1. MEBT SAR BUNCHER CAVITIES
Nagore Garmendia
(On behalf of Buncher Team)
Bilbao, 27 March 2019

2. MEBT SAR – Buncher cavities
Outline
Buncher team
Introduction
Specifications and requirements
Strategy: design, manufacturing and test plan
Design process
Manufacturing process
Test procedures
Cavity interfaces and elements
Experimental results
Conclusions and next steps
MEBT SAR – Buncher cavities

3. MEBT SAR – Buncher cavities
Buncher Team
Task Description
Team
Beam dynamics simulations
I. Bustinduy
EM Design and simulations
O. Gonzalez; J.L. Muñoz
Mechanical Design and drawings
A. Zugazaga; I. Rueda
Thermomechanical simulations
A. Paramo; J.L. Muñoz
Manufacturing
A. Zugazaga ; I. Rueda
Vacuum Test
A. Zugazaga; A. Conde; J. Martin
RF Test bench + bead pull
N . Garmendia;
High power RF test
N. Garmendia ; A. Kaftoosian
Assembly and Integration
A. Conde; J. Martin
Coupler and tuners
R. San Martin; I. Rueda
Motion control and EPICs
I. Mazkiaran
Project Manager (MEBT; RF)
I. Bustinduy ; P. Gonzalez
MEBT SAR – Buncher cavities

4. Introduction: MEBT Bunchers
MEBT: RFQ – DTL beam matching
BU#3
BU#2
BU#1
Longitudinal focusing
MEBT SAR – Buncher cavities

5. MEBT SAR – Buncher cavities
Specifcations
Specification
Doors ID
Description
Value
ACC.L1
ESS.SyR-430
Nominal operational repetition rate
14 Hertz.
ESS.SyR-450
Nominal operational beam pulse length
2,86 ms
ACC. L2
ACC.SyR-19
For beam energies greater than 1.0 MeV, the nominal bunch frequency
352,21 MHz
MEBT.EMR.Syr-36
MEBT.EMR.SyR-36
Cavity peak field; Kilpatrick
<1,5
MEBT-L4-EMR-090
MEBT.EMR.SyR-37
Maximum gap voltage
150 kV
MEBT-L4-EMR-140
MEBT.EMR.SyR-42
Maximum coupled peak power into the cavity
18 kW
MEBT-L4-EMR-150
MEBT.EMR.SyR-43
RF coupler power handling
22,5 kW
MEBT-L4-EMR-180
MEBT.EMR.SyR-46
Cavity aperture (diameter)
30mm
MEBT-L4-EMR-190
MEBT.EMR.SyR-47
Cavity longitudinal space (Lmax)
<190mm
MEBT SAR – Buncher cavities

6. MEBT SAR – Buncher cavities
Requirements
Parameter
Description
Particle Energy
3.62 MeV
Max RF pulse width
3,5 ms
Max RF Duty Cycle
4.9 %
Maximum RF input peak power
22.5 kW
Unloaded quality factor
>18000
Tuner linearity
> 15 kHz/mm
Nominal cooling water temperature
25ºC +/-1º
Coupling coupler coefficient
MEBT SAR – Buncher cavities

7. MEBT SAR – Buncher cavities
Strategy (I)
corrections 2
Design 1
Manufacturing
Manufacturing
Prototype
BU#1; BU#2;BU#3
Tests
Test procedures
CDR
Integration plan
MEBT SAR – Buncher cavities

8. MEBT SAR – Buncher cavities
Strategy (II)
Manufacturing Phases
PHASE
DESCRIPTION
PH1
SS Machining and welding (local supplier)
PH2
Copper plating (GSI)
Test Plan
PHASE MT VT
LPT CT
PH1 X
PH2
MT: Metrology + rugosity
VT: Outgassing (impurity) + Leak test (welding and sealing)
LPT: Low Power RF Test+ Bead-pull
CT: Conditioning test
MEBT SAR – Buncher cavities

9. MEBT SAR – Buncher cavities
Design process
Considerations
Taking into account the size and RF requirements ( Fr=352,2 MHz; EoT=150 kV) a nose-cone single gap type cavity is the optimal option
The internal buncher dimensions take into account electro- magnetic, thermo-mechanic, RF and beam dynamics
SS versus copper manufacturing has implications in vacuum sealing, cooling system, Rf perfmances,…
BEAM DYNAMICS
EM DESIGN
THERMO-MECHANICAL
MEBT SAR – Buncher cavities

