KICK-OFF MEETING - SRF FOR ELLIPTICAL
CAVITIES
HIGH BETA CAVITIES PROTOTYPES TESTED
AT SACLAY
23/06/2015
Franck PEAUGER
On behalf of CEA Saclay team
MECHANICAL FEATURES OF HIGH BETA CAVITY
PROTOTYPES
 Half cells, beam pipes and ports in pure Niobium RRR > 250
 He tank in Titanium grade 2
 Flanges in NbTi with hexagonal aluminium gaskets
 Assembly by electron beam welding (no brazing)
HELIUM RETURN
HOM port Fint =48.2 mm (for
RF measurements only,
removed on series cavities)
Ti INTERFACE PIECES
FOR TUNER
BEAM
FLANGE 1
Fint=140 mm
TANK STIFFENERS
Ti HYDROFORMED
BELLOW
BEAM
FLANGE 2
Fint=140 mm
Ti HELIUM TANK
5 CELLS CAVITY
FPC Fint=100 mm
CELL STIFFENERS
HELIUM SUPPLY
Total mass: 150 kg (including screws, flanges and
handling tooling)
Overall dimensions: 1316 mm length, 500 mm diameter
CAVITY MANUFACTURING
 Niobium from Tokyo Denkai, 4.5 mm thickness instead of 3.8 mm (before etching)
 Kick-off in Sept. 2012
 Trimming operations of dumbbells in presence of CEA staff
ESS086-P01
ESS086-P02
received after 13 months
received after 18 months
Fp = 703.704 MHz (-0.118 MHz)
L = 1322.9 mm (+6.7 mm)
Fp = 703.553 MHz (-0.269 MHz)
L = 1321.7 mm (+5.5 mm)
Field flatness: 86%
Field flatness: 60%
Target frequency, at 300 K before chemical etching: Fp = 703.822 MHz, target length = 1316.3 mm
FIELD FLATNESS TOOLING AT CEA
ESS 086 P01 (Zanon)
« Manual tuning »
Field flatness of 92 % after
~10 iterations
ESS 086 P02 (RI)
Automatic calculation of length adjustments
Field flatness of 90 % after
~20 iterations
4
FIELD FLATNESS SENSITIVITY
 After mechanical deformation of +/-1 mm
applied on the beam flanges: the field flatness
is measured at each step and stays around
92.5 %.
 Beadpull measurements done after the
two first BCP treatments: no significant
difference
ESS 086 P01 cavity (Zanon)
BCP CHEMICAL TREATMENT SET-UP
•
•
Cavities etched with a buffered chemical solution (‘BCP’ polishing using HydrofluoricNitric-Phosphoric acids with ratio, 1:1:2.4) in three steps
Acid temperature was kept below 15 °C to avoid any hydrogen contamination of the
niobium
Acid inlet
Acid inlet
→ Two independant installations at CEA Saclay compatible with 704 MHz
cavities (and one is fully qualified)
6
EFFECT OF BCP
Coupler port down
Coupler port up
Niobium thickness of ESS086 P01 after chemical etching (BCP)
2
3
4
5
6
7
8
-30 kHz/10µm
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
Niobium tickness removed (mm)
0
Iris 1
-0.1
Iris 2
Iris 3
Iris 4
-0.2
19/02/14( 1er chimie)
25/02/14 (2nd chimie)
29/04/14 (3rd chimie)
-0.3
Niobium thickness of ESS086 P02
ler port
-0.4 2
0
3
4
5
6
7
8
Tuning
system
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
Iris 1
Niobium tickness removed (mm)
-0.5
-0,1
Iris 2
Iris 3
Iris 4
-0.6
-0,2
apres 1er chimie
après 2eme chimie
après 3ème chimie
-0,3
-0,4
SAF
COUPLEUR
-0,5
-0,6
 Removal speed = 0.5 µm/min
 Average of 200 µm removed
CAVITY CLEAN ROOM ASSEMBLY WITH
HIGH PRESSURE RINSING
 The last BCP treatment is always followed by a filling of the cavity with pure water
and a transfer to the CEA clean room
 High Pressure Rinsing performed at 100 bars with ultrapure water and using a new HPR rod installed on the
existing set-up (the new rod has a shorter length).
