1. Synchrotron radiation research facility, SPring 8
Photons have been used both in materials science research and
in research in various other fields. These efforts have achieved
tremendous progress. A gigantic facility, SPring-8 - Super Photon
ring 8 GeV, is now being constructed. This facility will use photons
in a variety of scientific research acitivities. SPring 8, one
of the largest facilities of its kind in the world,is being constructed
by JAERI in cooperation with RIKEN.
In high-energy electron accelerators, electrons lose their energies
by emitting electromagnetic waves (photons) when their paths are
deflected by a magnetic field. These photons (synchrotron radiation
emission) were initially considered a disadvantage for circular
accelerators. The unique characteristics of this radiation, however,
were later recognized. These characteristics suggested an exceptional
future light source. Worldwide research on this radiation then
proceeded rapidly. In Japan, advanced studies are ongoing in PF
(2.5 GeV) of the KEK, in UVSOR (0.75 GeV), in INS (0.4 GeV) of
the Universityof Tokyo, and in other facilities.
2. Characteristics and advantages of synchrotron radiation
The characteristics of this radiation are as follows:
- It is emitted in a forward direction (tangen tial to the curve
of the ring) with a very strong intensity.
- It has a continuous energy spectrum below a certain energy, which
is determined by the energy and orbital radius of an emitting
electron.
- It is polarized in the electron orbital plane.
- It is possible to tune the light phase by reg ularly modulating
the electron orbit.
Because the intensity is extremely strong and the wavelength is
continuous for this radiation, it is possible to extract monochromatic
light having an arbitrary wavelength using wavelength monochrometers.
This allows the use of polarized monochromatic photons having
a much stronger intensity than ever available before.
3. Construction status
The accelerator for the synchrotron radiation research is composed
of an injector section, which accelerates electrons to the required
energies, and a storage ring section which stores electrons used
to emit synchrotron radiation.On SPring 8, JAERI's construction
responsibility is for the injector, which consists of a linac
(linear accelerator) and a synchrotron.
The linac accelerates electrons with an accelerator guide - a
circular waveguide through which electrons are accelerated by
a high-power electro- magnetic wave (a microwave). The total length
of the linac is 140 m; the attainable energy is about 1 GeV. For
synchrotron radiation, positrons are,in fact, more suitable than
electrons, because a positron beam is more stable than an electron
beam in the storage ring. However, positrons exist for only very
short periods in nature. Therefore, they must be produced artificially
for this linac. The linac under construction is capable of producing
and accelerating the required positrons. Figure 10-3 shows the
injector for the linac being tested.
The synchrotron has a circumference of 396 m. Electrons and positrons
in the circular orbit are periodically accelerated with an rf
(radio frequency) of 508.6 MHz (Fig.10-4). The synchrotron can
accelerate the injected electrons or positron shaving energies
of up to 1 GeV up to an energy of 8 GeV. This facility is scheduled
to start operation for users in FY 1997. |
