- Email: [email protected]
A new 5 MeV–300 kW dynamitron for radiation processing
ARTICLE IN PRESS
Radiation Physics and Chemistry 71 (2004) 549–551
Business paper
A new 5 MeV–300 kW dynamitron for radiation processing R.A. Galloway*, T.F. Lisanti, M.R. Cleland IBA Technology Group, Long Island Facility, Edgewood, NY 11717, USA
Abstract The high beam power required to deliver reasonably effective levels of X-rays for processing food and medical products has driven the development of a new high-power Dynamitrons system. For many years, RDI accelerators have been providing up to 200 kW of DC electron beam power at energies up to 5.0 MeV. This new system, designed to operate at 300 kW of beam power at 5.0 MeV, is also capable of producing up to 75 mA of beam current when operating at lower voltages. Achieving this high power level and maintaining the high reliability that Dynamitrons are known for has required new designs offering lower power losses yielding higher efficiency and reducing stress in critical components. Improvements in beam control and optics add to the stability and reliability of the system providing a basis for a highly reliable high-power system. r 2004 Elsevier Ltd. All rights reserved. Keywords: X-ray system; High-power electron beam accelerator; 5.0 MeV electron beam
The demand for high beam currents at 5.0 MeV, allowing delivery of attractive levels of X-rays for material processing, has driven the development of this accelerator. With electron-to-photon conversion efficiency at this energy level being about 8%, this system is designed to produce 24 kW of X-rays and provide the equivalent processing rate greater than 2.5 MCi of 60Co. Providing a collimated photon field in X-ray mode that can be efficiently captured utilizing modern material handling systems, large quantities of products and materials can be processed with this accelerator. Designed to operate in either electron or X-ray mode and operate over a wide energy range in electron mode, this system is the ideal tool for a diversified irradiation processing system. The Dynamitrons accelerator system is based on a parallel-fed, series-cascade voltage generator driven by an RF system operating at 100 kHz (Thompson and Cleland, 1969; Cleland et al., 1977, 1979). This true
*Corresponding author. Radiation Dynamics Inc., 151 Heartland Blvd., Edgewood, NY 11717 8374, USA. Tel.: +1631-254-6800; fax: +1-631-254-6810. E-mail address: [email protected] (R.A. Galloway).
parallel input, series output voltage multiplier system, operating at this relatively low frequency, provides a wide range of beam energies at very efficient power conversion rates. This configuration allows for highvoltage DC generation while, with its low coupling capacitance, it provides a very low stored energy which minimizes potential damage caused by system arcing. The high-voltage generator is housed inside a pressure vessel filled with SF6, an insulating gas providing the ability to achieve very high voltages in confined spaces without sparking. The high-voltage rectifier column is comprised of an insulating acrylic support structure that houses 98 solidstate rectifiers. These 100 mA rated rectifier assemblies are series connected to the terminal and parallel fed by capacitive coupling to the RF electrodes. Each rectifier assembly has a peak inverse voltage rating exceeding 280 kV, though operating nominally at just over 100 kV peak inverse. The design of these solid-state rectifier assemblies in their protective Faraday shield has been utilized for over 30 years and have proven to be very reliable. This newly configured system is larger in diameter than the standard 4.5 MeV line and has improved electrostatics to provide stable operation at 5.0 MeV which is crucial to X-ray production.
0969-806X/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2004.03.059
ARTICLE IN PRESS R.A. Galloway et al. / Radiation Physics and Chemistry 71 (2004) 549–551
550
Three-phase line power feeds the primary 17 kV DC power supply for the triode oscillator tube and the RF system. This phase-controlled thyristor system feeds the AC line voltage to a conventional iron-core step-up transformer and a three-phase bridge rectifier circuit. The resulting DC voltage is smoothed by a simple LC filter network and applied to the triode, which drives the RF transformer and resonant ‘‘tank’’ circuit. The resonant tank is a self-tuning circuit with a self-biasing grid configuration that requires no external or additional tuning to operate stably and efficiently through the life of the system. 100 90
RF Power in kW
80 70 60 50 40 30 20
Old Transformer
10
New Transformer
0 0
200
400
600
800
1000
Electrode Voltage Peak
Fig. 1. RF transformer efficiency comparison.
