The Lawrence Livermore Laboratory Shiva laser-target interaction facility is designed for experiments at 20 to 30 terawatts. At this power level there will be larger fluxes of neutrons, x-rays, electrons and ions than have been previously measured. The measurements of energy converted into the various reaction products is crucial both in target design and performance analysis of the actual experiment. The total energy absorbed is measured by a box calorimeter surrounding the target except for beam input holes. This measurement prevents the use of other diagnostics, so for normal operation an energy balance module was designed for location on ports on the Shiva target chamber. This module monitors the energy in scattered light at 10640 A and 5320 A or 7118 A. It also contains a faraday cup and plasma and x-ray calorimeters. The distribution of energy in scattered light, plasma and x-rays will be mapped by 58 such modules

Glaros, S.S.

Gunn, S.R.

Kornblum, H.N.

Phillion, D.W.

Rupert, V.C.

UNT Digital Library

M m PREPRINT UCRL- 79801 Lawrence Livermore Laboratory ENERGY BALANCE MEASUREMENTS FOR SHIVA /~~*\ S. S. Glaros, V. C. Rupert, S. R. Gunn, D. W. Phillion and H. N. Kornblum October 24, 1977 This paper was prepared for submission to the APS Plasma Physics Meeting of the American Physcial Society, Atlanta, Georgia, November 5-11, 1977. This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made. before publication, this> preprint is made available with the understanding that it wil. not be cited or reproduced without the permission of *ri.-> author. « * * - « M > » . DISTRIBUTION OF THIS DOCUMENT IS UNUMITBu) Abstract Submitted for the APS Plasma Physics Meeting of the American Physical Society November 5-11, 1977 Physics and Astronomy Classification Scheme Number 52 Bulletin Subject Heading in which Paper should be placed Plasma Diagnostics Energy Balance Measurements for Shiva.* S. S. Glaros, V. C. Rupert, S. R. Gunn, D. W. Phillion and H. N. Kornblum, Lawrence Livermore Laboratory.**— The Lawrence Livermore Laboratory Shiva laser-target inter­action facility is designed for experiments at 20-30 terawatts. At this power level there will t» larger fluxes of neutrons, x-rays, electrons and ic.s than have been previously measured. The measurements if energy converted into the various reaction products is crucial both in target design and performance analysis of the actual experiment. The total energy absorbed is meas­ured by a box calorimeter surrounding the target except for beam input holes. This measurement prevents the use of other diagnostics, so for normal operation an energy balance module was designed for location on ports on the Shiva target chamber. This module monitors the energy in scattered light at 10640 A and 5320 K or 7118 A. It also contains a faraday cup and plasma and x-ray calori­meters. The distribution of energy in scattered light, plasma and x-rays will be mapped by 58 such modules. * Submitted by A. J. Glass ** Supported by U. S. ERDA Contract W-7405-ENG-48 -NOTICE-Tfiii report wu prepiied u in account of work sponsored by the United Slittt Government. Neither Ihe United Suit! nor Hit United Slitei Depuiment of Entity, "Of »ny of their emptoyuei, nor irry of their contrition, tubconiraclon, or their employed, make* iny wvunty, expreu or Implied, or utumei tay lejil Uiblllty or fetpontibility foi the icruticy. eompkteneu a uierulnea of tny fnforracfon, ippmiu i , product or proas di tdntd, oi itptnenis tfui m me would not Infringe privately owned right*. Submitted by Alexander Glass University of California Lawrence Livermore Laboratory P. 0. Box 808, L-549 Livermore, CA 94550 DISTRIBUTION OF THIS DOCUMENT IS UNL'^ITEU ft? ENERGY BALANCE MEASUREMENTS FOR SHIVA* S. S. Glaros, V. C. Rupert, S. R. Gunn, . W. Phillion and H. N. Kornblum Lawrence Livermore Laboratory P. 0. Box 808 Livermore, California 94550 INTRODUCTION Measurement of energy converted into the various reaction products and scattered light, is crucial in the performance analysis of laser fusion experiments. These measurements develop laser-plasma interaction theory which ultimately results in increased understanding of laser-target coupling and output. Measurement of the laser light absorption indicates that for intensities of interest, inverse bremsstrahlung is not the dominant absorption mechanism^. Experiments?