- Email: [email protected]
Position indicating split toroid for the RACE experiment
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 261 (2007) 31–33 www.elsevier.com/locate/nimb
Position indicating split toroid for the RACE experiment B. Hurst a
a,*
, K. Folkman
b
Nuclear Engineering Teaching Laboratory, University of Texas, 10100 Burnet Road, Austin, TX 78758, USA b Idaho Accelerator Center, Idaho State University, Pocatello, ID 83201, USA Available online 14 April 2007
Abstract Aspects of the recent reactor accelerator coupled experiments (RACE) carried out at the University of Texas Nuclear Engineering Teaching Laboratory will be discussed. In particular, a compact instrument that allowed a continuous non-invasive means of determining the relative electron beam position was developed. The operation of the instrument is similar to an inductive current pick up toroid except that the core is sectioned radially, which allows spatial information to be derived from the induced voltages. Results of initial tests, both in beam and with a pulser, will be presented along with plans to optimize future designs. Ó 2007 Elsevier B.V. All rights reserved. PACS: 29.17.+w Keywords: Beam position; RACE; PIST; Split toroid
1. Introduction In the university-based reactor–accelerator coupling experiments (RACE), a series of accelerator-driven subcritical experiments are being conducted at the Idaho State University’s Idaho Accelerator Center (ISU-IAC), the University of Texas at Austin’s Nuclear Engineering Teaching laboratory (UT-NETL) and at the Texas A&M University Nuclear Science Center (NSC). In these experiments, bremsstrahlung from electron accelerators is used to induce photo-neutron production in heavy-metal targets [1]. The neutrons then initiate fission reactions. The experiments remain subcritical since sustained fission chain reactions are never established and quickly die away once the electron beam is turned off. In this paper, the experiments were conducted at The Nuclear Engineering Teaching Laboratory at the University of Texas at Austin where the accelerator was installed in Beam Port #5 of the Mark II TRIGA reactor. The TRIGA is a 1.1 MW research reactor using almost 20% enriched uranium zirconium hydride
*
Corresponding author. Tel.: +1 512 475 7812; fax: +1 512 471 4589. E-mail address: [email protected] (B. Hurst).
0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.04.117
fuel. Additional information on the methods and uses for accelerator-driven systems can be found elsewhere [2–6]. 2. Experimental The electron LINAC used in the UT RACE experiments was built by ISU-IAC. It was installed during the summer 2005 and the experiments began in fall 2005. The LINAC was designed around the Varian Clinac 20 accelerator guide, circulator, klystron, pulse transformer tank, modulator and RF driver. The system was designed to be modular and fit within the confines of NETL’s Beam Port #5 experimental area. The LINAC was designed to provide a 5 ls pulse of 22 MeV electrons with a maximum beam intensity of 180 mA/pulse and a frequency of up to 180 pulses/s. A quadrapole magnet at the exit of the LINAC was used to focus the electron beam. In addition, two sets of steering magnets were used to align the electron beam in the pipe. The optical elements for the electron beam were approximately 5.5 m upstream from the target. The electron beam pipe itself was a 5.0 m long, 3.5 cm diameter stainless steel pipe with NW35CF conflat flanges on each end. The exit end of the beam pipe was covered
32
B. Hurst, K. Folkman / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 31–33
of the reactor fuel to the neutron source – in this case, the tungsten/copper target. The target was about 6 cm from the fuel elements during the bombardment. During tuning of the LINAC, it became evident that there was no reliable way of determining if the electron beam was striking the target with the original beam line setup. Generally this is simple problem often solved using a movable phosphor screen and remote camera. However, the physical constraints of Beam Port #5’s pipe diameter, 10 cm, ruled out the use of a screen and remote camera as well as many other conventional diagnostic techniques. In addition, the proximity of the target to the reactor core introduced activation concerns that limited material selection to substances that have either low activation cross-sections or that activate producing only short-lived isotopes. Another requirement was that the instrument allows continuous real-time monitoring without interrupting the electron beam path. To satisfy these requirements within the design constraints, an inductive type instrument was developed at NETL. The position indicating split toroid (PIST) design is shown in Fig. 1. The PIST instrument design is very similar to an AC current loop; however, the toroid core is radially split in to four quadrants with independent coils wound around each quadrant. The core material is cold rolled steel machined to a right cylindrical shell and cut into four equal quadrants. These pieces were annealed overnight to stress relieve the steel. Once cooled, the quad-
