High-brilliance synchrotron radiation induced by the plasma ...
Directional x-ray radiation produced by plasma magnetostatic undulator proposal ID# 306041 P.I. C. Joshi1, W.B. Mori1 , C. Zhang1 and F. Fiuza2 1UCLA, 2 SLAC F. Fiuza, L. Silva and C. Joshi PRSTAB 13(8):080701, Aug 2010 W.B. Mori, Phys. Rev. A 44, 5118 (1991) Currently supported by DOE-NNSA, DOE-HEP What is a plasma magneto-static (MS)mode The two normal electrostatic modes (collective waves) in an unmagnetized plasma are Bohm Gross Waves or electron plasma waves and ion acoustic waves. Unmagnetized plasma can support another mode. It has zero frequency but a spatially periodic magnetic field magneto-static (MS) mode. How is it produced? it is produced by a periodic excitation of dc currents in the plasma. This mode has hitherto not been observed. There is a connection between this mode and the filamentation/Weibel instability produced magnetic field (see Chaojie Zhangs proposal) What happens when e.m. wave is incident on a relativistic underdense plasma ionization front? Ionization front
Transmitted Wave Drive Laser Magneto-static mode Incident wave Ionization front f = and 2 > Free Space Containing Gas Reflected Wave Boundary conditions at the ionization front are E and B must be continuous and J=0 since electrons are born at rest 3 boundary conditions allows for 3 modes Ref: F. Fiuza, L. Silva and C. Joshi PRSTAB 13(8):080701, Aug 2010 Physical Mechanism behind MS mode W.B. Mori, Phys. Rev. A 44, 5118 (1991) Relativistic m vosc2 = 1.5 kV for CO2 Ionization front must be narrower than wavelength of CO2 radiation
How is the magneto static mode produced? 1) An ultrashort 0.266 um (drive)laser pulse containing ~10 mJ of energy in a 50 fs pulse generates in a hydrogen gas cell a propagating ionization front (f) with density >1019 cm-3 2) A counter propagating 2 ps duration CO2 (incident)laser pulse with a peak intensity of 1x1013 W/cm2 (below the ionization threshold of H2) collides with the ionization front. The time dependent refractive index front reflects and and transmits the CO2 laser pulse and frequency upshifts it. At the same time a static magnetic field is left behind in the plasma that can reach very high B. Intensity Contours and Ionization fraction with 266nm 5mJ, 40fs pulse 90% in 11 fs 266 nm, 40fs Ideally we want It should at least be half the CO2 period = 16 fs Concept that gives rise to MS mode CO2 Laser pulse Ionizing Laser
MS Mode 50 MeV electron Beam Wait for the CO2 laser pulse to pass before sending the electron Beam through the static magnetic undulator left behind. Example of Spontaneous emission produced by 5 MeV beam nb=8x1016 cm-3, passing through 5x1020 cm-3density plasma MS mode undulator Initial B 1D OSIRIS Final B How can such an experiment be done? ATF has recently added a Ti Sapphire laser to their CO2 laser and nominally 50 MeV electron beam Ti-sapphire 80 mJ min. at IP in 75 fs (FWHM) They should be able to get >20 mJ in 50 fs at 0.4 um or 10 mJ at 0.266 um. E-beam 50 MeV, 10s pC in 100-200 fs CO2 laser 200 mJ in 2 ps at IP Need 0.4 um and e-beam to be collinear while CO2 laser to be counter propagating. Gas target 2 mm long He/H gas jet.
What do we want to do? (h Here = 0.12 eV For =100, h We can see these in a single photon counting mode. Average power 10 W or number of photons 104 Cone angle 1/ or 10 mrad. The spectral width narrows to 1/N where N are the number of undulator periods. For instance for a 1mm long undulator This is measurable using an X-ray CCD operating in the single photon counting mode. Why ATF for this experiment? Only place in the word that has (or will have) a 5-75 MeV electron beam, a TW class CO2 laser and a TW class Ti-sapphire laser under one roof All three are synchronize w.r.t. one another with ~100fs accuracy ATF has a mandate to explore novel sources of radiation What is needed from ATF? The 800nm Ti -sapph laser pulse needs to be frequency trippled without bandwidth narrowing (thin crystals) to give > 5mJ at 266 nm. The CO2 and the 266 nm laser pulses are counter propagating and meet at the center of the target chamber, that has a 2-3 mm H gas jet The 100 fs e-beam and the 266 nm pulse are colinear. The e-beam follows the 266nm pulse with a 50-several hundred fs delay (probably need two delay lines for the laser pulses). Need 2-3 years with 2 weeks of running time and 3 days of set-up time every year.
