- Email: [email protected]
A rep rate KrF system to address issues relevant to inertial fusion energy
Fusion Engineering and Design 44 Ž1999. 371]375
A rep rate KrF system to address issues relevant to inertial fusion energy J.D. Sethian a,U , S.P. Obenschain a , R.H. Lehmberg a , M.W. McGeochb a
Plasma Physics Di¨ ision, Na¨ al Research Laboratory, Washington, DC, USA b PLEX Corporation, Brookline, MA, USA
Abstract We present a conceptual design for a rep-rate krypton-fluoride ŽKrF. laser facility that will allow us to develop the technologies required for an inertial fusion energy ŽIFE. driver. Most of these have been partially developed elsewhere, but they have not been combined in a single integrated test. The facility we are evaluating would be modest in size Žabout 400 J laser output. and would run at 5 Hz. If this facility was built it would significantly improve our ability to assess the potential of direct drive KrF. Q 1999 Published by Elsevier Science S.A. All rights reserved. Keywords: KrF laser facility; Inertial fusion energy; Direct drive
1. Introduction We believe direct drive with a krypton-fluoride ŽKrF. laser is the most promising candidate for inertial fusion energy ŽIFE.. The physics of this approach is attractive because KrF has the short wavelength Ž l s 248 nm. required for efficient coupling and suppression of laser-plasma instabilities, and it has demonstrated w1x the broad bandwidth Ž1]3 THz. required for rapid optical smoothing. Also, the use of direct drive maximizes coupling. These physics issues are being validated on the Nike laser at NRL by studying ablatively accelerated planar targets w1,2x. Direct U
Corresponding author. Tel.: q1 202 7672705; fax: q1 202 7670046; e-mail: [email protected]
drive with KrF is also favorable from a reactor systems viewpoint: the ‘Sombrero’ w3x, and later ‘Sirius’ w4x reactor studies showed that a KrF-based IFE facility would be economically feasible, use existing technologies and materials Ži.e. dry or ‘wetted’ first walls., and be viable with a realistic KrF driver efficiency Žtypically 7]8%.. These encouraging developments in both the physics and reactor arenas call for a look at the engineering issues associated with this approach, and the appropriate next step is to develop an integrated rep-rate KrF laser. 2. Requirements for the rep-rate KrF facility We envision the rep-rate facility to be a test bed in which we can develop the technologies
0920-3796r99r$ - see front matter Q 1999 Published by Elsevier Science S.A. All rights reserved. P I I: S 0 9 2 0 - 3 7 9 6 Ž 9 8 . 0 0 3 6 0 - 3
372
J.D. Sethian et al. r Fusion Engineering and Design 44 (1999) 371]375
that meet the engineering requirements for IFE. These requirements are: Pulsed power driver efficiency Žprime power to laser gas. Rep-rate Durability Žnumber of shots between major maintenance intervals. Beam non-uniformity Cost
55% 5 Hz 108 - 1.5% per beam $200rJ
The facility we have in mind should be large enough to be convincing, yet small enough to be manageable. As a first step we are considering the facility shown in Fig. 1. The fundamental parameters are shown below: Laser output Main amplifier optical aperture Main amplifier E-beam voltage Main amplifier cathode area Main amplifier cathode current density
400 J 30 cm = 30 cm 500 kV 100 cm = 30 cm 80 Arcm2
This is about twice the size of the 20-cm electron beam pumped amplifier of the existing Nike facility w5x. The main issues to be addressed with this facility are rep-rate, durability, and pulsed power driver efficiency.
Fig. 1. Conceptual architecture of the rep-rate KrF laser facility, showing the key areas needing development and the proposed technologies.
