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Deposition of maximum laser energy into a small, high-Z enclosure in a short laser pulse creates a hot environment. Such targets were recently included in an experimental campaign using the first four of the 192 beams of the National Ignition Facility [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technology 26, 755 (1994)], under construction at the University of California Lawrence Livermore National Laboratory. These targets demonstrate good laser coupling, reaching a radiation temperature of 340 eV. In addition, the Raman backscatter spectrum contains features consistent with Brillouin backscatter of Raman forward scatter [A. B. Langdon and D. E. Hinkel, Physical Review Letters 89, 015003 (2002)]. Also, NIF Early Light diagnostics indicate that 20% of the direct backscatter from these reduced-scale targets is in the polarization orthogonal to that of the incident light.

Gas filled halfraum experiments were conducted at the National Ignition Facility which provided an excellent test of the tools needed to understand halfraum energetics in an ignition relevant regime. The experiments used a highly shaped laser pulse and measured large levels of backscattered laser energy. These two components challenge the ability of radiation hydrodynamic simulations to model the experiments. The results show good agreement between experimental measurements and simulations.

An experimental campaign to maximize radiation drive in small-scale hohlraums has been carried out at the National Ignition Facility (NIF) at the Lawerence Livermore National Laboratory (Livermore, CA, USA) and at the OMEGA laser at the Laboratory for Laser Energetics (Rochester, NY, USA). The small-scale hohlraums, laser energy, laser pulse, and diagnostics were similar at both facilities but the geometries were very different. The NIF experiments used on-axis laser beams whereas the OMEGA experiments used 19 beams in three beam cones. In the cases when the lasers coupled well and produced similar radiation drive, images of x-ray bumthrough and laser deposition indicate the pattern of plasma filling is very different.

The first experiments on the National Ignition Facility (NIF) have employed the first four beams to measure propagation and laser backscattering losses in large ignition-size plasmas. Gas-filled targets between 2 and 7 mm length have been heated from one side by overlapping the focal spots of the four beams from one quad operated at 351 nm (3ω) with a total intensity of 2 × 1015 W cm−2. The targets were filled with 1 atm of CO2 producing up to 7 mm long homogeneously heated plasmas with densities of ne = 6 × 1020 cm−3 and temperatures of Te = 2 keV. The high energy in an NIF quad of beams of 16 kJ, illuminating the target from one direction, creates unique conditions for the study of laser–plasma interactions at scale lengths not previously accessible. The propagation through the large-scale plasma was measured with a gated x-ray imager that was filtered for 3.5 keV x-rays. These data indicate that the beams interact with the full length of this ignition-scale plasma during the last ~1 ns of the experiment. During that time, the full aperture measurements of the stimulated Brillouin scattering and stimulated Raman scattering show scattering into the four focusing lenses of 3% for the smallest length (~2 mm), increasing to 10–12% for ~7 mm. These results demonstrate the NIF experimental capabilities and further provide a benchmark for three-dimensional modelling of the laser–plasma interactions at ignition-size scale lengths.

Continued operation of the tokamak fusion test reactor (TFFR) with a mixture of deuterium and tritium fueling has permitted the opportunity to measure the retention of tritium in the graphite limiter and to investigate the use of discharge cleaning techniques and venting to remove the tritium. The tritium was introduced into TFTR by neutral beam injection and by gas puffing. The limiter is subject to erosion and codeposition. While short term retention was high, the retention averaged over the 1993–1995 D-T campaign was 52 ± 15%. The tritium removal techniques resulted in lowering the in-vessel inventory from 16.4 kCi (1 Ci = 2.076 × 1019 tritium atoms and 10 kCi = 1.04 g) at the end of 1995 operation to 7.2 kCi at the start of the 1996 experimental program.

The effect of isotope on confinement in high‐recycling, L‐mode plasmas is studied on the Tokamak Fusion Test Reactor (TFTR) [see D. M. Meade, J. Fusion Energy 7, 107 (1988)] by comparing hydrogen and deuterium plasmas with the same magnetic field and similar electron densities and heating power, with both Ohmic and deuterium‐neutral‐beam heating. Following a long operational period in deuterium, nominally hydrogen plasmas were created through hydrogen glow discharge and hydrogen gas puffing in Ohmic plasmas, which saturated the exposed limiter surface with hydrogen and raised the H/(H+D) ratio from 10±3% to 65±5%. Ohmic deuterium discharges obtained higher stored energy and lower loop voltage than hydrogen discharges with similar limiter conditions. Neutral‐beam power scans were conducted in L‐mode plasmas at minor radii of 50 and 80 cm, with plasma currents of 0.7 and 1.4 MA. To minimize transport differences from the beam deposition profile and beam heating, deuterium neutral beams were used to heat the...

Recent experiments on the Tokamak Fusion Test Reactor have afforded an opportunity to measure the retention of tritium in a graphite limiter that is subject to erosion, codeposition, and high neutron flux. The tritium was injected by both gas puff and neutral beams. The isotopic mix of hydrogenic recycling was measured spectroscopically and the tritium fraction T/(H+D+T) transiently increased to as high as 75%. Some tritium was pumped out during the experimental run and some removed in a subsequent campaign using various clean‐up techniques. While the short term retention of tritium was high, various conditioning techniques were successful in removing ≊8000 Ci and restoring the tritium inventory to a level well below the administrative limit.

The National Ignition Facility’s full-aperture backscatter station (FABS) is described. The FABS uses five independent diagnostics on each of the four laser beams in the initial National Ignition Facility quad to measure the energy, power, spectrum, and near-field amplitude modulations of the stimulated Brillouin and stimulated Raman backscattered light. In initial tests CO2 and C5H12 gas-filled targets were used to create various laser–plasma interaction conditions which have shown the capability of producing ignition size laser plasmas with reflectivites on the order of 10%. Results are presented for tests in which 16 kJ on target produced between 0.3 and 2.5 kJ of backscattered light.

