WG3 Summary（6/12のまとめから抜粋）
Convenors:
Peter McIntosh (Daresbury)
Frank Marhauser (JLab)

Friday 12th June, 20091

2009.6.25 阪井寛志

WG3 Goals
Working group focusing on the RF/SRF developments
requiredi d ffor prototypet t
andd fullf ll scalel ERL ddevices.
i
1.
2.
3.
4.

2

What are theWh
h kkey SRF challenges
h ll
ffor ERL
ERLs?
?
What solutions are being investigated and havealreadyl d bbeen ddeveloped?
ld?
Which components still need more R&D work?
O
Organise
i R&D effort,
ff t tot coordinate
di t studies
t di anddidentify possible collaborations.

WG3 Topic AreasRF Guns (Joint WG1)–

Cryomodules

–

–
–
–
–



Thermal ShieldinggMagnetic Shielding
Microphonics Performance
Thermal Management

Cryomodule Components
–
–
–
–

3

RF Control

SRF and NC

–





Cavities
Input Couplers
TunersHOM Absorbers

–




LLRF
HPRF
Optimisation and
Limitations

HOMs and ImpedanceManagementa age e t (Jo(Jointt WG2)G )RF System Optimisation–––

Gradient
Cryogenic Losses
CostTalk Breakdown for WG3
Scheduled

Un-Scheduled

4

Institution

Number of Talks

AES

1

BNL

3

Cornell

5

Daresbury

2

FNAL

1

FZD

1

HZB (formerly BESSY)

1

Jlab

2

KEK

3

PKU

1

Total

20

ANL

1

HZB (formerly BESSY)

1

PKU

1

Total

23

11 Institutes!
ここをもっと多くすべき
By 阪井Cryomodules

5Cornell ERL injector linac status, S Belomestnykh














6

100-mA Cornell SRF ERL injector linac commissioning progresses well.
Comprises: NC buncher cavity, SRF accelerating cavities, NC deflecting cavity (pulsedmode) All at 1300 MHzmode).
MHz.
Buncher cavity processed to > 200 kV. Slow conditioning  multipacting in the narrow gap
between tuner plunger and port and small vacuum leaks:–
new tuners are ready for installation,  TiN coating
Deflector cavity  very useful instrument for beam diagnostics.
ICM first cooled in April of 2008, first RF turn on June, first beam in July. 4 mA average
beam current achieved in December.
After conditioning, ICM has total beam cceleration of 13.8 MV. Limited by heat flux inthe chimneys at 2 K and the pump skid capacity at 1.8 K,
caused by low intrinsic Q factors of all cavities.
Concern, but not show-stopper. Cause of the low Q is
still under investigation.
Using RF and DC kicks from input couplers  residual
highly non-linear magnetic field inside ICM in vicinity ofcavity 3  useful aperture extremely small. ICM waswarmed up and area degaussed successfully (confirmed
by beam scans).
Future ICM work will focus on further cavity (FE) andinput coupler (MP) conditioning, microphonics
compensation studies, and high beam current effects.

Cornell 100 mA ERL injector
deflector

cryomodule

photocathodeDC gun

b
beam
d
dump

buncherexperimental beam lines











7

Nominal bunch charge
Bunch repetition rate
Beam power
Nominal gun voltage
SC linac beam energy gain
Beam current
Bunch length
Transverse emittanceJune 9, 2009

77 pC
1300 MHz
550 kW
500 kV
5 to 15 MeV
100 mA at 5 MeV
33 mA at 15 MeV
0.6 mm rms
 1mmmrad
S. Belomestnykh: Cornell ERL
injector linac status

ICM performance: RF

While initial intrinsic Q was good, it degraded over time.
Field emission at higher Eacc. Plan to do pulse processing to reduce field emission.
Voltageo tage limitt iss due to thet e chimneycey heateat flux
u ttransfera s e at 2 K.
At the moment the ultimate ICM accelerating voltage limit is determined by the chimneys and is 13.8 MV
for 2 K operation, close to the maximum specification of 15 MV.
The limit at 1.8 K ((slightly
g y lower than at 2 K)) is due to heat removal capacityp y of cryogenic
y gsystem.
yCavities at the ICM ends have lower Q.








ICM Q vs E at 2 K

Q degradation overall cavities
time?

1.E+10cavity 1

cavity 3

cavity 4

chimney limit

cavity 5cavity 2

1.E+10
1.8 K
2.0 K (avg)

Q

Q

Detuned cavity 2:
0.77 W of additional RF losses for~5 kW of additional forward power;
most likely due to reactor grade Nb
used for input coupler ports

2

Chimney limit: ≥ 1 W/cm

1.E+09

1.E+09
0

2

4

6

8

10

12

0

2

4

6

8

10

Eacc [MV/m]

Eacc [MV/m]

8

14

June 9, 2009

S. Belomestnykh: Cornell ERL
injector linac status

12

Possible reasons:
Simulations and measurements indicate that losses in the
beam tube and coupler regions contribute significantly to
Cause
of
low
Q0overall dynamic cavity losses. Cavity flanges are
at 6K
the
thermally anchored to a "4.5 K" cooling circuit, but: "4.5 K"
system is actually at 6 K  increased BSC resistance inbeam tube sections ( RBCS  exp(T)).
Cryopumping of residual gases: degradation over time, end
cavities
iti hhave llower Q factors.
f tFerrite dust contamination. Was observed during HTC test,
but lower Q than in the ICM.
Hydrogen Q-disease:
Q disease: unlikely as 2 cavities were checked
during vertical tests and no sign of this was found.
2 1   f ( GHz )  17 . 67 
R BCS (  )  2  10  4    expp  

T
1
.
5
T 
 



3000

at 6K
att 6K

9

at 6K

R_(BCS) (n ohm)

2500
系列1

2000
1500
1000

4.5Kに比べ6kでは
R_BCSが２倍

500
0
0

2

4

6

8

10

温度 (K)

June 9, 2009

S. Belomestnykh: Cornell ERL
injector linac status










Beam studies with and w/o RF indicated that there are remnant magnetic fields inside the ICM.
“Pincushion” scans using corrector magnets inside the ICM proved very useful.
Investigated different sources of magnetic field outside the cryomodule: shielded cold cathode gauges,
no effect from ion pump magnets, put mu-metal dome on top of the ICS and narrow shield around the
upstream end cylindrical surface, iron shields at cavity 2 input couplers.
Improvements were marginal at best.
C l i theConclusion:
th residual
id l fieldfi ld isi iinside
id theth ICM.
ICM
As there is no BPMs inside the cryomodule, decided to use input couplers as “poor man” BPMs.
Studied beam deflection with RF & DC coupler kicks, the orbit is straight in vertical plane, but has“b“banana”” shapehiin hhorizontal
i t l plane.
lAlso, the orbit indicates that the parasitic field is in the vicinity of the cavity 3 couplers.