The RF power for the system is driven by an oscillator assembly utilizing an industrial triode tube. This triode, capable of 530 kW of output RF power running in class C operation, is expected to have a life of 20,000–25,000 h operating at the reduced output power required in this system. This triode was chosen for its ease of availability and long-proven performance in the induction heating industry. A newly configured air core toroidal RF transformer (Fig. 2) steps up the low-voltage RF from the triode to supply the RF electrodes. This RF transformer with a quality factor (Q) typically greater than 1000, has shown a 30% reduction in dissipated power allowing for higher system efficiencies as shown in Fig. 1. Impedance matching the triode to the RF transformer is achieved by proper choice of the primary or drive windings of the transformer and careful tuning of the transmission line coupling the two (Fig. 2). The RF voltage required for driving this system is fixed by the ratio of the coupling capacitance of the RF electrode to the rectifier column and the shunt capacitance of the rectifiers stage to stage. The RF voltage required per rectifier stage can be calculated by applying Kirchoff’s law of potential drops around closed paths. Fig. 3 shows the results of the RF tests performed on this 5.0 MeV system. This test was run with the rectifier column shorted to ground so that a no-load RF test would show the maximum RF voltage attainable for this design. Since achieving the 840 kV during this test, modifications of the spark gaps and protective shielding of the RF transformer have been completed which allow
Fig. 2. RF transformer.
ARTICLE IN PRESS R.A. Galloway et al. / Radiation Physics and Chemistry 71 (2004) 549–551
900
Electrode voltage in kV
800 700 600 500 400 300 200 100 0 0
5
10
15
20
Triode cathode voltage in kV Fig. 3. RF limitations for the system.
250 200 150 100
Beam Power in kW
300
50
0.0
0.5
1.0
2.0
3.0
4.0
0 5.0
Beam Energy in MeV
551
at greater than 15,000 h in good vacuum conditions and can easily be replaced. The power for heating the filament is derived from a small generator set coupled with an insulating shaft connected to the driven motor mounted at ground potential. Electron emission is determined by the filament temperature which is controlled with a closed loop asynchronous motor and drive controller. Setting the output voltage of the generator controls the power to the filament transformer. This system allows for the generation of 7 mA of beam limited by space charge at 500 keV, 10% of maximum operating voltage, and a maximum beam of 75 mA limited by deliverable maximum power at higher energy. The beam line, vacuum system components and system scanner provide the means to deliver the electrons directly to a product through a thin titanium window or to a water-cooled X-ray converter. The water-cooled tantalum foil X-ray converter design for this system is proven and is operating in a number of facilities today. The DPC-2000 (Dynamitron Process Controller) is the custom designed and programmed system equipped to handle all of the system operational control, graphical operator interface and diagnostic functions. Programmed in ‘‘C’’ and based on over 25 years of programmable controller code and operational logic for Dynamitron accelerators, this system provides seamless integration with a processing facility. Equipped with redundant control and monitoring systems for all of the critical parameters that affect absorbed dose, process validation can easily be achieved. This integrated system controller oversees the process and provides ‘‘hands free’’ operation reducing the risk of irradiating product incorrectly.
Fig. 4. Beam power over the system energy range.
us to achieve the required 800 kV of RF reliably in continuous operation (Fig. 4). The pressure vessel contains the RF and high-voltage generator and a multiple-gap electron acceleration tube mounted coaxially inside the rectifier column. This coaxial configuration reduces the physical size of the system and shields the beam tube inside the linear gradient of the high-voltage column. The new electron gun, mounted at the high-voltage end of the beam tube, is designed to deliver up to 100 mA of DC beam current. Improved beam optics has been realized with this new pierce style design virtually eliminating beam halo, which was evident in previous configurations. The lifetime of this tungsten-alloy filament has been recorded
References Cleland, M.R., Thompson, C.C., Malone, H.F., 1977. The prospects for very high power electron accelerators for processing bulk materials. Radiat. Phys. Chem. 9 (1–6), 547–566. Cleland, M.R., Morganstern, K.H., Thompson, C.C., 1979. High power DC accelerators for industrial applications. Proceedings of the Third All-Union Conference on Applied Accelerators, The D.V. Efremov Scientific Research Institute of Electrophysical Apparatus, Leningrad, USSR, TOMI, pp. 51–80. Thompson, C.C., Cleland, M.R., 1969. Design equations for dynamitron type power supplies in the megavolt range. IEEE Trans. Nucl.Sci. NS-16, 124–129.
