Advances in Large Grain Resonators Activities of DESY, W.C. Heraeus and RI

• material and fabrication aspects• preparation and RF test results

W. Singer, S. Aderhold, J. Iversen, G. Kreps, A. Matheisen, X. Singer, K. Tvarovski, H. Weise (DESY)M. Pekeler (Research Instruments GmbH)

F. Schölz, B. Spaniol, E. Stiedl (W.C. HERAEUS)

Presented by: B. Spaniol

Melting-/cooling behavior was investigated: beam figures (different numbers, position und shape); energy entry (different focusing of the beam and stay time); refrigeration parameters (bottom, crucible wall, split).

The complete process is not sufficiently stable in order to create a central crystal of big diameter and required orientation along the whole ingot. Parts of ingots with a big crystal of definite orientation can be reproducibly created

Large Grain Nb

Energy exchange in the electron beam melted Niobium

Ingot and disc fabrication W.C. Heraeus: Development of LG disc production was done within the framework of the R&D program of DESY and the W. C. HERAEUS.

Ingot and disc fabrication W.C. Heraeus: Development of LG disc production was done within the framework of the R&D program of DESY and the W. C. HERAEUS.

Cutting of the large grain Ingots by wire sawing at W.C.Heraeus

Ingot and disc fabrication W.C. Heraeus: Development of LG disc production was done within the framework of the R&D program of DESY and the W. C. HERAEUS.

Nb RRR LG discs by wire sawing (all values in mm)

    measurement point              

disc No thickness 1 2 3 4 5 6 7 min max delta

1 2,86 2,85 2,83 2,87 2,86 2,82 2,81 2,81 2,81 2,87 0,06

2 2,86 2,84 2,83 2,84 2,84 2,83 2,81 2,83 2,81 2,84 0,03

3 2,86 2,88 2,86 2,84 2,85 2,85 2,85 2,85 2,84 2,88 0,04

4 2,86 2,85 2,86 2,87 2,88 2,87 2,85 2,88 2,85 2,88 0,03

5 2,86 2,88 2,86 2,84 2,83 2,83 2,87 2,87 2,83 2,88 0,05

6 2,86 2,83 2,84 2,89 2,86 2,84 2,83 2,83 2,83 2,89 0,06

7 2,86 2,86 2,84 2,87 2,86 2,86 2,87 2,86 2,84 2,87 0,03

8 2,86 2,88 2,85 2,84 2,84 2,85 2,86 2,86 2,84 2,88 0,04

9 2,86 2,85 2,85 2,87 2,86 2,82 2,84 2,84 2,82 2,87 0,05

10 2,86 2,84 2,86 2,82 2,83 2,84 2,84 2,85 2,82 2,86 0,04

11 2,86 2,82 2,83 2,84 2,85 2,82 2,81 2,84 2,81 2,85 0,04

12 2,86 2,88 2,87 2,88 2,86 2,89 2,89 2,88 2,86 2,89 0,03

13 2,86 2,89 2,88 2,90 2,88 2,86 2,87 2,88 2,86 2,90 0,04

14 2,86 2,8 2,83 2,79 2,82 2,83 2,82 2,83 2,79 2,83 0,04

15 2,86 2,87 2,85 2,88 2,89 2,85 2,88 2,86 2,85 2,89 0,04

16 2,86 2,83 2,84 2,84 2,84 2,84 2,85 2,86 2,83 2,86 0,03

17 2,86 2,87 2,88 2,85 2,86 2,87 2,86 2,88 2,85 2,88 0,03

18 2,86 2,86 2,84 2,84 2,85 2,84 2,86 2,85 2,84 2,86 0,02

19 2,86 2,87 2,85 2,85 2,85 2,84 2,85 2,84 2,84 2,87 0,03

20 2,86 2,77 2,81 2,84 2,85 2,82 2,77 2,83 2,77 2,85 0,08

XXXMP1

MP2

MP3MP4

MP5

MP6

MP7

very small thickness variations by wire sawing process

Material and fabrication aspects

DESY fabricated 11 LG 9-cell and several single cell cavities at ACCEL (RI) from HERAEUS material

Fabrication:• Disc of W.C. HERAEUS with big central crystal of diameter >150 mm cut by diamond saw • No Eddy Current scanning

• Deep drawing

• Machining

• EB welding

• Grinding of steps on grain boundaries only on 2 of 11 cavities (AC155 and AC156)

• Very smooth (shiny) surface in grain areas after BCP

• the steps at grain boundaries are more pronounced as in polycrystalline material

