. . LOFT ORNLP 1576 EEEE 31 . MICROCOPY RESOLUTION TEST CHART NATIONAL AUREAU OF STANDAROS - 1963 - " . 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. 1 . .. . . .. re . ..t . RIZZO 2, 44 TL . T. . . . 16+ . . STY: .. . . 2 NY . Oror P4576 . MASTER SEP 21 1965 CONF-656666-9 LEGAL NOTICE The report we prepared u M account of current sponsored work. Helther the Dalt Mateo, por the couloodan, vor ay puroon acting an bhall of the Commutaaton: A. Makes Munruby or rapontadon, aged or implies will respect to the secr- racy, complemws, or wounds of the buforution ontained to the report, or that the w of way lubormation, pourate, method, or procesu diecloond ta do report may not latrings priravaty ownd reta; or B. Assumes any liabilities with respect to the woo ol, or for damages resulting from the ne of any information, apparate, wethod, or precio dechowed us to report. Ao wand in the abova, "person acties on Wall of the Commission" tecladne wy one ployer or contracbr al the Commission, or employee al mucha contractor, to the extent that ouch oneploys or contractor at the Conguinolen, stemployee of mucha contractor pre prou, destinate, or provides varu to, any larutou permend to be u s or contract with the Commission, or wo employment with such contractor. RELEASED FOR ANNOUNCEMENT IN NUCLEAR SCIENCE ABSTRACTS Ion Cyclotron Harmonic Spectrum Generated in an Energetic Ion Plasma* P. R. Bell G. G. Kelley N. H. Lazar R. F. Stratton Oak Ridge National Laboratory Oak Ridge, Tennessee U.S.A. ABSTRACT -,- - - - - - . . '. . Measurements have been made of the electric and magnetic fields produced in a plasma of 3 x 109 ions/cc density with a mean ion energy of about 700 kev. Spectral analysis of the signals show oscillations at the ion cyclotron frequency and its harmonics up to at least the 70th harmonic. The intensity ratio to an electrostatic probe is less than 30 db between the 3rd harmonic (usually the strongest) and the 60th harmonic. The plasma is contained in a nearly uniform magnetic field between mirror coils spaced 4 meters apart. As a result of the strong anisotropy of the particle velocities, most of the plasma 18 further restricted axially by a very small magnetic mirror to a region - +30 cm about the midplane. The plasma diameter is 30 cm. The electric field is strongly absorbed by the plasmas. Probes axially spaced by more than 10 cm show almost complete lack of phase correlation, although the spectral distributions are not very different. Wien the plasma decays, some of the fields persist for density reductions of more than an order of magnitude. In particular, the fundamental, whose width at full density 18 ~ 150 kc (f = 18.3 Mc), lasts for several seconds and shows a frequency shift of ~ 50 kc as well. *Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation. Since the initial report of observation of electron cyclotron harmonic radiation from a plasma, which was made at the fourth of these conferences /1/, there have been careful studies of this phenomenon in various kinds of plasma. This work has been reviewed by Crawford /2). The subject of ion cyclotron harmonic fluctuations, however, has received considerably less attention. The presence of electromagnetic fields at ion cyclotron harmonic frequenc!es in hot plasmas was reported first in 1961 - by groups working on the high energy injection thermonuclear experiments DCX-1 /3/,/4/, and OGRA /5/. The DCX-1 group saw proton cyclotron harmonics through the 7th, and the OGRA group saw molecular ion harmonics through the 9th. There has been a continuing study of the electron fields in DCX-l with the greatest attention given to the funda- mental and the first three higher harmonics /6/. Ion cyclotron harmonic fields have been reported also in other high energy injection experiments/»/, 18/. The device