What is the concept of rf heating in a Paul trap?

[kushal]

Hello,

I have a question on rf heating in Paul trap.

There are papers which say that in a Paul trap, the ion cloud
eventually comes to a state of thermal equilibrium with the background
gas. And at the same time there is a concept of "rf heating" in these
traps. I am slightly confused about it. If the ion cloud is coming to
an equilibrium, then in what context do we talk of "rf heating"? I
have read some papers on this issue but all seem to be too obscure on
this particular issue.

I would be glad if someone can please reply to this question.

Thanks,
Kushal.

 

[Thomas Smid]

On 24 Sep, 16:22, kushal <atmabo...@gmail.com> wrote:
> Hello,
>
> I have a question on rf heating in Paul trap.
>
> There are papers which say that in a Paul trap, the ion cloud
> eventually comes to a state of thermal equilibrium with the background
> gas. And at the same time there is a concept of "rf heating" in these
> traps. I am slightly confused about it. If the ion cloud is coming to
> an equilibrium, then in what context do we talk of "rf heating"? I
> have read some papers on this issue but all seem to be too obscure on
> this particular issue.
>
> I would be glad if someone can please reply to this question.
>
> Thanks,
> Kushal.

The rf-heating in a Paul trap would raise the equlibrium temperature
in a similar sense as a heater raises the equilibrium temperature in a
room.

Thomas

 

[kushal]

On Oct 7, 8:14 pm, Thomas Smid <thomas.s...@gmail.com> wrote:
> On 24 Sep, 16:22, kushal <atmabo...@gmail.com> wrote:
>
>
>
> > Hello,
>
> > I have a question on rf heating in Paul trap.
>
> > There are papers which say that in a Paul trap, the ion cloud
> > eventually comes to a state of thermal equilibrium with the background
> > gas. And at the same time there is a concept of "rf heating" in these
> > traps. I am slightly confused about it. If the ion cloud is coming to
> > an equilibrium, then in what context do we talk of "rf heating"? I
> > have read some papers on this issue but all seem to be too obscure on
> > this particular issue.
>
> > I would be glad if someone can please reply to this question.
>
> > Thanks,
> > Kushal.
>
> The rf-heating in a Paul trap would raise the equlibrium temperature
> in a similar sense as a heater raises the equilibrium temperature in a
> room.
>
> Thomas

So, do you mean to say that if the background gas temperature was T,
then after a long time, the plasma will also come to an equilibrium at
temperature T? Will happen even if the background temperature was lower
than the plasma temperature? So, its more like a relaxation process that
takes the plasma to equilibrium and not continuous heating. If that is
the case, then why is it called rf-heating? Even in the absence of the
rf field, the equilibration will, anyways, happen. What is the role of
the rf field in the relaxation process?

Thanks,
Kushal.

 

[Richard Saam]

kushal wrote:
> On Oct 7, 8:14 pm, Thomas Smid <thomas.s...@gmail.com> wrote:
>> On 24 Sep, 16:22, kushal <atmabo...@gmail.com> wrote:
>>
>>
>>
>>> Hello,
>>> I have a question on rf heating in Paul trap.
>>> There are papers which say that in a Paul trap, the ion cloud
>>> eventually comes to a state of thermal equilibrium with the background
>>> gas. And at the same time there is a concept of "rf heating" in these
>>> traps. I am slightly confused about it. If the ion cloud is coming to
>>> an equilibrium, then in what context do we talk of "rf heating"? I
>>> have read some papers on this issue but all seem to be too obscure on
>>> this particular issue.
>>> I would be glad if someone can please reply to this question.
>>> Thanks,
>>> Kushal.
>> The rf-heating in a Paul trap would raise the equlibrium temperature
>> in a similar sense as a heater raises the equilibrium temperature in a
>> room.
>>
>> Thomas
>
> So, do you mean to say that if the background gas temperature was T,
> then after a long time, the plasma will also come to an equilibrium at
> temperature T? Will happen even if the background temperature was lower
> than the plasma temperature? So, its more like a relaxation process that
> takes the plasma to equilibrium and not continuous heating. If that is
> the case, then why is it called rf-heating? Even in the absence of the
> rf field, the equilibration will, anyways, happen. What is the role of
> the rf field in the relaxation process?
>
> Thanks,
> Kushal.
>
Each atomic, molecular, ionic, nonionic entity absorbs RF (or EM in
general) at characteristic frequencies related to its vibrational,
rotational, translational modes. At a particular RF spectrum, one
entity may be 'hotter' than another but with time and constant RF input,
all entities should come to thermal equilibrium.