Radiation Physics and Chemistry 71 (2004) 549–551
Business paper
A new 5 MeV–300 kW dynamitron for radiation processing R.A. Galloway*, T.F. Lisanti, M.R. Cleland IBA Technology Group, Long Island Facility, Edgewood, NY 11717, USA
Abstract The high beam power required to deliver reasonably effective levels of X-rays for processing food and medical products has driven the development of a new high-power Dynamitrons system. For many years, RDI accelerators have been providing up to 200 kW of DC electron beam power at energies up to 5.0 MeV. This new system, designed to operate at 300 kW of beam power at 5.0 MeV, is also capable of producing up to 75 mA of beam current when operating at lower voltages. Achieving this high power level and maintaining the high reliability that Dynamitrons are known for has required new designs offering lower power losses yielding higher efficiency and reducing stress in critical components. Improvements in beam control and optics add to the stability and reliability of the system providing a basis for a highly reliable high-power system. r 2004 Elsevier Ltd. All rights reserved. Keywords: X-ray system; High-power electron beam accelerator; 5.0 MeV electron beam
The demand for high beam currents at 5.0 MeV, allowing delivery of attractive levels of X-rays for material processing, has driven the development of this accelerator. With electron-to-photon conversion efficiency at this energy level being about 8%, this system is designed to produce 24 kW of X-rays and provide the equivalent processing rate greater than 2.5 MCi of 60Co. Providing a collimated photon field in X-ray mode that can be efficiently captured utilizing modern material handling systems, large quantities of products and materials can be processed with this accelerator. Designed to operate in either electron or X-ray mode and operate over a wide energy range in electron mode, this system is the ideal tool for a diversified irradiation processing system. The Dynamitrons accelerator system is based on a parallel-fed, series-cascade voltage generator driven by an RF system operating at 100 kHz (Thompson and Cleland, 1969; Cleland et al., 1977, 1979). This true
*Corresponding author. Radiation Dynamics Inc., 151 Heartland Blvd., Edgewood, NY 11717 8374, USA. Tel.: +1631-254-6800; fax: +1-631-254-6810. E-mail address: [email protected] (R.A. Galloway).
parallel input, series output voltage multiplier system, operating at this relatively low frequency, provides a wide range of beam energies at very efficient power conversion rates. This configuration allows for highvoltage DC generation while, with its low coupling capacitance, it provides a very low stored energy which minimizes potential damage caused by system arcing. The high-voltage generator is housed inside a pressure vessel filled with SF6, an insulating gas providing the ability to achieve very high voltages in confined spaces without sparking. The high-voltage rectifier column is comprised of an insulating acrylic support structure that houses 98 solidstate rectifiers. These 100 mA rated rectifier assemblies are series connected to the terminal and parallel fed by capacitive coupling to the RF electrodes. Each rectifier assembly has a peak inverse voltage rating exceeding 280 kV, though operating nominally at just over 100 kV peak inverse. The design of these solid-state rectifier assemblies in their protective Faraday shield has been utilized for over 30 years and have proven to be very reliable. This newly configured system is larger in diameter than the standard 4.5 MeV line and has improved electrostatics to provide stable operation at 5.0 MeV which is crucial to X-ray production.
0969-806X/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2004.03.059
ARTICLE IN PRESS R.A. Galloway et al. / Radiation Physics and Chemistry 71 (2004) 549–551
550
Three-phase line power feeds the primary 17 kV DC power supply for the triode oscillator tube and the RF system. This phase-controlled thyristor system feeds the AC line voltage to a conventional iron-core step-up transformer and a three-phase bridge rectifier circuit. The resulting DC voltage is smoothed by a simple LC filter network and applied to the triode, which drives the RF transformer and resonant ‘‘tank’’ circuit. The resonant tank is a self-tuning circuit with a self-biasing grid configuration that requires no external or additional tuning to operate stably and efficiently through the life of the system. 100 90
RF Power in kW
80 70 60 50 40 30 20
Old Transformer
10
New Transformer
0 0
200
400
600
800
1000
Electrode Voltage Peak
Fig. 1. RF transformer efficiency comparison.
