Magnetic proton recoil neutron spectrometer
Encyclopedia
Magnetic Proton Recoil neutron spectrometer is a large high-resolution neutron
spectrometer
installed at JET
.
neutron
s are collimated into a neutron beam. The neutron beam is directed onto a thin plastic film (Polyethylene
) where the neutrons scatter elastically on the proton
s of the foil. The recoil protons emitted in the forward direction enter a magnetic part of the spectrometer where they are momentum analyzed and focused onto the focal plane. An array of plastic scintillator
s coupled to photomultiplier tubes (PMTs) register the spatial distribution of the protons. This proton distribution is then related to the neutron energy spectrum.
. The MPR has a 700 mm long cylindrical steel neutron collimator with a 10-cm2 bore. At a distance 170 mm behind the end of the collimator is placed a 10 cm2 polythene conversion foil, defining the active area of the spectrometer. The collimator-foil arrangement defines the spectrometers field-of-view into the plasma.
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
spectrometer
Spectrometer
A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...
installed at JET
Joint European Torus
JET, the Joint European Torus, is the largest magnetic confinement plasma physics experiment worldwide currently in operation. Its main purpose is to open the way to future nuclear fusion experimental tokamak reactors such as ITER and :DEMO....
.
History
The Magnetic Proton Recoil (MPR) neutron spectrometer is a thin-foil spectrometer which was installed at JET in 1996 and upgraded (MPRu) 2001-2005.Principle
In the MPR the fusionNuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s are collimated into a neutron beam. The neutron beam is directed onto a thin plastic film (Polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
) where the neutrons scatter elastically on the proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s of the foil. The recoil protons emitted in the forward direction enter a magnetic part of the spectrometer where they are momentum analyzed and focused onto the focal plane. An array of plastic scintillator
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
s coupled to photomultiplier tubes (PMTs) register the spatial distribution of the protons. This proton distribution is then related to the neutron energy spectrum.
Field-of-view
The MPR has a semi-tangential line of sight through the plasmaPlasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
. The MPR has a 700 mm long cylindrical steel neutron collimator with a 10-cm2 bore. At a distance 170 mm behind the end of the collimator is placed a 10 cm2 polythene conversion foil, defining the active area of the spectrometer. The collimator-foil arrangement defines the spectrometers field-of-view into the plasma.