A full aperture backscatter station (FABS) target diagnostic has been activated on the first four beams of the National Ignition Facility. FABS measures both stimulated Brillouin scattering and stimulated Raman scattering with a suite of measurement instruments. Digital cameras and spectrometers record spectrally resolved energy for both P and S polarized light. Streaked spectrometers measure the spectral and temporal behavior of the backscattered light. Calorimeters and fast photodetectors measure the integrated energy and temporal behavior of the light, respectively. This article provides an overview of the FABS measurement system and detailed descriptions of the diagnostic instruments and the optical path.

In November of 1993 the tokamak fusion test reactor began operating with a deuterium-tritium fuel mixture instead of the pure deuterium which it had used heretofore. The major portion of this tritium has been supplied as energetic neutral particles injected by the neutral beams. After an initial run in which some ion sources used a mixture of 2% T and 98% D to test tokamak systems, full tritium beam operations commenced, with some of the ion sources run on pure tritium and some on deuterium to optimize the fuel mixture in the core plasma. Hundreds of tritium source shots have now occurred, with reliability which is better than that typical of deuterium operation. The maximum power injected with deuterium and tritium beams was 39.6 MW. D-T fusion power levels of up to 10.7 MW have been produced. Energy confinement in D-T plasmas of the “supershot” variety appears to be better than in similar deuterium plasmas.

Analysis of Doppler‐shifted Balmer‐α line emission from the Tokamak Fusion Test Reactor’s (TFTR) neutral beam injection systems has revealed that the line shape, which is a direct measure of the velocity distribution function, is well approximated by the sum of two Gaussians, or, alternatively, by a Lorentzian. For the sum of two Gaussians, the wide‐divergence part of the distribution contains 40% of the beam power and has a divergence five times that of the narrow part. Assuming a narrow 1/e‐divergence of 1.3° (based on fits to the beam shape on the calorimeter), the wide part has a divergence of 6.9°. The entire line shape is also well approximated by a Lorentzian with a half‐maximum divergence of 0.9°. Up to now, most fusion neutral beam modelers have assumed a single Gaussian velocity distribution, at the extraction plane, in each direction perpendicular to beam propagation. This predicts a beam transmission efficiency from the ion source to the calorimeter of 97%. Waterflow calorimetry data, however,...

The Tokamak Physics Experiment (TPX) is planned as a long-pulse or steady-state machine to serve as a successor to the Tokamak Fusion Test Reactor (TFTR). The neutral beam component of the heating and current drive systems will be provided by a TFTR beamline modified to allow operation for pulse lengths of 1000 s. This paper presents a brief overview of the conceptual design which has been carried out to determine the changes to the beamline and power supply components that will be required to extend the pulse length from its present limitation of 1 s at full power. The modified system, like the present one, will be capable of injecting about 8 MW of power as neutral deuterium. The initial operation will be with a single beamline oriented co-directional to the plasma current, but the TPX system design is capable of accommodating an additional co-directional beamline and a counter-directional beamline.

Peak fusion power production of 6.2 ± 0.4 MW has been achieved in TFTR plasmas heated by deuterium and tritium neutral beams at a total power of 29.5 MW. These plasmas have an inferred central fusion alpha particle density of 1.2 x 1017 m ₋3 without the appearance of either disruptive magnetohydrodynamics events or detectable changes in Alfven wave activity. The measured loss rate of energetic alpha particles agreed with the approximately 5% losses expected from alpha particles which are born on unconfined orbits.

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

Tokamak Fusion Test Reactor (TFTR) deuterium neutral beams have been operated unintentionally with significant quantities of extracted water ions. Water has been observed with an optical multichannel analyzer. These leaks were thermally induced with the contamination level increasing linearly with pulse length. Up to 6% of the beam current was attributed to water ions, corresponding to an instantaneous value of 12% at the end of a 1.5 s pulse. A similar contamination is observed during initial operation of ion sources exposed to air. Operation of new ion sources typically produces a contamination level of ∼2%, with cleanup to undetectable levels in 50–100 beam pulses. Approximately 90% of the water extracted from ion sources with water leaks was deuterated, implying that there is the potential for tritiated water production during TFTR’s forthcoming DT operation. It is concluded that isotope exchange in the plasma generator takes place rapidly, most likely as the result of surface catalysis. The primary c...

The first 96 and 192 beam vacuum Hohlraum target experiments have been fielded at the National Ignition Facility demonstrating radiation temperatures up to 340 eV and fluxes of 20 TW/sr as viewed by DANTE representing an ∼20 times flux increase over NOVA/Omega scale Hohlraums. The vacuum Hohlraums were irradiated with 2 ns square laser pulses with energies between 150 and 635 kJ. They produced nearly Planckian spectra with about 30±10% more flux than predicted by the preshot radiation hydrodynamic simulations. To validate these results, careful verification of all component calibrations, cable deconvolution, and software analysis routines has been conducted. In addition, a half Hohlraum experiment was conducted using a single 2 ns long axial quad with an irradiance of ∼2×1015 W/cm2 for comparison with NIF Early Light experiments completed in 2004. We have also completed a conversion efficiency test using a 128-beam nearly uniformly illuminated gold sphere with intensities kept low (at 1×1014 W/cm2 over 5 ns) to avoid sensitivity to modeling uncertainties for nonlocal heat conduction and nonlinear absorption mechanisms, to compare with similar intensity, 3 ns OMEGA sphere results. The 2004 and 2009 NIF half-Hohlraums agreed to 10% in flux, but more importantly, the 2006 OMEGA Au Sphere, the 2009 NIF Au sphere, and the calculated Au conversion efficiency agree to ±5% in flux, which is estimated to be the absolute calibration accuracy of the DANTEs. Hence we conclude that the 30±10% higher than expected radiation fluxes from the 96 and 192 beam vacuum Hohlraums are attributable to differences in physics of the larger Hohlraums.The first 96 and 192 beam vacuum Hohlraum target experiments have been fielded at the National Ignition Facility demonstrating radiation temperatures up to 340 eV and fluxes of 20 TW/sr as viewed by DANTE representing an ∼20 times flux increase over NOVA/Omega scale Hohlraums. The vacuum Hohlraums were irradiated with 2 ns square laser pulses with energies between 150 and 635 kJ. They produced nearly Planckian spectra with about 30±10% more flux than predicted by the preshot radiation hydrodynamic simulations. To validate these results, careful verification of all component calibrations, cable deconvolution, and software analysis routines has been conducted. In addition, a half Hohlraum experiment was conducted using a single 2 ns long axial quad with an irradiance of ∼2×1015 W/cm2 for comparison with NIF Early Light experiments completed in 2004. We have also completed a conversion efficiency test using a 128-beam nearly uniformly illuminated gold sphere with intensities kept low (at 1×1014 W/cm2 over 5 ...

