Coherent Innova90-MRA

[nightlife]

Hello,

is there anybody who is able to refill my I90-MRA tube?

It actually works but has lost in power in the last years.

For information, the actual measured currents and voltages are:

12,6A 177,3V (Start Current)
20A 207,4V
25A 224,6V
30A 237,7V
35A 249,6V

My powersupply is an lightforce DLP4045 (switching-powersupply)

Is there a instruction when and how to use the reservoir solenoid?
i have no manual.

[mixedgas]

OK, I need to look at an MRA field install sheet before I comment, but your tube I-V plot actually is not that bad. That will take a day or two.

How often do you run it? How many hours has it had in the last year?

Correct sequence is to energize the ready solenoid, fill the intra solenoid chamber, turn off the ready solenoid, disconnect it from any power source, then energize the fill solenoid. We then close and disconnect the fill solenoid. Both solenoids must never be open at the same time because the resivoir is at nearly atmospheric pressure. In reality most of us use low voltage AC and "buzz" the fill solenoid to slow the flow.

Don't fill it yet. I'm not sure you you need a fill. In fact you may need to use the laser some. The data is borderline for a fill, but may indicate and overpressure from the natural leakage of the reservoir.

Optics peaked and clean? Do you have access to a laser power meter?

Your tube is Pure Argon, Pure Krypton, or White-light?

Where are you located?

[nightlife]

i ran it since 2009 till 2013 about 40hrs/year and since 2013 nearly zero till 1-2 h /year.
The last few hours it ran 2021 with about 3hrs

I am able to check a powermeter yes.

What do you mean with optics peaked?
Optics should be clean but i can check it again.

Its a mixed gas Ar/KR type.

I am located in Austria near Vienna.

[mixedgas]

Start running it now. Your laser is at over pressure. Mixedgas tube voltage is much lower then pure argon fill. Your tube is 10 volts too high from slow leakage that naturally occurs from the fill system

Do Not use the Fill Solenoid. Do not Fill.

Start running it daily for four hours or more for a a week, at 25 amps.. Then run it once a month for at least two to four hours

You have not ran it enough.

Steve

[nightlife]

Start running it now. Your laser is at over pressure. Mixedgas tube voltage is much lower then pure argon fill. Your tube is 10 volts too high from slow leakage that naturally occurs from the fill system

Do Not use the Fill Solenoid. Do not Fill.

Start running it daily for four hours or more for a a week, at 25 amps.. Then run it once a month for at least two to four hours

You have not ran it enough.

Steve

Now it runs since 2hrs at 25Amps and the voltage dropped from 223,9V to 223,4V.

Do you have a U-I chart or field service manual etc. for this type ?

Is mr. glassburn still active in laser business?

[mixedgas]

Dean Glassburn closed, Evergreen Closed, Cambridge Lasers Closed, Dynamic Laser does Aircooled and He is closing the business.

That leaves me for long tubes in the US, and I have the tooling and rare gas. I also have MRA magnets, the Pinchoff tool , Ion Pump, Turbo Pump, etc, so you would ship just the tube.

However, I assure you, start running it. Just start running it for two to four hours at a time, and get it down at least 5 volts at 35A.

I have curves for KR and AR, but mixed gas / white light was never a stock item in a Medical Reentrant Anode (MRA) So my personal MRA whitelight with a 15% mixture of Argon in Krypton runs at 233 @ 30. That was my target when I repumped it myself to allow for more yellow, as a lower pressure and lower magnetic field favors yellow, green, and violet. . As I had many MRA and I90 cores at the time, setting the pressure a bit low for more yellow was acceptable to me. I'd have set the mixture for 236V if I wanted optimal life in Krypton. Pure Argon tubes run around 8 volts higher then pure Krypton. . Very tiny changes in the AR/KR ratio dramatically change the I-V curve and lines lasing in white-lights. I do know that if it rises to 250-255V through lack of use, it will become hard starting, and power will fall dramatically.

The person who pumped the tube would have chosen a gas mixture ratio, based on a tradeoff between color balance, power, and the transmission of the optics used, so without knowing the chosen ratio, there is no curve.

IF YOU DO NOT RUN IT, your tube will develop the "Red-Blues", be hard to start and lase 482 and 647 only in time, then stop igniting. . RUN THE TUBE.