This facility is not large enough to properly address the issue of intrinsic efficiency. This is defined as the energy of the laser divided by the energy deposited in the gas. It needs to be about 12% for an IFE system. This is simply the overall efficiency of the Sombrero study Ž7%. combined with the 55% goal for the pulsed power driver. We believe this is achievable, and, in fact, intrinsic efficiencies of 12% have been reported on small systems w6,7x. However this needs to be demonstrated on a large system of the same scale as an IFE driver. 3. Components of the rep-rate KrF facility Fig. 1 shows the six key components of the facility that require development: the pre-amplifier, the optics, the pulsed power driver, the electron beam source, the pressure foil support structure Žor hibachi., and the laser gas conditioning system. In the next six sections we discuss concepts for each of these components. 3.1. The pre-amplifier The pre-amplifier needs to provide about 2]4 J of laser light. For the rep-rate facility we have two choices, either a discharged pumped amplifier or a small electron beam pumped system. The discharge-pumped amplifier was developed for Nike w8x. A voltage on the order of 100 kV is applied to a pair of parallel plates to form an electrical discharge in the laser gas. An X-ray preionizer is essential to make the discharge uniform. For rep-rate operation the laser gas would have to continually flow between the plates, and high flow gas-insulated spark gaps would replace the standard, static fill, switches. The high flow in the spark gaps substantially reduces electrode erosion. For example, the ‘Vortex switch’ based on this design w9x was run at 130 kV at 125 Hz for periods as long as 100 s. ŽThe length of the run was limited by the external gas supplies.. The charge transfer was 0.29 C per shot and the durability was 10 5 shots. The discharge-pumped amplifier would transfer 0.0003 C per shot, so the predicted durability is 10 8 shots.
J.D. Sethian et al. r Fusion Engineering and Design 44 (1999) 371]375
It may turn out that it will be too difficult to rep-rate a large volume discharge-pumped amplifier. The alternative is to build a small aperture Ž10 cm = 10 cm. electron beam pumped system, using the technology discussed in Section 3.3]3.6. 3.2. The optical system KrF lasers require angular multiplexing w10x. This requires a relatively large number of mirrors that need to be kept in alignment. The technology to do this was developed for Nike w1x and we believe it can readily be extended to larger systems. The mirrors and beam paths are located in an insulated, temperature controlled room that keeps the mirrors stable. A PC-based alignment system can align an entire 56-element mirror array, if needed, within a few seconds. 3.3. The pulsed power One of the principal issues with a rep-rate system is the development of a suitable pulsed power driver. The leading candidate is based on non-linear magnetic switches. In this approach a relatively low voltage solid state source is used to pulse charge a capacitor with a saturable inductor at the output. The magnetic core of the inductor is adjusted so that it blocks the current until the capacitor is charged to peak voltage. At that point the core saturates, its permeability Žand hence inductance. rapidly drops, and charge is quickly transferred through the inductor on a time that is much faster than the charge time. Typically this circuit can achieve about a factor of 10 in pulse compression. The circuit is replicated until the desired pulse compression is achieved. The required voltage and pulse shape are attained by including a step-up transformer between the stages and adding a linear induction voltage adder at the output. The major advantage of this technology is that all the components are solid state and should have an extremely long lifetime Ž) 10 9 shots.. A large area electron beam system based on this concept has been built at Sandia Laboratories w11x. Called RHEPP, for repetitive high energy pulsed power, this facility has parameters
373
that are within a factor of 2]5 of that required for a KrF facility: 2.2 MV, 25 kA, 60 ns, 10 cm = 100 cm cathode area. RHEPP runs at 120 Hz, which of course, is significantly faster. The overall system efficiency is 60% and the durability has been demonstrated to be at least 10 6 shots, with 10 9 pulses reasonably expected. RHEPP is so successful that the technology has been transferred to industry for materials processing. The main shortcoming of this technology is that it is expensive. The cost is dominated by the Metglass used in the saturable inductors. The cost for a KrF driver at today’s prices for Metglass Ž$100rkg. would be 10 times too high for an IFE driver. However, Metglass is being adopted by the electric utility industry and it is not unreasonable to expect the cost to come down dramatically. Another potential problem is that the 60% efficiency figure is too low for a KrF driver. Ongoing research in the pulsed power community is directed towards solving these problems. If they are not resolved, then we still have other pulsed power avenues to pursue. The most promising of these is either an oilrpaper dielectric cable that is charged by a DC supply w12x or a conventional water pulse forming line that is charged by a step-up transformer. In both of these cases the lines would be discharged by an array of vortexlike switches. 3.4. Electron beam source We would prefer to use a simple field emission cathode as in the Nike amplifiers w5x. In Nike the emitter material is velvet cloth and the lifetime is limited. However the emitter in RHEPP is a Cu-Be grid which has a reported lifetime of 10 8 shots w13x. The parameters Žarea ; 10 = 100 cm2 , current density 25 Arcm2 . are within a factor of two of what is required for the KrF facility. We should note that the KrF facility would require a magnetic field to guide the electron beam, whereas RHEPP does not, and the magnetic field may prevent this type of cathode from emitting uniformly. If this is the case we can use a cross field plasma cathode w14x. This approach adds some complexity in that we need an auxiliary
374
J.D. Sethian et al. r Fusion Engineering and Design 44 (1999) 371]375
power source to provide the plasma, but in small scale tests it has proven to provide a uniform source with high durability.
