Activities status on X-Band at LNF
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
.
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 p mode section at 11.424 GHz
• Design and characterization of a p/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 2011
February 9-10, 2011 SLAC National Accelerator Laboratory
Menlo 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).
the MOTIVATION …….
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
X-band
structure
RF compressor
Basic layout of the
SPARC Linac
Traveling Wave
accelerating
structures
RF GUN
US High Gradient Research Collaboration Workshop 2011 February 9-10, 2011 - SLAC National Accelerator Laboratory - Menlo Park, CA
Study and simulation of a 9-cell SW π-mode X-band structure
Structure with no coupling tubes
r = 10.54 mm
p = 13.121 mm
h = 2 mm
r2 = 4 mm
p
p
h
r2
Symmetry planes
r2/ = 0.15
Structure with coupling tubes
r = 10.477 mm
(End Cell)
r = 10.540 mm
(Central Cells)
r = 10.477 mm
(End Cell)
r1 = 1mm
p = 13.121 mm
h= 2 mm
r2 = 4 mm
p
h
r2
US High Gradient Research Collaboration Workshop 2011 February 9-10, 2011 - SLAC National Accelerator Laboratory - Menlo Park, CA
… simulation of 9-cell p-mode ….
100
80
60
40
Ez (MV/m)
20
0
-20
-40
-60
-80
-100
0
2
4
6
8
10
12
14
16
Z (cm)
With beam-tubes and constant cavity radius
u no flatness on-axis of the longitudinal E-field
60
Ez (MV/m)
40
20
0
-20
-40
Ez
-60
0
2
4
6
8
Z
10
12
14
(cm)
With beam-tubes and reduced end-cells radius
u flatness on-axis of the longitudinal E-field
16
… simulation of 9-cell p-mode ….
structure with mirrors
Frequency [MHz]
Mode [p]
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
f_Analytical ( ) 1.13 10 4
11416.834
7/8
f_with_Tubes
11427.704
1
DISPERSION CURVE
with and without beam-tubes
×106
4
1.145 10
1.14 10
4
4
1.135 10
f_mirrors
1.125 10
4
1.12 10
4
1.115 10
structure with tubes
4
0
0.5
1
1.5
2
2.5
3
mode1    mode3
Mode
K = 2.42 %
h = 2 mm
Coupling coefficient
Frequency [MHz]
Mode [p]
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
DETECTION OF THE FUNDAMENTAL MODE
RESONANCES BY THE INPUT COUPLER
Transmission coefficient
lateral probe-lateral probe
INPUT COUPLER INDUCED MODES
LONGITUDINAL INDUCED MODES
p-mode
11.424 GHz
22 MHz
Network Analyzer
s11
Frequency (Hz)
p-mode
11.424 GHz
Frequency (Hz)
Network Analyzer
s21
Dispersion Curve Before-After Brazing
HFSS
Superfish
Before
brazing
After brazing
f0
11.4244
11.4240
11.4239
11.4244
Q0
8500
8070
7900
8066
US High Gradient Research Collaboration Workshop 2011
February 9-10, 2011 SLAC National Accelerator Laboratory
Menlo Park, CA
NIM A 554 (2005) 1-12
π-mode Cu model RF measurements
p-mode ACCELERATING ELECTRIC FIELD
BEHAVIOR AFTER the 9-CELL TUNING
FIELD FLATNESS ±1%
Normalized longitudinal field profile
E2/EM
Length (arb. Units)
A p/2 biperiodic cavity: technical design
Tuners
p = 13.121 mm
h = 2 mm
r2 = 4 mm
gap (coupling cell ) = 1 mm
RF probe
location
The structure is
designed for
brazing
Accelerating cell
Axial Coupling cell
A p/2 biperiodic cavity: 17 cells copper
prototype NIM: A 586 (2008
Structure with closed stop-band
p/2
rc.c. = 11.7218 mm
r = 10.575 mm
Simmetry planes
Real structure with coupling tubes
r = 10.557 mm
(End Cell)
r = 10.575 mm
r = 10.557 mm
(Central Cells)
(End Cell)
r1 = 1 mm
4 mm
lc.c. = 1 mm
P = 13.121 mm
t = 2 mm
US High Gradient Research Collaboration Workshop 2011 February 9-10, 2011 - SLAC
National Accelerator Laboratory - Menlo Park, CA
p/2
dispersion curve
with and without beam tubes
Frequency (GHz)
11.6
The frequencies separation between
the operating p/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.
11.5
11.4
11.3
11.2
Mode (rad)
Q0  6850 (brased)
From the spacing of the lower
and upper cut-off frequencies,
the coupling coefficient is given
by K = 3.6%.
