Proceedings of the 2nd Annual Meeting of Particle Accelerator Society of Japanand the 30th Linear Accelerator Meeting in Japan (July 20 - 22, 2005, Tosu Japan)

IGBT INDUCTION-TYPE MODULATOR FOR X-BAND KLYSTRONSA)1

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B)

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Vladimir Vogel , Mitsuo Akemoto , Andrey Cherepenko , Yong Ho Chin , Hiroyuki Honma , Evgeniy Kokin ,A)
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C)
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Shuji Matsumoto , Hiromitsu Nakajima , Victor Revkov , Tetsuo Shidara , Shuichi Tokumoto , Uriy Valyaev ,B)A)
Askold Volkov , Shigeki Fukuda ,A)
KEK, 1-Oho, Tsukuba, 305-0801, JapanB)
Budker Institute of Nuclear Physics (BINP) 630090, Novosibirsk, pr. Lavrenteva 11, Russia
C)
Branch of Institute of Nuclear Physics (BINP) 142284, Protvino, Moscow reg. Russia

Abstract
A solid-state induction-type modulator was developed
at KEK for the JLC project. The modulator consists oftwo oil-filled tanks; the first is for two klystrons and thesecond for a pulse transformer. The pulse transformer
consists of 42 cores made from Finmet3 material. Eachcore is driven by a voltage of 3.2 kV by two IGBT plates;
one of them has core reset circuits. The total number of
IGBT plates is 84. The transformer has one turn at theprimary and four turns for the secondary. This modulator
can drive: pulse width up to 1.6 µs and high voltage up toa 500 kV pulse with a current of up to 540 A for two Xband klystrons. The pulse top flatness is 2%. The
expected modulator efficiency is about 75%. We plan totest the modulator during the summer of 2005. We report
here on the first status of this work, the result the core
testing, the IGBT driver’s electronics and protection
system testing, and the result from the high voltage
testing of some components of the modulator.

Fig. 1. Simplified concept of a linear induction-typemodulator.
from that of SLAC. The specifications of KEK’s LIM aregiven in Table 1. Although KEK has been designing andmanufacturing the LIM, after a decision of ITRP
(International Technology Recommendation Panel) tochoose the ILC accelerator technology over cold
technology, the priority of LIM study became lower. In1 INTRODUCTION
Since the rf efficiency and stability strongly depend on
the performance of the klystrons and modulators, intense
studies have been conducted for their development.
Various modulators were proposed for LC, and theinduction-type modulator was a strong candidate
modulator, which was possibly replaceable with a linetype modulator. SLAC had developed an induction-type
modulator, and used it for the 8-pack module in
NLCTA.[1] KEK also proposed the linear induction
modulator (LIM), the concept of which was different

Fig. 2. Waveform of the IGBT test. A very fast risetime was achieved.
order to demonstrate the feasibility of LIM, a final test of
LIM with a resistive load was performed. We obtained
test results of 280 kV (max) with a pulse width of 1.1 µs,
a repetition of 1Hz. The repetition was restricted by thepower supply, which was not an essential matter. This
report gives a general description and a test result of LIM.

Table 1 Technical Specification of Induction Modulator
Item
Unit
Number of PPM Klystron
2 Klystrons
Klystron Voltage
kV
500
Total Current
A540
Pulse width(70%-70%)
microsec
1.6
Pulse Top Flatness%
2
Efficiency%
65-85
Repitition RateHz100

1Fig. 3. Drawings of the LIM. Top is a cross section ofthe cores and the installed IGBT board. The bottom isthe core assembly and the klystron load.

He is now in DESY, Germany.
-E-22-

Proceedings of the 2nd Annual Meeting of Particle Accelerator Society of Japanand the 30th Linear Accelerator Meeting in Japan (July 20 - 22, 2005, Tosu Japan)

2 PRINCIPLE AND STRUCTURE OF LIM
The principle of the LIM is simple, as shown in Fig. 1.
If the number of the core is N, each current of the IGBTis IIGBT, and each IGBT commutates a voltage of U1, thefinal voltage (UOUT) is to be N*U1 and a total current(IOUT) is IIGBT*2.

