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SRF Gun Development for BERLinPro | T. Kamps | BERLinPro – an accelerator science and technology experiment – fully integrated ERL demonstrator Joint Accelerator Developments | T. Kamps | HZB3 SRF photo gun recirculation merger section main linac SRF modules spent beam beam dump SRF booster 1.5 MeV 100 MeV beam manipulation 5-10 MeV High fluxflexibility max. beam energy50-100MeV100MeV max. current100mA nominal bunch charge77pcup to ~10pC pulse length2psdown to ~ 100fs Rel. energy spread~10 -4 range~10 -2 rep. rate1.3GHzvariable normalized emittance< 1mm mradsome mm mrad funded by the Bundesminesterium für Bildung und Forschung and the State of Berlin
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SRF Gun Development for BERLinPro | T. Kamps | [email protected]
SRF Gun Development for BERLinPro
T. Kamps | [email protected] Bright Sources Workshop | Cockroft Institute29.06. – 01.07.2011
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Thorsten Kamps | [email protected] 2
Helmholtz-Zentrum Berlin build and operates accelerator facilities for fundamental and applied research
• Synchrotron radiation sources Bessy I (now Sesame), Bessy II and MLS for the generation of soft X-rays: 2500 users doing 700 experiments / year
• Vicksi, an ion and proton accelerator complex currently used for eye cancer treatment: several hundred patients treated
• HoBiCaT, a facility for the development of Superconducting radio-frequency (SRF) components for continous-wave operation of linear accelerators
22.09.2010
We will build BERLinPro, a feasibility study for an Energy-Recovery Linac (ERL)
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Joint Accelerator Developments | T. Kamps | HZB 3
BERLinPro – an accelerator science and technology experiment – fully integrated ERL demonstrator
27.06.2011
SRF photogun
recirculation
merger section
main linac SRF modules
spent beam
beam dumpSRFbooster
1.5 MeV
100 MeV
beam manipulation
5-10 MeV 5-10 MeV
High flux flexibility
max. beam energy 50-100MeV 100MeV
max. current 100mA
nominal bunch charge 77pc up to ~10pC
pulse length 2ps down to ~ 100fs
Rel. energy spread ~10-4 range ~10-2
rep. rate 1.3GHz variable
normalized emittance < 1mm mrad some mm mrad
funded by the Bundesminesterium für Bildung und Forschung and the State of Berlin
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 4
After evaluation of several options during CW Source Workshop in 2008 we concluded that SRF is the way to go for the electron source
17.05.2011
Courtesy B. Dunham / Cornell
Courtesy S. S. Kurennoy / LANL
Courtesy D. Dowell / Boeing / SLAC
Courtesy A. Burril / BNL / AESCourtesy J. Lewellen / NPS
DC
NCRF
SRF
SRF is the right choice to reach an average current of 100 mA with
1 mm mrad emittance, maximum control and flexibility
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 5
The longest running SRF gun: The HZDR/ELBE SRF injector. First beam in 2007, injection into ELBE in 2010
17.05.2011
• 3.5 cell geometry to achieve 9.5 MeV beam energy
• 10 kW average power required for 1 mA average current
• Sacrifice on transverse brightness, ok for the IR FEL application.
• Require 1 mA of average current normal-conducting Cs2Te cathode on LN2 cathode stock.
• No degradation in cavity performance due to cathode stock and material.
From J. Teichert, see NIM A 577 (2006)
Cathodestock Choke filter
RF / HOM portsTuner½ cell
3 full cells
Setup by collaboration between HZDR, MBI, HZB, DESY and funded by BMBF, CARE, EuCARD
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 6
The cathode: Motivation to choose CsK2Sb as baseline photocathode material
• QE of 4…12 % at 532 nm compatible with our requirements, o need at least 10% of QE in the VIS to relax requirements on laser
systemo fast, robust (see Cornell results), rel. low thermal emittance
• Experience in other labs shows good performanceo delivered 32 mA in Boeing NCRF guno delivered >22 mA in DC gun at U Cornell, proved to be more robust
than GaAs against RF trips in booster module• Need to establish comprehensive R&D programm
o undestand correlation between preparation and beam parameterso determine reliable means and procedures to operate this type of
NC cathode inside SRF cavity
17.05.2011
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 7
What are the challenges and current limits for SRF guns with respect to our target beam parameters?
• HZDR/ELBE gun shows feasiblity of the SRF gun concept SRF cavity with normal-conducting cathode works!
• For our application, we need different performance:o Beam dynamics: How can we have more control on the
transverse and longitudinal beam parameters? Mainly determined by field on cathode and setup of any focusing elements.
o Average current: How can we generate 100 mA? Need cathode with high QE at VIS, which can operate in SRF environment.
o Average power: How can we couple Pavg = 100 mA x Eb power into the SRF cavity?
