第77回ERL検討会
ERL2013 WG1(電子銃＆入射器関係) 報告
2013年10月24日(木) 14：00～
報告：山本将博

ERL2013の口頭発表スライドは下記のリンクよりほぼ全てが参照できます。
http://ssrc.inp.nsk.su/Conf/ERL2013/Presentations/報告の概要 ERL2013 WG1での報告（口頭９件、ポスター４件）
Cornell大、BNL、HZB、HZDR、BINP、IHEP(poster)、Peking(poster)
JAEA（西森）、KEK（坂中,本田,山本）
J-Lab, DaresburyからWG1での報告は今回は無かった。

 電子銃開発
DC-gun: JAEA, KEK, IHEP
SRF-gun: HZDR, HZB, BNL, Peking(DC-SRF Gun)
 入射器調整、ビーム診断
Cornell, HZDR, HZB, KEK
 フォトカソード開発、評価
Cornell (Na2KSb), BINP (GaAs), HZB&BNL (CsK2Sb)
 Laser開発
HZB、HZDR (MBI&DESY)SRF-Gun
設計値

 HZDR – 3.5 cell, 9 MeV, < 2 mA
 BNL – 1.5 cell, 2 MeV, 500 mA
 HZB – 1.4 cell, 2 MeV, 100 mA

INTRODUCTION - Radiation Source ELBE & SRF Gun
J. Teichert氏スライドより

ELBE User Facility
thermionic injector

SRF gun

New applications require-high bunch charges (1 nC)-ultra short bunches (< 500 fs)-low transverse emittance (1 mm mrad)
Accelerator Research an Development at ELBE:

Superconducting RF Photoelectron Injector

3
Seite
Jochen3 Teichert y j.teichertl@hzdr.de y www.hzdr.de y HZDR

Mitglied der Helmholtz-Gemeinschaft

INTRODUCTION – SRF gun for the ELBE CW Accelerator

Application•high peak current operation for CW-IR-FELs with 13 MHz, 80 pC•high bunch charge (1 nC), low rep-rate (<1 MHz) for pulsed neutron andpositron beam production (ToF experiments)•low emittance, medium charge (100 pC) with short pulses for THzradiation and x-rays by inverse Compton backscattering
Designmedium average current:
1 - 2 mA (< 10 mA)
high rep-rate:
500 kHz, 13 MHz and higher
low and high bunch charge:
80 pC - 1 nC
low transverse emittance:
1 - 3 mm mrad
high energy:≤ 9 MeV, 3½ cells (stand alone)highly compatible with ELBE cryomodule(LLRF, high power RF, RF couplers, etc.)
LN2-cooled, exchangeable high-QE photo
cathode4
Seite
Jochen4 Teichert y j.teichertl@hzdr.de y www.hzdr.de y HZDR

Mitglied der Helmholtz-Gemeinschaft

Cs2Te PHOTOCATHODES
Excellent lifetime of Cs2Te PC in SRF gun
Requirements for Transfer:

•
•
•

•

Load lock system with < 10-9mbar to preserve QE ≥ 1 %•Exchange w/o warm-up & inshort time and low particle
generation

fresh QE 8.5%, in gun 0.6%
total beam time 600 h
extracted charge 265 C

CathodeOperation days

Extracted
chargeQ.E. in gun#090508Mo

30

<1C

0.05%

#070708Mo

60

<1C

0.1%

#310309Mo

109

<1C

1.1%

#040809Mo

182

<1C

0.6%

#230709Mo

56

<1C

0.03%

#250310Mo

427

35 C

1.0%

#090611Mo

65

<1C

1.2%

#300311Mo

76

2C

1.0 %

#170412Mo

From 12.05.2012

265 C~ 0.6 %

01.08.2013

problems: multipacting, QE drop-down during storage
7
Seite
Jochen7 Teichert y j.teichertl@hzdr.de y www.hzdr.de y HZDR

Mitglied der Helmholtz-Gemeinschaft

TWO-CHANNEL UV LASERUV Laser system developed by MBI:n
Large flexibility in repetition rate and time structure (burst)nConversion to the UV (λ ~ 260 nm) at ~ 1 W powernSynchronisation with RF of the linac + full remote control of the lasernDifferent repetition rates + different pulse durations:a) 13 MHz: 3 ps FWHM Gaussian b) 100/250/500 kHz: 12 ... 15 ps FWHM Gaussian