this technology could operate at up to 10 Hz. This circulation system is actually an advantage for a reactor as it provides a means to recover the waste heat back into the thermal cycle w17x.
3.5. Pressure foil support structure (the ‘hibachi’) 4. Summary There are two issues with the hibachi: pressure foil lifetime and electron beam transmission. The lifetime issues have been addressed on the EMRLD laser at AVCO w15x by flowing high pressure helium gas between anode and pressure foils made of titanium. Typically EMRLD had a shot rate of 125 Hz and operated for 10 s. The latter figure was limited by the amount of stored energy. No degradation was seen in the foils and it appears that this points the way for long life components. To achieve our efficiency requirements the hibachi should transmit close to 75% of the electron beam energy, or about 1.5 times higher than that of the Nike 60 cm amplifier w5x. Achieving this may be possible if we use a new type of hibachi structure that has been developed and partially tested at Los Alamos w16x. This uses thin fibers under tension rather than the conventional deep ribs as the foil support. Preliminary experiments show the transmission efficiency can approach 90%. While both of these technologies seem viable, the major engineering challenge is to combine them to give both long life and high efficiency. 3.6. Laser gas conditioning
We have outlined the architecture for a reprated KrF laser facility that will allow us to develop and integrate the technologies required for a direct drive krypton-fluoride inertial fusion energy driver. To build this facility we would first test and develop the electron beam and hibachi foil, using a simple rep-rate pulsed power system based on relatively low life spark gap switches. We would then add a gas conditioning system and a high quality laser front end to look at amplification of high quality laser beams. As a final stage we would add a high efficiency, long life, pulsed power driver. If this facility were to be built it would significantly improve our ability to assess the potential of direct drive KrF for fusion energy. Acknowledgements This work is supported by the US Department of Energy. References w1x w2x
The gas in the laser cell must be cool and quiescent on each shot to ensure that the KrF laser beam is very uniform. Of particular importance is the elimination of short scale-length, ordered temperature variations perpendicular to the aperture. The EMRLD laser program successfully addressed this problem as well: the gas in the laser cell was circulated through a series of mixing plates, diffusers, and heat exchangers. This enabled the EMRLD laser to faithfully amplify a 1.3= diffraction limited laser beam w15x. The shot rate was 100 Hz, and the Žsupply-limited. duration was 10 s. As the largest aperture one would consider for an IFE driver is 100 cm, this suggests
w3x w4x w5x
w6x w7x
S.P. Obenschain, et al., Phys. Plasmas 3 Ž1996. 2098]2107. C.J. Pawley, et al., Measurements of laser-imprinted perturbations and Rayleigh-Taylor growth rate with the Nike KrF laser, Phys. Plasmas Žaccepted for publication.. I.V. Sviatoslavsky, et al., Fus. Technol. 21 Ž1992. 1470]1505. I.V. Sviatoslavsky, P. Sirius, An inertially confined direct drive laser fusion power reactor, Fusion Technol. Inst., Univ. of Wisconsin, March, 1993, UWFDM-950. J.D. Sethian, C.J. Pawley, S.P. Obenschain, K.A. Gerber, V. Serlin, T. Lehecka, W.D. Webster, I.D. Smith, P.A. Corcoran, R.A. Altes, The Nike electron beam-pumped KrF laser amplifiers, Digest of Technical Papers, Tenth IEEE Pulsed Power Conference, Albuquerque, NM July 10]13, 1995. IEEE, Piscataway, NJ, 1995, pp. 625]633. A. Mandl, D. Klimek, E. Salesky, Fus. Technol. 11 Ž1987. 542]547. Y. Lee, F. Kannari, M. Obara, J. Appl. Phys. 65 Ž1989. 4532]4541.
