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Microwiggler generated on the surface of an acoustic waveguide using high power ultrasonic waves
NUCLEAR INSTRUMENTS METHODS IN PHYSICS RESEARCH
Nuclear Instruments and Methods m Physics Research A 341 (1994) ABS 107-ABS 108 North-Holland
Section A
Microwiggler generated on the surface of an acoustic waveguide using high power ultrasonic waves Jeong-Sik Choi, Cheal-Ho So, Jong-Dae Moon, Deuk-Ryoung Kim
Institute of Basic Sciences, Dongshin University, Daeho 252, Chonnam 520-714, South Korea
A compact free electron laser with low energy electron beams usually consists of a microwiggler with a fixed period . We propose a new type of electrostatic wiggler with a very short wiggler period (0 .1 mm < 1W <_ 1 mm). The strong electric field of a tunable and short wiggler period is formed on the surface of piezoelectric materials because the internal stress in these piezoelectric bodies resulting from an electric field is proportional to the field itself, and the reverse effects also occur. When a high power ultrasonic wave propagates in a piezoelectric solid body as shown in Fig. 1, the ultrasonic wave travels as an internal stress wave and causes strain inside the piezoelectric body . From the strain the positive and negative charge concentrations are periodically repeated on the piezoelectric surface . In general, the strength of the evanescent electric field outside the piezoelectric material decreases expontially, depending on the distance from the surface as E=E o exp [-d/1W 1. Here, 1W is the period of the stress wave and d the distance from the piezoelectric surface . We prepared a PZT [Pb(Zr 052, Ti 048)0 3 1 ceramic bar of 6 mm X 4 mm X 30 mm as a piezoelectric acoustic waveguide [11 since PZT has a large piezoelectric coefficient of - 15 C/m 2. The velocity and the attenuation of the ultrasonic wave are measured by a pulse echo method with a Reflectoscope (Steveley Instrument QC-400). The measured velocity is 3.9 X 10 3 m/s for a 5 MHz longitudinal bulk wave mode and 2.2 X 10 3 m/s for 735 kHz Y-polarized Z-propagating shear wave . It is measured that the ultrasonic wave pulse is attenuated by 10% per round trip along the 30 mm PZT bar . We manufacture the transducer and the acoustic waveguide by cutting the PZT bar. A high voltage wave train produced from a 400 V pulse source and a matching network is feel into a gold electrode of which the width is 1 mm on the Y-surface of the transducer . The train is converted into an internal
* This work was partly supported by the Korea Research Foundation .
Charge Concentration
Ultrasonic Signal
Strain
Fig. 1. Surface charge distribution on a piezoelectric solid when a high power ultrasonic wave travels through the piezoelectric solid.
stress wave through the gold electrode. The Y-polarized symmetric plate mode propagates along the waveguide in the positive Z direction. The wave propagating in the negative direction is absorbed at the antireflection end to avoid interference between the stress waves. The monitoring electrodes are allocated on Y-surfaces to measure the electric field formed on the X-surface of PZT waveguide and on the antireflection end at one side . The waveguide is tapered for electric field intensity to be maintained constant from the loss . To estimate the characteristics of ultrasonic wave propagation in the PZT microwiggler device, the voltage signal produced by the ultrasonic wave propagating through the PZT acoustic waveguide has been measured with the monitor electrodes . An electric pulse, which has a center frequency of 735 kHz and an amplitude of about 2 kVPP , is fed into the transducer from the matching network. The voltage signal measured on the monitor electrode constructed at the position of 52 mm far from the transducer is obtained . This voltage signal on the monitor electrode spaced 1.2 mm apart consists of an amplitude of about 1.5 VPp , amplitude, 7 periods and a duration of - 12 ws. Two wave trains following these signals have been caused by the interference between multireflection waves in the acoustic waveguide with the tapered surface and the imperfect anechoic end. After a fine tuning of the
0168-9002/94/$07 .00 C 1994 - Elsevier Science B.V. All rights reserved SSDI0168-9002(93)E1139-0
EXTENDED SYNOPSES
ABS 108
II
01;
J.-S. Choi et al. / Nucl. Instr. and Meth . in Phys. Res . A 341 (1994) ABS 107-ABS 108
ME a MEN 0 M ME W . . MEM ROME
Fig . 2 . The variation of the collector current with about 1 .5 Vpp amplitude, 7 periods and -12 ws duration is measured by the spontaneous emission of the electron beam . The solid line and the open circles denote the electric pulse from the LC matching network and the current signal measured from the collector, respectively . Horizontal scale is 10 Ws/div and the vertical scale is m arbritary units . matching network circuits, a different behavior is measured for the interference echo signal . However, the main acoustic pulse for the generation of the wiggler
field is not severely affected and a wiggler electric field with the same pattern is produced . In Fig . 2, the spontaneuous emission of the electron beam is measured by means of the measurement of the collector current. After 24 g,s flight time from the electric crosstalk noise signal, the variation of the collector current occurs during - 12 [.Ls, consistent with the wiggler length (L . = N,,l w ) . We can evaluate that the electric field strength E on the surface is - 1 .3 kV/m . Also an electric wiggler with a period 1 . of 3 mm is produced on the PZT surface since the high voltage wave train with a frequency of 735 kHz is applied . In order to improve the wiggler field strength, we could change the acoustic waveguide design . If a surface wave, like a Rayleigh wave, propagates instead of a bulk wave, the acoustic wave energy is concentrated on the surface of PZT waveguide [2] and the wiggler field is increased . Then we can expect a strong electric field with E = 100 kV/m is produced, which is a tenth of the PZT poling field strength .
I I
[1] J .-S . Choi, C.-H So and D .-R . Kim, submitted to J . Kor. Phys . Soc [2] E . Meyer and E .G . Neumann, Physical and Applied Acoustics (Academic Press, New York, 1972) chap . 1 .