Important- 13 MHz allow to demonstrate high-current operation of the gun
9Parameters
fullfiltherequirements
foruser
operation
at
ELBE
Seite 9Jochen Teichert y j.teichertl@hzdr.de y www.hzdr.de y HZDR

Mitglied der Helmholtz-Gemeinschaft

BEAM CHARACTERIZATION
NEW: Emittance Measurements with Single Slit Scan
(a)

Beam
(b)

Dark current
SRF-Gunで発生した暗電流がそのまま主加速器へ運ばれないように途中でkickする装置をdogleg前に入れている。

Pengnan Lu

13
Seite
Jochen13 Teichert y j.teichertl@hzdr.de y www.hzdr.de y HZDR

Mitglied der Helmholtz-Gemeinschaft

First FEL Operation with SRF Photo Gun at ELBE
Ekin at gun exit

3.3 MeV

Micro pulse repetition rate

13 MHzMacro pulse repetition rate / length1.25 Hz / 2 ms

Beam energy at FEL

27.9 MeV

Bunch charge / beam current

20 pC / 260 µA

Photo cathodeCs2Te

RMS bunch length

1.6 psNormal. RMS emittance

1 mm mrad

ELBE infrared FEL (20 – 250 µm)

beforefirst lasing

optimized

April 11, 2013

stabilty

FEL spectra
Seite
Jochen20 Teichert y j.teichertl@hzdr.de y www.hzdr.de y HZDRFEL detuning curve20
Mitglied der Helmholtz-Gemeinschaft

NEW SRF GUN WITH HIGH ACCELERATION GRADIENT

11

Test#1 (Oct 13, 2010 ) afte r first treatm ent, de fects a ppeared
Test#4 (May 3, 2011 ) afte r m ech . grinding an re-tre atment
Test#9 (Fe b 13, 201 2) af ter h elium vessel welding
Test#12 (May 15, 20 13) a fter h elium vessel leak fixing
Test#13 (May 23, 20 13) a fter H PR retreatmen t
Q0 limit co rresponding to a refrigera tor p ower of 30 W

quality factor, Q0

10

JLABとの協力で新たな超伝導空
洞を製作。

10 10

低い加速電界でのQ値が低く、暗電流も問題corresponding to abeam energy of 8 MeV

existing SRF gun

9

10

0.0

10.0M

20.0M

Epk [V/m]
Seite
Jochen22 Teichert y j.teichertl@hzdr.de y www.hzdr.de y HZDR

30.0M

40.0M

50.0M
22
Mitglied der Helmholtz-Gemeinschaft

704 MHz SRF gun
Internal
Helium dewar

Cathodeinstallation
cart

BNL: Wencan Xu氏スライドより

Top cover withfacilities
feedthrough The 703.75 MHz ½ - cell

Cathodeisolation
Valve
Cavityassembly

SRF gun has two
Fundamental input Power
Couplers (FPCs) allowing todeliver 1 MW of RF power toa 0.5 A electron beam atenergy gain of 2 MeV.

 The cavity active length is 8.5
cm, tuning range is 1.2 MHz(1 mm of cavity deformation).
HOM
Ferrite HOM damping is provided by
an external beamline ferrite
load with a ceramic break.

Magnetic andthermalshieldingBeam line
isolation valve

Insulating
Vacuum Port
Adjustable supports

Power
Couplers (2)Vacuum vessel

9/11/13

Wencan Xu: Commissioning of the R&D ERL
SRF gun at BNL

5

Commissioning of SRF gun w/o a cathode insert

9/11/13

Prior to assembly into the gun cryomodule, its two
FPCs were conditioned off‐line in standing wave
mode with full reflection at variable RF phase.
Maximum power was 250 kW in pulse mode(limited by klystron collector) and 125 kW in CW(administrative limit).

The gun cryomodule was assembled last year andis installed in the ERL block house. Its 1 MW CW
klystron, cryogenic system and other ancillarysystems are fully operational.

