K. Yokoya LCCPDeb at ECFA LC 2016, Jun.1 gg and 1.5TeV at ILC K. Yokoya LCCPDeb at ECFA LC 2016, Jun.1 2016/6/1 LCCPDeb at Santander

gg collider Convert ee collider into gg by Laser-Compton scattering Needs longitudinally polarized electron Maximum photon energy Egmax = xEe/(1+x+x2) x = 4Eewlaser/m2 x2 = 0.3 (non-linear Compton parameter) Optimum of x : xopt = 2[ 2 +1] = 4.8 Large x for higher energy gamma But generated gamma is lost by pair creation in the same laser if x> xopt The threshold of this phenomena is a bit soft Including nonlinear effects, 　xopt ~ 4.8(1+x2)  Egmax = 0.8Ee Choice For Ee=500GeV, llaser = 1.5~2mm , Egmax ~ 400GeV 1TeV e-e- collider is just suited for Egg=700~800GeV 2016/6/1 LCCPDeb at Santander

Laser Laser parameters Candidates of Laser system llaser = 1.5~2mm 1mm may be OK.　Simulation needed Flush energy ~ several Joule Pulse length ~ 1-2 ps Must match with ILC beam pattern Average power O(100kW) Candidates of Laser system Big laser like LIFE (NIF: National Ignition Facility) Optical cavity with (relatively) low-power laser FEL Non of these are ready now for gg But if serious R&D is done, at least one of these would become feasible by the time ILC reaches 1TeV. If not, never progress. 2016/6/1 LCCPDeb at Santander

2016/6/1 LCCPDeb at Santander

Crossing Angle To go back to e+e- again is indispensable Low energy electrons are produced in multiple Compton scattering in the laser. They are deflected by large angles and create lots of background. A large crossing angle is needed to avoid the background. Best is thought to be around 25mrad for g-g . TDR: crossing angle 14mrad　(g-g is not mentioned) 20mrad had been adopted for e+e- in early stage of ILC design At the time of RDR study it was agreed to reduce the angle for e+e- from 20mrad to 14mrad When changing the angle for g-g later on Beam dump must be reconstructed To change 20mrad25mrad, old and new beam dumps overlap. Civil engineering almost impossible. To change 14mrad25mrad is easier in this respect To go back to e+e- again is indispensable 2016/6/1 LCCPDeb at Santander

An example of electron spewctrum with old TESLA parameters Emin ~ E0/(1+nx) n ~ 10 2016/6/1 LCCPDeb at Santander

14mr => 25mr A.Seryi, LCWS06 This doesn’t look realistic Big CFS work including new main dumps compatible with push-pull? (This plot was created before push-pull) May still be realistic, if the gg community is strong? 1400 m additional angle is 5.5mrad (=(25-14)/2) and detector need to move by about 3-4m 2016/6/1 LCCPDeb at Santander

IR Geometry crossing angle angle for outgoing beam 14 mrad 4.5 mrad The required angle for outgoing beam is proportional to sqrt(N/sz), independent of ECM 2016/6/1 LCCPDeb at Santander

gg Luminosity Reduction due to Small Crossing Angle Sqrt(N/sz) should be proportional to q (q = angle for out-going beam)  N is proportional to q2 sz  Luminosity proportional to ( q2 sz )2 Longer sz causes hour-glass problem. May be OK up tp x 1.5  If crossing angle is 20mrad, luminosity is about half compared with 25mrad. Too small if 14mrad Ideal g-g luminosity is about 1/3 of e+e- luminosity (TESLA-TDR) crossing angle q sz L/L0 14 mrad 4.5 mrad 450mm 0.016 20 mrad 10.5 mrad 0.47 25 mrad 15.5 mrad 300mm 1 Maybe, we can do a bit better with 14mrad At Ee=500GeV Accept some more background 2016/6/1 LCCPDeb at Santander

Transition to g-g Crossing angle 20mrad can be accepted for g-g But several changes still needed in transition to g-g Of course, addition of laser system Another polarized electron source and its injection line to DR Beam dump Main dump is to be used as ~10MW photon dump Photon beam from laser-Compton is stronger than beamstrahlung and is narrower (1/g). Cannot be bent, cannot be swept. Dump window for e+e- cannot stand Diffuse gamma beam by high pressure argon gas Hardware study is necessary 2016/6/1 LCCPDeb at Santander

Items to be done for now Construct consistent parameter set for g-g No design for 750GeV g-g Find best parameters with 14mrad and 20mrad What in the design should be changed if the crossing angle is 20mrad Detector, in particular Design issues for next step Compatibility of the detector and the laser path at IP 2016/6/1 LCCPDeb at Santander

Conclusions for gg The technology for gg will be feasible by the time ILC reaches 1TeV, if serious R&D is done. Luminosity of gg is presumably too small if we stay at TDR crossing angle 14mrad To change the crossing angle at the time of transition to gg is not realistic because of the big CFS work Therefore, if we go to gg laser, the angle should be ~20mrad from the beginning However, it is not too late to change the design when the importance of 750GeV gg is recognized within 1-2 years from now 2016/6/1 LCCPDeb at Santander

Higher Energies > 1TeV 2016/6/1 LCCPDeb at Santander

CM Energy vs. Site Length Under the assumption Upgrade scenario B of TDR (i.e., keep the 500GeV linac as the high energy part. Do not throw away the first stage cavities.) Available total site length L km Operating gradient G MV/m to be compared with 31.5 in the present design for 500GeV TDR assumed 45MV/m for 1TeV upgrade Assume the same packing factor Then, the final center-of-mass energy is Ecm = 500 + (L-31)*(G/45)*27.8 (GeV) e.g., L=50km, G=31.5MV/m  870GeV L=50km, G=45MV/m  1030GeV L=67km, G=45MV/m  1500 GeV L=67km, G=100MV/m  2700 GeV Does not take into account the possible increase of the BDS for Ecm>1TeV Present design of BDS accepts 1TeV without increase of length A minor point in increasing BDS length: laser-straight 2016/6/1 LCCPDeb at Santander

Development of Niobium Cavities Comparison of 1- and 9-cell performance There is large gap between 1-cell and 9-cell cavity performance! 2013/10/23 Tohoku Forum. K. Yamamoto 9-cell cavity Presumably, 45MV/m is within the reach of Niobium cavities 2016/6/1 LCCPDeb at Santander

Available Site Length at Kitakami 2013/10/23 Tohoku Forum. T.Sanuki Can be extended more to the north 14.9km + 50.2km + 1.9km = 67km 75km may be possible by further extension to the north 2016/6/1 LCCPDeb at Santander

A Local Problem at Kitakami Once the first stage machine is built, it is almost impossible to move the IP (interaction point) in later stages because of the crossing angle S N Asymmetric collider may be acceptable Asymmetric accelerator Asymmetric energy Energy asymmetry can be relaxed by moving all the old cavities in the south arm to the north at the time of upgrade, perhaps up to about 630GeV on 893GeV 2016/6/1 LCCPDeb at Santander

Luminosity and Power Consumption 1TeV parameter set in TDR is limited by the power consumption < 300MW Luminosity at 1.5TeV would be slightly lower than at 1TeV. 2016/6/1 LCCPDeb at Santander

An Example (only an example!) 2016/6/1 LCCPDeb at Santander

A minor technical problem Present design contains a dogleg in electron beamline after undulator to separate electron and photon This dogleg causes 8% increase of horizontal emittance at Ee=500GeV (Ecm=1TeV) Proportional to Ee6 90% with Ee=750GeV, 260% with Ee=893GeV 2016/6/1 LCCPDeb at Santander