The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Power Supply System for 324 MHz Klystron of the JHF Proton Linear Accelerator
Masaaki ONO, Shozo AN AMI, Masato KAWAMURA, Eiiti KADOKURA,Shoichiro KOSEK!*, Hiroshi KUBO*, and Yuuichi ICHIKAWA*
High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba-shi, lbaraki-ken, 305-0801, Japan*Hitachi Industrial System & Product Div ., Hitachi, Ltd., 1-1, Saiwaicho 3 chome, Hitachi-shi, lbaraki-ken, 317-8511, JapanAbstract
A proton linac of the JHF will consist of several frequency
rf-sources depending on the accelerating structures. The low
energy part of the linac (RFQ, DTL, and SDTL) are now
planned to be driven by 324 MHz Klystrons. High power andhigh duty power supply systems for these 324 MHz klystrons
will be reported The beam power of the klystron is supplied
from a cathode high voltage capacitor bank with modulating
the beam current by a modulation anode. The basic scheme ofthe power supply system is as follows. Four klystrons areconnected to the common cathode voltage but the beam currentof each klystrons are modulated independently. A crowbar
circuit is equipped to bypass the huge energy stored at thecapacitor if the shortening is happened at the klystron. Four
klystrons in one system will be operated through two level
control sequences of PLCs. The power supply system statedabove is now starting to construct. Preceding to othercomponents, one anode modulator has been already constructed.
The present status of a design work and the test result of themodulator will be described.

1 Introduction
In the present scheme of the JHF proton linac, the low
energy part of it (up to 200 MeV) will consist of RFQ, DTLand SDTL[ 1] accelerating structures and these will be driven by
324 MHz rf-power. Before starting a construction of the 200
MeV linac at the JHF site, a 60 MeV prototype linac isscheduled to be constructed at KEK site to clear the difficulties
that will be encountered at the actuallinac construction, and toshow that the designed linac is feasible. High power and highduty rf-sources are required for these structures, so the klystronis adopted as the rf-power generator. The maximum
operating-rate of the klystron is 2 MW power for 650 ~-ts
pulse-duration with 50 pps repetition rate. The rf-power statedabove must be well controlled both in the amplitude and in thephase, therefor the klystron that can generate 3 MW at thesame duty is required and will be operating at a condition for
2.5 MW saturated output. In this condition, the amplitude andthe phase can be controlled by the drive power of the klystron(low level control) up to 2MW output with reasonable wide
margin for stable klystron operation. The klystron equippedwith the modulation-anode is adopted, so the adopted schemeof the high voltage power supply system is consisted with thede-cathode voltage and the pulsed-modulating anode voltage.
The later anode voltage is generated by dividing the cathodevoltage with prefixed ratio. This configuration is almost thesame as the JHP klystron power supply system[2] that wasconstructed at KEK for UHF(432 MHz) pulsed klystron. The
basic configuration of new system is consisted with 4
klystrons connected to the common cathode voltage withindependent anode modulation for each klystron. In order tosuppress the cathode voltage sag within the reasonable range(<5% ), large capacitor bank is adopted. The crowbar circuit isequipped to the system to protect the klystron from the damage
caused by the stored energy at the capacitor. A special
modification is carried out only for one system. Because thepower required for the first klystron (for RFQ) of the linac is
not so high, one klystrron of this system is supplied thereduced cathode voltage even though 3 remain klystrons can besupplied the nominal cathode voltage. As a trade off of thisoption, the stabilization of the reduced cathode voltage is not
carried out; the stabilization of the nominal cathode voltage forMax. Rating comment
324 MHz620 1-!S50 pps
3 MW Vk> 11 OkV for max.
power
2.5 MW at operation Vk
Saturation power
2 MW linear region
max. Operation power
102 kV operation Vk
Cathode Voltage
44 A
Beam current
86 kV
Mod. Anode Voltage

