Mike Jenkins Lancaster University and The Cockcroft Institute.
High beta cavity simulations and RF measurements Alessandro D’Elia- Cockcroft Institute and...
-
Upload
peter-banks -
Category
Documents
-
view
215 -
download
0
description
Transcript of High beta cavity simulations and RF measurements Alessandro D’Elia- Cockcroft Institute and...
High beta cavity simulations and RF measurements
Alessandro D’Elia- Cockcroft Institute and University of Manchester
1
HIE-ISOLDE upgrading stages
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
3MeV/u* 5.5MeV/u* 10MeV/u*
* A/q= 4.5
1.2MeV/u*
2
High beta cavity
3
784.5mm
300mm
Beam
Coupler and Pick up seats
Resonator (/4)
Tools “calibration”
In order to get reliable cavity parameters values from simulations, a comparison between the results coming from HFSS and CST Microwave has been performed using Superfish as a benchmark
4
Superfish vs CST Microwave and HFSS
5
Frequency
6
HFSS Meshing (5m)
HFSS Meshing (20m)
CST Meshing
E field*
7
* All field values are normalized to give 1J stored energy in the cavity (CST Normalization)
H field*
8
* All field values are normalized to give 1J stored energy in the cavity (CST Normalization)
Comparison tables
9
Superfish CST HFSS ∆CST-SF (%) ∆HFSS-SF (%)
Frequency (MHz) 101.674 101.666 101.674
Hpeak
(kA/m)16.711 16.76 16.763 0.3 1.1
Epeak
(MV/m)11.38 11.5 11.6 1 1.9
Quality Factor ∆ (%)
Superfish 11795 -
CST 11844 0.4
HFSS 11746 -0.4
“Real” structure
10
Remarks
• Never being confident to post-processing results!!
• Even if HFSS and CST results are consistent and very close to Superfish, when we start to complicate our structure (tuner plate, coupler and pick-up), the possibility of having a finer refinement on surface meshing gets HFSS results more reliable
• The above statement are not general!!
11
Cavity Parameters
12
ISOLDE TRIUMF* SPIRAL 2**
Frequency [MHz] 101.28 141.4 88
(%) 10.3 11.2 12
Lnorm (mm) 30 18 41
Epeak/Eacc 5.4 4.9 4.9
Bpeak/Eacc[G/(MV/m)] 96 99 90
Rsh/Q0 [] 554 545 518
=Rs∙Q0 [] 30.34 25.6 37.5
* V. Zvyagintsev et al., “Development, Production And Tests Of Prototype Superconducting Cavities For The High Beta Section Of The Isac-ii Heavy Ion Accelerator At Triumf”, RuPAC 2008, Zvenigorod, Russia
** G. Devanz, “SPIRAL2 resonators” talk held at SRF05
Q0 values
13
ISOLDE(Eacc=6MV/m)
Pcav (W) Rs (n) Q0=/Rs
5 33 109
7 46 6.6∙108
10 65 4.6∙108
12 79 3.9∙108
15 98 3.1∙108
** G. Olry et al., “Tests Results Of The Beta 0.12 Quarter Wave Resonators For The Spiral2 Superconducting Linac”, LINAC 2006, Knoxville, Tennessee USA
* V. Zvyagintsev et al., “Development, Production And Tests Of Prototype Superconducting Cavities For The High Beta Section Of The Isac-ii Heavy Ion Accelerator At Triumf”, RuPAC 2008, Zvenigorod, Russia
TRIUMF*: Q0=7∙108 with Pcav=7W and Eacc=8.5MV/m
SPIRAL2**: Q0=109 with Pcav=10W and Eacc=6.5MV/m
Some word about the hot frequency
The cold frequency has to be 101.28MHz
In air: -32kHz
101.248MHzIn superconducting mode of operation (shortening of the length of the antenna,…): -332kHz
100.916MHz
Other contributions (chemistry,…): ????
