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~ ~ ~ ~ FERMILAB-SLIDES-18-121-TD Status of HOMS Spectra Measurements in 1.3 GHz Cavities for LCLS-II -------- ~ & ,. NATIONAL -- -- e ACCELERATOR ... LABORATORY Andrei Lunin CFermilab (on behalf of TD/SRF Group, Fermilab)

slide-1
SLIDE 1

Status of HOMS Spectra Measurements in 1.3 GHz Cavities for LCLS-II

Andrei Lunin

(on behalf of TD/SRF Group, Fermilab) HOMSC2018 ICFA Mini Workshop 1-3 October 2018

FERMILAB-SLIDES-18-121-TD This docu ment was prep ared by [COL LAB ORA TION NAM E] using the resou rces

  • f the

Ferm i Natio nal Accel erato r Labo rator y (Fer milab ), a U.S. Depa rtme nt of Ener gy, Offic e of Scien ce, HEP User Facili ty. Ferm ilab is mana ged by Ferm i Rese arch Allian ce, LLC (FRA ), actin g unde r Contr act No. DE- AC02

  • 07C

H113 59.

This document was prepared by [COLLABORATION NAME] using the resources of the Fermi National Accelerator Laboratory (Fermilab), a U.S. Department of Energy, Office of Science, HEP User Facility. Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under Contract No. DE-AC02-07CH11359.

  • @ENERGY
Office of Science

~ ~

~· & ,.

NATIONAL

  • - e

ACCELERATOR

~

...

~

LABORATORY

CFermilab

slide-2
SLIDE 2

10/01/2018

Outline

HOMSC2018 ICFA Mini Workshop

  • Overview of the LCLS-II 1.3 GHz Cryomodule (CM) assembly
  • CM RF quality control (RF/QC) procedure at Fermilab
  • Measurement of HOM spectra at CM Test Facility (CMTF)
  • HOMs data processing
  • Operating passband statistics
  • Dipole HOMs statistics
  • Monopole HOMs statistics
  • Cavity vendors performance
  • Summary

2

  • ----------------------0

Fermilab

slide-3
SLIDE 3

Motivation

10/01/2018 HOMSC2018 ICFA Mini Workshop

HOMSC2014, A. Sukhanov et., all

???

  • Measurement of actual HOMs parameters @2K insures a reliable

model of resonant HOMs excitation in the LCLS-II linac

  • HOMs statistics allows to estimate and to compare a consistency of

cavities mechanical tolerances for different vendors

3

Motivation

  • SRF cavities are very good resonance systems with multiple eigenmodes

(HOMs) with very low losses (high Q-factors)

  • Beam of charged particles interacts with HOMs in SRF cavities
►

Single bunch interaction

  • incoherent losses and wake fields
►

CW beam may have beam harmonics closet

  • resonance excitation of HOMs

~

~

,,'r

,, ,,

  • at exact resonance beam power loss may be high

,,,,

,,

  • for monopole modes:

Plass = /1

~ (R/Q)r@ ►

For a single cavity analysis of non-propagating modes is sufficient

OFermilab

slide-4
SLIDE 4

10/01/2018

LCLS-II Linac

HOMSC2018 ICFA Mini Workshop

  • 4 GeV CW SRF Linac: 35 (+5) 1.3 GHz CMs , 50/50 by JLab & Fermilab
  • Single 1.3 GHz CM: eight 9-cell TESLA-type cavities (280 cavities in linac)
  • CW Beam: 0.1-0.3 nC bunch charge, 1 MHz rep. rate, 0.3 mA (max)

average beam current

  • HOM damped Q-value: ≤ 106 for HOMs with high R/Q

4

LO

L1 L2 L3

(fJ = *

(p =- 21°

HL

(fJ = - 21° (fJ = 0

V0 =94 MV V0 =223 MV V0 =1447 MV V0 =2409 MV /pk = 12 A /pk = 12 A

(p =- 165° /pk = 50 A /pk = 1.0 kA Lb = 2.0 mm Lb =2.0 mm V0 =55 MV Lb= 0.56 mm Lb = 0.024 mm

CMOl CM2,3

3.9GHz

CM04 .. CMlS CM16 .. CM35

Functional Requirements Specification Document Document Title: 1.3 GH z Supe, rconducting IRF Cryomod ule Document ! Number: LCLSll-4.5-FR~0053-R1

