[american institute of aeronautics and astronautics 22nd aiaa aerodynamic measurement technology and...

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22nd AIAA Aerodynamic Measurement Technology and Ground Testing Conference

24-26 June 2002

AIAA-2002-3130

A 1 MW RADIATIVELY-DRIVEN HYPERSONIC WIND TUNNEL EXPERIMENT

Dennis K. Mansfield, Jay H. Grinstead, Philip J. Howard, Garry L. Brown,Ihab Girgis, and Richard B. MilesPrinceton University, Princeton, New Jersey 08544

Ron Lipinski, Gary Pena, Larry SchneiderSandia National Laboratory, Albuquerque, New Mexico

Robert HowardSverdrup Technology, Arnold Air Force Base, Tennessee

22nd AIAA Aerodynamic Measurement Technology and Ground Testing Conference24-26 June 2002, St. Louis, Missouri

AIAA 2002-3130

This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

22nd AIAA Aerodynamic Measurement Technology and Ground Testing Conference AIAA-2002-3130

American Institute of Aeronautics &Astronautics2

A 1 MW RADIATIVELY-DRIVEN HYPERSONIC WIND TUNNEL EXPERIMENT

Dennis K. Mansfield, Jay H. Grinstead, Philip J. Howard*, Garry L. Brown±,Ihab Girgis§, and Richard B. Miles**

Princeton University, Princeton, New Jersey 08544

Ron Lipinski, Gary Pena, Larry SchneiderSandia National Laboratory, Albuquerque, New Mexico

Robert HowardSverdrup Technology, Arnold Air Force Base, Tennessee

INTRODUCTION

This work describes the present status of the Radiatively-Driven Hypersonic Wind Tunnel (RDHWT) experiments that are being carried out collaboratively by Princeton University and the Sandia National Laboratory. The experiments to be described are being performed at the Hawk Electron Accelerator Facility at Sandia National Laboratory in Albuquerque, New Mexico. The purpose of the experiments is to demonstrate the viability of the energy addition concept at approximately ten times higher a level of electron beam power (1MW) than has been attempted heretofore. The experiments are being conducted to validate existing energy-addition models and to develop a further understanding of physics issues involved with the addition of electron beam energy to supersonic flows [1]. Of primary importance in these experiments is the predictability of the flow conditions throughout the heat addition region, the quality and uniformity of the flow, the possible effects of electron charge build-up, and the presence of electron beam and thermally induced air chemistry.

The 1 MW experiments represent a continuation of previous energy addition experiments carried out at the HAWK facility that culminated in the injection of 150 kW from a 700 keV electron beam for times of

____________________________________*

Research Staff, Mechanical & Aerospace Engineering, Member, AIAA±

Professor, Mechanical & Aerospace Engineering, Associate Fellow, AIAA§

Research Staff Member, Mechanical & Aerospace Engineering, Senior Member, AIAA**

Professor, Mechanical & Aerospace Engineering, Fellow, AIAA

This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

approximately 1 ms [2,3,4]. The HAWK accelerator has been modified for these experiments so as to allow for the efficient injection of more power (1 MW) at a higher energy (1 MeV) and for a longer duration (5 ms). In addition, modifications have been made to the accelerator so as to sculpture the spatial profile of the electron beam power density into a quasi-rectangular “top-hat” form. Improvements to the electron beam delivery system are described more fully below.

The electron beam from the upgraded Hawk accelerator is turned and focused into a judiciously designed expansion nozzle from downstream using externally applied magnetic fields. The flow in the nozzle is expanding supersonic air from a high pressure (2650 psi), heated (650 K) plenum. So as to ensure minimal interaction of the e-beam with the nozzle, the configuration of external magnets is designed such that the resulting field lines are approximately parallel to the nozzle wall. A series of measurements are being made to determine the flow field in both the e-beam-heated and the unheated cases over a range of plenum and electron-beam conditions. These measurements include high-speed pressure and temperature along the nozzle wall, as well as optical measurements of the flow field at the nozzle exit.

