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All Combo-Vacs consist
of an ion pump, cryoshroud and sublimation pump assembly together with the
appropriate cooling mechanism, control units, cables, internal heaters, 6
spare titanium sublimation filaments, and 2 UHV copper gaskets. Bolt the Combo-Vac
to your system in any position, rough it down, and it's ready for operation.
Features
- Ideal
for vacuum applications where many different gases must be pumped.
- Combo-Vacs integrate
three standard components in one unit for selective pumping: an ion pump,
a cooling unit, and a titanium sublimator.
- High speed, filament-type
titanium sublimator/baffle assembly works at a constant current setting for
reliable repetitive operation. Four separate, spiral titanium alloy filaments
are incorporated in the sublimator assembly to allow continuous pumping over
a 120-hour period. cycling the operation extends sublimator assembly life
proportionally.
- Replaceable noble
ion pumps with demountable high-voltage feedthrough.
- Can be supplied with
diode, hydrogen diode, or triode elements in a range of sizes. Please contact
the factory for custom details.
- Pumping port(s) are
fitted with metal gasketed flange and are blanked off for bakeout and shipment.
- Separate power supplied
for selective operation of sublimator and noble ion pump(s).
- Stainless steel construction.
- Internal bakeout heaters.
- Mounting brackets
are attached to pump body for assembly and support.
- Liquid nitrogen/water
shroud standard.
- Operates in any position.
What is a Combo-Vac
Pump?
Combo-Vac
pumps are a combination of titanium sublimation pumps and ion pumps in one
cryo-cooled package. (Model COV-500 is an exception, as it has an integral
water-cooled jacket rather than a cryoshroud.) They are often used in factory
processing of high power vacuum tubes, X-ray sources, etc. It is well suited
to the gases evolved by such devices in their initial processing. They are
tremendously cost-effective for certain applications, i.e., where reliable,
clean, contaminant-free pumping is a major consideration. Their high speed
is the result of the ability of a freshly deposited titanium film in vacuum
to chemisorb such gases as oxygen, nitrogen, water vapor, carbon monoxide,
and carbon dioxide. When the walls on which titanium is deposited are water-cooled,
speeds of 40 to 90 l/sec (depending upon gas species) for each square inch
of substrate are obtained. Thus total pump speeds can be quite large for large
deposition chambers. The ion pumps handle gases that are not pumped by the
sublimation pump--more about this later.
Because you control
the rate at which titanium is deposited on the walls, you can adjust pumping
speeds to suit your needs. For example, if you must pump down to a certain
pressure before starting a process, you can read that pressure more quickly
by increasing the sublimation rate. If your process liberates gas, you will
be able to speed the process with more speed at your disposal. Conversely,
when the system is not in active use, the ion pump alone will maintain it
at a low pressure indefinitely, thus conserving the titanium supply of the
sublimation pump.
At this point, you
might have a question about the ion pump: Since its speed is so much lower
than that of the sublimation pump, why include it at all? One reason has already
been mentioned. It's a reliable way to maintain a holding vacuum when the
system is not in active use. The most important reason, however, is the noble
ion pump's ability to pump the non-getterable gases such as methane and the
noble gases. Since these gases are generally present in small quantities in
most systems, a small ion pump is able to handle the load, providing it is
specially designed to pump noble gases. Caution: If your process produces
large quantities of non-getterable gases, this will determine the size of
ion pump needed.
All Combo-Vacs use
the SB-1000 sublimator assembly with a PS-500 control unit. The sublimator
assembly holds four separate spiral titanium filaments, each with 1.5 grams
of usable titanium. In normal operations, power is supplied to the filament
for 90 seconds and then removed for an interval. The OFF interval is continuously
selectable in the range of 2 to 120 minutes by means of a front panel control
knob.
