14th esls rf workshop elettra / trieste, italy / 2010 september 29 30 rf deflectors for the...

14th ESLS RF Workshop

ELETTRA / Trieste, Italy / 2010 September 29 30

RF Deflectors for the FERMI@Elettra Project

M. Petronio (Università degli Studi di Trieste)P. Craievich (Elettra, Trieste)

R. Vescovo (Università degli Studi di Trieste)

Marco

realization relaizascionallow alaudhrectional



Agenda:

RF Deflectors in the FERMI@Elettra Project Low Energy Deflector High Energy Deflectors

Marco

In the first part of this talk I will describe fermi@elettra project which is the background of the rf deflectors operation.Then I will talk about the deflector, in particular aboyt the low energy deflector which has been already installed and is now operating, and the high energy deflector which will be installed in the next months.



RF Deflectors in the FERMI@Elettra Project

TW Deflectors (2, both planes)

SW Deflector (Vertical plane)

Marco

This is the FERMI@elettra layout, the machine is a forth generation light source under development at elettra labouratory. The injector produces electron bunches temporized up to 10hez, then the electron travel in 5 accelerating section being accelerated up to 1.2 geV. In the last part of the machine 2 undulator chain are placed, one for fel 1 and one for fel II, where the free elctron laser process occurs.In order to produce beam at the correct specifiction for the fel, many beam diagnostic tool are placed along the machine. Between these, there are the RF deflector, which are cylindrical waveguide disk loaded.One will be placed after the first bunch compressor at low energy- the low energy deflector, and will be used to evaluate the bc efficiency-the other at high energy, just before to the undulator chain, to evaluate beam prperties before the fel.the RF deflector induces a transverse force which stretches the bunch, inducing a linear correlation between its longitudinal and its transverse position. The bunch after the deflection collides to an otr screen where important properties of the bunch, such its length its slice emittance can be observed.



Low-Energy RF Deflector

The cavity has been designed in collaboration with INFN-LNF and Università La Sapienza, Rome.

It has been installed in February 2010 and is now under commissioning.

It is a five cells structure fed by a central coupler which works at 2.998 GHz.

It operates at 350 MeV.

Marco

Tis is the low energy deflecor, which has been designed and realized in collaboration between infn lnf laboratory and university of rome.It has been installed at bthe beginning of this year and it is under commisioning.It is a 5 cell structure which work at 2.998 ghz at 350 mev




Marco

these are some plot of the electric field inside the cavity




Measurements performed with the network analyzer confirm the predicted value (courtesy of P. Craievich).

Marco

RF measurments performed at elettra have confirmed the predicted values simulated by the electromagnetic code-in particular with the bead pull technique the flat electromagnetic field profile has been observedn and the correct values of the resonces and scattering coefficient




Marco

this is the rf layout of the cavity which shares the same klystron of the rf gun-in the deflector arm an attenuator and a phase shifter has been placed, in order to independently modulate the input power inside the cavity- an rf setup which allows the estimation of the input power -and the reflected and the internal field has been inmplemented using directional coupler diodes and a scope



Operating with Low-Energy RF Deflector

The results presented in the next slides have been obtained working in control room with A. Lutman and G. Penco (Sincrotrone Trieste S.C.p.A.).

Marco

this is the graphical user interface which is use to automatically estimate the input power estimating from the direct trace at the scope




Calibration GUI with a sin fitting at Vt=0.16MV,

Zero crossing= 147 deg, B=2.9mm

sint S D DS

tot

VB

E

sinZ

y B C

Marco

Now i will start the description of the operation with the low energy deflector.The transveral force inside the cavity must be zero in the centroid and have opposite direction at the tail and the head of the bunch- these mean that we must be at 0 crossing- so before using the instrument a calibration has to be made to chose the correct phase- here we have an example we can see that moving the phase from 0 to 2 pi the centroide move and onlly for a certain phase it is on axes- this is 0 crossing-with this procedure we can estimate the calibration coefficient which is used to estimate the deflecting voltage and is relateded to it by energy and optical parameters




Vt=0.27MV

Vt=1.5MV

Vertical enlargement of the trace, which can be exploited for bunch length and emittance slice measurements.

