Anton’s fusor

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Anton Isaksen
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Anton’s fusor

Post by Anton Isaksen »

Hi, I’ve been working on my fusor for around a year now, so I think it’s about time that I start posting something regarding my progress. The fusor is mostly made of kf-parts, with the main chamber being a kf-40 cross. Vacuum is attained using a pfeiffer turbomolecular pump backed by a 2-stage mechanical pump. And like others here, I made a feedthrough consisting of a quartz glass tube and compression fittings. My power supply is a 30kv chinese precipitator supply. The pressure is measured by an inficon triple vacuum gauge, but just the pirani part works, so it only goes down to 0,75 mTorr. I haven’t bothered trying to fix it yet, but any suggestions are welcome.
Admitting deuterium is done through a swagelok needle valve and gate valve, which makes it very sensitive to adjustments, but still doable. And finally, my deuterium is acquired through electrolysis with the horizon PEM cell.

The pictures of my setup are a bit old, since im currently repairing the turbo and a few of the parts have been disassembled.
Bilde 1.jpg
Bilde 4.jpg
I got my first plasma a while back using a crudely made tungsten grid, but I soon moved on to a way more symmetric grid which seems to keep the plasma better contained. What I’m worried about is the placement of the plasma, which seems to be concentrated in the upper part of the grid instead of the middle, resorting in the heating of only certain parts of the grid. I tried moving the grid a little bit further up, but it didn’t help. Is this a problem or is it fine?
Any other criticism is also welcome.
First plasma.
First plasma.
Latest deuterium-plasma at approximately 27mTorr, 30kV and 2mA.
Latest deuterium-plasma at approximately 27mTorr, 30kV and 2mA.
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Richard Hull
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Re: Anton’s fusor

Post by Richard Hull »

Welcome to the plasma club, Anton.
I have placed your name on the list.
Images of gear and metering and reported image data on last image.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
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Liam David
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Re: Anton’s fusor

Post by Liam David »

Good job getting a plasma. It looks like all you need is a neutron detector.

Some feedback:

The plasma is pulled towards the feedthrough stalk for a number of reasons. The main cause is that neither of your grids is particularly symmetric or placed symmetrically in the chamber. At the very least, line up one of the "holes" in the grid with the long axis of the chamber. Also, a wire grid design is not the best for this kind of chamber. It works alright for spherical systems, but yours might fare better with a linear cathode. Will your current setup do fusion? Sure, but you will do much better with a newer cathode.

I don't know how you're taking pictures of the plasma, but please use a remote camera and some lead if you're not already. Your last picture was accompanied by lots of x-rays (100s of mRem/hr to >1 rem/hr).

I don't see a gate valve in your setup and one wouldn't typically find one in a gas line. Do you mean a needle valve followed by a shutoff valve? Also, neither valve in the bottom left of your first image is, functionally speaking, a needle valve. You mention that pressure control is difficult; this is because the valve is far too coarse.

I would suggest adding a valve between the turbo and chamber to save deuterium, as well as one between the rough and turbo pumps.

If that's a hard line between your rough and turbo pumps, I would definitely add a bellows for vibration isolation. If you touch the turbo while the rough pump is running, you should not be able to feel any vibrations.

Good work so far and we're looking forward to your new setup.
Anton Isaksen
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Re: Anton’s fusor

Post by Anton Isaksen »

Thanks for the tips! I certainly have some improvements to make.

My pictures of the plasma are taken from videos recorded on my phone(for now) up next to the viewport. I also have a piece of lead behind it to block the x-rays. As seen from the quality of the pictures, the whole chamber does vibrate from the mechanical pump. So I’ll try getting a piece of bellows tubing in the foreline to smoothen it out.

Regarding the inlet line, I did mean shutoff valve, not gate valve. My mistake. The other valve is an SS-1RS4 integral bonnet needle valve and I was gifted both of them by Swagelok Norway, as they didn’t have any finer ones in stock. I was however still able to gain a usable amount of control over the chamber pressure by putting the two valves in line and setting the shutoff valve to a position right at the limit of letting gas through.

