IMPROVEMENTS OF LINAC FOR PICOSECOND SINGLE
ELECTRON PULSE
Hitoshi Kobayashi, 'Ibru Ueda, 'Ibshiaki Kobayashi,
Seiichi Tagawa and Yoneho Tabata
Nuclear Engineering Research Lab. , Faculty of Engineering
Univ. of 'Ibkyo, Shirakata Shirane 2-22, 'Ibkai-muraIbaraki, 319-11, JapanAbstract
A 35 MeV S-band linac with capability of producing a picosecond single electron pulse (< 18 ps! -v 100 amp. peak) is available to ccrnpose a picosecond pulse
radiolysis system.l1 After the installation,2l same improvements of the linac
have been carried out. 3) Improvements of the synchronization circuit and of themaster oscillator of microwave have increased the stability of the picosecond
single electron pulse considerably. The next program is to increase the intensity of the output beam. For that p"l.JI'IX)se, electron guns suitable for high speed
pulse beam are being developed. Improvement of the focusing system of injector
will be also tried.
Synchronization Circuit
Microwave frequency of 119 MHz was used for the synchronization circuit inthe original design. Microwave frequency of 4(6 !lffi.z is used in the new circuit,and all of this circuit is constructed using the Motorolla MC-1600 .. series logicmodules. 4) The time jitter of the synchronized pulse output is < ± 5 ps. Thetime scheme of this circuit is shown in Fig.l. The time jitter of measuringsystem has been reduced in a factor of 3 compared with the previous value.
Cerenkov light accompanied with output beams was measured by a streak camera(Hamamatsu T. V) . A single shot .pulse, and an accumulated averaged signal optainedby memorizing 100 shots repeatedly are shown in Fig. 2.
Electron GunIn the case of S-band linac, allowable width (F .W.H.H.) of the injected beamfran an electron gun is 0.8 ns. The program of increasing the intensity of output
beam has started. At first the improvement of the grid modulator of an electron
gun has been done. The output pulse of the previous grid modulator (original)
had the half width of 2. 4 ns. An oscilloscope trace of output pulse gained by
the improved one is shown in Fig.3. The half width. is 1.6 ns. But the intensityof the output ·beam didn't increase as expected. Because the frequency responseof the electron gun is not. so good. Two different types of electron guns whichhave good frequency response are now being developed. One has a barium impregnated cathode (NJRC) and the other has a oxcide cathode ('Ibshiba) . They are nov.1
being improved using a test bench.

Master Oscillator
The microwave frequency of ll9 MHz was fundamental frequency and the stability of frequency was not so good (-v 10-5) • Fa a synchronization circuit is now
available for 476 MHz, the master oscillator system has been changed fran ll9 MHzto 476 MHz. In the new master oscillator system, the very stable synthesizer(ANRITSU MG545 B) is used and the stability is 3 x 10-8 /day.
Acknowledgement
The authors wish to thank Prof. J. Tanaka of National Lab. for High Energy
Phys. and Prof. K. Hasegawa of Univ.of 'Ibkyo for their co-operation during research.

-241-Reference1) s. Tagawa, Y. Katsurmrra, andY. Tabata, Chern. Phys. Lett., 64, (1979) 258
2) Y. Tabata, J. Tanaka, S. Tagawa, Y. Katsurmrra, T. Ueda, andK. Hasegawa
J. Fac. Eng. Uinv. Tbkyo, 34B, (1978) 619
3) H. Kobayashi et al. , J. Fac. Eng. Univ. Tbkyo, A-17, (1979) 48
4) H. Kobayashi et al. , J. Fac. Eng. Univ. Tbkyo, A-17, (1979) 71476MHz
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100 PULSES

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Fig.3

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Oscilloscope traceof grid modulator