Determination of two critical neutral beam parameters, power and divergence, are affected by the reflection of a fraction of the incident energy from the surface of the measuring calorimeter. On the TFTR Neutral Beam Test Stand, greater than 30% of the incident power directed at the target chamber calorimeter was unaccounted for. Most of this loss is believed due to reflection from the surface of the flat calorimeter, which was struck at a near grazing incidence (12{degrees}). Beamline calorimeters, of a V''-shape design, while retaining the beam power, also suffer from reflection effects. Reflection, in this latter case, artificially peaks the power toward the apex of the V'', complicating the fitting technique, and increasing the power density on axis by 10 to 20%; an effect of import to future beamline designers. Agreement is found between measured and expected divergence values, even with 24% of the incident energy reflected.

In the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Fusion 26, 11 (1984)], the highest neutron source strength Sn and D–D fusion power gain QDD are realized in the neutral‐beam‐fueled and heated ‘‘supershot’’ regime that occurs after extensive wall conditioning to minimize recycling. For the best supershots, Sn increases approximately as P1.8b. The highest‐Q shots are characterized by high Te (up to 12 keV), Ti (up to 34 keV), and stored energy (up to 4.7 MJ), highly peaked density profiles, broad Te profiles, and lower Zeff. Replacement of critical areas of the graphite limiter tiles with carbon‐fiber composite tiles and improved alignment with the plasma have mitigated the ‘‘carbon bloom.’’ Wall conditioning by lithium pellet injection prior to the beam pulse reduces carbon influx and particle recycling. Empirically, QDD increases with decreasing pre‐injection carbon radiation, and increases strongly with density peakedness [ne(0)/〈ne〉] during the beam pulse. To date, the best fusion resu...

TFTR long pulse ion sources have been operated with gas fed only into the neutralizer. Gas for the plasma generator entered through the accelerator rather than directly into the arc chamber. This modification has been proposed for tritium beam operation to locate control electronics at ground potential and to simplify tritium plumbing. Source operation with this configuration and with the nominal gas system that feeds gas into both the ion source and the center of the neutralizer are compared. Comparison is based upon accelerator grid currents, beam composition, and neutral power delivered to the calorimeter. Charge exchange in the accelerator can be a significant loss mechanism in both systems at high throughput. A suitable operating point with the proposed system was found that requires 30% less gas than used presently. The extracted D+, D+2, and D+3 fractions of the beam were found to be a function of the gas throughput; at similar throughputs, the two gas feed systems produced similar extracted ion fr...

Helium pumping on argon frost has been investigated on Tokamak Fusion Test Reactor (TFTR) neutral beam injectors and shown to be viable for limited helium beam operation. Maximum pumping speeds are ∼25% less than those measured for pumping of deuterium. Helium pumping efficiency is low, >20 argon atoms are required to pump each helium atom. Adsorption isotherms are exponential and exhibit a twofold increase in adsorption capacity as the cryopanel temperature is reduced from 4.3 K to 3.7 K. Pumping speed was found to be independent of cryopanel temperature over the temperature range studied. After pumping a total of 2000 Torr l of helium, the beamline base pressure rose to 2×10−5 Torr from an initial value of 10−8 Torr. Accompanying this three order of magnitude increase in pressure was a modest 40% decrease in pumping speed. The introduction of 168 Torr l of deuterium prior to helium injection reduced the pumping speed by a factor of two with no decrease in adsorption capacity.

A first set of shock timing, laser-plasma interaction, hohlraum energetics and hydrodynamic experiments have been performed using the first 4 beams of the National Ignition Facility (NIF), in support of indirect drive Inertial Confinement Fusion (ICF) and High Energy Density Physics (HEDP). In parallel, a robust set of optical and X-ray spectrometers, interferometer, calorimeters and imagers have been activated. The experiments have been undertaken with laser powers and energies of up to 8 TW and 17 kJ in flattop and shaped 1–9 ns pulses focused with various beam smoothing options. The experiments have demonstrated excellent agreement between measured and predicted laser-target coupling in foils and hohlraums, even when extended to a longer pulse regime unattainable at previous laser facilities, validated the predicted effects of beam smoothing on intense laser beam propagation in long scale-length plasmas and begun to test 3D codes by extending the study of laser driven hydrodynamic jets to 3D geometries.