17.05.2011
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 8
Put these three questions into three stages
Gun0 is a beam demonstrator experiment with SC Pb cathode (2011), study beam dynamics, cavity performanceFor Gun1 add NC cathode with high QE at VIS, study cathode lifetime, slice/projected emittance performance (2013)For Gun2 add RF input power coupler for 200 kW (2014), study high power operation
17.05.2011
HoBiCaTGun0
Source labGun1
BERLinProGun2
Goal Beam Demonstrator
Brightness R&D gun
CurrentProduction gun
Electron energy ≥ 1.5 MeV
RF frequency 1.3 GHz
Design peak field ≤ 50 MV/m
Operation launch field ≥ 10 MV/m
Bunch charge ≤ 77 pC
Repetition rate 30 kHz 54 MHz / 25 Hz 1.3 GHz
Cathode material Pb CsK2Sb CsK2Sb
Cathode QE 5*10^-4 at 258 nm 10^-1 at 532 nm 10^-1 at 532 nm
Laser wavelength 258 nm 532 nm 532 nm
Laser pulse energy 0.15 µJ 1.8 nJ 1.8 nJ
Laser pulse shape Gaussian Flat-top Flat-top
Laser pulse length 2.5 ps FWHM ≤ 20 ps 20 ps
Average current 0.5 µA ≤ 10 mA / 0.1 mA 100 mA
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 9
Gun0 takes advantage of the work done by Jacek Sekutowicz & Co for the hybrid Nb/Pb gun cavity
• Utilitzes a thin Pb film on the backwall of cavity as photo-electron emitter
• Pb is also a superconductor of type I with Hcrit = 8 mT at 1.3 GHz and 2K, and has QE at least one order of magnitude higher than bare Nb backwall
• Discussed first during Source workshop in Sep 2008, sketched during ERL09 at Cornell and then agreed on in June 2009.o Jacek and HZB elevate cavity design
from sketch to engineering designo Peter Kneisel builds and tests a cavity
ready for beam tests at HoBiCaTo Robert Nietubyc coats backwall of
cavity with Pb film.o HZB prepares HoBiCaT for beam tests
17.05.2011
J. Sm
edle
y et
al.,
PRS
T-AB
11,
013
502
(200
8)
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 10
Beam dynamics simulation of gun performance: UV laser on Pb cathode, thermal emittance sqrt(2) higher than VIS on CsK2Sb
17.05.2011
ASTRA simulation of energy and emittance versus injection phase.Electron bunch has 10 pC charge in 2.5 ps FWHM pulse length.Similar peak current as for Gun1/2. Learn about slice beam dynamics
(MV/m)
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 11
Turning the physics design of the SRF cavity into engineering design compatible with operation in HoBiCaT
17.05.2011
Target for em design was to optimze electric field on cathode
Need to add stiffening to back-plane as Helium pressure fluctuations cause frequency shift of fundamental mode
(All values are given in Hz/mbar)
With Ib < 2 µA and Eb < 3.8 MeV can run with 700 W forward power from solid state amp.
A. Neumann et al, Proc. of LINAC 2010
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 12
The cavity collected some 20.000 air miles… keeping its Q vs Epk performance…
17.05.2011
Production, RF-tests, Cleaning at JLAB in Newport News
Test of cold mass and beam operation at HZB in Berlin
Cathode depo at Soltan INS at Swierk
before
after
EM Design at DESY in Hamburg
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 13
Results from vertical tests at JLAB, from assembly of cavity to delivery for Berlin
17.05.2011
02/10 Initial test after assembly, tuning, BCP etching and rinsing of the cavity. The field flatness was only 66%.02/10 Further tuning improved field flatness to 94%, the following BCP treatment improved the RF performance.03/10 After installation of the helium vessel, limitation by moderate field emission.07/10 With first cathode coating07/10 Test after accidential loss of lead cathode and removal of remnants by grinding and BCP. 10/10 With second cathode coating
P. Kneisel et al, Proc. of PAC 2010
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
HZB Accelerator Physics Seminar 14
Installation of cold mass into HoBiCaTSRF cavity, solenoid and steerer package
24.05.2011
Solenoid sits close to cavity. Both cavity and solenoid are shielded. No performance degradation with respect to Q of cavity found, OK. Solenoid gets warm if driven > 5 A due to heat transfer from current leads. Improved cooling of those leads during last week. Check performance of this measure.