 The following sequence has been applied:
1. Cavity with power coupler down, orientation = 0°
2. Cavity with power coupler down, orientation = 180°
3. Cavity with power coupler up, orientation = 0°
4. Cavity with power coupler up, orientation = 180°
 After this sequence the cavity is dried under class
100 laminar flow during a full night.
 The flanges, the two feedthroughs with pick-up
antennas and the vacuum valve have been tightened
at 20 N/m with their corresponding aluminum
gaskets.
CALIBRATION OF PICK-UP ANTENNA COUPLING
• N type feedthrough in CF16 flange
• Set of antennas with different lengths
• Antenna diameter = 8 mm
Incident power Pi in FPC port
Transmitted power Pt in beam tube port
(tuner side)
1E+13
Transmitted
Pick-up Pt
L
1E+04
Qt = 6e12
1E+13
1E+05
1E+12
1E+03
1E+12
1E+04
1E+11
1E+02
1E+11
1E+03
1E+10
1E+01
1E+10
1E+09
1E+00
1E+09
1E+01
1E+08
1E-01
1E+08
1E+00
Qi = 6e9
1E+02
Qext
1E+07
1E-02
1E+06
Qext
1E+07
β pour Qo (5E10) à froid
1E-01
β pour Qo (5E10) à froid
1E-03
1E+06
L (mm)
1E-02
0
10
20
30
40
L (mm)
50
60
→ Calibration to be done on the pick-up port
70
Incident
Pick-up Pi
TESTS IN VERTICAL CRYOSTAT
 Tests done at CEA in the CV2 cryostat of the
supratech platform
 Tests done on bare cavities only (without the
tank) in vertical position (advantageous cooling
configuration)
 New cavity supporting system developed
 New RF power amplifier purchased (500 W)
 New biological protection installed
 New RF regulation system (PLL) anticipated
(0.5 GHz – 2 GHz)
 System developed at IPN Orsay (C. Joly)
COOL-DOWN AT 4.2 K AND 2 K
 Cavity instrumented with 16 thermal sensors (Cernox)
 Fast cool down performed before each RF test to avoid 100 K effect
Acquisition des températures en différents endoits de la cavité ESS P01(Zanon) le 15/05/2014
320
Acquisition des températures en différents endoits de la cavité ESS P01(Zanon) le 15/05/2014
300
Sonde 16
160
Sonde 15
280
Sonde 14
260
140
SondeSonde
16
Sonde 12
Sonde 14
Sonde 10
Sonde 11
SondeSonde
10
100
9
Sonde 9
Sonde 8
Sonde 8
SondeSonde
7
~ 30 minutes between
150 and 50 K
160
80
140
120
11
Sonde 12
Température (K)
Température (K)
180
SondeSonde
13
120
220
200
13
Sonde 15
240
7
Sonde 6
Sonde 6
Sonde 5
SondeSonde
4
5
Sonde 3
Sonde 4
Sonde 2
60
SondeSonde
1
100
3
Sonde 2
80
40
0
60
10
20
30
40
Temps (mn)
40
20
0
Date
50
60
70
Sonde 1
SURFACE RESISTANCE
 Measured residual resistance: Rres = 7.5 nOhm, compatible with
usual measured values on 704 MHz cavities
2
R BCS  2  10
4
1  f  17.67 / T

 e
T  1.5 
VERTICAL TEST RESULTS AT 2K
Test results (from May 2014 to Jan. 2015):
• Both prototype cavities already met the ESS requirements after the first test:
→ Very encouraging results
• only one multipactor barrier at 11 MV/m, easily processed
• heavy field emission from 10 MV/m to max gradient, but easily processed after few minutes
AFTER DEHYDROGENIZATION TREATMENT AT 650°C
• Slight degradation of the performances after thermal treatment (pollution?)
