TTC CW SRF workshop
Highlight
2013/7/17
ERL検討会
Hiroshi Sakai
6/12(Wed)～6/14(Fri)の3日間Cornell大学で行われた。
このworkshopはTTC meetingの番外編で主にCWのSRF cavityやcryomoduleにtopicを絞った会議であり、CEBAFやERLやその他のCWやhighdutyマシンについて色々発表があり、議論を行った。
詳しくは http://www.lepp.cornell.edu/Events/TTCWorkshop/
発表資料も載っております。

Scope of the CW SRF workshop
George Hoffstaetter (Cornell Univ.)• Cornell mainly works for the SRF for ERL
 it works CW condition and need high Q and high Eacc.
• Topics of this workshop(1) Cavity design (KEK, Jlab, Cornell, Berkeley, Fermilab)(2) SRF Gun (HZDR, HZB) & low beta (Fermi, IHEP, IMP) & transversal cavities (APS).
(3) CW cavity operation (Cornell, JLAB, HZB, Fermi)(4) High Q performance and treatment procedure (Fermi, Jlab, Cornell, HZB)
(5) CW couplers (Cornell , KEK, Fermi)(6) HOM absorbers (Cornell, KEK, Jlab, DESY, APS)
(7) CW cryomodule (Daresbury, Berkeley, Cornell, Fermi, Jlab, KEK)
• ERL activities at Cornell Univ.
– ERL apply for light sources, high energy physics, Nuclear physics– Low loss SRF cavities for CW linacs bulk BCP 650C final BCP bake 120C 
Q0=1*10^11 @ 1.6K
– 75mA with NaKSb / 52mA of GaAs and 80pC/bunch : 0.3mm.mrad (core)Cornell ERL project
全体設計
5GeV
100mA

ERL injector test beam lineが現在稼働中。100mAのDC Gunと5MeVまでの超伝導空洞入射器
によるビーム評価を行っている。
また ERL main linac用のcavityを1つ入れたcryomoduleを作成しhigh power testを行った。

(Cornell) ERL milestone(CW operation session) Bruce Dunham on Wednesday(2013.6.12現在)(High Q session) Nick valles on Thursday

(1) Cavity design• KEK main linac cavity (Kensei Umemori)• JLAB upgrade cavity (Gigi Ciovati)• Cornell main linac cavity RF design (Nick Valles)• NGLS and Project-X HOM calculations for couplerneeds (Alexander Sukhanov) calc HOM effect with project X(162.5MHz) &NGLS(1MHz)• Cornell main linac cavity mechanical optimization(Sam Posen: Cornell)
calc cavity structure and pressure dependence
まずは各空洞の設計思想についてCW対応として設計や縦測定、cryomoduleテストが進んでいるKEK,Jlab,Cornellについて主に紹介する。

KEK main linac cavity (K.Umemori)
Vertical test

KEK-ERL design
3GeV & 100mA
Qo=1*10^10@15MV/m#3
Onset =14MV/m#4Onset =22MV/m

Cryomodule test•

focus HOM damping
 600mAのHOM-BBU thresholdまで確保。
 monopoleも±40MHzで避けた計算( <6GHz)• Epk/Eaccがdesign上TESLAの1.5倍
V.Tでは問題なかったが cryomodule testでfieldemissionが増大 。運転のfield emissionが今後の課題
 CW運転ではfield emissionが最大の問題点(提言)Q0 degradiate#3#4
Field emission onset starts 8-9MV/m

CEBAF upgrade cavity (Gigi Ciovati)•

The LL-shape waschosen because of~20% lower Pwall than
HG-shape

Eacc=19.2 MV/m with Q0 ≥8×109 at 2.07 K in CW
operation

•
•

•
•
•

•

No stiffening rings, to increase tunability
New helium vessel design, to replacetitanium with stainless steel for cost and joint
reliability
Optimized waveguide input couplergeometry for Qext = 3.2×107
Nb HOM coupler probes confidently cooled
Optimized position and orientation of HOM
couplers (now only on “field probe” side) for
HOM damping
Pressure sensitivity: ~220 Hz/Torr

C100 cavity

CEBAF C100 Cavity treatments – Production process– 160 µm BCP and pre-tuned by vendor
縦測定後にHPRを– Receipt inspection – mechanical and rf
行っている。
– US >> Bake: 600 C, 10 hrs– US >> EP: 30 µm, @20°C regulated by external water spray– US >> Tune
– Helium vessel welding– Flange lapping– HPR– Partial assembly– HPR >> dry in Class 10 cleanroom– Final assembly, leak check– Bake: 120° C, 24 hrs– Vertical test @ 2.07 K– HPR >> dry in Class 10– String assembly•

