COLUTRON TECH NOTES

Some frequently asked questions concerning the operation of Colutron ion beam equipment are discussed below.

I. ION BEAM PROBAGATION PROBLEMS

Unstable beam conditions: ion sources, ion gun systems, velocity filters

Ion beam seems to be misaligned

II. ION SOURCE PROBLEMS

Unable to strike an arc with the source

Gaseous discharge in ion source gas inlet tube

Quartz ion source parts turn milky white and/or ion source ceramic parts cracked

Filament FAQ

III. MODEL CU-1 COOLING UNIT FAQ

Model CU-1 FAQ

Problem: Unstable beam condition

Cause: Floating ion source heat sink
Remedy: Make sure that a wire connection between either the filament or anode are made to the ion source receptacle. It is common practice however during low energy operation (E<200eV) to have the anode connected to the receptacle.

Cause: Dirty ion optics (beam drift). Beam charge-up of electrodes from non-conductive beam deposits/contaminants. This is a common problem when using charge materials that oxidize when exposed to air, or when using diffusion pumps that coat the vacuum system with oil, or when operating the ion gun for extended lengths of time.
Remedy: Clean ion gun system electrodes by dismantling gun system. The model 200-B extraction cup usually has the most deposits, and sometimes beam instability can be corrected by cleaning this lens element. Also, measure the impedance between each guard ring shim plate of the model 600/600-B velocity filter. If there is any measurable resistance, than the velocity filter shim plates will have to be cleaned. Clean all parts with an emery cloth to remove the contamination followed by an acetone and alcohol bath. Colutron also offers a cleaning/refurbish service. Please see http://www.colutron.com/products/repair.html.

Cause: Floating electrodes.
Remedy: Check the continuity of each electrode (model 200-B lens system, vertical deflection plates, velocity filter guard ring shims) to each of the electrical feed throughs. Use the wiring diagrams included with the instruction booklets as a reference.

Cause: Ion source gas leak will cause an unstable discharge.
Remedy: The model 100-Q ion source uses a flat contact seal between each quartz part. Check quartz parts for cracks or the sealing surfaces of all the quartz parts for excessive pitting. If this is the case, the parts should be replaced. Also, after prolonged use, the tungsten spring (PN-155-Q) will lose most of its spring tension. Try pulling the spring apart to restore some of its original spring tension, or replace the spring.

Cause: Missing 100-ohm power resistor in series with anode connection.
Remedy: Make sure that a 100-ohm, 50 watt resistor is connected between the anode supply and anode. This resistor is used to stabilize the ion beam by inductively damping plasma oscillations within the discharge.

Cause: Anode and filament power supplies are being operated in current control.
Remedy: Make sure that the ion source power supplies are VOLTAGE regulated.

Problem: Beam alignment problems

Cause: With the velocity filter magnet and electric field supplies turned off, the ion beam does not propagate on axis to a Faraday cup or other measurement device down stream. This is due to the residual magnetic field of the velocity filter.
Remedy
: Increase the voltage to the velocity filter electric field plates (horizontal deflection) to compensate for the velocity filter magnetic field. If this does not solve the problem, try switching the polarity of the electric field plates. If the velocity filter magnet and electric field plates are connected properly, increasing the magnetic field will deflect the beam in the opposite direction as when deflected by the electric field plates.

Cause: Floating electrodes
Remedy
: See remedy under beam alignment problems

Cause: Dirty electrodes
Remedy: See remedy under dirty ion optics

Problem: Unable to strike an arc with the ion source

Possible Causes: Filament voltage and/or anode voltage too low. Anode not connected to the anode contact wire. Inadequate gas or solid charge present. Ion source leaking gas.
Remedy
: Increase the filament voltage a maximum 14.5. Increase the anode voltage to a maximum 150 volts. Check the anode connection to the anode contact wire. A tungsten wire wrap is used to make the connection. Monitor the ion source gas pressure. Some gasses such as helium require a high source pressure (up to 500 milli-torr). Check the quartz ion source parts for pitting at the sealing surfaces that could cause a gas leak. Also, check the tungsten spring (pn-155-Q) for proper tension. If using a boron nitride source, make sure that the ion source cap is properly secured by the cap snap ring (pn-129) and that the anode snap ring (pn-114) is installed. In all cases once an arc is struck, decrease the discharge current to 150mA or less by lowering the anode voltage or gas pressure.

Problem: Gaseous discharge in ion source gas inlet tube

Cause: Ion source gas inlet valve not floating, but at ground potential resulting in an electrical discharge due to rarefied gas. Ion source gas pressure could also be too high.
Remedy: Make sure that the ion source gas inlet valve is floating. Adjust the gas valve using an isolated shaft. Keep source pressure below 500 millitorr.

