Also see the following:
These are the types of lasers generally used for large scale light shows as well as in some types of high performance phototypesetters or other digital imagers, and for use in holography and other optics research. Unlike diode and HeNe types, a serious interest in these also represents a very serious investment of time, money, and caution.
The Xerox 9700 (and possibly the 8400 as well) has an ALC-60X argon ion laser. The common ALC-60X laser was made to the Xerox "X" standard for a high speed duplicator/printer, hence the X in the part number. The NEC-3030 is also a printer laser. Many of these older but expensive systems are still being maintained and are now being retrofitted with newer technology such as high power IR diode lasers or Diode Pumped Solid State (DPSS) lasers. Therefore, more small air-cooled argon (mostly) ion laser heads and power supplies should be showing up on the surplus market at attractive prices.
However, many older laser printers and related equipment were based on HeNe lasers so don't assume there is an argon ion laser in that dusty thing at the salvage yard (even if quite large) just because it has a laser warning label! (Newer consumer/office type laser printers use relatively low power IR diode lasers.)
A module which is NOT part of this particular course, Argon Ion Laser Systems, goes into considerable detail on the theory as well as some more practical information related to argon ion lasers including the basic construction and principles of operation, power supply fundamentals, and more. It includes a number of diagrams as well (though some seem to be scanned at too low a resolution).
However, the course with which it is associated has apparently not been completed as no other modules exist at the present time. There is an outline at: LEOT, Course 3: Laser Technology. Note that both of these are likely to be unreliable links while the coarse is under development. My guess is that the URL will be Course 3: Laser Technology when it is complete.
I'm sure you've seen the posts on the sci.optics or alt.lasers newsgroups that go something like: "I just got a big laser. What type is it? What can I do with it? Etc." One of these guys is going to look down the bore and get blinded or worse. So I'd also like to see a site up for that reason. Well it turns out there is such a site. There is a excellent laser safety site at: Rockwell Laser Industries.
Note: Since comparisons are made throughout this discussion between argon (and krypton) ion lasers and helium-neon (HeNe) lasers, it is worthwhile to first read the Chapter: Helium-Neon Lasers if you are not familiar with those devices.
The basic design of the argon/krypton laser is conceptually similar to that of the HeNe (or other gas) laser - plasma tube containing the active medium (argon and/or krypton gas) mirrors forming a Fabry-Perot resonator. However, unlike HeNe lasers, the energy level transitions that contribute to laser action come from ions of argon or krypton - atoms that have had 1 or 2 electrons stripped from their outer shells. Spectral lines at wavelengths less than 400 nm come from atoms that have had 2 electrons removed. Longer wavelengths come from singly ionized atoms. There are many possible transitions in the UV, visible, and IR portions of the spectrum. With suitable optics coherent light from a single spectral line or many lines may be produced simultaneously. An adjustable intra-cavity prism can even be included to permit the desired wavelength to be selected via a thumb-screw adjustment.
Beam characteristics in terms of diameter and divergence are similar to those of HeNe lasers but the spectral line width is wider and therefore the coherence length (without additional optics) tends to be shorter.
To excite the ionic transitions and achieve a population inversion, much more current is needed than for a HeNe laser. A 'small' argon laser may use 10 AMPs of current (rather than the 3 to 8 mA typical of a HeNe laser tube). Even at a tube voltage of 100 VDC, this represents about 1000 W of power dissipation. (Think of a typical space heater inside a small box!) High flow rate forced air cooling is absolutely essential - the tube would melt down in short order without it. Larger ion laser tubes may pass more than 100 AMPs of current at up to 400 VDC or more - and require three-phase power and water cooling - figure on utility substation just for your laser!
Thus, while Ar/Kr ion lasers and HeNe lasers are conceptually similar, the approximately 3 orders of magnitude greater tube current and two orders of magnitude greater power dissipation compared to a HeNe laser mean that the construction details are vastly different. You won't find one of these in a laser pointer!
The following assumes a small air-cooled Ar/Kr ion tube like that used in the American Laser Corporation 60X/Omnichrome 532 or the Cyonics tube described in the section: Cyonics Argon Ion Tube.
Only a few modern air cooled tubes stand up to 12 A and most models peak out at 10 A, despite what Omnichrome says in their documents. The tubes will invariably come with a 10 A limit sticker. As far as I'm aware, no application ever used the 'special modifications' for 14 A for the Omnichrome 532, these special modifications are going to a tube that is twice as long with 2 huge fans, which is actually the next model up, the 543.