Add additional surface treatment– 30 μm EP: increase gradient– HPR (High Pressure Rinse)– 120°C bake: increase Q0

A. Reilly et al., SRF’11, TUPO061.

2 K Dynamic Heat Load vs. Cavity Gradients in CEBAF

P dissipated per cavity -- 2 K load - (Watts)

C20 2009

35

C50
C100-1, 2, 4, 5

Spec for 12 GeV cryomodules

30

*

C50
cryomodules
run here

25
20

C100
cryomodules
will run here

15
Bulk of CEBAF
experience is
here

10

CEBAF 1991

5*

0.7 m cavities

C50 Spec

0.5 m cavities

*

0
0

5

10

15

Eacc (MV/m)

20

25
cer 9/12

HOM absorber

7cell

Cornell main linac cavity design (N.Valles)

long

Optimize
CavityW.R.T. BBU
parameter

long

Introduce
realistic shapevariations(x400/error)

Computedipole HOMs
to 10 GHz
(1692 modes/cavity)

Goal: Maximize Ith > 100mA (under constraints)
Generaterealistic ERL(x100)

ComputeBBU
current±0.125 mm±0.250 mm±1.000 mm±0.500 mm

Fabrication error increase the HOM-BBU threshold current

Loosened machining tolerances
increase relative cavity-to-cavity
HOM frequency spread(good!)
Fabrication Variation (2D)

Design topic• Many cavity design meet requirement ofespecially HOM-BBU threshold current.
• HOM randomization can increase HOM-BBU
threshold.  Cornell make fabrication
variation and calculate by separate cavities• How much can be calculate more than 10GHz
HOMs ?
• Coupler kick
• Program for experimental study for HOM
effects on existing CW linacs.
• How to suppress field emission (Epk/Eacc) ?

(2) SRF Guns & low beta & Transversal cavities• Selected experiences of 6 years Rossendorf
SRF-Gun (Andre Arnold)• CW SRF Photoinjector experience at HZB(Andrew Burril)• Project-X cavities (Timergali Khabibouline)• APS crab cavities (Jim Kerby)• Progresses on China ADS Superconducting
cavity (Peng Sha)
• IMP’s low beta cavities (Yuan He)
SRF Gunの今までの運転経験や現状が前半のtopic。後半はいろんなlow beta & crab cavityについて。APSのCrab cavityは空洞横からLOMを取るというアイデアで斬新。(時間ないので省略)

(3) CW cavity operation• Experience with CW caity operation with highbeam loading at Cornell (Bruce Dunham)• Experience with high loaded Q cavity
operation at JLAB (Tomasz Plawski)• Experimece with high loaded Q operation at
HZB (Axel Neumann)• CW aspects of microphinics compensation(Yuriy Pischalnkov)  LFD compensation(みなさんの方が良く知っているので、省略)• Experience with high loaded Q cavity
operation at Cornell (Mathias Liepe) まとめ
Michrophonics を以下に抑えるかがtopicだった。

Experience with CW caity operation with high beam loading at
Cornell (Bruce Dunham) (Cornell Injector)

Requirements:• 5-15 MeV• 77 pC per bunch• 100 mA average current• 0.3 um emittance(normalized rms)•

Status:• Emittance goals met, simulations
verified• 75 mA maximum average current
63 hour 1/e cathode lifetime at 65 mA• Max energy 13 MeV

Issues
Coupler conditioning (with beam)
Coupler quadrupole fields –> beam
asymmetry
HOM RF absorbing tiles*
Coupler cooling*
Spurious trips, machine protection*

Some of the RF absorbing tiles facing
the beam became insulating at 80 K anddistorted the beam. We removed half ofthe tiles, which still provides adequate
HOM damping.

Beam distortiondue to tile charging

Cryomodule
Cornell ERLInjector
Injector
cryomodule
Complete cryomodule

5X 2-cell cavities(made in house)

HOM loads with
RF absorbing
tiles

Couplers (made byindustry)
Bruce Dunham – TTC Topical Meeting on
CW-SRF 201315

Results
Recent resultsRecent(Cornell
injector)
Ran 65 mA average
current at 4 MeV for 8hours – 2000
Coulombs of charge.
Had 2 RF coupler
trips and 2 spurious
trips.

Cathode lifetime (NaK2Sb
cathode) of 63 hours (1/e).
With the available laser
power, 1 week ofuninterrupted operation ispossible
Bruce Dunham – TTC Topical Meeting on
CW-SRF 201316

Coupler(Cornell
Adjustmentsinjector)
Coupler adjustment
Couplers are adjusted to provide ~0 reflection at the desired current.

