High-quality electron beams from a laser wakefield accelerator using plasma-channel guiding

Classified as probably not a substantial claim. May combine two claims.

Many applications including high energy physics and radiation sources require monoenergetic beams (percent energy spread or less) with at least 10^9 electrons.

“While these beams are useful for some users 9 , many applications including high energy physics and radiation sources require monoenergetic beams (percent energy spread or less) with at least 10 9 electrons [10][11][12][13] .”

• cites [10] Leemans, W. P. et al. Observation of terahertz emission from a laser-plasma accelerated electron bunch crossing a plasma-vacuum boundary. Phys. Rev. Lett. 91, 074802 (2003) sourceNot checked — no full text of the source
• cites [11] Catravas, P., Esarey, E. & Leemans, W. P. Femtosecond x-rays from Thomson scattering using laser wakefield accelerators. Meas. Sci. Technol. 12, 1828–1834 (2001) sourcePartly supported

  Section II explains that a broad electron-energy distribution degrades the Thomson-scattered radiation spectrum, and the Conclusion says low energy spread enables greater peak brightness. But the paper does not state that high-energy physics and radiation-source applications require percent-level energy spread and at least 10^9 electrons together. Its narrow-spread injector example in Section III.B instead gives approximately 0.5–1.5 × 10^7 electrons. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites [12] Wang, X. J., Qiu, X. & Ben-Zvi, I. Experimental observation of high-brightness microbunching in a photocathode RF electron gun. Phys. Rev. E 54, R3121–R3124 (1996) sourceNot checked — no full text of the source

May combine two claims.

The peak current is on the order of 10 kA with emittance comparable to the best state of the art RF facilities.

“The peak current is on the order of 10 kA with emittance comparable to the best state of the art RF facilities 11 .”

• cites [11] Catravas, P., Esarey, E. & Leemans, W. P. Femtosecond x-rays from Thomson scattering using laser wakefield accelerators. Meas. Sci. Technol. 12, 1828–1834 (2001) sourcePartly supported

  In Section III, the paper reports at least 5 nC per bunch for the self-modulated laser wakefield accelerator; Table I gives a 100 fs bunch length, implying a peak current on the order of 10 kA. Table I also lists a normalized emittance of 1 mm-mrad, but the paper does not establish that this is comparable to the best state-of-the-art RF facilities. Page numbers were not available in our copy. (LLM, conf=0.82)

  Experimental — accuracy not yet measured

May combine two claims.

Femtosecond bunches have been produced containing 2x10^9 electrons with geometric and normalized RMS emittances ε_x below 0.05 to 0.01 π-mm-mrad and below 1 to 2 π-mm-mrad RMS, respectively.

“Femtosecond bunches have hence been produced 25 containing 2x10 9 electrons with geometric and normalized RMS emittances ε x below 0.05 to 0.01 π-mm-mrad and below 1 to 2 π-mm-mrad RMS, respectively.”

• cites [25] Leemans, W. P. et al. Terahertz radiation from laser accelerated electron bunches. Phys. Plasmas 5, 2899–2906 (2004) sourcePartly supported

  The Abstract reports preliminary evidence of 30–50 fs bunches, and Radiation measurements reports bunches of about 0.3 nC, approximately 2×10^9 electrons. Electron beam properties estimates a geometric rms “emittance” of 0.01 mm-mrad, but cautions that a proper emittance value requires further measurements. It does not report the claimed normalized rms emittance below 1–2 π-mm-mrad; the normalized value it mentions is 3 mm-mrad from a similar setup. (LLM, conf=0.87)

  Experimental — accuracy not yet measured

May combine two claims.

Beams with 3x10^9 electrons have been observed at similar energies (78±3 MeV FWHM), and electrons were observed up to the limit of the 55 degree high resolution spectrometer (92 MeV).

“Beams with 3x10 9 electrons have been observed at similar energies (78±3 MeV FWHM), and electrons were observed up to the limit of our 55 degree high resolution spectrometer (92 MeV).”

May combine two claims.

At 9 TW the mode image showed an intense output spot of 24 μm FWHM, slightly larger than the input spot but much smaller than the unguided pulse.

“At 9 TW the mode image showed an intense output spot of 24 µm FWHM (Fig. 2b), slightly larger than the input spot but much smaller than the unguided pulse (Fig. 2d).”

May combine two claims.

The channel guided accelerator produced high charge electron beams with small energy spread at high energy, a unique feature not observed in previous laser plasma acceleration experiments.