Also see the section: Argon/Krypton Ion Laser Tube Life.
Unlike a HeNe tube, the Ar/Kr ion discharge may not present a large negative resistance once the arc has been struck. Some references suggest that the effective series resistance is on the order of 1 or 2 ohms positive while others indicate that it is a low negative value (or perhaps it depends on the particular tube design and operating conditions). In any case, the tube behaves so much like a dead short that without a regulator or some additional ballast resistance, this argument may be only of academic interest!
If the resistance is positive, tube current can theoretically be controlled by varying the voltage of the supply and a ballast resistor isn't strictly essential as with an HeNe tube just to maintain stability. However, this control would be extremely sensitive to EVERYTHING since a small change in input voltage would result in a large change in current. For example, assuming the effective discharge resistance is 1 ohm for a tube dropping 100 V at 10 A, a 5 percent variation in input voltage would result in more than a 50 percent change in tube current! Furthermore, due to changing conditions as the tube heats, a runaway condition is possible even if the resistance of the discharge is non-negative and must be avoided by using a proper current regulator (or adequate ballast resistance - for testing only).
In any case, if you acquired a head that is missing the HUGE fan - don't be tempted to run it until you have one in place and spinning up a storm!
The following patents are particularly relevant with respect to small io lasers:
While patents do not provide all the details needed to construct your own system, they are valuable nonetheless as a starting point for understanding basic principles of operation and system design. Some of the electronics are described in substantial detail.
However, some of these appear to match actual hardware very closely. Of particular interest are the two ALC patents. These outline the principles of operation and provide fairly complete schematics of the power supply for the ALC 60X/Omnichrome 532 laser.
Some information may also be available from the major manufacturers of ion lasers. See the chapter: Laser and Parts Sources for addresses and links.
454.6 nm 457.9 nm 465.8 nm 476.5 nm 488.0 nm 496.5 nm 501.7 nm 514.5 nm 528.7 nm
406.7 nm 413.1 nm 415.4 nm 468.0 nm 476.2 nm 482.5 nm 520.8 nm 530.9 nm 568.2 nm 647.1 nm 676.4 nm
A laser set up for multi-line operation will usually result in highest total output power but there are many applications where a monochromatic beam is required.
Multi-line operation requires a set of mirrors with reflectivities designed to achieve laser operation for all the desired spectral lines. Any intracavity prisms are removed.
Single line operation can be implemented in a couple of different ways:
An air-cooled argon tube will only lase at:
For krypton, the lines are:
The tables below list the relative strengths of all the important lines for a typical 30 watt argon/7 watt krypton laser with:
The 488 and 514 nm lines are lower then normal on this list - other manufacturers claim more power for these 2 lines.
Argon lines:
Wavelength Relative Power Absolute Power
------------------------------------------------
454.6 nm .03 .8 W
457.9 nm .06 1.5 W
465.8 nm .03 .8 W
472.7 nm .05 1.3 W
476.5 nm .12 3.0 W
488.0 nm .32 8.0 W
496.5 nm .12 3.0 W
501.7 nm .07 1.8 W
514.5 nm .40 10.0 W
528.7 nm .07 1.8 W
Krypton lines (magnetic field optimal for majority of lines, but not all).
Wavelength Relative Power Absolute Power
------------------------------------------------
406.7 nm .036 .9 W
413.1 nm .07 1.8 W
415.4 nm .02 .28 W
468.0 nm .02 .5 W
476.2 nm .016 .4 W
482.5 nm .016 .4 W
520.8 nm .028 .7 W
530.9 nm .06 1.5 W
568.2 nm .044 1.1 W
647.1 nm .14 3.5 W
676.4 nm .048 1.2 W
Depending on gas fill, current, optics, and luck, there may be other weak
lines present including: 437 nm (argon), and 457.7 nm, 461.9 nm, 657.0 nm,
687.0 nm, and 799.3 nm (krypton).
As a side note, the color saturation with an ion laser is unbelievable, it's possible to get 16.8 million distinct shades with off the shelf hardware. I know the eye can't resolve that but the results you can see are beautiful.
The most common white light lasers are large frame ion types with a mixture argon and krypton for the gas fill.
