SRF Gun Development for BERLinPro | T. Kamps | SRF Gun Development for BERLinPro T. Kamps | Ultra...

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


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)


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


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



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



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



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



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



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)



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)



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



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



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


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.



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.



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



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



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)



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



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



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


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


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.

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