-^ 4 have shown that polarization dependent absorption mechanisms such as resonance absorption are important. Scattered light dataS has shown that mechanisms such as Brillouin scattering exist and are related to such things as laser pulse length. The scattered light polarimetry and spectroscopy^ indicate the effect of radiation pressure on the steepening of the plasma density distribution in the region of the critical density. All these effects need to be explored in the higher intensity regions expected in Shiva. A basic goal of any energy balance measurement scheme, is to map the different reaction products in space, time and energy such as shown in figure 1. The Shiva startup configuration is with 30 energy balance modules (EMB}, 4 vertical rows nearly equidistant, shown in figure 2. The basic configuration of the EBM shown in figures 3 & 4, consists of a 1.06 micron scattered light photodiode, a broadband light calorimeter (LC-21), a Faraday cup to measure the ion spectrum *Work performed under the auspices of the U. S. Energy Research and Development Administration under Contract No. W-7405-Eng-48. 1 and a plasma calorimeter (LC-27). The EBM may also have either a 7118 A or a 5345 A tuned photodiode to measure the 3/2<» or 2m scattered light. The EBM also allows the inclusion of either a plasma sputtering-loss calorimeter (LC-26) or an X-ray calorimeter (LC-29). The X-ray calorimeter requires inclusion of a valve and quick-disconnect flange to allow frequent filter changes. In back of all the calorimeters are preamplifiers which boost the signal above the ambient noise to provide unambiouous daca. In front of the EBM's aluminum base is a tantalum X-ray shield to protect the diagnostics from direct and Compton scattered X-rays. There is an aluminum cover which envelops the EBM for protection from the high background EMP. The amount of light absorbed by a laser fusion target can be determined either directly by measuring the total energy of the laser-target interaction products (particles and x-rays) or indirectly by performing a balance between incident and scattered light. The light energy balance method requires measuring the incident laser energy, the energy scattered back into the focusing optics and the energy scattered in the balance of 4TT steradians around the target. The latter measurement is best accomplished using an all-enclosing calorimeter such as the one shown in figures 5 and 6. This is called the Shiva "box" calorimeter and it completely surrounds the target except for the holes provided for target insertion and passage of the laser light. The 1.06-micron radiation is internally transmitted through a shield of WG-280 glass which stops particles and X-rays with energies below 15 KeV (which is most of the X-ray energy). The light is absorbed in an adjacent aluminum-backed BG-18 glass slab. The resulting temperature rise is measured with a series of thermocouples in respect to a massive heat sink. Built-in electrical heaters are used to calibrate each of the panels. The majority of the 4n steradian scattered light energy can be obtained by summing the 24 panel outputs or the separate outputs can be used to determine the spatial dependence of the scattered light. 2 PHOTODIODES For monitoring the spatial and spectral distribution of the scattered light, each EBM has two silicon PIN photodiodes with special filters and housings shown in figures 7 & 8. The EBM has a lead glass window and black delrin retainer which allows rapid replacement of the diode package without breaking vacuum, as well as providing electrical isolation. The heavy-met housings block Compton scattered X-rays up to 300 KeV. The initial filter is a glass containing 75% lead which blocks X-rays up to 300 KeV. The next filter is a neutral density filter needed to keep the photodiode output in the linear range. One of each E8M's photodiodes is tuned always to the 1.06 o micron scattered light and in this one, the next filter is a 200 A FWHM o bandpass filter, flat to 5% over the 100 A centered at the laser wavelength. o The second of each EBM's photodiodes is tuned either to 5345 or 7118 A. The 2u> and 3/2w light parametrically generated