[time-nuts] homebrew H maser

J. Forster jfor at quik.com
Wed Sep 1 17:46:54 UTC 2010

> Hi
> My guess is that you put the adjuster entirely inside the vacuum
> enclosure.
> Pump the gizmo down, stabilize it, measure where it's at. Do some math,
> pop
> it open move the adjuster x.xx turns. Step and repeat. Possibly have a
> fine
> and a coarse mechanical adjust screw.

This kind of thing is done with Inchworms, totally in vacuum. Only a few
(4 to 6)small wires come out through a vacuum feedthrough. Or you can use
mechanical linkages and SS or copper bellows.

The Inchworms can have several inches of travel with sub-micron sized
steps. They are grab-move-release incremental piezoelectric actuarors.

> It's a one time only sort of thing. You can afford to do it the hard way.
> Another option would be to allow the screws to come through the envelope
> and
> leak a little bit during the adjust process. Once you were done with
> adjustment, seal them up with a low out gassing epoxy. My guess is that
> would be a problem thermally. If you need 0.001C gradients, you can't have
> more than one thermal path to the cavity.

With the vacuums in the MASER manual, you cannot have any leaks. Even so,
they rough pump the thing, pinch of metal seals, and then run Ion pumps.

If you try to cut corners with high vacuun technology, you will be
disappointed. Even with all new parts and carefull assembly, you will
almost certainly have to He Leak Detect the system to get it tight. I've
done this stuff. It is doable but certainly not trivial. And you cannot be




> That's all getting complicated, and we're only talking about the easy to
> understand and address stuff...
> My understanding is that the guys at Kvarz spent years poking at their
> design in the secret back room before it worked as well as it does today.
> Bob
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Attila Kinali
> Sent: Tuesday, August 31, 2010 12:13 PM
> To: jfor at quik.com; Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] homebrew H maser
> On Sun, 29 Aug 2010 10:03:02 -0700 (PDT)
> "J. Forster" <jfor at quik.com> wrote:
>> [snip]
>> >> complicating aspect is the self-tuning stuff for which several
>> >> strategies may be chosen.
>> >
>> > I'd start here at getting a cavity that is resonant at the frequency
>> > at all. Getting sub-milimeter precision in tooling is quite easy
>> > (given you have the tools and knowledge, or can pay someone to do it
>> for
>> > you),
>> > but if the cavity has to be resonant within a couple of Hz of the
>> > 1.4xxxGHz, then you have to get a precission in the range of 10^-9
>> > which basically impossible mechanically. So the cavity would need to
> have
>> > a mechanical tuning system too, but one that doesn't lower the
>> cavity's
>> > Q or add any additional resonant modes.
>> A tuning plunger driven with a Burleigh Inchworm, either through a
>> bellows
>> or with a vacuum Inchworm.
> Yes, but that's only half of the story. How do you make it vacuum tight?
> And how do you design the end in the cavity so that you do not create
> unwanted resonant modi?
> 				Attila Kinali
> --
> If you want to walk fast, walk alone.
> If you want to walk far, walk together.
> 		-- African proverb
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