with a thin 1 mil stainless steel window. The converter target was constructed out of an 80% tungsten and 20% copper alloy slug brazed onto a NW35CF conflat flange. The flange had a 3.8 cm diameter hole through its center to allow the beam to strike the tungsten/copper conversion target. In later experiments, the target was electrically isolated from the beam pipe with a hollow spacer made from Delrin and allowed the target to act as a faraday cup. A turbo molecular pump and three Terranova ion pumps were used to keep beam line and LINAC at a vacuum of 10 8 torr or below during operation. Polyethylene supports were used to maintain the beam pipe in the center of Beam Port #5. After exiting the thin stainless window, the electron beam traveled a distance of 4.5 cm in air before striking the converter target. The temperature of the target increases during bombardment, so it was machined to allow for water-cooling. Standard 3/8 in. copper tubing was used to provide water supply and return from a refrigerated circulator to and from the target. This copper tubing was also electrically isolated from the target with plastic hose. In addition, it was isolated from contact with the beam pipe using spiral plastic sheathing. Two K-type thermocouples were added near the target face to the rear of the target. These thermocouples were used to monitor changes in target temperature during electron bombardment. Once the accelerator was installed, 78 fuel rods were arranged to maintain sub-criticality and to ensure coupling
Position Indicating Split Toroid (PIST) (8) 8-32 All Thread
3.5 in 0.96 in
(8) 0.125 in thru bore
Section A
Section B Section C
R0.156 in R1.25 in 2.5 in 3.76 in 0.25 in
(4) 26 AWG Copper Coils (8) 8-32 Kurnled Nuts
0.759 in
Front View
Beam Direction
0.759 in
0.193 in
0.192 in
Side View
Section A -- Aluminum Section B -- Cold Rolled Steel Section C -- Aluminum
Fig. 1. Engineering drawing of the position indicating split toroid (PIST).
B. Hurst, K. Folkman / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 31–33
rants were wrapped with 5 mil kapton tape to ensure the wire windings would remain insulated from the steel. The quadrants were then wound with 22 turns of 18 AWG heavy polyamide insulated magnet wire (NEMA-MW80C). PIST is similar in operation to a clamp on an AC current meter, where the current flowing through a wire induces a voltage in the toroidal pickup loop surrounding the wire [7,8]. In this case, however, the beam plays the role of the current-carrying wire and the toroidal loop is split into four sections. This results in four sets of readout wires, one signal wire and a ground from each quarter-round core. A 1 MX resistor was placed in series with the ground. For testing purposes, an electron beam was simulated using a pulser and a movable 1/8 in. brass rod running through the center of PIST. The pulser signal was connected to the brass rod on one end and the other was terminated with a 1 MX resistor to ground. The rod could be moved from left to right and measurements of these displacements were made using 1 in. dial indicators. The indicators have a precision of ±0.001 in. The voltages induced in the each coil by the pulser were measured in pairs. These signals were then recorded and analyzed using a four-channel oscilloscope. Signals from opposing coils were inverted and added together with their non-inverted counterparts. This provided common mode noise rejection for the signals. The resulting differential voltages were recorded along with their displacements from the beam axis. The pulser frequency was 100 Hz with a width of 5 ls and a height of 9 V. Fig. 2 shows the results of these pulser tests. The abscissa shows the displacement of the pulser-simulated beam from the center axis. The ordinate records the differential voltage measured for that displacement. The dotted
Differential Voltage (mV)
40
0 -15
-5
lines are simple guides for the eyes. The squares (triangles) represent the horizontal (vertical) displacement. At the center of the plot (±10 mm to ±20 mV), the data are largely linear, implying that at least over this range, the differential voltage is simply proportional to the x- or y-displacement of the beam from the center axis. PIST was also tested in-beam using a LINAC at the ISU-IAC laboratory. However, unlike the pulser tests, these were not quantitative. Instead they were used to see if a pulsed electron beam would produce the same response and also to check if noise pickup from the RF would be a problem. During the tests, the aluminum supports were removed and the quadrants were temporarily attached to the hollow Delrin adapter piece with kapton tape. The original RG174 cables proved noisy during the in-beam tests and were replaced with 100 ft. RG58 cables. The cable replacement eliminated much of the noise. 3. Summary and conclusions A series of reactor and accelerator coupling experiments (RACE) were carried out at UT’s Nuclear Engineering Teaching Laboratory. During these experiments, a Position Indicating Split Toroid (PIST) was developed allowing our research team to continuously monitor the position of a pulsed electron beam within the beam pipe. Acknowledgements This work has been supported by a Grant from the Innovations in Nuclear Infrastructure Education (INIEE) program and from the US Department of Energy’s Advanced Fuel Cycle Initiative. References
20
-25
33
5
15
25
-20
-40 Displacement from center (mm) Fig. 2. Plot of the differential voltage versus the displacement from the center beam axis. These results are from the square wave pulser measurements having 100 Hz, 8.9 V and pulse width of 5 ls. The squares (triangles) represent the horizontal (vertical) displacement. Error bars are at a fixed ±10%. The dotted lines are guides for the eyes.