The initial commissioning of the gun without acathode is complete (Nov. 2012 to Mar. 2013) withthe gun cavity achieving 2 MV (the original design
voltage) and 220 kW of RF power in CW mode.

In pulsed mode, with a 0.7 ms pulse duration and
1 Hz repetition rate, the RF power was up to
400 kW. This allowed to do high‐power RF
processing of field emission in the cavity.

Wencan Xu: Commissioning of the R&D ERL
SRF gun at BNL

6

LFD & sensitivity to He pressure The Lorentz force detuning coefficient is ‐11.9 Hz/(MV/m)2.
 The cavity frequency is very sensitive to He bath pressure fluctuations: 704 Hz/Torr.

9/11/13

Wencan Xu: Commissioning of the R&D ERL
SRF gun at BNL

10

BERLinPro @ Helmholtz‐Zentrum Berlin
HZB: Roman Barday氏スライドより
BERLinPro = Berlin Energy Recovery Linac Project
100mA / low emittance technology demonstrator (covering key aspects of large scale ERL)
beam dump
modified Cornell booster
6.5MeV, 100mA = 650kW
3 x 2-cell srf cavities, 4.5MeV
linac module
3 x 7-cell srf cavities, 44MeV
srf-gun1.5-2MeV,
singlemergersolenoid,
doglegno buncher
cavityrecirculation arc
Basic Parameter

Project start 2011,
fully funded (36.5 Mio€)max. beam energy

50MeV

max. current

100mA (77pC/bunch)already 11,8 Mio€ spent(power transmitters, srf-gun
development)

normalized emittance

1 π mm mrad

bunch length (straight)

2 ps or smaller

rep. rate

1.3GHzlosses< 10-5

Status and Perspectives of SRF Gun Development for BERLinPro | ERL 2013 | BINP, Novosibirsk, Russia

11.09.20132

Gun0: Install SRF gun cavity in HoBiCaT cryomodule, add drive
laser and electron beam diagnostics

Study RF properties Æ Qo vs Eacc, LLRF microphonics, operation with TTF‐III coupler,interaction with SC solenoid, steering magnet
Beam dynamics studies Æ Viewscreens, slit mask, Faraday cups, dipole spectrometer
Cathode performance Æ measure QE maps, thermal emittance and dark currenet, dolaser cleaningÆ Learn for next generation SRF gun
Status and Perspectives of SRF Gun Development for BERLinPro | ERL 2013 | BINP, Novosibirsk, Russia

11.09.2013

7

Gun0 results from emittance and phase space measurements:
emittance dominated by rough and structured emission surface
PbカソードはCavityに直接蒸着からプラグ方式にすることでエミッタンスは改善。

M. Schmeißer, et al.,Proc. of IPAC 2013, MOPFI002

Findings with cavity 0.1,
Pb film directly on Nb wall:
Measured emittance at low
bunch charge with solenoid
scan technique
Found strong scaling ofemittance with laser spot size.
Largest contributions fromsolenoid astigmatism andbifurcated emission from
cathode.
Cathode film covered withprotrusions from Pb droplets.
Findings with cavity 0.2,
Plug coated with Pb:
Measured phase space withslit mask.
Emittanceof 0.2 three times
lower than 0.1, improved
cathode surface with lessprotrusions.
Shorter arc and slit aperture
avoid formation and reach of
micro‐droplets

Status and Perspectives of SRF Gun Development for BERLinPro | ERL 2013 | BINP, Novosibirsk, Russia

εn,slit/ σL = 1.94 mm mrad/ mm
εn,sol/ σL = 1.82 mm mrad/ mm

Emission spot imaged with solenoid
on first view screen
2mm

5mm

0.1: Pb coated backwall

0.2: Pb coated plug

Substrate

Pb protrusion

Center area film

20 µm

1 µm
11.09.2013

9

Beam dynamics requires…
high launch field for low intrinsic emittance,and rapid acceleration to mitigate spacecharge effects,
radial field in cathode region Æ initial
focusing to minimize emittance growth due
to aberrations.
SRF operations wants…
min. ratio Epk/Ecath to reduce probability offield emission,min. Hpk/Epk to minimize losses,
max. R/Q for TM010 π Mode,
propagation of HOMs out of cavity.
Elliptical 1.4 cell 1.3 GHz with Choke filter
Choke cell Cathode cell
Gun cellBeam pipe
Petrov filter

