James Potter - Academia.edu (original) (raw)
Papers by James Potter
2016 IEEE International Vacuum Electronics Conference (IVEC), 2016
We have built the first-ever klynac, consisting of a klystron and linac combined into a single in... more We have built the first-ever klynac, consisting of a klystron and linac combined into a single integrated structure using a single electron beam. This device has two resonant circuits, one for the klystron input and gain section, and one for the klystron output cavity and linac section. Here we describe this device's stability properties driven by its resonant properties.
IEEE Transactions on Nuclear Science, 1985
Ourlng the past few years the Defense and Electronics Center of Westinghouse Electric Corporation... more Ourlng the past few years the Defense and Electronics Center of Westinghouse Electric Corporation has developcl a solid-state, 250-kW Peak, rf ampllfler for use with the SPS-40 radar system. This system has a pulse length of 60 VS and operates across the frequency band from400 to 450 MHz. Because of the potential use of such a system as an rf source for accelerator applications, a collaborative experiment as Inltlated between Los Alamos National Laboratory ana Westinghouse to simulate the resonant load conditions of an accelerator cavity This paper describes the posltlve results of that experiment as well as the solid-state ampllfler architecture. It also explores the future of high-power, sollo-state amplifiers as rf sources for accelerator structures.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Mar 28, 2017
Physical Review Letters, 1974
don 7, 2109 (1974). 3H. HOrner, private communication. 4J. Sak, to be published.
IEEE Transactions on Nuclear Science, 1985
The mathematical background for a multiportnetwork-solving program is described. A method for acc... more The mathematical background for a multiportnetwork-solving program is described. A method for accurately numerically modeling an arbitrary, continuous, multiport transmission line is discussed. A modification to the transmission-line equations to accommodate multiple rf drives is presented. An improved model for the radio-frequency quadrupole (RFQ) accelerator that corrects previous errors is given. This model permits treating the RFQ as a true eightport network for simplicity in interpreting the field distribution and ensures that all modes propagate at the same velocity in the high-frequency limit. The flexibility of the multiport model is illustrated by simple modifications to otherwise two-dimensional systems that permit modeling them as linear chains of multiport networks.
IEEE Transactions on Nuclear Science, 1983
The NBS-LANL racetrack microtron (RTM) currently under construction at the National Bureau of Sta... more The NBS-LANL racetrack microtron (RTM) currently under construction at the National Bureau of Standards is a demonstration accelerator to determine the feasibility of, and to develop the technology necessary for building high-energy, high-current, continuous beam (CW) electron accelerators using beam recirculation through room temperature rf accelerating structures. Parameters of the RTM are: injection energy - 5 MeV; energy gain per pass - 12 MeV; number of passes - 15 or 16; final beam energy - 185-197 MeV; maximum current - 550 ¿A; rf frequency - 2380 MHz. At present, the electron gun and 100 keV beam transport line are operational, and most other major subsystems are in the construction or installation phase. Exceptions are the rf structure (under development), the 5 MeV beam transport line (in engineering design), and the extraction beam line (in conceptual design). Our studies of the original candidate accelerating structure, the disk-and-washer, have led to the discovery of beam steering modes which render this structure unsuitable for the RTM without at least substantial further development beyond the scope of the project. The most promising alternate for meeting the design goal of CW operation at 1.5 MeV/m is the side-coupled structure. A shunt impedance of 80 M¿/m has been measured in a test section of side-coupled structure at 2380 MHz, adequate cooling has been designed, and a 2.7 m long section of this design is under construction. The electron optics of the RTM have been studied in detail.
IEEE Transactions on Nuclear Science, 1979
IEEE Transactions on Nuclear Science, 1983
International Conference on Plasma Science (papers in summary form only received), 1995
Summary form only given, as follows. Free-electron laser (FEL) amplifiers have demonstrated high ... more Summary form only given, as follows. Free-electron laser (FEL) amplifiers have demonstrated high efficiency and high output power at microwave wavelengths. We discuss the design of a 500 MW FEL at 17 GHz that exhibits phase stability appropriate for accelerator applications. We also describe an experiment planned to verify this design.
