status of the apex project at lbnl · infn-lasa •cathodes from infn-lasa in milano expected...

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K. Baptiste, B. Bailey, D. Colomb, C. Cork, J. Corlett, S. De Santis,

J. Feng, D. Filippetto, G.Huang, R. Kraft, S. Kwiatkowski, D. Li, M.

Messerly, R. Muller, W. E. Norum, H. Padmore, C. Papadopoulos, G.

Portmann, M. Prantill, J. Qiang, D. Quintas, F. Sannibale, J. Staples,

M. Stuart, T. Vecchione, W. Wan, R. Wells, M. Zolotorev, F. Zucca.

Contributions: J. Byrd, D. Dowell, R. Falcone, E. Jongeward, A.

Nassiri, R. Rimmer, T. M. Huang, S. Lidia, J. McKenzie, R. Ryne, V.

Veshcherevich, S. Virostek, W. Waldron, L. Yang, Y. Yang, A.

Zholents, ... .

Photocathode Meeting - SLAC, December 3, 2010

Status of the APEX Project at LBNL

Fernando Sannibale

Array of 10 configurable FEL beamlines, up to 20 X-ray beamlines

100 kHz CW pulse rate, capability of one FEL having MHz rate

Independent control of wavelength, pulse duration, polarization

Each FEL configured for experimental requirements;

seeded, attosecond, ESASE, mode-locked, echo effect, etc

Beam transport and

switchingCW superconducting linac

2.5 GeV

Laser systems,

timing & synchronization

Low-emittance,

MHz bunch rate

photo-gun

≤ 1 nC

≤1 mm-mrad

Injector

Laser

heater Bunch

compressor


The LBNL FEL SchemeStatus of the APEX Project

F. Sannibale

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High-

brightness,

1 MHz rep-rate

electron gun

FEL Physics,

\Undulators

Laser systems,

timing & synchronization

Beam

manipulation

and

conditioning

Beam distribution and

individual beamline tuning

~2 .5 GeV CW

superconducting linac


An R&D Program and

Studies for the Critical Parts

Cathode/laser

Most of such R&D areas are funded

High-

brightness,

1 MHz rep-rate

electron gun

Status of the APEX Project

F. Sannibale

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• repetition rates up to ~ 1 MHz

• charge per bunch from few tens of pC to ~ 1 nC,

• sub 10-7 (low charge) to 10-6 m normalized beam emittance,

• beam energy at the gun exit greater than ~ 500 keV (space charge),

• electric field at the cathode greater than ~ 10 MV/m (space charge limit),

• bunch length control from tens of fs to tens of ps for handling space

charge effects, and for allowing the different modes of operation,

• compatibility with significant magnetic fields in the cathode and gun

regions (mainly for emittance compensation)

• 10-9 - 10-11 Torr operation vacuum pressure (high QE photo-cathodes),

• “easy” installation and conditioning of different kind of cathodes,

• high reliability compatible with the operation of a user facility.

To achieve the LBNL FEL goals, the electron source should

simultaneously allow for:

In a FEL the electron beam quality is defined at the gun/injector


F. Sannibale


Electron Source

Requirements

Such a source does not exist!


F. Sannibale

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• Based on mature and reliable normal-conducting RF and mechanical technologies.

The Berkeley normal-conducting scheme satisfies

all the LBNL FEL requirements simultaneously. Frequency 187 MHz

Operation mode CW

Gap voltage 750 kV

Field at the cathode 19.47 MV/m

Q0 30887

Shunt impedance 6.5 MW

RF Power 87.5 kW

Stored energy 2.3 J

Peak surface field 24.1 MV/m

Peak wall power density 25.0 W/cm2

Accelerating gap 4 cm

Diameter 69.4 cm

Total length 35.0 cm

• 187 MHz compatible with both 1.3 and 1.5 GHz super-conducting linac technologies.

K. Baptiste, et al, NIM A 599, 9 (2009)

J. Staples, F. Sannibale, S. Virostek, CBP Tech Note 366, Oct. 2006

2009 Free Electron Laser Conference - Liverpool - August 26, 2009

• At the VHF frequency, the cavity structure is large enough to withstand the heat load

and operate in CW mode at the required gradients.

• Also, the long lRF allows for large apertures and thus for high vacuum conductivity.


The LBNL VHF RF GunStatus of the APEX Project

F. Sannibale

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The Gun

Has Been Designed,


• The cavity design

finalized


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Underwent Construction,


• Most of the fabrication at the LBNL mechanical shop


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Was Completed,

and Partially Tested…


Successful vacuum leak test.

10-9 Torr pressure achieved with 1 (out of 20) NEG pump and no baking

Successful low power RF test


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Fundamental Question


Does the cavity go through the door?

