Experimental study of flibe vapor condensation

University of California, Los Angeles

Presented by:

P. Calderoni

Town Meeting on IFE Liquid Wall Chamber DynamicsLivermore, CAMay 5-6, 2003

Staged implementation of Flibe use

Stage ISource testing

Stage IIDiagnostic

Stage III

flibe

2/3 LiF + 1/3 BeF2in moles

Casting disks with ¼inch central bore forplasma source sleeve

Total amount ofpurified flibe availablefor experiments:1 liter from INEEL

Transparent plasticchamber for easyvisualization (low T)

Materials:• plastic polycarbonate(Lexan)• Teflon (CF2 molecularchain)• Metals (Tin, Al)• Flibe

SS chamber with viewports, insertion portsand heater for high T

Spectroscopy:• Teflon (CF2 molecularchain)• LiF

Pressure history - noncondensable gases:• LiF

Chamber pressure history

Endevco absolute sensor 8540-15:resonant frequency 140 kHzacceleration sensitivity 0.0004 psi / grange 15 psiasensitivity 26.55 mV / psia

Sensor mounted behind perforated screento protect from initial light emission anddiaphragm corrosion from free F

Sensor shows good sensitivity - it will be coupledwith standard Baratron sensors in the 0 - 1 Torrrange when non condensable gases areeliminated to compete the pressure history curve

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 960

-75.0x10

-61.0x10

-61.5x10

-62.0x10

-62.5x10

-63.0x10

-63.5x10

-64.0x10

-64.5x10

-65.0x10

Atomic Mass Units

Torr RGA Analog Scan Feb 06, 2003 01:26:13 PM

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 960

-61.0x10

-62.0x10

-63.0x10

-64.0x10

-65.0x10

-66.0x10

-67.0x10

-68.0x10

-69.0x10

-51.0x10

Atomic Mass Units

TorrRGA Analog Scan

Mass spectroscopy for residual gases analysis

Residual chamberpressure: 2 Torr

Residual chamberpressure: 32 Torr

LiF

CF2

28 peak accounts in both cases for morethan 50% of the total pressure. It is acomplex peak that accumulatescontributions from N2, CO, CO2 and traces ofmore complex hydrocarbons such as ethane

Air (Nitrogen) can be evaluatedby the 14 peak of dissociated N

Residual gas composition in thechamber for LiF shot evaluatedwith RGA correction factors:

CO, CO2, Hydrocarbons: 1100 mTorrN2: 180 mTorrHO2: 40 mTorrO2: 30 mTorr

LiF: 180 mTorr

Chamber pressure history

PCB dynamic sensor 112A22:resonant frequency 250 kHzacceleration sensitivity 0.002 psi / gdynamic range 50 psiresolution 0.001 psi Electrically coupled noise

reduced by correctisolation and grounding

Mechanical vibrationexcites resonant noise

Sensor has low sensitivity

Used only to measure initialpressure peak

Sensor mounted in the chamber with no screen

Sleeve ablated mass: CF2 experiments

The electro-thermal source

Characterization of superheated vapor generationshows measured parameters similar to SIRENS

Typical vapor parameters in the source :

n = 1019 - 1020 # / cm3

T = 1-3 eV

Cu triggering wire vaporizes (10-100nanos) forming initial plasma column

Close Ignitron switch

Energy stored in cap banks maintainsplasma at 1-3 eV for 100 micros

Injected electrical power radiated tosurface, ablates material of interest

Pressure gradient drives injection,ablation balances axial mass loss

The electro-thermal source

Chamber upper flange

Connection to return leg and vacuum sealing

LiF superheated vapor injection - lowtemperature materials configuration

Sleeve (LiF)configuration

Vaporsource

Condensationchamber

Experimental facility

Turbo pump andRGA system

Pressure sensors

Air-lockmechanism

-HV PS

C=52µF

R=10mΩJ

R=1-10Ω

R=1-10Ω

D1

IG1

Coaxial Plasma Gun

Tri-Plate Transmission Line

J

J J

IG2 (Optional Crowbar)

