Anami, S

Baba, H

Kihara, M

Kubo, T

Kubota, C

Kudo, K

Ono, M

Takasaki, E

Takenaka, T

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Particle Accelerators, 1990, Vol. 32, pp. 45-50Reprints available directly from the publisherPhotocopying permitted by license only© 1990 Gordon and Breach, Science Publishers, Inc.Printed in the United States of AmericaDESIGN AND CONSTRUCTION OF A PULSE TRANSFORMER FOR ALONG PULSE KLYSTRONTADASHI KUBO, SHOZO ANAMI, MASAAKI ONO, KIKUO KUDO,CIDKASHI KUBOTA, Ellcm TAKASAKI, TATERU TAKENAKA, IDTOsmBABA and MOTOIDRO KlliARAKEK, National Laboratory for High Energy Physics1-1 Oho, Tsukuba-shi, Ibaraki-ken, 305, JapanAbstract A pulse transformer which is used to be linked with the 15 MW line-type modulator was designed and constructed for an L-band high power rf sourceof I-GeV proton linac of the Japanese Hadron Project (JHP). This pulsetransformer steps up an output pulse voltage from the modulator to 140 kV with a600 Jlsec pulse width at 50 pps. The pulse transformer and its associated circuitcomponents were installed in an oil tank, and operated at 400 Jlsec of pulse widthfor a klystron load. ).INTRODUCTIONThe modulator for the power source of the I-GeV proton linac for the JHPl,2 consists ofthe high voltage DC power supply, charging circuit, PFN and thyratron switchingdevices which contain main and crowbar thyratrons. The PFN consists of 34 cells ofinductor and capacitor network at present and can produce the pulse with 20 kV heightand 400 Jlsec duration. Near future 50 cells will be installed to generate 600 Jlsec pulseduration. More detail discussions will be made and the parameters will be described inother manuscripts.3,4 The output pulse of the modulator is supplied to the L-bandklystron (1.296 GHz) through the step-up pulse transformer. The performance of themodulator influences the stable operation of the rf-system. The peak power. of the outputpulse is 15 MW, and the peak power of the klystron used is 6 MW.The pulse transformer for this purpose was designed and manufactured by thecompany. It was a first experience for KEK to develop such a pulse transformer withhigh power, high duty and long pulse duration. Its size is very large and the weight ofthe core itself is about 3 tons. In the operation it has been installed in the oil-tank toincrease the voltage tolerance. The pulse current and voltage monitors, the heatertransformer assembly for the klystron, and the bypass diode connected with the resisterserially have been assembled in the tank.PULSE TRANSFORMERThe pulse transformer was designed under the concept described above. The finalspecifications of it are as follows.primary pulse voltage 20 kVsecondary pulse voltage 140 kVprimary pulse current 740 Asecondary pulse current 105 Aset-up ratio 1:7pulse width 600 Jlsecrepetition ratio 50 ppssag <3 %The input pulse from the modulator will be transferred to the klystron through the step-uppulse transformer by satisfying these specifications. The wave form of the output pulsewill be varied in accordance with the design parameters and influences the performance[1487]/4546/[1488] T. KUBO ET AL.of the system. Thus the most appropriate parameters must be adopted for the pulsetransformer. For this purpose at the fIrst it is very important to decide what type of theiron core we have to use and secondly we have to investigate the winding method. Thecharacteristics of the designed pulse transformer have to be estimated lastly. These threepoints are closely connected with each other, hence it is necessary all these points areexamined at the same time. Here, the designed process and the results will be described.The frequency range of the long pulse comes up to DC to a few ten kHz, so it isnecessary to use the iron core material having good perfonnance, namely having high ,..LThis is also profitable for reducing the core size. As a result thin silicon annealed ironsheet of 40 mm width, 0.23 nun thickness and effective Jl, about 1500 has been used inthis case. The core is cut core style in general in order to be able to been inserted theassembled coil frames, and the cutting plane is the center of the core. The'geometrical sizeof the cut core is shown in Figure 1. The weight of the pair is about 120 kg. 25 pairs ofthese were assembled in one block and the whole size is 500 mm w x 1024 mm I x 900mm h including core space 1 mm and the weight comes up to 3 tons.The winding method of the primary and secondary coils are described in Figure 2.The coil winding method and voltage insulation length had to be considered carefully toprevent from the voltage breaking down, accordingly many experiences and know howhad to be taken into account. As in Figure 2 the coils are wound with auto transfonnerwinding. When the step-up ratio is not so high this configuration is often adopted. Thewire size and number were fixed corresponding to the average pulse current. The twosecondary coils in two parallel windings mainly came from the reason the wire size had tobe same as the primary