J.D. Sethian et al. r Fusion Engineering and Design 44 (1999) 371]375 w8x M.S. Pronko, IEEE J. Quantum Electron. QE10 Ž1994. 2147]2156. w9x R. Limpaecher, R. Litte, An application of a high energy spark gap in a repetitive mode, Digest of Technical Papers, Fifth IEEE Pulsed Power Conference, Arlington, VA June 10]12, 1985. IEEE, New York, pp. 477]480. w10x J.J. Ewing, R.A. Haas, J.C. Swingle, E.V. George, W.F. Krupke, IEEE. J. Quantum Electron. QE15 Ž1979. 368. w11x D.L. Johnson, et al., Results of initial testing of the four stage RHEPP accelerator, Digest of Technical Papers, Ninth International Pulsed Power Conference, San Diego, CA, 1993, pp. 437]444. w12x R. Limpaecher, R. Litte, S. Ghosroy, High voltage cable PFL test results, Proceedings Seventeenth International
w13x
w14x w15x w16x
w17x
375
Power Modulator Symposium, Seattle WA, June 23]25, 1996. IEEE, New York, 1996, pp. 264]270. S.D. Korovin, Long lifetime metal-dielectric cathodes, Contract report AF-0416, High Current Electronics Institute, Tomsk, Russia, 1993. M.W. McGeoch, J. Appl. Phys. 71 Ž1992. 1163. J. Moran, Textron Defense Systems, Everett MA, private communication. J.P. Brucker, E.A. Rose, Foil support structure for large area electron guns, Technical Digest of Papers, Ninth IEEE Pulsed Power Conference, Albuquerque, NM, June 21]23, 1993. IEEE, Piscataway, NJ, 1993, pp. 747]750. C.W. von Rosenberg, Fus. Technol. 21 Ž1992. 1600]1604.
A rep rate KrF system to address issues relevant to inertial fusion energy J.D. Sethian a,U , S.P. Obenschain a , R.H. Lehmberg a , M.W. McGeochb a
Plasma Physics Di¨ ision, Na¨ al Research Laboratory, Washington, DC, USA b PLEX Corporation, Brookline, MA, USA
Abstract We present a conceptual design for a rep-rate krypton-fluoride ŽKrF. laser facility that will allow us to develop the technologies required for an inertial fusion energy ŽIFE. driver. Most of these have been partially developed elsewhere, but they have not been combined in a single integrated test. The facility we are evaluating would be modest in size Žabout 400 J laser output. and would run at 5 Hz. If this facility was built it would significantly improve our ability to assess the potential of direct drive KrF. Q 1999 Published by Elsevier Science S.A. All rights reserved. Keywords: KrF laser facility; Inertial fusion energy; Direct drive
1. Introduction We believe direct drive with a krypton-fluoride ŽKrF. laser is the most promising candidate for inertial fusion energy ŽIFE.. The physics of this approach is attractive because KrF has the short wavelength Ž l s 248 nm. required for efficient coupling and suppression of laser-plasma instabilities, and it has demonstrated w1x the broad bandwidth Ž1]3 THz. required for rapid optical smoothing. Also, the use of direct drive maximizes coupling. These physics issues are being validated on the Nike laser at NRL by studying ablatively accelerated planar targets w1,2x. Direct U
Corresponding author. Tel.: q1 202 7672705; fax: q1 202 7670046; e-mail: [email protected]
drive with KrF is also favorable from a reactor systems viewpoint: the ‘Sombrero’ w3x, and later ‘Sirius’ w4x reactor studies showed that a KrF-based IFE facility would be economically feasible, use existing technologies and materials Ži.e. dry or ‘wetted’ first walls., and be viable with a realistic KrF driver efficiency Žtypically 7]8%.. These encouraging developments in both the physics and reactor arenas call for a look at the engineering issues associated with this approach, and the appropriate next step is to develop an integrated rep-rate KrF laser. 2. Requirements for the rep-rate KrF facility We envision the rep-rate facility to be a test bed in which we can develop the technologies
