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

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

A little bit of geography

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

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

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

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!!

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

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

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

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

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

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

Cryomodule

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

Cavity Parameters 9.7W In production Quarter wavelenght resonator

Manufacturing sequence 13 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

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

Cavity fabrication

CERN setup

Some word about the hot frequency The cold frequency has to be 101.28MHz In air:  -32kHz 101.248MHz In superconducting mode of operation (shortening of the length of the antenna,…):  -332kHz 100.916MHz skin depth variation:  -11kHz 100.905MHz Other contributions (chemistry,…): ???? ~ 100.900MHz

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

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 22 101.387 33 101.364 48.5 53 101.26 56.5 101.232 64 101.147 1.11 2800 5908 5322 101.224** 1.9 3800 11020 5800 68 101.063 81 100.765 87 100.610 91 100.430 * Pick up length=22mm ** Resonator shorter of 0.4mm (135kHz/mm)

Cavity Prototype Measurements vs MWS Model Tipgap variation gives 14.25kHz/mm 101MHz 101.147MHz Tipgap=70mm Tipgap=90mm MWS Model

“positive” structure “negative” structure

Frequency without tuner plate Tipgap**** 75mm Tipgap 90mm Short Coupler and pick-up* 101.191 MHz 101.410 MHz Long Coupler and pick-up** 101.013 MHz 101.233 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

Study of RF tuning plate

Tuner position +5 Tuner position -15

Simulation with tuner position +5, tipgap 70 100.684 MHz 1.220.000 Coupler length 5mm Pick up length -1mm Rin coupler 3.26mm Rin pick up 1mm Rout coupler 7.5mm Rout pick up 2.3mm

Simulation with tuner position -15, tipgap 70 100.929 MHz 1.066.710 Coupler length 5mm Pick up length -1mm Rin coupler 3.26mm Rin pick up 1mm Rout coupler 7.5mm Rout pick up 2.3mm

Frequency with tuner plate Tipgap 70mm Tipgap 90mm Tuner plate position +5mm 100.684 MHz 101.235 MHz ∆ Tipgap 27.55kHz/mm Tuner plate position -15mm 100.929 MHz 101.339 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

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)

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

Coupler 3.5 x 106 100.876MHz 100.826MHz Pick-up_in=0

Pick-up Freq= 100.867MHz Coupler_in=5mm

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!!!

Measurements vs Simulations 25/03/2009 Tipgap 90 Without tuner plate Tipgap 75 Tipgap 70 Simulation Measurements* Long coupler and pick-up 101.233 MHz (- 32kHz air) 101.201 MHz 101.246 MHz** (-77kHz Res) * 101.169 MHz 101.013 MHz 100.981 MHz 101.000 MHz 100.923 MHz 100. 899 MHz 100.867 MHz 100.916 MHz 100.839 MHz Short coupler and pick-up 101.410 MHz 101.378 MHz 101.483 MHz 101.406 MHz 101.191 MHz 100.159 MHz 101.240 MHz 101.163 MHz 101.083 MHz 101.051 MHz 101.150 MHz 101.073 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

Expected final hot frequency Measured frequency 101.150 MHz ∆ plate-tuner (pos-15) - 130 kHz ∆ tuner central position (-5) - 122.5 kHz Expected frequency = 100.897 MHz (goal f~100.900 MHz)

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

Results(1) ∆y=2.9mm z ∆y=0 z

Results (2) ∆y=2.9mm z

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

Results (4) With the courtesy of Matthew Alexander Fraser

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