Berkeley Lab Laser Accelerator (BELLA) Center

Lawrence Berkeley National Laboratory
Availability in Run 2

For Run 2, the BELLA center will support 1 to 2 PRP-selected experiments on the HTW laser system. The BELLA PW system is undergoing upgrades: while formal user experiments will not be accepted in this cycle, there may be the opportunity to participate in commissioning activities.

The Berkeley Lab Laser Accelerator (BELLA) Center offers two laser facilities to LaserNetUS  users.  The first offers a PW class laser with pulses of up to 40 Joules on target in as little as 30 fs at 1 Hz repetition rates. The second offers two amplifier arrays providing 50 TW class and 10 TW class pulses, respectively, in pulses as short as 40 fs (see BELLA HTW laser below). 

The Center’s own research focuses on the development and application of laser-plasma accelerators (LPAs), which may provide user opportunities in use of the generated beams. LPAs produce ultrahigh accelerating fields (1-100 GV/m) and may provide a compact technology for a variety of applications that include accelerators for high energy physics and drivers for high energy photon sources.  Electron beams at 0.01-8 GeV, and ion beams at a few MeV have been produced and measured. Femtosecond, keV band betatron radiation is produced from the acceleration process. Projects are under way to produce femtosecond quasi-monoenergetic MeV Thomson photons.

BELLA PW Laser

Petawatt peak power at high repetition rate (1 Hz) driving multi-GeV LPAs

 

BELLA PW laser and target area configuration
BELLA PW laser and target area configuration

 

The BELLA Petawatt Laser is a Ti:sapphire CPA laser providing laser pulses at petawatt-level peak power with a repetition rate, unprecedented at that power, of 1 Hz. It was designed, built and installed in collaboration with a commercial vendor (Thales).

From foreground to background, the plasma target chamber, part of the High Power Diagnostic system with the Electron Energy Spectrometer, and the Electron Beam Dump
BELLA PW laser target area: From foreground to background, the plasma target chamber, part of the High Power Diagnostic system with the Electron Energy Spectrometer, and the Electron Beam Dump

The laser consists of a front end system that outputs ~1.4 joules/pulse (uncompressed) at 10 Hz, followed by two final amplifiers that operate at the final 1 Hz repetition rate. The final uncompressed pulse energy is > 65 J. This is sent to a grating-based optical compressor that produces >40 J compressed pulses which can be shorter than 30 femtoseconds, reaching a peak power of ~1 petawatt. The laser is subsequently focused with a long focal length off-axis paraboloid mirror into the target chamber.

The laser is equipped with sophisticated diagnostics and controls. Control systems safely operate and continuously monitor its important parameters from a centrally located control room. A magnetic electron spectrometer using phosphor screens and multiple CCD cameras allows high repetition rate analysis. This is backed up by on-line neutron and gamma ray monitoring. Optical diagnostics monitor the energy, spectrum, and other parameters of the transmitted laser to infer its coupling to the LPA.

The primary activities are focused on the research and development of LPAs at energies expected to reach 10 GeV. This includes controlled production, detailed characterization, and applications of the electron beams.

The laser has been used to produce electron beams up to 8 GeV.  It has also been used to produce high charge ion beams, which have been diagnosed using a Thomson parabola spectrometer as well as RCF stacks available on the facility. The current target chamber has dimensions of  2” x 2” x 4”, a second target chamber is being built and will be available in future calls for higher intensity experiments. For details of the laser system see K. Nakamura et al., IEEE J. Quantum Electron. 53, 1200121 (2017).

BELLA HTW laser

50 TW peak power at up to 5 Hz driving GeV LPAs and MeV photon sources

Default configuration of target area and diagnostics
BELLA HTW default configuration of target area and diagnostics.

 

The BELLA HTW Laser is a Ti:sapphire CPA laser providing laser pulses in the primary arm at 50 TW-level peak power with a repetition rate of 5 Hz. A secondary laser arm provides 10 TW-level peak power at 5 Hz and is available in the same target chamber for multi-beam experiments.  It was designed, built and installed by LBNL staff, using a Coherent front end and Thales pump laser.  This system does not have a contrast cleaner and as a result has a femtosecond prepulse in the 1e-3 range at several ns range from the main pulse.

