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| THPPH034 |
Laser Pulse Length Dependence of Beam Emittance of Photocathode RF-Gun
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649 |
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- H. Dewa, T. Asaka, H. Hanaki, T. Kobayashi, A. Mizuno, S. Suzuki, T. Taniuchi, H. Tomizawa, K. Yanagida
JASRI/SPring-8, Hyogo-ken
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A pulse length of the UV laser is an important parameter of the Photocathode RFgun. Due to space charge effect, too short laser pulse increases the beam emittance. Therefore there should be an optimum pulse length if the electron beam charge is determined. To study the pulse length dependence of the beam emittance, the emittance was measured at several conditions of laser pulse length, which were prepared with a laser pulse stacker. The laser pulse can be stretched by dividing a laser pulse of a few pico second into two pulses and then combined them with time delay. The pulse stacker that consists of four sets of the divider and combiner could generate an arbitrary pulse length within 2 - 20 ps by changing delay time of each sets. The beam charge dependence was also measured. Beam emittance was measured with the magnetic quadrupole scanning technique. The results are compared with predictions of a 3-D beam tracking simulation that treats space charge effects.
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| TUPPH046 |
Free Electron Laser Pulse Control by Acousto-Optic Modulators
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427 |
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- T. Kanai, K. Awazu, S. Suzuki
Osaka University, Suita
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The free electron laser (FEL) at Osaka University can be continuously varied over a range from 5.0 to 20.0 um when using the 30 MeV electron beam. The FEL has a double pulse structure. The structure consists of a train of macropulses with a pulse width of 15 us, and each macropulse contains a train of 330 micropulses with a pulse width of 5 ps. The FEL's tunability and short pulse make possible new medical applications, such as investigating protein dynamics and ablating soft tissues. Precise control of the micropulse train is essential for FEL medical applications because macropulses of long pulse duration lead to undesirable thermal effects. An FEL pulse control system, using an acousto-optic modulator (AOM), was developed to investigate the non-thermal effects of FEL on living tissues. This system provides efficiency (~ 70%) and a fast switching speed (> 200 ns), and we predict that FEL will serve as a novel tool in many new applications.
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