Marco

here we have an example of strecthed bunch, at 0.27 mv and 1.5 mv-we can see the increasing of the vertica l trace




tσ =1.1ps

Bunch Length Measurement=1.1ps (uncompressed bunch)

Marco

here we have an example of bunch lentgth measurement-2 values of deflecting voltage and a straigth nline whose coefficient is proportional to the bunch length-a reconstruction of the longitudinal profile is on the rigth 1.1ps




Bunch Compressor Estimation and energy profile at BC1 spectrometer.Increasing Bunch

Compression

Factor

Marco

the deflector has been used to observe the bunch compression efficiency-we can see that increasing the bunch compression the vertical trace reduces-we can see also an image of the electron bunch in the bc1 spectrometer- we can see that the head and the tail of the bunch have a lower energy



High-Energy RF Deflectors

Ltot 2.5 m f 2.998 GHz

a 12.5 mm Vt 20 MV

b 59.33 mm

tf 3 μs

Lcell 33.33 mm

E 1.2 GeV

72 cells+ 2 couplers (HFSS design now under realization at PMB-France)

The high energy deflectors will be 2.5 meters long, working in 2/3 pi mode.

Deflection in vertical/horizontal planes.

Marco

After having talked of the low energy deflector i will show you something about the high energy deflector.It is a different deflector, because it will operate at 1.2 geV, before the fel-it will provide 20 mv.the rf design so it is different, and a travelling wave device has been used because a standing wave structure would be too long with too much cells and so with resonant modes to much near.the cavity will have 72 cells + 2 coupler, phase advance 2/3 pi and 2.5 meters long



High-Energy RF Deflector

D1 D2Dr

An analytical model which takes in account the wakefield effect have been implemented (Riunione Nazionale Elettromagnetismo 2010).

Marco

These cavities are 2.5 meters long with an small iris radius to increase the deflecting voltage.For this reason a dedicated study of the wakefield have been performed, wiht an analytical resolution of the bunch motion in the precence of the wakefield effect.Here we can see some example of the ideal bunch motion in the case in which the first deflector is on and the second is off (the two cavities are separeted by a drift) and the motion is parabolic and simmetric.if there is an offset and there si a small deflecting voltage a lack off symmetry is visible- but we have observed that in the normal operating condition our cavities are safe and have not no wakefield problem.




210

222

2

0

1

|H|

zz

H

32

Maste

r

Sla

ve

Marco

these are some details of the rf design, the basic cell performed by master slave condition of hfss and coupler designed with the short cuts technique to excite only the 2/3 pi mode-the simulated field profile is flat and the phase advance is the on predicted




.. work in progress.

Marco

the cavity is now under realization at pmb infrance -here we can see the copper device when rf measurments are performed



Conclusion

The RF deflectors are a very useful beam diagnostic tool. The Low Energy Deflector has performed the first diagnostic measurements. The High Energy Deflectors will arrive within few months and will be used to

observe the beam properties just before the FEL.

The work presented here have been done during my PhD under the supervision of prof. Vescovo and P. Craievich.

A big thank also to: A. Lutman, G. Penco, M. Dalforno, S. Di Mitri, E. Allaria, M. Trovò, S. Spampinati, S. Biedron, D. Lacivita and all the other people of the FERMI@Elettra team involved

Marco

As conclusion rf deflector are a powerful tool for beam diagnostic for a fel machine. the low rf deflector is now opersting and the firs intersting bunch operation are taking place.the high energy deflecotr which will describe the bunch before the fel will arrive within few months

14th esls rf workshop elettra / trieste, italy / 2010 september 29 30 rf deflectors for the...

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