ICM beam studies

pincushion scan indicatingpg bad field
inside ICM“Octopus”“Octops” beam with
ith RFon

10

June 9, 2009

S. Belomestnykh: Cornell ERL
injector linac status

KEK ERL cryomodule development H Sakai

Injector SC
design•1.3GHz 2cell - 3cavities• 14.7MV/m• 167 kW / coupler• modified HOM coupler

Target : 100mA cw operation for (compact) ERL
Prototype 2cell
Nb cavity

design•1.3GHz 9cell• 15-20MV/m• Qo > 10^10• 20kW power
100mm

2 input port
4 HOM coupler
Results of vertical test of ERL 2cell cavity

Achieve 30MV/m for a short second
Keep 15MV/m for 8 hours
Heat-up of probe of HOM coupler is problem
Assembly of cryomodule is scheduled in 201111

120mmEccentric Fluted Beampipe(EFB)

Results of vertical test of ERL 9cell cavityy

HOM absorber

9cell Nb cavity

Heat-up of
HOM probe

Points1) Large beampipe + HOM absorbers2) Optimize cell shape  HOM-BBU up-to 600mA
3) EFB for extracting Quad HOMs
Iris dia. 80mm

HOM absorber

Main linac SC

17MV/m





EFB
11

Maximum field is 17MV/m on 5 times VT.
Field emission was started above 10MV/m.
Assembly of cryomodule is scheduled in 2012

BNL ERL Cryomodule Testing Status, A Burrill








12

703 MHz, 5 cell LINAC cavity with 24
cm diameter beampipes employing
ferrite HOM absorbers
VTA measurements of 20 MV/m at Q
= 1x1010
Preliminary cryomodule testingunderway to reproduce VTA results
FPC re-conditioned with no vacuum
or arcing events.
RF and cryo systems work as
designed, preliminary tests havegiven us new thingsgg to work on.

Preliminary Cryomodule Test Data
1.00E+11

50000
45000
40000

30000
25000
20000
1.00E+09

Radiationn (mR/hr)

35000

1.00E+10

Q

rad

10000
5000
1.00E+08

0
0

5

10

15

20

25

Eacc (MV/m)

ERL Linac Cryogenic Test
120

300

100

250

Temperaature–

Significant Field
emission
Testing limited by LHe
available

VTA

15000

350

–

q

N2 shield
80
tuner
thermal tran
Cav He low
60
Cav He low
Cav he upperballast leve

200
150

dewar level
40

100
20

50
0
6:00:00

0

8:24:00

10:48:00

13:12:00

15:36:00

Time

18:00:00

20:24:00

22:48:00

Liquid Level p
percentage

 Testing Summary Overall test was a success!
– Cavity gradientmeasured using pick-up
probe– Q calculated using Ploss
Ploss = Pi-Pr-Pt– Next test will use
calorimetric Ploss– Multipacting barrier at
10-12 MV/m

G5 test layout
Solenoids

SRF 5cell cavity
SRF
Gun
Transport car

Faraday Cup

TripletDipoleBeam Profile Monitors
OTR/Yag Screens

quad

S

Pepp

Halo mFC

GUN S

iinterchangeablet hblscreen/slitS

5 cell RF

14ºFC

JLAB HC CM Development, F. Marhauser






Very compact Ampere-class CM developed at < 1GHz and 1.3-1.5 GHz.
First 2 Nb cavity prototypes (1.5 GHz) with waveguide endgroups exceeded goal of 16.7
MV/m CW at Qo=8e9 in VTA (one limited ~24 MV/m by available power,
power one quench
limited ~19 MV/m (with 4” Nb extensions), no mulpipacting seen in cavities/waveguides.
Design is different from conventional ERL cavities by relying on the benefits of waveguideand input power couplers rather than HOM beam tube loads and coaxial coupler.
Benefits are:
–
–
–
–



15

HOM damping efficiency is very efficient with 6 waveguides (simulated and measured)
Warm RF window (based on PEP-II design) can handle very large power (1MW CW @ LEDA)
Warm HOM loads warm designed to handle kW of HOM load power
Challenges: FPC warm-to-cold transition needs to be optimized thoroughly to limit 2K heat leak

New full spectrum extrapolation scheme presented,
presented which can forecast the fully
resolved impedance spectrum of cavities (very high Q SRF cavities) in time domain
speeding up cavity optimization/analysis process (by weeks or even months!).

Conceptual design of a cavity-pair injector
cryomodule (1497 MHz, L=2.6m)

Prototype 1497 MHz cavity with endgroups

Impedance Spectrum Extrapolation Method

Type 4 Crymodule (T4CM), A Hocker

Next step in evolution of
TTF/XFEL cryomoduleyMagnet/BPM package moved
from end to middle of CM–

Intended as a CM for largescale HEP machine (ILC,
Project X etc.)
Project-X,
etc )
–
–



16

Directly under center support
post for more stability

High gradient, high packing
factor, low RF duty factor
Dynamic
y a c heatea loadoad much
uc less
essthan typical ERL CM

First T4CM to be built at FNAL
in 2010, cooldown in 2011

ERL CM Collaboration Update, P McIntosh
Collaboration initiated early 2006:
–
–
–
–
–

Parameter

Value

Frequency (GHz)

1.3

Number of Cavities

2

Number of Cells per Cavity

7

Cryomodule Length (m)3.6

R/Q ()762

Eacc (MV/m)> 20

Epk/Eacc

2.23

Hpk/Eacc (Oe/MV/m)

46.9

CM Energy Gain (MeV)

> 32

Qo

>1 x 1010

Qext

4 x 106 - 108

17

Maximum Beam Current

100 mA

Max. Cavity Forward Power (kW)

25 SW



Daresbury Lab
Stanford and Cornell Universities
LBNL
DESY
FZD Rossendorf

New CM to be installed on ALICE
for beam evaluation May 2010.

