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New Japanese FEL program at Osaka
276
Nuclear Instruments and Methods m Physics Research A304 (1991) 276-279 North-Holland
New Japanese FEL program at Osaka C. Yamanaka
Institute for Laser TechnoloKv, Situa, Osaka 565, Japan
In this article, we discuss a new FEL project proposed at Osaka, Japan The final goal of this project is to develop a FEL for industrial applications
1 . Introduction
From these points of view, the civilian applications of
A FEL using a lmac system has several advantages,
such as its wide
tunability, high average power, no
the FEL m the high technologies are strongly desired to Japan [2].
For scientific applications, higher-gradient accelera-
lasing materials, etc., compared with the usual lasers [1].
tion, tokamak plasma heating, and inertial confinement
high repetition rate . Because of these facts, the FEL can
schemes are also discussed .
In addition, the linac has a sufficiently long life and a
be considered to have a high potential for applications in many scientific and industrial fields. For industrial applications, tunability over a wide
range to wavelength can make the FEL a flexible light source . If a compact and cheap FEL system can be developed, the FEL will open a wide range of industrial
applications for photochemistry, new material research, semiconductor processing, nuclear fuel cycle processing,
biophysical and medical research, etc., because of its fine and continuous tunability and high average power.
fusion (ICF) are listed . For the ICF application, several In this article, the FEL project for industrial applications proposed at Osaka is presented in section 2. The FEL applications to ICF are discussed in section 3.
2. FEL development and applications for industry Industrial applications of the FEL,
especially for
high-technology fields, are estimated to be very important in Japan. The tunability and sufficiently high
Table 1 The parameters of the new Japanese FEL project Output
1 FIR-IR ( - 20 1r m)
II NIR (-2 ~t m)
Ill Visible-UV (-0.2 ~L m)
Accelerator Energy Beam current Macropulse Micropulse Emittance e-beam gun
- 50 MeV 20 A 10 [is -10 ps lirt mm mrad conventional (thermionic)
- 75 MeV 20 A 10 ~L s -10 ps 0.3m mm mrad rf gun
- 230 MeV 80 A 20 Ws 10 ps 0.041T mm mrad photocathode rf gun
W iggler Period Gap distance Length
- 90 mm 47-54 mm -3m
-40 mm 12-20 mm -3m
Cavity Length Type
7m confocal
7m confocal
0168-9002/91/$03 .50
C>
1991 - Elsevier Science Publishers B.V . (North-Holland)
-30 mm 12-20 mm -6m
ring
55m
C Yamanaka / New Japanese FEL program at Osaka power of the FEL are considered suitable for fine and precise processing of semiconductors in quantum devices . More than a hundred stages of precise processing are required to produce the ULSI tips . In this processing, a thermal process becomes crucial and a nonthermal method is expected to apply . The rf linac FEL is proposed by the Committee of the FEL studies at Osaka . A conceptual diagram of the proposed project is shown in fig . 1 . As a final goal of the project, a FEL system appropriate for the integrated quantum processing manufacture (IQPM) is considered . IQP is a generic technology of the high-technical field required for the beginning of the next century . In IQPM, most of laser processing, including semiconductor processing, photochemistry, new material production, etc., will be performed and investigated in the central FEL facility where the expected laser power is more than 100 W in the wavelength range from 2000 f1 to 20 p m. To achieve
Electronics ULSI 3D Quantum-well Super Lattice
Quantum Processing Technology Atomic Level Control Lithography CVD, PVD, Epitaxy Etching, Dopeing Laser Chemistry Laser Separation
27 7
