1st ZEUS user webinar Q&As

General facility questions

Q:  Is there a facility resource/FAQ page? ie. For information on available and upcoming diagnostics?

A: We are in the relatively early stages of designing the system and therefore the final capabilities and full diagnostics are being developed. User input to this will be very important. A timeline is added to the website to show the planned progress and access to users should be available by the end of 2023.

Q: What will be the limit in stretching the short pulse? Something like a few 100s fs?

A: It should be possible to detune the compressor to produce a chirped pulse of a few 100 fs.

Q: How well the 3PW and 0.5PW beams will be synchronized and pointed?

A: The maximum power of the system is planned for 3 PW. One configuration for running will be splitting the beam into 2.5 PW and 0.5 PW. The relative timing between these beams should be good because they are from the same source. The pointing stability will be dependent on how stable we can make the foundations of the laser and isolate vibrations (from pumps, etc). Also, the very long focal length parabola will naturally be less stable. We are looking into methods for active stabilization to mitigate the oscillations.

Q: What is the envisioned rep rate of Zeus full intensity, two beam interactions?

A: For 3 PW shots, the rep rate would be once per minute (radiation limits applying).

Q: Will there be phase plates for the long pulse laser?

A: We are currently investigating what will be required for achieving smooth focal spots. But here, user input will be valuable.

Q: WIll be the facility 24 hours operated?

A: How the facility will operate will somewhat be dependent on the level of funding provided by the NSF to operate and staff the facility. However, we are not currently planning to operate 24 hours per day.

Q: As to the research on neutron stars, what do you have in mind with this kind of mid scale facility?

A: The magnetic fields generated during interactions should be very large, creating the opportunity to study plasma physics under extreme conditions. In the particularly strong fields of neutron stars known as magnetars, the fields can exceed the QED critical field. The perturbation theories for strong fields describing these environments can be explored in laser-beam collision experiments, as the theory for laser fields and magnetic fields becomes similar for ultrarelativistic particles.

Q: Will you have active/real-time radiation monitoring?

A: We are working with our local radiation officiers to arrange radiation monitoring.

Q: Will you have automatic pointing stabilisation?

A: The will be an automatic pointing stabilization in the laser chain. We will consider automatic pointing stabilization for a colliding experiment in the gas target area.

Q: Will there be other facilities available? Will T-Cubed and Lambda cubed will be moved, retired, or upgraded?

A: Lambda cubed is housed in a different building, entirely separate from Hercules/ZEUS and will continue to operate for internal use (it is not a user facility). T-cubed will be moved from its current location to make way for the ZEUS facility envelope.

Q: Any plan for future upgrade to 10 PW?

A: We are excited to make the 3 PW system work first before considering further upgrades. Our current building envelope would not accommodate a further upgrade.

Q: What is the bandwidth? Any chance for a flying focus?

A: The design is for the bandwidth to be ~ 60 nm. We’ll seek interested user input to see if this is sufficient for a flying focus.

Target area questions

Q: What is the present limit to 500 TW in the solid target area? The size of the available focusing optics?

A: This is due to the present size of the vacuum chamber, plasma mirror optic, deformable mirror and vacuum beamlines that will be available in the Target Area 2.  We have plans to upgrade operations to higher power in the future, funding permitting.

Q: Will the long-pulse be available in the solid target area?

A: Yes.

Q: Will the long pulse beam be only available in Target Area 1? Which configuration will it have?

A: The long pulse will be available in both Target Areas 1 and 2.

Q: What’s the limit on shielding? Will neutron generation be allowed?

A: The shielding is being designed for 10 GeV electron beams. Significant neutron generation is therefore expected. Shot limits will be determined by the type of experiment and radiation generated. However, our radiation shielding modeling included neutrons in dose limit calculations so target areas 1 and 2 will be able to accommodate neutron experiments

Q: What’s the a0 for long focus geometry?

A: The long focusing geometry for the Target Area 1 is designed to be ~f/70 (focal length ~ 18 m). a0~3-4.

Q: Will you be able to *collide* gamma beams (say 10 GeV each)?

A: This is not envisaged in the present configuration. However gamma ray collision experiments could be possible in the future.  However, gamma-gamma collisions are possible with only one beam being at high energy.

Q: Are there any concerns/limits to operating the 0.5 PW laser at the full repetition rate?

A: We will be initially running in burst mode because of compression grating damage considerations. Hopefully new technology will enable continuous operation in the future. We will also get input from our advisory board, which includes members designing the 10 Hz 1PW laser at the Rutherford Appleton Laboratory and 1 Hz 3 PW systems at LMU/MPQ Munich.

Q: It would be useful to distribute a floor plan with dimensions, thanks!

A:  This will be on the web-site soon. The architects are currently finalizing their drawings (June 2020).