coils, and are also possible to be used for supplying the heaterpower of the klystron in the next place.1fIabcdefRrt200mm135mm500mm40mm535mm900mm4 mm (outside only)8 mm (outside), 3mm (inside)1 mm max..FIGURE 1 Core Size ParameterspTl'Nen-.iss5 p 5FIGURE 2 Autotransformer WindingFrom the geometrical' size of the core, the coils, and the gaps between core andcoils, and between primary and secondary coils the various parameters were estimated.Here the typical wave fonn of the output pulse from the pulse transformer is shown inFigure 3. The parameters in the figure will be estimated by the simple equivalent circuit5,6 given in Figure 4. RG, ZL, Lp, LL, Co, and RE describe the impedance of themodulator output, load impedance, primary inductance, leakage inductance, total straycapacity including the the assumed stray capacity, 60 pF of the klystron, and the sum ·ofFIGURE 3 Output Pulseof the Pulse TransformerPULSE TRANSFORMERPower Supply Pulse Transfonner LoadFIGURE 4 The Equivalent Circuitfor the Pulse Transformer[1489]/47the eddy current, hysteresis and copper loss, respectively. Here Ra and ZL are both 27 Q.Other parameters are calculated according to the formula in Reference 5, 6. Lp, LL andCD are estimated as 0.36 Henry, 189 J.l Henry and 0.023 J.lF. From these data the risetime and fall time are estimated as 6.5 J.lsec and 7 J.lsec. It is expected no overshoot willappear in this case. These values are sufficient for our purpose. The sag or droop inFigure 3 is also one of the most important parameter for the pulse transformer andrestricts the reducing of the core size. The core size was determined by assuming themaximum magnetic flux becomes 1.4 Wb/m2 for the 140 kV pulse height and 600 J.lsecpulse duration.The heating from the eddy current loss (WE), hysteresis loss (WH), and copperloss (WI) were also taken into consideration. WE, WH and WI are estimated as 380 W,2110 Wand 3470 W respectively for the maximum core flux to be 1.4 Wb/m2 and are1300 W, 9800 Wand 3470 W respectively for the maximum core flux to be 1.7 Wb/m2.Total power losses become about 6 kW for the former case and about 15 kW for thelatter case. This is the one reason why we adopted fonner case. Still more, the powerloss are related with the thickness of the core material. The power loss becomes large inaccordance with increasing the core thickness. Thus we decided to use the mostavailable core material whose thickness is 0.23 mm. After the design the pulsetransformer were manufactured by the company and Figure 5 shows the assembledpulse transformer. The measured stray capacitance is 0.020 J.lF assuming the 60 pF forthe klystron. This is reasonable in comparison with the designed value.FIGURE 5 Manufactured and assembled Pulse Transfonner48/[1490] T. KUBO ET AL.The biased pulse transformer was investigated for reducing the core size for thealternative selection. But it turned out that the blocking choke would be very big, 0.8ton, even if the size of the pulse transformer would be reduced.ASSEMBLING OF THE PULSE TRANSFORMER IN THE KLYSTRON TANKFigure 6 shows the schematic diagram inside the tank. The bypass diode in the Figure isused in order to flow the charging current at the time of PFN charging to prevent thecharging voltage from becoming unstable, since the potential of the minus side of thePFN will be fluctuated by the large inductance of the primary inductance of the pulsetransfonner. That is, the inductance of the pulse transformer and the charging choke are0.36 Henry and 2 Henry respectively and the voltage ratio is 0.18 if the bypass diodewere not used. This cannot be negligible. The resistor serially connected with the diodehas a role of balancing the charging currents in pulse transformer and diode, and ofresetting the core flux. The charging peak current is 53 A for the 600 J.lsec pulse duration.The value of the resistance was fixed from the computer simulation including the PFN.Figure 7 shows the examples of the simulation for the 200 J.lsec pulse duration withrespect to the primary current. As can be seen, in case of 25 n the exciting current is nearto zero after PFN charging. The power loss by this resistor is estimated as 6.2 kW for400 J.lsec pulse width and 30 pps repetition rate. But the power loss amounts to 26 kWat the full rating operation. In this case the bypass diode and the resistor will be installedprobably in other water cooled oil tank.KlystronPFNVoltage MonitorVoltageWaveFonntIIIIIIVoltage Mon. :(average) II_ _ _ ~u~a~o_n.!:"~.:.._JFIGURE 6 Schematic Diagram inside the Oil TankPULSE TRANSFORMER [1491]/49The heater transformer assembled in klystron socket is used in the short pulsemodulator generally. The heater power is supplied through the two parallel windingswindings of the pulse transformer and the AC voltage will be stepped down by the heatertransformer. But in this case there remains a little anxiety about the heater transformer,because the pulse duration is very long and the bypass capacitor between the secondarytwo parallel windings coils