What will the experimenters provide X-ray CCD for detecting the forward emitted few KV X-rays A very high density H gas get. IR spectrometer to measure the frequency upshifted transmitted CO2 photons. A small dipole magnet to dump the incident electrons. An output flange for the radiated photons with an 500 um thick 2 Be window. This will be followed by the X-ray CCD. Miscellaneous optics and manpower (postdoc and a graduate student) What will be regarded as a success? Conclusive observation of X-rays of expected energy Observation of X-rays contingent upon all the null tests being successful: No CO2, no electron beam, No ionization front no X-rays Determination of the lifetime of the MS mode, its dependence on plasma density, ionization front width etc. Future work: control the phase velocity of the ionization front by using a spatially chirped pulse and spatially dispersive optic (flying focus), overdense plasma to increase the yield, increase the B field to 100 T. Summary Laser technology has now progressed sufficiently so that a magneto static mode can be excited in a plasma using a relativistic ionization front for the first time (future text book entry) This mode will act as a extremely small period but highly accurate undulator for a relativistic electron beam. Because of a large number of periods, it will produce a spectrally narrow beam of photons in the direction of the electrons.
At ATF this concept can be tested as a precursor to attempting gain in the uv . This experiment will also provide a known periodic B field for probing by an orthogonal e-beam (see Chaojies talk). Intensity Contours and Ionization fraction with 800 nm 80 mJ, 75 fs pulse 90% in 20 fs 800 nm Linearly polarized, 75 ps pulses to give peak Intensity of 4x1015 W/cm2 PPT theory (Courtsey Noa Nambu) Electron Beam Requirements Parameter Units Typical Values Comments Beam Energy MeV 50-65
Full range is ~15-75 MeV with highest beam quality at nominal values Bunch Charge nC 0.1-2.0 Bunch length & emittance vary with charge Compression fs Down to 100 fs (up to 1 kA peak current) A magnetic bunch compressor available to compress bunch down to ~100 fs. Beam quality is variable depending on charge and amount of compression required. Requested Values 50 Larger the better but >100pC 200Fs
NOTE: Further compression options are being developed to provide bunch lengths down to the ~10 fs level Transverse size at IP (s) mm 30 100 (dependent on IP position) It is possible to achieve transverse sizes below 10 um with special permanent magnet optics. Normalized Emittance mm 1 (at 0.3 nC) Variable with bunch charge Rep. Rate (Hz) Hz 1.5
3 Hz also available if needed Trains mode --- Single bunch Multi-bunch mode available. Trains of 24 or 48 ns spaced bunches. 20-100um fine CO2 Laser Requirements Configuration Parameter Units Typical Values Wavelength mm 9.2
Peak Power GW ~3 Pulse Mode --- Single Pulse Length ps 2 Pulse Energy mJ 6 M2 ---
~1.5 Repetition Rate Hz 1.5 Polarization --- Linear CO2 CPA Beam Wavelength mm 9.2 Wavelength determined by mixed isotope gain media Note that delivery of full power pulses to the Experimental Hall is presently limited to Beamline #1
only. Peak Power TW 2 ~5 TW operation is planned for FY21 (requires further in-vacuum transport upgrade). A 3-year development effort to achieve >10 TW and deliver to users is in progress. Pulse Mode --- Single Pulse Length ps 2 Pulse Energy J
~5 M2 --- ~2 Repetition Rate Hz 0.05 CO2 Regenerative Amplifier Beam Polarization Linear Comments Requested Values Wavelength determined by mixed isotope gain media 3 Hz also available if needed
Circular polarization available at slightly reduced power Maximum pulse energies of >10 J will become available in FY20 Adjustable linear polarization along with circular polarization will become available in FY20 High rep rate for setting up 200mJ Other Experimental Laser Requirements Ti:Sapphire Laser System Units Stage I Values Stage II Values Comments Requested Values
Central Wavelength nm 800 800 Stage I parameters should be achieved by mid-2020, while Stage II parameters are planned for late-2020. 266 nm FWHM Bandwidth nm 20 13 Transport of compressed pulses will initially include a very limited number of experimental interaction points. Please consult with the ATF Team if you need this capability. As short as possible 50 fs Compressed FWHM Pulse
Width fs <50 <75 Chirped FWHM Pulse Width ps 50 50 Chirped Energy mJ 10 200 Compressed Energy mJ
7 100 Energy to Experiments mJ >4.9 >80 Power to Experiments GW >98 >1067 Nd:YAG Laser System Units Typical Values Wavelength
nm 1064 Energy mJ 5 Pulse Width ps 14 Wavelength nm 532 Energy mJ 0.5
Pulse Width ps 10 5-10mJ Comments Single pulse Frequency doubled Requested Values Longer range plan: A possible SASE FEL action with 10 MeV beam
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