Solid state high power amplifier for driving the SLC injector klystron Page: 1 of 3
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A SOLID STATE HIGH POWER AMPLIFIER FOR DRIVING
THE SLC INJECTOR KLYSTRON*
J. G. Judkins, J. E. clrndbnm and H. D. Schwarz
Stanford Linear Accelerator Center
Stanford Ifuiveixily, Stanford, California 94305
The SLC injector klyetron RF drive 1i now provided by a
recently developed solid-state amplifier. The high gain or the
amplifier permit! the uie of a fast low-power electronic phase
shifter. Thus the SLC computer control system cut be used
to abHt the phase of the high-power RF rapidly during the
fill time of the Injector accelerator section. These rapid phase
shifts are used to introduce a phase-energy relationship in the
accelerated electron pulse fa conjunction with the operation of
the injector bunch compressor. The amplifier, the method of
controlling the RF phase, and the operational characteristics
of the system are described.
For the SLC (SLAC Linear Collider), electron and positron
single-bunch beams at $0 GeV are to be produced by an up-
graded SLAC tluac. The Ifaac is a traveling-wave RF accel-
erator operating at 2856 MHz (S-band). The SLC electron
injector ntitiiea sub-harmonic bunching prior to S-band bunch-
ing to achieve a charge of over g nC in a single S-band bunch
at relativistic energies.1 In the injector accelerator section, af-
ter approximately 30 cm, all the bunched particles travel syn-
chronously with the RF phase at 0 = pt w 1 so that no addi-
tional bunching takes place. The beam is farther accelerated
to 1.2 GeV and injected Into a damping ring (DR) to reduce
the transverse emiMance. Because the accelerating RF is si-
nusoidal, the energy spread of the beam in the Ifaac Increases
with bunch length. On the other hand, for extremely short
bunches, the energy spread increases due to the effect of lon-
gitudinal wasefield* generated in the accelerating sections.
Id order to optimise tbs bunch length at the injector, the
path-length of lbs bunch Is varied as a function of energy by
passing the beam through a bunch compressor consisting of
four dipole magnets.1 If the phase and energy of the particles in
the bunch are correlated, the compreesor can be used to adjust
the bunch length. The desired correlation can be accomplished
Fig. 1. SLC Injector RF block diagram. IPA—Isolator, Phase
Shifter, Attenuator, PDU—Programmable Delay Unit. PPG—
Programmable Poise Generator.
by shifting the phase of the injector klyetron In a lime that
is abort compared to the fill-time of the accelerating lection
(0.8 psec). The timing of the phase shift must then be adjusted
so that an electron bunch passing through the 3 m section
seen the phase shift somewhere between 30 cm and the end ot
the section. If the RF phaae is shifted bo that fa the latter
part of the acceleration the bunch is advanced in phase with
respect to the crest of the RF, then at the compressor the
lead particles wiD have less energy and consequently take a
longer path through the compressor than the particles fa the
tall of the bunch. By adjusting the strength of the compressor
magnets and/or the timing and magnitude of the phase shift
In the injector RF, the bunch length can be adjusted for a o,
fa the range of t to 4 mm.
A fast phase shifter for the high-power RF output of the
injector klystron does not exist. However, the bandwidth of
the klystron is quite sufficient if the phase of the RF drive is
shifted Instead (Fig. 1).
Amplifier System Description
The sew amplifier system consists of a four-siege pulsed
amplifier and low-level microwave signal conditioning circuits
(eee Fig. 2).
The amplifier is built around 60 Watt S-band transistors
developed by Microwave Semiconductor (MSC) and Acriau.
These silicon bipolar traaslstore have approximately 6 dB of
The 60 W translators are paired into a 12D W module us-
itg 3 dB microjUip hybrids. By combining the power of four
liO W modules, <50 W arc achieved. The amplifier output
goes through a variable attenuator and isolator with a com-
bined minimum loss of 14 dB before reaching the klystron.
This means a maximum drive of 320 W is available at the
klystron. Tbs combining is done by a four-way stripline hy-
brid system. The same four-way system is used fa a reciprocal
fashion to split the drive to each module. A fifth 120 W module
is needed to drive the output stage.
This 120 W module ie fed by a 32 W pulsed power amplifier.
It Is a two-stage 12 dB gain module uilng lower power versions
of the 60 W transistor. The 32 W amplifier requires 2 W of
drive which is supplied fay s commercially available high-gain
The low-level signal conditioning circuits consist of linear 0
to 180 degree phase shifter, FIN diode pube modulator, elec-
tronic variable attenuator, and ± s/2 phase shifter (PSK).
Poised Power Transistors
The high-power translitors are common base internally
'Work supported by the Department of Energy, contract DE-
grounded with collector efficiency of 35K. Internal matching
and bond wires to the die limit the bandwidth to 200 MBs.
Maximum pube width of 100 pa and 1096 duty cycle are lim-
ited by the device’s therms! time constant. Operation above
these limits decreases the lifespan. Accelerated life tests being
Presented paper to the 1005 Particle Accelerator Conference f)
Vancouver, B.C., Canada, May 13-10,1885. |)f TIBS DC®® B TO®01t-D
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Judkins, J.G.; Clendenin, J.E. & Schwarz, H.D. Solid state high power amplifier for driving the SLC injector klystron, article, March 1, 1985; California. (digital.library.unt.edu/ark:/67531/metadc1093760/m1/1/: accessed October 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.