in which the measurements to be described were made is the multiple-pass energetic ion injection experiment called DCX-2 /9/. In it a proton plasma of 300 kev initial energy is produced in a magnetic mirror configuration by the dissociation of molecular hydrogen ions injected in a spiral trajectory at 600 kev. Dissociation takes place upon interaction with the background gas but often a high-vacuum arc is provided on flux lines intersected by the molecular ion spiral to produce greatly enhariced dissociation (Fig. 1). The central field is 12 kilogauss * 2 gauss over an axial distance of 150 cm. Most of the measurements have been made using a short (2.0 cm) cylindri- cal antenna projecting iito the plasma region. Tests were made using a signal generator to inject a signal into the tank to determine the antenna response characteristic. It was found that the connection between the outer conducter of the coaxial signal lead and the copper shell surrounding the plasma region had to be made with care. If this connection is not of the lowest possible impedance or if the outer conductor projects into the plasma region, resonance . tric field which rises proportionally with the frequency below the frequency , .. -2- at which the capacitive reactance of the probe tip to the tank is equal to the characteristic impedance of the line and is flat above this frequency. It should be pointed our that the probe does not measure a radiation field over most of the frequency range considered. The frequencies of the fields observed all are less than about 2 Gc corresponding to free space wavelengths larger than 15 cm. The spatial distribution of the signals seen may come from single clumps of charge producing pulses of induced current at the probe as they pass by. A shielding of the disturbance by electron currents may increase the sharpness of the pulses and thereby the higher harmonics. There is evidence that the effects seen by the probes do come predominantly from charge fluctuations in the imme!iate vicinity. Fig. 3 shows a typical response Prom probes in the midplane of the plasma but at diametrically opposite positions. There is also a lack of similar- ity between probes at the same azimuth but at different axial positions. Phase correlation studies of the proton fundamental cyclotron frequency at .. low plasma densities do, however, show a phase shift equal to the angular displacement of the probes. In other words, two probes can see the same moving charge but their response to it may be quite different. The rf spectrum measurements were made using three analyzers having considerably different characteristics. One of them (Panoramic model SPA-3/25) is designed to cover the range from 200 cps to 25 Mc in sections as wide as 3 Mc with sweep recurrence frequencies from 1 to 60 per second. The bandwidth is adjustable from 50 cycles to 50 kc. Another analyzer ( Panoramic XPA-5) covers the range from 10 Mc to 100 Mc in a single range with normal sweep rates of 2 Mc/usec to permit rapid sampling of the spectrum. The bandwidths provided are 0.5; 1, and 2 Mc. The third analyzer, acquired recently, is a Hewlett-Packard 85514-85. A which has a maximum sweep of 2 Gc and a maximum frequency of 40 Gc at variable sweep rates up to 67 kc/usec. The response over a 2 Gc range is constant within : 2 db. These analyzers are connected to the probes through 125 ft. lengths of Andrews HJ4-50 cable. The spectrum of the signal seen in the midplane of the plasma region is shown in Fig. 4. for the plasma formed by gas dissociation at various pressures and correspondingly different plasma densities. The figure shows that the spectral response shifts to higher frequency as the pressure 18 -- - - - - . - . HL--. - . raised in spite of the fact that at the highest pressure thc hot plasma and mean energy