Page 3 of 15

1 Introduction Fermi ab and Jefferso Lab are collaboratiing w· h SLAG on their LCLS-I1 1 1 upgrade project by supplying SRF design and fabricaitiion expertise W- The .aocelernting strudures will l utilize

OFermilab

slide-5
SLIDE 5

10/01/2018

1.3 GHz LCLS-II Cavity Coupler Ports Changes

HOMSC2018 ICFA Mini Workshop 5

HOM antenna FPC antenna

Ø11 x 0.1 mm Ø7.8 x 0.5 mm

ILC LCLS-II ILC, XFEL LCLS-II

  • Smaller size of HOM antenna tip and larger the f-part gap for minimization
  • f local RF losses
  • Weaker FPC coupling (~ by one order) for matching with beam current

and lowering input RF power

Changes to accommodate CW operation:

Original antenna Antenna tip cut by 8.5 mm

..,....----

  • ,

I

O ext ~ 4e7 I

OFermilab

slide-6
SLIDE 6

CM assembly RF/QC at Fermilab

10/01/2018 HOMSC2018 ICFA Mini Workshop

Cavity RF/QC:

  • RT Spectra
  • HOM Notch
  • Cables Integrity
  • 2K Spectra
  • FPC tune-up

2K HOM Spectra

MP9 ICB

receiving

Income RF/QC)

IB1 (VTS)

shipping

CMTF IB4

6

J:

...

::, V)

I

TOTIJNHEL
  • I.

~

[

WEST SRFCAVITY VACUUM BAKE FURNACE AREA EAST CLOSED AREA OPENAAEA CLEANROOM DOORS

t

I I I

.l'a "•' '"J ANTE SRFCAVJTY 120C BAKE OVENS AREA CLEAN ROOM CLASS 1000 (311FT. X 24 FT.)
  • ·~
200 FT. CLASS 1000 SOFTWW. CLEAHROOM

t l

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Q)

E

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a:

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g

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! 25 FT.

,~E !I

  • ~ I
CAVITY STRING ASS EM Bly iEA

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i

fs'oE~:~~.

fLASS100 ~ so

~ Cl,.E#JIIIQOMMI HAIIDUMOUNIT ONE 25 TON CRANE z ~ J: O>

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slide-7
SLIDE 7

Cryomodule Cold Test @CMTF

10/01/2018 HOMSC2018 ICFA Mini Workshop

HOMs 2K Spectra Measurements

  • Cables: 20m ⅜” Heliax, ~3dB loss
  • HOM1 to HOM2 S21 signal
  • Agilent E5071C NWA, <4.5GHz
  • LabVIEW data acquisition
  • Frequency sub-ranges: 5
  • Step: 0.25 .. 2 kHz
  • Max Qext: 5E6

7

  • ----------------------0

Fermilab

slide-8
SLIDE 8

Frequency [MHz]

1500 2000 2500 3000 3500 4000

S21 [dB]

  • 100
  • 80
  • 60
  • 40
  • 20

Rǁ/Q, R⊥/Q, [฀ , ฀ /cm2] 10-2 10-1 100 101 102 103

S21 raw data R/Q - Dipole Bands 1&2&3 R/Q - Monopole Bands 2&3 R/Q - Monopole Bands 4&5

HOMs 2K Spectra @CMTF

10/01/2018 HOMSC2018 ICFA Mini Workshop

  • High risk HOMs: Dipole bands 1&2&3, Monopole band 2&5
  • Dipole #3 and Monopole #5 bands interferes with other HOMs (difficult to sort out)
  • Logged CM HOMs data: Dipole bands 1&2 and Monopole band 2

8 Frequency [MHz]

1500 2000 2500 3000 3500 4000

QEXT

1e+3 1e+4 1e+5 1e+6 Dipole Bands 1&2&3&4 Monopole Bands 2&3 Monopole Band 5 Quadrupole Band 1

  • I

I

  • \. '

~:

  • ·

E

  • ·
  • I
  • ., ,

. .....

