Hajime Kuwabara

Plasma light source

Abstract In confining this review to non-L.T.E. plasmas, it will be clear that the main emphasis, of relevance to beam-foil spectroscopy, is on separation of ion stages and line identification. Only rarely can lifetimes be determined. The majority of line classifications for highly-charged ions, carried out over the last forty years, have used the two-electrode vacuum spark, a source that is still in use today. Low inductance triggered vacuum sparks have produced spectra up to copper XXVIII and have some properties in common with the plasma focus source. Laser-generated plasmas with temperatures of 100 eV or higher offer unique facilities for separating neighbouring stages of ionization. Magnetically confined plasmas are more homogeneous in temperature and often allow ion separation in time, during the ionizing phase. Astrophysical plasmas have a particular interest for forbidden line studies. The forbidden coronal line identifications of nearly thirty years age are now being extended by new observations into the ultraviolet. Other new forbidden lines in the solar soft X-ray spectrum, have changed our understanding of helium-like ion lifetimes.

Head-On Inverse Compton Scattering X-rays with Energy beyond 10 keV from Laser-Accelerated Quasi-Monoenergetic Electron Bunches

Inverse Compton X-rays from laser-accelerated multiple electron bunches are observed. A Ti:sapphire laser (pulse energy: 500 mJ; pulse width: 150 fs) beam is divided into two beams. The main beam is focused onto an edge of a helium gas jet to accelerate electrons to energies of 14 and 23 MeV, which inversely scattered the head-on colliding secondary laser beam into 6 and 12 keV X-rays; this agrees well with that calculated from the electron spectra obtained. This demonstrates a first on-axis inverse Compton scattering X-ray energy detection beyond 10 keV induced by laser-accelerated electrons.

Counter-facing plasma focus system as an efficient and long-pulse EUV light source

A plasma focus system composed of a pair of counter-facing coaxial plasma guns is proposed as a long-pulse and efficient EUV light source. A proof-of-concept experiment demonstrated that with an assist of breakdown and outer electrode connections, current sheets evolved into a configuration for stable plasma confinement at the center of the electrode. The current sheets could successively compress and confine the high energy density plasma every half period of the discharge current, enabling highly repetitive light emissions in extreme ultraviolet region with time duration in at least ten microseconds for Xe plasma. Also, we confirmed operations of our system for Li plasma. We estimated the highest EUV energy in Li plasma operation at 93mJ/4π sr per 2% bandwidth per pulse.

Repetitive operation of counter-facing plasma focus device: toward a practical light source for EUV lithography

In this paper, the latest advances in the field of extreme ultra violet (EUV) light sources for application in counter-facing plasma focus devices are presented. EUV emission, plasma and electrical properties under two pulses operation are reported. Using this new plasma focus system, the total amount of supply material and the energy cost of the plasma source could be reduced. The physical behavior during a two-pulse experiment with a high repetition rate (1 kHz) is explained. Continuous operation for future practical use in advanced lithography systems is also investigated.

Ultra‐intense Laser Applications to the Industries at GPI

The laser accelerator provides us not only ultra high field, but also extremely short pulse radiation sources, the laser‐produced X‐rays. Using a 1.2 TW table‐top Ti:sap laser, we are pursuing the activities for the industrial application. First we proposed a new injection acceleration scheme using the ultra short beat‐wave accelerator for the economical radiation source. Then we proposed two applications both on the backward see‐through vision of distant objects using the laser X‐rays, and on the X‐ray illumination on Aspergillus awamori spores, which is 100 times effective of the current X‐ray tube cases.