A. Neumann, LINAC 2012

T. Kamps, LINAC 2012

Beam dynamics driven design of 1.4cell cavity
for 2.5 MeV ERL class, average power limited, SRF photoinjector

Loop through cavity design and optimize SRF
criteria, field flatness, target frequency
Check longitudinal beam dynamics withsingle particle energy vs. phase scans.
Take settled design to multi particle ASTRA
parameter studies
R/Q
Hpk/Epk
Epk/E0Ecath/E0= 150 (190) Ω= 2.3 (4.4) mT/(MV/m)= 1.5 (1.86)≈ 0.8 (1.0)

Values for 1.4cell (1.6cell)

Status and Perspectives of SRF Gun Development for BERLinPro | ERL 2013 | BINP, Novosibirsk, Russia

At E0
Epk
Ekin
ΦEmax
Ecath
Elaunch= 30 MV/m= 45 MV/m= 2.4 MeV
= 50 deg= 24 MV/m= 18.4 MV/m

11.09.2013

12

The cold mass includes cathode insert shaft, gun cavity, solenoidand steering magnets, HOM absorber and RF/cryo infrastructure
A. Burrill, A. Frahm

Tapered laser
input box

RF Shielded
Gate Valve

300 mm He Gas return
1.8K He volume

Steering
magnet80K HOM absorberSuperconducting Solenoid(on x, y, pitch, yaw mover)

1.4 cell Cavity

Status and Perspectives of SRF Gun Development for BERLinPro | ERL 2013 | BINP, Novosibirsk, Russia

Cathode insert of
HZDR mark 1 design(P. Murcek)
カソードプラグの形状等はHZDR方式を採用。カソードはアルカリ系薄膜（Cs2Te,CsK2Sb等）
11.09.2013132.) High average power 1.3 GHz repetition rate with fiber and
Yb:YAG booster amplifier for 60 W at IR serving BERLinPro

I. Will (MBI)(pulse shape + XFROG: measurement at another system at MBI)

Challenges on the path: Development of …
1.3 GHz oscillator with synchronisation ≤ 1ps to external master.
Booster amplifier to bring average power at IR > 60 W Æ thin‐disk geometry.
Diagnostics mode with reduced duty cycle and repetition rate, from 24 W at 1.3
GHz down to 0.2 µW single pulses at 10 Hz (108).
Pulse selector and picker with rise/fall time faster than bunch spacing of 770 ps.
Status and Perspectives of SRF Gun Development for BERLinPro | ERL 2013 | BINP, Novosibirsk, Russia

11.09.2013

21

Conclusions
Getting a head start with Gun0 proved very
valuable Æ many lessons learnt•Cavity design and operation.
•Beam diagnostics and phase spacecharacterization.
•Cold mass solenoid.
•Laser beam transport and diagnostics.
Now the focus is on•Realization of ERL class gun cavity.
•Cathode/ cavity interface.
•Photocathode growth and characterization.
•Field emission studies.
•Improvement of beam diagnostics of GunLab forslice measurements.
•Drive laser upgrade.
Plan to start Gun1 with beam September 2014.
Status and Perspectives of SRF Gun Development for BERLinPro | ERL 2013 | BINP, Novosibirsk, Russia

11.09.2013

25

Preparation and analysis system to grow CsK2Sb cathodes andstudy characteristics before/after use in gun and under gases
Analysis chamber:
XPS, LEIS, energy analyzer andmomentatron for chemicalcomposition, depth profiling,surface composition,
deposition rate, spectral
response and intrinisc
emittance measurement.