STATIC LORENTZ FORCE DETUNING
MEASUREMENT
 Measured LFD coefficient: KL = -7.65 Hz/(MV/m)², close to the calculated
value of -8.9 Hz/(MV/m)² in free ends conditions
FREQUENCY SENSITIVITY OF ACCELERATING
MODE 704.4 MHZ
Tuning sensitivity
DF/Dz (kHz/mm)
ESS086
Calculated
197
Measured
190
Stiffness (kN/mm)
ESS086
Calculated
2.59 (3.6 mm thick)
3.3 (4.5 mm thick)
Measured
3
Frequency shift DF due to
cooldown and vacuum (kHz)
300K to 4.2 K
Calculated
Measured
Calculated
Measured
Displacement
measurement
ESS086
+1.00138
Ɛr to Ɛo
+0.211
300K to 4.2K
~ +1.08
Ɛr to Ɛo
+0.015
Frequency shift DF due to
cooldown and pressure (kHz)
Weight on
cavity (up
to 157 kg)
ESS086
4.2 K to 2 K
~ + 0.207
Insert for
CV test
DANGEROUS HIGHER ORDER MODE
CLOSE TO 1408.8 MHZ
Both high beta prototype cavities are not conform with the ESS HOM Requirement
Reminder: HOM shall be at more than 5 MHz from beamline frequencies
Slater coefficient analysis which
represents frequency sensitivity to
volume changes:
704 MHz
1421,32 MHz
 3D measurements of the cavity shape have been done
 Shape have been reconstructed in the simulation software
HFSS
Calculated with
Calculated with
Measured on
measured
measured
ESS086-P02
shape (HFSS)
shape (HFSS)
Design
(at 300K)
Measured on
ESS086-P01
1418.178
1402.254
1403.8
1407.848
1418.674
1404.666
1406.8
1408.258
 On P01 cavity (from ZANON), a strong internal shape deviation in
this dome region (more than 1 mm instead of 0.3 mm) explains
very well the frequency decrease of the two dangerous HOM
 Study under progress on P02 cavity (from RI)
 Cells reshaping has to be implemented in the fabrication process of future
cavities
HOM BEAD PULL AND TUNING TENTATIVE
Good identification of the HOM but unsuccessful tests to reshape the cavities
with the field flatness tool.
Bead pull on ESS086 P02 (03/11/2014) after +/- 0,5mm traction / compression of cell 1
 Not possible to shift the HOM frequencies far enough by traction /
compression of the cells
TANK INTEGRATION OF ESS086-P01 AT ZANON
 DF = - 47 kHz only due to tank welding and pressure test
(703.043 -> 702.989 MHz)
 Pressure and leak test done successfully
 Field flatness OK
PROBLEMS SOLVED BEFORE OR DURING THE
TESTS
Problems
Solutions
1
Melting (2 times on SPL cavity) of RF N-type right angle
connector for incident coupling antenna during CV test at
full power (200W)
Change of the coupling factor Qx of the
incident pick-up antenna
2
Large X-rays radiation level during CV tests
Modification of the cryostat
configuration (deeper underground)
and adding of concrete blocks
3
Slight deformation of the field flatness tooling during
measurement of tuning sensitivity
Change of the measurement method
(adding of masses on cavity in vertical
position)
4
Degradation of the silver coating on screws
Change of the manufacturer
5
Accidental manipulation of the cavity on the insert (cavity
back to atmospheric pressure)
Additional clean room assembly
6
Leakage in clean room after pumping on HOM port
Replace stainless steel screws by
silver coated screws
No vacuum leakage observed at cold temperature
CONCLUSION AND NEXT PLANS
 The two high beta prototypes have been successfully tested in vertical cryostat and
reached an accelerating gradient of 20 to 24 MV/m and a Q0 above the specification
of 5e9
 Important parameters such as frequency shifts, tuning sensitivity and LFD have been
measured and are conform to the predictions
 Some dangerous HOM have been unexpectedly measured too close to beam
harmonics. The problem is partially understood
Next plans:
 Vertical test at 2 K of the Zanon cavity equiped with Helium tank (Sept. 2015)
 Follow-up of the He tank welding at RI (July/August 2015) and vertical test at 2 K
o Assembly of cold tuner and test at cold temperature ?
o Vertical electropolishing try ?
o Vertical test at INFN and STFC ?
THANK YOU
ESS high beta Cavity prototype team:
CEA:
E. Cenni
F. Peauger
G. Devanz
J. Plouin
D. Roudier
L. Maurice
P. Carbonnier
F. Eozenou
C. Servouin
ESS:
C. Darve
V. Hennion
Ph. Hardy
F. Leseigneur
P. Bosland
P. Sahuquet
O. Piquet