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					 Protection and Control of Accelerator Microwave Sources Using a High Power
                                 IGBT Switch
                                                  Marshall Loring
              Consultant, IDX Corp., 1741 Celeste Drive, San Mateo, CA 94402-2603,
                       Shinichi Moriyama *, Atsushi Kasugai*, Masayuki Terakado*,
                               Nobuyoshi Nakayama **, Toshimitsu Iiyama**
                   Japan Atomic Energy Research Institute, Naka Fusion Research Establishment
                801-1 Mukaiyama, Naka. Ibaraki. Japan 311-11193,
           IDX Corporation 568-113 Ishizuka, Sano, Tochigi, Japan 327-0130,

Abstract                                                      60 Fusion facility in Japan to protect megawatt level
   The control and protection of high power electron tubes    gyrotrons under development for ITER and JT-60. This
has been a serious problem throughout the history of          modern solution provides the control and protection for
power electronics. This paper briefly covers the history      110 GHz, 1 megawatt gyrotrons in the JT-60 Plasma
of approaches used to meet these needs and discusses a        Fusion facility in Japan and for a gyrotron development
modern solution which has uses in fusion research,            facility at the same site. In this application the switch
accelerator, and commercial applications. The paper           carries current of the order of 100 amperes DC at up to
describes the design, development and performance             100 kV DC and interrupts fault currents as high as 420
history of a family of high voltage IGBT switches used        amperes. The development of the switch was a joint effort
for the control and protection of megawatt level gyrotrons    of the Japan Atomic Energy Research Institute and the
in the JT60U facility. The switch systems described have      switch manufacturer, IDX Corporation.
been in use for several years. The demonstrated long,          The JT-60 facility in which these switches are used is
{over 20,000 system hours. (over 2x10 6 device hours)}        unusual in that large amounts of electrical energy are
life shows the inherent reliability of a well designed,       required. Power is supplied by three phase lines at 275
properly operated HV DC IGBT switch system. This              kV. Relevant to this paper are the three very different RF
device has many other uses in modern high power               and microwave systems used in the facility: (8) ~1 MW,
electronic systems.                                           120 MHz tetrode amplifiers, (16) 1 MW, 2 GHz
   In the application described, the switch carries current   klystrons, and, recently, (4) 1 MW, 5s 110 GHz gyrotrons
of the order of 100 amperes DC at 100 kV DC.                  using collector potential depression [CPD], Also at the
  The development was a joint effort of the Japan Atomic      Naka site is a test facility for 1 MW CW, 170 GHz CPD
Energy Research Institute and the switch manufacturer,        gyrotrons. The original systems and the entire JT-60
IDX Corporation.                                              tokamak were designed to operate at pulse top widths up
                                                              to 10 seconds. Recently tokamak pulse widths in excess
                I. INTRODUCTION                               of 65 seconds have been achieved. An upgrade to allow
 Many particle accelerators, plasma fusion facilities and     tokamak at pulse widths up to several minutes has been
other important scientific equipments require high power      considered and, while technically feasible, is not being
electromagnetic energy at RF and microwave frequencies.       pursued at this time.
This energy is provided by high power electron tubes          The tetrode and klystron systems were designed and built
which convert energy from electrical to RF or MW              in the 1980’s, early in the history of the facility. Both use
energy. Depending on the system requirements, the tubes       ignitron crowbars to protect the high power tubes from arc
may be any of several types. Tetrodes. IOT’s, klystrons,      damage. While crowbars protect the tubes, the inherent
magnetrons, or gyrotrons are typical of the tube types that   high surge currents subject the power supply equipment to
are used. A major advantage of the electron tubes is their    severe thermal and magnetic stresses. Figure 1, a line
ability to be controlled to produce modulated energy          current and voltage oscillogram of a short circuit fault
rapidly and readily. In varying degrees, all types of         protection test of one of the power supplies for
electron tubes have in common the fact that that they can
tolerate no more than a limited amount of energy
dissipated in their structure.                                                                      Line Currents
                                                                                                    2.4 kA RMS
                II. BACKGROUND
 The control and protection of high power electron tubes                                       Line to Line
has been a serious problem throughout the history of high                                      Voltage
power electronics. This paper discusses the design,                                            18 kV RMS
development and performance history of a modern               Figure 1. Simulated HV DC Arc Fault Protection Test[9]
solution that was developed in the early 1990’s at the JT-
(4) klystrons, illustrates this. The fault current (2.4 kA) is
six times the full load line current! The stresses,
proportional to I2, are 36 times normal! In addition, the
ignitron tubes that are used in most crowbars are no
longer widely manufactured.