A. Upgrade of Hawk Accelerator and E-Beam Delivery System

The 1 MW experiments involve numerous accelerator and electron beam delivery technology up-grades, several of which demonstrate technologies that are critical for a 200 MW, 1 meter test core scale hypersonic wind tunnel facility. Specifically, the up-grades include: (1) the capture of the electron beam by a magnetic field at the cathode so as to reduce the



transport and reflection losses observed in previous experiments, (2) the tailoring of the continuous magnetic field over various accelerator structures to minimize growth of beam oscillations, (3) the bending of the beam through a 45o angle into the nozzle, (4) the development of a plasma-aerodynamic window that eliminates the beryllium foil at the vacuum/air interface and allows long-duration high-power beams, (5) the establishment of a quasi “top hat” beam profile that is robust to scattering in the air, and (6) a tenfold increase in demonstrated power deposition. To meet the higher power requirements, the accelerator capacitor bank was increased in size, the driving electronics for the injector were upgraded, and the extraction grid was modified. Additional monitoring equipment also was installed on the injector, and a “plasma porthole” was added to the exit port.

Figure 1 shows the experimental configuration following the acceleration section of the Hawk. The electron beam exits the accelerator through the plasma porthole, bends 45o, and enters the blowdown nozzle to heat the air. The beam passes through its maximum constriction at the plasma porthole, where the small area minimizes the differential pumping requirements. That constriction is achieved with a 5 Tesla superconducting magnet at that location. Following the porthole, the 45o

bend is necessary to allow the high enthalpy air to miss the accelerator exit and the 5-Tesla magnet. This bend is prototypic of the configuration for a full-scale wind tunnel. Within the nozzle, the magnetic field increases from about 0.8 Tesla to 2.2 Tesla in order to compress the beam as it approaches the nozzle throat.

In order to reduce beam reflection losses and thereby improve e-beam transport, the accelerator cathode must be immersed in a magnetic field of approximately 0.2 Tesla. To create that axial field strength without extensive redesign of the Hawk, large pulsed solenoid magnets were externally wrapped around the Hawk accelerator pressurized tank. Figure 2 shows the final configuration of various solenoid magnets used from the cathode, through the plasma porthole, and to the nozzle. A fast valve is included to reduce the pumping load associated with the air drawn through the porthole. Figure 3 shows the resulting magnetic field strength along with the magnet positions along the beam path as determined by the Field Precision Bstat code [5]. The Field Precision electron trajectory code (Trak) has shown that the beam will follow the field lines and converge as desired in spite of the numerous steps in field strength. The 5 Tesla solenoid from American Magnetics [6], which has a 15-cm (6-inch) room-temperature bore, is large enough to allow the beam to bend around a 45o corner into the nozzle magnets while still allowing a clear path for the exit air. Figure 4

shows the Hawk accelerator with the large magnet windings wrapped around it and with magnets at the exit port. The superconducting magnet is not shown.

As the beam penetrates the nozzle air, scattering will occur and the beam density profile will evolve toward a Gaussian. A Gaussian profile leads to excessive wall heating and loss of efficiency. To help overcome this and flatten the center region, an annular cathode is used and high magnetic fields (up to 2.2 Tesla) in the nozzle are required. As scattering occurs in air the central hole fills in and results in a distribution that is more rectangular than Gaussian. Figure 5a shows the glowing annular cathode and Figure 5b shows the still doughnut shaped beam hitting a scintillator as it is extracted from the accelerator before it enters the air. The beam inner and outer diameters agree well with predictions of the Trak code, including transverse oscillations caused by step changes in the magnetic field strength. This demonstrates how well the beam follows the magnetic field lines in a vacuum.

