Comparative assessment of SC Structures

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


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.


All the cavities have been fabricated

Elliptic AElliptic B

3 SpokeCH

1 Spoke


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


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


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


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.


Mechanical parameters


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]


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


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


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)


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.


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


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


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


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


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.


Low power RF tests - 1

Quench

field emission

Elliptic A

Elliptic B

3 Spoke 352 MHz



CH

1 Spoke

3 Spoke 760 MHz



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


Real estate gradient


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 ?


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


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.


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.


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 !

Comparative assessment of SC Structures

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