Problem: Quartz ion source parts turn milky white and/or ion source ceramic parts cracked.

Cause: Ion source is operated at too high of temperature.
Remedy: Do not exceed 15V on filament and 250 mA anode emission current.

Cause: Insufficient cooling.
Remedy:Make sure that the ion source heat sink output coolant temperature does not exceed 100 F (40 C). Ensure that the heat sink coolant rate is at least 0.5 liter/minute. Also, adjust the ion source insertion depth on the ion source receptacle flange so that the ion source cap just barely (1/2mm-1mm) comes into contact with the end of the heat sink. Do not force ion source into heat sink. Ion source cooling is mainly accomplished by thermal contact of the cap and heat sink. The 1/2mm gap allows for expansion of parts.

 Filament frequently asked questions

Question: My filaments do not seem to last very long?
Answer
: The ion source filaments should last for about 100 hours. For maximum filament life, make sure that the filament current does not exceed 18 amps for a PN-120 (20 mil) filament and 12 amps for a PN-115 (15 mil) filament. Also, for most gasses, the ion source pressure should below 100 milli-torr. Filament lifetime will also be reduced if some reactive solids/gasses (especially water vapor or oxygen) are used as the charge material.

Question: What are the different applications for the two types of filaments offered by Colutron?
Answer
: The PN-120 (20) mil filaments are used when a greater source temperature and/or maximum beam current is desired. For some reactive gasses such as oxygen and chlorine, it is advisable to use a PN-115 (15 mil) filament because the source plasma temperature will be decreased. This reduces damage to ion source parts from the hot reactive gasses. The 15 mil filaments are also used when a smaller beam current is required.

Question: What is the best filament to use for oxygen ions?
Answer
: The PN-115 (15) mil filaments are used when a cooler plasma is required. This is important for generating oxygen ions. The best filament material is thoriated iridium wire. This is currently unavailable from Colutron, but we are working to add this filament to our product line. 

 Model CU-1 Cooling System frequently asked questions

Question: Where is the expansion or metering valve?
Answer
: The Colutron model CU-1 (HFC-134a) cooling system does not use a metering valve. The unit does not operate as a standard air conditioning system, but is used to remove heat from the refrigerant through the unit's condensing coils.The CU-1 compressor, cycles the refrigerant in a liquid and gas mix through the ion source heatsink and velocity filter magnet coils. When the hot refrigerant (80-100
F) returns to the CU-1 unit, the heat is removed by a fan blowing across the condensing coils. There may be some metering of the refrigerant however, since the coolant passages vary in diameter resulting in cold spots. This is normal.

Question: The refrigerant seems warm or hot to the touch. Is something wrong?
Answer
: The normal coolant temperature with the ion source operating is 80-100
F. A temperature switch is included with the cooling unit and should be used to monitor the coolant temperature. If the coolant temperature exceeds 100 F, then the switch will energize. This switch can be used in conjunction with an interlock system to switch off the ion source power supplies in case of a cooling failure.

Question: The cooling unit switches off after running for a short time. What's happening?
Answer
: The cooling unit pressure switch is set to shut the compressor off if the coolant pressure exceeds 150 pounds/square inch (PSI). Make sure that your pressure switch is set at 150 PSI. If the pressure switch is set for 150 PSI and the cooling unit still shuts off, the cooling unit may have been overfilled with refrigerant. The normal charge is 2 pounds HFC-134a (R-12 on older models). Also, if the lab temperature is hot (90-100
), the pressure will increase in the cooling lines and could exceed 150 PSI.

Question: I am having problems charging the cooling unit. What is wrong? How do I fill 2 pounds of refrigerant?
Answer
: Make sure that the compressor is running, and open the inlet valve on the suction side of the compressor. To fill 2 pounds, put the refrigerant tank on a weight scale and fill until tank weighs 2 pounds less.

Question: I have heard that the compressor will be damaged if it compresses liquid refrigerant. Is this true?
Answer
: Yes and No. Although the refrigerant is in a liquid and gas phase, when the liquid/gas is compressed in the compressor, it can expand into the storage tank, which is about 1/2 full. If the storage tank were completely full of refrigerant (unit overfilled), the compressor could then be damaged since the refrigerant has no room to expand.

Question: I have an old Colutron cooling unit that uses the now banned R-12. Can I use the new ozone safe HFC-134a in my unit?
Answer
: No. The old R-12 units use a mineral-based oil, and the new HFC-134a units use a poly-ester-ether based oil. They are non-compatible. It is possible however to retrofit the older units by completely draining the mineral oil and adding the poly-ester-ether oil. This process is difficult, since ALL the mineral oil must be removed. The compressor label should have information about the amount of oil required.


 
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