Beam Current (0-65mA)

Klystron reflected power (kW)All 5 cavities

Bruce Dunham – TTC Topical Meeting on
CW-SRF 201317

HOM damper
heat
load
with
beam
Do the HOM’s get hot?
(Cornell injector)

Beamcurrent(blue)
0.5 K
HOM
temperature(green)At most 0.5K temperature rise (65 mA, 4 MeV, 2-3 ps rms bunch
length)Bruce Dunham – TTC Topical Meeting on
CW-SRF 201318

Experimece with high loaded Q operation at HZB (Axel Neumann)•Test set up: Horizontal test facility HoBiCaT• Testing fully equipped cavities including
helium vessel, motor- and piezo tuner,
CW modified TTF couplers, magnetic
shielding, etc.
• Temperature range down to 1.5 K,
typically 1.8 K with 100 W@ 1.8 K: 16 mbar ±30 μbar rms• Coupling variable, installations down
to βc=1 possible• RF set up: 19 kW IOT, 400 W solid state
amplifier driven by PLL or Cornell’s
LLRF system• Two cavities tested in parallel orsample studies• Gun cavity tested with diagnostic beamline
Page 19

CW operation: Field stability determined by Microphonics (HZB) Field amplitude variation:
Dynamic Lorentz force, Δf/ΔEacc² = 1Hz/(MV/m)²

 Helium pressure fluctuations
Δf/Δp = 50-60 Hz/mbar,
Gun:100 Hz/mbar

16 mbarHeattransport
dynamics

2.5 mm Niobium walls

 Stochastic
backgroundnoise Deterministic,
narrow-bandsources:
Vacuum pumps

Mechanical oscillations of the Cavity:
Microphonics
Response of theCavity-Helium vessel-Tuner
system:(FEM simulations, e.g.:
Devanz et al. EPAC 2002)

222 Hz151 HzG. Bissofi
Page 20

A tested scheme: Least-mean-square based adaptive feedforward (HZB)FFTΔU (V)

t (s)

IFFT

·H-1

t (s)

Calculationof optimal
FIR filter
parameters

Detuningof the cavity

Δf (Hz)Compensating
signalΔl (nm)External mechanicaloscillationst (s)For white noise excitation
The FIR filter would be
H-1piezoΔf
21

Page 21

Compensation results (HZB)
Single-resonance control:

Results:

QL=6.4.107

ΣFFT

σf = 2.52 Hz

Open
loop
Feedback only
Feedbackand Feedforward

σf = 0.89 Hz
σf = 0.36 Hz

Multi-resonance control:
Piezo resolution seems
to limit control ofneighboring modes

Page 22LLRF studies with U Cornell: Limits of QL (HZB & Cornell)log(σφ)QL=5.107, f1/2=13 Hz
QL=1.108, f1/2=6.5 Hz

Best results:
5.107 0.008°
1.108 0.0093°
2.108 0.0236°

QL=2.108 , f1/2=3.25 Hz
9 cell TESLA cavity
Eacc= 10-12 MV/m
Tbath= 1.8 K
PI piezo loop
8/9-π filter optimized

LF detuning  IOT beam instable
Cavity field trip
Areas with σφ>0.1 were blanked out
Page 23

High QL challenge (JLAB)(Tomasz Plawski)
C100 GDR mode – Original/Modified Tuner

Phase noise
25.6 deg rms /14 Hz rms

Fundamental frequency f0

1497 MHz

Accelerating gradient Eacc

> 20 MV/m

Input coupler Qext

3.2 x 107

Active length

0.7 m

r/Q

1300 Ω/mTunning sensitivity

0.3 Hz/nm

Pressure sensitivity

420 Hz/torr

Lorenz force frequency sensitivity KL~2 Hz/(MV/m)2

Phase noise
7.5 deg rms /4 Hz rms

CEBAF C100 PZT Control (JLAB)

Piezo compensation bandwidth: 1 Hz
PI regulator
Wider bandwidth causes mechanical mode excitation/ instabilities
Substantial improvement for slow detuning ( helium pressure drift or slow microphonics)

C100 One Hour Run (JLAB)現状

2013年11月から本格的にビームoperationがstart(4) Cavity high Q performance & treatment procedures• High Q R&D at FNAL (Anna Grasselino)• High Q0 preservation (Andy Hocker) FNALでモジュール用の磁気シールドを作成＆測定。磁気シールドは重要という結論。。。
• High Q0 R&D at JLAB (Gigi Ciovati)• High Q R&D at Cornell (Fumio Furuta)  BCPとEPのに比較(BCPはHGに適さない)。7cell-Tmapの紹介など。
• Experience with cavity operation in cryomodules test at JLAB(Tom Powers)• High Q cavity operation in cryomodule at Cornell (Nick Valles)• HZB High-Q0 Optimization by thermal cycling (Axel Neumann)
HoBiCaTでの冷却thermal cycleの結果。これらの測定からThermocurrents due to temperature gradientsという仮定をし、その影響を調べた。温度をゆっくり均一に冷やすのが重要。
このsessionは結構盛り上がった。特にCW運転にはQ0を上げるのはdesirableなのでQ0を上げるためにはどれが効くのかなど議論が行われた。