Experientia Supplementum, 1980
Proceedings Particle Accelerator Conference, 1995
Research and Development program, under the auspices of the US Department of Energy, and by a Dep... more Research and Development program, under the auspices of the US Department of Energy, and by a Department of Energy STTR grant, grant number DE-FG02-94ER8602 1.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1996
Free-electron lasers (FELs) amplifiers have demonstrated high efficiencies and high output power ... more Free-electron lasers (FELs) amplifiers have demonstrated high efficiencies and high output power at microwave wavelengths. However, measurements and simulations have indicated that the present level of phase stability for these devices is not sufficient for driving linear accelerators. Fluctuations in the diode voltage, which is needed to accelerate the electron beam, are the largest cause of the shifts in the phase of the output power. Present-day pulse-power technology cannot keep the voltage fluctuations less than 1/4%. However, we have found a scheme that will make the output phase much less sensitive to these fluctuations by exploiting the traveling-wave nature of the FEL interaction. In this paper we study the phase stability issue by analyzing the dispersion relation for an axial FEL, in which the rf field is transversely wiggled and the electron trajectories are purely longitudinal. The advantage of using the axial FEL interaction instead of the common transverse FEL interaction is that the dispersion relation is not additionally complicated by how the transverse electron motion depends on the diode voltage and such a device is simpler and less expensive to construct than a transverse-coupling FEL because there is no wiggler. By examination of the dispersion relation it is found that the effect of the phase dependency on the beam's velocity can be cancelled by the effect of the phase dependency on the beam's plasma wave, for an annular electron beam. This cancellation leads to first-order phase stability, which is not possible for standing-wave devices, such as klystrons. Detailed particle-in-cell simulations are included to demonstrate the transverse wiggling of the rf mode and the axial FEL interaction.
IEEE Transactions on Nuclear Science, 1981
The data set that described the vanes contained about 10 million bits of tool position data. The ... more The data set that described the vanes contained about 10 million bits of tool position data. The vanes were cut from OFHC copper blanks. The tolerances achieved were approximately + 0.005 cm. The design and manufacturing procedures-are described. *Work performed under the auspices of the US Department of Energy.
IEEE Transactions on Nuclear Science, 1965
IEEE Transactions on Nuclear Science, 1971
IEEE Transactions on Nuclear Science, 1985
New permanent magnets for quadrupole focusing make possible smaller drift tubes in drift-tube lin... more New permanent magnets for quadrupole focusing make possible smaller drift tubes in drift-tube linacs (DTLs), resulting in higher shunt impedance. However, ordinary post couplers cannot stabilize a DTL whose drift-tube-to-wall spacing exceeds one-quarter wavelength (h/4) by more than a few per cent for the accelerating mode frequency. We have built and tested post couplers that operate in the 3X/4 mode. These 3X./4 post couplers, when substituted for X/4 couplers, had similar stabilization properties. In addition, the coupling between post and drift tube, and the post's resonant frequency can be independently adjusted.
![Research paper thumbnail of Publisher’s Note: Stability of an emittance-dominated sheet-electron beam in planar wiggler and periodic permanent magnet structures with natural focusing [Phys. Rev. ST Accel. Beams 8, 062001 (2005)]](https://attachments.academia-assets.com/90989804/thumbnails/1.jpg)
](Physical Review Special Topics - Accelerators and Beams, 2005
AIP Conference Proceedings, 2013
The concept of resonant coupling and the benefits that accrue from its application is well known ... more The concept of resonant coupling and the benefits that accrue from its application is well known in the world of room temperature coupled cavity linacs. Design studies show that it can be applied successfully between sections of conventional elliptical superconducting coupled cavity accelerator structures and internally to structures with spoked cavity resonators. The coupling mechanisms can be designed without creating problems with high field regions or multipactoring. The application of resonant coupling to superconducting accelerators eliminates the need for complex cryogenic mechanical tuners and reduces the time needed to bring a superconducting accelerator into operation.