Q0  7100 (theor.)
US High Gradient Research Collaboration Workshop 2011 February 9-10, 2011 - SLAC
National Accelerator Laboratory - Menlo Park, CA
Copper prototype (p/2 mode)
Field profile
simulation vs measurements
Field profile measurement
Field
Flatness
1.5
1
0.5
0
HFSS
SuperFish
Mafia
Measur.
-0.5
-1
±2.5%
-1.5
0
3
p/2
Dispersion curve
0
Log Mag (db)
p/2
Coupler feeding
-40
End cells
antennas
-60
-80
-100
1.12
1.13 1.14 1.15
Frequency (Hz)
9
12
15
18
21
z axis (cm)
(Rsh/L)/Q0 [ /m]
-20
6
1.16
10
x 10
HFSS
Superfish
Meas.
9452
9693
9150 (200)
p-MODE COPPER PROTOTYPE MAIN PARAMETERS
p- 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
Average accel.field = 42 MV/m
@ 3MW peak power
In red, the
theoretical
values
Peak surface electric field,
Esur = 105 MV/m
Power dissipation,
Pd = 2.45 KW/m
(assuming and duty
cycle of 10-4 )
p/2-MODE COPPER PROTOTYPE MAIN PARAMETERS
p/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 %
In red, the
theoretical
values
Peak surface electric field,
Esur (MV/m) = 102
Power dissipation,
Pd = 2.68 KW/m
(assuming a duty cycle
of 10-4 )
Number of cells (acc.) 9
Structure length
110 mm
US High Gradient Research Collaboration Workshop 2011 February 9-10, 2011
- SLAC National Accelerator Laboratory - Menlo Park, CA
X-band device realisation issue
Guidelines:
How to improve the high power performance (e.g. discharge rate) ?
using materials with higher fusion temperature;
avoiding the device heating at high
temperature as done in conventional brazing
R&D on material
R&D on
materials
R&D on
fabrication
techniques
• Sintered Molybdenum (Bulk)
• Electroforming
• Soft Bonding
R&D on fabrication
techniques
• Molybdenum sputtering on
Copper
• EBW (Electron Beam Welding)
Copper and Molybdenum prototypes for the breakdown studies
Photographs of the two X band cavities
manufactured @ LNF
Cu brazed
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 test
2.3 mm
deformation
tool
CU
MO
Δ = 0.9 mm
Δ = 0.8 mm
deform ≤ 0.6 mm
deform ≤ 0.3 mm
~1.6 MHz/mm3
Detail of the maximum deformation
obtained inside the cell [Master thesis of
M. Ronzoni – University La Sapienza –
Rome]
Frequency shift (MHz)
Breaking limit
US High Gradient Research Collaboration Workshop 2011
February 9-10, 2011 SLAC National Accelerator Laboratory
Menlo Park, CA
The reference case ...
…….. 3-cell Copper – p 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 COPPER model has been tested
to SLAC for power testing.
Results of high-power test of the 3-cell
standing wave structure performed by
… “V.A. Dolgashev, SLAC” 30 October
2008
The Palladium-Copper-Silver
(PALCUSIL) alloys were used
with different composition
(different melting points).
US High Gradient Research Collaboration Workshop 2011
February 9-10, 2011 SLAC National Accelerator Laboratory
Menlo Park, CA
US High Gradient Research Collaboration Workshop 2011
February 9-10, 2011 SLAC National Accelerator Laboratory
Menlo Park, CA
3-cell Sintered Molybdenum Bulk
p mode - SW structure
• Machining with the ‘tungsten carbide’
tools
•The PALCUSIL alloys were used for
brazing Molybdenum-Molybdenum and
Molybdenum-Stainless Steel joints.
The model was designed to
concentrate the RF field in
the mid-cell
Q0 = 4800 (measured)
Jim Lewandowski, SLAC, 1/14/09
Higher Power tests of the brazed
model have been carried out at
SLAC (V. Dolgashev et al.)
Bad
results
!
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 R&D and Test
B. Spataro, R&D on X-band Structures at LNF
“ 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.
Electroforming properties :
The speed of plating process
is ≈ 0.6 mm/day
Dimensional tolerances: ± 2.5 µm
copper metal
Surface finishing: 150 ÷ 200 nm (to be
improved, studies are in progress);
High device reproducibility.
Basic scheme for the electroforming
Aluminium mandrel of the RF
coupler and cell ready for the
electroforming
…… Electroforming R&D and Test
Mo discs are already machined to
be the iris of the electroformed cell
5 cells mandrel of
a Mo-Cu structure
Electroformed
RF coupler and cell
Another view of the coupler
mandrel is shown
US High Gradient Research Collaboration Workshop 2011
February 9-10, 2011 SLAC National Accelerator Laboratory
Menlo Park, CA
…… Electroforming R&D and Test
RF cells after removing the Aluminium core
with alkaline solution (sodium hydroxide
NaOH). Cross section of a Mo-Cu
electroformed structure.