After I had taken the above pictures of my setup I also acquired a butterfly valve to throttle the turbo. Like the needle valve, it isn’t very easy to use, but i don’t adjust it too often so it’s good enough for me. It’s maybe not too easy to see in the picture, but I’ve also got a ball valve between the turbo and mechanical pump. Though that one is open most of the time.
Anton Isaksen
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Re: Anton’s fusor

Post by Anton Isaksen »

I've finally made some progress on the fusor itself and gotten a neutron detector.
The turbomolecular pump is finally repaired and I've added a bellows pipe between the foreline and the turbo. It almost completely eliminated the vibrations of the vacuum chamber, as the turbo runs really smoothly. In addition, I acquired a remote USB camera, which makes monitoring the plasma way easier, though I don't have enough lead to completely shield the viewport with the camera in front. So, I was wondering whether a few pieces of steel plating would suffice or if that would present some other problems, as opposed to lead.

My neutron detector consists of an old снм-18 3He corona neutron counter tube that's attached to a steel box containing the preamplifier. The tube is powered by a stable DC 1,8kV high voltage supply contained in another box, and fed to the neutron counter through a BNC-cable. The anode of the tube is connected to the high voltage in series with a 100MΩ resistor for current limiting, and the output from the tube is coupled through a 100pF capacitor to the preamplifier circuit. Since the raw neutron pulses are in the order of 30mV and 20 microseconds long, they are first amplified by a TL082 opamp in a trans-resistance-amplifier setup. Thereafter, the signal is scaled down by a voltage divider and again amplified by a 2N3904 transistor amplifier. The transistor works to discriminate out most of the noise beneath the required bias voltage for the transistor base and makes pulses fitting for audio. These pulses are then fed into a modified analog to digital converter and sent to a pc through the USB-port. I use PRA for counting the pulses, in addition to plotting them in an energy spectrum for identifying the neutron pulses and fine tuning the discrimination threshold set by the program.
Raw pulse from coupling capacitor connected to the anode of the tube.
Raw pulse from coupling capacitor connected to the anode of the tube.
Neutron counter setup, with moderator.
Neutron counter setup, with moderator.
The moderator consists of a few HDPE cutting boards cut into pieces, and I'm able to detect what I assume are cosmic neutrons approximately every two minutes with the moderator around. To properly check that the detector was working, I got to test it up against a PuBe source at my local university, and it gave over 1000cpm close to the source. I also checked it up against a powerful gamma source, though it showed no observable increase in the count rate, so I'm very confident that it's counting neutrons. Exactly how efficient it is, isn't something I've found out yet.
Pulse height histogram from testing with neutron source.
Pulse height histogram from testing with neutron source.
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Richard Hull
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Re: Anton’s fusor

Post by Richard Hull »

A very rough guess could be made as to your efficiency could be made if you find out from the university the flux from their source. I am sure they must know.

Also what is your detector and its size.

I agree it is definitely counting only neutrons.

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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Anton Isaksen
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Re: Anton’s fusor

Post by Anton Isaksen »

I believe the neutron source had a total isotropic emission rate of 200 000 neutrons per second. It was encased in paraffin blocks and should only have emitted slow neutrons, so I didn't cover the detector itself with any moderator.
The active volume of the detector tube has a length of 30cm and a diameter of 1,8cm. At a distance of approximately 4 meters, I got a count rate of 2 neutrons per second, but positioning the detector around 0,5 meters directly above the source only gave 20 neutrons per second. Though there wasn't a lot of paraffin between the source and detector at that point, so that might explain the lower-than-expected count rate.

