PROPOSAL 2006 - G.I.A.F.(HYBRID GUN AT HIGH FREQUENCY)

INFN-LNF – UNIVERSITY OF ROME “LA SAPIENZA”- UCLA

• D. Alesini (T), M. Ferrario (R), A. Gallo (T), F. Marcellini (T), V.Fusco (art. 23), B. Spataro (T) (Resp. Naz.)

• LNF Full Time Equivalent 1.5 (1.3 tecnologist – 0.2 researcher)

• L. Ficcadenti (D), M. Esposito (AU), M. Migliorati (R), A.Mostacci (consultant), L. Palumbo (PO)

• University of Rome Full Time Equivalent 1.2 (0.6 tecnologist –0.6 researcher)

• J. Rosenzweig(PO)• UCLA Dept. of Physics and Astronomy Full Time Equivalent

1.0 (R)TOTAL FTE 3.7

HYBRID GUNELECTROMAGNETIC DESIGN

AND RF MEASUREMENTS

2) DESIGNED STRUCTURES:

a) Integrated accelerating structure;

b) Integrated velocity bunching (acceleration+longitudinalbunch compression);

3) POSSIBLE MEASUREMENTS ON PROTOTYPES

1) THE HYBRID STRUCTURE: ADVANTAGES

SW 1.6 Cell Gun

Input Cell

Emittance-CompensatingSolenoids

Cathode

TW structure

Input Port

1) THE HYBRID STRUCTURE

1) Eliminate transient reflection associated with SWstructures (especially needed for X-band);

2) Compactness:-simplicity (RF distribution system, etc.)

-energy efficiency from TW section

3) Promising good beam dynamics in term of beamemittance and reachable bunch length (velocitybunching)

1) THE HYBRID STRUCTURE: ADVANTAGES

2) DESIGNED STRUCTURES: GENERAL CONSIDERATIONS

The steps to design the structure are the following:

a) “Separate” tuning of the SW and TW sections in order to achieve a uniform fieldflatness of the E field in the SW gun and a zero reflection coefficient at the waveguideinput port of the TW section at the working frequency of the whole system;b) Final tuning of the whole structure to put the SW section perfectly on resonancewith a uniform field flatness of the E field in the first two cells;

1) the phase of the E field betweenthe SW gun and the TW sectiondoes not depend on the geometry ofthe input coupler cell, irisdimensions,… and is about 90 deg.This results has been found by 3Delectromagnetic simulations and hasbeen justified with an equivalentcircuit model;

2) the coupling iris aperturebetween the input coupler cell andthe SW structure allows adjustingthe ratio beween the amplitude ofthe fields in the SW cells and in theTW section: in particular if weincrease the radius we increase thisratio;

RESULTS (S-Band Case)

E.M. field characteristics @ gun resonance

Input coupler cell

∼90 deg

Ez(z,t)=E0(z)cos(ph(z)+ωt)

π Mode of the gun

4) Since the phase between the SWstructure and the TW one is fixed, thesynchronism between the acceleratingfield and the bunch passage can beadjusted by properly chosing thelenght of the input coupler cells.It is therefore possible to design twodifferent structure:-the first one obtainded choosing Dc=2/3λ in which the beam is accelerated inboth structures SW gun and and TWsection;-the second one obtained by choosingDc=5/12λ in which the bunch isaccelerated in the SW section andlongitudinally compressed (velocitybunching technique) in the TW one;

Dc

3) for reasonable values of thecoupling iris (that gives a ratiobetween the amplitude of the fields upto 5) the perturbation on thematching of the input couplerwaveguide is completely negligible.