this, a two-phase program is planned and discussed . In the first phase of the project, we will build the FEL system using a rf linac with an energy up to 250 MeV in the FEL Central Research Facility . Using this system, we will explore fundamental FEL technology . It is planned that there will be three outlets on the linac line : 50 MeV FIR FEL, 75 MeV IR FEL and 250 MeV UV FEL . Normalized brightness required to achieve each wavelength is shown in fig . 2 . An investigation of a photocathode was performed at ILT to obtain a high-current low-emittance beam using 2w and 3w of a Nd YAG laser . The materials mainly studied were LaB6 , TiC, Ta, Al, and W . A rf gun injector with a laser photocathode is under design . The total system is planned to be complete m 1993 . Table 1 shows the parameters of the FEL system. In the second phase, we will use the FEL for several applications . The FIR FEL, with a wavelength range of 20-100 wm, will be used to study solid state physics
Fission Fuel Chemical Synthesis Waste Patitioning Isotope Separation Super Fine Chemicals Chain Reaction
Analysis Technology Tunability High Space-Time Resolution Photo Luminecence Raman-Brillouin Spectro-Scopy Differencial Spectroscopy
New Material Research Super Conduction Materials High pure material Fine ceramics Semiconductor
IQPM(Integrated Quantum Processing Manufacture) FEL Laser Control System Quantum Processing Photo-Chemical Plant Analysis System
Free Electron Lasers Technology Development Basic FEL System IIigh Bright Accelerator Wiggler Optical Component Compact ITL System Higher Gradient Beam Recircular Micro Wiggler Fig . 1 . Conceptual diagram of the proposed FEL project for industrial applications. IV . PROPOSALS/STATUS REPORTS
27 8
N ß
C Yamanaka / New Japanese FEL program at Osaka
Wavelengths shorter than 1000 Pi are important for lithography for ULSI . This region is the subject of investigation for the next step . The disadvantage of the FEL for industrial applications is its size and initial cost . We have studied the feasibility of a compact FEL which is less than 3 x 8 inZ in area . Higher-gradient acceleration and microwiggler technologies in addition to high beam brightness are necessary to obtain this size .
11 10
N
E
r ß a>N ro
10 10
10
s
3. FEL facilities for ICF
E ô z
m
10
e
01
10
100
1000
wavelength (ltrn)
Fig. 2 . FEL oscillation condition for e-beam and wavelength . and, especially, high-temperature superconductor technology . It will also be useful as a continuously tunable source to excite magnons, plasmons and phonons. The IR FEL, with a wavelength range of 1-10 win, will be used to investigate biophysical and medical problems . A thermal processing in biomolecular studies seems to be a very interesting and suitable application for the laser's picosecond pulses . The FEL-computer tomograph system can be conceivable . Tunability of the FEL may play an important role in these applications. For a visible to UV FEL with a wavelength range of 2000-8000 Â, semiconductor processing, new material research, isotope separation, nuclear waste partitioning, photochemistry, etc., are possible applications . It is possible to induce selected chemical reactions; thus process is called quantum processing in fig. 1 . This fine selective processing may promote new important hightechnology areas in the next century. Table 2 Efficiency for the ICF solid state laser system pumped by flash lamp, laser diode and FEL Pumping source
Pumping light efficiency Transfer efficiency Absorption efficiency Quantum efficiency Transition efficiency Extraction efficiency Conversion efficiency Total
Flash lamp
LID
FEL
70% 35% 50% 70%
55% 90% 95% 75% 70%
55% 95% 98% 75% 70%
70%
70%
70% 11 .3%
40% 60% 1 .4%
60% 10.4%
60%