The RF power for the system is driven by an oscillator assembly utilizing an industrial triode tube. This triode, capable of 530 kW of output RF power running in class C operation, is expected to have a life of 20,000–25,000 h operating at the reduced output power required in this system. This triode was chosen for its ease of availability and long-proven performance in the induction heating industry. A newly configured air core toroidal RF transformer (Fig. 2) steps up the low-voltage RF from the triode to supply the RF electrodes. This RF transformer with a quality factor (Q) typically greater than 1000, has shown a 30% reduction in dissipated power allowing for higher system efficiencies as shown in Fig. 1. Impedance matching the triode to the RF transformer is achieved by proper choice of the primary or drive windings of the transformer and careful tuning of the transmission line coupling the two (Fig. 2). The RF voltage required for driving this system is fixed by the ratio of the coupling capacitance of the RF electrode to the rectifier column and the shunt capacitance of the rectifiers stage to stage. The RF voltage required per rectifier stage can be calculated by applying Kirchoff’s law of potential drops around closed paths. Fig. 3 shows the results of the RF tests performed on this 5.0 MeV system. This test was run with the rectifier column shorted to ground so that a no-load RF test would show the maximum RF voltage attainable for this design. Since achieving the 840 kV during this test, modifications of the spark gaps and protective shielding of the RF transformer have been completed which allow
Fig. 2. RF transformer.
ARTICLE IN PRESS R.A. Galloway et al. / Radiation Physics and Chemistry 71 (2004) 549–551
900
Electrode voltage in kV
800 700 600 500 400 300 200 100 0 0
5
10
15
20
Triode cathode voltage in kV Fig. 3. RF limitations for the system.
250 200 150 100
Beam Power in kW
300
50
0.0
0.5
1.0
2.0
3.0
4.0
0 5.0
Beam Energy in MeV
551
at greater than 15,000 h in good vacuum conditions and can easily be replaced. The power for heating the filament is derived from a small generator set coupled with an insulating shaft connected to the driven motor mounted at ground potential. Electron emission is determined by the filament temperature which is controlled with a closed loop asynchronous motor and drive controller. Setting the output voltage of the generator controls the power to the filament transformer. This system allows for the generation of 7 mA of beam limited by space charge at 500 keV, 10% of maximum operating voltage, and a maximum beam of 75 mA limited by deliverable maximum power at higher energy. The beam line, vacuum system components and system scanner provide the means to deliver the electrons directly to a product through a thin titanium window or to a water-cooled X-ray converter. The water-cooled tantalum foil X-ray converter design for this system is proven and is operating in a number of facilities today. The DPC-2000 (Dynamitron Process Controller) is the custom designed and programmed system equipped to handle all of the system operational control, graphical operator interface and diagnostic functions. Programmed in ‘‘C’’ and based on over 25 years of programmable controller code and operational logic for Dynamitron accelerators, this system provides seamless integration with a processing facility. Equipped with redundant control and monitoring systems for all of the critical parameters that affect absorbed dose, process validation can easily be achieved. This integrated system controller oversees the process and provides ‘‘hands free’’ operation reducing the risk of irradiating product incorrectly.
Fig. 4. Beam power over the system energy range.
us to achieve the required 800 kV of RF reliably in continuous operation (Fig. 4). The pressure vessel contains the RF and high-voltage generator and a multiple-gap electron acceleration tube mounted coaxially inside the rectifier column. This coaxial configuration reduces the physical size of the system and shields the beam tube inside the linear gradient of the high-voltage column. The new electron gun, mounted at the high-voltage end of the beam tube, is designed to deliver up to 100 mA of DC beam current. Improved beam optics has been realized with this new pierce style design virtually eliminating beam halo, which was evident in previous configurations. The lifetime of this tungsten-alloy filament has been recorded
References Cleland, M.R., Thompson, C.C., Malone, H.F., 1977. The prospects for very high power electron accelerators for processing bulk materials. Radiat. Phys. Chem. 9 (1–6), 547–566. Cleland, M.R., Morganstern, K.H., Thompson, C.C., 1979. High power DC accelerators for industrial applications. Proceedings of the Third All-Union Conference on Applied Accelerators, The D.V. Efremov Scientific Research Institute of Electrophysical Apparatus, Leningrad, USSR, TOMI, pp. 51–80. Thompson, C.C., Cleland, M.R., 1969. Design equations for dynamitron type power supplies in the megavolt range. IEEE Trans. Nucl.Sci. NS-16, 124–129.