EMSY (EMITTANCE MEASUREMENT EMSY (EMITTANCE MEASUREMENT SYSTEM) SYSTEM) AT PITZAT PITZ

– A SHORT INTRODUCTION – A SHORT INTRODUCTION – HOW IT WORKS – HOW IT WORKS – FOR WHAT IT IS NEEDED– FOR WHAT IT IS NEEDED

A.Shapovalov (DESY, Zeuthen) (MEPhI, Moscow, Russia)

Basic scheme of particle acceleration (3

phases): beam shaping and its injection beam acceleration beam extraction on target

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Source

accelerating chamber

TargetVacuum

The beam source has next basic parameters: average initial energy beam current cross-section size average angular divergence

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Source 1

Source 2

?

The beam source has next basic parameters: average initial energy beam current cross-section size average angular divergence

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Source 1

Source 2

The beam source has next basic parameters: average initial energy beam current cross-section size average angular divergence

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Source 1

Source 2

The beam source has next basic parameters: average initial energy beam current cross-section size average angular divergence

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Source 1

Source 2

The beam source has next basic parameters: average initial energy beam current cross-section size average angular divergence

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Source 1

Source 2

What are good parameters of a beam? average initial energy -> maximum beam current -> maximum cross-section size -> minimum average angular divergence -> minimum Interacted parameters -> the golden mean

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Good source

particle has in phase space.

all particles are in - 6d phase space volume

particles in phase-space density ->

phase velocity ->

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0 ,lim),( VV

pp

p dd

dQPrn

),,;,,( PPPP zyxzyxr

pVpdV

),(),,,,,(),( PrPPPzyxPrv zyxp

dQ

Liouville equation => The Liouville equation describes the

time evolution of phase space distribution

-phase-space density -phase velocity The equation is true for projections

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),( Prvp),( Prnp

constVconstndt

dnnv

t

npp

ppp

p

, ,0 )(

0

ppp

ngradvt

n

xpx dxdpcm

V 0

1

- phase space volume is constant (conservation law)

decrease of coordinate dispersion leads to increase of angular dispersion (divergence)

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pV

the representation of the phase space

=> the transverse divergence angles particles in the area

The transverse emittance in x-direction:

The normalized emittance:

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},,,,,{},,,,,{ pyxzyxpppzyx zyx

z

y

z

x

p

py

p

px ,

11

pp

dxdpp

xdxdA xz

x

xx A

rmsrmsn ,

x xp

zp

p

22 xxn

Emittance is key beam characteristic Quality index of injected beam The smaller is emittance, the greater is

quality PITZ: Development of electron sources

with minimized transverse emittance XFEL: after gun of at a

bunch charge of 1nC must be reached.

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mradmmx 9.0

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EMSY1EMSY2EMSY3 EMSY consists of two orthogonal actuators YAG or OTR screen for measurement of the transverse RMS beam sizeEMSY has four degrees of freedom: rectilinear vertical and horizontal motion and rotation around both transverse axes

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The Lorentz factors is measured using a dispersive section downstream of EMSY

The RMS size is measured directly by observing the beam profile on a screen (OTR or YAG) with scintillating material inserted at the position of the slit mask.

Scan&Grab is stopped.

CCDcamera

2xx

22 xxn

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The uncorrelated local divergence is estimated by cutting the electron beam into thin slices and measuring their size on a screen after propagation in a drift space.

Normalized RMS emittance

1

22 xxn

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The uncorrelated local divergence is estimated by cutting the electron beam into thin slices and measuring their size on a screen after propagation in a drift space.

2

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The uncorrelated local divergence is estimated by cutting the electron beam into thin slices and measuring their size on a screen after propagation in a drift space.

3

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The uncorrelated local divergence is estimated by cutting the electron beam into thin slices and measuring their size on a screen after propagation in a drift space.

4

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The uncorrelated local divergence is estimated by cutting the electron beam into thin slices and measuring their size on a screen after propagation in a drift space.

5

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The uncorrelated local divergence is estimated by cutting the electron beam into thin slices and measuring their size on a screen after propagation in a drift space.

6

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The uncorrelated local divergence is estimated by cutting the electron beam into thin slices and measuring their size on a screen after propagation in a drift space.

7

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The uncorrelated local divergence is estimated by cutting the electron beam into thin slices and measuring their size on a screen after propagation in a drift space.

8

6 beamlets

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Normalized RMS emittance The uncorrelated divergence is obtained by analyzing the profiles of

the beamlets produced from the slits which drift some distance downstream.

There the spatial distribution of the beamlets corresponds to the local uncorrelated divergence , which can be derived from the size of the beamlet using (1)

The total uncorrelated divergence of the beam is estimated by a weighted average of several measurements of the local divergence taken from different locations across the beam (2)

(1)

(2)

22 xxn

dL

localx 2

dlocal

L

xx

b

22

i

N

i

i xx

2

1

2

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