At the contemplated power levels and pulse duration of the 1 MW experiment, it is not possible to employ the standard thin Be window technology to couple the e-beam out of the high vacuum of the accelerator and into room air of the laboratory. Instead, an aerodynamic window has been developed consisting of several stages of differential pumping and a plasma porthole at the final interface with room air. The aerodynamic window serves as the transition between the high vacuum of the accelerator and room air. Because there is no material window involved, it is possible to deliver high power levels into the nozzle with low insertion losses. The plasma porthole, as developed by Hershcovitch at Brookhaven National Laboratory [7], produces an arc within the first aperture that heats the air to about 11,000 K. At this temperature the air is very rarified and has high viscosity. This greatly reduces the mass flow rate through the system and allows the use of much smaller pumps on the first stage. Figure 6 shows the plasma porthole installed at the end of the aerodynamic window.

B. The Wind Tunnel Facility

For the 1MW tests, a nozzle that duplicates the thermodynamic heat addition path of a radiatively driven, Mach 6.3, 150,000 foot altitude simulationfacility has been constructed. This represents a significant total enthalpy and pressure upgrade from the experimental configuration that was tested during the previous 100 kW energy addition experiments [4]. Clean, dry, compressed air is supplied in a commercial tube trailer that has a storage capacity of 124,000 ft3. The 2500 PSI delivery pressure is boosted to 6000 PSI



with a Haskel model 56131 air driven compressor and stored in a tank farm of twenty size 1U compressed gas cylinders. The pneumatic drive consumes about twenty percent of the supplied air in this boost process. The tank farm capacity is greater than 26 ft3 and, when charged to 6000 PSI, provides about 20 seconds of run time as the pressure drops to 5000 PSI. The booster compressor is capable of replenishing the 20 second runtime volume of air in about 6 hours.

The air is delivered to the test cell by a 1.5” schedule XXS stainless steel piping system that is acoustically and thermally insulated with two inch rock wool insulation with an aluminum skin. Upon entering the test cell, the gas passes through a triple set of rotary joints to comply with thermal expansion requirements and a dielectric union fitting to allow nozzle current measurements. Gas flow is started and stopped with a high speed (500mS to open) computer controlled pneumatically operated master control valve that is equipped with a spring operated fail safe closed position. The 6000 PSI delivery pressure is then reduced to 2650 PSI with a dome loaded pressure regulator. The regulator set point range of 500 to 3000 PSI is controlled from outside the test cell with a dome loader regulator and air supply. Downstream of the regulator, the piping size is increased to two inch schedule 160 stainless steel pipe. Air then passes through a “tee” fitting that has a pressure relief valve set at the maximum allowable working pressure of 3000 PSI in the branch leg. In the event of an overpressure condition, excess pressure is relieved through a 3” schedule 40 vent pipe to a safe direction from the building roof.

The cold air then enters a spring mounted pebble bed heater that has been preheated to 710°F. The heater is heated with electrical resistance band heaters at a rate of 6 KW and is designed for unattended operation. The storage media is a 40” long 10”schedule 160 stainless steel pipe filled with ¼” stainless steel balls. As shown in Figure 7, swivel joints and U bends are incorporated into the design of this heater to allow for both the large thermal expansion associated with the heating as well as the large thrust associated with the airflow. The design heat capacity of the heater allows four six second runs per day with a temperature droop of about 50°F at a 3kg/sec flow rate. Heated air follows piping to the stagnation section that is fabricated with three inch schedule 160 stainless steel pipe. A flange connects the stagnation section to an adapter flange that holds the nozzle and forms the upstream end of the nozzle magnet assembly.

