DATA ACQUISITION AND CONTROLS FOR HALL
Contents
1. correlating fluctuations of the probe current Figure 36 shows probe current oscillations during steady state operation of the T 100 thruster Probe Current Amps 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 time ms Figure 36 Probe current oscillations of the T 100 Another thruster characteristic of interest was the exhaust plume As mentioned earlier the Langmuir probe was mounted on a cantilevered arm connected to a stepper motor This made it possible to sweep the probe across the plume in approximately 7 seconds while maintaining a constant distance from the thruster The probe current shown in Figure 37 gave an approximation of the relative plasma density of a cross section of the thruster plume during steady state operation 34 0 3 Probe Current Amps 0 2 0 1 Angie from Centerline Deg Figure 37 Probe current during a sweep of the exhaust plume 35 CHAPTER V CONCLUSIONS A control and data acquisition system was built for the purpose of investigating characteristics of the Hall thruster The control system consisted of a six channel D A board solid state relays isolation amplifiers and controls software all integrated by use of a 486 50 MHz computer The data acquisition system consisted of two A D boards and two software packages Characteristics investigated were current and plasma oscillations This was achieved by use of current and Langmuir probes Several problems were discovered with the2. 200 mV p E 20 4Hz Chonreis JA40MHzZ Chonne 0000000 oad 0000000 Figure 28 Compuscope Lite A D board Gagescope software can be described as emulating an oscilloscope front panel Options include multiple channels high speed trigger view display that updates the screen as fast as 40 times per second continuous capture 16 kbytes of memory and zoom capabilities The Nyquist Theorem states that a function v t whose highest frequency component is fay must be sampled at a frequency F such that Fs gt 2 fmax 28 In other words if an A D device samples the input signal at a maximum frequency of F the signal will not be reconstructed properly unless it is guaranteed that the maximum frequency component of the input signal is 0 5F Current Probe During normal operating modes the Hall thrusters exhibit oscillations in the current flowing to the anode Discharge current oscillations can vary from 20 kHz to 100 kHz depending on the type of Hall thruster and other factors These oscillations are one of the characteristics of interest The setup for measuring these oscillations is shown in Figure 29 A Tektronix current probe is placed around the wire which feeds the thruster anode The current probe has a bandwidth of over 1 GHz The signal from the probe runs through the probe power supply and to the Compuscope board To Thruster Anode Tektronix Current Probe Display CompuScope Li
3. 26 Sensor compound block 0 5 Q resistor The signal is multiplied by a gain of 2 0 This is then displayed as the anode current A similar method is used for displaying the anode voltage from the signal produced by the 100 Q resistor The VisSim software 1s also used to monitor the mass flow of Xenon to the thruster Outputs from the mfc power supply are fed directly to the DAS16jr shown in Figure 27 These signals are used within VisSim to display the mass flow of the anode and cathode Units refers to the brand name of the mfc power supply mate MFC Flow Units MFC MFC 2 Flow Fate DAS16jr Power Supply Signal Common Figure 27 Mass flow measurement setup As mentioned earlier the DAS16jr is capable of sampling at 1 megasample per second However the VisSim software is capable of recording samples at only 1 kilosample per second Fortunately this software was not required to record high speed data but rather used only to monitor the parameters of the thruster during steady state 27 Operation The high speed data acquisition was performed by the Compuscope Lite A D board and the Gagescope software Compuscope Lite A D Board Compuscope Lite is a high speed low cost A D board shown in Figure 28 that is capable of sampling two channels simultaneously at 20 MSPS or one channel at 40 MSPS Input impedance is 1 megaohm Signal to noise ratio is 42 dB for a 1 MHz signal at 20 MSPS Input range is 1 volt and
