UCLA 10/1/2010C. Pellegrini, Towards a 5th generation light source 1 What is a 5th Generation light...

10/1/2010 C. Pellegrini, Towards a 5th generation light source

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UCLA

What is a 5th Generation light source?

C. PellegriniUCLA Department of Physics and Astronomy


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UCLAThe 4th generation

1992-2010

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Flash: 0.3 mJ at 4.45 nm,1.2 GeVJune 2010

LCLS, 1.5 Å, April 2009, 1-3 mJ at 13.8 GeV

SCSS, 2011European XFEL, 2013



Fermi@Elettra, 2011 New projects: Shangai, Suisse, Korea …


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UCLA4th generation: LCLS results at 250 pC

Design for 1.5 Å

Measured at 1.5 Å

Measured at 6-22 Å

Electron energy, GeV 13.6 13.6 3.5-6.7 Bunch charge, nC 1 0.25 0.25

Normalized slice emittance, 1.2 0.4 0.4 Peak current, kA 3.4 2.5-3.5 0.5-3.5 Gain Length, m 4.4 3.3-3.5 ~1.5

Coherent photons/pulse x1012 2 1.0-2.3 10-20 Pulse energy, mJ 1.5 1.5-3` 1-2.5 Peak power, GW 10 15-40 3-35

Pulse length, FWHM, fs 200 70-100 70-500 Bandwidth, FWHM, % 0.1 0.2-0.5 0.2-1

Peak brightness, photons/mm/mrad/0.1%bandwidth,

x 1032

8 20 0.3


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UCLARemarks on 4th generation

•The LCLS X-ray pulse duration and intensity can be changed from about 100 to a few femtosecond and 1013 to 1011 photons/pulse, over the full wavelength range of 2.2 to 0.12 nm, by varying the electron bunch charge from 250 to 20 pC. The X-ray pulse can be optimized for the experiment, not possible in storage ring sources.•Theory, simulations and experimental results agree quite well. We have now excellent simulations tools to predict the electron beam properties from the electron source to the undulator, and the X-ray pulse characteristics. We can use these tools to design new FELs.

•We know that we can generate high energy electron beams with phase space density larger than what we expected until recently.

•FLASH and LCLS have demonstrated outstanding capabilities, increasing by 7 to 10 orders of magnitude the photon peak brightness.


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UCLAWish list for 5th generation

Photon energy, keV 0.1-100

Pulse repetition rate, HX 102-106

Pulse duration, fs <1-1000

Coherence, transverse Diffraction limited

Coherence, longitudinal Transform limited, Lbunch to Lcooperation

Coherent photons/pulse 109-1014

Peak brightness, ph/mm2 mrad2

0.1% bandwidth1030-1034

Average Brightness 1018-1027

Polarization Variable, linear to circular


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UCLA

Wish list

It is likely that different FELs will be needed to fully satisfy all these requests. For instance an X-ray FEL oscillator is a very good candidate to have very long pulses, full longitudinal coherence, and MHz repetition rate, with a small number of coherent photons per pulse. The X-ray oscillator would use very low emittance, low charge electron bunches, at a repetition rate of about 1 MHz, would need low loss mirrors in the ngstrom to nanometer region, high repetition rate, one to a few MHz, electron guns with the required emittance and linear longitudinal phase space distribution, feeding a CW superconducting linac and producing a nearly transform limited pulse with a line width a small as 10-6-10-7. (K.-J. Kim, Y. Shvydko, S. Reiche, Phys. Rev. Lett. 100, 244802 (2008))


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UCLAMain FEL regimes

E-bunch charge

E-beam energy

Ph/pulse Longitudinal coherence

Short pulse, fs or< fs,

Small, few-10 pC

Low Low Single SASE spike, self-seeding or external laser seeding

Long pulse, 0.1-1ps

Large, 0.1-1nC

High High self-seeding, external laser seeding, oscillator


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UCLA

εN = 1.4 0.111Q2/3 + 0.18Q4/3 + 0.18Q8/3

Transverse emittance scaling with charge

LCLS results at 20 pC

Emittance scaling, Rosenzweig, Serafini. ε in m, Q nC For Q <0.3 nC the RF term is negligible.

Thermal Space charge RF

The red dots are LCLS experimental results.


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UCLA



Longitudinal emittance ~6keVps

Longitudinal phase space measurements after the second bunch compressor, and before the final acceleration. Under-compression and over-compression phase space and current profile. Beam energy ~4 GeV. The bunch head to the left.Ding and LCLS group

Longitudinal emittance


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UCLAPhoto-injector blow-out regime



Longitudinal emittance < 1 keV ps

A laser pulse < 100 fs illuminates the cathode. Space charge forces change the electron charge distribution from a pancake-like shape to a nearly ideal, uniformly filled, ellipsoidal distribution. Beam self-fields, beam dynamics and phase space are approximately linear.P. Musumeci, et al. UCLA




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UCLAMagnetic and velocity bunch compression

LCLS and other 4th generation Fels use magnetic compression with two chicanes as shown for LCLS.