A contoured nozzle is machined from two pieces of stock on a Bridgeport CNC milling machine and held together with stainless steel socket head cap screws and sealed with gold wire where required. The 56 cm-long nozzle was constructed of stainless steel and has a 11.4 mm throat diameter and a 25.6 mm exit diameter. Shaping of the nozzle contour was accomplished with a computer-numeric-control milling machine at Princeton. A typical blowdown lasting 10 seconds produces 30 Kg of heated air that must be exhausted into the ambient laboratory air. Two identical nozzles were machined: one from 316 stainless steel, and one from 6061 aluminum. The aluminum nozzle is used for unheated air alignment and testing runs. The heated air passes through the nozzle where pressure and temperature measurements are made at access points between the magnet coils. Cool process air flows down the outside of the nozzle through a 0.020” annulus and cooling water flows through each plate between the coils to keep the magnets cool.

After exiting the nozzle, the air is examined with diagnostic procedures before entering a cooler/diverter tunnel that cools and directs the air to the ceiling of the Hawk bay.

C. Predictive Modeling and the Design of the Nozzle Contour

In cooperation with Sandia, various numerical models of increasing complexity have been developed for the design and simulation of the axisymmetric fluid mechanics and energy addition for the 1MW experiment. A principal design target for this work is to have a throat diameter size as well as total enthalpy ratio, Hof/Ho, comparable to the Mach 12, 2000 psf dynamic pressure Missile Scale Hypersonic Wind Tunnel (MSHWT) design.

The ideal path for the 1MW experiment, compared with the MSWHT case, is shown in black in Figure 8. Taking into account the available pressure and temperature sources, the upstream stagnation pressure and temperature have been chosen to be 2600psi (~17.9MPa) and 650K, respectively. For the ideal path we have chosen, the flow is expanded isentropically to Mach 1.5 and then heat is added at constant Mach number. Heat is added until the desired total enthalpy ratio is achieved. For a test facility, the flow would then be expanded isentropically to Mach 6.3 to duplicate flight conditions in the atmosphere. In this experiment, only the heat addition process is under study, so the final expansion is a free jet into the laboratory. That jet is captured by the cooler/divertor and sent up toward the high bay ceiling.



To develop the nozzle shape an analytic form for the energy deposition was used. This analytic form was developed by the Sandia team fitting results obtained with the Monte Carlo, ITS code for a range of one-dimensional cases in which beam energy is deposited into uniform air. There is no particular physical basis for the formula (except possibly the Gaussian form), but it fits the ITS calculated data to better than 10% for beams in the 1MV to 5MV range. This formula was then used in conjunction with a quasi one-dimensional Euler flow solver. With this approach, an objective function and a simplex method was developed to find the optimized nozzle shape such that the thermo-dynamic path closely follows the ideal path. The results of the one-dimensional nozzle optimization for a 0.8MV e-beam are also shown in Figure 8, where the actual thermodynamic path that can be achieved is compared with the ideal path.

The quasi-optimized nozzle shape for the heat addition region was thus determined analytically. This one-dimensional calculation was only a first step towards a much more accurate Monte-Carlo simulation of the energy deposition and a fully coupled two-dimensional fluid mechanics calculation including a buffer annulus of air that removes the wall farther from the core flow and minimizes the e-beam wall heating. In this ideal case, it was assumed that the outer annular flow would not be heated. The corresponding outer annular area distribution was calculated by assuming an isentropic outer flow and a pressure at each downstream location that was the same as it was for the heated core flow determined by the one-dimensional solution.

The throat diameter determined from one-dimensional considerations was approximately 5.7 mm. This diameter was increased to 11.4 mm to provide for the outer annular flow and reduce the heat losses to the wall. This increased throat diameter resulted, of course, in a mass flux (2.89 kg/sec) that is four times larger than the ideal one-dimensional mass flux. The modified, optimal nozzle shape is shown in Figure 9. The white lines indicate the boundary between the outer annulus and the heated inner core flow.

With this overall approach to the development of the nozzle shape in the heat-addition region it was then possible to use the full two-dimensional Euler simulation, coupled with the detailed Monte-Carlo simulation for the energy addition, to determine how closely this idealized approach could achieve the desired test-section conditions. In addition, it was possible to evaluate whether a shock free flow could be obtained.