Approach for RBCS(B,T) (FNAL)
Approach
A. Romanenko and A.Grassellino
http://arxiv.org/abs/1304.4516

3.0x1011
2.5x1011
2.0x1011
1.5x1011

Q0• Obtain as many Q(B,T)
measurements as practical at
ALL fields (not only at a single
low field as is customary)

1.0x1011
5.0x1010
0.0
0

5

10

15

20

Eacc (MV/m)

20

15

Rs (nΩ)• At each fixed field fit
corresponding Q(T) to extract
Rres– Also gives Rbcs(T) = Rs(T)Rres

10

Rres = 0.53(2) nΩ
5

Δ/kTc = 1.84(8)

0
1.4

1.6

Bath temperature
28

1.8

T (K)

2.0

2.2

High Q R&D at FNAL (Anna Grasselino)•
Field Dependence ofSurface Resistance for•typical treatments

•
•
•
•

Obtain as many Q(B,T) measurements as practical at ALL fields (notonly at a single low field as is customary)At each fixed field fit corresponding Q(T) to extract Rres
– Also gives Rbcs(T) = Rs(T)-Rres  see backup slide in detail

Medium field Q slope is a combination of both R0(B) and RBCS(B)
RBCS decreases but becomes strongly field dependent after 120C
Medium field Q slope is NOT due to thermal feedback
Stronger R0(B) for BCP vs EP ここらへんは私の勉強不足でちゃんとした結論は言いません。

New surface processing techniques for Q maximization (1) (FNAL)

1.3 GHz, 2K• Systematically low R0• Extra cost savings fromskipping the post
furnace chemical
processing• See also G. Ciovati,
Phys. Rev. ST Accel.
Beams 13, 022002 30(2010)

Annealing with caps+ no chemistry produces
extra-low residual resistance (FNAL)
A.Grassellino et al, http://arxiv.org/abs/1305.2182

New surface processing techniques for Q maximization (2) (FNAL)
Heat treatmentの最後にN2gas
を10分くらい流すとQが良くなったという結果が得られている？
NbNを最初に作っておき、強い表面を作っておくということか？
Heat treatments in nitrogenproduce unprecedented
values of RBCS(B)31

1.3 GHz, 2K

A.Grassellino et al,
http://arxiv.org/abs/1306.0288

High Q0 R&D at JLAB (Gigi Ciovati)
HT extended up to 1400°C with new furnace• Ingot Nb cavity (RRR~200, Ta~1375 wt.ppm), treatment sequence after
fabrication: CBP, BCP, HT, HPR

Phys. Rev. ST Accel. Beams 16, 042001(2013)• Samples’ analysis after 1400°C show:– Reduced H content and ~1 at.% Ti content– Higher energy gap and reduced broadening
parameter– Unchanged mechanical properties

ここらへんは私の勉強不足でちゃんとした結論は言いません。

Experience with cavity operation in cryomodules test at JLAB
Q vs E results 1 (JLAB) (Tom)Jlab C100 moduleでのcryomodule測定の結果。80空洞 - 8空洞 =72空洞

Qo vs E Statistics (JLAB) (Tom)Jlab C100 moduleでのcryomodule測定の結果。割とrequirementに近い値を達成。

Radiation onset (JLAB) (Tom)但し、

Jlab C100 moduleでのcryomodule測定の結果。Field emission onsetの分布は幅広い。

High Q cavity operation in cryomodule at Cornell (Nick Valles)• HTC-1: Follow verticalassembly procedure as
closely as possible• HTC-2: Include side
mounted,• HTC-3: Full cryomodule
assembly-high power
RF input coupler and
N. Valles – High Q Cavity Operation in theCornell HTC – TTC Topical Meeting on CWSRF 201336

HTC-1 (Cornell, Nick)
Superconductor properties

10

10

10

10

-6

10

11

-7

Quality Factor

BCS Resistance [Ω]10Thermal Cycling Investigation-8-9

Measured data
SRIMP Calculation

-10

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

Temperature [K]• Tc = 9.15 K

10

2012/02/29 Pre-Quench
2012/03/12 Post-Quench
2012/03/15 W armup 1
2012/03/18 W armup 2
2012/04/06 100K warmup
2012/04/09 Fast Cool Down