            III. SWITCH SYSTEM
. When JT-60 first considered adding gyrotrons in the late
1980’s, a conventional tetrode regulated, crowbar
protected power supply was used [1]. Later gyrotron
development resulted in adding [CPD] capability to
increase efficiency and reduce the cost of the highly
regulated (0.1%) acceleration power. (for CPD typically
80 kV, @50 ma, for a.80 kV, 45 A beam). In designing
the power supply system for the CPD gyrotrons [3], [4],
the above cited crowbar shortcomings and the power loss
(100’s of kW) in the series tetrode led to the development
of a power supply using newly developed high voltage
IGBT switches combined with a thyristor primary voltage
regulator to compensate for line voltage variation and
power supply impedance effects. [2].
Figure 2.          IGBT
Protected      Gyrotron
Power Supply [2]
Figure 2 is a schematic
of the CPD gyrotron
test    stand      power
supply system. Only                                                                  2.67 m high x 1.5m x1.2 m, 1000 kg
the Acceleration Power                                                              Figure 4. IGBT Switch [10]
Supplies are regulated
in the (4) JT-60                                                                      Figure 4 is a photograph of the switch.
systems.                                                         The design takes advantage of the cleanliness of the JT-60
  One hundred Toshiba "MG360V1US41". IGBT’s in                   facility by building the switches to operate in air to avoid
series are used in each of four of the five switch systems       possible maintenance problems associated with operation
that are used in the JT-60 facility. These transistors are       of fiber optical and water cooled devices in oil.
rated 1700 V, 360 A DC, 720 A, 1 ms [11]. Forced water             All but one of the JT 60 switch systems are used for
cooling is provided for the IGBT heat sinks. Figure 3            “DC” operation only; the special unit is used for beam
shows a simplified schematic diagram of the switch.              pulse modulation in the gyrotron development facility.
                                                                 “DC” is single pulse operation at the pulse width set by
                                                                 either tokamak operation or the capability of the
                                                                 individual gyrotron tube, usually this is 10 seconds or
                                                                 less; the switches have demonstrated operation at 100
                                                                 amperes continuously. The special unit [5] is used for on
                                                                 –off modulation at 100 kV, 50 A at 1 kHz, 50% duty
                                                                 continuously and it can switch the gyrotron beam on and
                                                                 off and at a 10 kHz rate for 1 millisecond [6]., To handle
                                                                 the heating associated with this mode, higher power
                                                                 IGBT’s {Toshiba MG400V2Y60A [12]} were used along
                                                                 with improved snubber components and higher water flow
                                                                 (20 vs. 8 l/ min). The frequency of 1 kHz is limited by the
                                                                 switching losses of about 35.3 kW in the IGBT elements
                                                                 and snubber circuit for continuous switching operation. It
Figure 3. IGBT Switch [10]                                       is not restricted by the gyrotron. Reduction of switching
                                                                 losses is essential for more than 1 kHz switching.
                                                                   The maximum interrupting current is 420 amperes for
                                                                 the special switch, 350 amperes for the ordinary switch.
                                                                 Both switches have demonstrated the ability to interrupt a
                                                                 100 kV arc in less than us while limiting the energy
                                                                 delivered to the arcing device to less than 10J, the limit
set by gyrotron ratings. Figure 5 is an oscillogram of a                      IV. SUMMARY
typical “0.1 mm wire test”, the test wire survived, as      We have described the development, design, and long
usual.                                                     term performance of a family of IGBT switches used for
                                                           protection and control of high power microwave electron
                                                           tubes (gyrotrons). These five are among the first HV DC
                                                 (a)       IGBT switch systems to have demonstrated good
                                                           reliability over a significant life time in normal use. The
                                                           design and application principles used for these switches
                                                           have application in many systems which use high power
                                                           electron tubes for scientific and commercial purposes.

