SPARCLAB Source For Plasma Accelerators and Radiation Compton with Laser And Beam On behalf of SPARCLAB collaboration
EMITTANCE X X X X X X X X 2
BRIGHTNESS (electrons) B n 2I nx ny A m 2 rad 2 The current can be increased compressing longitudinally the bunch The emittance can be decreased with laser pulse shaping, transverse uniformity, good working point, better alignment etc. 3
SPARCLAB R&D on advanced beam dynamics R&D on FEL radiation Developing a THz source Developing a Thomson source R&D on plasma acceleration Thomson source THz source Plasma acceleration Plasma acceleration 300 TW, < 25 fs Ti:Sa laser THz source FEL source Photoinjector 4
LASER SYSTEM SPARC Laser system (Ti:Sa) 0.5 TW Diagnostic and Matching Seeding 5
S-BAND GUN Laser Port Undulators r = 500 nm 15 m Diagnostic RF power and Matching Cathode Long Solenoids S-band Gun Seeding Gun Solenoid THz Source UCLA/BNL design Solenoid ~3 kg Input Power 14 MW Max Acc. Field @ cathode ~130 MV/m 6
S-BAND LINAC 180 MeV S-band linac 12 m Undulators r = 500 nm Focusing solenoid 15 m Long Solenoids Beam axis Seeding THz Source SLAC constant gradient design Solenoid ~300 G Accelerating field ~20 MV/m 7
DIAGNOSTICS AND MATCHING Diagnostics and Matching SCREENS DIPOLE Quadrupoles Seeding THz Source RF DEFLECTOR
PHASE SPACE MANIPULATION Gun focusing field (~3kG) Emittance Bunches current, length Accelerating field ENERGY SEPARATION Inj. phase TIME SEPARATION Gun inj. phase and space charge Bunches distance at the linac entrance TW focusing field (~300G) Emittance Bunches current, length S2 phase ENERGY SPREAD Gun exit energy Beam brightness Compression phase stability Bunch separation stability 9
UNDULATORS 180 MeV S-band linac 12 m Undulators r = 500 nm 15 m Long Solenoids S-band Gun Beam Seeding Variable gap undulator Halbach type 10
INCREASE IN BRILLIANCE B d 4 N dtd dsd / Photons/ (s mm 2 mrad 2 0.1% of bandwidth) 11
LIGHT SOURCES VS COMPUTERS 12
QUANTUM LASER quantized energy levels energy pump to create population inversion stimulated emission of radiation 13
FEL energy source: kinetic energy of beam stimulated emission of radiation optical resonator or SASE TUNABLE!! 14
THE PLANAR UNDULATOR 15
TUNABILITY A magnet with a period of a few 10s of mm produces light with a wavelength on the order of nm because of the huge 2 term At the maximum magnetic field value, K is also maximum and so the output wavelength is longer than when K is small. In other words, the output wavelength of an undulator gets longer as the magnetic field increases. This is different to the synchrotron radiation emitted by a dipole where we saw that higher magnetic fields are used, especially in wavelength shifters, to produce shorter wavelength radiation The wavelength observed changes significantly with observation angle but since there is a θ 2 term the wavelength always lengthens as the observer moves away from the on-axis position (θ = 0). 16
ENERGY TRANSFER The x component of the electron velocity and the electric vector E x of the light wave must point in the same direction to get an energy transfer from the electron to the light wave 17
MICROBUNCHING The electrons losing energy to the light wave travel on a sinusoidal trajectory of larger amplitude than electrons gaining energy from the light wave The result is a modulation of the longitudinal velocity which eventually leads to a concentration of the electrons in slices which are shorter than the optical wavelength λ. 18
THE MOVIE! 19
COHERENT EMISSION The intensity of the radiation field grows quadratically with the number of coherently acting particles. The problem is, however, that this concentration of some 10 9 electrons into a tiny volume is totally unfeasible, even the shortest conceivable particle bunches are much longer than the wavelength of an X-ray FEL 20
EXPONENTIAL GROWTH The exponential growth of the FEL pulse energy as a function of the length z traveled in the undulator 21
SASE For wavelengths in the ultraviolet and X-ray regime the start-up of the FEL process by seed radiation is not readily done due to the lack of suitable lasers. The process of Self-Amplified Spontaneous Emission SASE permits the startup of lasing at an arbitrary wavelength, without the need of external radiation. The electrons produce spontaneous undulator radiation in the first section of a long undulator magnet which serves then as seed radiation in the main part of the undulator. The bunches coming from the accelerator do not possess such a modulation at the light wavelength. But due to the fact that they are composed of a large number of randomly distributed electrons a white noise spectrum is generated which has a spectral component within the FEL bandwidth 22
SLIPPAGE Due to resonant condition, light overtakes e-beam by one radiation wavelength per undulator period Slippage length = λ l undulator period (100 m LCLS undulator has slippage length 1.5 fs, much less than 200-fs e-bunch length) 23
COOPERATION LENGTH AND SPIKES Cooperation length (slippage in one gain length) L c = /4. Number of spikes : bunch length/2 L c 24
DEVELOPING OF SPATIAL COHERENCE 25
