DE . , . c | I OFI ORNL P. 1244 : 월월월 ​TI 125 LALE MICROCOPY RESOLUTION TEST CHART NATIONAL AUREAU OF STANDARDS - 1963 1 . . PAT 7 . . . . - ::1 S se the same o en go . . meira : " ::. . . ::::.. . noe som er mer enn .. mcm mne vieram y Yhe. ..r Et neerimiz PELAWAT .: . LEGAL NOTICE This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: A. Makes any warranty or representa- tion, expressed or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, appa- ratus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, "person acting on behalf of the Commission" includes any em- ployee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employ- ment or contract with the Commission, or his employment with such contractor. is 2 1 :1 2 . m ai... ... ALV.- . ... ... . . NA 7. Yifei WYM ** . . . 7 CONF-0505172-7 ORNU-P -1244 CONF-650572-3 ENGINEERING ASPECTS OF MASTER $. THE PRODUCTION OF "EXCITED STATE" HT FOR LORENTZ DISSOCIATION IN DCX-1 : ** .'nin yan ina.. "..1' T V R. S. Edwards JUN 2 4 1965 Oak Ridge Nat: og Oak Ridge National Laboratory, Oak Ridge, Tennessee DCX-1 is a steady state thermonuclear experiment at Oak Ridge. The experiment accumulates a plasma by means of high energy injection of diatomic ions into a magnetic mirror geometry. This paper describes some of the techniques and hard- ware used to produce this plásma, particularly those concerned with beam injection. The principle by which DCX-l operates has been described in many previous articles25 but will be repeated in abbreviated form for completeness. Diatomic molecular ion--H* in our case--are produced in a duo-plasmatron ion source and accelerated to 600 keV by a well regulated cascade transformer power supply. These energetic ions are focused and deflected so that they enter the 10 kg confining field midway between the mirror coils. . These ions make a single pass in this mid- plane and exit through the bottom of the vacuum chamber. In the process of making this single pass some of the diatomic ions dissociate to give protons and hydrogen atoms. Those protons which result from dissociation in a region close to the 3.25 in. equilibrium radius are trapped by means of the e/m change and continue to circulate with a frequency of about 15 Mc/sec until they are eventually lost. When the molecular ion beam is injected, the density of the circulating protons increases until the rate of trapping equals the rate of loss. Since in steady state the number of trapped protons is the prcduct of the proton injection rate and the mean proton lifetime, large injection currents at low pressures are desired. 1 Two methods of providing the required dissociation of the molecular ions have Research sponsored by the U. S. Atomic Energy Commission under contract with the inion Carbide Corporation. PATENT CLEARANCE OBTAINED. RELEASE TO THE PUBLIC IS APPROVED. PROCEDURES ARE ON FILE IN THE DESTAVING SECTION, LEGAL NOTICE The report mo pepurad u No Account of Goronment apoa Ord work. Nalthor da United Matas, nor Commission, nor ww pornos acting on WM of the Conmissioa: A. Makes wy nrruty or reprenatadon, express or implied, with rupect to Usa Accu- racy, completeness, or ux falnews of the laformation contains la the report, or that she was of way iaformation, appuritu, method, or procis disclor la the raport may bol falringo privately om rela; or B. AHAMI My llab uues with respect to the un of, or lor damages resulting from the uw of any lalor auton, apparatus, method, or proces dixcloud in the report. As und la ela aboro, "parada acting on babest of the Commission" lacludes way on- ployee or contractor of the Conalulon, or employu of such coatractor, to the extent that dok saployee or contractor of the Commission, or employs of such coatructor preparı, diamantes, or provides access to, way taformelon purnuant to do employant or contract with the Commluloo, or Wu omogweat with ancha cootractor. 2 been used in DCX-I in recent years. The first to be describea is one is wanneer diatomic ions are dissociated by collisions with background gas. Figure 1 is a schematic representation of the injector used for this purpose. It consists of a duoplasmatron ion source, einzel lens system, electrostatic pulser (for rapidly turning off the beam), analyzing magnet assembly, accelerator tube, and the associ- ated power supplies and protective equipment. The source is mounted on a platform insulated for 600 kV and was designed to produce 25 mA of *. The ion beam is approximately 65% H", the other 35% being h* and #*. The beam is extracted at 60 keV and focused in the lens assembly with approximately 45 kV retarding potential. The beam is accelerated directly into the analyzing magnetic field where