KlystronFrequency
RF pulse width
Repetition Ratemax. Output power

Max. Rating
DC power supply
4
No. ofKlystrons
110* kVVoltage
6.3 ACurrent
693 kWPower180* APulse current
700 I-tS
Pulse width
50 ppsRepetition rate
3.5%
Duty5%Voltage Sag
25.5 ~-tF
Capacitor Bank
154 kJ
Strd Energy at C-Bankcomment
cathode vtg.
ave. of Pulse current
beam+ M. pulse cur.
FWHM*(19.2, 6.4 ~-tF)

Max. Rating comment
M-Anode Modulator
93 kV depend on Kly.
Pulse Voltage
cur. at vtg. dividerlA
M. pulse current
FWHM
700 1-!S
Pulse width
Flat top_620 1-!S
Pulse width
pF**objective
250
Capa. of Floating box**cable+Kly.anode300 pF
Capa. of Load**; objective: 20 ~-ts40 I-tS
Pulse rise time**
130 J..lS
Pulse fall time
Table 1. Parameters of the klystron and the power supply
system. * : For the reduced voltage klystron, 73kV and 30A
be supplied at max. ** : Estimated values, so rise/fall time
may be changed depend on the actual capacitance values.
3 klystrons is carried out. And also, the crowbar circuit for
reduced voltage is not installed However, one merit of thisoption is that a degraded performance klystron can be used at
this station if these will be exist. As stated, one power supply
system contains many components to be operated or controlledsuch as 4 klystrons, the high voltage part of the power supply-275-

The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

and also low voltage power supplies; for focus coil, forfilament, and for ion pumps. The components concerning to
the high voltage generation are set at a high voltage yard placedat the outside a klystron gallery. On the other hand, thecomponents concerning to the klystron are set at the klystrongallery near to each klystron. These components scattered inplaces are all monitored their performances, and are controlled
following the operation procedures through the two levels
control sequences by the PLCs.

2 DC High Voltage
The maximum rating for one system as well as theparameters of the klystron are summarized in Table-]. The one
special system can generate nominal llOkV for 3 klystrons
and 73kV for one klystron as shown in Fig.l; the 120kV, and80kV shown in the figure are maximum voltages
corresponding to no loading condition (no beam current).
Neglecting this reduced voltage part, the rectifying method is
almost the same as the JHP power supply system[2]; step
down ac 6.6kV to ac 600V, controlled by thyristors to stabilize
the voltage and step up to generate the nominal de voltage. The
reduced voltage is given as a fixed ratio (2/3) of the nominal d:voltage; no direct voltage stabilization is carried out for reduced
voltage. The capacitor bank are chosen to satisfy the voltage

is adopted The sag of 5% may be practical choice from theseveral points of view; size, cost and the stored energy. The
last point is important if the crowbar circuit is installed in thesystem with using ignitrons as switching device. The phasecontrol of klystron output is another point to be discussed;
more than 10° shift for 1% voltage sag, this correspond to>60° phase shift at pulse duration at most. The smaller phaseshift (smaller sag) is preferable for precise phase control, if it
is required A bouncer circuit is one possibility forcompensating the sag by generating anti-sag voltage andimposing it to the cathode voltage at the pulse duration. The
rectifier/trans part is prepared to be isolated from the groundwith 20kV withstanding voltage, even though no practicaldesign of bouncer circuit is started yet. Four klystrons areconnected to the one power supply system via 4 disconnection
devices (DISC ON) prepared for each klystron; for the basic 4
nominal voltage system, dividing into 4 branches after passing
through the crowbar, and for 3 nominal+ 1 reduced voltage
system, branching into 3 after the crowbar but not passing
through the crowbar for 1 reduced line because the crowbar isomitted in this line. The DISCON is prepared to disconnect theklystron/socket easily and to insure the safety at the remaining
klystrons are operated. The area of the high voltage yard for one
system is -100m 2 • The rect/trans, the thyristor control unit,
the capacitor-bank, the crowbar and a local control unit of theseare placed there. The DISCON is placed in the klystron gallery
just before the modulator.