4. anode in the magnetic layer unlike the TAL The 100 refers to the length in millimeters of the acceleration region There is one Xenon feed line which splits between the anode and cathode internally with a 92 8 ratio respectively The magnet system consists of one internal and 4 external electromagnets all powered by the discharge power supply The thruster is equipped with two cathode assemblies for redundancy Each cathode consists of an emitter heater coil thermal screens and igniter similar to the D 55 y Cathode Assembly j E e LR BIOS A ee al Annular icsulotor A Xenon Gas 47 FIISSSSSSMGMMMG GSS 7A S 7 2 Magnetic Field Profiler Sinner Maanstic Coil Main Body Housing ond Primary Pole Piece Insulator Annular Anode Outer Mosretic Coils Figure 2 Cutaway view of the TML The Hall Effect thruster tested was the T 100 manufactured by the Institute of Thermal Processes NIITP in Russia The T 100 is similar to the SPT 100 in that it is a TML However like the D 55 its internal and external electromagnets require dedicated power supplies and the Xenon flow to the cathode and anode are controlled separately Theory of Operation The general theory of operation of the Hall Effect thruster is similar for both the TML and TAL concepts At startup electrons are emitted from the cathode by heating the flow of Xenon and by applying a high voltage around 2 kV to
5. circuit in Figure 15 was used only with the EMS 5 kW supply Isolation Amplifiers The EMS and Kikusui power supplies are equipped with an external voltage control capability An externally applied voltage from 0 to 5 V will vary the output of the individual power supplies from 0 to full rated voltage or current However the applied voltage is required to be isolated This is achieved by the use of an isolation amplifier The type used is an Analog Devices AD294A isolation amplifier shown in Figure 16 capable of common mode voltage protection of 8 kV and a frequency response of 3dB from 0 to 2 5 kHz COMMON OUT INPUT OFFSET ADJ Figure 16 The AD294 isolation amplifier 17 The AD294 s performance is attributed to the use of a hybrid magnetic ceramic transformer T1 shown in Figure 17 Windings are screened on two ceramic alumina substrates which are placed together separated by a ceramic isolation barrier Both power and signals are transferred between the amplifier s input stage and output via T1 The input signal is filtered and appears at the input of the inverting amplifier Al The gain of Al is set by placing a resistor between Rg and COM AD294 POWER AL e Al PORE OSCILLATOR Figure 17 AD294 block diagram For this application the input and output gains are both set to 1 The output of A1 is modulated carried across the isolation barrier by signal transformer T1 and de
6. less than 7 5 V is desired in order to turn on the mfc Consider first Ry 0 2 in the circuit of Figure 14 When the switch is opened Vj changes from 15 V in the ideal case to Rin 1 50 kQ A E S 8 33 V Rin Rout 50 kQ 40 kQ Vin 15 15 This is inadequate Therefore a resistor R is placed in parallel with R to lower the mfc input impedance If R is chosen to be1 kQ Ri n R1 159800 Vin 1 a Rin R1 Rout 980 Q 40 kQ 3 359 Y This V is much more desirable The other application of the ssr s is the remote turn on of the 5 kW EMS discharge power supply This is done by applying a dry contactor switch between two of the program terminals The circuit required shown in Figure 15 is a slightly more complex circuit than the relay mfc circuit Consider first the ssr switch open in the circuit of Figure 15 The V at the dry contact switch input terminals is approximately 7 2 V The dry contact switch requires 12 V to close Therefore the dry contact switch is open and the EMS power supply is off DT ES DRY CONTACT DISCHARGE SWITCH SUPPLY Figure 15 SSR discharge supply turn on circuit Next consider what happens when the ssr switch is closed The V at the dry contact switch input terminals is 14 3 V This closes the dry contact switch and the EMS 5 kW supply is turned on Unfortunately the Kikusui and EMS 3 kW supplies did not have remote turn on capability Therefore the
7. DATA ACQUISITION AND CONTROLS FOR HALL EFFECT THRUSTERS by JOHN J MANKOWSKI B S E E A THESIS IN ELECTRICAL ENGINEERING Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN ELECTRICAL ENGINEERING May 1995 qa ACKNOWLEDGMENTS A I would like to express my appreciation to Dr Magne Kristiansen for serving as the advisor of my graduate work and chairman of my committee I would also like to thank the other members of my committee Dr E O Hair Dr L Hatfield Dr T Trost and the department representative Dr D Merhl for their guidance I am also grateful to Jim Dickens for his assistance in the design and building of the project I would also like to express gratitude to Dr F Curran and J Sankovic The use of NASA LeRC s research facilities proved invaluable towards the completion of the project I would also like to thank John Bridges for his assistance in building the hardware Finally I would like to thank my family and especially my girlfriend Dona who has provided support and encouragement throughout my academic career TABLE OF CONTENTS e A E A 11 Pi a EA AA A EE 1V CHAPTER a AAA l I ESPERIMENTAL ELE casir ni a seein A rhs ies 4 SU MAA 4 sd si ase peaini naa co sae EAER bad ena ana se was ee 6 UTNE CASITA rn ina scion AN RRA 7 E o AA 8 DORE Supiy SIA rr ariete ett 9 LO CONTROL STSIEMI oo rindas pa ic c