~ 100.900MHz
skin depth variation: -11kHz
100.905MHz
14
RF CouplerPick-up
cavity
tipgap
Network Analyzer
• The Pick-up position is fixed (22mm inside the cavity)• The RF coupler position is varying
Cavity Prototype Measurements
15
Measurements on November 2008
* Pick up length=22mm
∆ coupler1=14kHz/mm
∆ coupler2=22kHz/mm
∆ coupler3(from 22 to 64)=5.7kHz/mm
16
“positive” structure
“negative” structure
17
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
Frequency without tuner plate
* “Short” means coupler length=22mm and pick-up length=22mm
** “Long” means coupler length=64mm and pick-up length=22mm
*** ∆ Coupler3 (measured)=5.7kHz/mm
**** Remind: tipgap is the distance of the bottom plate from the central resonator
18
Study of RF tuning plate
19
Tuner position +5 Tuner position -15
20
Simulation with tuner position +5, tipgap 70
100.684 MHz
1.220.000
Coupler length 5mmPick up length -1mm
21
Simulation with tuner position -15, tipgap 70
1.066.710
100.929 MHz
Coupler length 5mmPick up length -1mm
22
Frequency with tuner plateTipgap 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
∆ Tipgap 20.5kHz/mm
∆ Tuner plate 12.25kHz/mmTotal Coarse
range=245kHz
5.2kHz/mm
Pick up length=-1mm, coupler length=5mm
Triumf tuner coarse range 32kHz 23
Measurements vs Simulations25/03/2009
Tipgap 90Without tuner plate
Tipgap 75Without tuner plate
Tipgap 70Without tuner plate
Simulation Measurements* Simulation Measurements* 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(- 32kHz air)100.981 MHz
101.000 MHz(-77kHz Res) *100.923 MHz
100. 899 MHz(- 32kHz air)100.867 MHz
100.916 MHz(-77kHz Res) *100.839 MHz
Short coupler and pick-up
101.410 MHz(- 32kHz air)101.378 MHz
101.483 MHz(-77kHz Res) *101.406 MHz
101.191 MHz(- 32kHz air)100.159 MHz
101.240 MHz(-77kHz Res) *101.163 MHz
101.083 MHz(- 32kHz air)101.051 MHz
101.150 MHz(-77kHz Res) *101.073 MHz
* Resonator longer of 0.4mm with respect to the nominal length (135kHz/mm)
** These new measurements have been done in a much noisy environment that explain the 13kHz of difference with respect to the previous ones
24
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)
25
External Q
Let us assume Q0=5x108 and a condition of perfect coupling (c=1)
Therefore we want
• Qext of RF coupler of 2.5x106 in order to be undercoupled (c=200 ∆f 40Hz) (larger bandwidth)
• Qext Pick-up of 1010 in order to be overcoupled (negligible power flowing from the pick-up) 26
HzQff
Qff
loadload
4.01 0
0
Qload=2.5x108
Q measurements • Hot measurements are important to test and calibrate the coupler and pick-up
before going to cryostate• Very difficult to get reliable measurements allowing for such a high Qext
values • Cold measurements are needed for the final characterization• It is not possible going through standard frequency domain measurements as
• Two different strategies for hot and cold measurements
27
00
0
with 1 ffffQ
Qff
loadload
β measurements
28
RF Coupler Pick-up
Network Analyzer
Pc
PfPe
Pr
Pin
Pin = Pf-Pr = Pc+Pe
2
111
c
cfP
Dividing everything by Pe and rearraging, by considering that
puc
e
f
e
PPS
PP and21 2
22
2
21)1(
421
S
S
c
cpu
Note: the system is symmetric so that I can feed from the pick-up and meauring c
Qext hot measurements1) Measuring SWR from S112) Measuring S21 pu
3) Measuring Qload
4) Evaluating Qext
29
c S21 pu Qload Q0 Qpu Qc
1.019 - - 5636 11380 - 11168
1.73 2.21∙10-1 0.055709 3902 10870 1.95∙105 6283
1.84 1.67∙10-2 0.000306 3944.5 11204 3.66∙107 6089
1.84 3.52∙10-5 1.36∙10-9 3944.5 11202 8.24∙1012 6088
1.0157 1.75∙10-2 0.000307 5643 11376 3.70∙107 11200
0.9574 2.31∙10-1 0.056495 5504 11085 1.96∙105 11578
1 if11 if
c
c
c
SWR
SWR
pucloadQQ 10
extQQ0
Legend
W/o pick-up
Lpu_in=22mm
Lpu_in=-1mm
Max Error= 3.6%
Q cold measurements
ffQ
0
0 as Q0109 ∆f0.1Hz
Lt Q
UPdtdU 0
LQt
eUtU0
0)(
0
LLQ
By feeding the cavity by a rectangular pulse
pucpuccavt
L QUP
UP
UP
UP
Q
111
00000
Knowing c, we get Q0
By switching off I can measure
fc
cr PP
2
11
c
30
We can use for c value the one we got from the hot measurements or we can feed the cavity by a rectangular pulse, in the steady-state
Coupler
31• -10mm Linsertion 60mm 5∙109 < Qext < 7500
Macor
• Dust free sliding mechanism
Coupler
32
Internal Reflections
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
• First prototype of the tuner already available, sputtering on the end of June
• Mechanical design and fabrication of the coupler is started, deliviring date, end of July
• Starting the design of the low beta cavities34