The many theoretical and experimental studies show the important potential of the FEL for the future . A few of these studies examine the FEL as an ICF driver motivated by its high-efficiency, high-output-power and high-repetition capabilities [4-6]. There are two ways for the FEL to be applied to ICF. One is a direct energy source . The FEL does not store energy, but converts the energy of the e-beam to the laser. As a consequence, very high peak power is required in the accelerator to achieve high currents . If one can store the FEL power in a conventional lasing medium, such as solid state lasers, the required e-beam power may be significantly reduced. To use the FEL for pumping a sohd state laser, the FEL pulse length can be taken as 10 -3 s. This is a reasonable pulse duration for solid state laser pumping. The FEL can be tuned to the wavelength to match a resonance absorption line of the lasing medium . Therefore the pumping efficiency can be expected to be very high . The most important advantage of this method is that the peak power of the e-beam may be 10 -5 times smaller than that of a direct energy source [6]. For a 500 MeV accelerator, the average current during the macropulse is 8 A. Therefore it may be possible to use a rf linac FEL in this scheme . The total efficiency of a FEL-pumped solid state laser can be as high as 12% as shown in table 2. Very high efficiency of the FEL is required to achieve this value. Energy recovery of the e-beam after the wiggler may increase the efficiency significantly. The required wavelength for Nd 3+ pumping is 0.88 Win. A laser-diode-pumped solid state laser has been studied for a promising ICF reactor driver shown in table 2. A FEL-pumped solid state laser seems to be comparable to this scheme. In addition, the FEL system may be built at a lower cost than the LD-pumped system composed of 10 7 arrays of LD . 4. Summary A proposal for a rf linac FEL for industrial application has been presented. Application of the FEL for
C. Yamanaka / New Japanese FEL program at Osaka ICF was also discussed [7]. Direct FEL irradiation scheme and the FEL pumping scheme have been compared. Using the FEL as a solid state laser pump, the required parameters are significantly reduced compared with direct irradiation . These parameters may be achievable using extended rf linac technology .
279
References [1] [2] [3] [4] [5] [6] [7]
C.A . Brau, SPIE 738 (1987) 84 . K. Imasaki, J. IEE Jpn. 109 (1989) 903 . T. Akiba et al ., Appl . Phys . Lett . 56 (1990) 503. S. Segall, KMSF-U 806 (1975) . D. Prosnitz, LLNL, UCRL 92095 (1984). K. Imasaki, Rev . Laser Eng. 17 (1989) 71 . FEL Research Committee of IEE Japan, FEL and Its Application (Corona Publ ., 1990) m Japanese .
IV. PROPOSALS/STATUS REPORTS
Nuclear Instruments and Methods m Physics Research A304 (1991) 276-279 North-Holland
New Japanese FEL program at Osaka C. Yamanaka
Institute for Laser TechnoloKv, Situa, Osaka 565, Japan
In this article, we discuss a new FEL project proposed at Osaka, Japan The final goal of this project is to develop a FEL for industrial applications
1 . Introduction
From these points of view, the civilian applications of
A FEL using a lmac system has several advantages,
such as its wide
tunability, high average power, no
the FEL m the high technologies are strongly desired to Japan [2].
For scientific applications, higher-gradient accelera-
lasing materials, etc., compared with the usual lasers [1].
tion, tokamak plasma heating, and inertial confinement
high repetition rate . Because of these facts, the FEL can
schemes are also discussed .
In addition, the linac has a sufficiently long life and a
be considered to have a high potential for applications in many scientific and industrial fields. For industrial applications, tunability over a wide
range to wavelength can make the FEL a flexible light source . If a compact and cheap FEL system can be developed, the FEL will open a wide range of industrial
applications for photochemistry, new material research, semiconductor processing, nuclear fuel cycle processing,
biophysical and medical research, etc., because of its fine and continuous tunability and high average power.
fusion (ICF) are listed . For the ICF application, several In this article, the FEL project for industrial applications proposed at Osaka is presented in section 2. The FEL applications to ICF are discussed in section 3.