ERL Operation and RF
Control

18

ALICE SRF Commissioning, A Wheelhouse

SRF Commissioning:
–
–
–
–
–
–
–



Future Plans
–
–
–
–
–



19

Cavity Eacc reduction seen when tested at Daresbury c.f. DESY VTA tests.
FE radiation from ERL CM required introduction of lead wall:
LLRF electronic life extended from 1000hrs to 10,000hrs
Poor ancillary HVPS reliability resolved:
Future designs to ensure that the RF power sources are located with the HVPS
Beam loading effects resolved at low bunch charge levels by reducing Qext
E
Energyrecovery achievedhid att 20
20.8MeV
8M V iin D
Decemberb 2008Further investigations of Q0 v’s Eacc  He processing of cavities
Further investigation of beam loading required for higher bunch charge and long pulse train lengths
Reduce Q
Qext further
Improve LLRF response time
Investigate feed-forward

Installation of new 7-cell linac cryomodule in May 2010

Cornell ERL Main Linac and LLRF Control,
Control M Liepe
Real HOM absorber = ideal absorber; Real cavity = ideal cavity, as designed!
5

4

10

Ideal absorber

2

2

10

=25"=-8=1 "=0
=1010"=-0.1" 0 1=2.5
2 5"=5" 5(r/Q)Q/f [ /cm /GHz](R/Q)Q/f /[ cm/GHzz]

10

3

10

2

10

1

10
1500

10

10

6

4

Red: without
deformations
Blue: with 1/16
mm cell shapedeformations

2

0

2000

2500

f [MHz]

3000

3500

10
1 .5

2

Cornell LLRF System

2 .5
3H O M f re q ue nc y [H z ]

3 .5
x 10

9

Demonstrated:• Exceptional fieldstability at QL = 106 to 108• Lorentz-force
compensation and fast
field ramp up

20

A/A< 2·10-5

P < 0.01 deg•Piezo microphonics
compensation with ~20 Hz
bandwidthHLRF/LLRF for cERL@KEK, S MICHIZONO

30/300kW Klystrons plus 30kW IOTs will be
used at cERL.
New custom FPGA board for LLRF
developed based on uTCA (AMC module).
AMC module

30 kW klystron:
E3750 by Toshiba~55%efficiency

21

21
Custom FPGA board having four 16bit ADCs
and four 16bit DACs with Virtex5.

Fast Ferroelectric Phase Shifter Design for ERLs
ERLs, S
ShchelkunovFor ERLs, if beam loading issmall:–RF power requirements
determined by







If the beam loading is not small:
–
–
–

22

1) ohmic losses in walls,
2) imbalance between thebbeam
currentst3) microphonics
each may require change incoupling between the cavity
and feed line
line, typically resultsin bandwidth growth, and more
power.

there are “beam-driven”
beam driven phaseinstabilities;
the microphonics still are an
issue;
thus again
again, there isrequirement for more RF
power.

Phase shifters based on BST ceramicwith eps ~500, that changes its dielectric
constant with <50kV/cm
50kV/cm external bias.
Samples developed so far have shown
fast switching (intrinsic time < 10 ns).
3 designs described for L-band, out of
which 1) the planar-coax design is
attractive but the problem of parasitic
attractive,modes must be addressed; and 2)
sandwich-in-waveguide design was
successfully built and “cold” tested.

HOM Management(Joint WG2)

23

KEK ERL HOM Absorber Development, M Sawamura
Measurement

Calculation

Ferrite properties ()Optimization of ferrite condition

Frequency dependence

Ferrite length
2.5E+05

80K

Co2Z 80K μ”

2.0E+05

Ferrite50 80K μ”

10

5cm
6cm
7cm
8cm
9cm
10cm
11
11cm

Loaded Q

TT2-111 80K μ”

9μ”

N IB004-1
New
IB004 1 80K μμ”

TT86-6000 80K μ”

8TT2-4000 80K μ”

7

old_IB004 80K μ”

6

Nikko 80K
0 μ””

HIP ferrite
Comb-type RF Bridge

3

1.0E+05

5.0E+0454

1.5E+05

0.0E+00
35

2

2
1
0
0

2000

4000

6000
8000
Frequency (MHz)

10000

45
50
55
Damper Position from End-Cell-Iris (cm)60

65

Ferrite thickness

80

12000

40

1.4E+05
1.2E+05

Temperature dependence
12
10

μr"

8
6

1.0E+05

New IB004

Bellows

4K Thermal Anchor



2
0

0

50

8.0E+048.0E
04
6.0E+04
4.0E+04
2.0E+04

4

24

80K Thermal Anchor

Loaded Q

1.5GHz2.0GHz3.0GHz4.0GHz5.0GHz6.0GHz7.0GHz8.0GHz9.0GHz
10.0GHz100

150
Temperature (K)

200

250

300

0.0E+00

HOM absorber model under design
g
35
40
45
50
55
60
65
Damper Position from End-Cell-Iris (cm)–HIP ferrite of new-type IB004
 Firm bonding between ferrite and copper–
Comb-type RF bridge
 Lower impedance and lower thermal conductance than finger-type

1mm
2mm
3mm
4mm
5mm

HOM Absorber Development for Cornell ERL
Cryomodules, E Chojnacki






25

A high bandwidth (1GHz – 100GHz) beamline HOM absorber is likely
necessary for ERL BBU control.
The Cornell ERL Injector load using 3 types of absorbing tiles can be
modified to satisfy HOM absorption reliably.
A simpler, lower cost beamline load using a unitary absorbing cylinder
is still desirable
desirable, being developed at Cornell
Cornell, DESY
DESY, KEK
KEK, BNL
BNL, andelsewhere.
Carbon nanotube doping of ceramics may be the material to provide
broadband loss at cryogenic temperatures.

HOM Absorber Development for BNL ERL CMs,
CMs L
HammonsDevelopment of effective HOM absorbers crucial for R&D effort in three basic areas:
–
–
–
–



Prototype ERL facility
Coherent Electron Cooling experiments (CEC)
Medium energy electron-ion collider (MeRHIC)
Each of above have high-current, high-charge requirements and therefore require HOM mitigation.

