comparative assessment of sc structures
DESCRIPTION
Comparative assessment of SC Structures. HIPPI 2008 Annual Meeting CERN, 29-31 October 2008. Juliette PLOUIN CEA/Saclay. Objectives of this presentation. Give an overview on the work achieved through the HIPPI project. - PowerPoint PPT PresentationTRANSCRIPT
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 1/25
Comparative assessment of SC Structures
HIPPI 2008
Annual Meeting
CERN, 29-31 October 2008
Juliette PLOUINJuliette PLOUIN
CEA/SaclayCEA/Saclay
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 2/25
Objectives of this presentation
• Give an overview on the work achieved through the HIPPI project.
• Present together the main results collected for the cavities involved in the project, in order to prepare elements of comparison.
• Introduce the discussion.
• Prepare the final report.
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 3/25
All the cavities have been fabricated
Elliptic AElliptic B
3 SpokeCH
1 Spoke
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 4/25
The HIPPI program
Lab Type NameIn the frame
of HIPPI -design GapsFreq.
(MHz)Picture
INFN Elliptical Cavity A Tuning system + He tank + RF tests 0.47 5 704
CEA Elliptical Cavity BCavity + Tuning
system + He tank + coupler + RF tests
0.47 5 704
FZJ Spoke 3-Spoke Cavity + coupler (IPN) 0.48 4 352
FZJ Spoke 3-Spoke Tests 0.2 4 760
IPNO Spoke 1-Spoke Cavity + coupler + He tank + Tuning system 0.15 2 352
IAP CHCH-
prototypeTuning system
0.119 352
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 5/25
RF parametersElliptical AINFN
Elliptical BCEA
3 - Spoke FZJSpoke FZJ / IPN
CHIAP - FU
Number of gaps (Ngap) 5 5 4 2 19
Frequency [MHz] 704 704 352 352 352
Beta 0.47 0.47 0.48 0.15 0.1
Bpk/Eacc [mT/(MV/m)] 5.88 5.59 10.97 7.95 / 11.94 7.28
Epk/Eacc 3.57 3.36 4.65 3.97 6.56
G [Ohm] 160 161 101 67 56
Cell to cell coupling 1.34 % 1.35 % -
r/Q [Ohms] 180 173 420 88 3220
Beam diameter aperture [mm] 80 50 28
Lacc = Ngap./2 [mm] 500 500 818 128 810
Maximum energy gain @ Bpk = 100 mT 9 MeV
Operating Temperature (O.T.) 2 K 4 K 4K
Rs @ O.T. 8 n 0.4 (R_BCS) 83n
Q0 @ O.T. 2.1010 2.6*109 @R_BCS 6.8 108
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 6/25
Fabrication parameters
cavity Elliptic A Elliptic B 3 Spoke 1 Spoke CH
Nominal wall thickness [mm]
4 4 4 3 2-3
Length of the cavity [mm]
870 mm 832 mm 780 mm 1050 mm
Flanges material INOX St. steel
Helium tank material
INOX
Magnetic shield Yes Yes Yes Yes
Inner magnetic shield (inside the He tank)Outer magnetic shield
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 7/25
Mechanical simulations
• Calculations of mechanical parameters have been carried out for all the cavities in order to evaluate :
– the influence of the Lorentz Force Detuning (LFD) during the tests
– the influence of the Helium pressure
• Main parameters are :
– cavity stiffness [kN/mm]
– pressure sensitivity [Hz/mbar]
– Lorentz coefficient KL [Hz/(MV/m)²]
• KL depends strongly on the external stiffness, which is not easy to evaluate
• Meaningful informations must contain the extrem values of KL (free/fixed ends), and the theoretic curve between these points
• Calculations on the dynamics parameters (mechanical modes) have also been performed (EllA, EllB, CH), but their comparison is of poor interest because they strongly depend on the cavity surroundings not presented here
• The values correspond to the final design of the cavity with its stiffening system, without helium tank.
