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Investigation of Windowless Gas Target Systems for Particle Accelerators

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Investigation of Windowless Gas Target Systems for Particle Accelerators Investigation of Windowless Gas Target Systems for Particle Accelerators by William B. Gerber B.S. Mechanical Engineering, University of Texas (1996) Submitted to the Department of Nuclear Engineering in Partial Fulfillment of the Requirements for the Degree of Masters of Science in Nuclear Engineering at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 1998 © Massachusetts Institute of Technology 1998. All rights reserved. Author ........ ................ Nuclear Engineering Department May 10, 1998 Certified by ......... Richard C. Lanza Senior Research Scientist Thesis Supervisor Certified by ............ S....... .............. Lawrence M. Lidsky Professor of Nuclear Engineering Thesis Supervisor Accepted by ......... Lawrence M. Lidsky Chairman, Departmental Committee on Graduate Students t. 1CI~FQllllf~~ Investigation of Windowless Gas Target Systems for Particle Accelerators by William Gerber Submitted to the Department of Nuclear Engineering On May 8, 1998 in Partial Fulfillment of the Requirements for the Degree of Master of Science in Nuclear Engineering ABSTRACT The application of intense accelerator based neutron sources has been hampered in the past by the material properties of the target system and the requirements of passing the accelerated beam from the vacuum environment of the accelerator to the target. This investigation examines two different methods which remove the limitations of the window in gas target systems. The first system was initially developed by Iverson at MIT and relied upon low conductance nozzles and rotating disks which opened and closed the beam line. This system achieved pressures up to 75 mbar in the target chamber with pressures below 10-3 mbar in the first pumping chamber. Similar experiments conducted by Guzek, Tapper, and Watterson, at Schonland Research Centre at the University of Witwatersrand, were able to reach three atmospheres of pressure in the target chamber. Re-design efforts were conducted to improve the Iverson design and increase the stability of the rotating disks as well as increase the pressure in the target chamber. The second system examined utilized a "Plasma Porthole" developed by Hershcovitch of Brookhaven National Laboratory. This system relies upon the high pressure and high viscosity of a stabilized plasma arc to support the large pressure differential between the target chamber and first vacuum chamber. Previous experiments conducted by Hershcovitch had supported pressure differences of over 3.5 atmospheres. A system was assembled to fully test the performance of the plasma porthole and compare it against the mechanical system. With the utilization of windowless gas target systems, the limitations on beam current, energy focusing, and overall power output have been removed. This greatly increases the performance of many applications such as bomb detection in luggage, nuclear stockpile stewardship, and Accelerator-driven Transmutation of Waste (ATW). Thesis Supervisor: Richard lanza Title: Senior Research Scientist, Nuclear Engineering Department Thesis Supervisor: Lawrence Lidsky Title: Professor of Nuclear Engineering Acknowledgements This project was supported by a grant from the Federal Aviation Administration (FAA Grant 93-G-053) as well as funding from Lawrence Livermore National Laboratory. This project would not have been possible without the help and support of many people. James Hall and Frank Dietrich from Lawrence Livermore National Laboratory gave support in equipment, advice, and ideas. Jim Fraser of Ferrofluidics and the MIT Central Machine Shop gave assistance in designing and producing several of the mechanical components. Special thanks go to Ady Hershcovitch from Brookhaven National Laboratory. It was through his generous donation of equipment and expertise that allowed for the investigation of the plasma porthole. Similar thanks go to Erik Iverson whose previous work provided the foundation for the mechanical system and whose advice guided the path for the re-design efforts. Tremendous thanks go to Doctor Richard Lanza and Professor Lawrence Lidsky for their guidance, inspiration, and leadership. Table of Contents TABLE OF CONTENTS ....................................................................................................................... 4 LIST O F FIGU R ES ...................................................................................................................................... 5 LIST OF TABLES ............................................. 6 CHAPTER 1. INTRODUCTION ............................................................ 7 1.1 Neutron Sources......................................... 7 R eacto rs ............ .. .................................................................................................................................. 7 Isotopes ................................ ........................................ 8 A ccelerators....................................... .................. ....... 10 1.2. Accelerator Targets................................. ................... ................................... 12 S o lid Ta rg ets ............................................................................................................ .................. ...... 13 L iquid target................. ........... ............................................................ .. ................. 14 Ga s Ta rg ets ............................................................................................................... ................. ...... 14 1.3. Scop e of Study ........................................................................ 16 CHAPTER 2. EXISTING SYSTEM ........................................................................................................ 17 2.1. A cceleratorSpecifications ..................................................... .................. 17 2.2. Previous System Theory .......................................................... 20 2.3. Summary of Implementation (Iverson) ................................................ 22 2 .4. P ressure Tria ls ........................................................................................................................... 2 6 CHAPTER 3. REDESIGN EFFORTS..................................................................................................... 28 3.1. Mechanical Changes to System ............... .................. ............ 28 3.2. Vacuum Pump Alterations............................................. 32 CHAPTER 4. PLASMA ARC THEORY .......................................................................................... 34 4.1 Pressure and Density of Plasma Arc..................................... .................. 34 4 .2 P lasm a F lo w ................................................................................................................................ 3 5 4 .3 F o cusing Effect ............................................................................................................................ 3 7 CHAPTER 5. IMPLEMENTATION OF PLASMA ARC....................................... ............. 39 5.1 Plasma Porthole......................... ................................... ...................... 39 5.2 System Installation .................................... ................. ....... 42 5 .3 Exp ected R esu lts .......................................................................................................................... 4 3 CHAPTER 6. APPLICATIONS............................................................................................................... 44 6.1 Intense F ast Sources .................................................................................................................... 44 6.2 M onoenergetic Sources ............................................. 45 6.3. Accelerator-drivenTransmutation of Waste (ATW)................................. ............ 48 CHAPTER 7. CONCLUSIONS AND FUTURE WORK...................................... ............... 50 7.1 Co mp ariso n ........................................................................................................ ........... ...... 5 0 7.2 Future Work...................................... ................. 52 APPENDIX A. PUMP INFORMATION........................................................................................... 53 APPENDIX B. DIAGRAMS OF MECHANICAL SYSTEM ....................................... .......... 64 APPENDIX C. DIAGRAM OF PLASMA WINDOW SYSTEM ...................................... ....... 70 4 List of Figures Figure 1-1: Neutron energy spread from 252Cf spontaneous fission. ................................. 9 Figure 1-2: Neutron yields for different systems . .......................................... 12 Figure 2-1: Energies of neutron from D-D reaction ........................................ 20 Figure 2-2: Initial design of mechanical system. .......................................................... 23 Figure 2-3: Cross section of previouse mechanical system. ....................................... 25 Figure 3-1: Close up view of rotating disks ....................... ........... 29 Figure 3-2: N ew disk assem bly ................................................................................. 31 Figure 4- 1: Focusing from plasma lens on 5 MeV proton beam ................................ 38 Figure 5-1: Cross section of plasm a porthole .............................. ..................... 41 Figure 5-2: Plasm a porthole system ................................................................
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