Wave Sources Working group
Ives: Comparison of Multiple Beam and Sheet
| There is considerable
interest in distributed beam RF sources for the
next generation of high energy accelerators. Distributed
beam sources utilize unique circuits to extract
energy from electron beams with considerably increased
transverse area. This allows high power extraction
with significantly reduced current density beams
than from existing round beam sources. This allows
reduction of the voltage which drives much of the
cost of the power supply systems. With these distributed
beam sources, however, comes a number of issues.
These include considerably more complicated electron
guns and complex RF cavities and increased susceptibility
to parasitic oscillations. Coupling into and out
of these devices also becomes more complicated.
This presentation will explore the different designs
being used and proposed for these new sources and
examine the relative merits of each. CCR recently
completed a Phase I program to explore the feasibility
of a high power sheet beam klystron and is currently
developing a multiple beam klystron through a Phase
II grant. The design parameters of each will be
presented, and the predicted performance of each
will be compared. A key issue, of course, will be
manufacturing cost, and this will also be explored.
Ives: Operation of a Confined Flow Multiple
| CCR has completed
initial testing of a confined flow multiple beam
gun for a 50 MW klystron. The successful testing
of this gun provides the oportunity to employ a
new class of RF sources for high power accelerators.
The gun operates below 200 kV, which will allow
utilization of solid state power supplies rather
than pulse modulators. This will have dramatic impact
on the cost of RF sources and power supplies for
large systems. The voltage reduction also provides
improved efficiency, reduced radiation shielding,
and reduced electrical stress on the entire RF source
system. These improvements could dramatically reduce
the cost of accelerator systems.
The gun was tested in a beam analyzer specifically
designed for distributed beam sources. The analyzer
provides transverse profiles of the electron beam
at various distances from the cathode. This allows
precise measurement of the beam quality, including
scallop and spiraling. It also provides information
for confirming the accuracy of the computer codes
and for improving the performance of the gun itself.
The gun in test also allows application of voltage
to the focus electrode. This could be extended
to allow gridded operation of a multiple beam
gun, which could allow short pulse operation to
eliminate the requirment for pulse compressors.This
presentation will describe the gun design, construction,
test, and planned modifications for implementation
in a full power klystron, currently scheduled
for testing in 2005.
Read: Generation and Focusing of Sheet Beams
for High Power Klystrons
| Sheet beam klystrons
are a promising method for generation of high power
at high frequency. However, the generation and focusing
of the beam for this type of device requires 3D
design methods available only recently. We discuss
the design of the electron gun and ppm focusing
for a 100 MW beam for an X-Band klystron. The gun
has a beam voltage and current of 415 kV and 250
A, respectively. The cathode is 10 cm x 10 cm while
the beam is 10 cm x 0.8 cm. The cathode is non-immersed.
The gun is gridded, allowing the use of new hybrid
modulators being developed for the Department of
Energy. These modulators have a significant amount
of stored energy, and the gun has been designed
to reduce the possibility of a cathode-anode arc.
The ppm focusing is of the "cusp" type
with focusing in both transverse planes. In an
initial design, 96% of the beam was transmitted
over a distance of 80 cm.
Details of the gun and ppm design will be presented,
and prospects for designs at lower impedance and
higher frequency will be discussed.
Yakovlev : FAST X-BAND PHASE SHIFTER
| A phase shifter to
be the key element of an active high-power switch
is described. This phase shifter employs ultra-fast,
electrically–controlled ferroelectric elements.
This high-power switch will allow one to build an
active Delay Line Distribution System (DLDS), which
would provide substantial reduction in the length
of waveguide, compared to what would be required
for the traditional passive DLDS design for NLC.
The results of preliminary optimization of the phase
shifter at the NLC frequency of 11.424 GHz are presented
showing the feasibility of building the switch to
control a power of 500 MW. Initial tests at a power
of up to 50 MW are planned using the Omega-P/NRL
X-band magnicon. ______________________________________________________Research
supported by the Department of Energy, Division
of High Energy Physics.
Vikharev: Plasma Switch for X-Band Active
SLEDII RF Pulse Compressor
| As proposed by SLAC
 the efficiency of a pulse compressor of the
SLED-II type could be increased by changing both
the phase of the microwave source and the coupling
coefficient of the delay line. In the existing SLED-II
system the resonant delay line is coupled with the
source via an iris with a constant reflection coefficient.
Replacement of the iris with an active component
makes it possible to create an active SLED II system.