must be large enough to transmit the secondary long pulse.On the other hand the AC heater power will be consumed as a reactive power by thismean. Thus the insulation transformer for supplying directly the heater power is installedbeforehand the high power test for the sake of the spare. Figure 6 shows the situationwhich it is already used.The size and total weight of the oil tank which has been assembled the pulsetransformer and other miscellaneous parts are 1425 mm w x 1740 mm 1 x 1250 mm hand 9.5 tons including the klystron and the insulation oil, 22001.KKK PLOT N02"KK KKK PLOT N02KKKI.' I.'TIME20 msec/div..:i:~ I. 4Ndiv: I ~ ~ ~ ~ r ~ ~ I ~;j r I t I I f I I tOJr 1 / r I I 1 I Ig~ o.OAI I 1 II it I I I 1I~ I I I I It II :t I~~~I.' I.'TIME20 msec/div..:-~ 4 Ndiv-:11:11 t A A A 4 J1 A ~ 1\ A~ 0.0 A J J I I J I J I i11 J j If f ~ i1 I I!/ 'I ~~~~a) In case of 25 Q b) In case of 50 QFIGURE 7 Simulation with respect to the Bypass Resistance8 A/div2 msec/divCharging Current100 J,lSec/div.Jr----.".---------25 kV/div Cathode Vol. = 126 kV16 Ndiva) Charging Voltage and Current b) Secondary Voltage and CurrentFIGURE 8 Measured Wave Forms before and after the Pulse Transformer50/[1492]mGH POWER TESTT. KUBO ET AL.After installing the pulse transformer and the klystron we started high power test. Theoutput rf power is transmitted to the water cooled dummy load through the wave guideand absorbed. The first test with 200 Jlsec pulse duration was carried out in this Spring.At the fIrst stage the heater power of the klystron was supplied through the two parallelwindings coil of the pulse transformer, but as expected at the beginning it became clearthat the heater current was fluctuated by the effect of the repeating pulse current from themodulator. As a result the already prepared insulation transformer is used for supplyingthe heater power. The wave form of the output pulse has not been deformed by the straycapacity of it. The pulse transformer itself worked well and no trouble happened yet.After the extra 17 cells of the PFN was reinforced the high power test with 400 Jlsecpulse duration was carried out again.Up to now the high power test was done with peak cathode voltage, 130 kV, andwith beam current, 100 A with 30 pps. Peak power of 5 MW and average power of 160kW were detected by the monitors. Figure 8 describes the measured output pulse waveforms. In a) it can be seen the behavior of the charging current, and the peak values, 37A. The rise time and the sag are estimated as 30 Jlsec and < 3 %, respectively in b). Therise time is about 4 times larger than the designed value. The sag and the fluctuation onthe flat top will be improved in the range of adjustable PFN inductors. The temperaturerise of the water cooled insulation oil is about 10 degrees at present.CONCLUSIONThe R&D rf power source system for the JHP has been installed and works well atpresent. But as a next step we have to reinforce or improve the system by solving a fewproblems. The modulator must be reinforced to get 600 Jlsec output pulse. The mainthyratron becomes unstable in accordance with the long pulse and high duty operation.The I-GeV proton linac for the JHP needs 36 L-band klystrons, namely 36 modulators.Thus to achieve a stable operation of the linac more and -more stable thyratron orswitching devices have to be developed or introduced. The oil tank of the bypass diodeand the resistor suitable for the full power operation has to be prepared. Most importantproblem is to improve the pulse transformer. There is a possibility to make the pulsetransformer smaller than existing system by reducing the power to 340 kW in stead of450 kW, since the klystron power of the leal system requires 4.5 MW. There is a roomalso to decrease the pulse width, because the pulse beam width is to be 400 Jlsec. By thisway it will be possible to improve or make a new pulse transformer which has morecompact size and good petformance.REFERENCES1. Motohiro Kihara, Outline of the Japanese Hadron Facility, Invited talk given at theInternational Workshop on Hadron Facility Technology, Santa Fe, Inn at Loretto,U.S.A, Feb. 2-5, 1987.2. Y. Yamazaki et al., The 1 GeV Proton Linac for the Japanese Hadron Facility, theAdvanced Hadron Facility Accelerator Design Workshop, Los Alamos National Lab.,Los Alamos, U.S.A., Feb. 22-27, 1988.3. S.Anami et al., Design and Construction of a Long-Pulse Generator, Contributed tothe 1989, Particle Accelerator Conference, Accelerator Science and Technology, March20-23, 1989, Chicago, U.S.A.4. M. Ono et al., Development of L-band High-power RF Source for the JapaneseHadron Project Linear Accelerator, Contribution paper to this Conf.5. G.N.Glasoe and J.V.Lebacqz, Pulse Generators, McGraw-Hill, 19486. Jiro Tanaka and Hitoshi Baba, High Power Pulse Transformers (in Japanese), INS-TH-69.

Design And Construction Of A Pulse Transformer For A Long pulse Klystron

Design And Construction Of A Pulse Transformer For A Long pulse Klystron

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