8. In order to perform these tests a dedicated control and data acquisition system was designed constructed and used This thesis describes these efforts In order to investigate these characteristics most efficiently it was decided to centralize the controls and data acquisition system into a 486 computer A 6 channel 12 bit digital to analog converter board with 24 digital input outputs is dedicated for the control of the thruster The data acquisition system uses two boards One is a 16 channel single ended input 1 MHz analog to digital converter The other is a 2 channel high speed 20 MHz board All three boards are integrated using two different software programs both being Windows compatible The plasma thrusters require gas flow and several power supplies for operation The gas flow is required to deliver Xenon from either one or two feed throughs depending on the type of thruster Up to five different power supplies are needed including a discharge power supply capable of delivering 10 A at 500 V The gas flow and power supplies are all controlled and monitored using the controls computer software Controlling the power supplies requires isolation from the D A board A hybrid industrial isolation amplifier capable of common mode voltage protection of up to 8 kV is used Isolation is also required on some of the data acquisition specifically the discharge voltage and current which are obtained from a simple voltage divider and
9. d state relays CPU and DDAO6 digital to analog board it is possible to control the operation of a Hall thruster remotely All these devices are integrated with a real time controls software program The specific program used is Vis Sim RT and Vis Sim DACQ created by Visual Solutions Vis Sim RT makes it possible to send and receive data from digital to analog and analog to digital boards respectively The Vis Sim DACQ program links Vis Sim with Vis Sim RT Vis Sim is a controls simulation program which uses a block diagram programming method Vis Sim has block subroutines such as integrators differentiators and Fourier transforms as well as many others Under Vis Sim DACQ block diagrams are limited to 100 blocks The Vis Sim real time drivers consist of two parts a real mode Terminational Stay Resident TSR interrupt handler that is installed from the MS DOS prompt and a Vis Sim Dynamic Link Library DLL file that provides an MS Windows protected mode interface to the DOS TSR The command to load the DOS TSR for the DDA06 board is DAS8 EXE dDDA06 300 dPIO24 30A 16A DAS8 EXE is the TSR file name dDDA06 accesses the D A outputs of the DDA06 and sets the hexadecimal address at 300 dPIO24 accesses the digital I O of the DDA06 and sets 30A as its hexadecimal address This is done because the DDAO06 is comprised of separate D A channels and digital I O Finally 16A is the TSR interrupt address 20 Once the drivers are loaded th
10. e current DAS 16jr A D Board The DAS 16jr shown in Figure 24 is a 1 MHz A D board It has 16 channels in single ended mode and 8 channels in differential input mode The input range is programmable with a default mode of 0 to 5 V SINGLE ENDED OR DIFFERENTIAL INPUT BASE ADDRESS SWITCH fa IA ai DMA SELECT Figure 24 DAS16jr D A board Edo One of the uses of the DAS16jr board is monitoring of the thruster during Operation This includes parameters such as anode voltage anode current and Xenon gas flow Anode voltage and current are monitored by use of a voltage divider and shunt resistor respectively The setup is displayed in Figure 25 Typical values for anode voltage and current are 300 V and 5 A For an anode voltage of 300 V the voltage across the 100 Q resistor is approximately 3 V Similarly for an anode current of 5 A the voltage across the 0 5 Q resistor is 2 5 V The output of each of these resistors are sent through an isolation amplifier and then to the DAS 16jr Ballast Resistor Discharge Supply Figure 25 Thruster anode voltage and current measurement setup The signals received by the DAS16jr are used within the VisSim software The sensors block in the main menu Figure 20 receives these signals Figure 26 is a schematic of the sensor block Channel 3 of the DAS16jr receives the signal from the 26 DAS16jr CH 3 Anode Current DAS16jr CH 4 Anode Voltage Figure
