1. Alessandro D’Elia- CI/Univ. of Manchester PDRA
HIE-ISOLDE: superconducting upgrade
Alessandro D’Elia- CI/Univ. of Manchester PDRA
CLIC Workshop 2007

2. A little bit of history HIE-ISOLDE
CERN's ISOLDE, an acronym for Isotope Separator On Line, went into operation again in 1992, after a major upgrading that has placed the facility in a new building complex fed by the 1 GeV proton beam from the PS Booster. As an introduction you may look at some historic dates of ISOLDE:
1967, October 23
First experiments at ISOLDE fed by SC.
1990, December 17
Final shut-down of the SC, which had begun operation in 1957.
1992, June 26
First experiment at the ISOLDE PSB.
2001
REX-ISOLDE post-accelerator started operating
HIE-ISOLDE

3. A little bit of geography

5. REX-ISOLDE: Generalities
Developed in order to take advantage from the high gradient IH structure, the present scheme presents
No energy flexibility
Operation limited to pulsed mode
No longitudinal beam parameters gymnastic
Low reliability of the machine (if an RF system fails the beam cannot be delivered)
Moreover, during the acceleration the emittance growths by nearly a factor 3

6. From REX-ISOLDE to HIE-ISOLDE
Present structure
2.2 MeV/u < Final Energy < 2.8 MeV/u
3 < A/q < 4.5
Upgrade
1.2 MeV/u < Final Energy < 10 MeV/u
The replacement of the normal conducting structures will also allow to improve
the final transverse emittance

7. HIE-ISOLDE upgrading stages
1.2MeV/u*
3MeV/u*
5.5MeV/u*
10MeV/u*
* A/q= 4.5
Stage 1 is shown at the top, while stage 2 can be split into two sub-stages depending on the physics priorities: the low energy cryomodules will allow the delivery of a beam with better emittance; the high energy cryomodule will enable the maximum energy to be reached
M. Pasini, D. Voulot, M. A. Fraser, R. M. Jones, ”BEAM DYNAMICS STUDIES FOR THE SCREX-ISOLDE LINAC AT CERN”, Linac 2008, Victoria, Canada

8. Why Superconducting? (1)
Power dissipation on the wall >104 times smaller than Normal Conducting structures
In our case we want Eacc=6MV/m
U=7.6J
Superconducting case
Qo=5x108
Pd=9.7W
tot  0.001
Psyst=9.7kW
f=101.28MHz
Normal conducting case
Qo=104
Pd=485kW
kly  0.5
Psyst=970kW
f=101.28MHz
We save almost a factor 100 in power!!

9. Why Superconducting? (2)
Larger aperture
Use of 2 gap structure, meaning higher velocity acceptance
We can apply to all ions (coming at different velocities) always the maximum installed voltage

10. Superconductor Type II
Field limits: Hsh
Critical H field 2
Superconductor Type II
Normal status
Critical temperature
Vortices
Magnetic field
Critical H field 1
Superconductor Type I
Meissner
status
Temperature

11. Field limits: Hsh Super-current
The vortex (fluxons) can flows giving a certain resistance N
Super-current

12. Supercurrent The material impurities stop the vortex flux
Hsh for Niobium  240mT
If H>Hsh : diet coke with mentos!!! N N
Supercurrent

13. Field limits: E field
No theoretical limitations, in principle, but practical: electron field emission (multipacting, Nb:150eV<K<1050eV)

14. Sputtered Nb on Cu vs Bulk Nb cavities
Mechanical stability and rigidity with the consequence of very small resonant frequency perturbation due to the mechanical noise and LHe pressure variation (lead to a simpler tuning system)
High thermal stability (no quenches observed)
No Q-disease (No fast cooling required)
No mu-metal shielding required in the cryomodule
Performance maintained over the years
Reduced cost of the single cavity

15. Cryomodule

16. Cryostat High Beta (5 Cavités Ø320)
Ligne Faisceau
Ligne Mesure Alignement
G.VILLIGER EN/MME

17. Cavity Parameters
9.7W
In production
Quarter wavelenght resonator

18. Manufacturing sequence13 3 2 1 7 11 6 8 9 9 10 12 4 5
Rolling of half tubes, longitudinal welding, rough machining
Machining of end piece
E-beam welding
Fine machining of inner surface
“Bossage” and machining of beam ports
Manufacturing of baseplate of inner conductor
Manufacturing of central tube
Manufacturing of head
E-beam welding of the 3 parts of inner conductor
Fine machining of inner conductor
Drilling of beam line
Final long-distance e-beam welding
E-beam welding of top flange ensemble

19. Surface preparation Chemical etching: few microns
High pressure water rinsing
Baking: 80C
Sputtering
Clean assembly in the cryostate

20. Cavity fabrication

21. CERN setup

22. Some word about the hot frequency
The cold frequency has to be MHz
In air:  -32kHz
MHz
In superconducting mode of operation (shortening of the length of the antenna,…):  -332kHz
MHz
skin depth variation:  -11kHz
MHz
Other contributions (chemistry,…): ????
~ MHz

23. Cavity Prototype Measurements
RF Coupler
Pick-up
cavity
tipgap
Network Analyzer
The Pick-up position is fixed (22mm inside the cavity)
The RF coupler position is varying