Prototype ERL facility is testbed for technology to support CEC and MeRHIC:–

Features ceramic/ferrite loaded beamline HOM load for ½-cell SRF gun.



–
–

HOM mitigation through fundamental power coupler ports also found to extract HOMs in gun.
Facility also features ferrite HOM loads for five-cell RF cavity.



5-cell ERL cavity tested at room/SC temperatures and dipole
passbands at 0.8 – 1 GHz and 1.6 – 1.8 GHz have beenmeasured. Modes have also been simulated using MWS.

Work commenced to develop damping concepts for MeRHIC:––

Closely spaced RF cavities in highly modular CMs accommodated in a portion of the RHIC ring.
Project requires very compact damping structures.


26

Ceramic break can be operated at nitrogen temperatures and serves as effective thermal transition.
Break can also protect superconducting structure from potential damage to ferrite tiles.



Ferrite HOM loads
Loops and probes between RF cavities and inserted into existing ports in the RF cavity
Exponential pickup electrodes (similar to BPM electrodes)
Cloverleaf-shaped waveguides with coaxial pickups between cavities

C
CrymoduleC
Components

27

Cavity Tuners, O Kugeler



–
–
–
–
–
–
–
–

–

28

–

Stiff
Stiffness(group(delayd l ) crucial
i l fformicrophonics compensation
Sacrifice tuning range for stiffness: use
shorter piezos
Shorter piezos also reduce hysteresis
effects
Use high voltage piezos for stiffness
Use multiple piezos
Increase cavity wallsize to increase
frequency of lowest tuner resonanceImprove stability of microphonics
compensation algorithms
Incorporate piezo hysteresis into
compensation algorithm in order toeffectively increase piezo resolution
Use bipolar power supplies (and increasemechanical pre-stress on piezo)
Increase cavity stiffness to increase
frequency of lowest resonance

d

d

Group delay 

0

20

!

-20

15

lowest resonance

-40

10
-60

B
W

5

80
-80
amplitude (Hz)phase (°)

0
10

20

30

40

50

60

70

80

-100
90 100frequency (Hz)Transfer function of Saclay I tuner

phase
e (°)



Combined cold stepper motor and piezo
tuner is the tuner of choice for ERL
machines, but:
Most piezo tuners developed for pulsed
operation!
What could be improved in a CW-only
tuner?

amplitudde (Hz)Addressing SRF Input Coupler
Design Challenges, V Veshcherevich







Many couplers have been designed for different ERL cryomodules.
Coaxial and waveguide couplers are predominantly used.
Many coaxial coupler designs based on a few existing designs(TTF-III, TRISTAN coupler) though often with necessary upgradesor modifications.
Coaxial couplers can be built with additional cold windows whichgive
i some advantagesdbbut makek couplerslmore complex
l anddexpensive:
–








Variable coupling leads to additional complexity. It may be used inmachineshibuilt
b ilt ffor accelerator
l t researchh purposes. N
Nott neededd d fforuser facility!
Injector couplers are most challenging,  high power requirements.
Problems with low energy
gy beam motion  couplers should beplaced symmetrically (in pairs) or compensating stubs should be
used.
Main linac couplers much easier to build  lower power:–

29

Cold windows cannot be used for very high power applications.

Design should be cost efficient for multi-GeV ERL machines.

KEK ERL Coupler

S
SRF
G
Guns (Joint
(
WG1)
G )
ＷＧ１関係なのでここは飛ば
します。
します

30

Key
y WG3 Discussion Issues 1(ここからはconvenerの私見)Cryomodules:–

Many cavities showing low Qo performance, why?







Cornell (6e9 @ 8 MV/m) 2-cell – problem not yet identified
BNL (6e8 @ 20 MV/m) 5-cell – multipacting observed
KEK (5e9 @30 MV/m) 2-cell -- heating of HOM coupler probe above 16MV/m
KEK (3e9 @17 MV/m) 9-cell – limited by field emission
Are the large iris
iris’ss causing a systematic problem for these ERL cavities?
Or is it ferrite contamination from the HOM absorbers?
––

L-band 9-cells vs 7-cells? Decided by assessment of:Trapped HOMs
Peak surface fields

Tuners:–Cold vs Warm tuner motors:


C ld
Cold:
–
–
–



31

Lively discussion, but no real conclusion!

Takes ~ 1 week to replace
Heat from motor needs to be dissipated inside CM
TTF show good reliability, need to gather more statistics!

Warm:
–
–
–
–

Motor costs are large
Warm piezos difficult to utilise for microphonics compensation
Easy access for replacement
Requires additional warm-cold transition

Key WG3 Discussion Issues 2Input Couplers:–

Waveguide vs Coax?
L-band CW coax limit ~ 100 kW (injector issue)
 Waveguide can deliver much higher CW power Choice
Ch i ddoes not appear to b
be technicallyh i ll b
based,
d more ddrivenibbyprevious experience Waveguide solution can remove the cold window–C ld vs W
Cold
Warm windows?
i d?
Cold coax window used to heat sink centre coax, main advantage.
 No direct beam line of sight for cold coax window.
 Dog-leg for waveguide can remove line of sight problem.
 Multipacting controlled by bias for coax, however no problems
observed for waveguide (JLab).