by 45° deflection it is separated into its components. Space charge blow up of the beam 3 is thus reduced because the forces are only those of each individual beam instead of that of the entire beam. The analyzing magnet and focus potential are adjusted so that only the #* component can pass into the accelerator tube. If no beam is. desired, this component can be deflected to one side by applying a potential across the pulser plates. The H* beam is accelerated to 600 keV in passing through a five stage accelerator tube. Below the accelerator tube is a vacuum manifold containing one 6 in. oil diffusion pump and one titanium evaporator for absorption pumping. Operating pressure in this region is normally a few times 20°7 torr. Below the manifold the beam goes into a 6 in. tube around which is mounted a solenoid lens assembly. This assembly is a thin lens consisting of four pancakes of 18 turns each of 1/4 in. square hollow copper. Normal magnet current is about 300 A. This lens is used to bring the beam into proper focus for entrance into the plasma chamber. Just below the solenoid lens is mounted a steering magnet assembly for directing the beam through the fringing region of the confining field. The beam then makes a single pass through this field where a small portion is dissociated 3 •••.• * * to form 300 keV hydrogen atoms and the desired 300 keV protons. The undissociated portion of the beam is stopped on a water cooled rotating drum on which titanium 3 is deposited. The actual alignment of the entire assembly to produce the proper ion trajectory treet Miehet is accomplished by using an Englis variable focus telescope. The telescope is mounted s ori atthe i itto d in place of the ion source. Also required are a mirror jig between the pole pieces of the analyzing 'magnet assembly, a pin hole target at the exit from the source mounting assembly, a calibrated target at the top of the accelerator tube, and a similar target at the bottom of the tube. This arrangement gives three alignment points-the source mounting, the top of the accelerator tube and the bottom of the tube. Alignment is regularly achieved to within plus or minus .001 in. Since collisions with the background gas is the mechanism for dissociating the H' beam, the proton input current falls off with decreasing neutral density. At the base pressure of 1.X 10"9 torr, where the mean proton lifetime is longest, the . fraction of the #1 beam converted to proton input current by gas dissociation is only 107. Clearly a more desirable dissociating mechanism would be one providing a higher proton input current while still allowing operation at this base pressure. Results of calculations and experiments at other laboratories suggested that the magnetic confinement field itself might be such a mechanism.678 In passing through this field, the #* ions experience a polarizing force which, if strong enough, can dissociate these ions. For ICX-l, calculations showed that these Lorentz forces amounted to equivalent electric fields ranging from 6.5 x 104 V/cm at the outer edge of the trapping region to 7.3 x 10+ V/cm at the closest approach of the #1 beam to the magnetic axis. Any dissociations occurring in this region would result in trapped 300 keV protons. These fields, however, are too weak to dissociate any but the most loosely bound state of the H* ion, i.e., any but the uppermost vibrational level. Injection of H* obtained directly from the duo-plasmatron source 17, . 2 r 1 :11* . proved to give no measurable Lorentz trapping, so this beam is deficient in this. state. Other investigations had indicated that significant quantities of vibration- ally excited results from passing H* through a high pressure region, so it was decided to convert the DCX-l injector to such a system. Our ion source group had already developed sources that would yiela 50 percent HT. For practical reasons it was decided to use one of these sources in conjunction with the original lens U system and source mountings. Considerable modification was necessary. The entire rund."*.