has fallen. No reliable estimate of the density of the colder plasma, formed by interaction of the hot ions with the background gas, has been made, but it probably increases monotonically with pressure. A note- svorthy feature of these spectra is the predominance of the even harmonics of the proton cyclotron frequency with no appreciable odd harmonics, if the underlying molecular ion spectrum is assumed to be uniform. When a hydrogen arc is used to provide enhanced dissociation of the 600 kev molecular ion beam, the spectra seen in Fig. 5 result. In this care all of the proton cyclotron frequencies appear up to approximately the 100th harmonic with no apparent distinction between the odd and even harmonics. The expanded presentation of the lower frequency range shows that the 3rd harmonic is most intense even when the response is corrected for the frequency dependence of sensitivity. Some molecular ion harmonics are seen. The fundamental proton frequency response is quite small. The spectrum resulting when a lithium arc is used to provide enhanced . dissociation 18 seen in Fig. 6. The response to the arc alone also is shown. The spectra were made with an older probe which had resonance which influenced the response above about 300 Mc and illustrate the effect of improper probe design. No data have been obtained using a lithium arc since resonance free probes were installed. The lower harmonics using a lithium arc are seen in Fig. 7. The third harmonic is the strongest. The fundamental proton cyclotron frequency response is very broad during the time a beam 18 being injected. It has been studied as a function of time (using the fast 10 to 100 Mc analyzer) by deflecting the beam of an oscilloscope vertically with the spectroneter sweep voltage while the internal sweep circuit of the oscilloscope is producing a slower horizontal deflection. The spectrometer output is caused to modulate the intensity of the electron beam. In Fig. 8 is seen the result in one particular instance. The frequency shifts upward repeatedly after beam turnoff reaching a limit at the cal.culated cyclotron frequency. Under other conditions the shift occurs only once. During the interval of beam injection the frequency shifts , sporatically. When a lithium arc 18 present with no beam, 11thium ion harmonics are : not visible, but they appear when a beam 18 injected. Fig. 9 shows a . wimwen... i di . . U composite display of the low frequency spectrum photographed while the bean was being pulsed on and off. -5. .. . si!! ... ::!!ili . ... REFERENCES . .. . 11/ .. C. B. Wharton, "Microwave Radiation Measurements of Very Hot Plasmas," Proc. 4th Intern. Conf. on Ionization Phenomena in Gases, Uppsala, Sweden, August, 1959, North-Holland Pub. Co., Amsterdam, 2, 737 (1960). .. . ... - F. W. Crawford, Nuclear Fusion 5 (1), 73 (1965). - ... P. R. Bell et al., Thermonuclear Division Semiann. Rept. January 31, 1961, ORNL-3104, p. 17. -. ... -.-. J. L. Dunlap et al., Nuclear Fusion: 1962 Supplement, Part 1, p. 233. .. -.-. A. E. Bazhanova et al., Nuclear Fusion: 1962 Supplement, Part 1, p. 227. .-.-. . - - .a C. F. Barnett et al., Thermonuclear Division Semiann. Rept. Oct. 31, 1961, ORNL-3239; J. L. Dunlap et al., Ibid, April 30, 1962, ORNL-3315; Ibid, Oct. 31, 1963, .ORNL-3564; Ibid, April 30, 1964, ORNL-3652; Ibid, Oct. 31, 1964, ORNL-3760; Ibid, Oct. 31, 1962, ORNL-3392. . - Danm et al., Phys. Rev. Letters 10, 323 (1963); Kuo et al., Phys. Fluids 7, 988 (1965). ... . Bernstein et al., Nature 206, 812 (1965). P. R. Bell et al., Nuclear Fusion: 1962 Supplement, Part 1, p. 251; P. R. Bell et al., Thermonuclear Division Semiann. Rept. April 30, 1967, ORNL-3315; Ibid, Oct. 31, 1962, ORNL-3392; Ibid, April 30, 1963, ORNL-3472; Ibid, Oct. 31, 1963, ORNL-3564; Ibid, April 30, 1964, ORNL-3652; Ibid, Oct. 31, 