In the inviscid case, the axisymmetric Euler equations are discretized using a second-order cell centered, finite volume scheme in space and four point Runge-Kutta scheme in time. The Jameson-Schmidt-Turkel scheme is used so that any shock formation is captured. The steady-state heat addition to every cell is found by an iterative approach in which the density calculated from this Euler flow solver is provided as an input to the ITS, Monte-Carlo, e-beam simulation code and the resultant energy lost from the e-beam in each cell is then transferred to the Euler code as the local heat-addition for a given cell. This iterative approach was adopted and a converged solution was obtained in 3 iterations.

Taking into account the improvements in e-beam heating profile and with the approach and models described above, results were obtained for the fully coupled, inviscid simulation of the 1 MW experiments. Further calculations have been completed using the two-dimensional Reynolds Averaged Navier-Stokes equations and the Baldwin-Lomax turbulence model in order to include boundary layer effects. The nozzle area distribution was again increased in an iterative way to include the boundary layer displacement thickness. As shown in Figures 10 and 11, the heated core flow region closely follows the more primitive models.

Shown in Figure 8 is the corresponding thermodynamic path along the centerline. The overall design strategy has produced a thermodynamic path in the core flow that is close to the proposed ideal thermodynamic path. The temperature at the centerline, however, increases to approximately 1800 K and the Mach number drops to 1.2, as shown in Figure 8, because the real e-beam heating profile is not a uniform "top-hat" profile.

Figure 12 shows the predicted pressure distribution and exit flow profiles with and without heat addition. These results have been obtained from the fully coupled e-beam and 2D viscous flow solver. A smooth adiabatic wall has been assumed for the turbulent boundary layer that develops.

D. Flow Diagnostics

In order to characterize the flow field, both probes and optical diagnostics are being employed in the 1 MW experiment. Because these experiments are aimed at understanding the energy addition process, particular care is being taken to measure the electron beam power (both forward and backward going) and the current delivered to the nozzle assembly. These measurements are being taken to establish an energy accounting that facilitates a determination of the efficiency of the energy-addition process. Questions of stability are also being addressed. In particular, because the duration of



e-beam heating (5 ms) is longer than the transit time of the air in the nozzle (1 ms), instabilities in the heating process have sufficient time to develop. The existence of these instabilities is being investigated using an optical diagnostic suite that includes an ultra-fast CCD framing camera capable of taking images of the flow at a rate as high as 1 MHz. For these studies, the diagnostics records a high speed sequence of shadowgraph images so that fluctuations in the Mach number can be seen by observing the shock angle from a small cone model. With the use of a repetitively pulsed high-power laser, Rayleigh scattering is also used to capture the time varying density at the nozzle exit. An optical bore scope is used to examine the interior of the nozzle during the electron beam operation to identify local hot spots and observe the formation of localized arcs that may be associated with electron beam induced charge build-up. The nitric oxide contamina-tion of the exit air is examined using a multi-path absorption spectrometer [8] and laser-induced fluoresc-ence following excitation with an argon-fluoride ultraviolet excimer laser. Point measurements of flow static temperature are achieved by Laser-Induced Thermal Acoustic (LITA) scattering [9], and point velocity measurements by time-of-flight observations of local discontinuities or laser-induced breakdown regions.

In addition to the suite of optical diagnostics being employed, five uniformly spaced transducers measure the pressure along the length of the nozzle. In order to avoid excessive noise from the electromagnetic and x-ray burst associated with the electron beam, these pressure sensors are fiber-optically coupled Optrand sensors and use light rather that electronics to measure pressure. They are coupled into the nozzle though apertures in the “omega” shaped cooling plates that separate the solenoid magnets used to focus the e-beam into the nozzle. These pressure transducers have been designed to allow a measurement of the transient pressure rise caused by the 5 ms long e-beam pulse. The total pressure is measured at the nozzle exit in the absence of electron beam heating using the same type of pressure transducer mounted in a pitot tube. The pressure and temperature transducers are placed between the solenoid magnets at five locations downstream of the throat, as shown in figure 14. The last pressure tap is just inside the exit of the nozzle. The current return from the nozzle assembly is monitored to determine the fraction of the electron beam current that passes into the walls compared with the fraction the returns at low energy along the beam path and back to the plasma porthole.