*?7 source had to be raised to make room for the necessary components. These changes are shown in Figure 2. It was immediately apparent that the additional distance from the source to the analyzing magnet would increase the space-charge blow-up problem. It was believed that neutral.ization of the beam could be accomplished **bý" providing an electrostatic trap to prevent electron drain to the lens assembly. Such a trap was provided by placing a 4 kv negative potential on the former pulser plate located just below the central lens section. That neutralization could be achieved by this techr.ique is shown by the two photographs of the beam operating in a laboratory test facility (Figures 3 and 4). Difficulties with neutraliza- tion were experienced when the apparatus was initially installed on DCX-1. It was soon apparent that with the source raised to its new position, the electro- static field from the lead supplying the 45 kV lens potential had destroyed the electrostatic trap. This lead was relocated and brought into the top of the source mounting. Another problem developed when tests on the pulser indicated that the separation of the 40 keV #* and the 60 keV H* beam was insufficient to prevent some leakage of the 60 keV H* beam into the accelerator when the #component was pulsed off. The pulser plates were relocated below the analyzing magnet assembly, and the beam pulsed at right angles to its trajectory. No further leakage was WOS 1 ART detected. vit The heart of the new system is the gas cell. To produce excited state #* it is necessary to run the #* beam through a high pressure region. To maintain a suitable operating pressure in the rest of the system it is also necessary to confine the high pressure region to the smallest possible area. The gas cell employed is 5 1/2 in. long and 1 7/8 in. in inaximum diameter. The top and bottom sections are made of copper and are connected for continuous liquid-nitrogen acuU cooling in order to minimize leakage of water vapor from the cell. The liquid nitrogen is brought through specially designed "0" ring vacuum seals that are warmed by circulating water to prevent leaks that might result from freezing of the seals (Figure 5). The gas for the cell is water vapor fed directly to the center section, which is 5/8 in. stainless steel tubing. The water supply is a 250 ml flask at room temperature connected through a Granville-Phillips variable. leak valve. This valve is motor driven and remotely controlled from the operating console. With the cell cooling and water injection adjusted for maximum production of excited state *, the operating pressure in the source manifold is maintained at 4-6 X 108 torr. Data indicates that for each mA of H* passed through the cell approximately 100 HA of H" is available for acceleration into DCX. Barnett's data shows a maximum conversion ratio of 13 percent.. The lower value achieved in DCX- may be the result of inelastic scattering in the gas cell. However we have not attempted to verify this fact since 10 percent conversion of the available 8 ma n* has been sufficient for our needs. The source alignment and beam trajectory remain the same for excited state #* as it was for normal x The only other difference is the increase of accelerator voltage from 540 kV to 560 kV to compensate for tie 20 keV difference between 60 keV * and 40 keV excited state H*. The data to date indicate that the change to excited state #* injection was well justified. With a trapping fraction of about 10 4 for Lorentz dissociation . : A . "Invis 4LIO e We and an input current of 800 MA at base pressure we can inject into DCX-1 the equivalent of 800 mA of conventional H* with its gas dissociation trapping fraction of 10?. The author would like to thank 0. B. Morgan for his valuable assistance on numerous problems that arose during the work on the ion source; and R. G. YOU Reinhardt for the mechanical design of the gas cell and liquid nitrogen feed- thru. . ........ ...:-,+ 2 .it "S" ..- --' 17.11. , . .. V i REFERENCES 1. C. F. Barnett et al., Proc. 2nd U. N. Intern. Conf. on Peaceful Uses of Atomic Energy, United Nations, Geneva, 31(1958) 298. J. L. Dunlap, TRE Trans. Nucl. Sci: NS-7 No. 4, (1960) 19. 3. H. Postma, IRE Trans. Nucl. Sci. NS-3 No. 4 (1961) 77. 4. C. F. Barnetý et al., Nuclear Fusion 1 (1961) 264. J. I. Dunlap et al., Nuclear Fusion, 1962 Supplement, Part 1, 233. 6. J. R. Kiskes. Nuclear Fusion 2 (1962) 38. 7. J. R. Hiskes, Phys. Rev. 122 (1961 1207. 8. A. C. Riviere and D. R. Sweetman, The Dissociation of Molecular Ions by . Strong Electric Fields, Ionization Phenomena in Gases, Munich (1961) 1236. ...: C. F. Barnett, Production of H* in High Vibrational Levels, Thermonuclear Division Semiannual Progress Report for Period Ending April 30, 1963, Sec. 5.4, p. 63. an..obow?;; -ION SOURCE Reklerinin EINZEL LENS PULSER PLATES "*"'lm. 180 fer on 45° ANALYZING MAGNET H+ TARGET WILL H3 TARGET TO ACCELERATOR TUBE DCX-4 25 MA Hz+ SOURCE 065.3.6 . 30 w -ION SOURCE EINZEL LENS timet UNII -GAS CELL -45° ANALYZING MAGNET - peo ANN -NEUTRALS --60 kev Het 20 kev H+ 30 kev H+ S -PULSE PLATES 60 kev H+ - -60 kev Hgt ---40 kev Het DCX-1 ION SOURCE FOR HET WITH GAS BREAKUP CELL ABOVE ANALYZING MAGNET - ASSEMBLY ORNL-DWG 65-4235 WU LIQUID NITROGEN FEED - THRU A HD END DATE FILMED 0 24/65 La 17