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 15
Drive laser and diagnostics beamline for Gun0
17.05.2011
(m)Robust and reliable beam diagnostics to study cavity and cathode performanceShort pulses of 1 ps rms length less than 1 degL slice equals projected beam dynamicsCathode jobs: measure QE, QE map, emission surface, thermal emittance ( master thesis) before
and after laser cleaningCavity jobs: study microwave properties, Q vs E, LLRF, microphonics, dark current
0.26 µm, 30 kHz, 2…3 ps, 0.15 µJ pulses from Yb:YAG oscillator + regen. amp. + 4th harm conv.
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 16
The drive laser: cw with short pulses in UV to do beam diagnostics experiments with the Pb/Nb system
• Requirements from Gun0 operationo UV light for metallic cathode / existing cavity designo short pulses (2 ps)o easy and straight forward design of lasero avg. power high enough to do beam diagnostic (QE !)
• Specifications:o Wavelength: 260 nm (UV)o Pulse length: 2-3 pso Pulse Energy: 0,15 µJo Reprate: 120 Hz – 30 kHzo Synchronized to 1.3 GHz
• Good for average currents of 0.1 µA or bunch charges up to 20 pC17.05.2011
SESAM modelocked oscillator
Regenerative amplifier
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 17
Q vs Epk and dark current measurements at HoBiCaT
17.05.2011
• Qo slightly lower compared to last measurement at JLAB
• So far we set safety limit to 15 MV/m
• Dark current kicks in above 10 MV/m, increases exponentially field emission from cathode spot?
• SEM/EDX reveal Pb droplets and flawed Pb film on Nb surface
• Energy spectrum of dark current suggests emission around 90 deg of RF
R. Barday, T. Kamps, A. Neumann, S. Schubert et al Proc. of DIPAC 2011
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 18
Switch on RF, adjust phase, steer and focus with solenoidMeasure QE of 1*10^(-5) at 260 nmNext lasercleaning of cathode
First beam of photoelectrons from Pb cathode generated and accelerated at 21st Aptil 2011, < 2 years after project approval
17.05.2011
First beam21st April 2011
Start with steering of laser beam spot on backwall of cavity
T. Kamps et al, Proc. of IPAC 2011 (planned)
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 19
In parallel with commissioning of Gun0: Start activities for Gun1/2
• Gun0 was more akin to a task force project. o Two years from project approval by lab director to first beam.
• Gun1/2 will be embedded inside BERLinPro project structure.• Main activities in the next two years (for first beam with Gun 1 in 2013)
o Setup of preparation and analysis lab foro Beam dynamics simulation to fix parameterso Development of new gun cavityo Design and engineering of cathode insert, cold mass and cryomoduleo Get new drive lasero Change diagnostics beamline setup
• Put all this together in GunLab gun test area inside HoBiCaT bunker• For Gun2 start thinking about RF feeds for high average power
17.05.2011
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 20
Use surface and material science techniques to study growth of CsK2Sb photocathodes
The use of surface science already showed high potential to improve the injector performanceBessy II: XPS: determination of growth behaviour and stoichiometryUPS: determination of valence band maximumARPES: angular distribution of emitted electrons and depending on the film appearence maybe band structureBessy II infrastructure:PEEM: determination of areas of high and low work functionIPES: determination of conduction band minimumWhite light interferrometryIon source mounted on UHV chamber:LEIS: determination of the formation of 1 monolayer, the deposition rate and composition of topmost layerOther:SEM/EDX: surface topography and composition
17.05.2011
S. Lederer et al, Proc. of PAC99
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 21
Setup preparation system and DC setup to chase photoelectron properties from growth to use
17.05.2011
Ion gun
Evaporationsources
Ion and electronEnergy analyser
X-ray tube
Mass spectrometerTransfer and
transportation
U=60 kV
Photocathode Thermalemittance
QEMapper
Responsetime
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 2217.05.2011
2009 2010 2011 2012
build and comission Gun2
2013
build and comission Gun1
beam diagnostics for gunlab
new cavity, cold mass and cryomodule
high QE cathode
build and commission Gun0
SRF Gun Development for BERLinPro | T. Kamps | [email protected]
Ultra Bright Electron Sources Workshop | Cockroft Institute | 29.06 - 01.07.2011 2317.05.2011
work done by T. Kamps, W. Anders, R. Barday, D. Böhlick, A. Frahm, M. Dirsat, F. Hoffmann A. Jankowiak, S. Klauke, J. Knobloch, O. Kugeler, J. Rudolph, A. Matveenko, A. Neumann, T. Quast, M. Schenk, M. Schuster, S. Schubert , P. Kneisel (JLAB), R. Nietubyc (Soltan), J. Sekutowicz (DESY), J. Smedley (BNL), J. Teichert (FZD), V. Volkov (BINP), I. Will (MBI)
supported by the Accelerator Physics and SRF institutes and Experimental Support groups at HZB.