presented by Bruno Spataro on behalf of the SALAF team

presented by Bruno Spataro

on behalf of the SALAF team

.US High Gradient Research Collaboration Workshop 2011, February 9-10, 2011 SLAC National Accelerator Laboratory Menlo Park, CA

Activities status on X-Band at LNF

Contributors

This work is made possible by the efforts :

SALAF Group, INFN - LNF

V. Dolgaschev, S. Tantawi , A.D. Yeremian, SLAC

Y. Yigashi, KEK

M . Migliorati, A. Mostacci, L. Palumbo, University of Roma 1

J. Rosenzweig et. al., UCLA

R. Parodi, INFN-Genova

M.G. Grimaldi et. al., University of Catania

US High Gradient Research Collaboration Workshop 2011, February 9-10, 2011 SLAC National Accelerator Laboratory Menlo Park, CA

SUMMARY

• Design and characterization of a mode section at 11.424 GHz

• Design and characterization of a /2 mode section at 11.424 GHz

• Technological activity status on electroforming, molybdenum sputtering, soft bonding and electro-beam welding.

US High Gradient Research Collaboration Workshop 2011February 9-10, 2011 SLAC National Accelerator LaboratoryMenlo Park, CA

SALAF (Linear Acceleranting Structures at High Frequency)is the INFN r&d programm on“ multicell resonating structures” operating at X-band (10 ÷ 12 GHz).

To use in high brilliance photo-injectors (SPARC-phase-2) to compensate for the beam longitudinal phase-space distorsion, enhanced by the bunch compression of the acceleration process

To gain know-how in vacuum microwave technologies

the MOTIVATION …….

RF GUN

RF compressor

Traveling Wave accelerating structures

X-bandstructure

Basic layout of theSPARC Linac

US High Gradient Research Collaboration Workshop 2011 February 9-10, 2011 - SLAC National Accelerator Laboratory - Menlo Park, CA

r1 = 1mm

p h r2

p = 13.121 mmh= 2 mmr2 = 4 mm

Structure with coupling tubes

r = 10.477 mm(End Cell)

r = 10.540 mm(Central Cells)


Study and simulation of a 9-cell SW Study and simulation of a 9-cell SW ππ-mode-mode X-band structure X-band structure

p h r2

Symmetry planes

p = 13.121 mmh = 2 mmr2 = 4 mm

Structure with no coupling tubes

r = 10.54 mm

r2/ = 0.15


With beam-tubes and reduced end-cells radius

flatness on-axis of the longitudinal E-field

Z (cm)

Ez (MV/m)

-60

-40

-20

0

20

40

60

0 2 4 6 8 10 12 14 16

… simulation of 9-cell -mode ….

With beam-tubes and constant cavity radius

no flatness on-axis of the longitudinal E-field

Z (cm)

Ez (MV/m)

-100

-80

-60

-40

-20

0

20

40

60

80

100

0 2 4 6 8 10 12 14 16

Ez

0 0.5 1 1.5 2 2.5 31.115 10

4

1.12 104

1.125 104

1.13 104

1.135 104

1.14 104

1.145 104

f_mirrors

f_Analytical ( )

f_with_Tubes

mode1 mode3

Mode

structure with mirrors Frequency [MHz] Mode []

11152.818 0

11162.906 1/8

11191.717 1/4

11235.333 3/8

11287.522 1/2

11340.448 5/8

11386.000 3/4

11416.834 7/8

11427.704 1

Frequency [MHz] Mode []

11160.784 1/9

11183.868 2/9

11219.481 1/3

11263.701 4/9

11311.225 5/9

11356.593 2/3

11393.989 7/9

11418.634 8/9

11427.465 1

structure with tubes

DISPERSION CURVE with and without beam-tubes

h = 2 mm

… simulation of 9-cell -mode ….