2. FEL development and applications for industry Industrial applications of the FEL,
especially for
high-technology fields, are estimated to be very important in Japan. The tunability and sufficiently high
Table 1 The parameters of the new Japanese FEL project Output
1 FIR-IR ( - 20 1r m)
II NIR (-2 ~t m)
Ill Visible-UV (-0.2 ~L m)
Accelerator Energy Beam current Macropulse Micropulse Emittance e-beam gun
- 50 MeV 20 A 10 [is -10 ps lirt mm mrad conventional (thermionic)
- 75 MeV 20 A 10 ~L s -10 ps 0.3m mm mrad rf gun
- 230 MeV 80 A 20 Ws 10 ps 0.041T mm mrad photocathode rf gun
W iggler Period Gap distance Length
- 90 mm 47-54 mm -3m
-40 mm 12-20 mm -3m
Cavity Length Type
7m confocal
7m confocal
0168-9002/91/$03 .50
C>
1991 - Elsevier Science Publishers B.V . (North-Holland)
-30 mm 12-20 mm -6m
ring
55m
C Yamanaka / New Japanese FEL program at Osaka power of the FEL are considered suitable for fine and precise processing of semiconductors in quantum devices . More than a hundred stages of precise processing are required to produce the ULSI tips . In this processing, a thermal process becomes crucial and a nonthermal method is expected to apply . The rf linac FEL is proposed by the Committee of the FEL studies at Osaka . A conceptual diagram of the proposed project is shown in fig . 1 . As a final goal of the project, a FEL system appropriate for the integrated quantum processing manufacture (IQPM) is considered . IQP is a generic technology of the high-technical field required for the beginning of the next century . In IQPM, most of laser processing, including semiconductor processing, photochemistry, new material production, etc., will be performed and investigated in the central FEL facility where the expected laser power is more than 100 W in the wavelength range from 2000 f1 to 20 p m. To achieve
Electronics ULSI 3D Quantum-well Super Lattice
Quantum Processing Technology Atomic Level Control Lithography CVD, PVD, Epitaxy Etching, Dopeing Laser Chemistry Laser Separation
27 7
this, a two-phase program is planned and discussed . In the first phase of the project, we will build the FEL system using a rf linac with an energy up to 250 MeV in the FEL Central Research Facility . Using this system, we will explore fundamental FEL technology . It is planned that there will be three outlets on the linac line : 50 MeV FIR FEL, 75 MeV IR FEL and 250 MeV UV FEL . Normalized brightness required to achieve each wavelength is shown in fig . 2 . An investigation of a photocathode was performed at ILT to obtain a high-current low-emittance beam using 2w and 3w of a Nd YAG laser . The materials mainly studied were LaB6 , TiC, Ta, Al, and W . A rf gun injector with a laser photocathode is under design . The total system is planned to be complete m 1993 . Table 1 shows the parameters of the FEL system. In the second phase, we will use the FEL for several applications . The FIR FEL, with a wavelength range of 20-100 wm, will be used to study solid state physics
Fission Fuel Chemical Synthesis Waste Patitioning Isotope Separation Super Fine Chemicals Chain Reaction
Analysis Technology Tunability High Space-Time Resolution Photo Luminecence Raman-Brillouin Spectro-Scopy Differencial Spectroscopy
New Material Research Super Conduction Materials High pure material Fine ceramics Semiconductor
IQPM(Integrated Quantum Processing Manufacture) FEL Laser Control System Quantum Processing Photo-Chemical Plant Analysis System
Free Electron Lasers Technology Development Basic FEL System IIigh Bright Accelerator Wiggler Optical Component Compact ITL System Higher Gradient Beam Recircular Micro Wiggler Fig . 1 . Conceptual diagram of the proposed FEL project for industrial applications. IV . PROPOSALS/STATUS REPORTS
27 8
N ß
C Yamanaka / New Japanese FEL program at Osaka
Wavelengths shorter than 1000 Pi are important for lithography for ULSI . This region is the subject of investigation for the next step . The disadvantage of the FEL for industrial applications is its size and initial cost . We have studied the feasibility of a compact FEL which is less than 3 x 8 inZ in area . Higher-gradient acceleration and microwiggler technologies in addition to high beam brightness are necessary to obtain this size .