“As shown in Fig. 3, the channel guided accelerator produced high charge electron beams with small energy spread at high energy, a unique feature that has not been observed in previous laser plasma acceleration experiments.”

May combine two claims.

Below 15 MeV there is an essentially continuous distribution, and total beam charge was 1.7x10^10 electrons as measured by the ICT, subtending f/8.

“Below 15 MeV there is an essentially continuous distribution, and total beam charge was 1.7x10 10 electrons as measured by the ICT, subtending f/8.”

May combine two claims.

Structure in the energy spectrum did occur occasionally in the tail of the distribution above 15 MeV containing <2% of the charge, consistent with a beam accelerated over a short distance and with previous experiments.

“Structure in the energy spectrum did occur occasionally in the tail of the distribution above 15 MeV containing < 2% of the charge, consistent with a beam accelerated over a short distance and with previous experiments 1,2,9 .”

• cites [1] Modena, A. et al. Electron acceleration from the breaking of relativistic plasma waves. Nature 377, 606–608 (1995) sourceNot checked — no full text of the source
• cites [2] Malka, V. et al. Electron acceleration by a wake field forced by an intense ultrashort laser pulse. Science 298, 1596–1600 (2002) sourceNot checked — no full text of the source
• cites [9] Leemans, W. P. et al. Gamma-neutron activation experiments using laser wakefield accelerators. Phys. Plasmas 8, 2510–2516 (2001) sourceNot checked — no full text of the source

May combine two claims.

For the data shown in Fig. 3, the ±2% energy spread of the peak centered at 86 MeV is essentially limited by the spectrometer resolution so that the beam may in fact have narrower energy spread.

“For the data shown in Fig. 3, the ±2% energy spread of the peak centered at 86 MeV is essentially limited by the spectrometer resolution so that the beam may in fact have narrower energy spread.”

May combine two claims.

Optimal performance was found in channels detuned slightly from the low power guiding condition, with 40% less rise in density over the spot diameter than a matched channel.

“Electrons were trapped and accelerated using a 9 TW drive pulse, and optimal performance was found in channels detuned slightly from the low power guiding condition, with 40% less rise in density over the spot diameter than a matched channel 19 .”

• cites [19] Volfbeyn, P., Esarey, E. & Leemans, W. P. Guiding of laser pulses in plasma channels created by the ignitor-heater technique. Phys. Plasmas 6, 2269–2277 (1999) sourceNot checked — no full text of the source

May combine two claims.

Guiding efficiency at 4 TW was 35%, a reduction of 20% compared to the low power case (0.5 TW).

“Guiding efficiency at 4 TW was 35%, a reduction of 20% compared to the low power case (0.5 TW), suggesting that a significant amount of laser energy was depleted by excitation a plasma wave.”

May combine two claims.

The unchannelled electron beam had a total charge of 1.5x10^10 electrons, as measured by the ICT, with divergence near 50 mrad FWHM.

“The electron beam had a total charge of 1.5x10 10 electrons, as measured by the ICT, with divergence near 50 mrad FWHM.”

May combine two claims.

The investment of power in channel formation is less than 5% of the drive pulse power (20% of the energy), yet spectral density of these beams near 80 MeV is at least a factor of 200 above previous unchannelled experiments using several times the laser power, and peak energy observed is comparable.

“The investment of power in channel formation is less than 5% of the drive pulse power (20% of the energy), yet spectral density of these beams near 80 MeV is at least a factor of 200 above previous unchannelled experiments using several times the laser power, and peak energy observed is comparable 2 .”

• cites [2] Malka, V. et al. Electron acceleration by a wake field forced by an intense ultrashort laser pulse. Science 298, 1596–1600 (2002) sourceNot checked — no full text of the source

May combine two claims.

Without the guiding channel, the laser pulse diffracted strongly, limiting the acceleration length.

“As seen in Fig 2 c and d, the laser pulse diffracted strongly, limiting the acceleration length.”

May combine two claims.

Using a 600 μm long plasma at 4x10^19/cm3, which is close to the dephasing length observed in PIC simulations at this density, the unchannelled accelerator produced the same peak energy as in the 2 mm plasma, but with more structure in the spectrum.

“Using a 600 µm long plasma at 4x10 19 /cm 3 , which is close to the dephasing length observed in PIC simulations at this density, the un channelled accelerator produced the same peak energy as in the 2 mm plasma, but with more structure in the spectrum.”

May combine two claims.

