarization.
"We confirmed that there's a completely green switch of
polarization from electrons to the positrons," said Grames.
further, the researchers observed that it is also viable to
dial up the diploma of polarization that they're interested by by selecting
positrons of the right electricity. at the same time as the extra abundant
lower-power positrons are much less polarized, the positrons with highest-power
preserve nearly all the polarization of the authentic electron beam. In PEPPo,
the electron beam became eighty five percentage polarized and accelerated to
eight million electron-volts (MeV).
"Nuclear physicists usually need the best polarization
viable for his or her experiments," he explained. "Positrons amassed
at half the authentic electron power were about 50 percentage polarized, which
is still quite high. but, as we approached the maximum energy, we measured 82
percent, showing that a very big portion of the authentic electron polarization
is transferred."
The PEPPo test ran for 4 weeks within the spring of 2012.
The result has simply been posted in bodily overview Letters, and it is
featured as an Editors' notion.
Grames and his colleagues say now that they have their proof
of precept, they need to layout a source that is able to generating a beam of
polarized positrons for research.
"With this result in hand, we are now asking ourselves
what's the great way to gather those positrons into a beam that can be used by
nuclear physicists in experiments at Jefferson Lab and that may be beneficial
for different facilities. it's the following step."
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