10

0

5

10

15

20

Eacc [MV/m]• Resid. resistance = 6.5 nΩ• RRR of RF layer = 11.8

Temperature Cycling• First cycle > 10 K
• Second cycle > 15 K
• Final cycle > 100 K

N. Valles – High Q Cavity Operation in theCornell HTC – TTC Topical Meeting on CWSRF 201337

HTC-1: Results (Cornell, Nick)• Cavity exceeded Q
specification at 1.8 K by
50%, reaching 3x1010• Q(1.6 K, 5 MV/m) = 6x1010• Exceeded gradientspecifications• RF-based andcalorimetric-based Q
measurements yielded
consistent values
N. Valles – High Q Cavity Operation in theCornell HTC – TTC Topical Meeting on CWSRF 2013

38

HTC-2: Results (Cornell, Nick)
11

Quality Factor• Quality factor, gradientspecifications achieved• Administrative limits
prevented higher fieldmeasurements (notlimited by quench)• Lower Q (than HTC-1)
due to high radiationlevels101010Measurement at 1.8 K
Measurement at 1.6 K
1.8 K Design Specification
5

N. Valles – High Q Cavity Operation in theCornell HTC – TTC Topical Meeting on CWSRF 2013

10

15

20

Eacc [MV/m]

39

Q0>1*10^11 (??) ほんまか？

HTC-3: Results (Cornell, Nick)
Initial Cooldown
1.6 K
1.8 K
2.0 K

11

10

11

Quality Factor

Quality Factor

10

After 10 K Thermal Cycle

10

10

10

5

10

15

Eacc

Initial Cooldown at 16.2
MV/m

20

1.6 K Before Cycle
1.6 K After Cycle
1.8 K Before Cycle
1.8 K After Cycle
2.0 K Before Cycle
2.0 K After Cycle

10

5

10

15

20

Eacc

10 K thermal cycle at 16.2
MV/m

Q(2.0 K) = 2.5 x 1010
Q(2.0 K) = 3.5 x 1010
10
Q(1.8 K) = 3.5 x 10N.10Valles – High Q Cavity OperationQ(1.8
K)
=
6.0
x
10
in the10
10 40
Cornell
HTC–
TTC
TopicalMeetingon
CWQ(1.6 K) = 5.0 x 10
Q(1.6
K)
=
10.0
x
10
SRF 2013

High Q Cryomodules (Cornell, Nick)
He gasoutput• Magnetic shielding is essential• Thermal gradients across cavity should
be minimized to get high Qs• Cavity temperature gradient ~0.2 K• Cool down rate through Tc: ~ 0.4 K/hr

He gas input
6 Cernox temperature
sensors mounted on top
and bottom of end cells
and center cell
Thermal currentをなくしながら冷やせばQ0は上がるはずという結論。難し
いか？？

10 K
Tc
9.0 K
N. Valles – High Q Cavity Operation in theCornell HTC – TTC Topical Meeting on CWSRF 2013

41

Thermocurrents (HZB, Axel Neumann)
Thermoelectric effect:
Voltage due to material andtemperature dependent
charge carrier velocity

U thermo = (SNiobium - STitanium ) ⋅ ΔT
S are Seebeck coefficients

Set up model experiment

Cavity-tank system as „thermoelement“
Close circuit to obtain thermocurrent.
Master thesis Julia Vogt,
see poster WEPWO004
for further details

A. Neumann, TTC CW-SRF meeting, U
Cornell, Ithaca, NY

42

High Q0 Topic• What is the good material and treatment for HighQ0 ?
• Furnace temperture (with N2 gas)
• BCP or EP ?
• HF rinse for finalization• Large grain / fine grain• Baking 120C ?
• Magnetic shield is essential for High Q0• Thermal cycle near Tc is effective for high Q0• How to suppress field emission on string assembly(5) CW couplers• Cornell main linac coupler (Vadim Veshcherevich)• KEK ERL main linac coupler (Hiroshi Sakai)• Project-X couplers (Timergali Khabiboulline) chokeを使った形、ほんまにできるのか？
• JLAB waveguide couplers (Gigi Ciovati)• Cornell injector coupler (Vadim Veshcherevich)• KEK ERL injector coupler (Eiji Kako)
CW対応した各入力カプラーの状況報告がメイン。やはりコーネルのinjectorのカプラーが60kW程度のCWまで対応して、さらにbeam運転しているというのがすごいなという印象。
あとJlabのwaveguide couplerの現状などが知れたのが良かったか？KEKからも加古さんと阪井でcERL カプラーの現状報告。Jlabでは常温agingをしないというのは少し驚き。

Cornell ERL injector coupler (Vadim)

RF Power, kW

Variable :QL=9.2*10^4 – 8.5*10^5
Meet : 5MeV 100mA beam
One coupler : 50kW (TW)
Two window based on TTF coupler

Results of test stand
60

50

40

30

20

10

0
10:00

Traveling wave
11:00

12:00

13:00

14:00

15:00

16:00

17:00

18:00

19:00

Time

210

Present status
 Two of ten couplers were tested on the test
stand up to
61 kW CW.

