Energy, Baby!

Just to be different, today we will talk about physics. Mostly because I have done nothing of interest in the past few days, so I have nothing else to talk about. I previously mentioned the PRL cover we just got, so I thought I would explain the results a little better. It is, after all, a cover, so I feel it is well within my rights as the lowly graduate student to brag.

This explanation builds on some of the other previous entries. Specifically, the general introduction to acceleration and the specific introduction to plasma-based acceleration.

Okay, back to the basics. Sorry, I am using a slide from defense's powerpoint presentation. I am lazy. You gotta problem with it? Tough.

The top image is the schematic of what happens when the beam enters the plasma. The bottom image is the charge distribution of the incoming beam in maroon, as well as, the energy distribution of the beam before and after the plasma. The incoming beam (green) already has an energy chirp (i.e. the head particles are more energetic that the tail particles). When the beam goes through the plasma, the bulk of the particles lose energy to drive the plasma wake and then the tail particles gain energy when the plasma electrons land behind the beam – the green shaded region in the picture above.

Our diagnostic looks at the energy axis. Imagine that you take the blue and green lines and look at their energy profiles. In other words, you take a time integrated picture of the energy profiles with and without the plasma. This picture might help with that visualization (the green is profiled on the left and the blue is profiled on the right). It is a crappy picture, but you get the idea (hopefully).

Now to look at the data:

The image on the left is like the green profile, whereas the image on the right is the blue profile. Note that the particles that have been accelerated are all the particles above the top line. This means a peak energy gain of about 2.5 GeV over a 10 cm plasma or 25 GeV/m (presently, SLAC acceleration is about 20 MeV/m). The particles accelerated in the plasma are not helpful in a real particle physics experiment because there is a huge smear in the energy. This smear is because of the way we do our experiment – we should be able to improve this by beam shaping, but that will be in the future. Also, for the skeptics, about 8% of the beam's electrons are accelerated. There could be (really, should be) more particles accelerated, but since we cannot resolve the beam in time we can't actually measure it. In the future we hope to improve that number too.

Okay, I think that's enough physics. This should make up for my month traveling and doing strictly non-physics related things.

Comments

[Aaron F.]

Ooh, pretty! I'm surprised that the particles at the very head of the beam lose almost no energy, while the particles in the middle take a huge energy hit -- intuition says the exact opposite should happen! But I guess super-relativistic electrons don't behave *exactly* like a flock of geese. :)

p.s. I can't tell whether the white splooshy thing at the top of the slide is the crest of a wave or a foamy wake, but it's really cute! If I were on the thesis committee, that would be your Ph.D. right there. Which is probably why I'm not on any thesis committees...

[claire bertiaux]

Ok ma belle comme tu dis: with or without plasma.
J'ai écris: with or without grammar or something like this about which and what.
Je n'ai pas lu le reste.
I inform that statistically peoples gets in their mind only 700 words corpus to transmit their ideas in society: and you?.
In one word as in 100: it is ENOUGH.
I hope this time to have been clear.
So proud to have refused to get marry to one physiscist when i learn in one film that Marie Curie accused Pierre "d'avoir essayé de la violer" to get one sort of administrative statut...When and where will i find one high level and digne picture of physics in 2005?. You are informed that your grammar lesson was "truffée" of references to personnal things of me and adressed to one old and ill and perhaps future alzheimer person (i forgot all my english: why? You will learn later)and it is obviously known since i have given my true name.....
You take entirely the responsability of your words and sentences. You criticyzed me writing with bad fingers and old operated eyes, in your langage, with one French clavier in one domain that is not yours. With bugs and so on.
You are belonging to one generation ,and the more for the women, which will support to be evaluated in ethics personnal choice to be allowed to receive the Nobel Price. I swear.
Concerning which and that: the only thing i have to consider is: which is only one tool of syntax articulation in the sentence. That is something more subtil that as tool, that thing: You look at the virgule as the tree in front of the forest. But you noticed i had made one mistake on this which in place of who concerning you in one blog....
Do you know what? One day,i heard one conference about the swing inside the jazz tempo. The researcher said always " ça swing pour moi" when he was able to reconstruct 16 seconde of music, just cut at the good moment. The most important was to prove he was able to produce swing and that it was really swing: we heard it a lot a lot in the conference. Sterility.
I didn't read your post. I have read in my life a lot of articles in a lot of scientific domains. I know perfectly the limits of publications on the base, for exemple of this (one congress on artificial intelligence: expert system applied to archeology presented as announced. Theory etc.. the truth: only 20 fiches for the conclusions! If i would have only searched the topic in data bases i wouldn't have had this caracterization).
So i wasn't motivated to read you, even if it is aesthetic. The more: too aesthetic is soporifique. Qui veut trop prouver ne prouve rien. Me too.
Thanks everybody for your attention.

[Jules]

Hi, Caolionn. you were on TV here in the UK the other day, the programme was called E=MC² it was a two hour epic!

the equation was taken as a schematic - E for energy, meet Michael Faraday.

for M we met Lavoisier and his wife.

squared - Leibniz and Emilie du Chatelet ???

so where did you come in to it? well you were shown, clipboard in hand, walking along side your accelerater. you are the future of E=MC²

well done, and good luck with your future.

[Caolionn]

Aaron: Totally stole the splooshy thing from the Symmetry article on plasma wake field accelerators. Magazines actually have a budget for artwork, whereas grad students tend to be lacking in talent on those types of things.

Jules: The NOVA program doesn't air here until October. I haven't seen it yet. I don't really enter the equation, I just use it. I think I am supposed to be generic "young and enthusiastic scientist."

[Jules]

yes, you are correct, sorry if i caused confusion.