I initially got the name confused with SNM-18, but the datasheet and the look of the tube clearly show that it's an SNM-32 tube. The datasheet also says that it had an efficiency of 0,8, but that has definitely deteriorated over the years.
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Re: Anton’s fusor

Post by Richard Hull »

It sounds as if it is relatively efficient. We will be curious how it counts with a working fusor once in its own moderator.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Anton Isaksen
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Re: Anton’s fusor

Post by Anton Isaksen »

I recently tried my first fusor-run with the neutron detector.
It was hard to keep the deuterium pressure stable at the desired point, so I instead pulsed it around a fitting interval by switching the turbo on and off. I'll have to work on getting better pressure control in the future, but this method did seem to work, as I managed to keep approximately the same voltage and current for over a minute. The voltage hovered around 30kV, the current around 3mA, and the pressure around 27-30mTorr. The picture from the webcam shows a lot of x-rays, but I suspect some of them come from reflections inside the steel box containing the camera. My Geiger counter only shows a small increase in background around the fusor when operational, so the viewport shielding works well. It’s also apparent that the grid heats unevenly and isn’t very fitting, so I’ll soon replace it with a better cathode.
Current setup with the neutron detector encased in moderator in front of the fusor.
Current setup with the neutron detector encased in moderator in front of the fusor.
Screenshot of count-rate and pulse-height histogram from neutron detector, as well as webcam footage of grid.
Screenshot of count-rate and pulse-height histogram from neutron detector, as well as webcam footage of grid.
Anyways, it seems like I managed to detect some neutrons with the 3He tube. It was surrounded with 4cm of HDPE on the sides and 2cm of HDPE on the top and bottom. Counting over intervals of 10 seconds, I got a max count rate of 1,1 neutrons per second at the aforementioned voltage, current and pressure. The detector was placed tangentially to the center of the fusor, with around 11cm from the center to the closest point on the detector. Assuming an efficiency of 10-50%, that doesn’t work out to a very large neutron production number, but it’s at least a start. I probably need more moderator around the detector, and the deuterium wasn’t as pure as I’d liked, so I’ll have to do some more runs soon. To be sure I wasn’t counting electrical noise, I tried removing all the moderator while operating the fusor at the same conditions, and although it picked up some low-level noise, which anyways would have been discriminated out, it didn’t detect a single pulse in the “neutron zone” of the pulse height histogram for a whole minute.

I’m hoping to attempt a few activation experiments in the future with the small gamma spectrometer I constructed half a year ago, though I’ll have to increase the neutron numbers before then.
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Re: Anton’s fusor

Post by Richard Hull »

Keep at it. You need a stable environment it looks like. I hope you have a throttle "choke valve" on the throat of the turbo? Likewise, you have to have a smooth micro adjustment on the deuterium flow. Impure deuterium is a big issue if fouled with water vapor or other virtual leak materials within the fusor when the walls get hot. All the best on getting to a stable operating point.

I can't make heads or tails about your histogarm data. A good digital count of pulses from the neutron detector is to be desired. Finally I hope you have seen this excellent video showing how to prove neutron counts are real thermal neutron counts with a Russian tube. To my mind this video proves beyond any doubt that you are fusing deuterons.

https://www.youtube.com/watch?v=MFOrEsPDrZw

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Anton Isaksen
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Re: Anton’s fusor

Post by Anton Isaksen »

Recently did another run very similar to the last. Though this time with freshly made deuterium, unlike last time when it had been sitting in the plastic syringe for several hours. I suspect the pinched off syringe leaks in a bit of air over time, since this run gave 3 times the count rate that I'd previously gotten. I have yet to try drying the deuterium and finding a stable operating point, but I'll report back when I do.
There is a butterfly valve connected to the throat of the turbo and it works well for throttling, although it requires some fine movements when adjusting. The deuterium inlet needle valve also takes some precision and patience to adjust, so I might try finding another valve or making some sort of capillary tube for better flow restriction.

To properly verify that the neutron detector is counting what it's supposed to, I'll try making a video showing the count rate with and without the moderator like in the video you linked, but I first need more stable operation.
Attached is an excel graph of neutron detector counts over 5 second intervals for this run.
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Richard Hull
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Re: Anton’s fusor

Post by Richard Hull »

Anton your counts are not up enough to use the in-and-out probe method to great effect. (audible over statistical) A 200 CPM vs.10 CPM "in vs. out", (20 to 1) count is a very positive figure.
You are discovering that the operation of a fusor for the beginner is one of very fine and precise "tuning" of a whole lot of valves while working the power supply to advantage at the same time.
You are getting there, fast!