0920-3796r99r$ - see front matter Q 1999 Published by Elsevier Science S.A. All rights reserved. P I I: S 0 9 2 0 - 3 7 9 6 Ž 9 8 . 0 0 3 6 0 - 3
372
J.D. Sethian et al. r Fusion Engineering and Design 44 (1999) 371]375
that meet the engineering requirements for IFE. These requirements are: Pulsed power driver efficiency Žprime power to laser gas. Rep-rate Durability Žnumber of shots between major maintenance intervals. Beam non-uniformity Cost
55% 5 Hz 108 - 1.5% per beam $200rJ
The facility we have in mind should be large enough to be convincing, yet small enough to be manageable. As a first step we are considering the facility shown in Fig. 1. The fundamental parameters are shown below: Laser output Main amplifier optical aperture Main amplifier E-beam voltage Main amplifier cathode area Main amplifier cathode current density
400 J 30 cm = 30 cm 500 kV 100 cm = 30 cm 80 Arcm2
This is about twice the size of the 20-cm electron beam pumped amplifier of the existing Nike facility w5x. The main issues to be addressed with this facility are rep-rate, durability, and pulsed power driver efficiency.
Fig. 1. Conceptual architecture of the rep-rate KrF laser facility, showing the key areas needing development and the proposed technologies.
This facility is not large enough to properly address the issue of intrinsic efficiency. This is defined as the energy of the laser divided by the energy deposited in the gas. It needs to be about 12% for an IFE system. This is simply the overall efficiency of the Sombrero study Ž7%. combined with the 55% goal for the pulsed power driver. We believe this is achievable, and, in fact, intrinsic efficiencies of 12% have been reported on small systems w6,7x. However this needs to be demonstrated on a large system of the same scale as an IFE driver. 3. Components of the rep-rate KrF facility Fig. 1 shows the six key components of the facility that require development: the pre-amplifier, the optics, the pulsed power driver, the electron beam source, the pressure foil support structure Žor hibachi., and the laser gas conditioning system. In the next six sections we discuss concepts for each of these components. 3.1. The pre-amplifier The pre-amplifier needs to provide about 2]4 J of laser light. For the rep-rate facility we have two choices, either a discharged pumped amplifier or a small electron beam pumped system. The discharge-pumped amplifier was developed for Nike w8x. A voltage on the order of 100 kV is applied to a pair of parallel plates to form an electrical discharge in the laser gas. An X-ray preionizer is essential to make the discharge uniform. For rep-rate operation the laser gas would have to continually flow between the plates, and high flow gas-insulated spark gaps would replace the standard, static fill, switches. The high flow in the spark gaps substantially reduces electrode erosion. For example, the ‘Vortex switch’ based on this design w9x was run at 130 kV at 125 Hz for periods as long as 100 s. ŽThe length of the run was limited by the external gas supplies.. The charge transfer was 0.29 C per shot and the durability was 10 5 shots. The discharge-pumped amplifier would transfer 0.0003 C per shot, so the predicted durability is 10 8 shots.