K = 2.42 %

Coupling coefficient

×106

DETECTION OF THE FUNDAMENTAL MODERESONANCES BY THE INPUT COUPLER

US High Gradient Research Collaboration Workshop 2011February 9-10, 2011 SLAC National Accelerator Laboratory

Menlo Park, CA

HFSS Superfish Before brazing

After brazing

f0 11.4244 11.4240 11.4239 11.4244

Q0 8500 8070 7900 8066

LONGITUDINAL INDUCED MODES

-mode11.424 GHz

Network Analyzer

s21

Transmission coefficient lateral probe-lateral probe

Frequency (Hz)

-mode11.424 GHz

INPUT COUPLER INDUCED MODES

22 MHz

Network Analyzer

s11 Frequency (Hz)

Dispersion Curve Before-After Brazing

FIELD FLATNESS ±1%

ππ-mode Cu model RF measurements-mode Cu model RF measurementsNIM A 554 (2005) 1-12

-mode ACCELERATING ELECTRIC FIELDBEHAVIOR AFTER the 9-CELL TUNING

E2/EM

Normalized longitudinal field profile

Length (arb. Units)

A /2 biperiodic cavity: technical design

Accelerating cell

Axial Coupling cell

Tuners

RF probelocation

The structure is designed for brazing

A /2 biperiodic cavity: 17 cells copper prototype NIM: A 586 (2008

p = 13.121 mmh = 2 mmr2 = 4 mmgap (coupling cell ) = 1 mm

Real structure with coupling tubes

lc.c. = 1 mm

P = 13.121 mm

r1 = 1 mm



r = 10.575 mm(Central Cells)

4 mm

t = 2 mm

Simmetry planes

rc.c. = 11.7218 mm

Structure with closed stop-band

r = 10.575 mm


11.2

11.3

11.4

11.5

11.6

Fre

qu

en

cy (

GH

z)

Mode (rad)

dispersion curvewith and without beam

tubes

The frequencies separation between the operating /2 frequency and the adjacent ones frequencies is about given by ΔF= 39MHz and ΔF= 36MHz against the operating mode bandwidth ΔF= 1.6 MHz.

From the spacing of the lower and upper cut-off frequencies, the coupling coefficient is given by K = 3.6%.

(theor.) 7100Q

(brased) 6850Q

0

0


Copper prototype (/2 mode)

HFSS Superfish Meas.

(Rsh/L)/Q0 [ /m] 9452 9693 9150 (200)

FieldFlatness

2.5%

Field profile measurement Field profile simulation vs measurements

-1.5

-1

-0.5

0

0.5

1

1.5

0 3 6 9 12 15 18 21

HFSS

SuperFish

Mafia

Measur.

z axis (cm)

Dispersion curve

1.12 1.13 1.14 1.15 1.16

x 1010

-100

-80

-60

-40

-20

0

Log

Ma

g (d

b)

Frequency (Hz)

Coupler feeding

End cellsantennas

-MODE COPPER PROTOTYPE MAIN PARAMETERS

- mode frequency 11.424 GHz

Form factor r/Q (/m)

9400 (9165 )

Unloaded Q 8000 (8413 )

External Q 7900

E-Field flatness ± 1 %

Number of cells 9

Structure length 110 mm

/2-MODE COPPER PROTOTYPE MAIN PARAMETERS

2- mode frequency

11.424 GHz

Form factor r/Q (/m)

9150 (9452 )

Unloaded Q 6850 (7100 )

External Q 6910

E-Field flatness ± 2.5 %

Number of cells (acc.)

9

Structure length 110 mm


In red, the theoretical values

In red, the theoretical values

Average accel.field = 42 MV/m @ 3MW peak power

Peak surface electric field, Esur = 105 MV/m

Peak surface electric field, Esur (MV/m) = 102

Power dissipation, Pd = 2.45 KW/m

Power dissipation, Pd = 2.68 KW/m

(assuming a duty cycle of 10-4 )

(assuming and duty cycle of 10-4 )

X-band device realisation issue

How to improve the high power performance (e.g. discharge rate) ?