~--

.-

  • ----------------------0

Fermilab

slide-9
SLIDE 9

Operating Passband 2K Spectrum

10/01/2018 HOMSC2018 ICFA Mini Workshop

  • Operating band monopole modes may generate up to 1 W power, if in resonance

with the harmonic frequencies of 0.3 mA average beam current

  • High Q-value (up to 109): difficult to locate and measure
  • Slow S21 data acquisition: BW <20 Hz
  • We take data for 3 cavities in the CM (left, right and middle)

9

~ 1W

l.000E+09

<Q>

1.000E+08

I

l.000E+07

I

I

■

■

  • •

■

1

2 3 4

5

6 7 8 9 1.00E+07

R/Q<Q>

  • '
/

'

{

l

\

/

1.00E+06

' .....

  • 1.00E+0S

1.00E+04 1

2 3 4

5

6 7 8 9

  • ----------------------0

Fermilab

slide-10
SLIDE 10

HOMs Data Processing

10/01/2018 HOMSC2018 ICFA Mini Workshop 10

  • Data filtering issues: noise, spurious peaks, bands overlapping
  • Final sorted HOMs data are attached to each CM traveler

Mathcad script for finding F&Q Sorted HOMs data

10~-~ ~ ~ ~ - ~~---- ----- - -----~ ~ ------------------+-----+~ ---i

9-- 8 7 6 ' 5 3 2 O'------' 1e+9 ---------------------------

j 1e+8

1e+7

..

  • '
1275
  • ~ •

.

\ -
  • CAVITY#1

.

CAVITY#2

.

CAVITY#3

.

CAVITY#4

.

CAVITY#S

.

CAVITYl6

.

CAVITY#7

.

CAVITY#8

.

le+6
  • .

. . . .

.

CAVITY#1 CAVITY#2 CAVITYt3 CAVITYU CAVITY#S CAVITYl6 CAVITYt7 CAVITY#S
  • -~---------~---------~------ 1·

'

  • le+S --',:.-L---~---------,·---------+---------

LCLS-11 Cryomodule Testing at CMTF (RFCG)

464255 Rev. G

.;

.

,

  • .
I

.

.. '

.

  • i

.

  • le+3
1280 1285 1290 1295 1300 1600 1650 1700 1750 1800 1850 1900 Freq., [MHz] Freq., [MHz] e+6

r

e+5

'

i

' '

  • ---+-----t-----i-----r--

!

I

!

. .

I i,--,.,-....,.,,.-----,- 20

.

CAVITYl1

.

CAVITY#2

.

CAVITY fl

.

CAVITYIM

.

CAVITYU

.

CAVITY IN

.

CAVITYf7

.

CAVITY ff

'

  • 30
  • 40
A Et
  • 50
  • 60
  • 70
:!.9"103

' ! I

'

  • -----t----

' ' I

'

I I

  • .

..

t- ➔ -~

~----

..

.. .

..

..

  • - .

'

. '

  • -----1,-----L,
____ J

__

  • ___
  • L, ---e .J, _____
:-• e+4 .-. -~-----!-----.J-----!----- 2360 2370 2380 2390 2400 2410 2420 2430 2440 2450 2460 2470 Freq., [MHz]

OFermilab

slide-11
SLIDE 11

Statistics: Operating Passband Frequencies

10/01/2018 HOMSC2018 ICFA Mini Workshop 11

  • Cavity Vendors: pCM01 – 8 by AES, 9 production CMs – 50 by RI & 22 by EZ
  • AES cavities were procured for the ILC prototyping and passed many clean&tune steps
  • There is a large systematic frequency span between RI & EZ spectra (dies error, e/b welding ?)
  • The average length of RI’s cavities is ~1.5 mm shorter than the EZ’s after field flatness tuning

Cavity Length Error [mm]

  • 2
  • 1

1 2 Count 2 4 6 8

RI EZ

RI, EZ - Monopole Band 1

1.400

■ EZ

1.200

~

1.000

■

RI

~ 0.800

■

<EZ>-<RI>

Z 0.600 II ~

II II

D

VI 0.400

Ill

  • 1

0.200

II

  • ·

0.000

  • 1

2 3 4 5 6 7 8 9

Mode# RI, EZ, AES Monopole Band 1

1.000

■

EZ

~

0.800

■ RI N ■ AES :::c

~ 0.600

G: Q.400

I-

VI 0.200

I ■

I ■

I ■

0.000

  • • ·- --
  • - -

1 2 3 4 5 6 7 8 9

Mode#

OFermilab

slide-12
SLIDE 12

Statistics: Operating Passband Q-loaded

10/01/2018 HOMSC2018 ICFA Mini Workshop 12

  • Both RI and EZ spectra deviate from the spectrum of ideal cavity used in HFSS
  • There is a good agreement of average Q values with HFSS simulations