J.D. Sethian et al. r Fusion Engineering and Design 44 (1999) 371]375
It may turn out that it will be too difficult to rep-rate a large volume discharge-pumped amplifier. The alternative is to build a small aperture Ž10 cm = 10 cm. electron beam pumped system, using the technology discussed in Section 3.3]3.6. 3.2. The optical system KrF lasers require angular multiplexing w10x. This requires a relatively large number of mirrors that need to be kept in alignment. The technology to do this was developed for Nike w1x and we believe it can readily be extended to larger systems. The mirrors and beam paths are located in an insulated, temperature controlled room that keeps the mirrors stable. A PC-based alignment system can align an entire 56-element mirror array, if needed, within a few seconds. 3.3. The pulsed power One of the principal issues with a rep-rate system is the development of a suitable pulsed power driver. The leading candidate is based on non-linear magnetic switches. In this approach a relatively low voltage solid state source is used to pulse charge a capacitor with a saturable inductor at the output. The magnetic core of the inductor is adjusted so that it blocks the current until the capacitor is charged to peak voltage. At that point the core saturates, its permeability Žand hence inductance. rapidly drops, and charge is quickly transferred through the inductor on a time that is much faster than the charge time. Typically this circuit can achieve about a factor of 10 in pulse compression. The circuit is replicated until the desired pulse compression is achieved. The required voltage and pulse shape are attained by including a step-up transformer between the stages and adding a linear induction voltage adder at the output. The major advantage of this technology is that all the components are solid state and should have an extremely long lifetime Ž) 10 9 shots.. A large area electron beam system based on this concept has been built at Sandia Laboratories w11x. Called RHEPP, for repetitive high energy pulsed power, this facility has parameters
373
that are within a factor of 2]5 of that required for a KrF facility: 2.2 MV, 25 kA, 60 ns, 10 cm = 100 cm cathode area. RHEPP runs at 120 Hz, which of course, is significantly faster. The overall system efficiency is 60% and the durability has been demonstrated to be at least 10 6 shots, with 10 9 pulses reasonably expected. RHEPP is so successful that the technology has been transferred to industry for materials processing. The main shortcoming of this technology is that it is expensive. The cost is dominated by the Metglass used in the saturable inductors. The cost for a KrF driver at today’s prices for Metglass Ž$100rkg. would be 10 times too high for an IFE driver. However, Metglass is being adopted by the electric utility industry and it is not unreasonable to expect the cost to come down dramatically. Another potential problem is that the 60% efficiency figure is too low for a KrF driver. Ongoing research in the pulsed power community is directed towards solving these problems. If they are not resolved, then we still have other pulsed power avenues to pursue. The most promising of these is either an oilrpaper dielectric cable that is charged by a DC supply w12x or a conventional water pulse forming line that is charged by a step-up transformer. In both of these cases the lines would be discharged by an array of vortexlike switches. 3.4. Electron beam source We would prefer to use a simple field emission cathode as in the Nike amplifiers w5x. In Nike the emitter material is velvet cloth and the lifetime is limited. However the emitter in RHEPP is a Cu-Be grid which has a reported lifetime of 10 8 shots w13x. The parameters Žarea ; 10 = 100 cm2 , current density 25 Arcm2 . are within a factor of two of what is required for the KrF facility. We should note that the KrF facility would require a magnetic field to guide the electron beam, whereas RHEPP does not, and the magnetic field may prevent this type of cathode from emitting uniformly. If this is the case we can use a cross field plasma cathode w14x. This approach adds some complexity in that we need an auxiliary
374
J.D. Sethian et al. r Fusion Engineering and Design 44 (1999) 371]375
power source to provide the plasma, but in small scale tests it has proven to provide a uniform source with high durability.
this technology could operate at up to 10 Hz. This circulation system is actually an advantage for a reactor as it provides a means to recover the waste heat back into the thermal cycle w17x.