11. e boards need to be made compatible with the software This is done by using the file menu Real Time Configure menu shown in Figure 19 from within Vis Sim The DDA06 is actually configured as two boards One is used to access the D A channels and the other to access the digital I O Once all the boards are configured the simulation program can be written As mentioned earlier Vis Sim is a block diagram programming package From the main screen shown in Figure 20 the user is able to control fully the routine operation of the Hall thrusters The slider blocks control the analog outputs of the DDA06 Varying the Boord Number Boord Type Analog Input Range Analog Output Ronge LO is Interrupt Vector Base Address Figure 19 Real time configure menu slider from its minimum to maximum values will vary the analog output channel from 0 to 5 volts respectively The minimum and maximum values of the slider are chosen to represent the minimum and maximum values of the equipment that the slider is controlling For example the voltage range of the SkW EMS power supply is 0 to 600 volts which can be controlled with a 0 to 5 volt external voltage The slider ranges from 0 to 600 and its output is multiplied with a gain of 00833 see Figure 21 So the input to the DDA06 analog output is 0 to 5 volts 21 The button blocks labeled equipment on act as on off switches The on off buttons for the discharge supply and the two mfc s c
12. harge supply compound DIGG csc cei sica cono e inao iin ians 23 22 Internal magnet supply compound block eee ccceceeceeeeecensececsteeeeees 23 33 MEC err O siii decease de i 24 E AA DA DOT ci A emacs ai ave deal ui Aen dt 25 25 Thruster anode voltage and current measurement setup occ ooo 26 26 Senor compound MMM 2T 27 Mass flow measurement setup 00000008 a 27 28 29 ai 32 33 34 33 36 ay Compuscope Lite A D board Current oscillation measurement Setup ooo ninia Current oscillations of the D 55 at 300 V and 4 5 Au eee Current oscillations of the SPT 100 at 300 V and 4 Ao Current oscillations of the T 100 at 300 V and 4 5 A oococcoccccccccccocccoccnoncnonanos Thruster start up current at 300 V and 4 5 A ii cc ci n A o MA and ntact neian alae omen General I V characteristic for a Langmuir probe 0 cccccececeeseeeeeseeeteeees Probe current oscillations CHAPTER I INTRODUCTION The Pulsed Power Laboratory at Texas Tech University is presently investigating the characteristics of several stationary plasma thrusters In particular experiments were conducted on the Russian D 55 SPT 100 and T 100 thrusters With the opening of the Russian market the US space industry is exploring the feasibility of using these types of thrusters for satellite station keeping Performance and evaluation tests of these three thrusters were made at NASA Lewis Research Center in Cleveland Ohio
13. irst Hall Effect thruster tested was the D 55 stationary plasma thruster with anode layer TAL Figure 1 manufactured by the Central Scientific Research Institute of Machine Building TsNIIMASH in Russia Anode layer refers to the fact that the ionization and acceleration regions are near the anode The 55 refers to the diameter in millimeters of the anode There are two magnets an external and an internal each with a dedicated power supply The Xenon feed has two different lines one to the cathode and Cathode Assembly Se Py LES NS OSOS INN NOS OSOS LALA KAAAAANAANANAAN AAA AAS a SIS RAPA AA EXP RAS CA AAA SOROLLA S pS te Q RS A A a Ss Annular Anode bs Y A ERE ORT EE pee AP EA Y Xenon Gas Feed Lines Main Body Housing Do i and Primary Pole Piece Magnetic Field Projier Ce Inner Magnetic Coil A AR gt Insulator SSS e a Outer Magnetic Coils Figure 1 Cutaway view of the TAL the other to the anode The Xenon anode feed at the thruster is evenly spaced so as to uniformly distribute the gas flow The thruster is designed with a hollow cathode assembly consisting of an emitter heater coil and keeper The second Hall Effect thruster tested was the SPT 100 stationary plasma thruster with magnetic layer shown in Figure 2 designed and built by Fakel Enterprises also in Russia Thruster with magnetic layer TML refers to the fact that the acceleration region is away from the
14. mode and controlled using the D A converter board Both the mfc s and power supply are manufactured by Units Instruments Inc As mentioned before Figure 5 shows the gas supply setup for the D 55 and T 100 The SPT 100 however requires only one gas feed since the flow to the anode and cathode is split internally As a result only one branch is used see Figure 6 MANUAL VALVES a TO THRUSTER MASS FLOW CONTROLLER Figure 6 SPT 100 gas flow system Power Supply System The thruster discharge current is supplied by a 5 kW switching power supply manufactured by Electronic Measurements The supply is capable of delivering 10 A at 500 V which meets the requirements of all the thrusters tested The cathode heater external magnet and internal magnet currents are supplied by dedicated 360 W power supplies manufactured by Kikusui The supplies are capable of delivering 12 A at 30 V A 3 kW switching power supply manufactured by Electronics Measurements is used for the igniter This supply is capable of delivering 5 A at 600 V Figure 7 shows the setup of the power supply system for the D 55 There is a 10Q ballast resistor and a100 p F capacitor to attenuate the current oscillations caused by the thruster EMS SkW KIKUSUI 360W TO EXTERNAL KIKUSUI 350W TD CATHODE KIKUSUI 360W TO CAT EMS 3kW TO INTERNAL MAGSNET 100 AA 100uF T TO ANODE MAGNET A