[1] W K. Sinclair, et al., Neutron Contamination from Medical Electron Accelerators, NCRP Report No. 79 (1995) 5. [2] A.C. Mueller, Nuclear waste incineration and accelerator aspects from the european PDS-XDS study, Nucl. Phys. A 751 (2005) 453c. [3] M. Plaschy et al., Importance of the MUSE experiments for emerging ADS concepts from the nuclear data viewpoint, Ann. Nucl. Energ. 32 (2005) 843. [4] T. Sasa, Research activities for accelerator driven transmutation systems at JAERI, Prog. Nucl. Energ. 47 (2005) 314. [5] A. Brolly, P. Vertes, Concept of a small accelerator driven system for nuclear waste transmutation part 1: target optimization, Ann. Nucl. Energ. 31 (2004) 585. [6] J. Wallenius, M. Erikson, Neutronics of minor actinide burning accelerator driven system with ceramic fuel, Nucl. Tech. 152 (2005) 367. [7] D. Henry, Enhancing electromagnetism experiments with clamp-on Ammeters, Am. J. Phys. 69 (2001) 76. [8] P. Heller, Analog demonstrations of Ampere’s law and magnetic flux, Am. J. Phys. 60 (1992) 17.
Nuclear Instruments and Methods in Physics Research B 261 (2007) 31–33 www.elsevier.com/locate/nimb
Position indicating split toroid for the RACE experiment B. Hurst a
a,*
, K. Folkman
b
Nuclear Engineering Teaching Laboratory, University of Texas, 10100 Burnet Road, Austin, TX 78758, USA b Idaho Accelerator Center, Idaho State University, Pocatello, ID 83201, USA Available online 14 April 2007
Abstract Aspects of the recent reactor accelerator coupled experiments (RACE) carried out at the University of Texas Nuclear Engineering Teaching Laboratory will be discussed. In particular, a compact instrument that allowed a continuous non-invasive means of determining the relative electron beam position was developed. The operation of the instrument is similar to an inductive current pick up toroid except that the core is sectioned radially, which allows spatial information to be derived from the induced voltages. Results of initial tests, both in beam and with a pulser, will be presented along with plans to optimize future designs. Ó 2007 Elsevier B.V. All rights reserved. PACS: 29.17.+w Keywords: Beam position; RACE; PIST; Split toroid
1. Introduction In the university-based reactor–accelerator coupling experiments (RACE), a series of accelerator-driven subcritical experiments are being conducted at the Idaho State University’s Idaho Accelerator Center (ISU-IAC), the University of Texas at Austin’s Nuclear Engineering Teaching laboratory (UT-NETL) and at the Texas A&M University Nuclear Science Center (NSC). In these experiments, bremsstrahlung from electron accelerators is used to induce photo-neutron production in heavy-metal targets [1]. The neutrons then initiate fission reactions. The experiments remain subcritical since sustained fission chain reactions are never established and quickly die away once the electron beam is turned off. In this paper, the experiments were conducted at The Nuclear Engineering Teaching Laboratory at the University of Texas at Austin where the accelerator was installed in Beam Port #5 of the Mark II TRIGA reactor. The TRIGA is a 1.1 MW research reactor using almost 20% enriched uranium zirconium hydride
*
Corresponding author. Tel.: +1 512 475 7812; fax: +1 512 471 4589. E-mail address: [email protected] (B. Hurst).
