ARIES Documents -- Meetings ArchiveARIES Project Meeting, 7-8 June 2001
Documented by L. Waganer
Budget and DOE direction - Bill Dove explained that the FY02 budget is not firm at this date, but little change is expected from current funding levels - no major changes. The FY03 budget is just entering the planning stage. The big question is what project, or projects, should the ARIES team embark upon for FY03. Per Bill Dove, Sam Berk, and Farrokh Najmabadi; the likely candidates for a power plant study include a compact Stellerator (lots of interest in a POP experiment and community support), Reversed Field Pinch (also interest in a POP experiment and some advancements in confinement), or an IFE (also lots of interest and benefit of in-place ARIES team). A Z-pinch might be a possible IFE driver, per Craig Olson. The decision on which one or perhaps two design evaluations may depend upon the level of FY03 funding and the interest level in the near future.
Program status - Farrokh Najmabadi informed the group that about 35% of the current budget is allocated to MFE effort. This accomplishes an update of the ARIES systems code, collaboration with the EU on a new design study, and collaboration on a RFP design approach. The remaining budget is directed to IFE effort for investigation of wall and chamber design approaches as these are related to both direct and indirect drive targets. The DD dry wall evaluation is complete and is being documented. The DD and ID solid, protected wall and the ID dry wall concepts have just started on March 2001. The thick liquid wall for both DD and ID probably will not be considered due to time and money constraints and the difficulties associated with the large size penetrations.
Abstracts for the upcoming IEEE meeting should be sent to Farrokh Najmabadi for approval and coordination. If enough abstracts are received, the ARIES papers may be collected into a discrete session.
Next Meeting/Conference Call - It was recommended the next meeting be held in conjunction with the High Average Power Laser Workshop in October 2001 at LLNL. Farrokh Najmabadi will determine the best time for the ARIES meeting. The next ARIES conference call will be July 11, 2001 and Les Waganer will arrange for the conference call number.ARIES-IFE Study Presentations Systems Analysis and Integration
System Uncertainties - Ron Miller noted that he has modeled several target gain curves with polynomial curve fits to better work with the software he is using to evaluate major parameter uncertainties. He will continue to model the power balance similar to Prometheus, which he illustrated. Ron continues to assess the system uncertainties with available software tools.
Wetted Wall Chamber Trade Study Definition - On the May 2001 ARIES conference call, Les Waganer noticed that there did not seem to be an overall set of requirements for the wetted wall evaluation. To help develop a consensus of the desired and required wetted wall requirements, Les presented a strawman set of requirements and criteria for the wetted wall chamber system. The criteria addressed wall performance, lifetime, safety, and system availability. The team accepted most of the requirements. It was recommended the chemical and radioactive hazard should be changed to read ìAcceptable Hazardî. The chamber atmosphere and wall surface temperature should be low enough to minimize target heating. There should be no breakdown at the beam/chamber interface. The protectant should also help protect the first wall. Les also suggested a serial set of trade studies to narrow the choices in stages. (See revised charts on Web Site.) The team agreed with the concept, but noted a lot of overlap in the requirements, which suggested a single, multi-dimensional trade study, might be required.
Said Abdel-Khalik mentioned a problem concerning material properties being used by the ARIES team. He specifically was referring to the stated properties of liquid metals. Dai Kai Sze said that the basic data was correct, but errors occurred during unit conversions. Dai Kai Sze and Mike Billone will verify the correctness of all material database being used by the Team.Chamber Physics
Simulation of HI Beam Propagation - Dale Welch of Mission Research has been simulating HI beam propagation through the chamber. He told the ARIES team about the assisted pinch transport, self-pinch transport, and other transport issues. He described the physical layout of the beams, the final focusing system, pinch systems, and the chamber. The beams must be captured at small radius by 50 kA discharge current to form an adiabatic lens. A 6-MA electrical beam current has potential for huge self-fields given finite plasma conductivity. He noted a strong plasma return current could drive ìhoseî instability. Dale is using the quasi-3D EM hybrid IPROP code that simulates HIF beam interaction with discharge channel in both 2D and 3D. The specific input conditions were similar to those normally used for HI IFE power plant studies. The beam used Pb+72 ions. In his simulations, the effective current (the sum of discharge and self-currents) reached 80 kA. His results indicated a 87% of the beam energy was transported with a 3.5-mm RMS radius. He concluded the hose instability should not be a problem with the xenon gas case.
