Spare parts and self-service

The facility is responsible for purchasing and maintaining a stock of

‘consumables’ — small parts such as ion source cathodes and insulators, O rings, extractor and target foils, etc., which are expected to wear out and to be replaced regularly during normal operation of the cyclotron. At the beginning of the installation, and probably through the first year or two of operation, it is assumed that these consumables would be purchased in ‘kit’

form from the original equipment supplier.

However, with the necessary extra work and investment in time and effort in identifying and characterizing these parts, many of the items (or their functional equivalents) can also be found and purchased in normal commerce at a considerably lower price. The resulting savings in overall operating cost over the life of the system may be substantial.

3.5.4.2. Proprietary, non-consumable spare parts

The most common routine service interventions are replacement of ion source cathodes or filaments, replacement of extractor foils, and maintenance and repair of the target(s). In the ideal case, these interventions are carried out on a scheduled basis, after a pre-determined number of ‘beam-on’ hours, or after observing a (hopefully) gradual degradation in performance.

The small parts which are actually changed and replaced are drawn from the stock of consumable components which is maintained on-site. We recommend — in addition to the normal complement of standard consumable spare parts — that a specific set of spare, fully assembled vendor proprietary components also be purchased by the owner. Routine, scheduled system repairs are then easily done by ‘swapping’ these complete subassemblies and implementing the actual repair or replacement of worn out consumable components in the parts which are removed from the cyclotron, the work performed on the laboratory bench, at one’s leisure.

In the case of the ion source and target(s), it is highly advantageous and recommended to have a fully assembled spare ion source assembly and — depending on how many different types of targets are being used routinely — one or more spare target assemblies.

At least one — and preferably two — extractor foil-holder carousel assemblies should also be kept on hand.

3.5.4.3. Non-proprietary, non-consumable spare parts

With the exception of a half dozen or so proprietary subsystems and assemblies, such as the ion source, target changer and targets, extractor mechanism(s), etc., mentioned above, many component parts are non-proprietary and are available for purchase in normal commerce. However, identifying and characterizing these will require some work and investment of time and resources by the facility — and possibly some help from the outside — as it is generally not in the interest of the original equipment supplier to provide this information. There may be no particular reason or incentive to worry about this while the manufacturer’s warranty is in force, but once the warranty has expired this can be very important in maintaining economical operation and maximizing ‘up-time’ of the system.

Essential non-proprietary spare parts. The RF system final amplifier and intermediate power amplifier vacuum tubes, high voltage ceramic coupling and bypass capacitors should be kept in hand at all times as these items can take a significant amount of time to be delivered from the manufacturer.

3.5.4.4. Essential service tools, instruments and fixtures

First year warranty notwithstanding, it is vital that the owner purchase and maintain the tools, instruments, and other resources (including in-depth training of local, resident technical personnel) so as to conduct as much of the routine — as well as urgent, non-routine — service as possible to minimize the delays, down-time, expense, and aggravation associated with having to wait for technical support from abroad.

Having the right tools and instruments in hand can, at the very minimum, facilitate resident troubleshooting and diagnostic capability to the extent that support and advice from afar, especially on the more common problems, becomes feasible by telephone or email.

The following is a short list of recommended tools and instruments, arranged by category. The list is not necessarily all-inclusive, but is intended to serve as a general guide wherein the most important items are covered. It is always better to have too many — rather than too few — tools.

Small hand tools. For normal day-to-day mechanical equipment maintenance, a complete ‘mechanics tool assortment’ in a roll-about cabinet with locking drawers may be purchased through catalogues or from large department stores.

An assortment of ‘electronics technician’ hand tools is needed, including:

jeweller’s screwdrivers, small needlenose pliers, diagonal cutters, tweezers, wire strippers, crimpers (for attaching terminal lugs and assembling coaxial and multi-pin cables, etc.), soldering iron, and ‘solder-sucker’ (for repair of printed wiring boards).

Also needed are: precision calipers with digital read-out; portable, a battery operated drill motor with an assortment of ‘English’ and metric drill bits; tap and die set (‘English’ and metric threads); small hacksaw, tubing cutter, assortment of files, including miniature jeweller’s files; small flashlight;

portable, high intensity work lamp.

Small portable electronic and laboratory test instruments. Continuity tester, two and three phase mains tester; digital multi-meter with accessories, including: high voltage DC probe (20 KV), clamp-on ammeter, and (optional) temperature probe. A 100 MHz oscilloscope with probes; frequency counter;

signal generator with vernier frequency adjustment covering 70–80 MHz.

Specialized test and diagnostic instruments. Helium leak checker; residual gas analyser; Gow-Mac leak detector for leak testing high pressure targets;

RF ‘dummy load’ resistors for high and medium power (one each required for 10 KW and 500 W power ratings); medium power (500 W) RF directional coupler and power meter; an array of 50 ohm RF cable adaptors, tees, miniature directional couplers, attenuators; dual channel analog chart recorder or equivalent digital data logger.