Temperature, K

190

 High current beam operation will be continued.

150

130

90
10:00

11:00

12:00

13:00

14:00

15:00

Time

16:00

17:00

18:00

19:00

180

T= 180℃@ bellows160
140

Temperature, °C

 Beam current up to 75 mA was accelerated in
the ERL Injector.

170

110

 In the cryomodule, couplers were processed inpulse and CW modes w/o beam; finallyprocessing is going on during high current beam
operation.
 RF power up to 40 kW CW per coupler wasapplied so far during beam operation.

ΔT= 80K
Warm bellows

N Cold Bellow s M iddle Heat Sink
S Cold Bellow s Middle H eat Sink
S 8" Cold C F Flange
N Taper
S Taper
N Tube near TaperS Tube near TaperN W arm Bellows Far End
S W arm Bellow s Far End

N W arm Bellow s H eat Sink
S W arm Bellows Heat Sink
N W arm Bellow s C onvolutions
S W arm Bellows Convolutions

120
100
80
60
40
20
10:00

11:00

12:00

13:00

14:00

15:00

Time

16:00

17:00

18:00

19:00

Water Cooling

KEK ERL injector coupler (Kako)
Test stand results

Doorknob
Coaxialline
Warmwindow
300 K
80 K
5K

Zo =
41.5 Ω

Inner/outer conductor of warm parts were added water cooling

Now Beam operation of cERL started with
Eacc = 7.2, 7.3, 6.9 MV/m
PRF = 3.0, 8.9, 8.1 kW /2
QL = 12.0, 5.8, 4.8 x 105

200 kW, <2ms, 5Hz (1%), 30~40 kW, CW

Basic design
cavityKEK ERL main linac coupler (H.Sakai)Cold window

vacuumWarm window

Cu plate:30um

N2 gascooling

bellows

5K 80K
Cu plate:10um
Variable (±5mm)

Cu plate:150um

RF power

Cold window moved by rod•Basic parameters
frequency : CW, 1.3GHz
Accelerating gradient : Max 20MV/m (First)
input power：max 20kW , standing wave (michrophincs Δf=50Hz)
loaded Q(QL)： (1-4) * 107 (variable coupling)•47
arc signal coincidewith electron event
Power test @ test standPin_f(30us 5Hz) 75-76kW

Present status
105kW(20Hz,200us), 43kW CW power with traveling wave @ test standFiber arc sensor works effectively for ITL within 10us and see processing.
cryomodule test of 2K condition up to 15kW SW on detune condition.
We can keep 14MV with 4.5kW power feeding with QL=1.5*10^7 @2K
Michrophonics of Δf=7Hz of pk-pk. This is much smaller than expected.
No significant temperature rise was observed under 15kW power feeding.

Arc signal was delayed when we
processessed –> arc sensor works well

Original CEBAF pairs (Gigi Ciovati)••••

Two 5-cell cavities back to backWaveguide FPC’s with “stub on stub”
6 kW CW at full power (later 8 kW)
Ceramic cold windows close to beam line, inside helium vessel– Cold window charging by field emission and arcing was a major
cause of downtime– Managed by developing trip rate models for each cavity basedon Fowler Nordheim field emission• Waveguide HOM dampers cooled by helium (except for FEL)
• Polyethylene warm windows (later changed for ceramic)

Reworked “C50” pairs (Gigi Ciovati)• Reprocessed 10 weakest modules– Reworked original cavities (BCP + HPR)

– Gradients improved from ~5 MV/m to ~12MV/m• 8 kW CW maximum power• Added dogleg to shield cold window– Eliminated cold window arcing• Rework of tuners to reduce backlash
Dogleg waveguide• Next module will be the same except EP and remove somemagnetized components from the tuner

JLAB HC Cryomodule RF High Power Window (Gigi Ciovati)

High power capability required.
•

A waveguide RF window was preferred to a co-axial
design• Design is based on water cooled scaled PEP-II type window
design, (tested near 1 MW CW at 700 MHz for LEDA)• 1497 MHz prototypes have been built, window ceramic
thickness optimized in test fixture• High power tested to 60 kW CW at JLab FEL (limited by
klystron)