R&D on materials

R&D on fabrication techniques

using materials with higher fusion temperature;

Guidelines:

avoiding the device heating at high temperature as done in conventional brazing

R&D on material

R&D on fabrication techniques

• Sintered Molybdenum (Bulk)

• Electroforming

• Soft Bonding

• Molybdenum sputtering on Copper

• EBW (Electron Beam Welding)

Copper and Molybdenum prototypes for the breakdown studies

Cu brazed

Photographs of the two X band cavities manufactured @ LNF

Molybdenum brazed

US High Gradient Research Collaboration Workshop 2011, February 9-10, 2011 SLAC National Accelerator Laboratory Menlo Park, CA

Tuning with the wall deformation

Tool for deformation test2.3 mm

deformationtool

CU MO

Δ = 0.9 mm Δ = 0.8 mm

deform ≤ 0.6 mm deform ≤ 0.3 mm

~1.6 MHz/mm3

Frequency shift (MHz)Detail of the maximum deformation obtained inside the cell [Master thesis of M. Ronzoni – University La Sapienza – Rome] Breaking limit US High Gradient Research Collaboration Workshop 2011

February 9-10, 2011 SLAC National Accelerator LaboratoryMenlo Park, CA

Results of high-power test of the 3-cell standing wave structure performed by … “V.A. Dolgashev, SLAC” 30 October 2008 US High Gradient Research Collaboration Workshop 2011


The COPPER model has been testedto SLAC for power testing.

…….. 3-cell Copper – mode - SW structure

The model was designed to concentrate the RF field in the mid-cell to achieve high-gradient field, to investigate the discharge limits (V.A.Dolgaschev, SLAC)

The Palladium-Copper-Silver (PALCUSIL) alloys were used

with different composition(different melting points).

The reference case ...


Menlo Park, CA

3-cell Sintered Molybdenum Bulk

mode - SW structure

The model was designed to concentrate the RF field in the mid-cell

Higher Power tests of the brazed model have been carried out at SLAC (V. Dolgashev et al.)

•The PALCUSIL alloys were used for brazing Molybdenum-Molybdenum and Molybdenum-Stainless Steel joints.

• Machining with the ‘tungsten carbide’ tools

Q0 = 4800 (measured)

Jim Lewandowski, SLAC, 1/14/09

Badresults!

Sintered Molybdenum (bulk) issue

long time for machining the cavity

300 nm roughness using ‘tungsten

carbide’ tools

It is not easy to braze. It is likely to have a gas

contamination and an uneven loading stress in the braze

region (joints are not completely filled with alloy ).

“ Electroforming ” is a galvanotechnical process to fabricate a metal structure using electro-deposition of a metal (usually Copper) over a mandrel (usually Aluminum) in a

plating bath of Cu-SO4 + H2SO4 (copper sulphate + sulphuric acid ) The Al-core is afterward chemically eliminated with NaOH (sodium hydroxide) treatment

(for Al cores). Electroforming is a very attractive process, alternative to the brazing technology

Mixed processes, like electroforming after cell manufacturing with standard techniques (Electroplating process), are under development, too.

copper metal

Electroforming R&D and Test

Electroforming properties :

The speed of plating process is ≈ 0.6 mm/day

Dimensional tolerances: ± 2.5 µm

Surface finishing: 150 ÷ 200 nm (to be improved, studies are in progress);

High device reproducibility.

B. Spataro, R&D on X-band Structures at LNF

Basic scheme for the electroforming

…… Electroforming R&D and Test Aluminium mandrel of the RF coupler and cell ready

for the electroforming

Electroformed RF coupler and cell

5 cells mandrel of

a Mo-Cu structure

Mo discs are already machined to be the iris of the electroformed cell

Another view of the coupler mandrel is shown


…… Electroforming R&D and Test

π mode

Q0 = 5406

Fundamental mode response of Cu-Mo electroformed structureRF cells after removing the Aluminium

core with alkaline solution (sodium hydroxide NaOH). Cross section of a Mo-Cu electroformed structure.