DumpSwitch

R=20Ω

Pulse Forming Network scheme

Triggering wire eliminated thepossibility of secondary discharges

Enhanced reliability of thesource is key for flibe

Measured electrical parameters of typicalteflon shots during facility testing - powerinjected in the superheated vapor is V x I

Measured discharge parameters

Light emission characterization

0 0.1 ms 0.2 ms 1 ms 1.5 ms 2 ms 2.5 ms 3 ms

Frame sequences recordedwith high speed camera -10,000 frames per secondand shutter speed of 100 ms

Time 0

820 µs

1640 µs

Lexan shots

0.0001 0.0002 0.0003 0.0004 0.0005

0.0030 0.0032 0.0034 0.0036 0.0038

Light emission characterization

Metal vapors characterization:tin shot

With metal sleeves formation of aliquid metal layer occurs over theablated surface

The liquid falls by gravity in thechamber - droplet size too large tobe homogeneous volumetriccondensation

Discharge completed 300 µs after trigger

High energy flibe shot

Current peak 110 kA

Light emissioncharacterization

Injected debris

Emission spectroscopy

Objective:

Locally map the partial density of neutral Li, LiF and Be, BeF2as a function of time over the whole chamber clearing period

Neutral species temperature can also be inferred withadditional development

Injected vapor spontaneous emission is short lived, and superheatedvapor properties are far from optimal for spectroscopy measurements -high density and low temperature

The high-voltage arc is under testing in steady state conditionswith LiF vapors

The arc will excite the vapor locally, allowing to analyze the differentproperties of vapor in the volume bulk or near a condensing surface

An high-voltage arc is used to re-excite the condensing vapor and analyzeradiation emission at different times - excited vapor can reach up to 30 eVtypically and densities will drop as the vapor condenses

Emission spectroscopy - CF2 shot

Goal: find suitable lines fortime resolved spectroscopythat can be analyzed withall materials of interest (F)

Due to non-uniform excitedvapor generated with thetriggering wire, Cu linesdominate the spectrum inthe initial phase

Preliminary results oftime resolved analysisof a Cu line with aphoton multipliershowed metal emissionis confined in the firstmillisecond

Cu lines dominate because metalions are highly excited - mass isless then 1% of total vapor

F lines: 703.7 (610.3, 670.8) nm

Continuos recombination emissionintensity comparable to F lines - Fneutrals high excitation potential

Extensive analysis of theUV range with filtersperformed to find F linesunsuccessful

Emission spectroscopy - LiF shot

Key feature:low excitation potentialof Li (and Be) atoms

Strong Li lines:

548.3, 610.3, 670.8 nm

Jet velocity opticalmeasurement system

Diode axis separation:7.62 cmPeak time delay:6 microsecondsEstimated initial vapor velocity:12700 m/s

Jet velocity optical measurement system

Sensor closer tocenter of chambersees a second peakin the light, about2ms after triggering

Peak due to firstreflection of thevapor jet at thechamber bottom

Vapor cools andexpands in thechamber, emittingfront does not reachthe upper sensor

Estimated averagevelocity of vapor inthe chamber afterfirst reflection:320 m/s - 4 kV210 m/s - 3 kV

Experimental planReduce to minimum traces of non condensable gases in the chamber -extend pressure history to mTorr range:

add air-lock system in the plasma source to avoid open chamberto air each shot to change triggering wire

new, clean chamber for LiF shots - no C contamination

Measure LiF chamber clearing rates and characterize amount andcomposition of non condensable gas to define accurate simulationsconditions for Tsunami / condensation code

Complete development of emission spectroscopy system - measuredensity of Li atoms and LiF molecules at different times in the bulk volumeand near a condensing surface - analyze data and provide conditions foraccurate simulations with Tsunami / condensation code

Insert flibe disks in the source - measure the effect of the added presenceof BeF2 in the vapor