Plasma density was independently optimized for the unchannelled accelerator, and highest charge and electron energies were obtained at 4x10^19 cm^-3.

“Plasma density was independently optimized for the unchannelled accelerator, and highest charge and electron energies were obtained at 4x10 19 cm -3 .”

May combine two claims.

Using a 32 TW laser, bunches with more than 10^10 electrons were produced but less than 1% were above 60 MeV.

“For example, using a 32 TW laser bunches with more than 10 10 electrons were produced but less than 1% were above 60 MeV 2 .”

• cites [2] Malka, V. et al. Electron acceleration by a wake field forced by an intense ultrashort laser pulse. Science 298, 1596–1600 (2002) sourceNot checked — no full text of the source

Classified as probably not a substantial claim.

To differentiate the effects of channeling from pre-ionization, the ignitor pulse was fired 80 ps before the drive pulse.

“To differentiate the effects of channeling from pre-ionization, the ignitor pulse was fired 80 ps before the drive pulse.”

May combine two claims.

These results confirm that matching accelerator length to dephasing length is critical for structuring the spectrum, and that extending the length (for instance using a channel at lower density) results in higher energies.

“These results confirm that matching accelerator length to dephasing length is critical for structuring the spectrum, and that extending the length (for instance using a channel at lower density) results in higher energies.”

May combine two claims.

Large plasma waves, or wakes, can be driven by the radiation pressure of the intense laser, but the propagation length is limited to little more than the diffraction or Rayleigh length Z_R.

“Large plasma waves, or wakes, can be driven by the radiation pressure of the intense laser, but the propagation length is limited to little more than the diffraction or Rayleigh length Z R 8 .”

• cites [8] Najmudin, Z. et al. Self-modulated wakefield and forced laser wakefield acceleration of electrons. Phys. Plasmas 10, 2071–2077 (2003) sourceNot checked — no full text of the source

May combine two claims.

The shot-to-shot fluctuations were likely caused by laser pointing jitter that changes the overlap between the wake drive pulse and the channel formation pulses (and hence guide quality and incoupling) as well as laser power fluctuations.

“The quality of optical guiding as well as the pointing, quality, and charge of the electron beams at high energy fluctuated shot to shot, likely caused by laser pointing jitter that changes the overlap between the wake drive pulse and the channel formation pulses (and hence guide quality and incoupling) as well as laser power fluctuations.”

May combine two claims.

The narrow energy spread of the channel produced beams is consistent with simulations which also indicate that the bunch length is near 10 fs.

“The narrow energy spread of the channel produced beams is consistent with simulations which also indicate that the bunch length is near 10 fs.”

May combine two claims.

The best results have been obtained by increasing the laser spot size to increase Z_R, requiring ever greater laser power, but this approach has still been limited to distances of a few hundred micron.

“The best results have hence been obtained by increasing the laser spot size to increase Z R , requiring ever greater laser power, but this approach has still been limited to distances of a few hundred micron 8 .”

• cites [8] Najmudin, Z. et al. Self-modulated wakefield and forced laser wakefield acceleration of electrons. Phys. Plasmas 10, 2071–2077 (2003) sourceNot checked — no full text of the source

May combine two claims.

In the self-modulated wakefield regime, some self-guiding of the laser pulse occurs due to relativistic modification of the plasma refractive index, but the laser pulse is highly unstable.

“In this so called self-modulated wakefield regime 6 some self-guiding of the laser pulse occurs due to relativistic modification of the plasma refractive index, but the laser pulse is highly unstable 7 .”

• cites [6] Esarey, E., Krall, J. & Sprangle, P. Envelope analysis of intense laser pulse self-modulation in plasmas. Phys. Rev. Lett. 72, 2887–2890 (1994) sourceNot checked — no full text of the source
• cites [7] Esarey, E., Sprangle, P., Krall, J. & Ting, A. Self-focusing and guiding of short laser pulses in ionizing gases and plasmas. IEEE J. Quant. Electron. 33, 1879–1914 (1997) sourceNot checked — no full text of the source

May combine two claims.

The dephasing length and maximum energy increase as density decreases, so that accelerator lengths of several cm and energies up to several GeV/stage are then possible.

“The dephasing length and maximum energy increase as density decreases, so that accelerator lengths of several cm and energies up to several GeV/stage are then possible 5 .”

• cites [5] Esarey, E., Sprangle, P., Krall, J. & Ting, A. Overview of plasma-based accelerator concepts. IEEE Trans. Plasma Sci. 24, 252–288 (1996) sourceNot checked — no full text of the source

May combine two claims.