View of target area looking upstream.  From foreground to background:  the photon/neutron experiment table, the electron beam dump wall, the Electron Energy Spectrometer, and the plasma target chamber
BELLA HTW view of target area looking upstream.  From foreground to background:  the photon/neutron experiment table, the electron beam dump wall, the Electron Energy Spectrometer, and the plasma target chamber

The laser consists of a front end system that outputs ~2mJ/pulse (uncompressed) at 1kHz, followed by three final amplifiers that operate at the final 5 Hz repetition rate. The final uncompressed pulse energy is 4 J in the primary arm and 1 J in the secondary arm. These are sent to grating-based optical compressors producing compressed pulses which can be as short as 40 femtoseconds of >2 J and > 0.5 J respectively.

Both lasers are focused in a  off-axis paraboloid mirrors of 1.1 -1.5 m focal length in a common target chamber which has an experimental breadboard 47” wide by 131” long.  The laser is equipped with sophisticated diagnostics and controls. Control systems safely operate and continuously monitor its important parameters from a centrally located control room. A magnetic electron spectrometer using phosphor screens and multiple CCD cameras allows high repetition rate analysis. This is backed up by on-line neutron and gamma ray monitoring. Optical diagnostics can monitor the energy, spectrum, and other parameters of the transmitted laser to infer its coupling to the LPA. The target chamber has numerous ports on the sides, top and bottom, which can be fitted with windows, feedthrough ports, and target delivery systems. Standard target positioners to position a large array of targets. Gas jet targets have been used to date.   A large area downstream of the magnetic spectrometer and shielded from the primary target chamber is available for experiments using photon or neutron beams produced.

The primary activities are focused on the research and development of LPAs at GeV-class energies and their use to produce mono-energetic Thomson photon beams at MeV energies.  Betatron radiation in the keV band is also produced.   X-ray and MeV photon detectors are available including CCD cameras, scintillators, and Compton spectrometers.  Collaborative experiments using photon beams can be discussed.

The default configuration has the primary beam focused at 1.5 m focal length and directed towards the magnetic spectrometer.  The secondary beam is focused nearly counter-propagating using a 1.1 m focal length.  Other configurations can be considered and should be discussed with the facility.

Opportunities for LaserNet US at BELLA Center

Membership in and support from LaserNet US will provide an opportunity to explicitly support user experimental time on BELLA Center systems, outside of the normal BELLA Center experimental run program, allocated through the LaserNetUS proposal process.

Facility access

All members of an experimental team expecting to be present at the BELLA Center must be registered with LBNL through the LBNL onboarding process and complete all required courses before arriving (some courses are only required for specific activities). The spokesperson for an accepted LaserNetUS proposal (e.g. they who submitted the proposal) will be asked to name a principal investigator (PI) for the experiment. A BELLA Center Scientist Point Of Contact (POC) will be assigned, who will guide the PI through the steps of preparing for their laser time.

 

Reference:

K. Nakamura, H.-S. Mao, A. J. Gonsalves, H. Vincenti, D. E. Mittelberger, J. Daniels, A. Magana, C. Toth, and W. P. Leemans, IEEE Journal of Quantum Electronics vol. 53, no.4,  1200121 (2017).

Thomas Schenkel, t_schenkel@lbl.gov

1 PW Mode

Parameter Value Unit Additional Information
Center Wavelength 815 nm  
Pulse duration (FWHM) 30 fs  
Max energy on target 40 J  
Shot energy stability 2.5 % r.m.s.  
Focal spot at target:      
F/number 65    
intensity FWHM 65 μm  
Strehl ratio >0.9    
Energy containment 75 % within 67 µm radius
Pointing Stability 1.3 μrad r.m.s.      
Pre-pulse contrast:      
ns scale 10-9   @ 1 ns  
ps scale 10-6   @ 5 ps  
Repetition Rate 1 Hz    

Hundred TW Mode

Parameter Value Unit Additional Information
Center Wavelength 810 nm  
Pulse duration (I FWHM) 40 fs  
Max energy on target 2.5 J  
Shot energy stability 1 % r.m.s.
Focal spot at target      
F/number f/15    
intensity FWHM 13 µm  
Strehl ratio 0.9    
Energy containment 75 % within 17 µm radius
F/number f/20    
intensity FWHM 20 µm  
Strehl ratio 0.9    
Energy containment 75 % within 25 µm radius
Pre-pulse contrast      
ns scale 10-9   @ 1 ns (pedestal)
ps scale 10-6   @ 5 ps
Repetition Rate 5 Hz