In the case of self-pinch transport, it relies on beam ionization in a low-pressure gas to achieve a high current beam after the ballistic focusing of the neutral beams. An intermediate gas density in chamber is possible. Dale has confirmed the self-pinch transport mechanism with certain constrains of gas pressure and plasma densities. The pinch mechanism is sustained after detachment from the wall. Additional investigation of 3D beam-to-beam interaction is underway. Some remaining issues remain - beam/gas interaction, beam losses, hose instability, steering and capturing the beam, and beam expansion.HI Beams and Vacuum System Layout
Consideration of HI beam/Vacuum System Arrangement - Les Waganer has been sharing design approaches and solutions on the HI beam and vacuum arrangement with Phil Heitzenroeder and Tom Brown of PPPL. In the meeting, Les Waganer presented the similarities between the current HI design approaches being considered and those developed during the Prometheus conceptual study in 1990-1991. The shielding, beam layout, vacuum pumping and chamber to beam isolation are very analogous and some design solutions may be applicable in the current investigation. Les described the small beam penetration through the blanket and first wall was enabled by the use of a small, self-pinched beam (one from each side of chamber). The ballistic beams impinged on a lead vapor-stripping cell to create a highly charged beam suitable for self-pinch transport. This small opening significantly reduced the neutron streaming, chamber gas transport, and debris transport outward to the beamlines. At the bulk-shielding wall, small individual ports (just larger than the ballistic beams) helped reduce the streaming and transport of debris and chamber gases. Behind the shield, a vacuum chamber, with cryopumps, maintained an intermediate vacuum environment (10-5 torr) between the chamber environment (10 -1 torr) and the hard vacuum (10-9 torr) required in the beamlines. Additional shielding was also provided at the outer end of the vacuum chamber and down the interior of the beamlines for a suitable distance. The power core chamber was cylindrical with hemispherical ends to enable quick replacement of the first wall (5 year life) and the blanket (10 year life). Four Roots blowers are designed to maintain the chamber pressure at 100 mtorr Pb vapor.
Preliminary Studies of Plasma-Channel-Based Reactor Beam Transport Section - Paul LaMarche described the vacuum system analysis and physical layout of a vacuum system based upon a channel transport beam. This system is associated with the dry wall chamber concept filled with xenon gas. The final focus of 124 beams is 22 meters away (from the center of the power core?). The vacuum system assumes a transition region and then a seven stage pumping region, staged from 5 torr to 10-6 torr in the final focus magnets. He matched the pressure and pumping speed in each region. He also described how there are four sections in each region, with three active sections and one being regenerated. This effort concludes this years work and no more effort is planned until next year.Chamber Wall Engineering and Chamber Clearing
Dry Wall Response to the HIB (Close-Coupled) IFE Target - Don Haynes discussed the dry wall chamber response to the HIB target. The buffer gas is the best defense for the wall. He explained the HIB target has substantially more x-rays than the DD targets (25% vs. 5%) though the yields may be similar. Also the spectra are harder. Thus the protective gas must be more efficient in protecting the first wall. For the DD NRL target, little or no gas was required with a 6.5-m radius chamber. The SOMBRERO target required around 0.1 to 0.2 torr of buffer gas for a similar sized chamber. But for the HIB target and a 6.5-m radius wall, the chamber wall at 1000ƒC will survive with 240 mtorr or 1450ƒC with 300 mtorr. Survive is defined to be less than one monolayer of mass lost per shot. However this level of gas is still less than previously thought on SOMBRERO (5 torr). Increasing the pressure to absorb and re-emit target energy increases the wall temperature. The amount of xenon required to protect the first wall from vaporization by x-rays is sufficient to stop all but the energetic knock-on ions. Don asked if an accumulation of H and He isotopes in the first mm of the wall is a problem?