PEP-II 476 MHz waveguide
window assembly

LEDA 700 MHz waveguide
window assembly

JLab 1497 MHz window on test box

High power IR image

Rimmer, Elliott, Marhauser, Powers,
StirbetCW coupler topic• Cold窓は必要か？ 割れない実績があるならCold窓
なしでもいいというのはJLABの主張。Mollerは反対していたようだが？？
• 窓が割れた時や運転でビームに対してITLを如何に早く落とすか？  arc sensor や Electron probeなど、使えるのかと聞かれたので私からはCold窓でfiberを使って a few usでITLが可能であると主張しておいた。
• Wavegude とcoaxialどちらがいいか？結論はでなかった。Wave guideのCold窓は無い方がいいが、それをwarmに置いて運転する分には今のところ問題なし。static入熱に関してはメラーはwavegudeの方がcoaxialより4倍大きいと主張。またvariableができないのは難点などの主張あり。Jlabからは内導体の発熱をどう抑えるかなどの反論あり。

(6) HOM absorbers• Cornell HOM beamline loads (Ralf Eichhorn)• KEK HOM couplers (Eiji Kako)• KEK HOM beamline loads (Kensei Umemori)• CEBAF waveguide absorbers (Gigi Ciovati)• XFEL beamline loads and HOM couplers for CW(Denis Kostin)• HOM dampers development for the APS upgrade
short pulse X-ray (Geoff Waldschmitt)このsessionも盛り上がったsessionの一つ。特にCW運転にはコーネルなどでSiCを使ったHom absorberをテストしているが、leakに悩まされている。KEKからはHOM coupler
は現在発熱が問題であると加古さんが発表。HOM absorberはcERLに組み込んで動作的には問題ないが、ferrite with HIPでクラックが入るとの報告を梅森さんから報告。CW
用のHOM absorber開発が難しいと再認識。ここらへんで、 CW用ではないが、Denisが
XFEL用に設置したHOM coupler &HOM absorber (AlN)がうまく動いているとの報告。
これとは別にCEBAFのwaveguide absorberはこれからが期待か？

Cornell Main Linac HOM Absorbers (Ralf)
40 to 80K intercept

Flange for disassembly

5K intercept

No HOM Loads
With HOM Loads
Q0 > 2*1010 for thefundamental mode
Flange to cavity

Shielded bellow

SiC absorber ringbrazed to metal ring

Cavity for HTC3

• Full-circumference heat sink to allow>500W dissipation @ 80K• Broadband SiC absorber ring
• Includes bellow sections• Flanges allow easy cleaning• Zero-impedance beamline flanges
Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 201353

Issues for cornell SiC absorber (Ralf)

Shrink-fitting SiC to Ti-5

• We have a vacuum to vacuum
leak in HTC 3• Tungsten becomes porous underbrazing cycle• SiC is not a nice material• Strong outgasing• High particle contamination• Tends to chip
• How reliable is the material?

Flange to Cavity

Finding on a full cylinder

3.5E+04

at ~145K

3.0E+04
2.5E+04
2.0E+04
1.5E+04
1.0E+04
5.0E+03
0.0E+00

6.0

Conductivity σ [1/Ωm]

Resistivity (Ω)

Tip off

Ti Cylinder withintegral cooling

Flange to Cavity

4.0E+04

Next Version

マテリアルonly

5.8
5.6

Thermal Shrink Fit

5.4
5.2

SiC

5.0
50

resistivity

0.00

150
250
Temperature [K]100.00200.00 300.00 400.00
SiC Temperature

今回のダンパーに関してもかなり自信がなさそう。

•

350

Use AlN instead of SiC?
Jlabのマテリアルを使うのか？？

Ralf Eichhorn, Cornell – Cornell’s HOM Beamline Absorbers – TTC Topical Meeting on CW-SRF 2013

54

(CEBAF) Cold measurement of new materials• Special waveguide test insert allows cryogenic
RF measurements of test loads and material
samples
Graphite loaded SiC

Example: Reflection response ofdifferent
AlN-basedcomposites
measured at room temperature (r.t.)
and 2 K, compared to original CEBAF
load.

Test setup in the vertical Dewar (left),
CEBAF absorber (top right) and two
different wedge absorber assemblies(bottom right) made of ceramic AlNbased composites.
MARHAUSER PAC09

KEK ERL HOM absorber (K.Umemori)
HOM absorber (SBP 1つ, LBP 2つ)・HIP ferrite (IB004) on Copper beampipe
・Outside: bellows, Inside Comb-type RF
bridge・Operation at 80K. (expected 150W
HOM power 3ps bunch length)
・Check enough absorption ability offerrite at 80K
Their behavior, frequency and loaded Q
values, were generally agreed withcalculation results on cryomodule test
107
106

•

PU
HOM1
HOM2
HOM3
calc (Dipole)calc (Monopole)

Loaded Q

105
104
103
102
101
1000

1500

2000
Frequency (MHz)

2500

3000

Under thermal cycle between 300K and
80K, we observed some crack aroundedge of ferrite damper.