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 8/25
Mechanical parameters
cavity Elliptic A Elliptic B 3 Spoke 1 Spoke CH
Nominal wall thickness [mm]
4 4 4 3 2-3
Cavity stiffness K [kN/mm]
1.25 2.25 22.4 24 6.5
Tuning sensitivity F/l [kHz/mm]
353.4 295 182.7 964 400
kL with fixed ends
[Hz/(MV/m)²]-3.7 -2.7 -3.1 -20 -8
kL with free ends
[Hz/(MV/m)²]-54 -20.3 -4.1 -72
Pressure sensitivity [Hz/mbar] (fixed ends
84.7 29.2 1.6 41 250
Max detuning before plastification [Hz]
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 9/25
Curves KL/Kext (1)
KL = -2.7 Hz/(MV/m)²
KL = -20.3 Hz/(MV/m)²Elliptic B
KL = -4.1 Hz/(MV/m)²
KL = -3.1 Hz/(MV/m)²
3 Spoke
(in red) stiffening rings
Elliptic A :
CARE Conf-05-055-HIPPI
stiffening rings
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 10/25
Curves KL/Kext (2)
stiffeners
1 Spoke
KL = -72 Hz/(MV/m)²
KL = -20 Hz/(MV/m)²
stiffening ribs – additional stabilization rings
CH
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 11/25
Comments about the mechanical parameters
KL(fixed ends)
KL(free ends)
If |KL(free ends)| is small : the external stiffness is not a critical value to have a small Lorentz detuning
KL(free ends)
KL(fixed ends)
If |KL(free ends)| is high : the external stiffness (stiffness of the tuner) has to be high enough : ~100 kN/mm
For high values of the cavity stiffness, it is necessary to have a high stiffness for the tuner, to be able to tune the cavity.
The value for |KL(fixed ends)| determines the minimum Lorentz detuning expected on the cavity (external stiffness is infinite)
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 12/25
Mechanical measurements (cold tests)
• Static : Lorentz coefficients have been measured, in the mechanical environment of the low power tests conditions (Kext only approximatively known), with almost good agreement with the simulations. Several cavities presented a thickness lower than expected.
• Dynamic : at this time, measurements in the pulsed mode have been performed only for the CH resonator.
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 13/25
Experimental Lorentz Force Detuning – statics
1 Spoke
measured KL :
between -55 and -47 Hz/(MV/m)²
simulations :
-20 Hz/(MV/m)²(fixed ends)
-72 Hz/(MV/m)²(free ends)
Elliptic B
measured KL
-3.8 ± 0.4 Hz/(MV/m)2
simulation :
this value could correspond to an external stiffness kext = 100 kN/mm, and a cavity thickness ~3.3mm (measured thickness)
CARE Conf-05-055-HIPPI
Elliptic A
External stiffness has been evaluated for each test, and the exp. data are compatible with the simulated curve.
3 Spoke
Presented by E. Zaplatin
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 14/25
Experimental Lorentz Force Detuning – dynamics
Microphonics at cryogenic temperatures and the impact on the rf-resonance
RF pulse
VCO signal
Reflected power
Transmitted power
exp. value for the static KL ?
numerical value for the static KL with free ends ?
CH structure
gives the frequency detuning
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 15/25
Tuners - 1
Elliptic A : blade tuner, between two parts of the He tank
Tuning range 420 kHz
piezo
stepping motor
stepping motor
Elliptic B : tuner between the He tank and the cavity flange
Tuning range +/- 2.5 MHz
Mechanical stiffness ~30 kN/mm (estimated)piezo
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 16/25
Tuners - 2
CH structure : tuner between the inner cold mass containing the helium and the outer vacuum vessel.
Tuning range +/- 1 MHz
Spoke cavity (helium tank)
Piezoelectricactuators
CM0 Cryostat
(80K shield)
Cold tuning system(copper braid for
cooling)
1 Spoke
piezo
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 17/25
Tuners - 3
cavity Elliptic A Elliptic B 1 Spoke CH
Tuning range
420 kHz +/- 2.5 MHz 1 MHz
Mechanical stiffness
~30 kN/mm
Each tuning system has been especially adapted to its own cavity and to its surrounding.