A summary of the diagnostic suite presently being employed to characterize the flow field is given in Table 1.

E. Summary

The detailed design has been completed for the flow field in the 1MW RDHWT experiment, and the contour for the supersonic nozzle has been determined. Detailed predictions for the flow fields with and without heat addition have been obtained. These results are being used in the development of the instrumentation for the experiment and will be compared with the experimental results.

Acknowledgement

This work was supported as part of the MARIAH II Wind Tunnel Project, with funding from the U.S. Air Force Arnold Engineering Development Center in Tullahoma, Tennessee, and in conjunction with MSE Technologies, Inc., Butte, Montana.

References

1. R. Miles, G Brown, W. Lempert, R. Yetter, G.J. Williams, S.M. Bogdonoff, D. Natelson and J.R. Guest, “Radiatively-Driven Hypersonic Wind Tunnel,” AIAA Journal 33, August 1995, pp. 1463-1470.

2. A.E. Morgan, P.F. Barker, R.W. Anderson, J.H. Grinstead, G.L. Brown, and R.B. Miles, “Preliminary Experiments in the Development of the Radiatively-Driven Wind Tunnel,” Paper #AIAA-98-2498, 20th AIAA Advanced Measurement and Ground Testing Technology Conference, Albuquerque, NM, June 15-18, 1998.

3. P.F. Barker, J.H. Grinstead, A.E. Morgan, R.W. Anderson, G.L. Brown, R.B. Miles, R. Lipinski, K. Reed, G. Pena, L. Schneider, “Radiatively-Driven Wind Tunnel Experiment with a 30 KW Electron Beam,” Paper #AIAA-99-0688, 37th Aerospace Sciences Meeting, Reno NV, Jan. 11-14, 1999.

4. P.F. Barker, J.H. Grinstead, P.J. Howard, R.W. Anderson, G.L. Brown, R.B. Miles, R. Lipinski, G. Pena, L. Schneider, R. Howard, “A 150 kW Electron Beam Heated Radiatively-Driven Wind Tunnel Experiment, Paper #AIAA-2000-0159, 38th

Aerospace Sciences Meeting, Reno NV, Jan 10-13, 2000.

5. Field Precision, PO Box 13595, Albuquerque, New Mexico 87192 USA, www.fieldp.com.

6. American Magnetics, Inc., Oak Ridge, TN, 37831-2509, www.americanmagnetics.com



7. A. Hershcovitch, “Review of Electron Beam Macro-Instabilities and Other EBIS-Related Stability and Issues,” Rev. Sci. Instr. 69 (2) Feb. 1998, pp. 668-670.

8. P.F. Barker, J.H. Grinstead, and R.B. Miles, “Single-Pulse Temperature Measurement in Supersonic Air Flow with Predisssociated Laser-Induced Thermal Gratings,” Optics Communications 168, Sept. 1, 1999, pp. 177-182.

9. R.P. Howard, etal., “Nonintrusive Nitric Oxide Density Measurements in the Effluent of Core-Heated Air Streams,” Paper #AIAA-90-1478, AIAA 21st Fluid Dynamics, Plasma Dynamics and Lasers Conference, Seattle, WA, June 18-20, 1990.