Eighty-four IGBT plates, each of which produced 3.2
kV, were carefully designed and all of them were tested
before installing to the tank. Figure 4 shows pictures ofIGBT plates. A block diagram of the IGBT plate is shown
schematically in Fig. 5. This figure also shows the IGBT
protection schemes. Each IGBT driver plate has a
microcomputer, which is connected through the RS485
line to a local personal computer, and can be controlled.
IGBT protection signals come from the following
detectors: an over-current detector, an over-voltage
detector, a dI/dt detector, a temperature detector, a reset
current detector, a 20-micron thin iron fuse, and a gate
driver with fast logic. Some of the protection schemes areFig. 4. IGBT plate (left) and installed boards for the 2core setup test (right).
Although the principle is simple, there are several
points to be carefully considered: IGBT protection,weight of the core material, the electrical field strength inoil, a switcher IGBT, the type of capacitors, and thesystem of modulator control and monitoring. In thismodulator, the IGBT driver was specially designed tohave a very fast rise time. Figure.2 shows the waveformof the test result. This is a special feature of this model.
Variants for LIM for the JLC were considered at the firststage. Variants included a number of turns of thesecondary winding, a 2-pack or a 4-pack for the klystronload, and the method of how to feed the power to theklystron (direct connection in the oil, cable connection, or
coaxial line). Finally, a multi-turn induction modulator of
the 2-pack type was adopted (four turns for the secondary
winding were chosen). The pulse transformer consisted of
42 cores made from Finmet-3 material; each core wasdriven by a voltage of 3.2 kV by two IGBT plates, andone of them had core reset circuits. Therefore, the total
number of IGBT plates was 84. In this case, a length ofcore was 2 m long and the weight of the cores was 1.4tons, as shown in the drawing of Fig. 3.
For applying a high voltage, it was necessary toconsider IGBT protection, the klystron’s arcing detection,and the design of a 3.2kV feed-through from the plate tothe core. The rise time and impulse flatness were also
important issues. These are described later.

Fig. 6. Control systems.
shown in Fig. 5 along with the waveforms.
Temperature information and the status, such as theprotection status, HV status, core reset status and p/sstatus, are sent from the board to the pc if IGBT
protection is not ready. The pc sends IGBT various
signals related to a delay, the pulse length, estimatedcurrent and voltage, a HV control and a board reset.
For klystron arc protection, we prepared several
counter measures, such as an additional inductance in anoil tank for each klystron, an X-ray detector,[2] fast logic
in the gate driver and a current-limited circuit. Theseprotections were achieved through the RS485 networkwith a pc, as shown in Fig. 6.
For the 3.2kV feedthrough from the IGBT plate to thetank, since there were no commercial ones available, wedeveloped a special feedthrough comprised of aconductor plate molded with rubber packing, which
sealed the insulation oil. The durability for 3.2 kV wastested, and the obtained results were good.

3 IGBT PLATE AND CONTROL SYSTEM

Fig. 5. Block diagram of the IGBT plate and theprotection. scheme.

4 FABRICATION AND TESTING
Selection of the core material was an important issue
for the LIM, since loss of the core was strongly related tothe modulator efficiency and the total weight of thesystem. We compared the loss of various core materials,
such as FinmetTM, MetglasTM, AmetTM and oriented
silicon steel material. From the toroidal-core loss data
(f=10kHz, B=0.1Tesla), Finmet was found to be less than
0.5W/kg and showed the nicest performance among them.
We determined to use FInemet3TM as the core material forthe pulse transformer. The performance of the first-E-23-

Proceedings of the 2nd Annual Meeting of Particle Accelerator Society of Japanand the 30th Linear Accelerator Meeting in Japan (July 20 - 22, 2005, Tosu Japan)

prototype of the Finmet cores was good for theacceptance test.
Before manufacturing the boards, a prototype model
was tested in May, 2004 with the configuration of the 2core setup having 4 IGBT plates, as shown in Fig. 4(right). A high voltage was tested in the air, and weobtained a voltage of 6 kV and a current of 2 kA with apulse width of 1.6 µsec and a repetition rate of 100 Hz.
These results confirmed the design validity, and weFig. 7. Loss data of the Finmet3 core. The line shows
the upper limit of the allowable loss.