–

32

Adjustability not necessary for user facility, can be achieved
externally over a wide range (>10 demonstrated) for both coax/wg

Key WG3 Discussion Issues 3


HOM management:–

If using beam
beam-pipe
pipe absorbers
absorbers, do we need loop couplers also?
Multipacting problems experienced with loop couplers.
 Excessive fundamental power heating of probe.
–How can we mitigate possible ferrite contamination?
Vendor coating of the material
 Shield ferrites in beam-pipe with a ceramic tube
 New materials being investigated Variability in ferrite material requires tighter control

RF Guns:
–
–

33

–

Problem calculating HOM power damping requirements
Would like BBU calculations performed, taking into account beam
velocity change
Similar Qo degradation observed at ELBE, fabrication issues

WG2 SRF Worked Example Request


Asked to evaluate SRF system requirements for:––––7 GeV ERL
Operating at 1.3 GHz
20 MV/m
100 mA beam current

ＷＧ３でdiscussionに時間を割いて行った議論。
Case study

34

Worked Example

Parameter
10 MeV Injector (Cornell ICM) Injector RF Power
Injector Cryo Heat Load

ERL

設定 速勾
設定加速勾配Q0の目標値
Static loss per cavity
2K Heの冷凍機負荷が変わる。
Microphonicsの値
Returnのphaseのずれ 入力パワーが変わる。
冷凍機効率→Total の冷凍機負荷
Total

どうも2*10^10くらいQ0が欲しいという設計にしたいようだ
欲しいという設計にしたいようだ。
実際は難しいであろう。

35

Units
kW
W

Pessimistic
Value
1000
40

Optimistic
Value
1000
40
16
1.8
2.00E+1010
6.50E+07
2
13.3
1
179.95
4.80E+07
2.8
421
10
950
1286
6.0
5.7
0.4
50
800
6.1
39
3.9
4.57
7.29
11.19
11.86

Eacc
Operating TemperatureQo
P k Microphonics
Peak
Mi
h i
Qe (Perfect ER)
RF Power per Cavity (Perfect ER)
Pdiss per cavity
Static Load per Cavity
Second Pass Phase
Qe (Imperfect ER)
RF Power per Cavity (Imperfect ER)
Total Number of Cavities
RF Power Overhead
ERL RF Power (Perfect ER)
ERL RF Power (Imperfect ER)
ERL Cryo Power

MV/m
K

%
kW
kW
kW

20
2
1.00E+1020
3.30E+07
6.4
41.6
2
179.8
2.10E+07
10
337
25
2699
4229
14.7

Total Dynamicy
LoadTotal Static Load
Cryo Safety Factor
Cryo Efficiency
Total Cryo Capacity
Total AC RF Power (Perfect ER)
Total AC RF Power (Imperfect ER)
Total AC Cryo Power
Total AC Power (Perfect ER)
Total AC Power (Imperfect ER)

kW
kW
%
ACW/W
kW
MW
MW
MW
MW
MW

14.1
0.7
50
800
14.8
74
7.4
10.46
17.7
25.1
28.16

H
Hz
kW
W
W
Deg
kW

SRF Facility Survey (foster new ERL collaborations)

Institute

Gun Test

ANL

BCP

EP

HPR

VTF

HTF

Assembly

YES

YES

YES

YES

YES

YES

YES

YES

YES

YES
YES

Module Test

BNL
CORNELL

YES

Daresbury

YES

YES

YES

FNAL

YES

YES

YES

FZD

YES

KEK

YES
YES

HZB
JLAB

YES

YES
YES

YES

YES

YES

YES

YES

YES

YES

YES

YES

YES

YES

YES

YES

PKU
Oth
Others36

To be completed offline!

WG3 Collaborative Publications


ERL SRF System Specifications:–

HOM Absorber Material Evaluation:–



Cornell, BNL
Cornell
BNL, FNAL
FNAL, HZBHZB, JLab,
JLab Daresbury – Coordinator O
Kugeler (HZB)

ERL RF Control Optimisation:
p
–

37

C
Cornell,ll KEK
KEK, BNL
BNL, JlJlab
b – CoordinatorC di t M Li
Liepe (C(Cornell)ll)

CM Microphonics Characterisation:–



Cornell, ANL, KEK, BNL – Coordinator A Nassiri (ANL)

JLab, Cornell, KEK, BNL – Coordinator T Powers (JLab)Achievement of WG Goals?
1.

What are the key SRF challenges for ERLs?






2.

What solutions are being investigated and have already been developed?




3.





Minimisation of microphonics, drives RF power demand for an ERL
HOM absorbers,
absorbers reduce cost,
cost improve fabrication processes
Input couplers (coax and wg, cold/warm windows), simplify, reduce cost
Tuner (warm and cold) motors

Organise R&D effort, to coordinate studies and identify possible collaborations.


38

Improved HOM damping materials identified and are being investigatedL-band 50 kW CW coax coupler demonstrated<0.01o and <2 x 10-5 LLRF stability achieved

Which components still need more R&D work?
4.

Understand Qo degradation being observed
C it ffabrication
Cavityb i ti ttoleranceliimpactt on HOM
HOMs highlighted,
hi hli ht d requiresimore realistic
li ti
simulations to be performed using real boundary conditions
Need to understand ferrite magnetisation issues
Assess improved ferrite HOM absorber fabrication
Perform isolated HOM absorber characterisation
characterisation, to determine performancevariability

C ll b ti WG publications
Collaborative
bli tiare a start,t t tot hopefullyhf ll strongertcollaborations
ll b tiここからは私の感想






39

ERLに関して、超伝導空洞で２年前より、進歩している部分があったのが、KEK以外ではコーネル大、あとBNLくらいか？？ダラスベリーはERLの運転は実現まで持っていったが、自分たちで空洞の製作などを行っていがないため、空洞の性能評価を行えれたかどうかは疑問？（辛口に言うと、まったく評価ができていない。）JLABは1A級の空洞の縦測定でわりといい
結果を出しており これからが期待 但し
結果を出しており、これからが期待。但し、wave
guideを使った方式なのid を使 た方式なので、入熱は度外視。
Input Coupler, HOM damperなどのコンポーネントについては特にreviewのみで終わっている感があり、どこの部分がＲ＆Ｄ進んでいるなどの成長は終わる感があり ど部分が進んるなど 成長はあまり見受けられなかった。(Cornellだけが頑張っている印象。)
議論の時間を多く設けてくれていたようだが、convenerが超伝導空洞のことをそこまで理解しているわけでもなく、大した議論ができなかった。(も
を
解
わ
もなく
議論が きなもう少しいうと空洞製作側からの議論はない。)むしろ、発表を多く（ポスターなどにして発表できるようにする）して、参加者を増やして、いろい
ろ細かいdiろ細かいdiscussionを個別で議論できる場が欲しかった。
i を個別で議論できる場が欲しか た