Fabrication aspects

• Some spring back after the deep drawing, making the half cells “elliptical”. The same happens after the trimming for EBW• Large single crystal at centre, no problems on iris area for deep drawing• Difficulties on assembly for EBW• In order to overcome the difficulties a special tool has been build by the company. • Successful assembly of dumb bells with new tool and EB welding of all equator welds

CavityPlane parallel

to sheet surface

half cell

half cell

half cell

half cell

half cell

AC151 (100) H150 H143      

AC152 (100) H202 H189      

AC153 (100) H219 H214      

AC154 (211) H112 H105      

AC155 (221) H231        

AC156 (221) H123        

AC157 (221) H168 H163 H162 H160 H156

AC158 (211) H180        

Each cavity has a main central crystal of definite orientation.Half cells measured by tactile 3D-measurement

Tactile 3D-measurement shows deviation from tolerances (tolerance: +/-0,2 mm).

Deep drawing of LG half cells

Dependence of the half cell shape accuracy from the crystal orientation of the main central crystal

0

10

20

30

40

50

60

70

80

Dis

trib

uti

on

of

shap

e to

lera

nce

s, %

>0,3 0,2 - 0,3 0,1 - 0,2 0,1 - (-0,1) -(0,2 - 0,1) -(0,3 - 0,2) > -0.3

Tolerances, mm

(100)

(211)

(221)

Averaged deviation from ideal shape of the half cell for different crystal orientations. Crystallographic plane (100) parallel to the sheet surface

produce more shape deviation on deep drawing, compare to (211), (221)

Half cells from different material

-2

-1

0

1

2

3

4

5C

N CL

CS

WN TN

WL TL

WS TS

AC

CE

L

MH

z

Frequency deviation [MHz] Standard deviation [MHz]

Deviation of the frequency from defined value of 6 end half cells (L and S) and 48 middle half cells (N) for LG AC112-114. C – LG. W and T - fine grain material. The

shape accuracy of LG material is lower as of conventional fine grain.

Shape accuracy: frequency measurement

All LG cavities are successfully tuned to the correct resonance frequency

1,0E+09

1,0E+10

1,0E+11

0 5 10 15 20 25 30 35

Eacc, MV/m

Q

AC114 AC112 AC113

First test Q(Eacc) curve of the LG nine cell cavities AC112- AC114 at 2K after 100µm BCP, 800°C 2h, 20µm BCP, HPR

Preparation and RF tests of AC112 – AC114

XFEL Spec.

1,0E+09

1,0E+10

1,0E+11

0 10 20 30

Eacc, MV/m

Qo

AC114 AC113 AC114 baked AC113 baked

Q(Eacc) curve of the LG nine cell cavities AC113- AC114 at 2K after additional 20-30 µm BCP and 125°C, 50 h baking

Very similar behavior, good reproducibility

Preparation and RF tests of AC112 – AC114

DESY: Q(Eacc) curve of the LG single cell cavity 1AC4 after EP and BCP treatment. EP at Henkel, preparation at DESY (D. Reschke et al)

What treatment EP or BCP??DESY data on one single cell cavity; it seems that EP works better

1,00E+09

1,00E+10

1,00E+11

0 10 20 30 40

Eacc; MV/m

Qo

Test 1: 190µm EP; 800°C, 2h; 128°C, 48h

Test 2: add 40µm BCP; 135°C, 48h

Test 3: add 100µm EP; 138°C, 12h

1AC4

1,00E+09

1,00E+10

1,00E+11

0 5 10 15 20 25 30 35 40 45

Eacc, MV/m

Qo

AC113, add 50 µm EP AC112, add 230 µm EP AC114, add 100 µm EP

3 LG cavities: additional EP of 50 -100 µm, combined with additional “in situ” baking. Enhancing the acceleration gradient by approx. 10 MV/m can be seen on two cavities (AC112 and AC113). AC113 installed into cryomodule PXFEL1

Degradation of Eacc from 28 to 14 MV/m for the cavity AC114 (quench without field emission)

Preparation and RF tests of AC111 – AC114, after EP

Large groups of small craters on the entire surface of all cells found by optical inspection

with high resolution camera in AC114

T-maps of AC114: for π-mode, the quench in cell 2 above and near equator.

In other modes, quench was also found in cell 1 and 9. In addition, many other smaller

hot spots were found.

Depends the pits creation on the crystal orientation? More results needed.

Recently fabricated 8 LG cavities AC151-AC158. Treatment: 100µm BCP, 800°C 2h, 20µm BCP, HPR and

125°C, 50 h baking. 100 µm BCP done at Fa. RI.