White light lasers are now even available in air cooled format. All use a mix of argon and krypton. Many are made for a roughly 60:20:20 ratio of red, green, and blue lines for proper white balance. Their reliability is increasing with cost staying a little above normal Ion laser prices. Spectra Physics, Coherent and Lexel all manufacture tubes for this, and LaserPhysics Inc sells the air-cooled version that runs off single phase 220 VAC and does 400+ milliwatts. Most of these lasers are modified for reduced operator skills with sealed mirrors and simplified power supplies. So yes they are out there, and laser company reps tell me the demand is going up as people start to use them for lab and industrial applications as well as display. CREOL in Florida and quite a few other labs have demonstrated RGB as well in diode pumped frequency doubled YAG lasers so smaller and more practical is just around the corner as soon as ways are found around the materials and QC problems with solid state laser components, right now they have to test 4 or 5 crystals for every good one they get.
Note that other technologies can be used for white light lasers. For example:
(From: Colin Evans (c.j.evans@goose.ac.uk)).
A white light laser was developed in this department several years ago. It was based on a helium-cadmium mixture which could lase simultaneously at red, green and blue wavelengths. There was no automatic balance between the three colours and had to be carefully adjusted using the pressure and temperature. Also, I don't know whether the three colours could be regarded as "coherent" in any sense. Advantages are very strict polarization, and narrow parallel beams, neither of which are much use in a projector.
(From: Marco Lauschmann (lauschm@hrz.uni-kassel.de).
The only real white laser I know of used a Bucky-ball (carbon) compound which was optical pumped by the 488 nm line of a argon ion Laser. The emission was a real white light continuum - not like the 488 nm, 514, nm and 647 nm lines of an Ar/Kr ion laser system which looks like white light to the human eye. Researchers at the University of Manchester Institute of Science and Technology have demonstrated that confined buckyballs emit strong white light when excited by blue light from an argon-ion laser. Although work is at an early stage, the group has already identified some possible applications for this new material. They suggest that it may form the basis of a new laser material or new types of optical displays.
Another source for a white light continuum is a Ti:Sapphire regenerative amplifier with a frequency doubler. So, a white light continuum could be produced with 800 nm output of 150 Fs, 500 uJ pulses at 1 KHz from a Ti:Sapphire regenerative amplifier, which extends from 400 to 1500 nm. A 5 cm long piece of fused silica is the non-linear element and was used to generate the continuum. This is only an example - there are systems which deliver a white light spectrum with average power of more than 1 W with repetition rates of 250 KHz or more.
An air-cooled tube is a neat little thing about four times the diameter of an average glass HeNe tube. Most have external mirrors and Brewster windows, but many are of the sealed mirror variety. What they all have in common is a heated cathode (like a vacuum tube such as a magnetron) requiring 3.2 volts at 10 to 25 amps. They operate from a range of 4 to 10 AMPs through the arc (Yes, that is AMPs) at around 100 VDC. The tube current is fed to the cathode via a center tap on the filament winding of the transformer to balance the arc on the center of the cathode to avoid plasma etching of the cathode supports. Hence the need for a beefy transformer with #14 or #10 wire on the secondary. Rewound microwave oven transformers work well for this purpose.
The tube is designed for a 100 to 105 V voltage drop, and is ran directly off the rectified and filtered AC line. This makes regulating the tube current a very interesting problem in design because we also have a series injection igniter (similar in function to a HeNe starter) which is a 3" toroid with 80 turns on the secondary and one turn on the primary. A 10 uF cap is charged to 110 or 400 V depending one the model of laser and is dumped directly into the 1 turn primary through an SCR which has a reverse connected fast switching (10 ns) diode across it. You end up with a 500 Khz 30 KV ringing wave pulse applied to the tube, which can blow the arc out as well as ignite it. The winding on the igniter transformer is also #14 wire as it also carries the entire tube current. There is no ballast resistor (as would be found in a HeNe laser power supply) as it would have to dissipate up to 1,000 watts at times. There is a .2 ohm resistor in the anode lead inside the head to sense the current for feedback to the supply, and a beam-splitter sampler that drives a solar cell for the fine loop, which keeps the light level constant to .05% and is used to cancel out noise and oscillations in the beam.
