Ion Mill Dan's Notes ----------------------- Initial Rev. 1-June-21 Current Rev. 26-Aug-21 ID-2500 Power Supply Specification and Typical Operation: --------------------------------------------------------- Power 3 cm Ion Mill Supply 3 cm Mill Power Supply Regul- Mill Our Ion Mill Max. Output ation Maximum Typical Power Supply Specification Mode Load Setup ------------ ------------- ------ ------- ------- Cathode 15 Volts Current Filament 8 Amps 8.5 A 4.2 A 120 Watts Discharge 75 Volts Voltage 40 V 40 V 3 Amps see 3 A 0.3 A 225 Watts notes Beam 1500 Volts Voltage 1500 V 300 V 125 mAmps 80 mA 9 mA 188 Watts Accelerator 500 Volts Voltage 23 V 20 mAmps 5 mA 0.4 mA 10 Watts Neutralizer 15 Volts Current Filament 8 Amps 8 A 2.9 A 120 Watts Neutralizer Measurement -- 90 mA 10 mA Emission Only - Not a Power Supply As operated on the 3cm gun test on 1-July-2021: Vacuum: 3.1 10e-4 Torr Argon Gas Flow Rate: standard value used with 3 cm gun which is I think 5 standard cc per minute of Argon gas flow into the ion gun Achieved Milling Rate: 5.5 Angstroms/sec Notes about this Table: ----------------------- - The 3 cm Mill Maximum Load column is a list of the highest values that I found mentioned in the instruction manual for the 3 cm Mill. The intent of this column is to allow a comparison between how we typically operate the 3 cm Mill and the apparent maximum capability of this mill as indicated in its instruction manual. - The Discharge power supply needs to working into a gas arc which typically has a negative dynamic resistance. A standard old way to keep a regulated supply stable in this condition was to include a series resistor to swamp out the negative resistance of the gas discharge. The manual says that actual maximum open circuit output voltage of the Discharge supply is 300 Volts. Making this supply work into a negative resistance load may also have been achieved by tailoring its control loop rather than by an old wasteful power resistor. - Functions of the various Power Supplies: The Cathode supply heats the tungsten Cathode Filament so that it can emit electrons. The Cathode supply Filament current display indicates the amount of current flowing though this filament to heat it. The Discharge supply draws electrons from the Cathode Filament and these electrons flow to the Anode. This flux of electrons is used to ionize the Argon gas. The Discharge supply current display indicates the amount of electron emission from the Cathode Filament. The Beam supply gives the positive Argon ions the bulk of their kinetic energy. It does this by elevating the whole Cathode Filament and Anode structure to a positive potential with respect to the ground potential of the Screen Grid, your sample target, and the rest of the vacuum chamber metal structure. The Beam supply current display indicates the amount of positive Argon ions flowing towards the Screen Grid - the bulk of which flow out of the ion gun and to the target. The Accelerator supply biases the Accelerator Grid at a small negative potential with respect to ground. This facilitates drawing the bulk of the positive Argon ions through the two grids with very few of them impinging on either grid. The Accelerator supply current display indicates the amount of Argon ions that impinge on and are captured by the Accelerator Grid. Obviously this should be a small fraction of the Beam supply current described above. The Neutralizer supply heats the tungsten Neutralizer Filament so that it can emit electrons. The intent is that the total flux flowing toward your sample target (electrons plus positive Argon ions) will have a neutral charge - to prevent charging your sample target. The Neutralizer Filament supply current display indicates the amount of current flowing though this filament to heat it. You can also display the Emission current from the Neutralizer filament which indicates the amount of electrons in the total flux flowing towards your sample target. Switch Positions: ----------------- - The Mode switch must be in the Manual position. Do NOT use the Automatic Mode without first setting up the 7 trim pots that are on the Logic card to fit the characteristics of the ion gun that you are working with. - The Signal Source switches must both be in the Local position. - The "Source Beam" switches were at first confusing to me because the words Source and Beam are written so close together on the front panel. The function of these switches is in fact quite rational. The Source switch starts the generation of positive Argon ions - it turns on the: Cathode, Discharge, and Neutralizer supplies. The Beam switch enables the gun to start actually emitting a beam of Argon ions - it turns on the Beam and Accelerator supplies. Digital Displays: ----------------- Viewed from the front the left-hand digital display shows either the Beam Voltage or the Beam Current. The default display is Beam Current as indicated by the spring loaded Beam lever switch in the bottom row being in its default up position, i.e. the