ERL09言った収穫？？（主に超伝導空洞関係）
コーネル大にてinjector部分を見て色々見学したが、特に縦測定の場合と違い、横測定や運転に際して、Q0が半分くらいであり 非常に入熱やfieldが出ないことが非常に問題であるとあり、非常に入熱やfieldが出ないことが非常に問題であるという認識を得た。 向こうのS Belomestnykhや、 E Chojnackiと話した時に先ほどのべたフランジの効果以外にoperation中にもQ0が下がることがあるとの話があり それはGunや間のbuncher
Q0が下がることがあるとの話があり、それはGunや間のbuncherなどからガスなどが出ていて両端の空洞のQ0が下がっているのではないかとの見解があった。
 そのうえでコーネル大にてcryomoduleについて議論。特にそのうえでコーネル大にてcryomoduleについて議論 特にalignmentの方法、組み立て方法を議論また入熱対策をもう一度見直し我々のmain linacの cryomoduleの原案を見てもらい、いろいろ議論した。
いろいろ議論した
 こちらで作成したHOM damperの材料(TT2-111, IB004 withHIP)をいくつか持っていき、向こうの測定システムで吸収特性を見てもらい 我々の測定と同じかどうかをcheck 今後
性を見てもらい、我々の測定と同じかどうかをcheck。今後
さらに材料を送り、40Ghzまでの吸収測定と時間があれば低40温試験も行ってもらえることになった。


THANK YOU

Lookingg forward to ERL11
41

42

Peking SRF Gun Development, K Liu








43

An upgrade DC-SC Photocathodeinjector has been developed at
Peking university.
The designed acceleration gradientis 13MV/m and energy gain is 5MeV.
The first vertical test of large grain
Nb 3.53 5 cell cavity is 7MV/m limited
by field emission in the half cell. Further processing (Bake andBCP).
M t parts
Most
t off theth cryostatt t hash bbeen completed
l t d andd willill bbeassembled soon.
Commissioning of upgrade 3.5cell DC-SC photo-injector is
expected in 2010.

NC CW RF Gun, H Bluem











44

CW 1.5 GHz NCRF gun developed (tested at JLab).
All copper structure for simplified fabrication.
Potential for simplified cooling channel structure.
Capable of high cathode gradient (23 MV/m at 37 MV/m peak surface gradient)
CW RF.
Good RF efficiencyy with only
y 40 kW of p
power requiredq
for cavity
y wall losses.
Calculated stress at 23 MV/m cathode gradient is within acceptable limits.
Very small frequency shifts in simulations.
1 micron emittance at 1 nC electron bunch charge with suitable downstream
booster accelerator system.
systemFurther optimization of RF design might be possible.
On-axis coupling minimizes specialized outer wall disturbances that lead to highlocal heat loads and readily provides high coupling factors for high beamloadingFZD SRF Gun Development and Testing, J Teichert







First Run of SRF Gun in 2008
2 MeV,, about 100 h with Cu cathode,, 400 h with Cs2Te
Iav = 1 µA, total 5 C (diagnostic mode & radiation safety
permission)
basic principle (NC photo cathode) works well, no cavity degradation
found
Current Second Run in 2009
–
–
–



Problems during commissioning
–
–
–
–

45

Cs2Te photo cathode with 1 % QE, up to
now ca. 50 h lifetime
2.2 MeV -> 3 MeV
Imax= 16 µA -> 100 µA (400 pC @ 250 kHz)–

Cavity cleaning and low gradient – fabrication issues
wrong cavity π-mode frequency at 2 K (has been corrected now)
insufficient vacuum in cathode transfer system (under improvement)
multipacting in the gap between cathode and half-cellhalf cell, DC voltage
essential
depends on the cathode (surface quality of the Cu stem?)

46

47

Overall SRF System
Optimization for ERLs
Matthias LiepepCornell University

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 48

Outline Introduction: SRF System Optimization for

ERLs– What we want

 Optimization: What we can get– Operating temperature and RF frequency– Operating field gradient, Q0, reliability, and cost
– Loaded Q, RF power, microphonics– Cavity design and HOM damping and BBU
M tthi Li
Matthias
Liepe, ERL
2009

 Outlook: Whatwehope for
Cornell University,
Ithacamight
New
York

Slide 49

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 50

What we want
A miracle: No cost (well(well, low cost) Great performance (at least
meet specs)
 Perfect availability / reliability… easy to simultaneously get 2
out of these 3…

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 51

Optimization (I)Objectives:
 Minimize cost
 Meet specs
 Maximize availability
Constrains: Cavity performance (Q0, fieldemission…),
 Site constrains
 …

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 52



Optimization (II)Important to be realistic, but notpessimistic nor too optimistic!!
pessimistic,–

Remember: You may want to built your ERL
in a few years from now…

• Identify high risk / impact parameters– Cavity intrinsic Q0 ($$$)– Microphonics
Mih i llevell / peakk cavity
it ddetuningt i ($$$)–…
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 53



Optimization
(III)
More
truths:–Optimization is only as specific as objectives and constrains are/canbe specified–

In the following,g I’m not trying
y g to optimizep
ERLs for all p
proposalspout
there…
 Focus on Cornell ERL as example
 But: most conclusions also valid for other ERLs–

Not all of you will agree with all of my conclusions
 “Optimization”
Opt
at o influenced
ue ced by myybbiases,ases, bacbackground…
g ou dM tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 54

Cornell
Beam
Parameter ERL
Cornell
ERL Parameters
XFEL
consequence
250 * 2K load per cavity,
pulsedoperation modecw
factor 3 larger total 2K load

linac energy gain

5 GeV

20 GeVaverage current

0.1 A* 2

3· 10-5 A

bunch charge

77 pC

1 nC

(IERL/IXFEL)2=4· 107(PHOM,ERL/PHOM,XFEL)=400

bunch length

2 ps

80 fs - 1 ps

f < 100 GHz for HOMs

0.3 mrad·mm

1.4 mrad· mm

Cavity alignment, …

2e-4
2e
4

1.25e-4
1.25e
4emittance (norm.)energy spread(rms)

Similar, but much higher
beam currents, QL!
Tcav, fTM010, Eacc, Q0, QL, PRF,peak, IBBU,… = ?