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Anton Isaksen
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Re: Anton’s fusor

Post by Anton Isaksen »

It’s been some time since my last update, the reason being that my turbo suddenly crashed while I was trying to maintain a stable vacuum pressure. It dropped from 90% to 0% rotation speed in only a fraction of a second, but after taking it apart I found that the crash only had taken out the two lower turbine stages and the lower bearing. It also looked to be caused by a failure in the improvised ball bearing that had thoroughly pulled itself apart.

I could have tried replacing the broken bearing, seeing that the rest of the pump was in working condition, but I didn’t want to take the risk of another improvised ball bearing, and the originally intended one would cost more than I paid for the pump itself. Constant problems and attempts at repairing the turbo were also getting tiring, so I started looking for other options. While scouring ebay I suddenly found a nice-looking and relatively well-priced diffusion pump from the UK, so I jumped at the opportunity and bought it. It’s quite large for my vacuum chamber and needs water-cooling, but the smaller air-cooled diffusion pumps seem to be way more expensive and I had enough diffusion pump oil laying around already. The only two things that needed to be made was a water-cooling system and an adapter from the large top-flange to the kf40-flange of the chamber.

The closed-circuit water-cooling didn’t take long time to set up, it simply consists of an aluminum pot with a bilge pump, which can be placed in another bucket filled with snow from the outside for cooling, though I’m working on a more long-term solution. However, the adapter took a bit longer to construct since I had to machine a steel-plate and silver-solder a flange onto it. Armed with only two butane/propane torches in freezing cold, it took many passes to thoroughly seal the whole rim of the flange, because the gas-tanks kept freezing over, impeding the gas flow and turning the torches into mere lighters. The adapter is finished now, but before bolting everything together I took apart the jet-assembly inside the diffusion pump for a quick acetone-rinse and found out that there was still a good amount of clear silicone oil left in there. The pump also looked to have remained well sealed and clean, so I left the oil in there, only cleaning out the jet-assembly.

Once everything was in place and the diffusion pump connected to the vacuum-chamber, the whole system was pumped down over several hours by the mechanical pump with the boiler on the diffusion pump on for a short time to remove water and other outgassing compounds. Despite the large size of the diffusion pump, the chamber reached a substantially lower pressure than with the turbo, as I suspect the upper flange on the turbo was leaking from small scratches. I later turned on the water-cooling system and let the boiler stay on. It took about 20 minutes of slow pressure increase before the pressure suddenly plunged into the sub-microns, confirming that the diffusion pump was working and the fusor ready. I haven’t yet had time to do a deuterium run, but I’ll soon find out if it’s successful. Despite the long warmup-time, I at least don’t have to worry about my pump suddenly self-destructing any longer, which makes running the fusor a whole lot more enjoyable.
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Re: Anton’s fusor

Post by Richard Hull »

The great advantage of a Diff pump is no moving parts and no electronics. With proper operation they are perfect for a fusor.

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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Anton’s fusor

Post by Anton Isaksen »

It’s been a while since the last update, as I’ve been occupied with school and exams, but I’ve made some more progress on the fusor in the last month.

Firstly, I’ve installed a water-cooling system for the diffusion pump utilizing a car radiator, which in addition to some fans keeps the diff-pump body cool, even in summer temperatures. The grid has also been substituted by a tungsten carbide ring, which is symmetrical and should fit the fusor better. Additionally, a metering valve has been added to the deuterium line, granting better pressure control. Today’s deuterium run gave approximately 1000 n/s TIER from the He3 neutron detector for a period of about a minute, with more counts in the later fusion intervals. There are still some things outgassing, especially when heating up the grid and chamber, which doesn’t come as a surprise since it was open to air not long ago. So, a bit more vacuuming and conditioning over the following days should hopefully yield better results. To be certain the neutron detector was still working as it should, I first tried using the detector without the moderator, but with deuterium in the fusor. Then I tried using it with the moderator, but with air in the fusor. Neither run gave any more counts than background, so I still believe it works like before.