1,00E+09

1,00E+10

1,00E+11

0 5 10 15 20 25 30 35

Eacc. MV/m

Qo

AC151AC155AC153AC154AC157

No any conspicuousness for AC155 where the grinding of steps on grain boundaries has been done

XFEL

1,00E+09

1,00E+10

1,00E+11

0 5 10 15 20 25 30 35

Eacc. (MV/m

Qo

AC112AC151AC155AC153AC154AC157AC114AC113

XFEL requirements Eacc =24,3 MV/m fulfilled in first test. Eacc 25 - 30 MV/m stably reachable after ca. 120µm BCP

All available at DESY up to now Q(Eacc) of LG 9-cell cavities (AC112 was not baked)

XFEL

Comparison of the Eacc performance of large grain (LG) 9-cell cavities with similarly treated fine grain TTF cavities.

BCP works for LG better compare to fine grain cavities

0

5

10

15

20

25

30

35

150 200 250 300 350 400 450 500 550

RRR of Cavity measured by Eddy Current method

Eac

c, M

V/m

TTF, 800°C+BCP LG, 800°C+BCP

Profile and step heights of the three grain sample at the

grain boundary intersection

AFM image of LG Nb, BCP etched up to 100 µm

AFM roughness measurement (X. Singer, A. Dangwal-Pandey). Roughness of fine grain Nb after EP is 251 nm (A. Wu) .

(110)(111)

(100)

Is LG good enough? Single grain is better

Fabrication of TESLA shape single crystal single cell cavities was proposed at DESY

Following aspects have been investigated and taken into consideration during cavity fabrication

• Definite enlargement of the discs diameter is possible without destroying the single crystal structure in an existing state.

• Appropriate heat treatment will not destroy the deformed single crystal

• The single crystals keep the crystallographic structure and the orientations after deep drawing and annealing at 800°C

• Two single crystals will grow together by EB welding, if the crystal orientations is taken into account.

Single Crystal Option

Grain boundaries GBs contribute eventually to reduction of the cavity performance

DESY single crystal cavity 1AC8 build from Heraeus disc by rolling at

RWTH, deep drawing and EB welding at ACCEL

Q(Eacc) curve after 112 µm BCP and in situ baking 120°C for 6 hrs.

Eacc vs. material removal on single crystal single cell cavity (left).

Preparation and RF tests of P.Kneisel, JLab

Single Crystal DESY Cavity, Heraeus Niobium112 micron bcp 1:1:2

1,00E+09

1,00E+10

1,00E+11

0 5 10 15 20 25 30 35 40

Eacc [MV/m]Q

0

T=1.99K, 6hrs at 120C baked

T=1.8K, 6 hrs at 120C baked

Eacc vs Material RemovalDESY Single Crystal Single Cell Cavity

0

10

20

30

40

50

0 50 100 150 200

Material Removed, µm

Ea

cc

[M

V/m

]

FE limit

6 hrs 120C

3 hrs 120C12 hrs 120C

Cavity # Eacc,max (MV/m)

Bpeak,max (mT)

Q0(Bpeak,max) Treatment

1 38 162 4109 200m BCP, 800°C 3h, HPR, 120°C 48h

2 45 160 7109 200m BCP, 800°C 3h, HPR, 120°C 24h

3 (1AC6) 41 177 1.21010 250m BCP, 750°C 2h, 120m EP, HPR, 135°C 12h

4 (1AC8) 38.9 168 1.81010 216m BCP, 600°C 10h, HPR, 120°C 12h

5 38.5 166 7.6109 170m BCP, HPR, 120°C 12h

Summary of test results on single crystal single cell cavitiesP. Kneisel et al EPAC2008

One large grain (single crystal) is still a very perspective option that allows stably reach very

high gradient by simple BCP treatment

Summary

Fabrication of multi cell cavities from large grain niobium by deep drawing and electron beam welding is feasible. 11 nine - cell LG cavities have been produced in frame of DESY order at company ACCEL from W.C. Heraeus material and treated at DESY

Performance up to 30 MV/m can be achieved on the nine cell cavity after only 120 µm BCP treatment.

EP preparation on multi-cell LG cavities is ongoing. Up to 41 MV/m was measured on a LG single cell cavities after EP. Several single grain (single crystal) single cell cavities of TESLA shape are build with very encouraging results.

Acknowledgments

We would like to thank our colleagues

A. Ermakov, B. van der Horst, L. Lilje and D. Reschke

for support of this work