Radiation protection is another critical factor for storage ring operation, which
has to consider worst-case scenarios such as complete loss of electron bunches down
a beamline. Many beamlines have lead shielding placed at the height of the storage
ring to protect from direct exposure to high energy electrons.
2.5 Insertion Device Hardware
We saw in Chap. 1 (Fig. 1.2) that synchrotron radiation is produced when the
trajectory of a relativistic electron is bent by a magnetic field. It is not a great leap
to conclude that if bending by one magnet is good, then using 10 or even 100 magnets would be better. These arrays of magnets are called insertion devices (IDs),
because they are inserted into “straight sections” of the lattice and ideally do not
affect the overall orbit of the beam. Here we focus on the hardware for producing the
requisite alternating N–S magnetic fields. In Chap. 3, we will illustrate the special
properties of the radiation that is produced.
2.5.1 Superbends
The simplest insertion device for boosting synchrotron radiation is a superbend
magnet—a very high field magnet that replaces one of the normal dipole bend
magnets in a storage ring. Superbend magnets increase the amount of radiation,
but more importantly, they increase the average energy of the photons produced. At
the ALS, superconducting superbend magnets with a field of 5 Tesla have been used
to replace the normal 1.3 Tesla bend magnets [29], and the modified lattice is shown
in Fig. 2.14. The Nb-Ti superconductor magnet coils are maintained at close to 4 K
by a Gifford-McMahon cryocooler. As backup in case of cryocooler failure, the
magnet is immersed in an 85 liter liquid He vessel, which will support operation for
about 18 h without refilling. (Technically, superbends are not really insertion
devices—if they fail or are turned off, the beam no longer follows its proper orbit.)
2.5.2 Wavelength Shifters
To allow for an even greater magnetic field, machine physicists use a device called a
wavelength shifter—which is essentially a very strong one-pole magnet preceded
and followed by weaker dipoles that restore the beam to its original trajectory. At
SPring-8, the orbit change produced by a superconducting 10 Tesla dipole magnet is
balanced by two 1.9 Tesla magnets, resulting in no net deflection of the beam
trajectory (Fig. 2.15).
28
2 The Storage Ring Complex
has to consider worst-case scenarios such as complete loss of electron bunches down
a beamline. Many beamlines have lead shielding placed at the height of the storage
ring to protect from direct exposure to high energy electrons.
2.5 Insertion Device Hardware
We saw in Chap. 1 (Fig. 1.2) that synchrotron radiation is produced when the
trajectory of a relativistic electron is bent by a magnetic field. It is not a great leap
to conclude that if bending by one magnet is good, then using 10 or even 100 magnets would be better. These arrays of magnets are called insertion devices (IDs),
because they are inserted into “straight sections” of the lattice and ideally do not
affect the overall orbit of the beam. Here we focus on the hardware for producing the
requisite alternating N–S magnetic fields. In Chap. 3, we will illustrate the special
properties of the radiation that is produced.
2.5.1 Superbends
The simplest insertion device for boosting synchrotron radiation is a superbend
magnet—a very high field magnet that replaces one of the normal dipole bend
magnets in a storage ring. Superbend magnets increase the amount of radiation,
but more importantly, they increase the average energy of the photons produced. At
the ALS, superconducting superbend magnets with a field of 5 Tesla have been used
to replace the normal 1.3 Tesla bend magnets [29], and the modified lattice is shown
in Fig. 2.14. The Nb-Ti superconductor magnet coils are maintained at close to 4 K
by a Gifford-McMahon cryocooler. As backup in case of cryocooler failure, the
magnet is immersed in an 85 liter liquid He vessel, which will support operation for
about 18 h without refilling. (Technically, superbends are not really insertion
devices—if they fail or are turned off, the beam no longer follows its proper orbit.)
2.5.2 Wavelength Shifters
To allow for an even greater magnetic field, machine physicists use a device called a
wavelength shifter—which is essentially a very strong one-pole magnet preceded
and followed by weaker dipoles that restore the beam to its original trajectory. At
SPring-8, the orbit change produced by a superconducting 10 Tesla dipole magnet is
balanced by two 1.9 Tesla magnets, resulting in no net deflection of the beam
trajectory (Fig. 2.15).
28
2 The Storage Ring Complex