In this paper use of a plasma switch as the active
element is discussed. This plasma switch is a similar
to that which has been developed for active Bragg
compressors . Designs and low-power tests of
some versions of the plasma switch are described.
Low-power tests showed that such plasma switches
could provide variation of the reflection coefficient
in the range from Ro = 0.89 – 0.92 to Rd =
0.4 – 0.2. Experiments with a compression
system that consisted of the plasma switch and a
6 m resonant delay line with round trip power losses
of 1.5% showed that it is possible to achieve the
following parameters for an active SLED II compression
system: compression ratio C = 10 – 16, power
gain M = 7 – 12, and compression efficiency
h = 65 – 75%.
 Tantawi S.G., Ruth R.D. and Vlieks A.E., Active
radio frequency pulse compression using switched
resonant delay lines, Nuclear Instruments and
Methods in Physics Research A, 1996, v.370, pp.297-302.
 Vikharev A.L., Gorbachev A.M., Ivanov O.A.
et al., Active microwave pulse compressors employing
oversized resonators and distributed plasma switches,
AIP Conf. Proc., 1999, v.472, p.975.
*Research supported by US Department of Energy.
Nezhevenko: INITIAL OPERATION OF 34 GHZ,
45 MW PULSED MAGNICON*
| A high efficiency,
high power magnicon at 34.272 GHz has been designed
and built as a microwave source to develop RF technology
for a future multi-TeV electron-positron linear
collider. To develop this technology, this new RF
source is being perfected for necessary tests of
accelerating structures, RF pulse compressors, RF
components, and to determine limits of breakdown
and metal fatigue. After preliminary RF conditioning
of only about 2´105 pulses, the magnicon produced
an output power of 10.5 MW in 0.25 ms pulses, with
a gain of 54 dB. Slotted line measurements confirmed
that the output was monochromatic to within a margin
of at least 30 dB. __________*Research supported
by the Department of Energy, Division of High Energy
Hirshfield: Whispering gallery pulse compressor
| If the
classical SLED  were scaled immediately from
the S-band to a higher frequency, the power capacity
of the rf pulse compressor would be drastically
reduced. For the X-band, the most adequate equivalent
of the SLED seems a barrel-like cavity operating
at a whispering gallery mode: with azimuthal index
. The rf breakdown threshold of the compressor
can be raised to a still higher level, if the perforation
coupling of the cavity with the input-output waveguide
 is changed for a coupler based on a wave tunneling
effect .The pulse compressor of the latter type
can be designed by simple analytical and numerical
methods. An 11.4 GHz / model of the compressor tested
at a low power had a performance consistent with
the theory and similar to that of the classical
SLED: depending on combinations of parameters, the
efficiency was between 55% and 80 %. A preliminary
technical design for an evacuated high-power compressor
has been developed. According to a theory, a twin-cavity
version of the device can efficiently compress microwave
pulses produced with sources of a limited frequency
band, in particular, chirped pulses.Such robust
and relatively compact compressors can be used to
test components of novel electron-positron colliders
and to feed relatively small medical electron accelerators.
The work was supported by a DoE SBIR grant.
References1. Farkas Z.D. et al, SLED: A Method
of Doubling SLAC’s Energy, Proc. 9th Conf.
On High Energy Accelerator, SLAC, Stanford, CA,
USA, May 2-7, 1974, p. 576, SLAC-PUB-1453.2. Balakin
V.E., Syrachev I.V. VLEPP RF Power Multiplier
// Proc. III-rd Int. Workshop on Next Generation
Linear Collider, Branch INP, Protvino, Russia,
1991. P. 145–156. 3. M. I. Petelin, J. L.
Hirshfield, S.V. Kuzikov, A. L. Vikharev. High
power microwave pulse compressors: passive, active,
and combined. SPIEs 14th Annual Symposium on Aerosense,
24-28 April 2000, Orlando, Florida USA.
Yu: NEW DEVELOPMENTS ON PBG RF CAVITIES
and design features of metal PBG and rod-loaded
cavities for single-beam and multi-beam rf accelerating/generating
devices are considered. Fundamental differences
of the performance between single-defect and multi-defect
structures are identified. A six-beam cavity design
with external coupler is optimized for a multi-beam
PBG klystron. Preliminary design of a compact, 6-beam,
X-band MBK demonstrates feasibility of generating
high power with high efficiency.
*Work supported by DOE SBIR grant number DE-FG02-03ER83845