It is not meaningfull to compare the performances of the different tuning systems without considering at lot of parameters depending on the cavity and on the cryostat.
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 18/25
Low power RF tests - 1
Quench
field emission
Elliptic A
Elliptic B
3 Spoke 352 MHz
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 19/25
Low power RF tests - 2
CH
1 Spoke
3 Spoke 760 MHz
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 20/25
Low power RF tests - 3
The performances of the cavity strongly depend on the cavity preparation (BCP, HPR, EP...) – detailed in the report.
A realistic comparison should include a representative sample for each cavity to take into account the spread generally observed in the results for a batch of identical cavities prepared and tested in the same conditions.
In order to take the size of the cavity into consideration, it is meaningfull to evaluate the real estate gradient...
cavity Elliptic A Elliptic B 3 Spoke 352 MHz
3 Spoke 760 MHz
1 Spoke CH
best value for Eacc
15.2 MV/m
15 MV/m ~ 5.8 MV/m
~ 5 MV/m 10.48 MV/m
7 MV/m
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 21/25
Real estate gradient
cavity Elliptic A Elliptic B 3 Spoke 1 Spoke CH
Eacc max 15.2 MV/m 15 MV/m ~5.8 MV/m 10.48 MV/m 7 MV/m
Lacc 500 mm 500 mm 818 mm 128 mm 810 mm
U| 7.6 MeV 7.5 MeV 4.7 MeV 1.3 MeV 5.7 MeV
Lcav 870 mm 832 mm 780 mm 1050 mm
Vacc/Lcav 8.7 MV/m 9 MV/m 6 MV/m 5.4 MV/m
Lreal ??
Eacc = |U|/(q.Lacc) = Vacc/LaccU is the energy received by a particle while crossing the cavity
Is it possible to give an evaluated value for Lreal, with the same criteria for each structure type, taking into account the external environment of the cavities ?
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 22/25
Couplers
Elliptic B
250 kW peak power
duty cycle 10 %
doorknobs
whole coupler
copper plating of the outer conductor
2 loops to intercept the conduction flux from 300K 4K
RF cavity port (T=4K)
RF window (T=300K)
1 Spoke
20 kW cw
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 23/25
Considerations about the estimated cost
Indications for the effective cost of a prototype has been given for two cavities :
• Elliptic B : – cavity manufacturing (with He tank) : 120 k€
– coupler + magnetic shield + tuner : 75 k€
• CH structure :
– The costs for structure only without magnetic shielding and without helium vessel amounts to 350 k€.
We know that a cost comparison between the cavities cannot really be used, because in some cases, the laboratories have carried out the fabrication by their own, while the fabrication has been performed by an industrial society in some other cases.
Furthermore, each cavity is a prototype, and the cost for its fabrication is necessarily different from the cost of one item into a series of cavities.
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 24/25
Contents of the final report
• We have values for the RF and the mechanical parameters which can be presented together. The comparisons can be made by beta families : =0.47 / = 0.1-0.2
• The experimental results will be presented for the low power RF tests ; experiments for high power won’t have progressed enough at the end of the program to give meaningful results.
• For the couplers, the tuners, .. it could be more meaningful to present the different technical solutions including their own constraints and their characteristics, rather than to make a real « comparison ».
(e.g. 352 MHz-20kW / 704 MHz 250kW pk)
• This comparison shows the performances that can be achieved from the different kinds of cavities. However it is difficult to conclude that one cavity is better than the others. In particular, it would be necessary to have statistical results about theses cavities.
HIPPI 2008 Annual Meeting CERN, 29-31 October 2008 25/25
Preparation of the report
A –very- first draft has been prepared, with the contributions received before the meeting.
This draft and this presentation are a tool for the discussion, about the data that should appear in the report, and about the conclusions.
This last WP3 session should lead to an agreement concerning the headlines of the final report, in order to achieve the redaction before december 08
Thank you !