Some of these pparameters are given
gby
y the state-of-the-art in SRF
technology, others are found by optimizations.
Optimization discussed in the following is done for the beam parameters listed
above
above.
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 56

Operatingttemperature
t
and
d RF
frequencyqyM tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 57

Dynamic
Losses (I)
SRF
resistance Cavity
small but finite
because Cooper pairs have inertia.
 nc electrons “see”
see an electric field!
BCS theory: Frequency andtemperature dependence of surface
resistance at low RF fields (Tc: S.c.
transition temperature)

RBCS  f 2 e (  const *TC / T )More resistance themore the electrons are
jiggled around.
More resistancethe more
nc electrons are
excited.
i dResidual resistance

1.5 GHz

Real live: Rs=RBCS+RRES
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 58

Dynamic
Losses(II) wall: Totalpower Cavity
dissipatedinto cavity
2
 2
1
V acc
Pdiss R s  H ds RS
2
R /Q GS
 (R/Q)G given by cell shape and number of cells

 minimize surface resistance Rs
 operate cavity at temperature such that
RBCS < residual resistance Rres
 Rs  Rres, i.e. independent of frequency!
 For given accelerating field gradient Eacc:
Pdiss / cavity length  1/f
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 59

Cooling Power for Dynamic Cavity Losses (f(f,T)T) forgiven Eacc
(dream…)(still quite optimistic)

 1.8K. Note: Lower T is unproven and might
Slide 60
cause instability in the cryo-system.
M tthi Li
Matthias
Liepe, ERL
2009

Cornell University, Ithaca New
York

Choice of Operating Temperature:
The lower the better?
 Lowering the temperature seems to be effective

as long as Q = Q(T) follows BCS and thetemperature dependent dynamic loads dominate((reasonable lower limit 1.5 K)) He-II cooling might become unstable below 1.8 K– tests requiredq Another cold compressor stage is required foreach 0.2 K temperaturep
step
p to lower
temperatures – investment costs and systemcomplexity increase See also: Talk by B. Petersen, ERL 2005
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 61

Choice of Frequency (I) Unless extremely small residual surface
resistances become reality in main linac
cavities in some distant future, higher
frequency (~1(~1.33 GHz) SRF cavities give smaller
dynamic cavity losses at optimized temperature– Important for multi-GeV ERLs!
– Also: Cavity
y surface area  1/f2

 Higher frequency gives smaller risk of cavity performance
reduction by surface defects, electron field emission by
dust, …
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 62

Choice of Frequency (II) Why chose <1 GHz anyway in highest current
ERLs (BNL…)?
(BNL )?
– BBU threshold current  1/f (assuming same numberof cells per cavity, same quality factor Q of HOMs)– Average HOM losses  f2
– But: Construction cost increases with lower frequency!
– But:B t O
Operationaltil costt increasesiwithith lowerlfrequency!
f!
– But: Risk of surface contamination increases withlower frequency.
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 63 Conclusion
For 5 GeV, 1001mA ERL:–

Fundamental mode frequencyqy of 1.3 GHz and realistic operatingpgtemperature of ~1.8 K minimize AC cooling power

Lower frequency only potentially beneficial if highest
BBU threshold is required–––

Can increase BBU threshold by factor of ~ 2 (for same number
of ce
o
cells
s pe
per cacavity)ty)
Note: Other things can have similar / larger impact on the BBU<
threshold current
More later…
later

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 64

Operating field
gradient,
di t Q0 ,reliability,
y and cost
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 65

SRF Linac Cost Estimation
TunnelSRF cyomodules• # of cavities• # cells per cavity• Linaclength• Cryo-loads at various
temperatures• Field gradient• fill factor•…

Cryo-Plant• Operating temperature
Cost model(main linac
only!)• …
• Note: cost  power0.4

RF Power Sources• Power per cavity• QL, microphonicsp•…
• # of cavities

Note: R&D cost and facility cost are notincluded!
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 66

0.5

1500

15
20
25
field gradient [MV/m]

0.6
0.4
0.2
0
10

30

tunnel length

800

15
20
25
field gradient [MV/m]

10

Q

10

30

200
10

IOT peak power

15

10
5
15
20
25
field gradient [MV/m]

15
20
25
field gradient [MV/m]

30

10cryo AC power

11

15
20
25
field gradient [MV/m]
cavity Q 0

30

15
20
25
field gradient [MV/m]

30

10

10
5

M tthi Li
Matthias
Liepe, ERL
0
30
10
15
2009

20
25
field
Cornell University, Ithaca
Newgradient [MV/m]
York

9

10

10
power [MW]

15
20
25
field gradient [MV/m]

15

0
10

0.1

400

power [MW]power [kW]

20

0.2

0
10

number of cavities

RF
cryo

600

500
0
10

0.3

30

#

1000

normalizedd cost1

tunnel
linac
RF
cryo

0

normalizedd cost

total

0
10

length [mm]normalizedd costExample: Dependence on Accelerating Field
capitaltotal costcapital cost
10 Yr operating cost
1.5 Gradient
operation
0.8
0.4

30

5

0
10

cryo power fractions
cav. dyn.
HOM
input Cstatic15
20
25
field gradient [MV/m]Slide 6730

Main Linac Cost Distribution for
Eacc=16.2 MV/mreelative coost [%]

50
40
30
20
10
0

TunnelRF power

Cryomodules Cryogenic plant Costs
C t ffor cryomodules,d lcryogenici plant,l t anddthe RF power sources are similar.
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 68

10
OptimalField Gradientconstruction
Cavity Q
11

04
0.4

Construction andoperation cost

10

10

0.2
0
10

case 1case 230
Cryo ACC power [M
MW]

0.8
0.6

0

10 yr operation

Q0

norm
malized cos
st

1

9

15
20
25
30
field gradient [MV/m]

10

10

15
20
25
30
field gradient [MV/m]

cryo AC power

25
20
15
10
5
0
10
20
30
field gradient [MV/m]

 Q0-value has significant impact on cost (high impact and risk

parameter)
 Construction cost changes only moderately for gradients between~16
16 and ~27
27 MV/m Operating cost / AC power increases with gradient Less risk for same cost!
 Select gradient at lower end: 16.2 MV/m
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 69

Gammaradiationmeasured at DESY/FLASH • Exponential growth in FE
Field
Emissionfrom cavity field emission
with gradient(PULSED CAVITY OPATION!):• Serious problem in cw cavity
operation• Low trip rate essential for lightsource!!
• Favors lower gradients• High reliability: don’t pushgradient and RF power to limit•  16.2 MV/m
•For ERL : 10Gy/h * 200 (for cw)= 2 mGy/h = 0.2 rad/h•10
10 years of operation: 100 Gy = 10,000 rad (at 5000h/year)•Same as FLASH/XFEL at ~ 25 MV/m
 Need strong shielding of electronics in tunnel!
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 70Conclusion
2A in ERLs favors operation at modest field
CW
cavity operation
gradients of 15 to 20 MV/mg
 Near cost optimum
 Reduced operation cost (AC power) Reduced risk of field emission and poor cavity performance
Note: Cavity designs with high surface electric peak fields might require
operatingpg at even lower fields!