Besides the improvements on the fusor, I’ve also built a Geiger counter based on the SBT10A, which is extremely sensitive and especially suitable for beta detection. When my neutron numbers get a bit higher, I’m hoping to detect some silver activation with the new counter. The advantage of having a smaller chamber is that I can place the item to be activated closer to the fusor, thereby increasing the neutron flux density and not needing as high a total neutron output.
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Richard Hull
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Re: Anton’s fusor

Post by Richard Hull »

Mica windowed counters are ideal for beta counting of most activated materials.

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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Anton’s fusor

Post by Alexey Khrushchev »

Very good work, Anton! Can you elaborate on how you made the diffusion pump flange seal? Did you use viton or teflon?
Anton Isaksen
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Re: Anton’s fusor

Post by Anton Isaksen »

Once again, I’ve found time to start up the fusor after being absent for a while due to military service. I might be a bit late, but to answer the question about the pump seal: It consists of a large viton o-ring pressed between a steel plate and the flange of the diff pump, all held together by screws and nuts. The viton ring came with the pump.
 
I recently tried to film a video comparing counts from the neutron detector when it’s inside and outside the moderater.
The fusor hasn’t been conditioned or operated for a while, so the neutron numbers are relatively low, though easy to differentiate from background. I’ve added an LED to the neutron detector to make it easier to see the counts in real-time. This works by taking the audio output from PRA and using it to trigger a monostable 555-timer, which produces a visible pulse for the LED. The advantage of this is that I can filter the pulses from the detector within PRA. It’s now adjusted to filter out as much electronic noise as possible, but that also includes some of the neutron counts. Still, as you’ll see in the video below, there is a great difference in counts between when the detector is in or near the moderator, and when it’s not. I also try to demonstrate turning the power on and off, as can be seen on the two amp-meters. The one to the left measures the high voltage current, while the one on the right measures the current from the high voltage through 750 megaohms. 40 microamps therefore equal 30 kV, while 50 microamps equal 37.5 kV.
Also, the pressure during the recording was constantly at or near 30 mTorr with newly made deuterium from D2O.

Here’s the video link:
https://youtu.be/Muu7MpHVglE?feature=shared
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Re: Anton’s fusor

Post by Richard Hull »

Anton, You have proven beyond all doubt that you are doing fusion! Welcome to the neutron club! Nothing proves fusion neutrons more than a video of moderator counts versus no moderator counts, (usually zero) when using a 3He tube. Great work and stick with the effort to get those numbers up for activation.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Anton’s fusor

Post by Paul_Schatzkin »

Congratulations on reaching the Neutron Club, Anton.

It's nice to see all the dedication and persistence paying off.

--PS
Paul Schatzkin, aka "The Perfesser" – Founder and Host of Fusor.net
Author of The Boy Who Invented Television: 2023 Edition – https://amz.run/6ag1
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Liam David
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Re: Anton’s fusor

Post by Liam David »

Nice work and welcome to the club!
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Re: Anton’s fusor

Post by JoeBallantyne »

Congrats Anton! Great work.

Joe.
Anton Isaksen
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Re: Anton’s fusor

Post by Anton Isaksen »

Thanks! The amount of information and tips and tricks on this forum is truly astonishing, and I would have gotten nowhere without it.
All the instruments and materials required for activation detection are on hand, so all I need now is more neutrons. I’ve noticed that the neutron count is very dependent on the amount of deuterium flowing through the system, the more the better. Which leads me to believe that the gas purity within the fusion chamber is the greatest limiting factor, likely due to outgassing or leaks. I’ll therefore first go leak hunting to try to find any possibly leaky components or flanges, and see if fixing them improves the neutron count.
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Liam David
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Re: Anton’s fusor

Post by Liam David »

Sounds like a good next step. Once leaks are hunted down, you could try baking the chamber at ~100C for a while to lower the base pressure. That will help clean things out a lot (and perhaps give you an excuse to repair that gauge).
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Re: Anton’s fusor

Post by Dennis P Brown »

I did an experiment to show the effect of chamber volume and gas pressure on neutron output. Of course, higher pressure leads to more fusion. I decreased the chamber size simply by using a grounded steel wire grid to create a smaller effective chamber volume inside the existing large chamber. This enabled the far larger chamber to effectively operate as a small chamber and at a higher pressure. This resulted in a 50% increase in fusion events.
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