The Mo discs with an external ribs improve the mechanical properties.

Next step: to improve the quality of the Cu surface altered by the alkaline solution by depositing silver on the core or using other methods .…to be investigated !!! )

Q0 = 5788First Cu-Zr ElectroformedElectroformed

model after baking

Electroforming: other materials

The color is due to Oxidation effectUS High Gradient Research Collaboration Workshop 2011


A 3 cell Cu OFHC structure, encapsulated by galvanoplastic

procedure under vacuum leak test.

From electroforming to elecroplating

Cu encapsulated (electroplating) structure: measured -mode field profiles by bead-pull technique.

Q0 = 7700 (measured)Higher Power tests of the model have been carried out at SLAC (V. Dolgashev et al.) US High Gradient Research Collaboration Workshop 2011


Experimental set up for the RF Magnetron Sputtering

Power 60 WVacuum level 4*10-2mbar

Sputtering activities ongoing at LNF …..

Deposition rate about 0.5 nm/sec

HUNZIGER COMPANY DEVICE

Schematic diagram of a DC magnetron plasma sourcee

Aluminium dish treated with copper Two euro cents covered with aluminium

A titanium-steel screw covered with copper film Aluminium cylinder covered with gold

Sputtering activities ongoing at LNF …..

AFM (Atomic Force Microscopy) shows the surface of a copper sample before molybdenum sputtering

Roughness behaviour of the Sputtered molybdenum on a Copper sample

AFM (Atomic Force Microscopy) image of deposited Molybdenum (100nm) on a copper sample by sputtering technique . The roughness of the film is comparable to that of the substrate. This indicates that the roughness is determined by the substrate.

The XPS (X ray Photoelectronic Spettroscopy) Depth Profiling technique using the PHI 5600Ci system is available at the

unit of Genova of the INFN. The sputtering parameters are 1µA Argon Ion at 4Kev energy on a raster covering an

area of 5x5mm centered on the monochromatic X Ray spot on the sample.

Actually, measurement of the carbon concentration is affected by a strong error (

up to ~ 30% of the measured value)

XPS (X ray Photoelectronic Spettroscopy) depth sensitivity is ~ 5-10 nm

(depending by the analyzed materials).

Chemical composition as function of the Depth Profile of the 300nm molybdenum film on a copper with a thermal treatment [ measurements carried out by R. Parodi (INFN-Genova)

Results are in good agreement with RBS measurements carried out at the

Catania University (G.M. Grimaldi et al.)except for the carbon (much less)

Mo

Cu

O2

C

200 300 400 500 600

Channel

0

20

40

60

80

Nor

mal

ized

Yie

ld

0.8 1.0 1.2 1.4 1.6

Energy (MeV)

MoO

Mo and O surface scattering contributions are reported as green labels. The Mo film contains oxygen. The deposited film is characterized by a Mo concentration lower than a pure Mo film with a 100 nm thick (~20 % reduction with respect to a pure Mo film).

The electrical measurement using the Van der Pauw configuration, gives a resistivity of 10-3 Ω cm by about two orders of magnitude higher compared to a pure Mo film with a 100nm thickness, a difference compatible with the presence of oxides in the Mo.

RBS (Rutherford backscattering spectrometry) spectrum(black line) and simulation (red line) obtained on Mo film 130 nm thickness deposited on a 2 μm SiO2 layer on top of a Si substrate (University of Catania).

Mo film on a SiO2 layer

roughness is in the range of 1- 2 nm

Grain of powder

zoom

The study of the sputtering approach as function of the deposited material depth , thermal treatment, chemical composition, morphological properties is in progress.