Dry Wall Evacuation Calculations - John Pulsifer discussed the requirements to sufficiently clear the dry wall chamber to restore equilibrium conditions up to a 10 Hz repetition rate. He found it was not possible to evacuate the xenon to down to 1/100 of equilibrium pressure (~ 1 mtorr), as it would take as much as 2.4 seconds. He checked the pumping rate for a single species (xenon) with the effects of D, T, and He production. He found that to get less than 10 mtorr at 10 Hz, a larger pumping area is needed or smaller xenon input rate. A reasonable leak rate of 8000 mbar-liter/sec of targets and xenon for an aperture of 50 cm diameter would achieve a repetition rate of 10 Hz.
Preliminary Dust and Debris Clearing Studies in an IFE Chamber - At the last ARIES meeting, Dave Petti posed the question, ìIs the chamber environment conducive to forming a fog of recondensing vapor?î Dave summarized the chamber environment issues and requirements: vaporized material might recondense between shots, dust production rate may be high, removal of dust must be fast and efficient, and safety consequences due to activated and/or chemically reactive dust. He described potential mechanisms for formation and growth of dust/particulate for the HYLIFE-II design and possible mobilization mechanisms. His analysis indicated nucleation, growth by condensation, and coagulation times are on a time scale less than the repetition rate, and thus this might be a potential concern to be studied in more detail in the future.
Completion of Assessment of Dry Chamber Wall Option - Rene Raffray graphically presented the results of his analysis of the dry wall thermal behavior for different chamber radii. As an example, for a chamber radius of 5 m, the annual sublimination loss is 1-10 µm with a surface temperature of 2,500ƒC. For a tungsten surface, the radius could be 4 m with no melting. At 3.5 m, the annual evaporation loss would be 1-10 µm/y with a surface temperature of 3765ƒC.
Rene also addressed the effect of unintended laser light on wall. He summarized that one must avoid or minimize shots with laser reflectance and must find an insitu repair technique.
Rene also presented the proposed outline for documenting the dry chamber wall report.
Initial Planning Activity for Assessment of Wetted Wall Option - Rene Raffray highlighted the wetted wall chamber issues: film flow (assure full coverage, uniformity, avoid dripping, droplet injection) and clearing (conditions suitable for target injection and beam propagation), energy deposition, aerosol creation, scope time scales for return to stable conditions, and model thermal and fluid dynamic behavior). This list is similar to that presented by Waganer.
IFE Wetted-Wall Chamber Engineering - Mofreh Zaghloul discussed the consequences the early evaporation of the protecting wet wall by the prompt x-rays and the trade study to choose protecting materials, direct or indirect drive, and after-blast effect. He described the expected vapor pressure, x-ray spectra and photon attenuation, and deposition for no gas and 0.5 torr xenon. He also discussed film response as modeled by kinetic model and volumetric model. The volumetric model proved the better one. The ID spectrum showed high mass evaporation rate.Chamber and Final Optics Nuclear Analysis
Neutron Wall Loading at Mirrors - Laila El-Guebaly reviewed the highlights of key shielding features, issues, concerns, findings, and recommendations from all the major IFE power plant studies accomplished over the past few decades. She gathered these data to develop shielding criteria for ARIES-IFE and propose a viable protection scheme for the ARIES-IFE optics. The optics (primarily addressing the optic nearest to the chamber) is a strong function of:
Laila reviewed candidate materials for the optic coatings, substrates, and coolants. She discussed the degradation mechanisms and associated effects. She presented data that indicated an Al 2O3 coating exhibit high swelling as compared to MgO or Spinel. Laila also compared the radiation effects at the first mirror for a target yield of 160 MJ and 400 MJ (bare Al mirror at 30 m). Laila proposed these shielding criteria for ARIES-IFE:
One of the main design approaches to establish is the use of open or shielded beamlines or a combination of these. Laila recommended the enclosure of the multiple beamlines with a thin tube to confine tritium and the vacuum region in a smaller volume. This also controls spread of condensables and dust while allowing atmospheric pressure in the surrounding building. The neutron traps can be made more effective. The beam ports should be as small as possible. Spinel should be used on the GIMM to lower neutron swelling. Anneal transmissive optics at as high a temperature as possible. Multiple defense systems should be used to help stop x-rays and ion debris.