Low temperature RF character (Umemori)Good absorption at low temperature. In cryomodule test , this damper works well.
But under HIP condition some crack was observed.
And we also see the high resisitivity on 80K  charge up. And no-bakable.
We also would like to search another material like SiC and/or AlN.

KEK ERL HOM coupler (Kako)
Design and Measurement

By K. Watanabe
Eiji Kako (KEK, Japan)

TTC at Cornell, 2013 June 13

Qextは問題なし。

58

RF Feedthroughs (Kako)
By K. Watanabe

Cu
Cu
Sus
Nb
Mo
Al2O3
Sus

Type-II’m (i.c: Mo, o.c: Cu) “male pin”
Eiji Kako (KEK, Japan)

Order for next,
Type-III ; Al2O3  Sapphire
Sus flange  Ti

TTC at Cornell, 2013 June 1359

Dynamic Temperature around HOM Couplers (No.3 cav in module) (Kako)
No.3 Cavity (CW)

No.3 Cavity (50 ms, 2 Hz, 10%)
HOMfeedthrough

HOMfeedthroughHOM-top

Eacc atantenna quench
現状の問題点
低い電圧でHOMのprobeがクエンチしている。
Eiji Kako (KEK, Japan)

HOM-topNo.3 Cavity (10% Duty)

No.3 Cavity (CW)

HOM-1: 4 MV/m

HOM-1: 1.7 MV/m

HOM-2: 6 MV/m

HOM-2: 2 MV/m

HOM-3: 3 MV/m

HOM-3: 1.7 MV/m

HOM-4: 15 MV/m

HOM-4: 5 MV/m

HOM-5: 3 MV/m

HOM-5: 3 MV/m

TTC at Cornell, 2013 June 1360

XFEL beamline loads and HOM couplers for CW (Denis)
0.27 W 0.74 W
1 fo
Modes under cut-off

10

1.75 W

1.08 W100

1000∑ propaga ng= 3.6 W
f [GHz]Propagating Modes

The XFEL beam line absorbers suppressing propagating modes have capacity of 100 W, whichmakes them suitable for large DF operations .

Bellows
Beam

Ceramic ringto 40-70 K

Copper stubAbsorbing ceramic ring
Chamber housing absorbing ringWorks well
Beam test said
1.5 Phom  1K
temperature rise

XFEL HOM coupler simulation work (Denis)

Gap :1.27mm

plot max. 0.022 A/m with 1
W input tube power

HOM absorbers topics• Are we happy? (Cornell case  no)• Maybe not! (cornell ,KEK, Jlab , DESY)– What is the best broad-band absorbing material?
– How reliable is it? (blasing ? , HIP bonding)– How to realize the vacuum barrier?
– How much should we care about cleaning issues?

• HOM coupler or HOM damper ?  damper
can absorb the large heat load.
• Waveguide or beamline load ?
waveguide is better than beamline load on
the view points of packing factor.

(7) CW cryomodule• International ERL module (Alan Wheelhouse)• NGLS modules (John Corlett)• Cornell MLC (Ralf Eichhorn)• CW cryomodule design for Project X (Yuriy Oriov)• JLAB upgrade module cost and optimization (TomPowers)• KEK ERL injector module (Eiji Kako)• CW operation of XFEL module (Wolf-Dietrich
Moeller)• KEK ERL main linac module (Hiroshi Sakai)
今まで色々出てきたので、詳細は割愛。Daresburyでinternational ERL moduleがようやく冷却試験を開始。Cornellなどは6個入り空洞の1 moduleを検討しており、曲がりや
michrophonicsなどを検討。あと、XFELはHOMの改善が課題 CWの熱負荷テストも行った。
KEKではcERLに組み込んだinjectorはビーム運転開始を報告。Main linacはパワーテスト。

TTC next special topicsの提案(G.Hoffstatter) &次回• Next special topics agenda– High Q (Fermiが主催でやるか？)– Michrophonics suppression (Cornell , HZB ??)– Field emission (KEK ??)– Power source (Solid state ampなど)– LLRF (これは別でやっている)– HOM absorbers (potential for collaboration)– Couplers and copper coating– Warm cold transition (?)
非常に好評だったので、次回も色々テーマを絞ってspecial topicをやっていければとのこと。

TTC general meeting：次回は2014年3月24日～3月27日 @DESY

TTC CW SRF meeting (写真)