JAERI-Conf95-021

PA19
MODULATORS FOR SPring-S LINAC
Akihiko MIZUNO, Toshihiko HORI, Hiroshi YOSHIKAWA, Masahiko KODERA, Hideo MISAW A*,Hiroshi TERAMURA*, Naoki AKASHIGE*, Yoshimichi OHNISHI*, Shinsuke SUZUKI, Ken-ichi YANAGIDA,Hironao SAKAKI, Yuichi ITOH, Tsutomu TANIUCHI, Hideyuki KOTAKI, Atsushi KUBA and Hideaki YOKOMIZOJAERI-RIKEN SPring-8 Project Team, Kamigori, Ako-gun, HYOGO, 678-12 JAPAN*Toshiba Corporation, 1-1-6, Uchisaiwai-cho, Chiyoda-ku, TOKYO, 100 JAPAN
AbstractPulse modulators for 80MW klystrons(TOSHIBA E3712) had been designed. The modulator isa line-type pulser, consists of rectifier section (a rectifiercircuit, IVR and step-up transformer), charging section(de'Qing circuit) and discharging section (PFN) . In thecharging section, re-chargeable de'Qing circuit are used,
and the discharging section is composed of four parallel
coupling type PFN (Pulse-Forming-Network). A firstmodulator was already constructed and tested in June
1995. The test data were good enough compared withdesign parameters. In this paper, modulator design arementioned, and performance test are reported.
l.Introd uction
As the SPring-8 is a commercial operatingmachine, it is to be desired that shutdown or maintenancetime is shorter as possible. So even if one or two klystrons
failed, beams of which energy is more than 1GeV has to·be provided, to the Synchrotron. For this reason, we
selected TOSHIBA E3712's, of which peak output power
are 80MW, for main klystrons. The number of E3712's
are 13, and each klystron feeds rfpower to two accelerator
structure except of first klystron for just after bunching
section. Usual operating power from E3712 klystron will
be about 52MW compared with design parameter of80MW. 1l
So in this system, 13 sets of 190MW Modulators
for E3712 are required. Design of the modulator had beenaccomplished and now, 7 units of modulators are delivered
to the SPring-8 site, another 6 modulators are now underconstruction by· TOSHIBA Corporation. All modulators
will be delivered to SPring-8 site until this November.

transformer, and rectifier circuit. Input voltage of the IVR
is 3<jl420V, and output voltage is 580V maximum. We
selected the IVR that minimum output voltage is 260V,
not OV, so that it is smaller compared with the same class
IVR. Output voltage of the step-up transformer is 25kVmaximum. In order to keep phase balance, halves of the 13modulators are delta-star connection, and others are deltadelta connection. Input power of the modulator is 95kVA.
2.2 Charging Section
For regulating charging voltage, we adopted ade'Qing circuit in a usual way. A de'Qing circuit is arechargeable type circuit2l, and has a range of 7% regulation.
·Almost all energy stored in charging choke are fed back tothe rectifier circuit. So This section can be made compact.
2.3 Thyratron
Originally, thyratron F-157 (ITT) is adopted asswitch tube?l Its maximum anode voltage and current are
75kV and 15,000A respectively. These tubes are mounted
in several modulator and tested for two months. But prefire trouble were appeared. The number of pre-fires aredifferent in each tube case, they were averagely occurred
twice or three times during 8 hciurs operation. So wedecided to replace thyratrons. New thyratron is F-351(ITT). It is remodeller of F-241, which has been used at
SLAC for many years and had few pre-fire trouble. ButF-351 is a new tube and does not have operation data.
Maximum anode voltage is 55kV and current is lO,OOOA.
Major difference between F-351 and F-157 is the numberof gaps. F-157 is three gap type but F-351 has two gaps.