Coherent synchrotron radiation can increase the beam emittance and distort the phase space.


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LCLS measurements of emittance and compression at 250 pC. Coherent synchrotron radiation blows up the emittance for large compression. The effect is larger at large charge.


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Velocity bunching, with emittance preservation, demonstrated recently at SPARC, can help reduce the problem. Ferrario et al.

Left: measured envelopes and PARMELA simulations. Right: PARMELA simulations of the emittance along the linac,. No compression (curves a), compression with solenoids off (curves b), same compression with solenoids at 450 G (curves c).


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SPARX S-band photo-injector: 1 pC charge; bunch length compression 175 m-> 9 m; injector energy 17.9 MeV. Transverse normalized emittance growth-> 0.03 to 0.06 mm. The phase space is single spike, slice, distribution. Longitudinal emittance 0.12 ps keV.

Simulations, Frascati, UCLA collaboration, Rosenzwieg et al.


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UCLA

Single spike SPARX simulations at 3 nmS. Reiche, et al





Spectrum at saturationFEL radiation temporal profile (horizontal axis) along the undulator (vertical axis)


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UCLAWavelength and energy scaling with charge

Satisfying the transverse phase space matching, ε requires a smaller beam energy at low charge.

Using a shorter undulator period reduces the beam energy needed for a given wavelength.

Electron energy vs 1.5 cm period, K=1 undulator (red line); 0.5 cm period, K=1 undulator (black line). As changes the charge is adjusted in the range 1 to 250 pC, to satisfy the phase space matching condition


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UCLAExamples: a 1nm, short pulse FEL

Energy, Gev

Charge, pC

U, cm /K

nm

L, fs

LG,m/x103

P, GW

Npho/pulse

109

Nspikes

1.17 1 0.7/1 1 1 0.26/1.7 0.7 3.4 1.3

1.17 10 0.7/1 1 4 0.21/1.9 2.2 44 6.3

1.7 1 1.5/1 1 1 0.5/2 1 4.5 1.4

1.7 10 1.5/1 1 4 0.4/2 3.2 63 7.2

7.2 1 4.1/4.3 1 1 1.7/2.2 2.7 14 1.1

7.2 10 4.1/4.3 1 4 1.2/2.5 11 230 6


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UCLAShort period undulators

A short period undulator, U~<1.5 cm, K~1, can reduce the size and cost of the FEL. Undulator with 1.5 cm, K-1 gap 5 mm exist.A 9 mm period undulator using a cryogenically cooled Pr-SmCo-Fe hybrid cooled to 30 oK, field >2 T/m (K=2.2), is being tested at UCLA and at HZ-Berlin as part of a project to develop table top FELs using a plasma accelerator. OShea, F. H. et al., Phys. Rev. ST Accel. Beams 13, 070702 (2010).

An LBNL group is investigating sub-centimeter period, K=1, gap 4-5 mm, superconducting undulators using Nb3Sn superconducting material, which gives a larger peak field than NbTi. R. Schlueter, et al. Synchrotron Radiation News, 17, 33 (2010).

X-band RF undulators can give periods<1cm,K~1, large gaps. Tantawi et al


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UCLALinacs and electron guns

Tesla and LCLS electron guns are working very well. The LCLS gun has generated record breaking high brightness beams.

A new RF electron gun for very high repetition rate, 0.1 to a few MHz, X-ray FELs, is being developed at LBNL with the cathode inserted in a low frequency, 75MHz, normal conducting cavity. J. W. Staples et al., in Proceedings of Part. Acc. Conf., Albuquerque, New Mexico, 2990 (2007).

S-band and superconducting linacs are well established.

A C-band linac, with larger accelerating gradient, is used for SCSS, reducing the accelerator length. X-band linacs could be used. Both C band or X-band linacs could also be used at low accelerating gradient to increase the linac repetition rate, up to 1-10 kHz.


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UCLALinacs and electron guns

Laser/plasma/dielectric wake-field based accelerators are being developed. They could become available for light sources in the future and decrease the accelerator length to a small fraction of its present size. One example is the HZ project at Berlin to develop tabletop sources. Other projects to develop high gradient laser/plasma based accelerators as future linac to drive light sources and high energy physics colliders are being developed at Berkeley by Wim Leemans and coworkers, at SLAC/UCLA by C. Joshi and coworkers, and in Europe within the framework of the European Extreme Light Infrastructure. The dielectric wakefield accelerators will discussed by Rosenzweig.Leemans, W.P. et al., IEEE Trans. On Plasma Science 33, 8 (2005).I. Blumenfeld et al., Nature 445, 05538 (2007). http://www.extreme-light-infrastructure.eu/


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UCLAIntensity and pulse duration control

Charge, pC 20 50 100 250

Peak current, kA 3.5 5 5 4

Normalized emittance, m 0.15 0.3 0.35 0.6

FEL pulse duration, fs 2 4 10 60

Coherent photons/pulse x1011

3 3 10 10

LCLS simulations at various charges. The largest number of photons/fs is obtained at 100 pC.