The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. IEEE Conference Record - Abstracts., 2004
ABSTRACT form only given. A sheet beam traveling-wave amplifier has been proposed as a bighpower ... more ABSTRACT form only given. A sheet beam traveling-wave amplifier has been proposed as a bighpower generator for rf from 95 to 300 GHz, using a microfahricated rf slow-wave structure [I]. The planar geometry of microfabrication technologies matches well with the nearly planar geometry of a sheet beam, and the greater allowable beam current leads to high-peak power, high-average power, and wide bandwidths. Simulations of nominal designs using a vane-loaded waveguide as a slow-wave structure have indicated gains in excess of 1 dB/mm, with extraction efliciencies greater than 20%. We have identified stable sheet beam formation and transport as the key enabling technology for this type of device. Also, due to the high aspect ratio in the slow-wave structure, the rf coupling is complicated and requires multiple input and output couplers. The rfmode must be transversely flat over the width of the electron beam, which impacts both the vane design and the input and output coupling. We are pursuing a high-power demonstration experiment using a 120- kV, 20-A sheet electron heam with transverse size of 1 cm by 0.5 mm. This beam will interact at 95 GHz with a, as follows. A Class of the hybrid optimal problem is formulated and a hybrid dynamic programming principle (DPP) is presented which constitutes a generalization of the celebrated dynamic programming principle of Richard Bellman.
Physical Review Special Topics - Accelerators and Beams, 2005
Two-plane focusing of sheet electron beams will be an essential technology for an emerging class ... more Two-plane focusing of sheet electron beams will be an essential technology for an emerging class of high-power, 100 to 300 GHz rf sources [Carlsten et al., IEEE Trans. Plasma Sci. 33, 85 (2005)]. In these devices, the beam has a unique asymmetry in which the transport is emittance dominated in the sheet's thin dimension and space-charge dominated in the sheet's wide dimension. Previous work has studied the stability of the transport of beams in the emittance-dominated regime for both wiggler and periodic permanent magnet (PPM) configurations with single-plane focusing, and has found that bigger envelope scalloping occurs for equilibrium transport, as compared to space-charge dominated beams [Carlsten et al., this issue, Phys. Rev. ST Accel. Beams 8, 062001 (2005)]. In this paper, we describe the differences in transport stability when two-plane focusing is included. Two-plane wiggler focusing degrades the transport stability slightly, whereas two-plane PPM focusing greatly compromises the transport. On the other hand, single-plane PPM focusing can be augmented with external quadrupole fields to provide weak focusing in the sheet's wide dimension, which has stability comparable to two-plane wiggler transport.
2016 IEEE International Vacuum Electronics Conference (IVEC), 2016
We have built the first-ever klynac, consisting of a klystron and linac combined into a single in... more We have built the first-ever klynac, consisting of a klystron and linac combined into a single integrated structure using a single electron beam. This device has two resonant circuits, one for the klystron input and gain section, and one for the klystron output cavity and linac section. Here we describe this device's stability properties driven by its resonant properties.
IEEE Transactions on Nuclear Science, 1985
Ourlng the past few years the Defense and Electronics Center of Westinghouse Electric Corporation... more Ourlng the past few years the Defense and Electronics Center of Westinghouse Electric Corporation has developcl a solid-state, 250-kW Peak, rf ampllfler for use with the SPS-40 radar system. This system has a pulse length of 60 VS and operates across the frequency band from400 to 450 MHz. Because of the potential use of such a system as an rf source for accelerator applications, a collaborative experiment as Inltlated between Los Alamos National Laboratory ana Westinghouse to simulate the resonant load conditions of an accelerator cavity This paper describes the posltlve results of that experiment as well as the solid-state ampllfler architecture. It also explores the future of high-power, sollo-state amplifiers as rf sources for accelerator structures.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Mar 28, 2017
Physical Review Letters, 1974
don 7, 2109 (1974). 3H. HOrner, private communication. 4J. Sak, to be published.
IEEE Transactions on Nuclear Science, 1985
The mathematical background for a multiportnetwork-solving program is described. A method for acc... more The mathematical background for a multiportnetwork-solving program is described. A method for accurately numerically modeling an arbitrary, continuous, multiport transmission line is discussed. A modification to the transmission-line equations to accommodate multiple rf drives is presented. An improved model for the radio-frequency quadrupole (RFQ) accelerator that corrects previous errors is given. This model permits treating the RFQ as a true eightport network for simplicity in interpreting the field distribution and ensures that all modes propagate at the same velocity in the high-frequency limit. The flexibility of the multiport model is illustrated by simple modifications to otherwise two-dimensional systems that permit modeling them as linear chains of multiport networks.