 Increased reliability
 Simplified cavity preparation (compared to ILC)

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 71

Conclusion
2B at operating gradient has high impact on
Cavityquality factor
cost!
–

Q0 of 21010 at 1.8 K is realistic for the near future Best performing TTF/FLASH module:

Module 6 CMTBM
Meas
Qo/Eacc
Q /E
average gradientdi t 10H
10Hz 500/800
500/800us
Status:13-Mar-07 Esch/Kos/Lil/Lan MKS

3.0E+10
2.5E+10

1.6 K

Qo 2.0E+10
2 0E+10

18K
1.8

Q
Qo



1.5E+101.0E+10((Courtesy
y of
R.Lange et al.
DESY MKS)

2.0 K0

M tthi Li
Matthias
Liepe, ERL
2009

5 University,
10 Ithaca
15 New 20
Cornell
EaccYork[MV/m]

Eacc[MV/m]

25

30

35

Slide 72

Loaded Q,
Q RF power,
power
and
d microphonicsih i
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 73

10, optimal
Cost
vs.Q0=210
PeakCavityFor 16.2
MV/m,
QL: Detuning

1

14
12
power [kW
W]

t

0.8

10
8

Realistic Microphonic Levels• Realistic: 10 Hz to 20 Hz peak detuning• QL= 3.25
3 25 10
107 … 6.510
6 5 107• Microphonics compensation is underway…
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 75



Conclusion
3 is a strong cost driverPeakcavity detuning–

10 Hz peak detuning should be achievable

Needs good mechanical cryomodule design

Need to address / quantify substantial differences in microphonics
levels beween individual cavities!
 QL= 6.5 107

Much higher QL > 108 is not much more beneficial:–

Extra power required for beam loading from path length errors, turn ontransients, …

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 76

Cavity design andHOM ddampingianddBBU
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 77

Cost vs. (R/Q) of Fundamental Mode (G=const)1

norma
alized cost

0.8

 Cavity design should

construction
10 yr operation

0.6

 Few % decrease in

0.4
02
0.2
0
45

be optimizedbti i d ffor llow
cryogenic losses of the
f dfundamentalt l mode.
d50
55TM010 (R/Q)/cell [  ]60(R/Q)G tolerable if
modified cell shape
improves HOM
dampingdap g ssignificantly
g ca t y

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 78

Cost vs. Number of Cells per
Cavity625
2.5

construction
10 yr operation

10

7 cell2

4

Q

normalize
ed cost

3

1.5
1

M
Monopoles
l

10

2

10

0.5
0
0

8 cell9 cell2

4
6
C ll per C
Cells
Cavity
it

8

10

1500

2000

2500
3000
frequency [MHz]3500• >6 cells per cavity desirable, if OK with BBU limit– Q and R/Q of HOMs will increase with number of cells– Risk of trapped modes with very high Q increases as (number of cells)2
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 79

4000



ERL
CavityDesign:Be down
realistic!
Goal ofthe gameis to bring
the BBU figure of merit(R/Q)Q/f for the worst HOMs–



For longer linacs: also (R/Q)G for fundamental mode important tominimize cryo-losses

BUT:–

Real HOM absorber–

Real cavity= ideal absorber= ideal cavity, as designed!

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 80=25  "=-8 =1 "=0
=10  "=-0.1 =2.5 "=5

10

4

Ideal absorber

(R/Q
Q)Q/f

2

[ /cm //GHz]

5
Ideal
RF HOM Beampipe Absorber vs. Real Absorber
10

10
0

10

3

2

1

10
1500

2000

2500

3000

3500

f [MHz]M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 81Effect of Small Cavity Deformations

 Small cavity shape deformations introduce HOM

ffrequency
spreadd betweenb tcavitiesiti ((good)d) But: theyy also influence the R/Q and Q of the HOMs

(bad)!
– Factors of 10 to 100 increases in real cavities have been

observed for certain HOMs at TTF/FLASH and JLAB!
 To study thisthis, we did set up parallel computing of

HOMs in non-ideal cavities with CLANS/CLANS2(cluster with 120 parallel processor cores)
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 82

7-cell Cavities with Small Shape Deformations

 Started by assuming +-1/16 mm random

deformations of all cavity dimensions:
r [cm
m]

15
10
5
0
0

50

100

150

x [cm]

 All cavities have been re-tuned for the fundamental

mode frequency and field homogeneity
 Calculated dipolepmodes a in large
g number of
deformed (realistic!) cavities to be used in realistic
BBU simulations
M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 83

Example: Cavities with+-1/16 mm Deformations
10

10

10

2

0

-2

8

10





Conclusion
4 per cavity, if
Costfavors > 6 cells–

HOM damping and BBU threshold current is sufficient–

R/Q per cell is not lowered too much by requirement to increase iris
diameter for increase cell-to-cell couplingp g in many-cellycavities–

Sensitivity to small shape perturbations is under control

Cornell ERL: 7
7-cellcell cavity with high (R/Q)G

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 85

M tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 86

Outlook Future might bring:– Higher Q0 (Rres<10n), lower field emission

 higher optimal field gradients Eacc
– New SRF cavity materials (Nb3Sn)

 higher optimal field gradients Eacc, higher operating
temperature– < 5 Hz peak cavity detuning, QL = 108

 lower RF power,
power simplified RF input coupler
coupler,…
– More cells per cavity???

 lowero e Matthias
cost Liepe, ERL
M tthi Li
2009

Slide 87
None of these will happen tomorrow, though…
Cornell University, Ithaca NewYorkM tthi Li
Matthias
Liepe, ERL
2009
Cornell University, Ithaca New
York

Slide 88