15. modulated The demodulated output voltage is filtered and then buffered by A2 The 200 kHz square wave power oscillator drives the primary windings of transformer T1 The secondary windings of T1 then energizes the input power supply and drives both the modulator and demodulator 18 A total of 8 isolation amplifier circuits were used for this experiment Two printed circuit boards were built both with 4 isolation amplifier circuits Each circuit consists of an isolation amplifier and a 15 V power supply A dedicated power supply for each isolation amplifier was required to provide isolation of one amplifier from the others A circuit for one of the isolation amplifiers is shown in Figure 18 The boards were mounted inside a rack mountable aluminum chassis Banana T V Voltage y poa Figure 18 Isolation Amplifier Circuit and DB ribbon cable connectors were mounted on the exterior of the chassis for inputs and outputs to and from the isolation boards One of the isolation boards is dedicated for use with the DDA06 analog outputs Channel 0 3 4 and 5 outputs are connected to the inputs of the isolation amplifiers The outputs of these isolation amplifiers are connected to the external voltage controls of the SkW EMS and the three Kikusui power supplies The other isolation board is used for data acquisition and will be discussed in the next chapter 19 Software By using the isolation amplifiers soli
16. oltages 13 The solid state relays ssr mount on the SSR RACK 24 shown in Figure 12 and interface directly to the DDA06 LLY Sy A meee es k A RLR ASSN 9 SA SON DO SEREN ee Figure 12 SSR Rack 24 Figure 13 shows a model of a typical solid state relay The ssr can be modeled as a simple switch with a certain input and output impedance The supply voltage V is 5 V Digital input is the O or 5 V signal from the digital output of the DDA06 board The application of the external voltage Vex across Vy is controlled by the ssr These ssr s are capable of controlling voltages up to 600 V dc An ideal ssr has infinite input and output impedance When a digital low is sent from the DDA06 to an ideal ssr the switch is open and Vow is 0 V When a digital high is sent the switch is closed and Vy is equal to Vez Realistically values for Rin and Rou are approximately 1 MQ and 40 KQ respectively Figure 13 Solid state output relay One application of the ssr s is the remote turn on of the mass flow controllers mfc shown in Figure 14 The control turn on voltage Vin for the mfc s on the power AFC POWER SUPPLY Figure 14 SSR MFC circuit supply is asserted low A Vj of 0 to 7 5 V turns on the mfc while a Vi of 7 5 to 15 V turns off the mfc With the switch closed there is 15 V across R so that the mfc is turned off since it is asserted low When the switch is opened a voltage of
17. ontrol the solid state relays However since the Kikusui supplies are not equipped for remote turn on the buttons are not used to control ssr s Instead the buttons turn on and off the voltage from the analog outputs Dischorae RS ON A Es El us c6 6 390 Discharge PS e 9 Maanet PS 1 ON 2 kusu T Magnet Discharze Current Amps Oo sen es External Magnet ischorae Voltage e A i 00 dW Volts Sensors Cathode Heater Anode MFC us img s Se o Ourc ass Controllers Cathode MFC LAA m s Figure 20 Vis Sim main screen The equipment blocks 1 e discharge PS and mass flow controllers are actually compound blocks That is they contain a group of blocks Figure 21 displays the compound block of the discharge power supply Note that the outputs from the button 22 and slider enter the compound from the left As mentioned earlier the output of the slider gets multiplied by a 0 00833 gain and is then sent to analog output channel 1 of the DDAO6 Figure 21 Discharge supply compound block The output of the buttons is sent directly to digital output channel BO When the button is in the on mode a digital high is sent by channel BO to the SSR This closes the dry contact switch and turns the discharge power supply on The internal magnet compound block is shown in Figure 22 Notice that the output of the button is multiplied with the slider When the but