Figure 8 shows the final assembly of LIM. Due to hightolerances between the pulse transformer assembly andthe oil tank, insertion of the core assembly to the tank was
not easy. The testing was limited to a lower repetition rate
due to the rating of the resistive load and the power
supply. We had prepared a power-supply of sufficientcapability, while the remote control shown in Fig. 6 was
not available in time. A test was performed with a power
supply having a low-power capability of 3 kW, arepetition rate of 1Hz, a voltage of 280 kV (max) andpulse width of 1.1 µs. The limits came from the load.
A flat-top adjustment was also difficult since thefluctuation of the each core forced us to perform wider
range tuning of each IGBT board adjustment than theoriginal tuning range. Figure 9 shows the waveform of
the output voltage from the LIM. In Fig. 9, three lines
show the variation of the pulse top flatness by adjusting
the timing and width of the IGBT driver. It is thus
possible to obtain a flat top of the pulse within 2% after
successive trials.

started to manufacture all boards and cores.
During the manufacturing process, several problems
were found: the surface insulation of Finmet was
sometimes destroyed during the winding process of thefoil, which led to a serious loss increase, as shown inFig.7. The mechanical tolerances for the core werechosen to be high so as to make a tight contact with theconductor from the IGBT board: The architecturetechnology of installing the high-voltage parts on theprint board was not performed well in the company
product. Especially, the first problem was serious. For thesecond one, in order to make the core within the tolerance,

0-20

Uout (kV)

-40

-60

-80

-100

-120

-140
-2.0e-70.0

2.0e-7

4.0e-7

6.0e-78.0e-71.0e-6

1.2e-6

1.4e-61.6e-6

1.8e-6Time (Sec)Fig. 9. Waveform of the LIM output pulse.

5 SUMMARYWe developed an IGBT induction-type modulator andperformed the first successful tests up to 280 kV (max).
This kind of modulator was thus proved to be operated in
the rf source of a linear collider. We found several tasks
to solve, such as the process control of manufacturing theFinmet core and a more flexible design considering theease of maintenance. If these can be solved, the IGBT
type modulator is promising for the future, by replacing
the usual line-type pulse modulator.
Fig. 8. LIM assembly under testing.

6 ACKNOWLEDGEMENT

the core manufacturer reformed the dimensions after
epoxy-impregnation process, and the resulting corecharacteristics became poor. Figure 7 shows thefluctuation of the losses after core manufacturing. Weshould pay attention to the jig to prevent the cores fromsurface-insulation damage and from deformation during
the epoxy-impregnation and drying process. Delaying theassembling and the ITRP choice forced us to reduce theactivity for the LIM project. Finally, a test using a
resistive load instead of using a klystron load wasplanned and performed in the summer of 2005.

The authors deeply thank Mr. Kageshima of Nihhon
Denji Kogyo for his efforts to manufacture and assemble
the pulse transformer assembly.
REFERENCES[1][2]-E-24-R.L Cassel, et al., “NLC Hybrid Solid State Induction Modulator”,
LINAC’04, Lubeck, Germany August 16-20, pp.697-699, 2004.
V.Vogel and S. Matsumoto, “Detection of X-ray Due to Gun
Arcing of High Power Klystron", Proc. of 1st Annual. Meeting ofParticle Accelerator Society in Japan, Funabashi, Japan, pp.269271, 2004.