within the underdense plasma, is observed to be quite broad and red shifted from their nominal frequencies by o an average of 25 A. Thus the normally 5320 and 7093 A spectral filters are tuned to 5345 and 7118 A. Along with the 5345 or 7118 A filter is a color O filter and a 250 A FWHM bandpass filter. The sensitivity of the resulting o photodiode assemblies to wavelength is 0.18%/A. The photodiodes are each biased at 45 volts so that the charge collecton from the intrinsic region is almost total, by a special charge amplifier and their signals are digitized and recorded by the diagnostic computor system. SCATTERED LIGHT CALORIMETER The LC-21 scattered light calorimeter shown in figure 9, is a minature version of the LLL laser-beam calorimeters. A wedged lead glass window transmits the 1.06 micron radiation but stops particles and all but the most energetic X-rays. The laser light is absorbed in BG-18 glass mounted on an aluminum disc, the temperature rise of which is measured by a sensitive thermoelectric module which produces a voltage which is compared with that of 3 an identical dummy absorber unit. The net output is sent to the attached preamplifier, then digitized and recorded by the diagnostic computor facility. The calibration of the LC-21's is accomplished by use of an attached electrical heater or with respect to a reference laser calorimeter using a split beam CW YAG laser with a timed shutter. PLASMA CALORIMETERS There is one LC-27 differential plasma calorimeter shown in figures 10 and 11, in each EBM. The main aluminum absorber is heated by particles, x-rays and a small fraction (7%) of the scattered 1.06 micrcn radiation. The compensating absorber receives only the (same small fraction) scattered laser light. The compensation is performed electrically. Each absorber has a built-in heater for calibration purposes. Moreover a split beam CW YAG laser system and a times shutter are used to verify the fraction of 1.05 micron radiation absorbed by each receiver. This determines the precise value for the resistors in the compensating circuit. The calorimeter output signals are amplified by a preamplifier contained in the EBM, digitized and recorded by the diagnostic computer system. The LC-26 sputtering-loss calorimeter shown in figure 12, receives the flux on a similar aluminum disc; a thin aluminum cylinder in front of the disc intercepts approximately 85% of the reflected and sputtered particles to determine the effective absorption efficiency. The LC-26 is utilized for correction LC-27 results for sputtering losses and replaces the LC-29 in selected locations. Figure 13 shows a typical output from a calorimeter in Argus. 4 X-RAYS CALORIMETER « The LC-29 shown in figure 14, is a differential x-ray collecting calorimeter. There is a valve in front of the calorimeter and a quick disconnect flange which allows rapid replacement of a thin paralene or formvar ion shield. One of the two receivers has a lead glass window over the receiver; thus it receives only a negligible amount of very high energy x-rays but all the scattered light. The second receiver has no cover and thus measures both light and x-rays. The differential signal is the X-ray signal which is amplified by an attached preamplifier and then digitized for processing by the diagnostic computer. Calibration is accomplished with built-in heaters. FARADAY CUP The faraday cup charge collectors shown in figurel5, utilize two unconventional techniques to suppress secondary electron con;-ibution. In addition to a 67.5 volt bias utilized to reject secondaries, a diametrically polarized ring magnet surrounds the body to keep the secondaries produced internally within a specially designed de<?p cup. The elimination of secondary electrons keep the data unambiguous since there is some question as to their contribution. The output is digitized and recorded by the diagnostic computor facility. A sample undigitized trace is shown in figure 16. ACKNOWLEDGEMENTS The authors wish to thank Ray Bantz for substantial contributions in the design of the calorimeters and the energy balance module. We also wish to acknowledge the excellent design efforts of Bill Laird in his interaction with the Shiva box calorimeter. 