SEEDING VS SASE 26
OUR SEEDING @266 nm the SASE FEL does not reach saturation and the output energy is about 12 nj. The FEL gain length L G =1.1m When the FEL amplifier is seeded, the output energy increases up to 2.6 J corresponding to an amplification factor of 20 (the seed energy at 266 nm, measured at the end of the undulator was 120 nj) and more than 200 times the energy available in the SASE mode 27
NARROW BANDWIDTH FEL:SELF- SEEDING SASE-FEL process in the first undulator is interrupted well below saturation SASE radiation from the first undulator is monochromatized and used as a seed in the second undulator. 28
2 COLORS FEL 1 two bunches with a two level energy distribution and time overlap 2 1 2 18 nm produce two wavelength SASE FEL 29
22 fs pulse Beam A B Beam A B 22.8 nm 23.8 nm frog 17.9 nm 18.6 nm Spectral domain Time domain t 112 fs 91 fs t 26.7 fs 22.5 fs 30
A NEW WORLD 31
WHAT WE CAN DO WITH A XFEL? 32
THOMSON COMPTON SCATTERING 33 33
BANDWIDTH CONTROL dn/de 0,004 0,003-5 0 0 5 10 10 E(MeV) E(MeV) E(MeV) 20 E(MeV) E (kev) 15 20 The energy angle correlation permits the control of bandwidth and divergence 0,002 By introducing irides or collimators one can diminish the bandwidth, by selecting only the photons close to the axis Y 0,001 0,000-0,001-0,002-0,003-0,004-0,004-0,003-0,002-0,001 0,000 0,001 0,002 0,003 0,004 X 34
MAMMOGRAPHY Photons of energies other than the one maximizing dose efficiency would lead to lower contrast (in case of high energy) or higher dose to the patient(provided by the energies lower than the optimal one) The energy spectrum of conventional mammographic X-ray tube systems is polychromatic, and even after k- edge filtration, it shows a significant number of photons in the whole range between about 10 kev and the maximum photon energy Compton or Thomson scattering can provide quasimonochromatic, high-flux X-ray beams 35
APPLICATIONS WORLDWIDE Radiography done at BNL, Brookeven Radiographies done at CLS, Palo Alto Absorption Dark field Phase contrast 36
A GOOD SOURCE OF INFORMATION 37
THz GAP THz radiation is non ionizing and highly penetrating in a large variety of insulating materials THz part of the spectrum is energetically equivalent to many important physical, chemical and biological processes including superconducting gaps and protein dynamical processes 38
THz GENERATION Transition radiation emitted by electrons on a target if λ>σ z, coherent emission dominates on incoherent one λ<σ bunch emitted incoherently λ>σ bunch emitted coherently 39
SCIENTIFIC MOTIVATION THz radiation as Coherent Radiation from sub-ps high brightness beams intense source because of high THz field Ultra-fast and non-linear phenomena Potential of conditioning and controlling matter Probing feature of THz radiation THz pump THz probe spectroscopy Imaging in biological applications 40
BIO APPLICATIONS THz radiation is absorbed by polar liquids (such as water), thus it might be used to detect differences in body tissue density Using THz spectroscopy, diseased human tissues like tumors would image differently than do normal tissues and, since this radiation is non ionizing, it also is a safer medical and dental imaging alternative Region with tumor appears more transmissive since it originally contained more fluid 41 41
Pump-Probe Spectroscopy Temporal evolution of excitations THz Pump THz Probe Spectroscopy Optical T=0 Pump Optical Probe Spectroscopy Accordable THz Pump T=Δt Pump and Probe pulses pulses; (often at a single frequency) fall in the visible/near IR Possibility to resonate and/or selectionate several Pumping at high frequency; fundamental excitations;? Pump Strong scattering effects; Intrinsic dynamics Extrinsic dynamics Probe 42
Insulator to Metal Transitions Many materials are insulating although band theory suggests a metallic ground state: V 2 O 3, VO 2, NiO, NiSe 2, La 2 CuO 4, Cs 3 C 60 Strong Electronic Correlations (Basic Ingredient for High Tc Superconductivity) 43
PLASMA ACCELERATION In conventional Radio-Frequency (RF) cavities, the accelerating gradients are limited to about 50 MV/m (dielectric breakdown of cavities). Ionized plasmas: can sustain electron plasma waves with electric fields 3 orders of magnitude higher, and the accelerating field strength is tunable by adjusting the plasma density. Two Plasma-based accelerator techniques are possible: Self-injection: plasma and particle created by TW-laser pulse; External-injection: particles injected externally; driven by laser-pulses (LWFA) driven by particle-bunches (PWFA) Accelerating gradients of GV/m reached! 44
PWFA Gas ionization is externally generated (discharge or high energy electrons). Wakefield is generated by the first bunches (comb like structure). COMB like electron bunches are injected inside the preformed plasma. The first bunches create the wakefield, which is then seen from the last bunch (witness) which will be then accelerated. Synchronization with an external laser is not needed. Challenge: creation and manipulation of driver bunches and matching all the bunches with the plasma. 45
5 bunches Time Space 46
PWFA 47