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A definition of a Potential Well

by jonlg_uk
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jonlg_uk
#1
Jun14-12, 03:26 PM
P: 141
Hello I read the following sentence when reading about ion traps:

"By changing the trapping voltage we are changing the depth of the potential trapping well, therefore at the same axial position there is a corresponding increase in the potential well, which means that the ion will have to have greater kinetic energy to achieve the same axial amplitude"

I don't understand what a potential well is? Can anyone explain it in laymans terms for me?

I thank you in advance


J
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mfb
#2
Jun14-12, 04:03 PM
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A potential well is a region in space where the potential is lower than in the neighborhood. Particles can get trapped in these potential wells, if their energy is too low to escape (because the potential outside is too high).
jonlg_uk
#3
Jun14-12, 04:07 PM
P: 141
Quote Quote by mfb View Post
A potential well is a region in space where the potential is lower than in the neighborhood. Particles can get trapped in these potential wells, if their energy is too low to escape (because the potential outside is too high).
Thank you, but what does an increase in potential well mean?

mfb
#4
Jun15-12, 05:05 PM
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A definition of a Potential Well

I think the text means an increased potential "outside", which is an increased depth of the potential well.
sophiecentaur
#5
Jun16-12, 05:30 AM
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Quote Quote by mfb View Post
I think the text means an increased potential "outside", which is an increased depth of the potential well.
Or increase in the 'depth' of the well? In the case of electrons that could just involve increasing the positive potential on an electrode (Deepening the well). It would probably have been better if the word 'magnitude' had been put after "increase" to avoid the 'up-ness' implied by the word and resolving any ambiguity.
jonlg_uk
#6
Jun16-12, 10:29 AM
P: 141
Quote Quote by sophiecentaur View Post
Or increase in the 'depth' of the well? In the case of electrons that could just involve increasing the positive potential on an electrode (Deepening the well). It would probably have been better if the word 'magnitude' had been put after "increase" to avoid the 'up-ness' implied by the word and resolving any ambiguity.
By "deepening the well" you mean that because the positive potential on the electrodes has increased the electrons are less compressed towards the center of the qudrupole trap?
jonlg_uk
#7
Jun16-12, 10:33 AM
P: 141
Basically:

what happens to the potential well as you make it more trapping potential more positive?

what happens to the potential well as you make it more trapping potential more negative?
sophiecentaur
#8
Jun18-12, 05:24 AM
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Quote Quote by jonlg_uk View Post
By "deepening the well" you mean that because the positive potential on the electrodes has increased the electrons are less compressed towards the center of the qudrupole trap?
Quote Quote by jonlg_uk View Post
Basically:

what happens to the potential well as you make it more trapping potential more positive?

what happens to the potential well as you make it more trapping potential more negative?
Absolute potential is defined for a unit positive charge but, for electrons and positive charges, the sums still give you a negative value of potential for an attractive field.
Afaik, the potential is defined as relative to a zero value at infinity so increasing the positive charge on an electrode (or increasing the positive voltage) would be regarded as making the well deeper. If your 'trapping potential' is negative then it is not a potential well for a negative charge; it is a potential Hill (repulsion). The Field will be the gradient of the potential.


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