10. MEBT SAR – Buncher cavities
Manufacturing (I)
Considerations
Applicable standards: ISO ; ISO and ISO 5817
Critical tolerance definition for a manufacturing from stainless steel copper plated (copper layer of 30 μm)
Certificated materials and thermal treatment for mechanical stress relief
Drawings and manufacturing procedure for Helicoflex for vacuum seal
The cavity resonant frequency deviations due to manufacturing are corrected by means of the fixed tuner (tuning range)
Finger strips are foreseen in coupler, tuners and pick-up to increase the cavity efficiency (Qo)
VACUUM SEAL
FINGER STRIPS
MEBT SAR – Buncher cavities

11. MEBT SAR – Buncher cavities
Manufacturing (II)
SS THERMAL TREATMENT
MACHINING
PORTS: TIG WELDING
COPPER PLATING
MEBT SAR – Buncher cavities

12. MEBT SAR – Buncher cavities
Test procedure
Metrology
Roughness
Cooling System
Vacuum: Outgassing + Leakage
Low Power RF
Bead-pull
Conditioning
Not ready:
Coupler
SSPA
LLRF and RFLPS rack
MEBT SAR – Buncher cavities

13. MEBT SAR – Buncher cavities
Metrology
Performed by the manufacturer after the manufacturing in SS by means of a three-dimensional measuring machine (CMM) in a temperature controlled room at 20 ± 1 °
Repeated at ESS Bilbao Metrology facility before and after copper plating
SS cavity: manufacturer
SS and Cu cavity: ESS Bilbao
MEBT SAR – Buncher cavities

14. MEBT SAR – Buncher cavities
Roughness
Different roughness specifications are required for :
Helicoflex vacuum sealing contact
Assure the cavity efficiency ( Qo)
Performed by the manufacturer after the SS machining
Repeated at ESS Bilbao laboratory before and after copper plating
SS cavity: manufacturer
SS and Cu cavity: ESS Bilbao
MEBT SAR – Buncher cavities

15. MEBT SAR – Buncher cavities
Cooling system
Two independent circuits for body and cover cavity to optimised the design
Specifications: static pressure test at 16 bar during15 minutes with a decrease < 0.1 bar
Performed by the manufacturer after SS machining and repeated at ESS Bilbao after
Simulations
Manufacturer test
ESS Bilbao test
MEBT SAR – Buncher cavities

16. MEBT SAR – Buncher cavities
Vacuum test
Leakage level specification <2*e-10 mbar*l/s
Tests: pressure evolution , outgassing (RGA) and leakage test performed by the manufacturer after SS machining and repeated after copper plating at ESS Bilbao vacuum lab
ESS Bilbao Vacuum Test bench
RGA
Leak Detection
Pressure Evolution
MEBT SAR – Buncher cavities

17. MEBT SAR – Buncher cavities
Low power RF Test
Implementation of a test bench with a automatic data acquisition for S- parameters and with a precise algorithm to determine the quality factor
The tuning system is validated with two manual dummy tuners
Figure of Merit
Test
Res. Frequency, [MHz]
T01
HOM2; HOM3 (MHz)
T02
Quality factor
T03
Coupler coupling factor
T04
Pick-up coupling factor
T05
Cavity insertion loss
T06
Frequency tuning range
T07
Tuner linearity
T08
MEBT SAR – Buncher cavities

18. MEBT SAR – Buncher cavities
Bead-pull
Implementation of bead-pull test bench based in the Slater´s perturbation theory to obtain the accelerating field profile from the bead frequency shift
Main figures of merit: Ez,T, RT2; Pdiss
Bead-calibration with a pillbox cavity to assure accurate results
Bead calibration
Bead-pull test bench
Accelerating electric field profile
MEBT SAR – Buncher cavities

19. Mechanical interfaces
Port
Description
Dim. A
Vacuum port
CF60 B
Fixed Tuner C
RF input power coupler D
Movable tuner E
Pick-up port
CF40 F
Gauge port G
Cavity support
RAFT2
MEBT SAR – Buncher cavities

20. Power coupling Coupler
Magnetic loop in charge of the transmission the RF power
to the cavity
ESS Bilbao design based in Alumina ceramic window (the peek coupler
design was rejected due to vacuum requirements)
Manufacturing and brazing under procedure validation in ESS Bilbao Welding Center
Manufacturing
EM simulations
Drawings
MEBT SAR – Buncher cavities