195 tritium ion source shots were injected into Tokamak Fusion Test Reactor (TFTR) high power plasmas during December 1993–March 1994. In addition, four highly diagnosed pulses were fired into the calorimeter. Analysis of the Doppler shifted Tα emission of the beam in the neutralizer has revealed that the extracted ion compositions for deuterium and tritium are indistinguishable: 0.72±0.04 D+; 0.22±0.02 D+2; 0.07±0.01 D+3 compared to 0.72±0.04 T+; 0.23±0.02 T+2; 0.05±0.01 T+3. The resultant tritium full‐energy neutral fraction is higher than for deuterium due to the increased neutralization efficiency at lower velocity. To conserve tritium, it was used only for injection and a few calorimeter test shots, never for ion source conditioning. When used, the gas species were switched to tritium only for the shot in question. This resulted in an approximately 2% deuterium contamination of the tritium beam and vice versa for the first deuterium pulse following tritium. Data from the calorimeter shots indicate th...

The TFTR neutral beam computer system has expanded to provide an easy-to-use windowing and graphics environment for running the TFTR neutral beam injection system for D-T operations. Two SUN workstations are used for interactive analysis and display of neutral beam diagnostic and operational data. These systems are interfaced via Ethernet to another SUN computer which is used for data transfer and real-time analysis. The real-time analysis computer is linked to the TFTR Encore computer system via a DMA interface. Data acquisition and device control is performed on the Encore computers, and raw data is transferred via a memory-mapped approach to memory partitions and files on the SUN Analysis computer. Real-time analysis programs provide numerous displays to operators and engineers of operational data every 150 seconds. Physicists use X-window and OSF/MOTIF-based graphical user interfaces (GUIs) on the Diagnostic workstation to display interactive analysis of diagnostic data. These include X-window graphical displays of thermocouples, OMA, waterflow calorimetry, H-alpha duct and ion gauge data to the workstation. Neutral beam operations engineers also use a similar GUI to display interactive summary, power and ion source waveforms on the Operations workstation. In addition, these engineers have access to INGRES databases, which contain operational and analyzed data for the past several TFTR run periods. The Operations computer has a hard disk drive, which contains these INGRES databases and a database of restored analysis and raw data files. These files can be restored on demand from the TFTR computer system VAX cluster. The real-time Analysis computer also has a hard disk drive, which contains a database of the most recent analysis and raw data files.

The Tokamak Physics Experiment (TPX) will require a minimum of 8.0 megawatts of Neutral Beam heating power to be injected into the plasma for pulse lengths up to one thousand (1000) seconds to meet the experimental objectives. The Neutral Beam Injection System (NBIS) for initial operation on TPX will consist of one neutral beamline (NBL) with three ion sources. Provisions will be made for a total of three NBLs. The NBIS will provide 5.5 MW of 120 keV D/sup 0/ and 2.5 MW of partial-energy D/sup 0/ at 60 keV and 40 keV. The system also provides for measuring the neutral beam power, limits excess cold gas from entering the torus, and provides independent power, control, and protection for each individual ion source and accelerating structure. The Neutral Beam/Torus Connecting Duct (NB/TCD) includes a vacuum valve, an electrical insulating break, alignment bellows, vacuum seals, internal energy absorbing protective elements, beam diagnostics and bakeout capability. The NBL support structure will support the NBL, which will weigh approximately 80 tons at the proper elevation and withstand a seismic event. The NBIS currently operational on the Tokamak Fusion Test Reactor (TFTR) at the Princeton Plasma Physics Laboratory (PPPL) is restricted to injection pulse lengths of two (2) seconds by the limited capability of various energy absorbers. This paper describes the modifications and improvements which will be implemented for the TFTR Neutral Beamlines and the NB/TCD to satisfy the TPX requirements.

The TFTR (Tokamak Fusion Test Reactor) neutral beam injection system (NBIS) has performed injection experiments on TFTR since 1984. During the 1990 run period the NBIS exceeded previous levels, reaching a record 48 MJ (24 MW for 2 s) of neutral injected energy and, at a later date, a record neutral power of 33 MW, which produced a record plasma neutron source rate. The operation of the NBIS resulting in this performance, the equipment changes and operational improvements from the 1989 operating experience which contributed to achieving this result, and the techniques used to analyze the effects of these changes are discussed. >

The authors describe the design of the TFTR (Tokamak Fusion Test Reactor) NB (neutral beam) D-T Gas Injection System and the results of tests conducted to confirm its functionality. Detailed design is progressing for a NB TGIS (tritium gas injection system) which includes the option of injecting either H/sub 2/, D/sub 2/, or T/sub 2/ into each of the 12 neutralizers at ground potential based on limited experiments to date. Most commercial components have been ordered and fabrication of special hardware is underway. Additional tests are planned to confirm LPIS (long pulse ion sources) operations compatibility with neutralizer gas injection, to inject the gas through shorter tubes which would simplify installation and interactions in LPIS parameters with alternating gases between pulses from H/sub 2/ to D/sub 2/ /sup 3/He. Tests of piezoelectric valves operated with the plenum pressure feedback controller will be conducted and a prototype NB TGIS will be installed and tested on TFTR during the September 91 to May 92 operational period. Installation of the complete system will take place during the pre-tritium shutdown presently scheduled for 1992-3. >

Moderate atomic number neutral atoms have been injected into TFTR (Tokamak Fusion Test Reactor) plasma in an attempt to enhance plasma confinement through modification of the edge electric field. TFTR ion sources have extracted 9 A of 62-keV Ne/sup +/ for up to 0.2 s during injection into deuterium plasmas, and for 0.5 s during conditioning pulses. Approximately 400 kW of Ne/sup 0/ have been injected from each of two ion sources. Operation under these conditions was at full bending magnet current, with the Ne/sup +/ just contained on the ion dump. Modifications to permit operation up to 120 keV with krypton and/or xenon are described. Such ions are too massive to be deflected up to the ion dump with the beamlines as designed. The plan is to procure a 3600-A power supply and pulse it into the magnet for initial Kr/Xe experiments. Information relevant to heavy ion operation was acquired during the course of ion source operation with small water leaks. Spectroscopic analysis of certain pathological pulses indicates that up to 6% of the extracted ions were water. After dissociation in the neutralizer, water produces oxygen ions which, as with Ne/sup +/, Kr/sup +/, and Xe/sup +/, are underdeflected by the magnet. Damage to a calorimeter scraper, due to the focal properties of the magnet, resulted. A power density of 6 kW/cm/sup 2/ for 2 s, from approximately 90 kW of O/sup +/, is the probable cause. >