The plasma channel guides the laser beam and transversely shapes the plasma wakes.

“Much as in a RF accelerator where cavities provide confinement and field shaping for the RF-power, the plasma channel guides the laser beam and transversely shapes the plasma wakes.”

May combine two claims.

To reach high intensities with a typical 10 TW peak power laser system operating at 800 nm, the laser pulse must be focused to spot sizes near 8 μm, giving Z_R ~200 μm and necessitating guiding over many Z_R in order to reach the dephasing condition and high energies.

“To reach high intensities with a typical 10 TW peak power laser system operating at 800 nm, the laser pulse must be focused to spot sizes near 8 µm, giving Z R ~200 µm and necessitating guiding over many Z R in order to reach the dephasing condition and high energies.”

May combine two claims.

The high density allowed acceleration before the laser diffracted since self modulation and dephasing both occur more quickly at high density, but this also reduced the peak energy compared to the channelled case.

“The high density allowed acceleration before the laser diffracted since self modulation and dephasing both occur more quickly at high density, but this also reduced the peak energy compared to the channelled case.”

May combine two claims.

This dephasing condition can alternatively be met by a short plasma at high density or by using a larger laser spot size to extend Z_R, but these alternatives are less efficient since high density lowers peak energy while large spot size requires many times greater laser power.

“This dephasing condition can alternatively be met by a short plasma at high density (see below) or by using a larger laser spot size to extend Z R , but these alternatives are less efficient since high density lowers peak energy while large spot size requires many times greater laser power.”

May combine two claims.

Only one accelerating bucket contributes to the high energy beam due to beam loading in these simulations, so that the bunch length is less than a plasma period; for the experimental parameters the bunch length is near 10 fs FWHM.

“Only one accelerating bucket contributes to the high energy beam due to beam loading in these simulations, so that the bunch length is less than a plasma period; for the experimental parameters the bunch length is near 10 fs FWHM.”

May combine two claims.

The beams from channel guided accelerators such as those described here, with a few 10^9 electrons in percent level energy spread and mrad divergence as well as intrinsic synchronization to the laser beam, open up a new class of experiments with laser accelerators.

“The beams from channel guided accelerators such as those described here, with a few 10 9 electrons in percent level energy spread and mrad divergence as well as intrinsic synchronization to the laser beam, open up a new class of experiments with laser accelerators.”

May combine two claims.

A parabolic transverse density profile can be matched to guide a Gaussian laser mode without distortion in the low intensity limit, and guiding has been previously demonstrated over many Z_R at input intensities below 2x10^17 W/cm2.

“A parabolic transverse density profile can be matched to guide a Gaussian laser mode without distortion in the low intensity limit, and guiding has been previously demonstrated [18][19][20][21] over many Z R at input intensities below 2x10 17 W/cm 2 .”

• cites [18] Durfee, C. G. & Milchberg, H. M. Light pipe for high intensity laser pulses. Phys. Rev. Lett. 71, 2409–2412 (1993) sourceNot checked — no full text of the source
• cites [19] Volfbeyn, P., Esarey, E. & Leemans, W. P. Guiding of laser pulses in plasma channels created by the ignitor-heater technique. Phys. Plasmas 6, 2269–2277 (1999) sourceNot checked — no full text of the source
• cites [20] Kim, K. Y., Alexeev, I., Fan, J., Parra, E. & Milchberg, H. M. Plasma waveguides: Addition of end funnels and generation in clustered gases. AIP Conf. Proc. 647, 646–653 (2002) sourceNot checked — no full text of the source

Classified as probably not a substantial claim.

The channelling technology offers the ability to control the laser beam propagation much as a copper structure provides guiding and field shaping to RF accelerators.

“The channelling technology offers the ability to control the laser beam propagation much as a copper structure provides guiding and field shaping to RF accelerators.”

Classified as probably not a substantial claim.

For optimum acceleration, accelerator length should be matched to the dephasing length, which is the distance it takes the accelerated electrons to outrun the plasma wave and slip into decelerating phase.

“For optimum acceleration, accelerator length should be matched to the dephasing length, which is the distance it takes the accelerated electrons to outrun the plasma wave and slip into decelerating phase 15 .”

• cites [15] Leemans, W. P. et al. Plasma guiding and wakefield generation for second-generation experiments. IEEE Trans. Plasma Sci. 24, 331–342 (1996) sourceNot checked — no full text of the source