AN ALTERNATIVE APPROACH TO LOW FREQUENCY RF ACCELERATORS AND POWER SOURCES. Page: 4 of 4
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The above example has not been optimized. The beam
velocity may affect the data, but not critically. For
different frequencies the cavity length or the number of
sections should be changed correspondingly. Lengthening
and deforming the bar to form a spiral can significantly
increase the inductance. It can bring down the frequency
to 30 MHz or lower without increasing the transverse
dimensions. Unfortunately, MAFI[A couldn't give a
precise result for this case due to the complexity of the
shape. Thus one has to rely on experiment or a more
powerful code, if available.
-0.5 0 Z(m) 1.0
Fig.7 The electric field Ez along axis
Usually, a lumped device such as a coil can not achieve
a very high Q. The Q value of 26000 listed above is not
bad. But, one may question the precision of the result
from MAFIA. Surely this is a topic requiring further
studies. However, one advantage of this kind of structure
is that the capacitance is very low in comparison with
other LF cavities. This means, to get a given accelerating
voltage, one needs less energy to fill it. This is important
for short pulse operation. A muon collider is just such a
Another concern is the required power. Although the
mentioned structure has the potential to get a relatively
high average gradient, and consequently one has to supply
a huge LF peak power. This is difficult at present. The
next section proposes an alternative power source.
5 A LF POWER SOURCE SCHEME
Fig. 8 shows the principle of a compression scheme
using energy storage and a unique switch. To charge
the storage cavity, one might employ a CW tetrode
(power source marked as PS in Fig. 8). The output of the
storage cavity is connected to a half-wavelength cable
with a switch at the other end and a load at the midpoint.
When the switch is open, as shown in Fig. 8 (a), the load
branch is at the node of the voltage. Therefore no power
goes to the load, and the storage cavity sees an open
circuit, which means little power leakage. When the
switch is closed as in Fig. 8 (b), the right quarter-
wavelength cable acts as an open circuit. The storage
cavity then connects directly to the load (e.g., the
accelerator cavity), to which the energy drains.
The energy storage is a superconducting cavity (S.C. in
Fig. 8) so it has little loss during the long charging time.
This makes it possible to use a moderate power tetrode.
The switch is a key component. A thyratron is
considered suitable. Although thyratrons are usually used
in modulators or video switches, they may also be
applicable at LF. The switch should hold off a voltage V
without breakdown when the switch is open, and should
carry a current I = V/ZO when closed. There are many
thyratrons on the market with enough power to satisfy
() PS S.C.
Fig.8 Principle set-up of storage - switch
A special apparatus would need to be designed to hold
the thyratron inside a rigid cable. In addition, a special
bias current circuit would need to be provided to
guarantee that the current is always positive as required
by a normal thyratron.
This scheme has the potential to supply large peak
powers. The major restriction is breakdown inside the
cable. Since the cable is a low impedance device, the
voltage can be in the tens of kilovolts range and should
not be a big problem.
This work was supported by the US DOE under
Contract No. DE-AC02-98CH10886. Thanks also to
many colleagues in BNL's CAP group who showed
interest, participated in discussions and gave comments.
 R. Palmer, A. Tollestrup and A. Sessler, "Status
Report of a High Luminosity Muon Collider and
Future Research and Development Plans". BNL-
63865, CAP-154-MUON-96C, Nov., 1996
 Y. Zhao, "An alternative approach for the low
frequency acceleration," Neutrino Factory and Muon
Collider Collaboration Meeting, LBNL, Dec. 1999.
 Y. Zhao, "Power compression of low-frequency RF by
means of a thyratron," BNL-67709, , Sep. 2000.
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ZHAO, Y. AN ALTERNATIVE APPROACH TO LOW FREQUENCY RF ACCELERATORS AND POWER SOURCES., article, June 18, 2001; Upton, New York. (digital.library.unt.edu/ark:/67531/metadc717536/m1/4/: accessed October 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.