0.5deg/kHz

Integrated velocity bunching (1/2)

Amplitude of the E fieldalong the structure (E0(z))

Phase (ph(z)) of theelectric field along thestructure: the sensitivity ofthe phase with respect tothe resonant frequency ofthe SW structure requiresvery good stabilization ofthe temperature or an RFfeedback

Ez(z,t)=E0(z)cos(ph(z)+ωt)

Eacc

z z

Inputcoupler

Outputcoupler

Traveling wave structure

zbunch

Integrated velocity bunching (2/2)

EaccEacc

Integrated velocity bunching dimensions

ac

bc

dc

t

ab

d

aw bw/2

w/2

hbf

bh

df

dh

tg

tc

ag

35.2w

12.5ag

41.67bh

31.49dh

41.7bf

52.48df

19.05tg

72.14bw

30.21aw

2h

34.99d

42.89b

16a

8t

43.74dc

40.93bc

19.05tc

9[mm]

ac

Integrated accelerating structure dimensions

ac

bc

dc

t

ab

d

aw bw/2

w/2

hbf

bh

df

dh

tg

tc ag

33.3w

12.5ag

41.67bh

31.49dh

41.7bf

52.48df

19.05tg

72.14bw

36.09aw

2h

34.99d

42.89b

16a

8t

69.98dc

40.53bc

19.05tc

9[mm]

ac

3) RF MEASUREMENTS

Steele method (C.W. Steele, IEEEtrans. on micr th. and tech., 1965)is applicable to SW and to TWstructures separately;

Difference between the reflection atthe input port with and without theperturbing object at z longitudinalposition

Pertubing objects

Hybrid gun NA

( ) ( ) ( )zph22

011

j

e ezEKzS!="

z

( )zS11

PARMELA simulationsInput Beam Parameters:

Q=1 nCLTW=3 m

T0 =10 psecRb=1.57 mmφ0=40 deg

Magnetic field

Energy gain and Momentumspread evolution

Bunch length and Transversebeam size evolution

Emittance evolution

<4<2<2<2Rms norm. emittance [µm]400100800100Peak Current [A]1.50.31.00.1Energy Spread [%]2250180220Energy [MeV]331212Total Length [m]

RFCompr.

NormalRFCompr.

NormalModeHYBRID (S Band)SPARC (S Band)

Work planning

20071 Design of the hybrid structure at 3 GHz (velocity bunching);2 Construction of a prototype at 3 GHz with no cooling and brazing for the

measurements at room temperature; beam dynamic simulation ;3 Some tests for brazing on some cells.20081 Design of the hybrid structure at 11 GHz (velocity bunching);2 Construction of a prototype at 11 GHz with no cooling and brazing for the

measurements at room temperature; beam dynamic simulation ;3 Tests for brazing on some cells.20091 Design of a hybrid structure at 11 GHz included the cooling system;2 Construction of a brazed hybrid structure and measurements at room

temperature;3 High power tests for structures at 3 GHz and 11 GHz

Estimates costs2007 Costs ( 3 GHz)1 hybrid structure 61.0 KEuro2 waveguide tapers 10.0 KEuroBrazing tests 5.0 KEuroConsumable 3.0 KEuroDurable equipment 8.0 KEuro2008 Costs (11 GHz)1 hybrid structure 37.0 KEuro2 waveguide tapers 8.0 KEuroBrazing tests 5.0 KEuroConsumable 3.0 KEuroDurable equipment 8.0 KEuro2009 Costs (11 GHz)1 hybrid structure 90.0 KEuro2 waveguide tapers 10.0 KEuroBrazing tests 5.0 KEuroConsumable 13.0 KEuroDurable equipment 8.0 KEuroDomestic travel/year 2.0 KEuroAbroad travel/year 5.0 KEuro

SUMMARY COSTS

201.024.029.030.06.0Total

90.08.013.010.02.02009

40.08.08.010.02.02008

71.08.08.010.02.02007

Equipmentconstructions(KEuro)

Durableequipment(KEuro)

Consumable(KEuro)

Abroadtravel(KEuro)

Domestictravel (KEuro)

Consumable : attenuator, connectors, cables, vacuum components (flanges,gaskets, valves), ceramic transitions, brazing alloys etc.

Durable equipments : guide transitions, loads, directional coupler, powersupplyEquipment constructions : hybrid structure included 2 waveguide tapers