3.5. Pressure foil support structure (the ‘hibachi’) 4. Summary There are two issues with the hibachi: pressure foil lifetime and electron beam transmission. The lifetime issues have been addressed on the EMRLD laser at AVCO w15x by flowing high pressure helium gas between anode and pressure foils made of titanium. Typically EMRLD had a shot rate of 125 Hz and operated for 10 s. The latter figure was limited by the amount of stored energy. No degradation was seen in the foils and it appears that this points the way for long life components. To achieve our efficiency requirements the hibachi should transmit close to 75% of the electron beam energy, or about 1.5 times higher than that of the Nike 60 cm amplifier w5x. Achieving this may be possible if we use a new type of hibachi structure that has been developed and partially tested at Los Alamos w16x. This uses thin fibers under tension rather than the conventional deep ribs as the foil support. Preliminary experiments show the transmission efficiency can approach 90%. While both of these technologies seem viable, the major engineering challenge is to combine them to give both long life and high efficiency. 3.6. Laser gas conditioning
We have outlined the architecture for a reprated KrF laser facility that will allow us to develop and integrate the technologies required for a direct drive krypton-fluoride inertial fusion energy driver. To build this facility we would first test and develop the electron beam and hibachi foil, using a simple rep-rate pulsed power system based on relatively low life spark gap switches. We would then add a gas conditioning system and a high quality laser front end to look at amplification of high quality laser beams. As a final stage we would add a high efficiency, long life, pulsed power driver. If this facility were to be built it would significantly improve our ability to assess the potential of direct drive KrF for fusion energy. Acknowledgements This work is supported by the US Department of Energy. References w1x w2x
The gas in the laser cell must be cool and quiescent on each shot to ensure that the KrF laser beam is very uniform. Of particular importance is the elimination of short scale-length, ordered temperature variations perpendicular to the aperture. The EMRLD laser program successfully addressed this problem as well: the gas in the laser cell was circulated through a series of mixing plates, diffusers, and heat exchangers. This enabled the EMRLD laser to faithfully amplify a 1.3= diffraction limited laser beam w15x. The shot rate was 100 Hz, and the Žsupply-limited. duration was 10 s. As the largest aperture one would consider for an IFE driver is 100 cm, this suggests
w3x w4x w5x
w6x w7x
S.P. Obenschain, et al., Phys. Plasmas 3 Ž1996. 2098]2107. C.J. Pawley, et al., Measurements of laser-imprinted perturbations and Rayleigh-Taylor growth rate with the Nike KrF laser, Phys. Plasmas Žaccepted for publication.. I.V. Sviatoslavsky, et al., Fus. Technol. 21 Ž1992. 1470]1505. I.V. Sviatoslavsky, P. Sirius, An inertially confined direct drive laser fusion power reactor, Fusion Technol. Inst., Univ. of Wisconsin, March, 1993, UWFDM-950. J.D. Sethian, C.J. Pawley, S.P. Obenschain, K.A. Gerber, V. Serlin, T. Lehecka, W.D. Webster, I.D. Smith, P.A. Corcoran, R.A. Altes, The Nike electron beam-pumped KrF laser amplifiers, Digest of Technical Papers, Tenth IEEE Pulsed Power Conference, Albuquerque, NM July 10]13, 1995. IEEE, Piscataway, NJ, 1995, pp. 625]633. A. Mandl, D. Klimek, E. Salesky, Fus. Technol. 11 Ž1987. 542]547. Y. Lee, F. Kannari, M. Obara, J. Appl. Phys. 65 Ž1989. 4532]4541.
J.D. Sethian et al. r Fusion Engineering and Design 44 (1999) 371]375 w8x M.S. Pronko, IEEE J. Quantum Electron. QE10 Ž1994. 2147]2156. w9x R. Limpaecher, R. Litte, An application of a high energy spark gap in a repetitive mode, Digest of Technical Papers, Fifth IEEE Pulsed Power Conference, Arlington, VA June 10]12, 1985. IEEE, New York, pp. 477]480. w10x J.J. Ewing, R.A. Haas, J.C. Swingle, E.V. George, W.F. Krupke, IEEE. J. Quantum Electron. QE15 Ž1979. 368. w11x D.L. Johnson, et al., Results of initial testing of the four stage RHEPP accelerator, Digest of Technical Papers, Ninth International Pulsed Power Conference, San Diego, CA, 1993, pp. 437]444. w12x R. Limpaecher, R. Litte, S. Ghosroy, High voltage cable PFL test results, Proceedings Seventeenth International
w13x
w14x w15x w16x
w17x
375
Power Modulator Symposium, Seattle WA, June 23]25, 1996. IEEE, New York, 1996, pp. 264]270. S.D. Korovin, Long lifetime metal-dielectric cathodes, Contract report AF-0416, High Current Electronics Institute, Tomsk, Russia, 1993. M.W. McGeoch, J. Appl. Phys. 71 Ž1992. 1163. J. Moran, Textron Defense Systems, Everett MA, private communication. J.P. Brucker, E.A. Rose, Foil support structure for large area electron guns, Technical Digest of Papers, Ninth IEEE Pulsed Power Conference, Albuquerque, NM, June 21]23, 1993. IEEE, Piscataway, NJ, 1993, pp. 747]750. C.W. von Rosenberg, Fus. Technol. 21 Ž1992. 1600]1604.