Daniil Stolyarov

Efficient extreme ultraviolet plasma source generated by a CO2 laser and a liquid xenon microjet target

We demonstrated efficacy of a CO2-laser-produced xenon plasma in the extreme ultraviolet (EUV) spectral region at 13.5nm at variable laser pulse widths between 200ps and 25ns. The plasma target was a 30μm liquid xenon microjet. To ensure the optimum coupling of CO2 laser energy with the plasma, they applied a prepulse yttrium aluminum garnet laser. The authors measured the conversion efficiency (CE) of the 13.5nm EUV emission for different pulse widths of the CO2 laser. A maximum CE of 0.6% was obtained for a CO2 laser pulse width of 25ns at an intensity of 5×1010W∕cm2.

Multiple photon excitation and ionization of NO in and on helium droplets

The photoexcitation of NO embedded in superfluid Hen nanodroplets having n approximately 10(4) has been examined. Two-photon excitation prepares electronically excited states (NO(*)), most notably, the embedded analog of the A 2Sigma state of gas phase NO. Vertical excitation to this low Rydberg state is blueshifted and broadened relative to its gas phase counterpart because of the repulsive electron-helium interaction. Transport to the droplet surface is believed to be facile in the superfluid. For example, NO* prefers (energetically) to reside at the droplet surface rather than at the droplet center, in contrast to NO. Photoionization of surface-bound NO* occurs over a significant photon energy range. This yields small cluster ions NO+Hek) with approximately 90% of these clusters having k< or =10. The variation of ion yield with photon energy displays a precipitous change in the region of 24 300-24 400 cm(-1) for all values of k. Possible photoionization mechanisms are discussed and it is suggested that intermediate levels with high-n Rydberg character play a role. This work underscores the important role played by transport in the photophysics of species embedded in the superfluid host.

Plasma wakefield acceleration utilizing multiple election bunches

We investigate various plasma wakefield accelerator schemes that rely on multiple electron bunches to drive a large amplitude plasma wave, which are followed by a witness bunch at a phase where it will sample the high acceleration gradient and gain energy. Experimental verifications of various two bunch schemes are available in the literature; here we provide analytical calculations and numerical simulations of the wakefield dependency and the transformer ratio when M drive bunches and one witness bunch are fed into a high density plasma, where M is between 2 and 10. This is a favorable setup since the bunches can be adjusted such that the transformer ratio and the efficiency of the accelerator are enhanced compared to single bunch schemes. The possibility of a five bunch ILC afterburner to accelerate a witness bunch from 100 GeV to 500 GeV is also examined.

Plasma Density Measurements in Hydrogen‐Filled and Ablative Discharge Capillaries Based on Stark Broadening of Atomic Hydrogen Spectral Lines

Results of plasma density measurements in ablative and hydrogen‐filled discharge capillaries are presented. The method of plasma density measurement is based on Stark broadening of atomic hydrogen spectral lines in the plasma due to interaction of the hydrogen atoms with free charges. To ensure the measured plasma density corresponds to the internal portion of the discharge volume, we also examine a possibility to collect the plasma light emission with an optical fiber inserted inside the capillary channel. We studied the time dependence of the plasma density relative to the beginning of the discharge with a temporal resolution of 150 ns. The plasma density was found to vary over a range of 1017–1015 cm−3. The dependence of the plasma density upon discharge voltage and hydrogen pressure in the hydrogen‐filled capillary was also studied. The possibility of designing a hybrid ablative hydrogen‐filled capillary that allows us to simplify the high voltage generator scheme and reach high plasma densities is di...

Resonant Plasma Wakefield Experiment: Plasma Simulations and Multibunched Electron Beam Diagnostics

In the multibunch plasma wakefield acceleration experiment at the Brookhaven National Lab’s Accelerator Test Facility a 45 MeV electron beam is initially modulated through the IFEL interaction with a CO2 laser beam at 10.6 μm into a train of short microbunches, which are spaced at the laser wavelength. It is then fed into a high‐density capillary plasma with a density resonant at this spacing (1.0 × 1019cm−3). The microbunched beam can resonantly excite a plasma wakefield much larger than the wakefield excited from the non‐bunched beam. Here we present plasma simulations that confirm the wakefield enhancement and the results of a series of CTR measurements performed of the multibunched electron beam.