The Tokamak Fusion Test Reactor (TFTR) vacuum system is being upgraded to trap SF/sub 6/ gas which may leak from the neutral beam injectors during the planned deuterium-tritium experiments. This is necessary since SF/sub 6/ can, in 25% of a gram-mole, completely inactivate the platinum catalyst in the tritium cleanup system (TCS). Any SF/sub 6/ leaking into the injectors will initially be held on the liquid helium or liquid nitrogen cryopanels. During regens of the liquid helium panel, the deuterium and tritium will pass to the TCS, with the SF/sub 6/ being retained on the cryopanels. In the final phase of the accident recovery scenario, the cryopanels will be warmed to room temperature and the SF/sub 6/ collected by a liquid-nitrogen cooled cold trap. Design of the cold trap and measurements of the vapor pressure of SF/sub 6/ at 77 K as a function of surface coverage are presented. The SF/sub 6/ vapor pressure at 77 K, with only a few monolayers absorbed, was found to be >

A method of analyzing the divergence characteristics of particle beams that utilize a Pierce geometry accelerator is described. The technique combines measurements of gradient grid current and arc current to develop an analytic expression, (perveance function), that could prove beneficial to beam operations. Unlike thermocouple or Doppler measurements of beam divergence, which only indicate the magnitude of the beam angle, the perveance function exhibits bipolar linearity with arc current changes. Additionally, the value of the arc current at which the perveance function equals zero is the operating point for minimum beam divergence. As a result, a single measurement with the perveance function can indicate whether the beam is overfocused or underfocused, and also determine the change in the magnitude and direction of the operating point to achieve optimum focus. This method is superior to present procedures, which tune the source by hunting for the minimum divergence. The perveance function is a relatively simple relationship that can be easily realized in hardware electronics or computer software. >

Early operation of the TFTR long pulse ion sources identified the full-energy ion dump as the critical constraint for long pulse operation. Full power, two second operation resulted in severe stress cracking of this component. Subsequent to this discovery, the dumps on all beamlines were replaced and new operating procedures implemented that restricted the surface temperature to that consistent with 120 kV for 0.65 s. In November, 1996 the ion dump in a tritium contaminated beamline was remotely inspected. No new damage was observed and the pulse length limit was relaxed to allow 95 kV, 5 A operation in support of enhanced reversed shear experiments. Two techniques have been proposed and partly tested that reduce ion dump power densities and permit longer pulse lengths. These are: 1) rastering of the ion beam across the ion dump, and 2) a vertical adjustment of the impact point on the full-energy dump. The latter of these techniques has applicability to the proposed Korean tokamak, KSTAR, which is currently using the TPX beamline (an upgraded TFTR beamline) as the basis for its design. Rastering consists of moving the ion beam laterally across the dump, thereby increasing the heated area. Based on static rastering experiments, the power density reduction due to several rastering patterns have been modeled. A 40% decrease in power density is predicted. Technique 2 stems from the curved nature of the full-energy ion dump-ions from the outer two ion sources strike lower on the dump than do ions from the center source. A small increase in the magnetic field moves the impact point higher up on the ion dump and farther from the magnet's focal point. The result is a 20% reduction in power density.

The Tokamak Fusion Test Reactor (TFTR) was supplied over 7.5/spl times/10/sup 5/ Curies combined through the vacuum vessel and Neutral Beam (NB) tritium gas injectors. Out of this quantity approximately 29,530 Curies (Ci) has entered the vacuum vessel as neutral atoms, including cold streaming gas and 20,270 Ci as direct vessel injection. TFTR has had two short term outages during DT operations Outage 1('95) and 2('96), plus the final shutdown, Outage 3 ('97), after DT operations in which tritium held up in the vessel and NB's has been actively recovered. The respective recovery values are: Outage (No.1) 8,257 Ci, (No.2) 4,668 Ci and (No.3 final shutdown) 3965 Ci. The methods for recovering this included: 1. Vessel baking to 150/spl deg/C during Deuterium Glow Discharge Cleaning (DGDC), 2. Helium/Oxygen GDC (HeOGDC), 3. Pulse Discharge Cleaning (PDC), 4. Continuous moist air purges and 5. Dry air, moist air (40% RH), and deuterium vent/soak/pump. The processes showing equivalent efficiency are the GDC, HeOGDC, and moist air purges at elevated temperatures. A small amount of tritium is introduced in the vessel at high energy through the NE /spl sim/3% relative to that supplied to the beam lines and /spl sim/1/2 of this is essentially buried in the carbon composite tiles and has a longer time constant for removal than the direct vessel injected tritium. Data shows that the bulk of surface tritium is removed by active cleaning methods and in the presence of moist air purges (room air at /spl sim/40% relative humidity) combined with elevated temperatures which accelerates its removal. Continuous outgassing at low levels in the presence of moist air (750 Torr) follows the active tritium removal processes and moist air purges. The TFTR tritium removal processes and their corresponding removal rates and quantities are reported. An ion chamber is used to measure the tritium accumulated in the Gas Holding Tanks (GHT) from the vessel throughout all the active and passive processes. The ion chamber compensation for varying gas mixtures was found to be critical in accurate measurement of this recovery and is discussed.