Preparation chamber:
Four evaporation sources(two simultaneous), mass
spectrometer, two quarz
crystal microbalances,photocurrent
measurement, and sputter
gun for substratepreparation
Manipulator
allows sample heating
and cooling, applicationof bias voltage

Transfer chamber/ suitcase:under development

Transfer system

Cathode plug on sample holder

S. Schubert,
D. Böhlick

Status and Perspectives of SRF Gun Development for BERLinPro | ERL 2013 | BINP, Novosibirsk, Russia

P. Murcek,
V. Dürr

Vacuum suitcase

11.09.2013

16

DC-Gun
現状の到達点 Cornell – 350 kV, 8MeV, 65 mA,
0.3 mm mrad @77 pC
 JAEA (1st Gun) – 500 kV, 1.8mA
我々の結果の報告については割愛します。
 KEK (2nd Gun) – 480 kV (HV Conditioning)Cornell ERL Injector

Cornell: Bruce Dunham氏スライドより

ERL Injector Prototype:
Achievements to date:¾75 mA average current @4 MeV¾0.3 μm emittance @ 77
pC, 8 MeV

Bruce Dunham, Cornell University

Injector Requirements
Parameter

MetricStatus

Notes

Average Current

100 mA

75 mA (1300 MHz)

Bunch Charge

77 pC

Pulsed mode (50 MHz)

Energy5 to 15 MeV

14 MeV max (due to cryo limits)

Laser Power> 20 W> 60 W at 520 nm (1300 MHz)

Laser Shaping

beer can dist.

Adequate for now

Gun Voltage

500 kV

Currently operating at 350 kVEmittance< 2 μm (norm, rms)

Ultimate ERL goal 0.3 μm, with merger

Operational
Lifetime> 1 day

Recent improvements with new cathodes

Bruce Dunham, Cornell University

High Currents – Na2KSb

Using a Na2KSb photocathode, ran over 8 hours at
65 mA (2000 C) with a 2.6 day 1/e cathode lifetime.
Reached as high as 75 mA for a short time.
*L. Cultrera, et al., Appl. Phys. Lett., 103, 103504 (2013)*B. Dunham, et al., Appl. Phys. Lett., 102, 034105 (2013)

Emittance Results – Projected
0 pc

γβy X 1000

data

19 pc

Vertical

GPT

77 pc

Projected Emittance for 19 (77) pC@ 8MeV:
Vertical Phase Space
Data Type en(100%)[microns]en(90%)[microns]

Projected(EMS)

0.20(0.40)

0.14(0.29)

GPT

0.16(0.37)

0.11(0.25)

y (mm)

γβx X 1000

data

Horizontal Phase Space

Horizontal

GPT

x (mm)

Data Typeen(100%)[microns]en(90%)[microns]

Projected(EMS)

0.33(0.69)

0.23(0.51 )GPT

0.31 (0.72)

0.19(0.44)*C Guilliford, et al, PRST-AB 16, 073401 (2013)9

GPT Simulations

Emittance (mm-mrad)• Strong asymmetry after first cavity couplers• Beam size asymmetry is accurately reproduced in the lab• At minimum y emittance, the x emittance is 2x larger• This is for a beam straight ahead (no merger)

Distance (meters)

カプラによって加わる４極成分の電磁場をGPTに組込んでシミュレーション。
入射器後でX,Yのエミッタンスが非対称になる現象が説明できる。
我々のcERL入射器ではカプラが上下方向なのでXとYの関係が逆になる？

Alignment Accuracy
Aligning the magnetic andelectrical centers of all elements
to the beam axis is crucial for
obtaining low emittance andminimizing aberrations.

Had to add remotecontrol of the solenoids

Procedure:
1.Align laser at cathode center
2.Center on buncher using correctors(+/- 10 um)
3.Center on first 2 SRF cavities using
correctors (+/- 10 um)
4.Center solenoid #1 by physicaladjustments (+/- 50 um)
5.Center solenoid #2 by physicaladjustments (+/- 50 um)
Bruce Dunham, Cornell University

Lessons Learned• High average currents with good lifetime froma photocathode are a reality• Low emittance (near thermal) beams (withreasonable bunch charge) from a DC gun/SRF
booster are a reality• Extremely high DC voltages are not necessary
to achieve our requirements (350 kV okay)• Space charge simulations + genetic
optimizations match experiments accurately• Halo/beam loss can be maintained at or below
1 part in 107 to 108• Cathodes are still the key for any
photoemission gun
Bruce Dunham, Cornell University