Q: Do you have any plans for target debris mitigation for solid interaction?

A: At a high rep rate we have previously used a pellicle in front of the target to limit damage to the optics. For the new system at higher power we will consider additional techniques such as B-fields.

Q1:What level of contrast can users expect at 3 PW with and without using plasma mirrors? Are there specific peak intensity diagnostics that you plan to use for 3 PW pulses?

Q2: Roughly what will be the typical temporal contrast on the full 3 PW beam?

A: The inherent temporal contrast (nanosecond timescale) is anticipated (and being designed) to be similar to the existing Hercules 0.5 PW system at 10^-11 (without plasma mirrors). The “solid” target area (0.5 PW) is intended to have a double plasma mirror setup to further improve the contrast.

Q: Will the chambers allow top access? Would be nice if you could show some details of the chambers, thanks.

A: The target chambers are in the process of being designed and technical drawings prepared. It is planned for them to be accessed from both the top (lifting the lid using a crane) and from the side. Once we have drawings, these could be shared with the community.

Q: In a two PW beam experiment, would two gas jets/cells be available?

A: Yes, gas jets and cells are envisaged as a main target for many experiments. Two beam experiments would be 0.5 PW and 2.5 PW split.

Q: Will the solid targets insertion be compatible with the high-rep operation?

A:  We have significant experience with rotating solid targets and liquid targets however other possibilities include liquid crystal thin film targets and cryogenic hydrogen gas targets.

Q: (I think this question is on the slides) Will there be motorized stages etc. for high-rep-rate solid targets?

A: Presently a 500 TW experiment is operational in a single shot mode due to strict requirement for target positioning for an F/1 geometry and because of the use of a double plasma mirror setup.  This will still continue for some time until both problems are solved.

Q: Is there a plan for an adaptive optic in the solid target area? Possibly after the plasma mirrors.

A: There will be a deformable mirror for 500 TW and a 10-12” DM for 3 PW for the gas target area.  A larger deformable mirror enabling 3 PW in the solid target area is planned for the future.

Q: Will doubled light be possible?

A: For the short-pulse, doubled light would be possible for 0.5 PW. A full aperture crystal has not yet been proven for the 3 PW beam size.

Diagnostic questions

Note that we will be developing in house diagnostics that will be made available to external users. However what will be available will be somewhat tied to funding levels. User input is very valuable and diagnostic development will be ongoing.

Q1: Is there a plan for facility diagnostics development?

Q2: Any plans for what diagnostic capabilities will be available?

A: We have many standard diagnostics available from Hercules and hope to well diagnose the laser parameters. We are planning experimental diagnostic development specifically for the higher power operation, such as a high energy electron spectrometer.

Q: For many experiments involving high energy particles, large magnet sets may be required; will they be provided by the facility?

A: A 10 GeV electron-positron spectrometer is being planned for. Other large magnet geometries may be accommodated, but now is a great time for us to get feedback about the expected requirements of the user community to best plan within our budget and space constraints.

Q: Do you prepare any detecting device for high energy gamma ray such as over 100 MeV to GeV level?

A: Currently, we have scintillator based detectors/diagnostics. There is clearly a need to further develop diagnostics in this area.

Q: Will you have a small energy probe beam? And could it be off-harmonic?

A: Our approach to creating an optical probe beam has previously been to pick off a small portion of the main beam to use as a diagnostic. This is the approach we envisage for ZEUS. Creating an off-harmonic probe may be possible with development (time and money).

Q: Do you have a pulse power available, like to power coils? Would this be available to users as well?

A: Gennady Fiksel is a Research Scientist at CUOS and has developed in house pulsed magnet capabilities up to 30T. The integration of this type of technology may be possible in the target chamber (we have done this in other target chambers here at Michigan. For other pulsed power systems, such as a z-pinch or x-pinch type device, this may be possible in the future, but would need further funding and user interest.

Q: I would suggest planning right from the start the integration of ZEUS with a 1 MA plused-power driver. The driver could fit easily under the chamber and allow combined experiments between high power lasers and pulsed-power.

A: That would open more possible experiments, but we do not currently have funding to do this.

Q: Is there a plan for automated data collection / laser parameter saving?  (particularly at higher repetition rate?)

A: We are looking into automated / high rep rate data collection and storage. We are also considering how outside users may be able to access their data remotely (since the volume might be very large). These issues have been addressed by other facilities, who we will consult.

Q: Are there shared data standards and formats that will be used by ZEUS, NEXUS, and similar facilities?

A: No, not yet. But this is a good point that we can investigate.

Q: Will experimental results be made openly available (perhaps after an embargo period of ~1-2 years) to facilitate scientific reproducibility?

A: This has not yet been considered, but should be discussed within the community to determine the facility protocols.