Electronic components. If there is no convenient local supplier for common, small electronic components such as resistors, capacitors, semiconductor products, fuses, lamps, terminal lugs, etc., then a selection must be purchased and stocked on-site.

3.5.4.5. Special topics

There are some specific technical support issues which may be unfamiliar to those who are new to the field, or which are particularly important and must be emphasized and understood in advance — particularly for cyclotron systems which will be installed overseas or in remote areas, far from the manufacturer.

Bead blaster. This is a particularly useful accessory for maintenance of the ion source and its internal components. It is used for cleaning oxidation and

‘invested’ contaminants from metal and ceramic surfaces by means of tiny (micrometre sized) glass beads driven at high velocity by a jet of air supplied by a small compressor. The action takes place inside a transparent, sealed glove-box compartment with an internal, recirculating air filter and reservoir to maintain cleanliness and to prevent leakage of glass particles into the room.

Vacuum leak detection: Leaks in the cyclotron vacuum system may occasionally occur due to operator error or a momentary lapse during a service or maintenance intervention. Often such leaks can be fixed by simply ‘back-tracking’ to correct the mistake. However, vacuum leaks can also occur due to mechanical wear of shafts or other penetrations, or radiation damage or overheating of elastomer O-ring seals. In these cases it can be very difficult to pinpoint the problem, and a methodical and systematic process of ‘leak chasing’ must be undertaken.

The general subject of methods and techniques for leak detection is best covered in a ‘hands-on’ training course, supplemented by technical documentation and textbooks such as Basic Vacuum Practice by Varian, Inc.

If not repaired in a timely manner, a vacuum leak can get worse and may lead to overall degradation in system performance, severe wear and tear on other subsystems such as the ion source and RF system, and possible further damage or disruption and shut down of the entire cyclotron system.

Fortunately, severe vacuum leaks do not occur often, but it is the very rarity of the problem that can also render vacuum leaks among the most difficult and frustrating problems to resolve. Generally, the instrument which is used to find a vacuum leak is the ‘classic’ helium leak detector. The overseas customer should either purchase — or at least have ready access to — a good quality helium leak detector. The choice of which leak detector depends on how one chooses to trade off between the most automated, high end (and highest price) systems versus manual, lower end (and substantially lower priced) systems.

The high end, fully automated systems are, of course, easier for the novice or occasional user to learn and operate — especially when used only occasionally — with advanced features like ‘auto-calibration’. The less expensive manual systems will require an extra investment of time and effort in operator training, but are entirely satisfactory for the job at hand. Moreover, test equipment also needs occasional service and maintenance; the less expensive manual systems can generally be maintained by the user, on-site, with kits of replacement parts available from the manufacturer, while the fully automated systems may require factory only service. One should always, if at all possible, choose a leak detector system which incorporates the newer turbomolecular type of vacuum pump, as opposed to the oil diffusion pump.

The turbopump systems are more easily started up from a ‘cold’ state whenever they are actually needed, whereas the diffusion pump systems often have to be left plugged in and running at all times (24 hours per day, seven days per week) in order to maintain these machines in a reliable ‘ready’ state.

Finally, one does not necessarily have to purchase a new leak detector, as they are also available used — but carefully reconditioned and guaranteed by reputable suppliers.

Residual gas analyser: An extremely useful and valuable supplement to the helium leak detector is a new, relatively inexpensive, very rugged and compact ‘residual gas analyser’ (RGA) which provides additional information which, in turn, can significantly enhance the speed and efficiency of finding and fixing vacuum leaks. The fully configured RGA (approx $7500) also incorporates a ‘leak detector’ operating mode, which may often substitute for

— though not entirely eliminate — the need for access to a ‘classic’ helium leak detector.

Dual channel analog chart recorder. A digital data logging facility is usually included in the cyclotron’s control system software, but the temporal sampling rate may not be sufficient for characterizing every problem; the solution to some problems may require recording two or more operational parameters in real-time. A compact, relatively inexpensive, dual channel analog strip-chart recorder is very useful for this task. Alternatively, a dual or multi-channel analog to digital data logger with 1 s or less sampling interval may also be used.

Special test fixtures. After finishing repairs or replacing consumables on an ion source or extractor assembly, it is highly recommended that these components be checked for vacuum integrity before they are stored or have to be reinstalled in the cyclotron itself. This will require some simple vacuum test fixtures which may be designed and built locally by qualified engineering/metal fabricating shops.

Additional recommended spare parts are:

— RF coupling loop assembly;

— Mechanical pump oil and filters;

— Diffusion pump oil;

— Spare diffusion pump heaters;

— Diffusion pump temperature switches;

— Spare solenoid coils;

— Spare pneumatic valves;

— Spare high vacuum gauge filaments;

— Spare TC gauges.