Effect of Calcium on TBR of ARIES-RS Li/V Blanket - Laila El-Guebaly (inputs provided by W. Wiffin) discussed the effects of calcium on the breeding capability of the ARIES-RS blanket. Ca is used as an electric insulator over the V coolant duct material. Ca is one of the most efficient coatings and can be replenished in-situ during operation. However, more development is required on this Ca coating approach. There was a question about a negative impact on the tritium breeding if Ca is used. Laila conducted an analysis and the results indicated calcium degrades the TBR in a linear relationship (roughly - 0.012 TBR/atom%). The ARIES-RS has a high enough TBR to accommodate a calcium coating of up to 2 atom% and still achieve the requisite TBR = 1.10 without a design change. Higher Ca content is possible with design changes.Target Fabrication, Injection, and Tracking
Indirect Drive Target Injection - Ron Petzoldt discussed the major issues and related analyses for HIB ID targets used in a thick liquid jet-protected chamber. Ron described the main design features of the ID hohlraum and capsule target. The injection speed is assumed to be 100 m/s with an acceleration of ~ 2500 m/s2, yielding an acceleration length of 2 meters. The exterior of the hohlraum is assumed to be covered with flibe to be compatible with the flibe wall protectant. The capsule support membrane will probably accommodate the assumed acceleration and not experience excessive deflection or vibration. Heating of the capsule is not expected to be a problem. Ron described a flowing helium gas stream in the launch tube toward the chamber plus a mechanical shutter that should minimize flibe vapor up the tube.
A tracking experiment was accomplished at LBNL in 1996-1998. Accuracy must be improved for the accuracy required. Current target requirements are thought to be up to a velocity of 180 m/s with a position prediction accuracy of ±100 µm transverse position and ±300 µm axial position at the chamber center and 6 Hz for the power plant system. With a suitable environment inside the chamber, in-chamber tracking may not be necessary.
Progress in IFE Target Fabrication - Dan Gooding reviewed the progress in IFE target fabrication. Three different potential target designs along with fabrication and injection scenarios are being investigated. Dan discussed the different methods to (currently) fabricate and inspect different target designs. In addition, mass production methods are being considered to transition to experimental and commercial applications. Fluidized bed is one potential manufacturing process. Dan described in detail the fabrication and inspection of the high-Z coatings, target coatings, and layering. After the meeting, Ken Shultz took a small group to GA to inspect their (low production rate) target production facilities.Assessment of Off-Normal Events
The Impact of Off-Normal Shots on IFE Power Plant Performance - Don Steiner informed the team of the approach and objectives of the off-normal shot assessment study:
Don and his team have concentrated on identifying off-normal shots, their cause, and consequences. Specifically, off-normal shots with reduced yield and off-normal shots with zero yield. Presently, the team results are limited to observations. Action items have been proposed to improve the fidelity of the results.Safety Analysis
Progress on Accident Initiating Events Study for IFE Power Plant Designs - Dave Petti summarized the work on accident initiator identification based on the SOMBRERO as a representative commercial IFE power plant design. Other designs will be assessed later this year. Based upon similar and historical data, preliminary hazards analyses, and master logic diagrams, expected classes of initiators have been identified:
The SOMBRERO assessment did uncover several serious safety questions and concerns (primarily dealing with lithium oxide and radiological confinement). Radiological confinement was also a concern in OSIRIS and HYLIFE-II, which is just starting to be assessed. The use of flibe in several power plants is also a concern. Commercial operation of a very large KrF lasers also pose a safety risk.