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UCLA

PRLPRL 9292, 074801 (2004, 074801 (2004).

P. Emma,P. Emma,M. Cornacchia, M. Cornacchia, K. Bane,K. Bane,Z. Huang,Z. Huang,H. Schlarb (DESY),H. Schlarb (DESY),G. Stupakov,G. Stupakov,D. Walz D. Walz

Slotted spoiler initial results. Slotted spoiler initial results. Concept (idea from 2003)Concept (idea from 2003)

Courtesy P. Emma


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UCLA

= 363 mm (BC2 peak dispersion)= 363 mm (BC2 peak dispersion)RR5656 = = 24.7 mm (BC2)24.7 mm (BC2)

hh = = //zz11 = (0.315%)/(84.4 = (0.315%)/(84.4 m) = 37.3 m (chirp),m) = 37.3 m (chirp),

εε = 44 = 44 m (non-dispersed m (non-dispersed xx beam size). beam size).With With IIpkpk = 3 kA and laser heater at 7 = 3 kA and laser heater at 7 J we have:J we have:

00 = 0.003% (sliced rms energy spread entering BC2), = 0.003% (sliced rms energy spread entering BC2),

and for 2and for 2xx = 220 = 220 m (larger full slot width)…m (larger full slot width)…

= 7 fs FWHM = 7 fs FWHM (3 fs, if laser heater is OFF)(3 fs, if laser heater is OFF)(almost same for smaller 125 (almost same for smaller 125 m slot width)m slot width)

= 363 mm (BC2 peak dispersion)= 363 mm (BC2 peak dispersion)RR5656 = = 24.7 mm (BC2)24.7 mm (BC2)

hh = = //zz11 = (0.315%)/(84.4 = (0.315%)/(84.4 m) = 37.3 m (chirp),m) = 37.3 m (chirp),

εε = 44 = 44 m (non-dispersed m (non-dispersed xx beam size). beam size).With With IIpkpk = 3 kA and laser heater at 7 = 3 kA and laser heater at 7 J we have:J we have:

00 = 0.003% (sliced rms energy spread entering BC2), = 0.003% (sliced rms energy spread entering BC2),

and for 2and for 2xx = 220 = 220 m (larger full slot width)…m (larger full slot width)…

= 7 fs FWHM = 7 fs FWHM (3 fs, if laser heater is OFF)(3 fs, if laser heater is OFF)(almost same for smaller 125 (almost same for smaller 125 m slot width)m slot width)

Estimate X-ray Pulse Length for 3 kA at 250 pCEstimate X-ray Pulse Length for 3 kA at 250 pC

Chirp is least well known and ±10% uncertainty will change Chirp is least well known and ±10% uncertainty will change by a factor of 2 by a factor of 2


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UCLA

ECHO experiment



Radiation spectrum with one laser only, a and b, and two lasers.

G. Stupakov et al.


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UCLAConclusions

X-ray FELs can be developed to fulfill most of the wish list: femto-second to atto-second pulse duration, very small line width, MHz repetition rates. Utilizing the extraordinary brightness of low-charge bunches it is possible to reduce the size and cost of the accelerator, particularly so for short pulses and when coupled to new short period undulators. Longitudinal coherence can be pushed near to the transform limit using single spike, self seeding, seeding, or with an X-ray oscillator. Such high-power, ultrashort x-ray pulses may open up new applications in many areas of science. In addition, the achieved beam brightness may enable a more compact design of a future hard x-ray FEL facility, where a lower-energy linac than the LCLS and a shorter-period undulator can be envisioned to drive a hard X-ray FEL.


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UCLA

Conclusions

The number of coherent photons/pulse and other characteristics can be tailored to the experiments to explore biological, physical and chemical phenomena in a novel way.Systems providing only a subset of these characteristics, in particular short pulses, can be built at lower cost.. Ongoing research on laser/plasma/wakefield accelerators, high frequency, high repetition rate linacs and electron beam injectors can lead in the future to very compact, university scale, X-ray FELs. Support for accelerator and FEL research and training of students in this field is of great importance to realize the full potential of future light sources.

UCLA 10/1/2010C. Pellegrini, Towards a 5th generation light source 1 What is a 5th Generation light...

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