Several ion sources failed during the last months of TFTR operation. Four suffered are chamber vacuum leaks which admitted SF/sub 6/ into the source. One of these also had warped accelerator rails which resulted in damage to a water cooled scraper. The arc chamber leaks occurred at the boundary between the probe plate and either the bucket or interface plate. Vacuum seals at those locations consist of a mylar insulator sandwiched between two o-rings. At the failure point, the mylar had been punctured back to the o-ring. Are tracks were observed along the plasma facing surfaces of the probe plate and were funneled into every other gap between magnet. This evidence is suggestive of J/spl times/B forces driving the arcs toward the interface between the various plates and toward the o-ring. Damage is correlated with high arc power and the failure to expeditiously extinguish the arc. Operation with additional anode area is suggested as a means to avoid are creation. On the source with the warped grid rails, a section of a nearby scraper was melted. TFTR ion sources are masked down versions of the US Common Long Pulse Ion Source. Four rails on either end of the source are masked creating an ion beam that is /spl sim/43 cm tall. Rails under the mask were the most deformed (0.055" out of tolerance). Damage is believed to have occurred during 3 s pulses when 15 MJ were extracted over 3 s under slightly overdense conditions. The rails were deflected back towards the arc chamber causing the edge beamlets to be directed away from the axis.

750,000 Ci of tritium have passed through the TFTR neutral beamlines since December, 1993. During the course of 725 tritium heated discharges, 47,000 Ci have been extracted as ions from the ion sources and 27,000 Ci injected into TFTR as neutral atoms. Prior to the commencement of deuterium-tritium (DT) experiments, Los Alamos and Sandia National Laboratories made estimates of tritium retention in each beamline due to implantation in the 2 m/sup 2/ of copper beam absorbers and absorption on the 250 m/sup 2/ of internal surface area. Their estimates were: 500 Ci embedded per beamline in beam absorbers after 1000 DT Shots; and 100 Ci adsorbed per beamline after exposure to 1 torr of tritium for 1 hour. Both estimates were revised downward since the estimates assumed pure tritium operation, whereas the neutral beams used orders of magnitude more deuterium than tritium. Deuterium competes with tritium for implantation and adsorption sites, reducing the uptake of tritium relative to the use of pure tritium. Data from neutron detectors indicated that the quantity of tritium implanted is equivalent to the revised estimate. The amount of adsorbed tritium exceeds the prediction. While tritium operation was highly successful, there were problems with the failure of several ion sources and gas injectors. Ion source failures were not due to the use of tritium as the working gas. However, their removal yielded information regarding tritium retention. Ten tritium injectors failed during the three and a half years of tritium experiments; six were replaced. At the conclusion of TFTR operation, all working tritium injectors had throughput leaks. By comparison, the deuterium injectors, which used the same valves, had only two minor fill valve leaks, and no repairs were necessary. Tritium contaminated component removal required purging until the concentration of tritium in any released air was

The TFTR Neutral Beam Tritium Gas Injection System (TGIS) has successfully performed tritium operations since December 1993. TGIS operation has been reliable, with no leaks to the secondary containment to date. Notable operational problems include throughput leaks on fill, exit and piezoelectric valves. Repair of a TGIS requires replacement of the assembly, involving TFTR downtime and extensive purging, since the TGIS assembly is highly contaminated with residual tritium, and is located within secondary containment. Modifications to improve reliability and operating range include adjustable reverse bias voltage to the piezoelectric valves, timing and error calculation changes to tune the PLC and hardwired timing control, and exercising piezoelectric valves without actually pulsing gas prior to use after extended inactivity. A pressure sensor failure required the development of an open loop piezoelectric valve drive control scheme, using a simple voltage ramp to partially compensate for declining plenum pressure.

Since December 1993, TFTR has performed DT experiments using tritium fuel provided mainly by neutral beam injection. Significant alpha particle populations and reactor-like conditions have been achieved at the plasma core, and fusion output power has risen to a record 10.7 MW using a record 40 MW NB heating. Tritium neutral beams have injected into over 480 DT plasmas and greater than 500 kCi have been processed through the neutral beam gas, cryo, and vacuum systems. Beam tritium injections, as well as tritium feedstock delivery and disposal, have now become part of routine operations. Shot reliability with tritium is about 90% and is comparable to deuterium shot reliability. This paper describes the neutral beam DT experience including the preparations, modifications, and operating techniques that led to this high level of success, as well as the critical differences in beam operations encountered during DT operations. Also, the neutral beam maintenance and repair history during DT operations, the corrective actions taken, and procedures developed for handling tritium contaminated components are discussed in the context of supporting a continuous DT program.

It is customary in high power neutral beam systems to use a 'V'-shaped calorimeter to stop and measure the beam. With proper instrumentation, it is possible to determine both the neutral beam power and divergence. By utilizing a near-grazing angle of incidence, the area over which the beam is in contact with the surface is increased, thereby decreasing the power density over the case of normal incidence. Thermocouples on the back of the calorimeter, in conjunction with real time fitting algorithms, are used to deduce the divergence from the thermal profile. This measurement implicitly assumes that the measured-profile corresponds to that of the incident beam. It is shown that such is not the case. Energetic particle reflection at near-grazing angle causes the thermal profile on the calorimeter to be more peaked than the incident distribution. The implications of this on the non-linear multiple regression technique of determining the divergence are discussed. With the aid of a reflection model, developed and applied to the beam from a typical TFTR ion source, it is shown that a peaked power density can be modelled. Neural networks are being studied as a means of supplanting the older regression technique of measuring divergence. Y-direction divergences have been successfully derived using a one-dimensional neural network.

A new diagnostic has been designed and commissioned that measures the profile of the beam in the halo channel of the Low Energy Demonstration Accelerator at the Los Alamos National Laboratory. This paper describes the algorithms written to analyze the data from that diagnostic, a combined wire scanner and halo scraper. These algorithms determine the safe insertions limit of the scrapers, spatially differentiate the scraper signal, amalgamate the wire scanner data with the differentiated scraper data, determine when both the core and combined distributions rise above the noise floor, and compute the moments of the combined distribution. Results of applying the algorithms to data acquired during experiments matching the beam into the halo channel are presented.