Fundamental mode response of
Cu-Mo electroformed structure
Q0 = 5406
π mode
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 !!! )
Electroforming: other materials
First Cu-Zr Electroformed
model after baking
The color is due to Oxidation effect
Q0 = 5788
US High Gradient Research Collaboration Workshop 2011
February 9-10, 2011 SLAC National Accelerator Laboratory
Menlo Park, CA
From electroforming to elecroplating
A 3 cell Cu OFHC structure,
encapsulated by galvanoplastic
procedure under vacuum leak test.
Higher Power tests of the model
have been carried out at SLAC (V.
Dolgashev et al.)
Cu encapsulated (electroplating)
structure: measured p-mode field
profiles by bead-pull technique.
Q0 = 7700 (measured)
US High Gradient Research Collaboration Workshop 2011
February 9-10, 2011 SLAC National Accelerator Laboratory
Menlo Park, CA
Sputtering activities ongoing at LNF …..
Schematic diagram of a DC
magnetron plasma sourcee
HUNZIGER
COMPANY DEVICE
Experimental set up for the RF
Magnetron Sputtering
Power 60 W
Vacuum level 4*10-2mbar
Deposition rate about
0.5 nm/sec
Sputtering activities ongoing at LNF …..
Aluminium dish treated with copper
A titanium-steel screw covered
with copper film
Two euro cents covered with aluminium
Aluminium cylinder covered with gold
Roughness behaviour of the Sputtered molybdenum on a Copper sample
AFM (Atomic Force Microscopy) shows the surface
of a copper sample before molybdenum sputtering
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.
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)
Actually, measurement of the carbon
concentration is affected by a strong error
( up to ~ 30% of the measured value)
Mo
Cu
XPS (X ray Photoelectronic Spettroscopy)
depth sensitivity is ~ 5-10 nm
(depending by the analyzed materials).
O2
C
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)
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.
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
Energy (MeV)
0.8
80
1.0
1.2
1.4
1.6
Normalized Yield
60
roughness is in the range of 1- 2 nm
40
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.
20
O
0
200
Mo
300
400
500
600
Channel
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).
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
zoom
Grain of powder
The study of the sputtering approach as function of the
deposited material depth , thermal treatment, chemical
composition, morphological properties is in progress.
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. 3 : Copper dish machined at very low
roughness sputtered with 600nm of Molybdenum
after a thermal treatment of 2 hours at 300 °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. 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
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
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
Standard model should be
realized with the soft bonding
plus electroplating technique
Triple choke standing wave structure
(A.D. Yeremian, V.A. Dolgashev, S.G. Tantawi, SLAC)
http://accelconf.web.cern.ch/accelconf/IPAC10/papers/thpea065.pdf
Preliminary 3D Model
Studies on the mechanical
drawings are in progress in order
to separate vacuum and RF-joint
to test molybdenum and hard alloy
structures
Use of the Electron Beam Welding technique
Prototype ready to be
used for the EB technique
EBW was used for a welding test of an X-band cavity sample.
Cross section of
the prototype
3 mm
cavity
Tool to keep together
the 2 half-cavities
during pre-bonding
Sample pre-bonding @ 300°C
EB welded sample
The pre-bonding is used in order to prevent :
0.04 mm
0.6 mm
1) microgaps left by welding (on the cell surface)
[vacuum leakage tests gave about 10-10 mbar litre/sec
2) accidental pocket air inclusions
3) EBW damages in the internal surface of the structure
…… use of the Electron Beam Welding technique
Macrographic inspection of EB welded joints, made on a X-band test specimen
pre-bonding zone
EBW zone
The welding meets the requirements
of the applicable specification SI 01.003 revA
No cracks have been found in the fusion zone
and 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.
The joints in the pre-bonding region
Moreover dimensional mechanical tests before demonstrated to work well and
additional tests are in progress, too.
and after welding gave negligible difference.
Status of the R&D and future programs
•Two X-band structures (p and p/2 modes) have been characterized at low power
RF;
• One p-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 brazingelectroplating - 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 SLACKEK-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.
US High Gradient Research Collaboration Workshop 2011
February 9-10, 2011 SLAC National Accelerator Laboratory
Menlo Park, CA
Thank you very much for your
attention !!!
US High Gradient Research Collaboration Workshop 2011
February 9-10, 2011 SLAC National Accelerator Laboratory
Menlo Park, CA