3 Crowbar Circuit-BP V; N1

Fig.l Schematic diagram of de high voltage part.
The C-bank and the crowbar are also placed in this yard. The
area size of these are, 2.3x 2.5 for rec/trans, 1.8 x 2.5 for Cbank, 1.2 x 3.5 for crowbar in the basic system. In the specialsystem, more larger or extra parts are added.
sag below 5% at pulse duration; 25.5J.1F for 4 klystrons (for3+1 reduced system, 19.2f.IF and 6.4J.1F are separatelyequipped). The maximum repetition rate is 50pps, so aresonant frequency of the rectifier is chosen as -10Hz with-1 OH choke coil. Some fear may rise if we try low repetition
rate (1 - 10Hz) operations that will be reasonably expected atconditioning periods ofthe klystron or cavities. However, theexperience at JHP power supply and the result of the numericalsimulation indicate the stable operation at such low repetitions.
So we adopt these parameters with the reasonable size of choke
coil; the JHP system was designed as almost the same
parameters except the number of klystron for one system. The
generation of de high voltage stated so far, is simple inprinciple and may be cheap for construction, but the relatively
large sag is inevitable consequence unless a big capacitor bank

The crowbar equipped with 6 series ingnitrons (NL-35391)
is designed to install just after the C-bank in the high voltage
yard. The long distance between the crowbar and the klystron isexpected in the present layout of the linac; the high voltage
yard is placed at outside the klystron gallery and the expectedco-axial cable length connected between them may vary from a
few 1Om to 1OOm. Even though the energy stored at the coaxial cable is not so small compared to 20J (the maximum
allowed dissipation energy at shortening), we adopt thisconfiguration. The one reason is that a large portion of thestored energy at the cable is reflected back to the power supply
side when the flash over happened at the klystron. The
dissipation power is usually estimated as arcing voltage times
current (60-100 V xI A), then the small dissipation energy isexpected for first one pulse duration which is determined bycable length; 2 x 'tcable. The dissipation energy contributed
from the following pulses is negligibly small because of
approximate cancel out caused by an alternate polarity change,
and because of the damping of the magnitude of pulses by aseries resistance that is installed in the high voltage line at theklystron side after the long co-axial cable (actually installed in
the anode modulator tank). These behavior were observed
experimentally in the cu-wire shortening tests carried out at
TRISTAN klystron power supply with using long cables (50,100, 200m length), and discussed in ref. [1]. The energy flowfrom the primary line (ac 6.6kV) is also expected to be small,because of a quick shut off (-5ms) the primary power with
reducing ac current by the thyristor control. Therefor the speedof crowbar work and the value of the series resistance are majorparts to determine the <,tctual dissipation energy for the given
capacitance of C-bank and de high voltage, irrelevantly to thecrowbar position; whether it is before or after the long cable. In-276-

The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

the JHP system, a relatively larger series resistance such as
27.5!1 is adopted with <6j.!s crowbar speed for intending <1 OJ
energy dissipation. Still rough but a little more precise
estimation may indicate 10-20 resistance with the same
crowbar speed for < lOJ dissipation even for larger C-bankcapacitance. The larger the value of the resistance is preferable
for decreasing the dissipation energy at the shortening, but thesmaller the value of it is preferable for dissipation power at thisresistance in the normal operation; -20kW dissipation for
27.5!1. The cu-wire shortening test at the actual system may
decide final value of the resistance. Because the other importantparameter Leff' s ( a inductance for the flash over current fromC-bank) are depend on the actual layout and hard to estimate.

4 Anode Modulator
The high voltage for the modulation is generated by aresister-chain voltage-divider which is installed between thecathode voltage and ground level, and is pulsed by a hard tube
switching device (TH-5188), as shown in Fig.2. A de reverse
bias voltage (-2 to -3kV) is imposed on anode voltage withfollowed by 1OkQ to insure a cut off state of klystron atinter-pulse period An isolation transformer for klystronfilament, and the series resister at cathode voltage are also
installed The pulse current stated in Table- I (as 1A) is thecurrent at the voltage-divider in the pulse duration, and thislarge value current insure the almost constant voltage dividing