# 1 2 3 4 5 6 7 8 9 F [MHz]

1276.62 1278.67 1281.82 1285.73 1289.91 1293.87 1297.12 1299.25 1300.00

Q-loaded

6.71E+8 1.73E+8 8.13E+7 4.92E+7 3.45E+7 2.69E+7 2.27E+7 2.07E+7 4.0e+7

ANSYS HFSS

<Q>

1.000E+08

I

1.000E+07

I I I

I

I

I

I

1274.656 1276.883 1280.313 1284.981 1288.584 1293.337 1296.870 1299.198 1300.000

■ EZ

5.402E+08 1.464E+08 7.445E+07 4.941E+07 3.407E+07 2.797E+07 2.478E+07 2.418E+07 4.000E+07

■

EZ 7.058E+o8 2.014E+o8 9.004E+o7 6.435E+o7 4.038E+o7 3.495E+o7 3.000E+-07 3.021E+o7 4.000E+-07 QMAX

<Q>

1.000E+08

I

1.000E+07

I I

I

I

I

I

I

1275.974 1278.113 1281.362 1285.383 1289.659 1293.716 1297.052 1299.248 1300.000

■ RI

5.907E+08 1.510E+08 6.438E+07 4.494E+07 3.359E+07 2.785E+07 2.568E+07 2.402E+07 4.000E+07

■ RI

9.519E+o8 2.616E+o8 9.547E+o7 6.001E+o7 4.580E+o7 3.391E+o7 3.094E+o7 3.250E+o7 4.000E+-07 ~AX

OFermilab

slide-13
SLIDE 13

HOMs Statistics: Monopole Passband #2 Frequencies

10/01/2018 HOMSC2018 ICFA Mini Workshop 13

Frequency [MHz]

2445 2450 2455 2460 2465 2470

Count

2 4 6 8 10 12 14

RI EZ

Mode #9

12.000 10.000

,.

::c: 8.000

~

>

6.000 w C 4.000 I- VI 2.000 0.000 35.000 30.000

,.

25.000 ::c:

~ 20.000

Z 15.000 ~ VI 10.000 5.000 0.000

1.

11

I ■

11

RI, EZ, AES Monopole Band 2

  • I. 1

. I. 1

. 1.

12 13 14 15 16

Mode# RI, EZ, AES Monopole Band 2

1 .1 111 1

.. 1 .. 1

  • 12
13 14 15

Mode#

16 ■

EZ ■

RI ■

AES

I ■

I ■ I ■

17 18 19

i

D

t

■

EZ ■ RI ■ <EZ> - <RI>

I ■■

111 111

17 18 19

vFermilab

slide-14
SLIDE 14

Q-loaded 1e+4 1e+5

Count

2 4 6 8 10 12 14 16 RI EZ

HOMs Statistics: Monopole Passband #2 Q-loaded

10/01/2018 HOMSC2018 ICFA Mini Workshop 14

~ 10W

Mode #9

  • 5 RI cavities have high Q-loaded of the M2_9 mode, EZ’s are OK

1E+6 1E+5 1E+4 I I I I <

;

I

I

I I

1E+3

2.69SE+o6 5.475E+o5 3.127E+o5 1.311E+o5 7.336E+o4 2.803E+o4 3.660E+o4 1.078E+o5 6.825E+o4 ~AX

~

.