21. MEBT SAR – Buncher cavities
Pick-up
The magnetic loop takes the RF sample for LLRF,
interlock and control system
ESS Bilbao design with an commercial flange and
EM simulations
Drawings
Manufacturing
Test and validation A B C D
MEBT SAR – Buncher cavities

22. MEBT SAR – Buncher cavities
Fixed Tuner
To compensate the frequency deviation due to the
manufacturing and copper plating tolerances
ESS Bilbao design to avoid the brazing between the copper cylinder and the commercial SS flange
EM simulations
Manufacturing
Test and validation
Drawings
MEBT SAR – Buncher cavities

23. MEBT SAR – Buncher cavities
Movable tuner
To compensate frequency deviation during the beam operation
Commercial linear actuator controlled by the LLRF system
Motion control test and EPICs integration done and validated
EM simulations
Drawings
Test and validation
MEBT SAR – Buncher cavities

24. Low Power and Bead-pull Test Results
Figure of Merit
BU-1
BU-2
BU-3
C/NC
Res. Frequency, [MHz]
352.21 C
Penetration Tuner 1, L1[mm] 50
40,5 40
Penetration Tuner 2, L2[mm] 32 25
Sensitivity, [KHz/mm/tuner]
16.3
16.2
βcoupler / βpickup_max
0.94 / 0.136
1.1 / 0.15
1.09 / 0.14
IL_min(dB)
9.3 9 10 Ql
8108
8125
8144 Qo
16883*
18415
18250
BW, [KHz]
43.3 43
43.2
RTT/Q [Ω]
73.85
76.7
76.9
RTT [MΩ]
1.25
1.41
ZTT [MΩ/m]
9.89
11.2
11.14
Transit Time Factor (T)
0.65
0.654
0.645
Effective Voltage VoT [KV]
160/100
160/120
160/140
Dissipated Power, Pd [Kw]
20.5 / 8
18.1 / 13.8
18.2 / 13.9
Max Acc. Field Ez_max [MV/m]
9.4
9.36
9.28
*for 160 kV, the specifications is 150 kV
MEBT SAR – Buncher cavities

25. MEBT SAR – Buncher cavities
Cavities in MEBT
Taking into account the beam dynamics simulations the first buncher cavity requires less effective accelerating field and the last one is the most demanding, therefore the less and the most effective cavities are located as first and third in the MEBT after analysing all the experimental results.
Parameter
BU#1
BU#2
BU#3
EoT sim (kV) 60
130
150
RTT/Q [Ω]
73.85
76.7
76.4
Location in MEBT
1st
2nd
3th
ESS official name
MEBT-010:EMR-Tnk-001
MEBT-010:EMR-Tnk-002
MEBT-010:EMR-Tnk-003
MEBT SAR – Buncher cavities

26. MEBT SAR – Buncher cavities
Conditioning
A first version procedure has been defined for the conditioning:
Previous checking list
State machine and start-up procedure
Conditioning steps with a foreseen configurations: pulse width, frequency repetition rate (i.e. duty cycle ) and RF power level
MEBT SAR – Buncher cavities

27. MEBT SAR – Buncher cavities
Conditioning
BUNCHER component
Status
Cavities
Tested
Pick-ups
Fixed tunners
Movable tuner + actuator
Motion control
MC EPICs integration
Coupler
Manufacturing at ESSB (end of May)
SSPAs
Manufacturing at BTESA (end of July)
RF Rack control
To be provided by ESS
MEBT SAR – Buncher cavities

28. MEBT SAR – Buncher cavities
Conclusions
The design, manufacturing and test procedure were defined and validated with a complete experimental characterization of a buncher prototype (BU#0)
The three buncher cavities have been measured with the low power RF test and the results are in agreement with the simulations and requirements.
The pickups, fixed tuner and movable tuner have been also measured and validated
The power alumina coupler is under manufacturing at ESS Bilbao facilities (brazing
end of May)
The SSPAs are under manufacturing (BETESA, Spain. 1st for end of July))
The RF control to be provided by ESS
Next step : Coupler and cavity conditioning strategy :
Totally advisable at ESS Bilbao ( cavities delivery?)
Alternative: buncher versus test box to be study: time, cost, resources, delivery time, breakdown risk,…
MEBT SAR – Buncher cavities

29. MEBT SAR – Buncher cavities
THANK YOU FOR YOUR ATTENTION
Questions ?
MEBT SAR – Buncher cavities