                                                                           VI. REFERENCES
                                                 (b)          [1] M. Shioto and M. Goto, “High voltage power
                                                                  supply for radio frequency plasma heating
                                                                  system”, Journal of Institute of Electrical
                                                                  Engineers of Japan [IEEJ] v108 p.623 – 625, 1988
             (a) Cathode Voltage (25 kV/div)                  [2] M. Tsuenoka et. al., “Development of DC 100 KV,
              (b) Beam Current (100 A/div)                        100 A, 360 A Break IGBT Switch”, Transactions
Figure 5. 0.1 mm Wire Test [5]                                    [IEEJ]. v116D, 497-498, 1996
 Figure 6 is an oscillogram of currents, voltages and RF      [3] M. Tsuenoka et. al., ”Development of dc power
output for a modulated developmental 170 GHz gyrotron.            supply for gyrotron with energy recovery system”,
As shown by the “Oscil(lator) waveform, gyrotron                  Fusion Engineering and Design v.36 461 – 469,
operation was stable.                                             1997
                                                              [4] Masaki Tsuenoka et. al., “Development of high
                                                                  efficiency and crowbar switchless dc power
                                                                  supply for 1 MW CW CPD gyrotron”, Int, J.
                                                                  Electronics, 1999. v 86, n. 2, 233 – 243
                                                              [5] Masaki Tsuneoka, Tsuyoshi Imai, Nobuyoshi
                                                                  Nakayama, Toshimitsu Ilyama, “A Development
                                                                  of 1 kHz, 50A, 100 kV IGBT Switch, with 420A
                                                                  Breaking Current Capacity,” Letter, IEEJ Trans.
                                                                  IA, Vol. 123. No. 2., 2003
                                                              [6] A.. Kasugai, K. Sakamoto, K. Takashi, K.
                                                                  Hayashi, S. Moriyama, M. Seki, T. Fujii, T. Imai,
                                                                  “Recent Progress of Gyrotron Performance in
                                                                  JAERI”. First U.S./Japan/EU RF Technology
                                                                  Exchange Workshop, February 12-14, 2003
                                                              [7] A. Kasugai, et., al, "Development of Gyrotron
                                                                  System for High Frequency Power Modulation”,
                                                                  Conference Digest of The 28th International
                                                                  Conference on Infrared and Millimeter waves,
                                                                  p127-128, Sept 29-Oct 2, 2003 (Otsu Japan)"
                                                              [8] T. Fujii to A.B. Sterk, Private Communication
Figure 6. Gyrotron Operation, 1 kHz modulation [7]                May, 2003
                                                              [9] T. Fujii** and S. Moriyama**, Private
                                                                  Communication –April 2004
                     IV. History                              [10] IDX technical brochure, “Model HIS-100K350
  The first of these systems went into operation in 1996          Large Capacity IGBT Switch”
[2]. The five switch systems have operated for an             [11] Toshiba Product Specification, "MG360V1US41
aggregate total of well over 20,000 system hours. (over           IGBT”
2x106 device hours). The only problem, aside from a           [12] Toshiba Brochure, “Semiconductor for Inverter”,
water leak, was caused by unstable operation of the IGBT          p21,                          Nov.           2003
drivers control circuit when system control power was   
first turned on. This problem has been overcome and               sen/inverter_e.pdf ,
operation has been trouble free. [8]
                 VII. APPENDIX
  These references will be of interest to those who want
additional information on the subject.
 1) A.B. Sterk and A.G.A. Verhooven, “DESIGN AND
      Symposium On Fusion Technology 2002
 2) T. Fujii, M. Seki, S. Moriyama, Y, Ikeda, A.
      Kasugai, M. Terakado, K. Sakamoto, T. Imai,
      “Performance of the 110 GHz ECRF System on JT-
      60U”, First U.S./Japan/EU RF Technology
      Exchange Workshop, February 12-14, 2003

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