0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.04.117
fuel. Additional information on the methods and uses for accelerator-driven systems can be found elsewhere [2–6]. 2. Experimental The electron LINAC used in the UT RACE experiments was built by ISU-IAC. It was installed during the summer 2005 and the experiments began in fall 2005. The LINAC was designed around the Varian Clinac 20 accelerator guide, circulator, klystron, pulse transformer tank, modulator and RF driver. The system was designed to be modular and fit within the confines of NETL’s Beam Port #5 experimental area. The LINAC was designed to provide a 5 ls pulse of 22 MeV electrons with a maximum beam intensity of 180 mA/pulse and a frequency of up to 180 pulses/s. A quadrapole magnet at the exit of the LINAC was used to focus the electron beam. In addition, two sets of steering magnets were used to align the electron beam in the pipe. The optical elements for the electron beam were approximately 5.5 m upstream from the target. The electron beam pipe itself was a 5.0 m long, 3.5 cm diameter stainless steel pipe with NW35CF conflat flanges on each end. The exit end of the beam pipe was covered
32
B. Hurst, K. Folkman / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 31–33
of the reactor fuel to the neutron source – in this case, the tungsten/copper target. The target was about 6 cm from the fuel elements during the bombardment. During tuning of the LINAC, it became evident that there was no reliable way of determining if the electron beam was striking the target with the original beam line setup. Generally this is simple problem often solved using a movable phosphor screen and remote camera. However, the physical constraints of Beam Port #5’s pipe diameter, 10 cm, ruled out the use of a screen and remote camera as well as many other conventional diagnostic techniques. In addition, the proximity of the target to the reactor core introduced activation concerns that limited material selection to substances that have either low activation cross-sections or that activate producing only short-lived isotopes. Another requirement was that the instrument allows continuous real-time monitoring without interrupting the electron beam path. To satisfy these requirements within the design constraints, an inductive type instrument was developed at NETL. The position indicating split toroid (PIST) design is shown in Fig. 1. The PIST instrument design is very similar to an AC current loop; however, the toroid core is radially split in to four quadrants with independent coils wound around each quadrant. The core material is cold rolled steel machined to a right cylindrical shell and cut into four equal quadrants. These pieces were annealed overnight to stress relieve the steel. Once cooled, the quad-
with a thin 1 mil stainless steel window. The converter target was constructed out of an 80% tungsten and 20% copper alloy slug brazed onto a NW35CF conflat flange. The flange had a 3.8 cm diameter hole through its center to allow the beam to strike the tungsten/copper conversion target. In later experiments, the target was electrically isolated from the beam pipe with a hollow spacer made from Delrin and allowed the target to act as a faraday cup. A turbo molecular pump and three Terranova ion pumps were used to keep beam line and LINAC at a vacuum of 10 8 torr or below during operation. Polyethylene supports were used to maintain the beam pipe in the center of Beam Port #5. After exiting the thin stainless window, the electron beam traveled a distance of 4.5 cm in air before striking the converter target. The temperature of the target increases during bombardment, so it was machined to allow for water-cooling. Standard 3/8 in. copper tubing was used to provide water supply and return from a refrigerated circulator to and from the target. This copper tubing was also electrically isolated from the target with plastic hose. In addition, it was isolated from contact with the beam pipe using spiral plastic sheathing. Two K-type thermocouples were added near the target face to the rear of the target. These thermocouples were used to monitor changes in target temperature during electron bombardment. Once the accelerator was installed, 78 fuel rods were arranged to maintain sub-criticality and to ensure coupling
Position Indicating Split Toroid (PIST) (8) 8-32 All Thread
3.5 in 0.96 in
(8) 0.125 in thru bore
Section A
Section B Section C
R0.156 in R1.25 in 2.5 in 3.76 in 0.25 in
(4) 26 AWG Copper Coils (8) 8-32 Kurnled Nuts
0.759 in
Front View
Beam Direction
0.759 in
0.193 in
0.192 in
Side View
Section A -- Aluminum Section B -- Cold Rolled Steel Section C -- Aluminum
Fig. 1. Engineering drawing of the position indicating split toroid (PIST).