current display position. The right-hand digital display can show any of the following quantities: Accelerator voltage or current, Discharge voltage or current, Cathode Filament current, Neutralizer Filament current, Neutralizer Filament Emission current. What is being displayed is indicated by which spring loaded lever switch in the bottom has been activated by the operator. The default display is Accelerator current as indicated by that switch defaulting to its up position. Front Panel Beam Current 10-Turn Knob: ---------------------------------------- In the Manual operation Mode this knob does nothing. Leave Beam Current turned fully counter-clockwise. Tune-Up i.e. Rational Order of Adjustments: -------------------------------------------- - The goal is to get about 10 mA of Beam current without operating either the Cathode Filament or the Neutralizer Filament at a higher temperature than necessary, i.e. at a higher filament current than necessary. Operating either one of these filaments hotter than necessary will just shorten it life. - If you do not know that the 6 front panel 10-turn knobs are near their good operating positions then turn all of them fully counter-clockwise. - Verify the the pressure in the vacuum chamber is correct and that the Argon gas flow rate into the ion gun is correct. - Turn on just the Source switch and set the Discharge Voltage control for 40 Volts. This is a fixed operating point and we will always adjust the Discharge Voltage to 40 Volts. This sets the kinetic energy achieved by the electrons that are emitted by the Cathode Filament. 40 Volts is plenty of kinetic energy to ionize a neutral Argon atom. - With the Cathode Filament control fully CCW the Cathode Filament will not be hot enough to emit a significant number of electrons and a discharge will not be established. Slowly increase the Cathode Filament control until the Discharge LED illuminates. This should happen with between 3 and 4 Amps of Cathode Filament current. Then increase the Cathode Filament control until you have about 0.3 Amps of Discharge current, i.e. about 0.3 Amps of electrons flowing from the Cathode Filament to the Anode and trying to bump into Argon atoms and ionize them. In any case I would not go over about 5 or 5.5 Amps of Cathode Filament current because that much current should have the Cathode Filament well hot enough to emit the required flux of electrons. - Increase the Neutralizer Filament control until you have about 10 mA of emission from the Neutralizer Filament. This should happen with about 2.5 to 3.5 Amps of Neutralizer Filament current. In any case I would not go over about 5 Amps of Neutralizer Filament current because that much current should have the Neutralizer Filament well hot enough to emit the required 10 mA of electrons. - At this point the Source function of the gun should be working so now turn on the Beam switch and see if the gun can make a beam of Argon ions. - Set the Beam Voltage to 300 Volts - this sets the kinetic energy of the Argon ions emitted by the gun. - Set the Accelerator Voltage to 30 Volts - this biases the Accelerator Grid negative to help pull the positive Argon ions through both the Screen Grid and the Accelerator Grid. - At this point you should have about 9 to 10 mA of Beam Current. If the Beam current is lower than this make small adjustments to the Cathode Filament current, the Accelerator Voltage, and the Neutralizer Filament current in an attempt to maximize the Beam Current while not operating either filament hotter than necessary. - The final adjustment of the Neutralizer Filament current should be to make the electron Emission from the Neutralizer Filament about equal to or 10% larger than the positive Argon ion Beam Current. - As the ion gun warms up over its first few minutes of operation some re-adjustment of the controls may be necessary to achieve the highest Beam Current possible with moderate filament currents (temperatures). The re-adjustments are necessary because as the overall ion gun warms up the effective pressure of the Argon gas within it changes. Automatic Operation - do not use the Automatic Mode Inventory List of the ID-2500 Power Supplies: --------------------------------------------- - 1 cm gun Power Supply is: SN 3956-2138 MNID-2500 C2 I have not seen inside this power supply so I know nothing about its condition. Made a new power output cable for this ID-2500 power supply. This power supply and its 1 cm gun were working OK in July 2021. - 3 cm gun Power Supply is: SN 12744 MN 2001-002-A This supply had burned up power output connectors on its Cathode and Filament modules and their backplane connector pins. Jumper wires have been added to route these high current supplies directly to the back panel power output terminal strip. Made a new power output cable for this ID-2500 power supply. The Beam module in this power supply was modified so that its maximum output voltage is now 500 V instead of the stock 1500 V. R19 stock 22k was