196/, ORNL-3760. .." ... .. FIGURE CAPTIONS Fig. 1. Longitudinal section through DCX-2. Rings of detector ports are located in the space between the coils. Fig. 2 Dual probe used for most of the measurements reported. Fig. 3 Simultaneous time response to the fundamental proton cyclotron frequency of probes located at same axial position, but diamet- rically opposite, during lithium arc breakup. The beam was turned on at the beginning of the sweep and the sweep speed : was 100 MBec/com. - - - Fig. 4 Spectra found with gas dissociation at various pressures showing enhancement of the even proton cyclotron harmonics. Fig. 5 Spectrum found with hydrogen arc breakup of the injected molecular hydrogen ion beam. Fig. 6 Spectrum found with lithium arc breakup of the injected molecular hydrogen ion beam. Fig. 7 Spectrum in the 10 Mc to 100 Mc range with lithium arc breakup of the injected molecular hydrogen ion beam. Fig. 8 Time resolved behavior of the fundamental proton cyclotron response with the injected molecular hydrogen ion beam pulsed on and off. The curved lines are superimposed signals from another kind of detector. Low frequency spectrum with lithium arc breakup while the molecular ion beam 18 being p8lsed on and off. The cyclotron harmonic lines of ?L1* appear when the beam 18 on. Fig. 9 ORNW-Dwa, 63-62074 A ... .. re LEGEND 1. ELECTROMAGNET COILS 2. MAIN VACUUM TANK 3. COOLED LINER 4. DIFFUSION PUMP AND BAFFLE 5.ION SOURCE AND ACCELERATOR 6. INJECTION SNOUT 7. PLASMA 8. ARC ELECTRODES 9. ACCELERATOR X-RAY SHIELD 10. DIAGNOSTIC PROBE (ONE OF MANY) 11. TITANIUM EVAPORATOR 2. BEAM TARGET . . Fig. l. Longitudinal section through DCX-2. Rings of detector ports are located in the spaces between the coils. : .. : BRONZE WOOL :. . ' 1 4 * . . .. .. . . IL - -. - ........--. - . - -- --. .- -. . .. U1212 25 TEL ". .. -. - . . . i11 . VK . .. . : SLI KE N 1111111 T TA 1 . ! 1 1. It " IR 1 H . .. ! .., ri . . . Tº . IN- * LT . . ** . . . 17 .. -. . 1 H 1 . . . + 2 . . .. 10 IME 101 ... . . . . UNCLASSIFIED PHOTO P-61707 AK MS649 . 9 M R . III ' UNCLASSIFIED PHOTO p. 61708 .. SI . . . . . 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Li ARC + H+ PLASMA FIELD 32,000 -10,400 - 32,000 GAUSS 3-26-65 GC-4 ,.. · ..mimozath. imamo , . 1.DK . L o'mc 1000'' 1800 Li ARC ONLY FIELD 32,000 -10,400 - 32,000 GAUSS 3-26-65 GC-2 . 1 . ... is... LE . ن نننننننننننننممممنننننننننننننننننننممنمننننماميننمننننهمين . - ci . hierdie boer. internet 11 i ". , * OX * . . ÖNCA HARMONIC CV . 11 . Sólmc 1ooo !! 2000 / ...Ho ARC IN DCX-2 .;.:, FIELD 37,000 - 12,000 - 37,000 GAUSS 5-7-65 GC-8 - - . . . - - . + 14: 洪 ​我 ​一一一一 ​. | 37 | || …..…. ... …:: 3 - 4:3 - . . . . . . , ….... .. . ... . . . . . . . . . . .-.- ,*, - 一一一 ​- . . .. 杜 ​4 -宁​"号​: -- - iviny i - -- N A Pi-t' -r tw + 4 . 4 " 中 ​“ . UCKSS:..) PH070 69000. YT TAT U yang managers Wy more .o-mong ! FAST NEUTRAL PARTICLE IVTEGRALS R4P8 ANO 64, 2, 4, 6, 7, P8 . . . 1 . .:. FREQUENCY SPECTRUM 18.0 - 18.5 MC 0.1 sec/cni 4/10/64-P25 .... m imo . .:: .' . . นนนนนนนนนนนนนนนนนนน "},"widw: 44. 44i .... . . Fig. Porto RF Spectrum and Foil Noutral Detector Integrals vs Timo. Sweep spoed 0.1 sec/cm. Upper trace, integral from ring position 8 with 3.3 x 10-10 coulomb/cm. Lower traco, intagral of the sum of five detectors along the machine axis with 10*9 coulomb/cm. Rodio-frequency has some froquoncy spread as Fig. 2.3. Sinanini.. XL , 40 ML . : o centr - TY PS GREY " Y VULP 1 SA 179 ..:: TWIT.. * - AROWA NI. i n sorin...ti f o rsti.:,*voimme toimi..terrow.... 11" 1.polecenie svesting is wrote: nast kunna matot a punt, un any, a 0 1 2 3 4 5 6 Ï . 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 FREQUENCY (mc) DCX-2 RF SPECTRUM, LITHIUM ARC 18a, Het BEAM 30ma, PRESSURE 4 x 10-7mm Hg, OPTIMUM FIELD END HAN - in DATE FILMED 10/ 20 / 65 . 1 .