INSTRUMENTATION FOR TXRF AND GI-XRF - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 136

wigglers, and FELs, and by the improvement of X-ray optics [10-13]. The
scientific projects aim at material research with extremely small spatial struc-
tures (10

12 m or picometer) or with extremely fast time processes (10 15 sor

femtosecond).

3.3.1BasicSetupwithBendingMagnets

The passageway for the electrons is a metallic pipe with an octagon cross-
section. The pipe is shaped like a doughnut, some 100 m to some kilometers
long and with a cross-section of about 50 cm 2 . It is made of copper, stainless
steel, or an aluminum alloy. The latter is nonmagnetic, corrosion resistant, and
can be well processed by the extrusion method.
The ring is usually evacuated by several pumps, mostly ion pumps, down to

10 mbar (UHV). They are normally filled 1-2 times per day. Hundreds of
electron bunches are injected at intervals of 1 s. In top-up operation, the lost
electrons are replaced continuously and injected 1-3 times every 1 min or every
5 min. Normally, the beamline runs 10 months a year with a shut-down of twice
a month. The storage-ring and a part of the beamline are enclosed in concrete
walls to protect the staff and users from X-rays. Because of the relatively high
magnetic field strength, people with a pacemaker have to stay away from the
area around the storage ring. All users have to obey proper safeguards and
fulfill respective safety requirements.
Usually, the bending magnets are dipole magnets with a horse-shoe shape
and with a field strength of 0.1-2T. 1 Electromagnetic dipoles, quadrupoles, and
sextupoles are installed in the actual synchrotron ring because their field
strength can be adjusted synchronously with the increasing energy of the
electrons. In the case of superconducting coils, the magnets have to be cooled
down below the boiling point of helium ( < 4.22 K or < 269 ° C). The costs for the
electrical power supply are low but the supply with liquid helium is expensive.
For the storage ring, permanent magnets can be used consisting of a sintered
material made of neodymium, iron, and boron. Their bending radius is between
3 and 50 m.
The beamlines are tangentially attached to the storage ring and lead the light
beam to the experimental stations covering a distance up to several 10 m. These
light pipes made of metal, for example, stainless steel or copper, are shielded by
lead and steel pipes. At the front end of each beamline, there is a water-cooled
beam stopper that absorbs the“bremsstrahlung”and scattered electrons. A
beam shutter is added for switching the beam on and off. Radiation-proof
hutches with walls of sandwiches (aluminum, lead, aluminum) are built up
along each line. Figure 3.5 gives a typical floor plan of an X-ray beamline. The
first hutch usually contains specific optics like shutters, windows, filters, slits,

10

1 A magnetic necklace or bracelet has a field strength of about 0.1-0.3 T. MRI (magnetic resonance
imaging) devices of high-tech medicine have a strength of about 1.5 T. The magnetic field of our
earth shows a much smaller strength of only some 0.00005 T.