B. Hurst, K. Folkman / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 31–33
rants were wrapped with 5 mil kapton tape to ensure the wire windings would remain insulated from the steel. The quadrants were then wound with 22 turns of 18 AWG heavy polyamide insulated magnet wire (NEMA-MW80C). PIST is similar in operation to a clamp on an AC current meter, where the current flowing through a wire induces a voltage in the toroidal pickup loop surrounding the wire [7,8]. In this case, however, the beam plays the role of the current-carrying wire and the toroidal loop is split into four sections. This results in four sets of readout wires, one signal wire and a ground from each quarter-round core. A 1 MX resistor was placed in series with the ground. For testing purposes, an electron beam was simulated using a pulser and a movable 1/8 in. brass rod running through the center of PIST. The pulser signal was connected to the brass rod on one end and the other was terminated with a 1 MX resistor to ground. The rod could be moved from left to right and measurements of these displacements were made using 1 in. dial indicators. The indicators have a precision of ±0.001 in. The voltages induced in the each coil by the pulser were measured in pairs. These signals were then recorded and analyzed using a four-channel oscilloscope. Signals from opposing coils were inverted and added together with their non-inverted counterparts. This provided common mode noise rejection for the signals. The resulting differential voltages were recorded along with their displacements from the beam axis. The pulser frequency was 100 Hz with a width of 5 ls and a height of 9 V. Fig. 2 shows the results of these pulser tests. The abscissa shows the displacement of the pulser-simulated beam from the center axis. The ordinate records the differential voltage measured for that displacement. The dotted
Differential Voltage (mV)
40
0 -15
-5
lines are simple guides for the eyes. The squares (triangles) represent the horizontal (vertical) displacement. At the center of the plot (±10 mm to ±20 mV), the data are largely linear, implying that at least over this range, the differential voltage is simply proportional to the x- or y-displacement of the beam from the center axis. PIST was also tested in-beam using a LINAC at the ISU-IAC laboratory. However, unlike the pulser tests, these were not quantitative. Instead they were used to see if a pulsed electron beam would produce the same response and also to check if noise pickup from the RF would be a problem. During the tests, the aluminum supports were removed and the quadrants were temporarily attached to the hollow Delrin adapter piece with kapton tape. The original RG174 cables proved noisy during the in-beam tests and were replaced with 100 ft. RG58 cables. The cable replacement eliminated much of the noise. 3. Summary and conclusions A series of reactor and accelerator coupling experiments (RACE) were carried out at UT’s Nuclear Engineering Teaching Laboratory. During these experiments, a Position Indicating Split Toroid (PIST) was developed allowing our research team to continuously monitor the position of a pulsed electron beam within the beam pipe. Acknowledgements This work has been supported by a Grant from the Innovations in Nuclear Infrastructure Education (INIEE) program and from the US Department of Energy’s Advanced Fuel Cycle Initiative. References
20
-25
33
5
15
25
-20
-40 Displacement from center (mm) Fig. 2. Plot of the differential voltage versus the displacement from the center beam axis. These results are from the square wave pulser measurements having 100 Hz, 8.9 V and pulse width of 5 ls. The squares (triangles) represent the horizontal (vertical) displacement. Error bars are at a fixed ±10%. The dotted lines are guides for the eyes.
[1] W K. Sinclair, et al., Neutron Contamination from Medical Electron Accelerators, NCRP Report No. 79 (1995) 5. [2] A.C. Mueller, Nuclear waste incineration and accelerator aspects from the european PDS-XDS study, Nucl. Phys. A 751 (2005) 453c. [3] M. Plaschy et al., Importance of the MUSE experiments for emerging ADS concepts from the nuclear data viewpoint, Ann. Nucl. Energ. 32 (2005) 843. [4] T. Sasa, Research activities for accelerator driven transmutation systems at JAERI, Prog. Nucl. Energ. 47 (2005) 314. [5] A. Brolly, P. Vertes, Concept of a small accelerator driven system for nuclear waste transmutation part 1: target optimization, Ann. Nucl. Energ. 31 (2004) 585. [6] J. Wallenius, M. Erikson, Neutronics of minor actinide burning accelerator driven system with ceramic fuel, Nucl. Tech. 152 (2005) 367. [7] D. Henry, Enhancing electromagnetism experiments with clamp-on Ammeters, Am. J. Phys. 69 (2001) 76. [8] P. Heller, Analog demonstrations of Ampere’s law and magnetic flux, Am. J. Phys. 60 (1992) 17.