78 unifying physics of accelerators, lasers and plasma
of power systems with frequencies ranging from a few MHz
to several GHz.
Recalling Maxwell ' s equation and its integral form
∂B
d
∇ × E = −
or
E · dt = −
B · dS
∂t
dt
∂Σ
Σ
we see that if the particle moves on an enclosed orbit, like in
a synchrotron, finite acceleration (i.e., nonzero contour integral of E) would not be possible without a time-dependent
magnetic field B. On the other hand, time-dependent magnetic flux can provide acceleration when — either in a linac
or a synchrotron — the EM field oscillates in the resonant
cavity and the particles receive a finite energy increment at
each pass through the cavities.
5.1.3 Widero ¨e linear accelerator
In 1925, Ising inspired the new technological branch of accelerators by realizing that limitations imposed by corona
formation and discharge in electrostatic accelerators can be
overcome with the use of alternating voltages. This was carried further by Wider¨ oe who, in 1928, performed the first
successful test of the linac based on this principle.
The Wider¨ oe linac has a series of drift tubes arranged
along its beam axis and connected with an alternating high
frequency RF voltage: V (t) = V max sin(ωt) as shown in Fig.5.7.
During the first half of the RF period in the acceleration process, voltage applied to the first drift tube accelerates charged
particles emerging from the ion source. Particles then enter
the first drift tube and pass through it. Meanwhile, the direction of the RF field reverses without affecting the particles —
seeing as the drift tube acts as a Faraday cage and shields the
particles from external fields. When the particles reach the
gap between the first and the second drift tubes, they accelerate and the process repeats in the following gaps as well.
'ULIWWXEHV
,RQVRXUFH
%HDP
5)JHQHUDWRU
L
L
O O O
O
O L
O L
FIGURE 5.7
Widero ¨e linear accelerator.
of power systems with frequencies ranging from a few MHz
to several GHz.
Recalling Maxwell ' s equation and its integral form
∂B
d
∇ × E = −
or
E · dt = −
B · dS
∂t
dt
∂Σ
Σ
we see that if the particle moves on an enclosed orbit, like in
a synchrotron, finite acceleration (i.e., nonzero contour integral of E) would not be possible without a time-dependent
magnetic field B. On the other hand, time-dependent magnetic flux can provide acceleration when — either in a linac
or a synchrotron — the EM field oscillates in the resonant
cavity and the particles receive a finite energy increment at
each pass through the cavities.
5.1.3 Widero ¨e linear accelerator
In 1925, Ising inspired the new technological branch of accelerators by realizing that limitations imposed by corona
formation and discharge in electrostatic accelerators can be
overcome with the use of alternating voltages. This was carried further by Wider¨ oe who, in 1928, performed the first
successful test of the linac based on this principle.
The Wider¨ oe linac has a series of drift tubes arranged
along its beam axis and connected with an alternating high
frequency RF voltage: V (t) = V max sin(ωt) as shown in Fig.5.7.
During the first half of the RF period in the acceleration process, voltage applied to the first drift tube accelerates charged
particles emerging from the ion source. Particles then enter
the first drift tube and pass through it. Meanwhile, the direction of the RF field reverses without affecting the particles —
seeing as the drift tube acts as a Faraday cage and shields the
particles from external fields. When the particles reach the
gap between the first and the second drift tubes, they accelerate and the process repeats in the following gaps as well.
'ULIWWXEHV
,RQVRXUFH
%HDP
5)JHQHUDWRU
L
L
O O O
O
O L
O L
FIGURE 5.7
Widero ¨e linear accelerator.