Photocathode BINP - NEA surface analysis
MTE measurement

2. Actual models of (Cs,O)-activation layer.
BINP(ISP): Aleksandr Terekhov氏スライドより

Dipole layer model

Heterojunction model

cb

cb

vac

vac

F

F

vb

vb

z
Semiconductor

CsxOy

VacuumSemiconductor

Vacuumz

3. Photoelectron escape model.

32. Actual models of (Cs,O)-activation layer.
Dipole layer model

Heterojunction model

Prolonged activation

Ne( lon)-distributions

HJ-modelDL-modelQEの波長依存性を励起エネルギーで微分すると得られるデータ。
弾道的に放出される電子エネルギーの位置から真空5準位の位置がわかる

3. Photoelectron escape model.

3. Photoelectron escape model.
NEA-photocathode band diagramand surface scattering processes

1. Surface opticalphonons.

(Cs,O)-layer

12

2. Surface
plasmons.
3. BBR- induced
randomelectric field.

cb

Vs ≈ 0.6 eVvac

BBR ≈ 10 nm

4. (Cs,O)-induced
randomelectric field.

vbhole plasmaz
4. Parallel plate electron spectrometers.

7

3. Photoelectron escape model.
NEA-GaAsカソードでは、表面10nm程度のエリアで起こる現象で電子のエネルギー分布のほとんどが決まる。

(Cs,O)-layer
ballistic
thermalized

hot

cb

ħ

surface phonon losses≥ gsurface plasmon lossesvb

spectrometersz
4. Parallel plate electron spectrometers.

9

3. Photoelectron escape model.
Experiment

表面光学フォノン励起の影響
で電子のエネルギー分布に特徴的なピークが見える。

D.A. Orlov et.al., JETP Letters v.71, p.220 (2000)

4. Parallel plate electron spectrometers.

11

Principles of the technique
BINP(ISP):Heinrich Scheibler氏スライドより

photocathodevacuumtrtransverse
componentlonlongitudinalcomponent

=

lon +

ERL-2013

tr

2

TESS measurements conditions
ND filter

laser

grids

2 MCP

lens

luminescentscreenCCD
cameraGaAs(Cs,O)photocathode

d

Uacc

lens

Umcp
Ulc

ERL-2013

d = 10-53 mm
Uacc = 0-1000 V
Umcp = 900 V
Ulc = 3.5 kV
QE( = 635nm) = 1 2%
9Principles of the techniqueElectron transit time from photocathode to MCP front surface is equal tod

2 mee U acc

1

lon

lon

e U acce U acce * Uacc >> Elon

where d – distance between photocathode and MCP, Uacc – accelerating voltage,
applied between photocathode and MCP,

lon – longitudinal energy of theelectron, me- free electron mass, e – electron charge.
In photocathode plane electron moves a distance r
r

tr

2 me

and

ERL-2013

tr

me r 2
2 2

4

TESS

PPF

7

TEDC measurementswith different light wavelength
21.06.2013 p-GaAs(Cs,O) photocathode d 43 mm T = 300 K= 532 nm
= 635 nm

Uacc = 60 V

Uacc = 230 V
5 mm

ERL-2013

16

TEDC measurementswith different light wavelength
21.06.2013 p-GaAs(Cs,O) photocathode dScreen luminescence profiles

43 mm T = 300 K

Transverse energy distribution curves

0 = 100 meV

0 = 45 meV

MTE635=45 7 meV MTE532=100 15 meV

ERL-2013

17

まとめ 100mA ERLがかなり現実味を帯びてきた。 （Cornell大の成果）
 Na2KSbカソードの寿命 ~2000 Coulomb (=65mAで2.6日）
 65mAで8時間以上運転のdemonstration
 εn.90% ~ 0.3 mm mrad @77 pC （Gun voltage: 350 kV) SRF-Gun開発の現状は、
 HZDRでIR-FEL発振。（20pC, 13MHz, 2msで1.25Hzのmacro pulse）
 まだ暗電流の影響が大きい。(HZDR,HZB)
カソードプラグ、電子銃空洞の構造のupgradeが進行中。
 HZB,HZDR（の他DESY Flash等）のLaser systemはMBIが開発協力。
 100kW以上のCW大電力試験が始まった。(BNL) カソード開発・評価
 表面物性とMTE・カソード寿命の関係の究明
結晶構造、結合状態、相互作用、表面粗さ、、、