2370.886 2377.146 2386.554 2398.397 2411.573 2425.189 2437.375 2446.661 2452.890

■

EZ

6.134E+05 1.935E+05 1.056E+05 3.694E+04 3.229E+04 1.347E+04 2.250E+04 3.624E+04 4.339E+04

<Q>

1E+5 1E+4 I I I I

I

I

I I I

2.202E+o6 7.112E+oS 7.490E+o5 2.776E+o5 4.760E+o4 3.404E+o4 7.511E+o4 1.906E+o5 4.854E+o5

1E+3

~AX----~--

2383.383 2388.410 2396.326 2406.715 2419.070 2432.331 2444.692 2454.672 2460.997

■

RI

4.184E+05 1.299E+05 6.128E+04 4.813E+04 1.544E+04 1.720E+04 2.967E+04 4.452E+04 1.002E+05

1E+8 1E+7 1E+6 1E+5 1E+4 1E+3 1E+2 2375 2380 I 2385 I 2390 2395 2400

R/Q*Omax

I

I

I

2405 2410 2415 2420 2425 2430 2435 2440

D

2445 2450 2455 2460

OFermilab

slide-15
SLIDE 15

HOMs Statistics: Dipole Passband 1&2 Frequencies

10/01/2018 HOMSC2018 ICFA Mini Workshop 15

The triangle shape of RI and EZ dipole spectra frequencies span might indicate the difference of the dies aperture between vendors

Frequency [MHz]

1870 1871 1872 1873 1874 1875

Count

5 10 15 20 25

RI EZ

Mode #28

Sensitive to cell’s apertures

RI, EZ, AES Dipole Bands 1&2, Frequencies Deviation

6.000

■

EZ

~

5.ooo

■

RI

;

!Iii II II II II II II II II II II II II II II II J

.

.t 1

1 I .. .

J

1 .J 1 1 1

II 1

J

11 ..

t

,I

  • ~ ••
  • • I_

,

  • ~

; . .. .

l .. _j

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 12.0~

V V

RI, EZ Dipole Bands 1&2 Frequencies Span

■

EZ

10.000 ~

■ RI

1

II 111 ~ ~ I

I

I

I

1 1 1 1 ~

I

1 1 I

~

1 1 1 I

~

I ~

I ll

I~

1 1 1

II Il

l

I ~

I ll

I ll I~

d i

1 l1 1 l1

1 1 , .i: .

;:z ~ :

~ : ~ ,I. L

I_

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Mode#

D

  • -------------OFermilab
slide-16
SLIDE 16

HOMs Statistics: Dipole Passband 1&2 Q-loaded

10/01/2018 HOMSC2018 ICFA Mini Workshop 16

1e+4 1e+5 1e+6

Count

5 10 15 20 RI EZ

Mode #28 RI EZ

... ... ... ... ... ... ... ... ...

m m m m m m m m m

+ + + + + + + + +

I-' I-' I-' I-' I-' I-'

w

. I > , u, a,
  • .J

w

. I > , u, a,

m m m m m m

1 6 1 7 . 1 2 7 1605.335

+ + + + + +

I-' N

w

.I>, V ,

a,

I-'

1617. 6 7 9 1605.897

a,

I-'

w 1624.744 1613.786

I

1625.326 1614.335

I-'

I

i

w 1 6 3 7 . 4 4 2 1627.828 1638.051 1628.301

I-'

I I

a,

  • -.J

1655.288 1646.672

.I>,

I I

1655.956

I

1647.075

I I-'
  • -.J

I I I I

1677 .536 r:::::a 1669 . 837

V ,

1678.229 1670.129

I-' I
  • -.J

I

1 7 3 . 2 1 2 1696.068 w

V ,

1 7 3 . 9 4 2 1696.530

I-'

I I

1730.881 1724.406

  • -.J

;o

a, a,

...........

1 7 3 1 . 5 8 7 1724.754

□

*

1158.790 E772 I 1753.079 __

1 I-' I
  • -.J

3

I

□

1753.453

I

IJ:)

I

a,

"'

X

1759.491

'

I

I I

1 7 8 6 . 1 5

QJ I-'

1781.613 - 0. 1786.784 c::::::::z I

(1) N

0.

  • -.J
I

1782.106 -.,

I

QJ

1795.814 0. 1792.986

(1) I-'

I

00

0.