replaced with 60k and a 30k to pin #7 signal common. The Accelerator module in power supply was modified so that its maximum output voltage is now 100 V instead of the stock 500 V. R19 stock 22k was replaced with 100k and a 24.8k to pin #7 signal common. Details of these modifications are on page 129 of the note book. The modification was made to improve safety and operating convenience. This keeps the 22k effective series Z to the Logic card control circuit. No change to any scales or monitoring circuits. Very easy change back to stock output range - just pull out the two new resistors and install a 22k at R19. This power supply and its 3 cm gun were working OK in July 2021. - "For Parts Only" Power Supply is: SN 1128 MNID-2500 This supply had burned up power output connectors on its Cathode and Filament modules and their backplane connector pins. All of the power module had mechanically broken up connectors and were "forced" to lean over. There was no insulating plastic cover plate over the tops of the modules in this power supply to hold them in mechanical alignment. This supply is a Frankenstein collection of modules. Repaired various power modules which typically had either open or shorted driver or main switch transistors. Replaced drivers with IRF540 and main switch with FJP13009H2TU. Machined the heat-sinks so that the modules will all plug in without mechanical interference. Replaced all connectors on the power nodules. Added jumper wires to route the high current Cathode and Neutralizer directly to the back panel power output terminal strip. Found a never soldered pin in the backplane in the 150 V bus. Replaced dead front panel 7-segment displays. Replaced all the cheep 85C aluminum caps on the power modules and the front panel with new good quality parts. The backplane output traces had a modification that shorted the Discharge module output - returned the backplane output traces to stock configuration. On modules that did not use it I removed the high Z trace that ran right adjacent to the 150 V fuse. Made a top insulating cover to hold the boards mechanically in place - at least for careful local use. Replaced the line cord. Soap and water bath for all mechanics. Made a new power output cable for this ID-2500 power supply. The Beam module in this power supply was modified so that its maximum output voltage is now 500 V instead of the stock 1500 V. R19 stock 22k was replaced with 60k and a 30k to pin #7 signal common. The Accelerator module in power supply was modified so that its maximum output voltage is now 100 V instead of the stock 500 V. R19 stock 22k was replaced with 100k and a 24.8k to pin #7 signal common. Details of these modifications are on page 129 of the note book. The modification was made to improve safety and operating convenience. This keeps the 22k effective series Z to the Logic card control circuit. No change to any scales or monitoring circuits. Very easy change back to stock output range - just pull out the two new resistors and install a 22k at R19. This power supply was tested for many hours with the resistor load board at a higher power level than it will see in normal operation. All working OK July 2021 and it's now a good spare supply.. Cables from the ID-2500 Power Supply and their Ion Gun: ------------------------------------------------------- All of these cables have now been setup with a standard wiring and pinout of their Amphenol series 97 connectors. Any of the 3 power supplies may be used with either of the ion guns. The resistor test load for these ID-2500 supplies has been setup with the same type of connector and pinout as the ion guns so this resistor test load may be plugged into any of the 3 supplies. The cable wiring to the ion guns now includes an explicit return line for the ion Beam current and a safety ground to make certain that the equipment frame where the gun is located is at the same potential as the chassis of the power supply. The cable connector pinout and wire colors: ID-2500 Power Amphenol Supply Output Connector Function Terminal Number Wire Color Pin Number -------- --------------- ---------- ---------- Cathode Filament 11 and 12 Yellow A and B Anode 10 and 8 Red C Power Rtn Safety Gnd 1 and 2 Green G and External Accelerator Grid 6 White D Neutralizer Filament 4 and 5 Orange E and F Notes: ID-2500 Output Terminals: 3, 7, and 9 are not used. NC ID-2500 Output Terminals: 1 and 2 are tied together in the backplane are are internally connected to the circuit common power return and to the power supply chassis. ID-2500 Output Terminals: 8 and 10 must be jumpered together. A green power return wire runs through pin G of the Amphenol connector and then to the body of the ion gun. A separate green safety ground wire runs through an external lug at the Amphenal connector and then runs to the frame of the setup that holds the ion gun. 5 standard cc per minute of Argon gas flow into the ion gun could make about 0.37 Amps of positive Argon ions if all of it were ionized.