An air cooled tube's current is usually regulated by either a series pass-bank of 4 high power NPN power transistors in linear mode, with two 700 V, 20 A PNP transistors ahead of them in switch mode. Alternatively, two 400 V, 25 amp FETs are used in a buck mode converter at 80 Khz. Larger water cooled lasers which run off three-phase and need 20 to 35 amps of tube current use about 100 large NPNs in series/parallel strings for fine adjust and SCR's on the incoming phases for course adjustment.
The fun part starts when you buy the laser, the power supplies are scarce and run about $900 to $1,250 used. When the laser tubes are pulled for a rebuild every 5,000 hours the PSU stays in the photocopier/printer/medical instrument/typesetter or whatever until the whole unit is discarded. So the laser heads show up, but supplies keep their initial value.
A tube is good for 2 to 3 rebuilds, and after 5,000 hours they usually have 1,000 to 2,000 or more hours left for they hobbyist to enjoy. Most of the lasers are built as 150 milliwatt units and ran at 20 milliwatts to enhance lifetime, so even an old laser still has a lot of potential.
There is no book on how to maintain these things either and since it is the Holy Grail of laser hobbyists to own one, maybe its time they learned how to maintain them, clean the optics, align the mirrors, peak the performance and find out how to avoid paying $3,800 for a used one when you can get one for less then $1.000. I (Steve Roberts) paid $125 for my head, and built my own power supply.
CAUTION: These are very fragile where the glass to metal seal joins them to the tube body. Try not to put pressure on them. Running the laser at full current with a finger print on the window can damage the quartz face. Do not make the mistake of trying to remove the window to clean it, it will let air into the tube. :-(.
CAUTION: The black and red jacks are across a resistor in series with the tube and are at 60 to 100 VDC referenced to the case. You will read a voltage from 0 to 3 VDC on the meter, at .2 V/A.
WARNING: Cross connecting the red and black current jacks to the blue and yellow light jacks can blow up the laser system. Even through a voltmeter, the button is there to remind you and protect you. Like they said in Ghostbusters, don't cross the streams!!! For power supplies on lasers over 20 milliwatts, the light jack is not an accurate measure of power, it is there for you to keep track of performance and for tuning the cavity (for best results use a analog meter while tuning).
Also see the section: Typical Behavior of Wavelength Tuning Assembly.
Spectral Plasma Tube Current Thumb-Screw Rotation
Line 6 A 8 A 10 A Clockwise from 514 nm Line
-----------------------------------------------------------------------
514 nm 6.8 mW 24.0 mW 48.0 mW 0 Turn
501 nm 0.0 mW 1.2 mW 5.0 mW 1/4 Turn
496 nm .9 mW 4.5 mW 10.8 mW 3/8 Turn
488 nm 17.6 mW 37.0 mW 60.0 mW 1/2 Turn
476 nm 2.4 mW 7.3 mW 14.3 mW 3/4 Turn
472 nm 1.0 mW 3.5 mW 7.5 mW 7/8 Turn
465 nm 1.5 mW 2.3 mW 11.5 mW 1 Turn
457 nm 1.3 mW 4.6 mW 10.0 mW 1-1/4 Turn
454 nm 0.1 mW 1.1 mW 2.5 mW 1-1/4 Turn
When filled with krypton, the same tube with a 45 cm radius OC and a 45 cm radius HR outputs 647 nm and 676 nm red at about 35 mW while dropping ONLY 85 volts at 10 A. These were the only optics we could find, and were less then optimal.
Krypton runs at a lower voltage, but unlike argon which is a semi-log curve in output versus current, krypton has a knee curve for gain. There is a certain threshold above which all hell breaks loose. I doubt we were at that threshold and we didn't have time to experiment with the pressure of the fill. Below the curve you get mostly 676 nm. A 60X emitting a cherry red beam is a rare sight indeed and we did it just to see if it could be done as many people told us it could not be! We even took it to a conference to ensure witnesses!
There are a couple of tricks to making a small air-cooled tube like the 60X operate with a krypton fill including a large gas ballest and special cathode processing. It will only last a few minutes if you just chop and pump the tube with krypton. NEXT UP, a 60X white light laser, I (Steve) have the optics on order!!
Answer: It is possible but you would only get 15 to 20 mW of red or 7 mW of yellow but not both at the same time. (Maybe slightly more, see the section: Comparison of Argon and Krypton Ion Tube Characteristics.)