IEEE Transactions on Nuclear Science, 1983
The NBS-LANL racetrack microtron (RTM) currently under construction at the National Bureau of Sta... more The NBS-LANL racetrack microtron (RTM) currently under construction at the National Bureau of Standards is a demonstration accelerator to determine the feasibility of, and to develop the technology necessary for building high-energy, high-current, continuous beam (CW) electron accelerators using beam recirculation through room temperature rf accelerating structures. Parameters of the RTM are: injection energy - 5 MeV; energy gain per pass - 12 MeV; number of passes - 15 or 16; final beam energy - 185-197 MeV; maximum current - 550 ¿A; rf frequency - 2380 MHz. At present, the electron gun and 100 keV beam transport line are operational, and most other major subsystems are in the construction or installation phase. Exceptions are the rf structure (under development), the 5 MeV beam transport line (in engineering design), and the extraction beam line (in conceptual design). Our studies of the original candidate accelerating structure, the disk-and-washer, have led to the discovery of beam steering modes which render this structure unsuitable for the RTM without at least substantial further development beyond the scope of the project. The most promising alternate for meeting the design goal of CW operation at 1.5 MeV/m is the side-coupled structure. A shunt impedance of 80 M¿/m has been measured in a test section of side-coupled structure at 2380 MHz, adequate cooling has been designed, and a 2.7 m long section of this design is under construction. The electron optics of the RTM have been studied in detail.
IEEE Transactions on Nuclear Science, 1979
IEEE Transactions on Nuclear Science, 1983
International Conference on Plasma Science (papers in summary form only received), 1995
Summary form only given, as follows. Free-electron laser (FEL) amplifiers have demonstrated high ... more Summary form only given, as follows. Free-electron laser (FEL) amplifiers have demonstrated high efficiency and high output power at microwave wavelengths. We discuss the design of a 500 MW FEL at 17 GHz that exhibits phase stability appropriate for accelerator applications. We also describe an experiment planned to verify this design.
Experientia Supplementum, 1980
Proceedings Particle Accelerator Conference, 1995
Research and Development program, under the auspices of the US Department of Energy, and by a Dep... more Research and Development program, under the auspices of the US Department of Energy, and by a Department of Energy STTR grant, grant number DE-FG02-94ER8602 1.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1996
Free-electron lasers (FELs) amplifiers have demonstrated high efficiencies and high output power ... more Free-electron lasers (FELs) amplifiers have demonstrated high efficiencies and high output power at microwave wavelengths. However, measurements and simulations have indicated that the present level of phase stability for these devices is not sufficient for driving linear accelerators. Fluctuations in the diode voltage, which is needed to accelerate the electron beam, are the largest cause of the shifts in the phase of the output power. Present-day pulse-power technology cannot keep the voltage fluctuations less than 1/4%. However, we have found a scheme that will make the output phase much less sensitive to these fluctuations by exploiting the traveling-wave nature of the FEL interaction. In this paper we study the phase stability issue by analyzing the dispersion relation for an axial FEL, in which the rf field is transversely wiggled and the electron trajectories are purely longitudinal. The advantage of using the axial FEL interaction instead of the common transverse FEL interaction is that the dispersion relation is not additionally complicated by how the transverse electron motion depends on the diode voltage and such a device is simpler and less expensive to construct than a transverse-coupling FEL because there is no wiggler. By examination of the dispersion relation it is found that the effect of the phase dependency on the beam's velocity can be cancelled by the effect of the phase dependency on the beam's plasma wave, for an annular electron beam. This cancellation leads to first-order phase stability, which is not possible for standing-wave devices, such as klystrons. Detailed particle-in-cell simulations are included to demonstrate the transverse wiggling of the rf mode and the axial FEL interaction.
IEEE Transactions on Nuclear Science, 1981
The data set that described the vanes contained about 10 million bits of tool position data. The ... more The data set that described the vanes contained about 10 million bits of tool position data. The vanes were cut from OFHC copper blanks. The tolerances achieved were approximately + 0.005 cm. The design and manufacturing procedures-are described. *Work performed under the auspices of the US Department of Energy.