Nuclear Instruments and Methods m Physics Research A 341 (1994) ABS 107-ABS 108 North-Holland
Section A
Microwiggler generated on the surface of an acoustic waveguide using high power ultrasonic waves Jeong-Sik Choi, Cheal-Ho So, Jong-Dae Moon, Deuk-Ryoung Kim
Institute of Basic Sciences, Dongshin University, Daeho 252, Chonnam 520-714, South Korea
A compact free electron laser with low energy electron beams usually consists of a microwiggler with a fixed period . We propose a new type of electrostatic wiggler with a very short wiggler period (0 .1 mm < 1W <_ 1 mm). The strong electric field of a tunable and short wiggler period is formed on the surface of piezoelectric materials because the internal stress in these piezoelectric bodies resulting from an electric field is proportional to the field itself, and the reverse effects also occur. When a high power ultrasonic wave propagates in a piezoelectric solid body as shown in Fig. 1, the ultrasonic wave travels as an internal stress wave and causes strain inside the piezoelectric body . From the strain the positive and negative charge concentrations are periodically repeated on the piezoelectric surface . In general, the strength of the evanescent electric field outside the piezoelectric material decreases expontially, depending on the distance from the surface as E=E o exp [-d/1W 1. Here, 1W is the period of the stress wave and d the distance from the piezoelectric surface . We prepared a PZT [Pb(Zr 052, Ti 048)0 3 1 ceramic bar of 6 mm X 4 mm X 30 mm as a piezoelectric acoustic waveguide [11 since PZT has a large piezoelectric coefficient of - 15 C/m 2. The velocity and the attenuation of the ultrasonic wave are measured by a pulse echo method with a Reflectoscope (Steveley Instrument QC-400). The measured velocity is 3.9 X 10 3 m/s for a 5 MHz longitudinal bulk wave mode and 2.2 X 10 3 m/s for 735 kHz Y-polarized Z-propagating shear wave . It is measured that the ultrasonic wave pulse is attenuated by 10% per round trip along the 30 mm PZT bar . We manufacture the transducer and the acoustic waveguide by cutting the PZT bar. A high voltage wave train produced from a 400 V pulse source and a matching network is feel into a gold electrode of which the width is 1 mm on the Y-surface of the transducer . The train is converted into an internal
* This work was partly supported by the Korea Research Foundation .
Charge Concentration
Ultrasonic Signal
Strain
Fig. 1. Surface charge distribution on a piezoelectric solid when a high power ultrasonic wave travels through the piezoelectric solid.
stress wave through the gold electrode. The Y-polarized symmetric plate mode propagates along the waveguide in the positive Z direction. The wave propagating in the negative direction is absorbed at the antireflection end to avoid interference between the stress waves. The monitoring electrodes are allocated on Y-surfaces to measure the electric field formed on the X-surface of PZT waveguide and on the antireflection end at one side . The waveguide is tapered for electric field intensity to be maintained constant from the loss . To estimate the characteristics of ultrasonic wave propagation in the PZT microwiggler device, the voltage signal produced by the ultrasonic wave propagating through the PZT acoustic waveguide has been measured with the monitor electrodes . An electric pulse, which has a center frequency of 735 kHz and an amplitude of about 2 kVPP , is fed into the transducer from the matching network. The voltage signal measured on the monitor electrode constructed at the position of 52 mm far from the transducer is obtained . This voltage signal on the monitor electrode spaced 1.2 mm apart consists of an amplitude of about 1.5 VPp , amplitude, 7 periods and a duration of - 12 ws. Two wave trains following these signals have been caused by the interference between multireflection waves in the acoustic waveguide with the tapered surface and the imperfect anechoic end. After a fine tuning of the
0168-9002/94/$07 .00 C 1994 - Elsevier Science B.V. All rights reserved SSDI0168-9002(93)E1139-0
EXTENDED SYNOPSES
ABS 108
II
01;
J.-S. Choi et al. / Nucl. Instr. and Meth . in Phys. Res . A 341 (1994) ABS 107-ABS 108
ME a MEN 0 M ME W . . MEM ROME
Fig . 2 . The variation of the collector current with about 1 .5 Vpp amplitude, 7 periods and -12 ws duration is measured by the spontaneous emission of the electron beam . The solid line and the open circles denote the electric pulse from the LC matching network and the current signal measured from the collector, respectively . Horizontal scale is 10 Ws/div and the vertical scale is m arbritary units . matching network circuits, a different behavior is measured for the interference echo signal . However, the main acoustic pulse for the generation of the wiggler
field is not severely affected and a wiggler electric field with the same pattern is produced . In Fig . 2, the spontaneuous emission of the electron beam is measured by means of the measurement of the collector current. After 24 g,s flight time from the electric crosstalk noise signal, the variation of the collector current occurs during - 12 [.Ls, consistent with the wiggler length (L . = N,,l w ) . We can evaluate that the electric field strength E on the surface is - 1 .3 kV/m . Also an electric wiggler with a period 1 . of 3 mm is produced on the PZT surface since the high voltage wave train with a frequency of 735 kHz is applied . In order to improve the wiggler field strength, we could change the acoustic waveguide design . If a surface wave, like a Rayleigh wave, propagates instead of a bulk wave, the acoustic wave energy is concentrated on the surface of PZT waveguide [2] and the wiggler field is increased . Then we can expect a strong electric field with E = 100 kV/m is produced, which is a tenth of the PZT poling field strength .
I I
[1] J .-S . Choi, C.-H So and D .-R . Kim, submitted to J . Kor. Phys . Soc [2] E . Meyer and E .G . Neumann, Physical and Applied Acoustics (Academic Press, New York, 1972) chap . 1 .