5 REFERENCES H. G. Ahlstrom, "Laser Fusion Implosion and Plasma Interaction Experiments"; UCRL 79819; CECAM Meeting, Menton, France, Sept., 1977; 11th European Conf. on Laser Interaction with Matter, Oxford, England, Sept. 1977. V. C. Rupert, D. W. Phillion, J. M Auerbach, P. Y. Lee, K. R. Manes, J. E. Swain; "Scattering Scale Height and Angle Dependent Absorption"; LLL Internal UCRL 79786 for 1977 APS Plasma Physics Meeting. K. R. Manes, V. C. Rupert, J. M. Auerbach, P. Lee and J. E. Swain; "Polarization and Angular Dependence of 1.06 m Laser Light Absorption by Planar Plasma"; Phys. Rev. Lett, Vol 39, No. 5, P. 281, Aug. 1977. V. C. Rupert, S. R. Gunn, J. F. Holzrichter; "Particle and X-Ray Energy Measurements in Laser Plasma Interaction Experiments", accepted by the Journal of Applied Phys. for publication. D. W. Phillion, W. L. Kruer, V. C. Rupert; "Brillouin Scattering in Laser Produced Plasmas"; LLL internal UCRL 79785 for 1977 APS Plasma Physics Meeting. D. W. Phillion, R. A. Lerche, V. C. Rupert, R. A. Haas, M. J. Boyle; "Evidence for Profile Steepening of Laser Irradiated Plasmas"; accepted for publication by the Phvs. of Fluids. NOTICE "This report was prepared as an account of work sponsored by the United States Government. Neither the United Stales nor the United States Department oflinergy. nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liahility or respon­sibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately-owned rights." Reference lo a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Department of Knergy to the exclusion of others that may be suitable. 6 FIGURE CAPTIONS 1. Argus Scattered Light, Particle & X-Ray Energy Distribution 2. Shiva Startup Energy Balance Diagnostics 3. Energy Balance Module 4. Energy Balance Module Detail Configuration 5. Shiva Box Calorimeter 6. Shiva Box Calorimeter retails 7. Photodiode Assembly 8. Photodiode Detail Configuration 9. LC-21 Scattered Light Calorimeter 10. LC-27 Plasma Calorimeter 11. LC-27 Plasma Calorimeter Details 12. LC-26 Plasma Calorimeter 13. Typical Calorimeter Output 14. LC-29 X-Ray Calorimeter 15. Faraday Cup 16. Argus Faraday Cup Output IRRADIATION OF MICROSHELLS WITH F/1 FOCUSING LENSES SHOW A STRONG POLARI2ATION DEPENDENCE OF THE SCATTERED LIGHT AS WELL AS THE PARTICLE AND X-RAY ENERGIES ,i£S Shot #36120702: I ncident energy 153 J, 37 ps Neutron yield 2.8 X 10 8 90% incident energy 180' 5 0 5 Scattered light 10 15 20 Perpendicular to the plane of polarization In the plane of polarization 0' J/sr 90% incident energy In the plane of polarization Perpendicular to the plane of polarization Particle and x-ray energy (calorimetry) Figure 1 Shiva start-up configuration 324 Tower Tower Figure 2 Energy balance module details Figure 3 Figure 4 t « Absorber (beam) Shield ion (beam) Receiver plate #2 (beam) Figure 5 BOX CALORIMETER TO MEASURE THE ABSORBED LIGHT ENERGY L j - * •- \ *m Pyrex paitidV i^MS§ and x-ray shield ^ ^ BG18 absorbing glass Copper plate •wor**' Aluminum jacket Thermoelectric modules Aluminum ?jnk Figure 6 Figure 7 Photodiodes f Filter, neutral density ^-Filter, color { Filter, interference, bandpass5345 Filter, interference, bandpass 7118 ' ~Y</<frrvVYrVftrT7l ^Keeper r Retainer, window , lead glass -Filter, interference, bandpass 1.66 pm PIN-6LC photodiode-j Figure 8 Scattered light calorimeters r Window, wedged -Thermoelectric, module WA Y 'xfo&s { ' y / / / / l v v v v \ < Absorber f o /\t \wv / ; s / \ s / JJ / /\ i / ; ; A Base block Disc, receiver V Jacket Figure 9 SELF COMPENSATING CALORIMETERS MEASURE THE PARTICLE AND X-RAY FLUX J3 THE DUAL ABSORBER CONSTRUCTION ALLOWS CANCELLATION OF THE SMALL (7%) FRACTION OF 1.06 ixm RADIATION ABSORBED Disk absorber Ring absorber Heater wires -. Thermoelectric »x / modules Pyrex shield Protective jacket Heat sink Figure 10 9/76 Plasma calorimeters r Window, wedged rThermoelectric module r Resistor Ring Disc, receiver Jacket Base block LC-27 rWindow wedged rThermoelectric module S3) Cylinder* Receiver disc^ Base block -Figure 11 Figure 12 o 0) CO CO 0) gure E si|OA X-ray calorimeter -Window, wedged Jacket Base block • 2 \ Thermoelectric module-1 esistor Figure 14 Faraday cup Cover Screen 100 LN pairs/in. Spacer Figure 15 Figure I f 

Energy balance measurements for Shiva

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