Red Team/Blue Team

ALEGRO Workshop, SLAC

March 6, 2025

Propositions

1. Physics case: The Physics Case for a 10 TeV Wakefield Collider is compelling and competitive with other 10 TeV pCM concepts, regardless of collision type (e+e-, e-e-, gamma gamma).
2. Detector backgrounds: Particle detectors can operate with the large beamstrahlung backgrounds that come from 10 TeV collisions.
3. Cost: Recent work by the HALHF collaboration indicates that major costs for plasma-based colliders come from “conventional” systems, such as the drive beam RF linac. Nevertheless, wakefield colliders will ultimately be cheaper than other 10 TeV pCM options.
4. Operations:
1. The 10 TeV collision energy can be held constant, even if a wakefield acceleration stage is “lost”. Brief deviations in energy are acceptable.
2. Sub-nanometer-wide beams can be brought into collision and remain aligned.
3. Beam losses in the wakefield accelerator linac will be manageable and in-person maintenance can be performed.
5. Roadmap: A path to a 10 TeV Wakefield Collider exists, regardless of whether the 10 TeV machine is an upgrade of an existing Linear Collider or a green field project.

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Panelists

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Michael Peskin

SLAC

Simone Pagan Griso

LBNL

Caterina Vernieri

SLAC

Jens Osterhoff

LBNL

Mark Hogan

SLAC

Andre Seryi

JLab

Robert Szafron

BNL

Charlie Young

SLAC

Angira Rastogi

LBNL

John Power

ANL

Carl Schroeder

LBNL

Patric Muggli

MPP Munich

Arguing Against

Arguing For

Format

• Physics case
• Red Team
• Blue Team
• Detector backgrounds
• Blue Team
• Red Team
• Cost
• Red Team
• Blue Team
• Operations
• Blue Team
• Red Team
• Roadmap
• Red Team
• Blue Team

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• Physics case: The Physics Case for a 10 TeV Wakefield Collider is compelling and competitive with other 10 TeV pCM concepts, regardless of collision type (e+e-, e-e-, gamma gamma).

Red (Michael)

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Blue (Robert)

• New physics must exist, but theory does not give us any guidance on where to look for it
• Many ideas have been tested but so far without any clear signal
• Each mode gives us unique opportunities and synergies with low-energy searches.
• 10 TeV Wakefield Colliders give us a chance to broaden our searches significantly!
• VBF allows us to scan a wide range of masses.
• Secondary particles in the beam help offset the drawbacks of a particular collision type!
• Every mode allows us to perform precision searches (e.g., t-channel processes help us understand running couplings at high scales).

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Pathfinder approach: A technically less challenging option allows us to explore new physics faster, using adaptive operation—allowing technically simpler modes to drive early discoveries and facilitate later, more focused investigations.

• Physics case: The Physics Case for a 10 TeV Wakefield Collider is compelling and competitive with other 10 TeV pCM concepts, regardless of collision type (e+e-, e-e-, gamma gamma).

2: Particle detectors can operate with the large beamstrahlung backgrounds that come from 10 TeV collisions.

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From Nicole’s talk

Incoherent pair production

Particles from beamstrahlung

Blue (Charlie, Angira)

2: Particle detectors can operate with the large beamstrahlung backgrounds that come from 10 TeV collisions.

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1. Beamstrahlung is a concern for detectors that should not be taken lightly; however, there are knobs that can be tuned to reduce the impact of this background. This needs to be a broad collaborative effort where all aspects are on the table to achieve global optimization, e.g. beam properties, beam pipe geometry, detector magnetic field, sensitive detector parameters etc,
2. We have lived through backgrounds previously deemed scary, e.g. high pileup at LHC. While this does not mean we can overcome all future challenges, we should not back off so easily on a long-term undertaking.
3. In the spirit of ““no battle plan survives first contact with the enemy”, strive to preserve further design and operational flexibility.
4. Members of the Red Team contributed to presentations in this workshop that painted a picture of challenges that are not insurmountable, we would therefore welcome them to move their chairs to the Blue side!

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Blue (Charlie, Angira)

2: Particle detectors can operate with the large beamstrahlung backgrounds that come from 10 TeV collisions.

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Red (Simone, Caterina)

3: Cost: Recent work by the HALHF collaboration indicates that major costs for plasma-based colliders come from “conventional” systems, such as the drive beam RF linac. Nevertheless, wakefield colliders will ultimately be cheaper than other 10 TeV pCM options.

