Marcus Babzien

Observation of the nonlinear effect in relativistic thomson scattering of electron and laser beams

Thomson scattering of high-power laser and electron beams is a good test of electrodynamics in the high-field region. We demonstrated production of high-intensity X-rays in the head-on collision of a CO2 laser and 60-MeV electron beams at Brookhaven National Laboratory, Accelerator Test Facility. The energy of an X-ray photon was limited at 6.5 keV in the linear (lowest order) Thomson scattering, but the nonlinear (higher order) process produces higher energy X-rays. We measured the angular distribution of the high-energy X-rays and confirmed that it agrees with theoretical predictions.

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.

Photoinjected energy recovery linac upgrade for the National Synchrotron Light Source

We describe a major paradygm shift in in the approach to the production of synchrotron radiation This change will considerably improve the scientific capabilities of synchrotron light sources. We introduce plans for an upgrade of the National Synchrotron Light Source (NSLS). This upgrade will be based on the Photoinjected Energy Recovering Linac (PERL). This machine emerges from the union of two technologies, the laser-photocathode RF gun (photoinjector) and superconducting linear accelerators with beam energy recovery (Energy Recovering Linac). The upgrade will bring the NSLS users many new insertion device beam lines, brightness greater than 3rd generation light-sources and ultra-short pulse capabilities, not possible with storage ring light sources.

Laser-induced damage threshold at chemical vapor deposition–grown diamond surfaces for 200-ps CO 2 laser pulses

We report laser-induced damage thresholds (LIDTs) at chemical vapor deposition (CVD)-grown diamond surfaces for 200-ps CO(2) laser pulses, obtained with photoacoustic diagnostics. The results are compared with those at ZnSe and Ge surfaces under the same experimental condition. For 200-ps laser pulses, CVD diamond, ZnSe, and Ge were measured and found to have damage fluences of 1.2, 0.45, and 0.2 J/cm(2) , respectively, for a laser waist radius of 134 mum. Acoustic measurement indicated a relatively large variation in the LIDT of the CVD-grown diamond because of its polycrystalline structure.

Plasma-based advanced accelerators at the Brookhaven Accelerator Test Facility

The Accelerator Test Facility at Brookhaven National Laboratory (BNL ATF) offers to its users a unique combination of research tools that include a high-brightness 70-MeV electron beam, a mid-infrared (λ = 10 μm) CO2 laser of terawatt power, and a capillary discharge as a plasma source. These cutting-edge technologies have enabled us to launch a new R&D program at the forefronts of advanced accelerators and radiation sources. The main subjects that we are researching are innovative methods of producing wakes in a linear regime using plasma resonance with the electron microbunch train periodic to the laser’s wavelength and so-called “seeded” laser wakefield acceleration (LWFA) that is driven and probed by a combination of electron and laser beams. We describe the present status of the ATF experimental program, including simulations and preliminary experiments; in addition, we review previous ATF experiments that were the precursors to the present program. They encompass our demonstration of longitudinal-and transverse-field phasing inside the plasma wave, plasma channeling of intense CO2 laser beams, and the generation of e-beam microbunch trains by the inverse FEL technique.

A Multibunch Plasma Wakefield Accelerator

We investigate a plasma wakefield acceleration scheme where a train of electron microbunches feeds into a high density plasma. When the microbunch train enters such a plasma that has a corresponding plasma wavelength equal to the microbunch separation distance, a strong wakefield is expected to be resonantly driven to an amplitude that is at least one order of magnitude higher than that using an unbunched beam. PIC simulations have been performed using the beamline parameters of the Brookhaven National Laboratory Accelerator Test Facility operating in the configuration of the STELLA inverse free electron laser (IFEL) experiment. A 65 MeV electron beam is modulated by a 10.6 μm CO2laser beam via an IFEL interaction. This produces a train of ∼ 90 microbunches separated by the laser wavelength. In this paper, we present both a simple theoretical treatment and simulation results that demonstrate promising results for the multibunch technique as a plasma-based accelerator.

Submicron emittance and ultra small beam size measurements at ATF

This paper covers improvements to a photoinjector that lead to the realization and measurement of submicron normalized emittance for a 0.5 nC electron beam at the Brookhaven Accelerator Test Facility. A fitting procedure utilizing beam size measurements from multiple beam profile monitors along the transport line was used instead of more traditional techniques. Such a small emittance beam in combination with a tight focusing scheme allowed us to achieve 10 μm RMS beam sizes at 60 MeV. The behavior and limitations of different BPM screens is compared for such beams.

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.

Commissioning results of the BNL/SLAC/UCLA symmetrized 1.6-cell S-band emittance-compensated photoinjector

The BNL/SLAC/UCLA symmetrized 1.6 cell S-band emittance- compensated photoinjector has been installed at the Brookhaven Accelerator Test Facility (ATF). The commissioning results and performance of the photocathode injector are presented. This photoinjector consists of the symmetrized BNL/SLAC/UCLA 1.6 cell S-band photocathode radio frequency gun and a single solenoidal magnet for transverse emittance compensation. The highest acceleration field achieved on the cathode is 150 MV/m, and the normal operating field is 125 MV/m. The quantum efficiency of the copper cathode was measured to be 4.5 multiplied by 10-5. The measured quantum efficiency of the magnesium cathode is a factor of ten greater than that of copper after using both laser and laser assisted explosive electron emission cleaning. The transverse emittance and bunch length of the photoelectron beam were measured. The optimized rms normalized emittance for a charge of 329 plus or minus 12 pC is 2.0 plus or minus 0.3 pi mm-mrad. The bunch length dependency of photoelectron beam on the rf gun phase and acceleration fields were experimentally investigated. Electric and magnetic field asymmetries studies are presented.