Answer: No. Water cooling it will not increase available power as you are limited by the cathode and what the PSU can source off of the 110 VAC line not to mention needing 2 or three isolated cooling loops.
It was a real bit of luck. I study physics at Heriot-Watt University and was walking by the physics department skip (dumpster?) and saw this dirty great metal box with Coherent Radiation Model CR-5 Ion Laser printed down the side.
How could I resist. At this point I knew zero about argons and assumed it was capable of maybe tens to low hundreds of milliwatts and would make a nice contrast to the red HeNes and diodes that everyone thinks are so cool (they are but blue is better :) ). So I dragged it out of the skip and loaded it into the back of my car, drove it back to the flat (apartment) and opened it up.
Oh dear :-(. The cathode end of the tube has shattered and someone has been raiding the electronics for parts. I asked the department about the head and this is the story. It worked. Perfectly. As did four other argon and krypton head they threw out later despite my attempts to get hold of them first. The tubes break when the heads drop four feet onto metal and concrete. Apparently the lasers are "too old to use" and "we use solid state now" so they throw them out . Sorry about the mild rant but it kind of annoys me to see several perfectly good lasers destroyed just because they bought new ones and they don't want curious undergrads messing with the old ones. Grrrrr...
(It would drive me nuts to think that perfectly good lasers were trashed when I can think of so many good homes for them! Probably too many lawyers or whatever you call them over there! --- sam)
They're called solicitors - yet soliciting is a crime. Go figure :). I think the judge is called "My Lord" too. And they wear funny wigs. I don't pretend to understand the legal system......
Well that is sort of the reason. For a while (10 years or so) now there has been all sorts of crud flying about worker safety and dangers at work. Now as you know a 5W argon and PSU presents a fair few ways to injure yourself and the uni is VERY strict about safe working with them in the labs. NO-ONE is allowed in a lab with an operable laser unless they have had an eye test, read the rules about laser safety and have appropriate eye wear. If you want to chat to your mate in the laser labs they have to shutter off the beam, leave the lab, close the door. If there is no-one left in the lab the laser must be turned off etc.
So you can imagine their mild horror when I go round asking for help to get their old lasers running in my flat. They do have a valid point and I agree that they would get a good roasting if they GAVE me a laser and I fryed myself but I promised any lasers they were chucking would get anonymised (labels peeled, ID numbers ground off, etc) and I'd deny everything as it were but they still insisted on breaking them. Still, I have rescued one and should get it working so I am happy.
In defense of the university who are (perhaps rightly) getting a mild roasting here, when Nigel (mate and laser enthusiast) and I asked the optoelectronics boss about the chucking out policy he did give us a dead 1W Nd:YAG with parts missing and said as long as we didn't take it off campus we could fix it up and tinker with it. As it is missing Q switch, cavity, PSU and most of the head electronics it is unlikely to work any time soon. We may end up converting it to pulsed operation. More likely we will let it rot in Nigel's lab. He also offered us a tour of one of the laser labs which has argons, kryptons, excimers and I believe a TEA. I get the impression personally he'd have liked to help.
Anyway, I phoned Coherent UK. They said "you are not a company so we can't deal with you". They wouldn't even send me schematics on a laser that is 30 years old and hasn't been supported for the past 10? 15? years. So I looked around the Web and emailed a few companies asking for schematics and/or parts. Laser Innovations said they had a tube I could have (for free! if I pay shipping so I don't mind if it isn't up to commercial rebuild standards) so I am very close to having a complete head.
I already have a design for the PSU. It was initially going to be a line powered switcher with a small linear pass-bank but it turned out it was easier and cheaper to build a BIG pass-bank (40 - IRF740 power MOSFETs) and water cool the heatsink. It's loosely based on the original Coherent design but missing a few of the more exotic bits (due to price and parts availability). The Lexel 88 schematics are pretty much identical to those in the Coherent manual. I guess there's only so much you can do with a linear design.
I doubt my design is as good as Lexel's or Coherent's and I doubt it meets CE standards but it will (slowly) charge the caps, fire the starter and regulate the current all without melting. :) Ferrites, chokes and other moderately exotic parts are very hard to get hold of in UK unless you are a business or university or lab.
I will buy PSU parts soon, a major capacitor manufacturer have generously donated a big filter capacitor so I estimate 200GBP for the rest of the bits and pieces.