Yes, it does!!!

This was just virtuality, does it really do?


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On November 9, 2010

We Got the Answer


From 7 a.m. to 3 p.m.

From Bldg. 77 to the BTF~ ¼ of mile in 8 hours

Average speed ~ 164 feet/hour ~ 50 m/hour

The cavity is installed in its

final position and ready for

further tests


F. Sannibale

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The RF Power Source


• RF power test under way at the factory.

• Expected delivery in December (large delay respect to original schedule)

• The 120 kW CW RF amplifier required to operate the VHF gun is being

developed and manufactured by ETM Electromatic.


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Laser


• Temporarily, the laser is at LBNL in BL

5.3.1 laser hutch for commissioning and

testing.

When the test is completed it will be

transferred in the BTF roof tent

• The first laser to be used with the

VHF gun comes from a LLNL

collaboration.

• The nominal 1 W at 1064 nm has been achieved.

Work in progress for achieving the required power at 532 nm and 266 nm


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Other ActivitiesStatus of the APEX Project

F. Sannibale


Many Diagnostics systems under development:

-Emittance meter system

-Transverse deflecting cavity (Cornell-like)

-BPM (SNS-like)

-BPM Electronics (modified version of Mike Chin’s FPGA scheme

developed for the ALS transfer lines)

- Current monitors

- …

Control System (EPICS based –

developed as R&D for NGLS)

Low level RF (Doolittle boards)

Magnets

…

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The VHF Gun Test Facility

All the photo-injector system will be accommodated in the existing

ALS Beam Test Facility (BTF) for full characterization.

The BTF footprint is large enough to accommodate also the structures

to accelerate the beam to few tens of MeV.



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APEX Phase I

Fully funded

• Perform cold and full power RF tests of

the VHF cavity

• Demonstrate the system vacuum

performance

• Test and characterize different possible

cathodes.

• Characterize the electron beam at the

gun energy (750 kV) at full repetition rate


In phase I, only the gun, the vacuum

load lock system and a low energy

beam diagnostics installed in the BTF


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Future Plans:

APEX Phase II

Requires funding continuation

• Develop and install accelerating section

for few tens of MeV energy

• Develop and install high energy

diagnostic beamline

• Perform full characterization of the

beam parameters at high energy (at low

repetition rate)



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• The long RF wavelength allows for large apertures and for

high vacuum conductivity. The vacuum system has been

designed to achieve an operational vacuum pressure down

into the low 10-11 Torr range. NEGs pumps are used (very

effective with H2O, O2, CO, …).

This arrangement will allow testing a variety of cathodes

including "delicate" multi-alkali and/or GaAs cathodes.

A Cathode Test Facility

The nominal laser illumination

configuration for the cathode is

quasi-perpendicular with laser

entrance in the beam exit pipe.

An additional 30 deg laser entrance port has been

also added for extended flexibility (testing of surface

plasma wave cathodes, ...)

• Cathode area designed to operate with a vacuum load-lock

mechanism (INFN/FLASH –like) for an easy in-vacuum

replacement or “in situ” reconditioning of photocathodes.



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The INFN/FLASH/FNAL

Cathode Plug

Modified version of the FLASH plug for reduced

field emission. Not tested yet!

(presently in molybdenum but could be made

also with different materials)



F. Sannibale

Any photocathode deposited on a same geometry plug can be

potentially tested at the VHF gun

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PEA Semiconductor: Alkali Antimonides (CsK2Sb) - <~ps pulse capability (studied at BOEING, INFN-LASA, BNL, Daresbury, LBNL, ….)

- reactive; requires <~ 10-10 Torr pressure

- high QE > 1%

- requires green/blue light (eg. 2nd harm. Nd:YVO4 = 532nm)

- for nC, 1 MHz reprate, ~ 1 W of IR required

PEA Semiconductor: Cesium Telluride Cs2Te (used at FLASH for example)

- <~ps pulse capability

- relatively robust and un-reactive (operates at ~ 10-9 Torr)

- successfully tested in NC RF and SRF guns

- high QE > 1%

- photo-emits in the UV ~250 nm (3rd or 4th harm. conversion from IR)

- for 1 MHz reprate, 1 nC, ~ 10 W 1060nm required

FLASH

INFN-LASA

• Cathodes from INFN-LASA in Milano

Expected delivery January 2011

• Under development by H. Padmore’s group.

• Very promising initial results

Ongoing photo-cathode collaboration research: Diamond (BNL), GaAs (Jlab),

Photo-Cathodes



F. Sannibale

status of the apex project at lbnl · infn-lasa •cathodes from infn-lasa in milano expected...

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