• Red Team (Jens)
• The first part is likely true and the second part has no basis in fact and needs further study (see e.g. ITF Report).
• Admittedly the comparison is not easy because nobody knows how much the dipoles for FCChh will cost and this assumes that FCCee will go forward despite its own budgetary challenges
• Same is true for muon collider. How do we cost that given explosion in costs at FNAL for neutrino program?
• Almost regardless, even if the plasma is free, things are still expensive and dominated by traditional accelerator systems, tunnels, etc. A 10 TeV wakefield collider may have the same infrastructure budget and footprint as e.g. a Muon collider, so similar cost?�Are laser drivers a solution to reduced cost? Unclear. Needs study.

Also, does it matter if one is 4x too expensive and the other is 5x too expensive? It is still too much… (That’s still > $10B and, likely, many billion too many)* The first part is likely true and the second part has no basis in fact and needs further study.

* Admittedly the comparison is not easy because nobody knows how much the dipoles for FCChh will cost and this assumes that FCCee will go forward despite its own budgetary challenges

* Same is true for muon collider. How do we cost that given explosion in costs at FNAL for neutrino program

* All this points to the physics community not being good (or honest) at real estimations

* Almost regardless, even if the plasma is free, things are still too expensive so does it matter if one is 4x too expensive and the other is 5x too expensive?

* HALHF optimizer is a good example that shows that plasma systems are 1/3 of the cost - conventional systems are still $10B and many billion too many

• Blue Team (John) on next 3 slides

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4: Operations:

1. The 10 TeV collision energy can be held constant, even if a wakefield acceleration stage is “lost”. Brief deviations in energy are acceptable.
2. Sub-nanometer-wide beams can be brought into collision and remain aligned.
3. Beam losses in the wakefield accelerator linac will be manageable and in-person maintenance can be performed.

• Blue (Carl)

a. This needs to be studied carefully, but for beams with energies larger than the energy gain per stage, the loss of stage is not catastrophic because beam parameters do not change significantly from stage to stage, and the loss of energy is ´adiabatic´, i.e., what happens in the next stage is weakly dependent on what happened in the previous one.

b. Collision between two beam is maintained through feedback systems. These are used at all colliders (LHC, KEK with nm beam sizes, etc.) and will be implemented in the new collider. Effects such as ground motion have been included and collisions successfully maintained.

c.. At high energies, the beam beta function is long enough that, while the beam will not reach the collision point with required parameters, it will be transported and properly handled by collimators, etc. Proper handling of ´off beams´ is included in the design (e.g., see BDS presentations). That means that handling of equipment by repair teams will be possible.

• Red Team (Mark) – see next slide

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Question/Provocation 4 – Red Team

Operations:

a. The 10 TeV collision energy can be held constant, even if a wakefield acceleration stage is “lost”. Brief deviations in energy are acceptable.

• Carl’s longitudinal correction scheme is encouraging and gives hope that there may be self-stabilization techniques for the energy
• This does not however account for what happens when the focussing of the plasma column vanishes. The plasma is both the strongest accelerating element AND the strongest focussing element with many *2-pi betatron phase. What happens when this 14m plasma stage turns into a drift
• This likely means the beam gets lost at that location and with such enormous beam power the shielding and activation concerns need to be addressed

b. Sub-nanometer-wide beams can be brought into collision and remain aligned.

• Maybe
• Tolerances might be similar to CLIC and thus at least have a chance and if the plasma has beams at a rate of 10KHz as opposed to a few tight trains, this is better for feedbacks
• However - what happens to e-e- or gamma-gamma when you don’t have the attraction of the beams to guide you into collisions? There is no answer there that we have seen.

c. Beam losses in the wakefield accelerator linac will be manageable and in-person maintenance can be performed.

• In an ideal world but see part a
• Many (all?) plasma experiments now currently loose percentages of the beam in a single stage. This is not even close to acceptable at the large beam power we are discussing
• Some loss requirements need to be defined that keep the activation to a level consistent with other such accelerators and this hasn’t been done. Once we know the requirements (10^-2, 10^-3,…10^-6 we can say something but not before

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5: : A path to a 10 TeV Wakefield Collider exists, regardless of whether the 10 TeV machine is an upgrade of an existing Linear Collider or a green field project.

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• Red Team (Andrei)
• Blue Team (Patric)

This is very clear and documented. Otherwise we would not be here.

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