Table 1: The 1 MW Experiment Diagnostic Suite

Parameter Technique EquipmentNozzle PressureProfile(time resolved)

Optical Transducers Optrand Probes

Density Profile(time resolved)

Rayleigh Scattering Pulse Burst YAG LaserFast CCD CameraSHG YAG Laser (back-up)

Exit Pressure(time resolved)

Pitot Tube Optrand Probes

Temperature(single point, not time resolved)

Laser Induced Thermal Acoustics (LITA)

ArF Laser Ion Argon Laser Fast PMT tube

Mach Angle(time resolved)

Shadowgraphy Diode pumped YAG LaserFast CCD Camera

Velocity Profile Particle Imaging Velocimetry

Pulse Burst YAG LaserSHG YAG Laser (back-up)

Velocity(single point)

Laser Induced Breakdown

YAG Laser SHGFast Camera

Line-Integrated NO Concentration

Absorption Spectroscopy NO Spectrometer

e-Beam – Wall Interaction Image Nozzle Fiber Imaging ProbeFast CCD Camera

NO, O2 Concentration, Vib Non-Equilibrium

Laser induced fluorescence(LIF)

Alexandrite Laser ArF Laser

e-Beam Current Return Path Floating Nozzle Return Current to Ground



Nozzle and Nozzle Magnets

0 10 20 30 40 50 60 cm

New throat location

Air Flow

Plasma Porthole

5 Tesla magnet

½ inch cooling plates

0.020 inch air cooling gap

Top View

Plenum

Nozzle and Nozzle Magnets

0 10 20 30 40 50 60 cm0 10 20 30 40 50 60 cm

New throat location

Air Flow

Plasma Porthole

5 Tesla magnet

½ inch cooling plates

0.020 inch air cooling gap

Top View

Plenum

Figure 1. Configuration of the blowdown nozzle and accelerator beam exit.



-100

-50

0

50

100

150

-50 0 50 100 150 200 250 300 350 400 450 500 550 600 650

Distance from Throat (cm)

Ver

tica

l Po

siti

on

(cm

)

Nozzle 1-5

Window 1, 2, 3

Hawk 1 Hawk 2 Hawk 3

Cathode

Cryo Pump

Fast Valve

Figure 2. Configuration of magnets from the Hawk accelerator to the nozzle.

0.010

0.100

1.000

10.000

0 100 200 300 400

Distance from Throat (cm)

B (

Tes

la)

Cathode

Nozzle Aerowindow

Figure 3. Magnetic field versus distance from nozzle throat.



Figure 4. Hawk accelerator with beam transport magnets and aerowindow.

Figure 5. (a) Glowing annular cathode. (b) Annular beam hitting scintillator.



Figure 6. Plasma porthole at end of aerowindow.



Figure 7. Details of the air delivery system. In particular, the pressure control stack and the pebble bed heater are shown leading up to the plenum / nozzle assembly.

Figure 8. Centerline Thermodynamics Path compared with the One Dimensional and Ideal Path. Mach Number Profile.

Figure 9. The Modified Nozzle Shape (x-axis and y-axis have different scales).



Figure 10. The temperature profile. Figure 11. The Mach Number profile.



Figure 12. Nozzle Exit Profiles with and without Energy Addition, from upper left to lower right (a) Centerline Pressure Distribution, (b) Density Profile, (c) Velocity Profile, (d) Mach Number Profile, (e)

Energy Flux Profile, and (f) Total Enthalpy Profile.

1

10

100

0.00 0.10 0.20 0.30 0.40 0.50 0.60x (m)

PC

L (a

tm)

Not Heated

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0 2 4 6 8 10ρρρρ (kg/m3)

r (m

)

Not Heated

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0 200 400 600 800 1000u (m/sec)

r (m

)

Not Heated

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0 0.5 1 1.5 2 2.5 3 3.5

Mach Number

r (m

)

Not Heated

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00

ρρρρuH (GW/m2)

r (m

)

Not Heated

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.0E+00 5.0E+05 1.0E+06 1.5E+06 2.0E+06 2.5E+06 3.0E+06H (J/Kg)

r (m

)

Not Heated



Figure 13. The nozzle/steering magnets assembly showing the location of the fiber-optic based pressure transducers and the placement through the magnet cooling plates.

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