18. pl HEATER HODE IGNITOR Figure 7 Power supply system for the D 55 The SPT 100 setup shown in Figure three power supplies are used as opposed to 8 1s slightly different than the D 55 Only five used on the D 55 The magnet coils are powered by the discharge supply Consequently the magnetic field cannot be controlled independently from the electric field LOQ 10 ancoe ano macuers Ms 1004F T KTKUSU CATHODE HEATER T TO CATHODE IGN TOR TO Figure 8 Power supply system for the SPT 100 The T 100 setup shown in Figure 9 is very similar to the D 55 with the only difference being the absence of the cathode heater 100 TO ANODE EMS SkW 1004 T TO EXTERNAL MAGNET KIKUSUI 360W KIKUSUI 360W TO INTERNAL MAGNET EMS 3kW TO CATHODE IGNITOR Figure 9 Power supply system for the T 100 CHAPTER III CONTROL SYSTEMS The major requirement of the control system is to control remotely the gas flow and power to the thruster from a central location This is most easily achieved by integrating a personal computer a digital to analog board control software isolation amplifiers and solid state relays Figure 10 shows the overall view of the control system for the D 55 Notice that the EMS 3 kW power supply is not contained in the control system This is for two reasons First this supply is dedicated for the cathode igniter which is only used during initial star
19. roceedings of the 23rd International Electric Propulsion Conference Sept 1993 Chung P M Talbot L and Touryan K J Electric Probes in Stationary and Flowing Plasmas Applied Physics and Engineering Vol II Springer Verlag New York 1975 37 PERMISSION TO COPY In presenting this thesis in partial fulfillment of the requirements for a master s degree at Texas Tech University or Texas Tech University Health Sciences Center I agree that the Library and my major department shall make it freely available for research purposes Permission to copy this thesis for scholarly purposes may be granted by the Director of the Library or my major professor It is understood that any copying or publication of this thesis for financial gain shall not be allowed without my further written permission and that any user may be liable for copyright infringement Agree Permission is granted 5 8 85 Stud nt s Signature Date Disagree Permission is not granted Student s Signature Date
20. s of each are very similar Each work off of four 32 diffusion pumps Each have roughly the same dimensions 1 5 m inside diameter by 4 m long Refer to Figure 4 for a schematic diagram The base pressure of each tank was approximately 10 torr with an operating pressure of 5 10 torr which is 5 10 torr which is well below the 2 10 torr operating pressure suggested by the thruster s manufacturers The thruster is located at the end of the vacuum chamber A cylindrical Langmuir probe is mounted inside the chamber in the middle of the exhaust plume and at a certain distance from the exit plane THRISTER LANGMUIR PRIS DIFFUSION DIFFUSION PUMP PUMP DIFFUSION DIFFUSION PUMP PUMP Figure 4 Vacuum chamber with thruster setup Gas Flow System The propellant system is supplied with 99 99 pure Xenon A schematic diagram of the propellant system for the D 55 and T 100 is shown in Figure 5 Three manual valves are used one main valve and one valve on each branch The mass flow for the cathode branch is controlled using a 20 standard cubic centimeter sccm mass flow controller mfc The anode is controlled with a 100 sccm mfc The conversion of units from sccm to milligram second mg s for Xenon is l sccm 0 1mg s MANUAL VALVES MASS FLOW CONTROLLERS Figure 5 D 55 and T 100 gas flow system The mfc s are controlled with a power supply controller The channels are operated in automatic
21. shunt resistor respectively This thesis details the integration of the data acquisition and control system The system had three major requirements The system hardware was assembled at Texas Tech University while the actual experiment was done at NASA Lewis Research Center in Cleveland Ohio therefore the system had to be portable Also at the beginning of the project the actual characteristics of the thruster to be examined were yet to be determined therefore the system had to be flexible Finally being able to run three different thrusters required the system to be generic The thruster characteristic studied was plume fluctuations specifically plasma oscillations Diagnostics used to measure the plasma oscillations are a current sensor and a Langmuir probe The current sensor was used to measure the oscillations of the discharge current The Langmuir probe was used to detect the oscillations of the electron density Both were recorded using the 20 MHz A D board Chapter II of this thesis describes the experimental setup of the project which includes a description of the thrusters and the hardware required to operate them Chapter III explains the control system including the D A board isolation system and software Chapter IV details the data acquisition system which includes A D boards measurement setup and software Finally Chapter VI entails the conclusions CHAPTER II EXPERIMENTAL SETUP Hall Effect Thrusters The f