MonitorFig. 2 Anode modulator tank. Stray capacitance areschematically showed; Csl and Cs2.
ratio even for -1 OOmA anode current. The actual dividing-ratio
may depend on the required power and the klystron performance.
The module of the resister-chain-set can be replaced easily. The
Ru is selected from 3 taps of the module. The rise and falltimes of the pulsed anode voltage are proportional to a sum ofstray capacitance's formed by a floating box (Csl) that
contained the hard tube, and by the anode line load (Cs2); coaxial cable (-2m) and klystron anode with its socket. The
modulator is set in the klystron gallery close to its klystron;
just after the DISCON. An effort to reduce these capacitance's
has been tried in the design work, and is almost realized in an
actual modulator that is already constructed preceded to othercomponents. It has been installed at JHP de high voltage, andtested with a beam-test-tube for 324 MHz klystron[3]. The
results are compared with a simulation and with old modulator
as shown in Table 2. The simulation reproduces the data quite
well, so this result indicate that the stray capacitance of theklystron-anode setting at the socket is -260pF, if 200pF
coming from 2m long cable is assumed; Cs2 - Ccable"' 260pF.
In the design work, -20j..ls and -130j..ls are assumed as
objective values for rise and fall time, respectively. Further
efforts which may include a using of other type switching
device, are required to attain (or to close to) these value under alimiting spacecondition. Thesizeofthepresent tankis 1 (+.3)
x 1.2 (+.32) x 1.5h (+.32) m 3 , where the value in theparenthesis indicate an amount of convex part. Thecomponents of the modulator displayed in the square box infigure 2, are all immersed in insulator oil.
Attained *Simulation
31.3 j.!S
32 j.!SIRise time: 10-90%
178 I.!S
183 I.!S
IFall time :10-90%
Table 2. Comparison of nse/fall time.

JHP:old50 j.!S390j..ls*Simulation condition; Ru=17kQ, Rd=9lkQ, R4=10kQ,
Cs 1=285pF, Cs2=463pF. Also capacitance of hard tube
(plate-HV case) is included; 104pF. Csl is measured without
hard tube and Cs2 is also measured value of -5m cable.
Objective(Tablel): Cs1=250, Cs2=300pF.

5 System Layout and Control
The components of one power supply system are placed in
two major separated areas such as the high voltage yard and theklystron gallery as stated before. In the klystron gallery, thecomponents belonging to each klystron are grouped and set
close to their klystron with other components such as the lowlevel rf control modules. The gallery is placed just above thelinac tunnel, and the klystrons are placed in 7m pitch in there,
therefor the grouped components are also placed in the sameinterval. The places to be local control-station are scattered inwire area. From the point of view of the maintenance's of
klystron and/or the power supply system, we must be able tooperate the system in situ; at each klystron station and at thehigh voltage yard. Sequencer's (PLC) are adopted to control thesystem even in the most basic level controls; hard-wired relay
sequence are almost all rejected, except at the safety control orat emergency controls. Two control levels (PLCl andPLC2)
are prepared. The level of PLC 1 control the basic operations ofthe system, and this level alone can operate the system safely
but in primitive ways. On the other hand, more sophisticatedcontrols are carried out by PLC2 level with the safety of thesystem being relayed on the PLC 1 and hard-wired relay
sequences. Each control station in situ is selected exclusively
as a master controller of the system, except for the operation ofsafety; high-voltage-off operation can be done at any station
and at any time. The remote control of this system from thehigher level network is obvious option.

References[1] "JHF Accelerator Design Study Report",
KEK Report 97-16, JHF-97-10, March 1998, A[2] M. Ono et. at., "432-MHz RF source for the JHP protonlinac", Proc. of IEEE Particle Ace. Conf.(1993), p.1163.
M. Kawamura et. al., Proc. of the 20th Linear Ace.
Meeting in Japan (1995), p.266.
[3] M. Kawamura et. al., "High-power tests of a klystronbeam-test-tube and an anode modulator", Proc. of the 24thLinear Ace. Meeting in Japan (1999), p.200.

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