Progress in UCSD Chamber Simulation Experiments Farrokh Najmabadi Sophia Chen, Andres Gaeris, John Pulsifer HAPL Meeting December 5-6, 2002 Naval Research Lab, Washington, DC Electronic copy: http://aries.ucsd.edu/najmabadi/talks UCSD IFE Web Site: http://aries.ucsd.edu/ife
Thermo-mechanical Response of the Wall Is Mainly Dictated by Wall Temperature Evolution Wall response depends strongly on the spectrum of incidence energy from the target blast. Target designs are not finalized and target spectrum is not known; There is no simulation source that can completely simulate the energy spectrum from the target. Most phenomena encountered depend on wall temperature evolution (temporal and spatial) and chamber environment. Only sputtering and radiation (ion & neutron) damage effects depend on how the energy is delivered. In In order to to develop predictive capability: Focus on on achieving temperature profiles similar to to those expected in in a laser-ife wall wall (Laser, ion ion source and and X-rays can can all all do do this). this). Measure and and understand the the wall wall response in in the the relevant range of of wall wall temperature profiles and and in in real real time. time.
Thermo-Mechanical Response of Chamber Wall Can Be Explored in Simulation Facilities Requirements: Laser Laser pulse pulse simulates Capability to to simulate a variety temperature evolution of of wall wall temperature profiles A suite suite of of diagnostics: Real-time temperature Per-shot Per-shot ejecta ejecta mass mass and and constituents Rep-rated experiments to to simulate fatigue fatigue and and material material response Relevant equilibrium temperature Vacuum Chamber provides a a controlled environment Capability to to isolate isolate ejecta ejecta and and simulate a a variety variety of of chamber environments & constituents
Components of Simulation Experiment Optical train Vacuum Chamber High-Temperature Specimen Holder Master Timing Control System Data Acquisition System Diagnostics: PIMAX & Spectrograph Thermometer IR Camera Quartz Microbalancing RGA Specimen preparation Operational. YAG laser is upgraded with injection seeding for reproducible and smooth temporal profile. Operational. Capable to below 10-8 Torr. Operational. Specimen equilibrium temperature can be maintained at up to 1,200 o C. Endurance runs of several hours have been made at 1,000 o C. Operational (~100ps gitter). Capable of single shot to 10 Hz. Operational (1GHz, 1.25 GS/s, upgradeable to 2.5GS/s). Operational. Calibrated externally (< 2% error). In-chamber shake-down and tests are in progress. Purchase is deferred (exploring alternatives). Purchase order is being placed. Purchase order is being placed. Procedure in place. Need measurement of thermophysical properties at elevated temperatures.
High Temperature Specimen Holder is tested to 1200 o C with endurance runs at 1000 o C. Specimen holder operating at 1000 o C Specimen holder is made of Mo Specimen Stainless steel vacuum seal Specimen is is heated heated by by radiation from from a a tungsten element element located located behind behind the the specimen. Thermocouple feed through Power feed through
Real-time Temperature Measurements Can Be Made With Fast Optical Thermometry Spectral radiance is is given by by Planck s Law Law (Wien s approximation): L(λ,T) = C 1-5 2 /λt) 1 ε(λ,t) λ -5 exp(-c 2 /λt) Since emittance is is a strong function of of λ, λ, T, T, surface roughness, etc., etc., deduction of of temperature from from total total radiated power has has large large errors. Temperature deduction by by measuring radiance at at fixed λ One-color: Use Use tables/estimates for for ε(λ) ε(λ) Typical error error < 25% 25% Two Two colors: Assume ε(λ ε(λ 1 ) ε(λ 2 ) 1 ) = ε(λ 2 ) Typical error error < 5 % Three colors: Assume d 2 2 ε/dλ ε/dλ 2 2 = 0 [usually a linear interpolation of of Ln(ε) is is used] Typical error error < 1 %
MCFOT Is a Natural Extension of Multi-color Optical Thermometry Published work work with with Multi-color Optical Thermometry: Complicated optical design Use Use fiber fiber optics Response time time of of > 10-100 µs µs Use Use fast fast PD PD or or PMT PMT MCFOT Multi-Color Fiber Optical Thermometry Simple design, construction, operation and and analysis. Can Can be be easily mounted inside a vacuum vessel. Easy Easy selection of of spectral ranges, via via filter filter changes.
Schematic of Multi-Color Fiber Optical Thermometer
Sensor Head can be focused to < 1mm 2 spots. Rugged design with accurate swivel controls allows sensor head to be focused to < 1mm 2 spots with a high degree of position accuracy. Steel Steel foil foil protects the the sensor head head from from thermal radiation.