11 10
N
E
r ß a>N ro
10 10
10
s
3. FEL facilities for ICF
E ô z
m
10
e
01
10
100
1000
wavelength (ltrn)
Fig. 2 . FEL oscillation condition for e-beam and wavelength . and, especially, high-temperature superconductor technology . It will also be useful as a continuously tunable source to excite magnons, plasmons and phonons. The IR FEL, with a wavelength range of 1-10 win, will be used to investigate biophysical and medical problems . A thermal processing in biomolecular studies seems to be a very interesting and suitable application for the laser's picosecond pulses . The FEL-computer tomograph system can be conceivable . Tunability of the FEL may play an important role in these applications. For a visible to UV FEL with a wavelength range of 2000-8000 Â, semiconductor processing, new material research, isotope separation, nuclear waste partitioning, photochemistry, etc., are possible applications . It is possible to induce selected chemical reactions; thus process is called quantum processing in fig. 1 . This fine selective processing may promote new important hightechnology areas in the next century. Table 2 Efficiency for the ICF solid state laser system pumped by flash lamp, laser diode and FEL Pumping source
Pumping light efficiency Transfer efficiency Absorption efficiency Quantum efficiency Transition efficiency Extraction efficiency Conversion efficiency Total
Flash lamp
LID
FEL
70% 35% 50% 70%
55% 90% 95% 75% 70%
55% 95% 98% 75% 70%
70%
70%
70% 11 .3%
40% 60% 1 .4%
60% 10.4%
60%
The many theoretical and experimental studies show the important potential of the FEL for the future . A few of these studies examine the FEL as an ICF driver motivated by its high-efficiency, high-output-power and high-repetition capabilities [4-6]. There are two ways for the FEL to be applied to ICF. One is a direct energy source . The FEL does not store energy, but converts the energy of the e-beam to the laser. As a consequence, very high peak power is required in the accelerator to achieve high currents . If one can store the FEL power in a conventional lasing medium, such as solid state lasers, the required e-beam power may be significantly reduced. To use the FEL for pumping a sohd state laser, the FEL pulse length can be taken as 10 -3 s. This is a reasonable pulse duration for solid state laser pumping. The FEL can be tuned to the wavelength to match a resonance absorption line of the lasing medium . Therefore the pumping efficiency can be expected to be very high . The most important advantage of this method is that the peak power of the e-beam may be 10 -5 times smaller than that of a direct energy source [6]. For a 500 MeV accelerator, the average current during the macropulse is 8 A. Therefore it may be possible to use a rf linac FEL in this scheme . The total efficiency of a FEL-pumped solid state laser can be as high as 12% as shown in table 2. Very high efficiency of the FEL is required to achieve this value. Energy recovery of the e-beam after the wiggler may increase the efficiency significantly. The required wavelength for Nd 3+ pumping is 0.88 Win. A laser-diode-pumped solid state laser has been studied for a promising ICF reactor driver shown in table 2. A FEL-pumped solid state laser seems to be comparable to this scheme. In addition, the FEL system may be built at a lower cost than the LD-pumped system composed of 10 7 arrays of LD . 4. Summary A proposal for a rf linac FEL for industrial application has been presented. Application of the FEL for
C. Yamanaka / New Japanese FEL program at Osaka ICF was also discussed [7]. Direct FEL irradiation scheme and the FEL pumping scheme have been compared. Using the FEL as a solid state laser pump, the required parameters are significantly reduced compared with direct irradiation . These parameters may be achievable using extended rf linac technology .
279
References [1] [2] [3] [4] [5] [6] [7]
C.A . Brau, SPIE 738 (1987) 84 . K. Imasaki, J. IEE Jpn. 109 (1989) 903 . T. Akiba et al ., Appl . Phys . Lett . 56 (1990) 503. S. Segall, KMSF-U 806 (1975) . D. Prosnitz, LLNL, UCRL 92095 (1984). K. Imasaki, Rev . Laser Eng. 17 (1989) 71 . FEL Research Committee of IEE Japan, FEL and Its Application (Corona Publ ., 1990) m Japanese .
IV. PROPOSALS/STATUS REPORTS