Micro-cracks investigations carried out with the Scanning Electron Microscope (SEM) on Copper dish machined at very low roughness (70 nm) sputtered with 600 nm of Molybdenum after a thermal treatment of 2 hours

at 600 °C

Some SEM RESULTS as fuction of the temperature and depth profile

Fig. 1 : Micro crack on Copper dish machined at very low roughness sputtered with 600nm of

Molybdenum after a thermal treatment of 2 hours at 600 °C.

Fig. 2 : Copper dish machined at very low roughness sputtered with 300nm of Molybdenum after a

thermal treatment of 2 hours at 600 °C.

Fig. 3 : Copper dish machined at very low roughness sputtered with 600nm of Molybdenum

after a thermal treatment of 2 hours at 300 °C.

Fig. 4 : Copper dish machined at very low roughness sputtered with 300nm of Molybdenum

after a thermal treatment of 2 hours at 300 °C.

Soft bonding 3 cells Cu prototype

A Cu OFHC structure under vacuum leak test

If contact surfaces are machined at a very low roughness (70nm), the thermal treatment after Sn deposition could be unnecessary.

Vacuum tight very good has been obtained with a proper pressure applied to the structure with three bars

By brazing like at temperature a little less than 230°C ( Sn melting point) we obtain a good mechanical structure stability. Some tests with copper OFHC remade with different shapes among the contact

surfaces gave good results in term of helium vacuum leak

Standard model should be realized with the soft bonding plus electroplating technique

Triple choke standing wave structure

Studies on the mechanical drawings are in progress in order to separate vacuum and RF-joint to test molybdenum and hard alloy structures

(A.D. Yeremian, V.A. Dolgashev, S.G. Tantawi, SLAC)http://accelconf.web.cern.ch/accelconf/IPAC10/papers/thpea065.pdf

Preliminary 3D Model

http://accelconf.web.cern.ch/accelconf/IPAC10/papers/thpea065.pdf

Use of the Electron Beam Welding technique

EBW was used for a welding test of an X-band cavity sample.

Sample pre-bonding @ 300°C

0.04 mm

0.6 mm

cavity

Tool to keep together the 2 half-cavities during pre-bonding

The pre-bonding is used in order to prevent :

1) microgaps left by welding (on the cell surface)[vacuum leakage tests gave about 10-10 mbar litre/sec2) accidental pocket air inclusions3) EBW damages in the internal surface of the structure

3 mm

EB welded sample

Prototype ready to beused for the EB technique

Cross section of the prototype

…… use of the Electron Beam Welding technique

The welding meets the requirementsof the applicable specification SI 01.003 revANo cracks have been found in the fusion zoneand in the heat affected zone.There are only small porosities at the root-side of the weld joint which are, however, within the limits of the specs.

Moreover dimensional mechanical tests before and after welding gave negligible difference.

Macrographic inspection of EB welded joints, made on a X-band test specimen

pre-bonding zone

EBW zone

The joints in the pre-bonding region demonstrated to work well andadditional tests are in progress, too.

Status of the R&D and future programs

•Two X-band structures ( and /2 modes) have been characterized at low power RF;

• One -mode 9-cells Cu section has been manufactured for higher power tests;

• Hybrid photo-injector at 11.424 GHz (see J. Rosenzweig and A. Valloni talks)

•Technological activity :

a) R&D on sputtering method, soft bonding and new alloys with the SLAC, KEK, INFN/Genova, University of Catania collaboration;

b) Production of a 3-cell standard prototype (combination of the soft brazing-electroplating - molybdenum sputtering) with the SLAC-KEK collaboration;

c) Electron Beam Welding (EBW) activity with the SLAC-KEK collaboration;

d) Triple choke standing wave cavity realization with the EBW technique SLAC-KEK-LNF- University of Roma 1;

e) Power tests at SLAC (have been already carried out) in the frame of a M.O.U with INFN, on design, fabrication and test of X-band devices and high gradient power tests of innovative structures.


Thank you very much for your attention !!!


Menlo Park, CA

Documents

presented by Bruno Spataro on behalf of the SALAF team