Thermal radiation is injected by the Sensor Head into four bundled low-oh Silica fibers and relayed into fast PMTs
Each branch of the fiber bundle is filtered in a narrow spectral band by an interference filter and connected to a fast PMT
MCFOT is calibrated using the Optronics UL-45U lamp with a total error of < 3% 0.03 MCFOT calibration 8cm lens 0.02 (T cal -T 3C )/T cal 0.01 0-0.01-0.02-0.03 1200 1400 1600 1800 2000 2200 2400 2600 2800 T [K] 14 14 Calibration points points One One adjustable parameter (c (c 1 c 3 /c 22 ) 1 c 3 /c 22 ) cc i =V i (PMT) / i (Sensor head) i =V i (PMT) / L i (Sensor head)
MCFOT is installed in the chamber and shake-down tests are in progress System Improvements: Issue: Limited range of of voltage from from PMTs (need > ~ 5 mv mv for for good good SN SN ratio, ratio, PMT PMT output saturates around 200 200 mv) mv) Channel balancing by by using neutral density filters in in each each channel Balance between voltages from from calibration lamp lamp filament and and specimen to to be be handled by by a neutral density filter filter in in sensor head. Reliability Issues: Calibration: How How long long it it is is dependable? Speed: Individual PMT PMT response is is better than than 700 700 ps. ps. Would thermometer achieve the the same same response time? Sensitivity: what what is is the the minimal T measurable? Ease Ease of of use: use: mounting, alignment, interference, vacuum. Maintenance: Is Is it it foolproof? PMTs electrode degradation? Heat/vacuum damage to to optics/mechanicals? Fiber breakage?
Several Tungsten samples have been prepared for initial simulation experiments. Each Each sample has has its its own own pedigree. Samples have have been been prepared with with different initial polishing and and cleaning method. Pre-shot surface examination has has been been performed. Similar samples are are also also prepared for for testing at at RHEPP. Surface photograph of samples polished with 1 µm grit 500X Microscope WYKO
Development of predictable capability for the thermo-mechanical response of the chamber wall is the goal of UCSD simulation facility Experiment Assembly: Thermometer shakedown should be be completed by by Mid Mid January. Quartz Micro-balancing and and RGA should be be also also operational in in January. Experimental Studies: Temperature Response studies Impact of of surface morphology and and impurities/contaminants, etc. etc. Thermal Fatigue Studies Different temperature gradients, equilibrium temperature, etc. etc. Material Loss Loss Studies Survey of of impact of of surface temperature, surface morphology, impurities, etc. etc. NEED: Characterization of of thermophysical properties of of specimen at at high high Ts Ts
Backup Slides
QCM Measures Single-Shot Mass Ablation Rates With High Accuracy QCM: Quartz Crystal Microbalance Measures the drift in oscillation frequency of the quartz crystal. QCM has extreme mass sensitivity: 10-9 to 10-12 g/cm 2. Time resolution is < 0.1 ms (each single shot). Quartz crystal is inexpensive. It can be detached after several shots. Composition of the ablated ejecta can be analyzed by surface examination.
Prediction of chamber condition at long time scale is the goal of chamber simulation research. Chamber dynamics simulation program is is on on schedule. Program is is based on: on: Staged development of of Spartan simulation code. Periodic release of of the the code code and and extensive simulations while development of of next-stage code code is is in in progress. Documentation and and Release of of Spartan (v1.0) Two Two papers are are under preparation Exercise Spartan (v1.x) Code Use Use hybrid models for for viscosity and and thermal conduction. Parametric survey of of chamber conditions for for different initial conditions (gas (gas constituent, pressure, temperature, etc.) etc.) Need a series of of Bucky runs runs as as initial conditions for for these these cases. We We should run run Bucky using Spartan results to to model the the following shot shot and and see see real real equilibrium condition. Investigate scaling effects to to define simulation experiments.
Several upgrades are planned for Spartan (v2.0) Numeric: Implementation of of multi-species capability: Neutral gases, ions, ions, and and electrons to to account for for different thermal conductivity, viscosity, and and radiative losses. Physics: Evaluation of of long-term transport of of various species in in the the chamber (e.g., (e.g., material deposition on on the the wall, wall, beam tubes, mirrors) Atomics and and particulate release from from the the wall; wall; Particulates and and aerosol formation and and transport in in the the chamber. Improved modeling of of temperature/pressure evolution in in the the chamber: Radiation heat heat transport; Equation of of state; Turbulence models.