22. system after the initial assembly Cables running from the power supplies to the computer induced small currents in the each other Therefore care was taken to properly ground and shield all cables Another problem was the introduction of noise from the internal programming circuitry of the power supplies In order to solve this problem bypass capacitors were inserted where necessary There was also a problem with the control software freezing up after ismi hours of use This was corrected by increasing the RAM of the computer from 4 megabytes to 8 megabytes Once the system was assembled and debugged it worked flawlessly Over 100 hours were logged on the system without failure The system is very flexible and could be used on other projects in the future REFERENCES Anode Layer Thruster Operating Instructions Kaliningrad Moscow Region 1993 Brophy J R Stationary Plasma Thruster Evaluation in Russia JPL Publication 92 4 Mar 1992 CIO DDA06 User s Manual Computer Boards Inc Mansfield MA 1991 Analog Devices Data Converter Reference Manual Analog Devices Norwood MA 1994 Vis Sim User s Guide Visual Solutions Inc Westford MA 1994 CIO AD16jr User s Manual Computer Boards Inc Mansfield MA 1991 Gagescope Technical Reference and User s Guide Montreal Canada 1993 Myers R M and Manzella D M Stationary Plasma Thruster Plume Characteristics IEPC Paper 93 096 P
23. t et 12 EPR SR ata 13 DOMO E NAS ra A AAA A Bete 13 TOUR AUIELAC o y nieri ita av a e ci 17 TIA rr ch a esl Cp E 20 a A rri eraren esas sateen A aeons eens 25 EE AM Bomi AAA Ze Compuscopea Lite AID Board os scene came sss o es apa visa 28 COIE ri E A E ANE 29 Lanen e FODE iiaee aasta AA 32 L ti ULA O din EEE 36 dis AAA A 37 111 LIST OF FIGURES l Cutaway view of the TAL A a Ra 4 2 COTA view of the TME cari ina ae aia tw tide at a i 5 3 Cutaway view of the TAL with E and B field directiOMS ooooononnnnccncnccncccccconnnnos 7 Vagoum Spb er with uster SEMID car rs Ns cn 8 3 1235 amd T 100 gas Ow SN co io irc o eee ns mae E ER 9 G APDO Tow E a ra 9 T Power supply system for the D 55 cc oo erre suns semen o a se 10 8 Power supply system for the SPT 100 oo norris corte ra 11 9 Power supply system for the TADO occ comica ip nr a ar ai oto 11 10 Contrel system of ihe D 55 Drier iiini A a A erect 12 11 DDAO6 digital to analog converter board ooocococccocococococococonononononononnnnnoroccnnnoss 13 AA A og cs bleh een end 14 13 Soig Tah FUMIE CU La A 15 CN A A 15 15 SSR discharge supply tmi on circuit o conoci o e e a ra tenes 16 16 ADZ94 Isolation ampie sei coca ir OR A A v5 Adena naw vane dd mcs nous 17 17 ADZ94 block CUE eri rr A O A dd 18 18 Isolation amplifier ciretit nesiims omo 1 roce E A EAEE S a E 19 19 Real time CONS IO o aida rr A ee sea ele 21 20 WE TES ET ii id a denen cd a dida 22 21 Disc
24. te A D Board Tektronix Current Probe To Thruster Cathode Figure 29 Current oscillation measurement setup Samples of current oscillations for each of the thrusters are shown in Figures 30 through 32 Data was taken during normal steady state operation 29 Anode Current Amps 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 time ms Figure 30 Current oscillations of the D 55 at 300 V and 4 5 A Anode Current Amps 0 0 1 0 2 0 3 0 4 0 5 time ms Figure 31 Current oscillations of the SPT 100 at 300 V and 4 A 30 Anode Current Amps 10 0 0 1 0 2 0 3 0 4 0 5 time ms Figure 32 Current oscillations of the T 100 at 300 V and 4 5 A Care was taken to sample fast enough to prevent aliasing The fastest current oscillations are those of the D 55 roughly 80 kHz Therefore samples were taken at a speed faster than 200 kSPS Another area of interest is the anode current during shutdown and startup of the thruster Figure 33 displays the anode current of the D 55 during a typical shutdown and startup sequence Since we were not concerned with the current oscillations but rather the steady state value the aliasing effects were disregarded 31 Anode Current MW Amps ily NOD Ht Wl M N TIN NI MN ii WF Hh 3 3 5 4 4 5 time ms Figure 33 Thruster start up current at 300 V and 4 5 A Langmuir Probe The Langmuir probe se
25. the igniter A voltage is then applied to the anode and the magnets The electrons emitted from the neutralizer are attracted to the anode by the established E field When the electrons initially enter the magnetic field they experience a force described by F Q U xB where Q is the electron charge U is the electron velocity and B is the magnetic flux density The electrons are then caught in this magnetic field moving in a cyclotron motion and forming a virtual cathode at the end of the anode chamber A diagram of the TAL with E and B field directions is shown in Figure 3 Xenon atoms diffuse down the anode chamber until they collide with the circulating electrons These collisions produce Xenon ions which are attracted to the virtual cathode at the end of the chamber The Xenon ions are then propelled out the end of the chamber 4 ta a ae PRI 220 DORIA o TT COSA A Figure 3 Cutaway of the TAL with E and B field directions The Xenon ions are accelerated by the electric field to velocities of about 16 000 m s Electrons from the cathode serve to neutralize the ion beam Due to the relatively large mass of the Xenon ions they are largely unaffected by the magnetic field However some bending of the ion trajectories occurs and results in a small torque about the z axis Vacuum Chamber The experiments were performed at NASA Lewis Research Center at Cleveland Ohio in tanks 3 and 8 The vacuum facilitie