Pumping results are
better with cyclic operation than with continuous operation. One reason has
to do with the characteristics of heated surfaces in vacuum. The power dissipated
has two undesirable effects. One is that it causes outgassing of interior
substrates just as a bakeout does though in lesser degree. The second is the
formation of methane at the hot filament. This is thought to be a catalyzed
reaction between hydrogen or water vapor and carbon or carbon dioxide at the
hot filament. Because methane is not pumped by the sublimator, it must be
pumped by the ion pump. Obviously, intermittent operation produces less methane
and less work for the sputter ion pump. What is observed during operation
of the sublimation pump is a brief pressure rise as the filament comes up
to sublimation temperature, followed by a gradual decline in pressure as the
fresh titanium deposits and cools at the substrate. When the power is removed
from the filament, the pressure will generally drop by an order of magnitude.
No new titanium will be needed until the pressure begins to rise again. This
last period of time is dependent on the rate of gas evolution in the system
but is usually within the range of the sublimator control unit timer.
COV-500
The model COV-500 is the smallest combination pump offered by Thermionics.
It has an 8" O.D., 6" I.D., UHV flanged pumping port. A reducing flange
can be used to interface the pump with a manifold or with small individual
devices. The pump operates in any position and is easily disassembled for
cleaning and/or replacement of elements. This pump uses a water-cooled shroud. |
COV-750
The model COV-750 offers an increase in speed and throughput for two reasons.
First, there are 4 noble diode* pump
elements available to handle a larger throughput of non-getterable gases.
Second, a liquid nitrogen cryoshroud is added. The lower temperature of
the cryoshroud as a deposition surface improves the intrinsic speed of the
pump. As is the case for all the Combo-Vacs, it is simple to operate and
is field proven. It can be used in tube processing, vacuum deposition systems,
ion accelerators, and surface research. |
COV-1000
The COV-1000 is the pump of choice when the non-getterable gas load is larger
than the COV-750 can comfortably handle.
As with the other Combo-Vacs, it is shipped complete with all the components
needed to get your system operational. You simply remove the blank-off flange
and attach the Combo-Vac to your system. the control units are designed
for rack mounting and are supplied with the high voltage and high current
cables which attach to the pump. Filaments are already mounted in the sublimator
assembly. Rough the system down, add LN2 to the cryoshroud (or
use TLI model LNC-400 liquid nitrogen level controller), and turn on the
control units. The final adjustment, made at operating pressure, is to adjust
the sublimator interval so that the sublimator turns on after the pressure
has risen 60 to 100% over its previous low value. |
COV-2000
The COV-2000 offers additional throughput because the ion pump's capacity
is double that of the COV-1000. That means additional speed for non-getterable
gases. The overall system speed is increased by use of a larger flange and
a shorter pump neck. |
Ordering
Information and Specifications
| |
COV-500 |
COV-750 |
COV-1000 |
COV-2000 |
| Nom. nitrogen speed,
l/sec (sublimator & ion pump) |
500 plus |
1000 |
1000 |
2000 |
| Nom. air speed, l/sec
(ion pump) |
30/60 |
120 |
220 |
400 |
| Max. argon speed,
l/sec (ion pump) |
7 |
28 |
56 |
112 |
| Sublimator control
unit |
PS-500 |
PS-500 |
PS-500 |
PS-500 |
| Ion pump control
unit |
PS-100 |
PS-350 |
PS-350 |
PS-1000 |
| Number of internal
heaters |
2 |
4 |
4 |
8 |
| UHV flange size (I.D./O.D.
in inches) |
6.0/8.0 |
6.0/8.0 |
6.0/8.0 |
6.0/8.0 |
| Substrate coolant |
water |
LN2 |
LN2 |
LN2 |
| Price |
$7,500. |
$8,950. |
$10,500. |
$13,450. |
| Shipping Weight (lbs.) |
85 |
130 |
200 |
304 |
*Note:
Due to the current shortage of Tantalum material, TLI may recommend a standard
diode or triode pump to replace the noble diode pump. Please call our Applications
Engineers at 1-800-962-2310 or 360-385-7707 for more information.
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