V ,

/--.., 1796.519

1793.368

00

I ) 1 8 3 6 . 9 7 5 1831.388

■ ■

I-'
  • ,-

~ :t> gg

l

I

QJ

<

1837.176 1831.565

(1)

m

~- ""'

3

QJ

1851.961 1848.165

O'Q C (1)

3

1852.201

■ ■

1848.457

s

:t> 1863.928

< 1861.436

QJ (1)

~- ""'

1864.164

3

QJ

1861.763

O'Q C (1)

1872.599

3

1871.212 1 8 7 2 . 8 5 8 1871.419 1878 . 6 5 4 1877.920 1 8 7 8 . 8 7 3 1878.128 1 8 8 2 . 7 5 1882.082

.,,

I I I I

1882.938 1882.690

(1) I

1 1

1 8 8 5 . 1 9 2 1884.851

"'"'

3 I

I

1 1

1 8 8 5 . 3 7 5 1885.261

=1

I 1886.411

1886.129

~I

I 1886.687

1886.513

slide-17
SLIDE 17

10/01/2018

Cavity Vendors Evaluation

HOMSC2018 ICFA Mini Workshop 17

Vendor Monopole Operating Band Dipole Bands 1&2 Monopole Band 2 rms span rms span rms span RI <0.20 <0.6 <1.5 <8 <2 <9 EZ <0.15 <0.5 <1.9 <6 <5 <18

HOMs frequencies [MHz]

Vendor Mode 7/9 Operating Band Mode #14 Dipole Bands Mode #9 Monopole Band 2 rms max rms max rms max RI 2.5E7 3.0E7 4.6E4 6.0E5 1.0E5 4.9E5 EZ 2.4E7 3.1E7 3.8E4 7.8E4 4.3E4 6.8E4

Danger HOMs Q-loaded

  • ----------------------0

Fermilab

slide-18
SLIDE 18

10/01/2018

Cavity Vendors Evaluation cont.

HOMSC2018 ICFA Mini Workshop

  • HOMs frequencies
  • Both RI and EZ demonstrate similar HOMS frequencies r.m.s.
  • There are significant offsets between RI and EZ HOMs spectra, few time

larger than frequencies rms for operating and dipole bands.

  • RI cavities are longer than EZ by about 2 mm
  • HOMs Q-loaded
  • Both RI and EZ demonstrate similar Q-loaded for the operating band
  • Few RI cavities have significantly high Q-values of danger dipole and

monopole HOMs

  • Maximum measured danger HOMs Q-loaded are about 2-3 times larger

than ones predicted by simulation for the ideal cavity geometry.

  • Danger HOMs Q-values are below the LCLS-II requirements (<106)

18

  • ----------------------0

Fermilab

slide-19
SLIDE 19

10/01/2018

Discussion

HOMSC2018 ICFA Mini Workshop

  • Danger HOMs: 7/9 pi, dipole 2nd #14, monopole 2nd #9
  • Shall we try to track dipole 3rd and monopole 5th passbands? How danger they are?
  • HOMs spectra of RI and EZ vendors are significantly different
  • Is there an optimum solution how to put them in a linac? Randomly? Neighbor cavities of different vendors

might reflect the HOM signal of propagating modes. Too late to change for the LCLS-II but we can think about for the ILC

  • Control cavity production stabilities
  • HOMs spectra are a sensitive indicator of the cavity imperfections. Shall we ask vendors to perform HOMs

2K measurement at VTS/HTS and to sort out/reject “bad” cavities?

  • Can we estimate operating mode field flatness ?
  • How we may use the accumulated HOMs data?
  • Coherent HOMs excitation might be an issue for the high-current or large scale machines (ILC). Using

measured HOMs data for the beam dynamics analysis would secure our understanding of machine

  • peration and ensure project reliability
  • Verification of numerical simulations results is a challenging question. Experimental HOMs data is a reliable

source of the HOMs statistical parameters.

  • What else …?

19

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Conclusions

HOMSC2018 ICFA Mini Workshop

  • Production of 1.3 GHz LCLS-II cryomodules is ongoing at Fermilab,

11 CMs passed the final cold test @CMTF facility

  • RF/QC procedures are implemented through the CM assembly and

testing

  • HOMs signals acquisition procedure during the CM cold test is

developed along with further data processing

  • Both RI and EZ cavity vendors show similar results in terms of

HOMs frequencies deviations

  • Few RI cavities have a larger spread of HOMs Q-loaded
  • Most of danger HOMs are identified and tracked
  • Danger HOMs Q-values are below the LCLS-II specification (<106)

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Acknowledgments

HOMSC2018 ICFA Mini Workshop

We would like to thank Elvin Harms and the CMTF team for their support and assistance during the 2K HOMs spectra measurements of LCLS-II cryomodules.

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