26. ton output is 0 there is no voltage sent from the DDA06 channel 3 When the button output is 1 the DDA06 channel 3 output is determined by the slider The external magnet and heater compound blocks have the same setup as the internal magnet block From Button Internal Magns DDAO6 CH 3 From Slider Figure 22 Internal magnet supply compound block 23 The mass flow controller compound block is shown in Figure 23 The button output goes through a not gate and then to the digital output Remember that the mass flow controller enables are asserted low So in order to stay consistent with the discharge supply on off button a not gate is used The slider control controls the set point of each respective mfc Blocks labeled DAS16jr are used for reading the actual flow of Xenon through each mfc These will be discussed in the next chapter Enable MFC 1 To Display DDAO6 B1 From Slider MFC 1 Set Pt 0 05 DDAO6 CH 1 To Display Enable MFC 2 DAS16jr CH 2 oS DDAO06 B2 MFC 2 Set Pt 0 05 DDAO6 CH 2 From Slider Figure 23 MFC compound block CHAPTER IV DATA ACQUISITION Data Acquisition for this project is broken up into two parts First a DAS16jr analog to digital A D board is used for the slow speed monitoring of Wii gas flow and thruster anode voltage and current Second a 20 MHz Compuscope Lite A D board is used for the high speed monitoring of thruster current oscillations and Langmuir prob
27. tup and is then immediately shut off Second the control of this supply would require one more D A channel than was available from the board used CONTROL SOFTWARE ISOLATION AMPLIFIER MASS FLOW CONT S POWER SUPPLY ISOLATION AMPLIFIER D A BOARD ISOLATION AMPLIFIER GAS LINES Figure 10 Control system of the D 55 thruster 12 CPU and D A Board The PC is a 486 50 MHz IBM clone with 8 Mbytes of RAM The D A board is the CIO DDA06 12 made by Computer Boards Inc The DDA06 shown in F igure 11 is actually two boards in one It is equipped with 24 bit digital input outputs and 6 analog output channels with 12 bit 1 part in 4 095 resolution The analog output range is fully switch selectable from 0 1 67 to 0 5 V in unipolar mode and 1 67 to 10 V in bipolar mode The range selected for this application is 0 5 V unipolar which gives 1 22 mV bit resolution The digital output range is 2 4 V minimum for output high and 0 5 V maximum for output low teem G 135330 San S NIVO tv 135330 v NIYO 135330 L NIVD SN NIY MZ 135330 ZZA 135330 gt R Seen Z NIVO EN O Nvo RR TA ZZA fe Figure 11 The DDA06 digital to analog converter board Solid State Relays The digital input outputs work in conjunction with solid state relays to provide over 4 kV isolation and allow the DDAO6 to sense or control high AC and DC v
28. tup was similar to the type described by Myers and Manzella A cylindrical Langmuir probe was mounted on a cantilevered arm refer back to Figure 4 The arm was mounted to a stepper motor This made it possible to sweep the Langmuir probe 180 degrees about a radius of 40 cm Since the thruster could not be mounted at the end of this radius the varying distance of the probe from the exit plane of the thruster had to be accounted for The Langmuir probe was a 1 57 cm long 0 051 cm diameter piece of tungsten wire extending from a 1 mm outer diameter 5 cm long alumina insulator The probe was biased relative to the tank wall using the circuit shown in Figure 34 The power supply placed the Langmuir probe at a positive potential of around 50 V The probe current was measured using a10 Q shunt resistor Isolation of the resistor 32 from the Compuscope board was unnecessary since one end of the resistor was grounded to the tank cs To Langmuir Probe TCR Supply CompuScope Lite A D Board Ground To Tank Figure 34 Langmuir probe setup According to thin sheath probe theory a general current voltage characteristic curve for single probe operation is depicted in Figure 35 Figure 35 General I V characteristic for a Langmuir probe The voltage on the probe was sufficient to place the I V characteristic in the positive current saturation region Therefore fluctuations in plasma electron density will result in 33
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