24. Measurements Before welding ∆ coupler1=14kHz/mm ∆ coupler2=22kHz/mm
∆ coupler3(from 22 to 64)=
5.7kHz/mm
Coupler length* (mm)
Before welding
Frequency (MHz)  Ql Q0
Qext
After welding 22 33
48.5 53
101.26
56.5 64
1.11
2800
5908
5322 **
1.9
3800
11020
5800 68 81 87 91
* Pick up length=22mm
** Resonator shorter of 0.4mm (135kHz/mm)

25. Cavity Prototype Measurements vs MWS Model
Tipgap variation gives 14.25kHz/mm
101MHz
MHz
Tipgap=70mm
Tipgap=90mm
MWS Model

27. “positive” structure
“negative” structure

28. Frequency without tuner plate
Tipgap**** 75mm
Tipgap 90mm
Short Coupler and pick-up*
MHz
MHz
Long Coupler and pick-up**
MHz
MHz
∆ Coupler3
4.24kHz/mm***
4.24kHz/mm
* “Short” means coupler length=22mm and pick-up length=22mm, no 50Ω line
** “Long” means coupler length=64mm and pick-up length=22mm, no 50Ω line
*** ∆ Coupler3 (measured)=5.7kHz/mm
**** Remind: tipgap is the distance between the bottom plate the central
resonator

29. Study of RF tuning plate

30. Tuner position +5
Tuner position -15

31. Simulation with tuner position +5, tipgap 70
MHz
Coupler length
5mm
Pick up length
-1mm
Rin coupler
3.26mm
Rin pick up
1mm
Rout coupler
7.5mm
Rout pick up
2.3mm

32. Simulation with tuner position -15, tipgap 70
MHz
Coupler length
5mm
Pick up length
-1mm
Rin coupler
3.26mm
Rin pick up
1mm
Rout coupler
7.5mm
Rout pick up
2.3mm

33. Frequency with tuner plate
Tipgap 70mm
Tipgap 90mm
Tuner plate position +5mm
MHz
MHz
∆ Tipgap
27.55kHz/mm
Tuner plate position -15mm
MHz
MHz
20.5kHz/mm
∆ Tuner plate
12.25kHz/mm
Total Coarse range=245kHz
5.2kHz/mm
Pick up length=-1mm, coupler length=5mm, modeled as a 50Ω line
Triumph tuner coarse range 32kHz

34. Qext Let us assume Q0=5x108, we want
Qext RF coupler of 2.5x106 in order to be undercoupled (larger bandwidth)
Qext Pick-up of 5x109 in order to be overcoupled (negligible power flowing from the pick-up)

35. Qext Tipgap 70 Tuner pos-15 coupler inner conductor radius 3.26mm
pick up inner conductor radius 1mm
coupler outer conductor radius 7.5mm
pick up outer conductor radius 2.3mm
Note: pick and coupler are configured as a 50Ω line

36. Coupler
3.5 x 106
MHz
MHz
Pick-up_in=0

37. Pick-up
Freq= MHz
Coupler_in=5mm

38. Q measurements  as Qo109 ∆f0.1Hz
By feeding the cavity by a rectangular pulse
By switching off I can measure
If I know e , I know Qo
Always by feeding the cavity by a rectangular pulse, in the steady-state 
Very important: due to the very narrow bandwidth, a frequency locking system
is required!!!

39. Measurements vs Simulations 25/03/2009
Tipgap 90
Without tuner plate
Tipgap 75
Tipgap 70
Simulation
Measurements*
Long coupler and pick-up
MHz
(- 32kHz air)
MHz
MHz**
(-77kHz Res) *
MHz
MHz
MHz
MHz
MHz
MHz
MHz
MHz
MHz
Short coupler and pick-up
MHz
MHz
MHz
MHz
MHz
MHz
MHz
MHz
MHz
MHz
MHz
MHz
* Resonator longer of 0.4mm with respect to the nominal length
** These new measurements have been done in a much noisy environment
that explain the  13kHz of difference with respect to the previous ones

40. Expected final hot frequency
Measured frequency
MHz
∆ plate-tuner (pos-15)
- 130 kHz
∆ tuner central position (-5)
kHz
Expected frequency
= MHz
(goal f~ MHz)

41. Deflecting fields
An intrinsic aspect of the particle acceleration by means of Quarter Wavelength Resonators is the deflecting electric and magnetic fields experienced by the beams. This can lead to emittance growth. Ey Hx

42. Results(1)
∆y=2.9mm z
∆y=0 z

43. Results (2)
∆y=2.9mm z

44. Results (3)
∆y=2.9mm z
∆x=1mm
A/q=2.5
A/q=2.5
∆y=2.9mm z
∆x=0mm

45. Results (4)
With the courtesy of Matthew Alexander Fraser

46. Conclusions E-m design of the high beta cavity is finished
The machining of the copper part is finished
Measurements show a very good agreement with simulations
Mechanical design of the coupler, pick-up and tuner plate is ready to start
The sputtering procedure is imminent
The design of the cryomodule is started
Starting the design of the low beta cavities
The studies of the field defocusing have been terminated
The study of the misalignment error is started