Terawatt CO 2 laser: a new tool for strong-field research

We describe the physical principles and architecture of a multi-stage picosecond terawatt CO2 laser system, PITER-I, operational at Brookhaven National Laboratory (BNL). The laser is a part of the DOE users facility open for international scientific community. One of the prospective strong-field physics applications of PITER-I is the production of proton- and heavy-ion beams upon irradiating thin-film targets and gas jets. We discuss the possibilities for upgrading a CO2 laser to a multi-terawatt femtosecond regime.

Vacuum laser acceleration in proof of principle at BNLATF

The novel and revolutionary concept of real Vacuum Laser A acceleration proof of principle is described in this paper. The simulation with the current BNL-ATF parameter shows that electron beam can get net energy from intense laser beam. The initial 20MeV electron beam with energy spread of 10−3 can get hundreds of KeV energy gain with energy spread of 10−2 by interacting with a laser a0 = 1. The proposal has been presented and approved by BNL-ATF. The experiment for this proof of principle is going to be scheduled.

A multibunch plasma wakefield acceleration experiment at the Brookhaven National Laboratory

Plasma-based particle accelerators have made remarkable progress in the recent years. In particular the doubling of the energy of 42 GeV trailing electrons has been demonstrated in a bean-driven plasma wakefield accelerator (PWFA) at the SLAC National Accelerator Laboratory [I. Blumenfeld et al., Nature 445, 741–744 (15 February 2007)]. The next significant step for a PWFA is to demonstrate the acceleration of a witness bunch with a narrow energy spread. We have recently demonstrated experimentally a simple mask method to generate a train of drive bunches followed by a witness bunch with variable spacing in the picosecond range [P. Muggli et al., Phys. Rev. Lett. 101, 054801 (2008)]. The train of drive bunches resonantly drives the wakefield, while the witness bunch is accelerated. The number of drive bunches, and therefore the accelerating wakefield amplitude can be selected. In a multi-drive-bunch configuration the witness bunch energy can be multiplied by a factor larger than two, and the transformer ratio and the transfer efficiency can in principle be maximized. The plasma is generated by a H2-filled capillary discharge. The plasma density measured and time-resolved using Stark broadening of the Hα atomic line. It is adjusted to the resonance by varying the delay between the capillary discharge time and the arrival time of the electron train.

Plasma wakefield acceleration experiments using two subpicosecond electron bunches

Two subpicosecond electron bunches, separated in energy by approximately 2 MeV and in time by 0.5-1 ps, are sent through a capillary discharge plasma. The plasma density is varied from ~1014 cm3 to ~1018 cm3. A 1-D plasma wakefield acceleration (PWFA) model indicates the net wakefield produced by the bunches will depend on their relative charge, temporal separation, and the plasma density. The wakefield of the first bunch will also affect the amount of energy gain or loss of the second bunch. During measurements of the energy spectrum of the bunches, we observed a difference in the amount of loss depending on the plasma density. Indication of gain was also observed.

Optical parametric amplifier test for optical stochastic cooling of RHIC

Optical Stochastic Cooling (OSC) of gold ions in the Relativistic Heavy Ion Collider (RHIC) operating on wavelength ~12 mum has been proposed by Ilan Ben-Zvi and use of Optical Parametric Amplifier (OPA) for OSC was suggested by Max Zolotorev [1, 2]. We have tested the performance of the OPA suggested to be used in OSC for RHIC. Our OPA is based on a single CdGeAs2 crystal that has been pumped by a second harmonic of pulsed CO2 laser system. Particle emission was emulated by output of another hybrid CO2 laser operating in single longitudinal mode regime at wavelength 9.552 mum. The maximum amplification was achieved at a pump intensity value of 9.2times106 W/cm2. Further increase of the pump intensity caused amplification quenching which we attribute to nonlinear multiphoton absorption of the pump beam. We also performed interferometric measurements that demonstrate that amplification of the radiation in OPA preserves its coherence.