The Low Energy Demonstration Accelerator (LEDA), located at Los Alamos National Laboratory, utilizes a slow wire scanner to measure beam profiles. The beam energy is 6.7 MeV and the peak current is 100 mA. This wire scanner profile measurement is located in the High Energy Beam Transport (HEBT) section of the LEDA beam line. This section of beam line is used to expand the proton beam coming out of the LEDA Radio Frequency Quadrupole (RFQ) prior to impacting the beam-stop. The purpose of the scanner is to provide horizontal and vertical beam profiles. The wires or fibers are a Silicon Carbide (SiC) material, and are attached to an actuator driven by a stepping motor. The actuator drives the fibers through the beam in incremental steps. At each step, the amount of secondary electrons generated by the interactions of the proton beam and the wire are measured. From these incremental measurements the beam profile is constructed. This paper will discuss the operation of the scanner, two of the experiments conducted to understand the capability of the SiC wire to survive and some of the different uses of the beam profile data acquired during the ongoing commissioning of LEDA.

An optical multichannel analyzer has been used to measure beam divergence and composition. This measurement is usually performed near the center of the neutralizer or beyond the magnet. In the past, these locations suffered difficult beam composition analysis and low light intensity, respectively. It has been determined that the light emission is relatively independent of neutralizer line density in the near field, allowing near‐field measurements to overcome both difficulties. At optimum perveance, but under conditions of high gas throughput, the helium 1/e divergence angle was measured to be 1.5°. Further investigation found that the divergence decreased with gas throughput down to 1.25°. Minimum divergences for the full‐, half‐, and third‐energy hydrogen components were 1.1°, 1.2°, and 1.4°, respectively. Relative neutral hydrogen particle fluxes available for injection into TFTR are a function of perveance. At maximum perveance, the full‐, half‐, and third‐energy atom fractions were 0.25±0.04, 0.5±0.04, and 0.25±0.05, respectively.

The Tokamak Fusion Test Reactor has operated since November of 1993 with a deuterium-tritium fuel mixture for selected discharges. The majority of the tritium has been introduced as energetic neutral atoms of up to 120 keV injected by the neutral beam systems, with some of the twelve ion sources run on pure tritium and some on deuterium to optimize the fuel mixture in the core plasma. A maximum beam power of 39.6 megawatts has been injected, and deuterium-tritium fusion power production has reached 10.7 megawatts, achieving central fusion power densities comparable to or greater than those expected for the International Thermonuclear Reactor, and allowing the first studies of fusion-produced alpha particle behavior in reactor grade plasmas. Energy confinement in deuterium-tritium plasmas is better than in similar deuterium plasmas for most plasma regimes. Innovative techniques to manipulate the plasma current and pressure profiles are permitting studies of enhanced confinement regimes.

A peak fusion power production of 9.3±0.7 MW has been achieved on the Tokamak Fusion Test Reactor (TFTR) in deuterium plasmas heated by co and counter injected deuterium and tritium neutral beams with a total power of 33.7 MW. The ratio of fusion power output to heating power input is 0.27. At the time of the highest neutron flux the plasma conditions are: Te(0)=11.5 keV, Ti(0)=44 keV, ne(0)=8.5×1019 m−3, and 〈Zeff〉=2.2 giving τE=0.24 s. These conditions are similar to those found in the highest confinement deuterium plasmas. The measured D‐T neutron yield is within 7% of computer code estimates based on profile measurements and within experimental uncertainties. These plasmas have an inferred central fusion alpha fraction of 0.2% and central fusion power density of 2 MW/m3 similar to that expected in a fusion reactor. Even though the alpha velocity exceeds the Alfven velocity throughout the time of high neutron output in most high power plasmas, MHD activity is not substantially different from that in co...

The Tokamak Fusion Test Reactor (TFTR) has performed initial high-power experiments with the plasma fueled by deuterium and tritium to nominally equal densities. Compared to pure deuterium plasmas, the energy stored in the electron and ions increased by ~20%. These increases indicate improvements in confinement associated with the use of tritium and possibly heating of electrons by α-particles.

TFTR deuterium neutral beams have been operated unintentionally with significant quantities of extracted water ions. Water has been observed with an Optical Multichannel Analyzer (OMA) during beam extraction when small water leaks were present within the arc chamber. These leaks were thermally induced with the contamination level increasing linearly with pulse length. 6% of the beam current was attributed to water ions for the worst leak, corresponding to an instantaneous value of 12% at the end of a 1.5 s pulse. A pre-calorimeter collimator was damaged as a result of this operation. A similar contamination is observed during initial operation of ion sources exposed to air. This latter contamination is attributed to the synthesis, from adsorbed air, of either D[sub 2]O or the indistinguishable ND[sub 3]. Initial operation of new ion sources typically produces a contamination level of [approximately]2%. These impurities are reduced to undetectable levels after 50 to 100 beam pulses. Once a water molecule is present in the plasma generator, it is predominantly ionized rather than dissociated, resulting in the extraction of only trace amounts of hydrogenated ions. The addition of water to the extracted beam also reduces the optimum perveance, moving the typical underdense operating point closermore » to optimum, causing the frequency of grid faults to increase. Close to 90% of the water extracted from ion sources with water leaks was deuterated, implying that the potential exists for the production of tritiated water during TFTR's forthcoming DT operation. Isotope exchange in the plasma generator takes place rapidly and is believed to be surface catalyzed. The primary concern is with O implanted into beam absorbers recombining with tritium, and the subsequent hold up of T[sub 2]O on cryopanels. Continuous surveillance with the OMA diagnostic during DT operation will ensure that ion sources with detectable water are not operated with tritium.« less