2.Design of Modulator

Table.1

The modulator is separated into two units, control
unit and high voltage circuit unit. Size of the high voltage
circuit unit is 3900Wx1900Dx2300H. The control unit are
mounted in two 19 inch racks. The parameter of themodulator is shown in Table. I. Outline of circuit is also
shown in Fig.l.
2.1 Rectifier Section
The rectifier section consists of IVR, step-up-76-Modulator parameters

Input Power95KVA

Output Voltage

391kV

Output Current

474A

Pulse Width (FWHM)

5 f1 sec

Pulse Width (flat top)-;ap sec

Voltage Regulation at flat top<±0.5%

Regulation Value of de'Q?.7%

Repetition Rate

60pps

Pulse Trans. Turn Ratio

1:16

JAERI-Conf 95-021

Fig.l

Outline of the modulator circuitSo F-351 is more compact and volume of inner gas are
smaller compared with F-157. Two F-351's are tested in
two different modulators individually. There were noknock out during 8 hours operation.

::::: :j:: ::::::\:::::=1 ::::: :I:·:: I ::No.2

2.4 Discharging Circuit

modulator
Design value of pulse width of flat top is morethan 2J.1sec with fluctuation ofless than ±0.5%. In order toobtain this design, pill-box type oil condensers, of whichleakage inductance are less than 250nH (This includes va"
lue of circuit between the condenser and an analyzer) areselected for pulse-forming-network (PFN) condensers.
And moreover, pares of adjoining coils in the PFN havemutual inductances which decrease leakage inductance ofthe condenser equivalently. In this case, value of mutual
inductance is arranged equal to the leakage inductance.
But It is difficult to form large mutual inductances. So, inorder to obtain small leakage inductance of the condensers,
we selected small capacitor. Therefor, the PFN forms 4
parallel networks. Each network has 14 sections.
Capacitance is 0.015J.1F, and maximum voltage is 50kV.
Simulation data of this coupling type PFN cleared thefluctuation level.
Imp~dance of the PFN is about 3.3Q. The PFN isdesigned not to be negative mismatch, but slightly positive mismatch during discharge. But if positive mismatch
keeps after discharge, stored energy in primary side ofpulse-transformer backs to the PFN and the condensers
become to have initial storage charge. In order to avoid
this, the PFN designed to be slightly negative mismatchafter discharge and the storage charge of condensers aredischarged by shunt circuit.
Assemblies of modulator output cable are triaxial, made by STANGENES, where two cables are connected parallel to a pulse-transformer tank. A pulse
transformer and the tank are also made by STANGENES.

No.3
modulator

Fig.2 Magnifications of klystron beam voltage after
8 hours operation with keeping full power.
(ordinate: 500ns/DIV,-77-abscissa : 1.0%/DIV)JAERI-Conf 95-021

2.5 Control
The modulator itself is controlled by a sequencer
unit, and communicates to the upper control systemthrough VME-boards, which are mounted near themodulator body. And analog signal between thesequencer and the modulator are range ofless than lOV.
So it is very important to reduce noise level of themodulator. Three kinds of filters, isolators, passive
filters or bypass condensers, are inserted in cable lines.
3. Test Results

Now 7 modulators had finished performance
test and all of them achieved output power level (seeTable.l) which are needed to drive klystrons.
Fig. 2 shows the fluctuation of klystron beam
voltage with connection to a dummy klystron. Thesewaveforms are after 8 hours operation with keeping fullpower. Length of pulse top with fluctuation of less than
± 0.5% are about 2.1J..lsec in each case.
Noise level of the analog signal connected
between the sequencer and the VME board are observed.
Magnitude of signal is lOV maximum but there was
spike noise of about 20V at the point of thyratron trigger.
Earth level fluctuations or noise at another timing were
not occurred. Something like LC filters for reducing thespike noise are needed.
Control test from the VME had been also done.
We could confirm expected communications.
4. Conclusion

Halves of the modulators have been constructed
and they were cleared the design value. Noise level wererelatively smaller than predicted level.
All modulators are accomplished by thisNovember and operation start will be next year April.
5. References[1] S. Suzuki et al. ;"RF System of SPring-8 Linac;',Proc. of this symposium[2] Akemoto et al. ; "Pulse Modulator for 85MW
Klystron in ATF Linac", Proc. of 17th Intentional
Linac Conference, 1994, Vol. 1, p.414-417[3] T. Hori et al. ;"Pulse Modulator for 80MW Klystronin SPring-8", Proc. of 20th Linear Accelerator
Meeting in Japan, Osaka, 1995.

-78-