Consider a frozen dinner in a microwave oven. The meat, vegetables and
dessert each heat a different rates (cover some and not others) such
that after the instructed cook time, all are at a different but
acceptable temperatures.

Now for arguments sake, keep the dinner in the microwave oven for an
extended period of time (hours?) and the whole thing would be at some
type of unpalatable thermal equilibrium.

Richard D. Saam

 

[kushal]

On Oct 9, 9:58 pm, Richard Saam <rds...@att.net> wrote:
> kushal wrote:
> > On Oct 7, 8:14 pm, Thomas Smid <thomas.s...@gmail.com> wrote:
> >> On 24 Sep, 16:22, kushal <atmabo...@gmail.com> wrote:
>
> Each atomic, molecular, ionic, nonionic entity absorbs RF (or EM in
> general) at characteristic frequencies related to its vibrational,
> rotational, translational modes. At a particular RF spectrum, one
> entity may be 'hotter' than another but with time and constant RF input,
> all entities should come to thermal equilibrium.
>
> Consider a frozen dinner in a microwave oven. The meat, vegetables and
> dessert each heat a different rates (cover some and not others) such
> that after the instructed cook time, all are at a different but
> acceptable temperatures.
>
> Now for arguments sake, keep the dinner in the microwave oven for an
> extended period of time (hours?) and the whole thing would be at some
> type of unpalatable thermal equilibrium.
>
> Richard D. Saam

Yeah, that makes sense if one accepts that the plasma comes to some
kind of thermal equilibrium.

However, I was going through the literature on rf traps and came
across two statements that seem to say different things:

1) I. Siemers, R. Blatt, Th. Sauter and W. Neuhauser, Phys. Rev. A 38,
5121 (1988)
"On the other hand, in experiments on ion clouds in rf traps,
efficient cooling is impossible, since collisions between the ions and
with the surrounding background gas in the presence of the time-
dependent trap potential leads to heating."

2) F. Vedel, International Journal of Mass Spectroscopy and Ion
Processes 106, 33 (1991)
"Since the earliest experiments with Paul traps, it has been
recognized that collisions with a light buffer gas enhance the
lifetime by reducing ion kinetic energy"

How does one reconcile these two statements?

Thanks,
Kushal.

 

[ustcligang]

These two statements have different criterion of what is efficient cooling.
In the first case, it means the ions can not be cooled at efficient as MOT trap, which could achieve 10^-12 K on atoms.

In the second case, it means buffer gas reducing ion kinetic energy compared with NO buffer gas.

It's like to say, A human is "bigger" than an ant, but "smaller" than an elephant.


---------------------------Quoted--------------------------------

However, I was going through the literature on rf traps and came
across two statements that seem to say different things:

1) I. Siemers, R. Blatt, Th. Sauter and W. Neuhauser, Phys. Rev. A 38,
5121 (1988)
"On the other hand, in experiments on ion clouds in rf traps,
efficient cooling is impossible, since collisions between the ions and
with the surrounding background gas in the presence of the time-
dependent trap potential leads to heating."

2) F. Vedel, International Journal of Mass Spectroscopy and Ion
Processes 106, 33 (1991)
"Since the earliest experiments with Paul traps, it has been
recognized that collisions with a light buffer gas enhance the
lifetime by reducing ion kinetic energy"

How does one reconcile these two statements?

Thanks,
Kushal.[/QUOTE]