Yellow and green will come back up in power over time as the gas pressure falls from burying gas in the tube' ceramic walls.

The half volt you gained back last night was the cathode re-seasoning itself and absorbing some gas.

In your case the tube would be pumped down through the reservoir fill stem, steps taken to remove impurities from the reservoir, and then the reservoir refilled to a very specific pressure and sealed. It would never see air. However, you must cold weld the copper tube closed, and only a few of us have the tooling and the gas, and the gauges to correctly reset the reservoir pressure. This is done with the tube lit for various reasons, including verifying the fill solenoids only add the correct amount of gas to preserve the color ratio.

RUN THE TUBE at 3/4 current, run it and run it and run it. You'll be fine. MRA is an overbuilt ceramic tube designed to not fail in medical service, ie eye surgery, for years. It is a derivative of I90 with a more optimal magnet, and longer bore, for visible light generation. They were very common and cheap on the used market, and makes a good, tough, whitelight. It was built to run at high currents, allowing the cavity optics to drift in medical service without a lab tech or field service engineer around to tune it.

The re-entrant anode is a design addition to allow for prolonged service at high current with less internal gas return issues. MRA has a similar internal CoolDisk(tm) structure to Purelight IIs. If you run it, you'll gain lifetime back and it will not die from high pressure.

Ultra Pure Rare gases are very expensive now as most of the world's rare gas refining had moved to Mariupol in the Ukraine.

Run the tube, and peak the cavity optics adjustments with a LPM after an hour or so warmup. You'll be fine. It may take months of operation, but the power will come back over time.

Make sure your power supply is happy and not overloaded, but RUN the tube.

Make sure your flow switch works if you must leave it alone for any length of time, and that children and adults cannot access the laser without supervision.

See "walking the cavity optics" in Sam's Laser FAQ on peaking the optics. On an MRA resonator, the optics adjustments are very touchy, so only a tiny turn of the wrench will be needed. Mark the starting points on the tubing screw hex faces with a pencil. Move only both of the vertical axis at first, then move the only the horizontal axis, then switch back to vertical etc. Usually when fine tuned, on a MRA, we move only the rear mirror to avoid loss of lasing once peaked. You probably should leave your Bore adjust screws alone, and move only the mirrors.

I will scan you an MRA manual soon. However your laser is a hybrid made by whomever converted it to whitelight. It looks like you have a lab type supply and I know that is a medical laser resonator from a 910, 920, or 930 Medical Laser.

See attached for a link to a very bad copy of a I-90 Scientific Manual, and note that your laser has very little in common with the lab laser. It is missing many refinements needed in a lab, that are removed for medical use. Lower cost and high stabilty are a goal of the MRA. The large base is intentional, it was preferred that surgical lasers are very heavy so as not to be upset in the operating room by fast moving nurses and panicking patients.

https://www.artisantg.com/info/Coher...0207415744.pdf The file size exceeds this site's limits.



Steve

[mixedgas]

see attached, this is typical of the 910,920,930 family of medical lasers...

Your laser was the top deck under the wood lid of one of those...

Around 250 KG without the crate and ophthalmic gear.

Steve

[nightlife]

Thanks Steve for all the information.

I will now always let it run as long as i have time.

Two things i have noticed.

1) small parts are sticking inside the front brewster. that might also be a big problem. They are "new" because from the last cleaning session the brewsters were clean.


2) the tube seems to be misaligned to the mirrors. that means, if i put out the front mirror, the plasma shine is not round, so i loosend the mounting screws and put the tube little down, now the plasma spot is round and evenly.

I have to do a alignment of the mirrors again and measure the performance.

[mixedgas]

The beauty of an Innova is the ability to move the bore and get around the dust. Dust like that appears when it was used to pump a dye laser in the past, and as they say about Horses in the US, "Ridden Hard and Put Away Wet", generating four or more watts to pump the dye.

It can go a long, long time like that. The dust is likely tungsten.

Steve

[nightlife]

I'm so glad that there is still someone who really knows their way around the old tubes

What grade of gas do you need, is this special made for laser filling or is there a product name for that special grade?

Are you able to send a pic from your filling stand, i am very interested about this technique.

Where are you located ?