The extreme physics of targets shocked by NIF's 192-beam laser is observed by a diverse suite of diagnostics. Many diagnostics are being developed by collaborators at other sites, but ad hoc controls could lead to unreliable and costly operations. A diagnostic control system (DCS) framework for both hardware and software facilitates development and eases integration. Each complex diagnostic typically uses an ensemble of electronic instruments attached to sensors, digitizers, cameras, and other devices. In the DCS architecture each instrument is interfaced to a low-cost WINDOWS XP processor and JAVA application. Each instrument is aggregated with others as needed in the supervisory system to form an integrated diagnostic. The JAVA framework provides data management, control services, and operator graphical user interface generation. DCS instruments are reusable by replication with reconfiguration for specific diagnostics in extensible markup language. Advantages include minimal application code, easy testing, and high reliability. Collaborators save costs by assembling diagnostics with existing DCS instruments. This talk discusses target diagnostic instrumentation used on NIF and presents the DCS architecture and framework.

A technique is described whereby the ion dumps inside the TFTR Neutral Beam Test Stand were used to measure thermal profiles of the full-, half-, and third-energy ions. 136 thermocouples were installed on the full-energy ion dump, allowing full beam contours. Additional linear arrays across the widths of the half- and third-energy ion dumps provided a measure of the shape, in the direction parallel to the grid rails, of the half- and third-energy ions, and, hence, of the molecular ions extracted from the source. As a result of these measurements it was found that the magnet was more weakly focusing, by a factor of two, than expected, explaining past overheating of the full-energy ion dump. Hollow profiles on the half- and third-energy ion dumps were observed, suggesting that extraction of D{sub 2}+ and D{sub 3}+ are primarily from the edge of the ion source. If extraction of half-energy ions is from the edge of the accelerator, a divergence parallel to the grid rails of 0.6{degrees}{plus minus}0.1{degrees} results. It is postulated that a nonuniform gas profile near the accelerator is the cause of the hollow partial-energy ion profiles; the pressure being depressed over the accelerator by particles passing through this highlymore » transparent structure. Primary electrons reaching the accelerator produce nonuniform densities of D{sub 2}+ through the ionization of this across the full-energy dump was examined as a means of reducing the power density. By unbalancing the current in the two coils of the magnet, on a shot by shot basis, by up to 2:1 ratio, it was possible to move the centerline of the full-energy ion beam sideways by {approximately}12.5 cm. The adoption of such a technique, with a ramp of the coil imbalance from 2:1 to 1:2 over a beam pulse, could reduce the power density by a factor of {ge}1.5.« less

An Optical Multichannel Analyzer has been used to measure beam divergence and composition. This measurement is usually performed near the center of the neutralizer or beyond the magnet. In the past, these locations suffered difficult beam composition analysis and low light intensity, respectively. It has been determined that the light emission is relatively independent of neutralizer line density in the near field, allowing near-field measurements to overcome both difficulties. At optimum perveance, but under conditions of high gas throughput, the helium 1/e-divergence angle was measured to be 1.5{degree}. Further investigation found that the divergence decreased with gas throughput down to 1.25{degree}. Mimimum divergences for the full-, half-, and third-energy hydrogen components were 1.1{degree}, 1.2{degree}, and 1.4{degree}, respectively. Relative neutral hydrogen particle fluxes available for injection into TFTR are a function of perveance. At maximum perveance, the full-, half-, and third-energy atom fractions were 0.25 {plus minus} 0.04, 0.5 {plus minus} 0.04, and 0.25 {plus minus} 0.05, respectively. 10 refs., 5 figs.

Experiments done at the National Ignition Facility laser [J. A. Paisner, E. M. Campbell, and W. Hogan, Fusion Technol. 26, 755 (1994)] using gas-filled hohlraums demonstrate a key ignition design feature, i.e., using plasma pressure from a gas fill to tamp the hohlraum-wall expansion for the duration of the laser pulse. Moreover, our understanding of hohlraum energetics and the ability to predict the hohlraum soft-x-ray drive has been validated in ignition-relevant conditions. Finally, the laser reflectivity from stimulated Raman scattering in the fill plasma, a key threat to hohlraum performance, is shown to be suppressed by choosing a design with a sufficiently high ratio of electron temperature to density.

A platform for analysis of material properties under extreme conditions, where a sample is bathed in radiation with a high temperature, is under development. Depositing maximum laser energy into a small, high-Z enclosure produces this hot environment. Such targets were recently included in an experimental campaign using the first four of the 192 beams of the National Ignition Facility [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technol. 26, 755 (1994)], under construction at the University of California Lawrence Livermore National Laboratory. These targets demonstrate good laser coupling, reaching a radiation temperature of 340 eV. In addition, there is a unique wavelength dependence of the Raman backscattered light that is consistent with Brillouin backscatter of Raman forward scatter [A. B. Langdon and D. E. Hinkel, Phys. Rev. Lett. 89, 015003 (2002)]. Finally, novel diagnostic capabilities indicate that 20% of the direct backscatter from these reduced-scale targets is in the polarization orthogonal to that of the incident light.

Neutral beam injection into Doublet III has been considered with regard to the calculation of non thermalizing particle orbits and the confinement of such orbits. Injected particle loss, based upon these orbits, toroidal gyro-radius effects, and plasma transparency, is calculated to be on the order of 5 percent for coinjection. Near-perpendicular injection at 80 keV has been chosen with the resulting available injection window of 1014 cm-3 ? n(0) ? 3 × 1014 cm-3. Injection into plasmas with n(0) ? 1014 cm-3 will yield large losses due to the increasing transparency of the plasma, whereas injection into plasmas with n(0) ? 3 × 1014 cm-3 shifts the deposition profile toward the plasma edge.