IEEE Transactions on Nuclear Science, 1965
IEEE Transactions on Nuclear Science, 1971
IEEE Transactions on Nuclear Science, 1985
New permanent magnets for quadrupole focusing make possible smaller drift tubes in drift-tube lin... more New permanent magnets for quadrupole focusing make possible smaller drift tubes in drift-tube linacs (DTLs), resulting in higher shunt impedance. However, ordinary post couplers cannot stabilize a DTL whose drift-tube-to-wall spacing exceeds one-quarter wavelength (h/4) by more than a few per cent for the accelerating mode frequency. We have built and tested post couplers that operate in the 3X/4 mode. These 3X./4 post couplers, when substituted for X/4 couplers, had similar stabilization properties. In addition, the coupling between post and drift tube, and the post's resonant frequency can be independently adjusted.
Physical Review Special Topics - Accelerators and Beams, 2005
AIP Conference Proceedings, 2013
The concept of resonant coupling and the benefits that accrue from its application is well known ... more The concept of resonant coupling and the benefits that accrue from its application is well known in the world of room temperature coupled cavity linacs. Design studies show that it can be applied successfully between sections of conventional elliptical superconducting coupled cavity accelerator structures and internally to structures with spoked cavity resonators. The coupling mechanisms can be designed without creating problems with high field regions or multipactoring. The application of resonant coupling to superconducting accelerators eliminates the need for complex cryogenic mechanical tuners and reduces the time needed to bring a superconducting accelerator into operation.
The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. IEEE Conference Record - Abstracts., 2004
ABSTRACT form only given. A sheet beam traveling-wave amplifier has been proposed as a bighpower ... more ABSTRACT form only given. A sheet beam traveling-wave amplifier has been proposed as a bighpower generator for rf from 95 to 300 GHz, using a microfahricated rf slow-wave structure [I]. The planar geometry of microfabrication technologies matches well with the nearly planar geometry of a sheet beam, and the greater allowable beam current leads to high-peak power, high-average power, and wide bandwidths. Simulations of nominal designs using a vane-loaded waveguide as a slow-wave structure have indicated gains in excess of 1 dB/mm, with extraction efliciencies greater than 20%. We have identified stable sheet beam formation and transport as the key enabling technology for this type of device. Also, due to the high aspect ratio in the slow-wave structure, the rf coupling is complicated and requires multiple input and output couplers. The rfmode must be transversely flat over the width of the electron beam, which impacts both the vane design and the input and output coupling. We are pursuing a high-power demonstration experiment using a 120- kV, 20-A sheet electron heam with transverse size of 1 cm by 0.5 mm. This beam will interact at 95 GHz with a, as follows. A Class of the hybrid optimal problem is formulated and a hybrid dynamic programming principle (DPP) is presented which constitutes a generalization of the celebrated dynamic programming principle of Richard Bellman.
Physical Review Special Topics - Accelerators and Beams, 2005
Two-plane focusing of sheet electron beams will be an essential technology for an emerging class ... more Two-plane focusing of sheet electron beams will be an essential technology for an emerging class of high-power, 100 to 300 GHz rf sources [Carlsten et al., IEEE Trans. Plasma Sci. 33, 85 (2005)]. In these devices, the beam has a unique asymmetry in which the transport is emittance dominated in the sheet's thin dimension and space-charge dominated in the sheet's wide dimension. Previous work has studied the stability of the transport of beams in the emittance-dominated regime for both wiggler and periodic permanent magnet (PPM) configurations with single-plane focusing, and has found that bigger envelope scalloping occurs for equilibrium transport, as compared to space-charge dominated beams [Carlsten et al., this issue, Phys. Rev. ST Accel. Beams 8, 062001 (2005)]. In this paper, we describe the differences in transport stability when two-plane focusing is included. Two-plane wiggler focusing degrades the transport stability slightly, whereas two-plane PPM focusing greatly compromises the transport. On the other hand, single-plane PPM focusing can be augmented with external quadrupole fields to provide weak focusing in the sheet's wide dimension, which has stability comparable to two-plane wiggler transport.