Side note: I like the magnetic oscillator in the Lexel 88 starter, very clever.
(From: Richard and Debora Everett" (everett@oz.net)).
I just bought two argon medical lasers from a local auction. One of them is a Coherent model 900. It has a manufacture date of 1981, and the little meter inside says 79 hours. It is water cooled and rated for 9 watts output. The funny thing is, it takes three-phase 208 V at 35 amps! This thing must really be inefficient!
The second laser is much newer with a manufacture date of 1988. When I got it home, I was pleasantly surprised to find it has TWO tubes in it, a 10 watt argon and a 3 watt krypton. Both of these tubes are water cooled and made by Spectra-Physics. The laser itself was made by Cooper Vision and Hewlett Packard.
Now I have little (okay, zero) experience with ion lasers, although I have worked with HeNe and CO2 lasers before. I am a little concerned about the integrity of the Cooper Vision/Hewlett Packard laser tubes, because the &#$# loading dock guy dropped the whole cabinet assembly about 4 to 6 inches from his pallet jack. I have looked at the tubes (very cool looking) and see no visible cracks, although most of the tube seems to be in a metal jacket. I am not sure how to tell if either tube survived all of this.
Anyway, I only paid $200 for all of this, so I guess I will not be out that much if they don't work.
"When I was visiting a local laser company (Latronix AB) to acquire my first HeNe tube, a Russian made 1.2 mW tube manufactured only a year ago and probably never used, price ~$12 :), I saw something pretty interesting on display in a locker. Stupidly, I didn't ask about it, but maybe someone here knows anything about it.(From Sam):Here's an ASCII illustration:
+-------+ | \ | \ ____________________ +--+ \---------+--------------------------------------+ | | | | +--+ /------------------------------------------------+ | / | / +-------+The base of the tube was wide, and the rest was maybe 1 inch or so. A thin glass tube was spiraled around the long tube (the strange looking thing on the illustration :). The total length was about 16 inches.3 wires stuck out from the base. The only thing readable on the label (from my viewing angle) was "made in Russia" and some obscure model number. I don't remember anything about the electrodes. I think it had mirrors on the ends, but it might have had Brewster windows. Any ideas about what this laser might be?
Label on My Tube:
PLASMA HeNe Gas Laser <Number (S/N??)> 04-97 Made in RussiaLabel on Strange Tube:PLASMA ????? ???? ???? Made in RussiaThe only things readable from my angle was a bit of the logo and "Russia".Hmmm.. I will pay the company another visit in a month or so to get a larger HeNe tube and maybe a diode laser and then I'll take another look at it. I wonder if they would sell the strange tube to me. At least it would look good as a hi-tech glass display :)."
Since there aren't that many types of low power gas lasers, it might be a HeNe but the spiral tube thing is really strange. Any chance of getting another look? Conceivably, it could be a high quality tube designed to have ring magnets on the outside to focus and stabilize the beam or something.
Of course, it could be a lot of other things!
"Maybe.. But the spiral tube would be in the way.. And 3 connection wires? And, it had the same type of label as my HeNe."(From:Chris Livingston chrisliv@aol.com)).
I may be wrong here, but it sounds like a NEC Type Argon tube, The wide part, sounds typical of the NEC tubes, and the cathode is normally suspended inside this "Wide Part" which on my nec is about 4-5" and the "spiral" sounds to me like it may be the gas return like used on the NEC tubes, which is from the wide part back toward the anode region. The mirrors are connected on both ends.
(From: Sam).
But glass? Argon ion tubes are usually made of materials like beryllium oxide and tungsten to withstand the intense heat of the discharge.
"Today, I paid the local laser company a visit again. Result: One REALLY small Siemens HeNe tube (total length 11.6 cm, diameter 2.3 cm, power 0.7 mW, makes a nice laser pointer) and a large ~10 mW Uniphase tube which I'm going to use for a laser show.Most important result (for this letter's purpose at least):
The strange unidentified beast is indeed an argon ion tube (I asked them). I thought argons had large cooling fins and a lot of metal structure, but this one is mostly glass. Now, I just wonder what power it might be. Can't be too high since there seems to be no means of cooling (though the spiral tube might also be a water jacket). The tube also has a strange vent port in the wide section, In all, really strange. :-)"