HE-JLEIC: Boosting Luminosity at High Energy Yuhong Zhang June 28, 2018

JLEIC and eRHIC Ring-Ring Luminosity Y. Zhang, 06/19/2018

Boosting Luminosity at Highest Energy Higher proton beam current needs stronger high energy cooling Stronger collective effects Improving high energy cooling efficiency Higher cooling electron beam current Dispersive cooling Higher electron beam KEKB LER current 3.6 A Higher SR power, 15 even 20 kW/m  higher RF power More SR at IR Smaller beta-star Short detector space Unmatched beam spot size at IPs Beam-beam very weak (~10% of nominal design value) at these energies

JLEIC and eRHIC Ring-Ring Luminosity: Optimized

HL-JLEIC Optimized Parameters CM energy GeV 63.3 (high) 89.4 98 p e E Beam energy 200 5 10 12 Collision freq. MHz 476 Particles/bunch 1010 0.49 3.9 5.2 0.66 0.93 1.4 0.72 0.54 0.81 Beam current A 0.375 3 4 0.5 0.71 1.07 0.55 0.41 0.62 Polarization % 80 75 RMS bunch cm 1 Norm. emitt., h. μm 54 2.5 432 1.5 2.7 746 Norm. emitt., v. 0.1 10.8 86 0.3 149 Horizontial β* 6.5 1.3 Vertical β* 0.8 7.5 2 Spot size, h µm 14.9 29.6 29.7 21.3 35.5 Spot size, v. 3.0 5.9 4.3 7.1 p vs. e 72% 60% Vertical B-B 0.011 0.03 0.015 0.001 0.006 .0004 0.004 vs. BB limit 7.3% 3.6% Laslett tuneshift 0.005 0.002 0.003 Hourglass (HG) 0.85 0.83 0.86 0.87 Lumi,w/HG,1033 /cm2s 14.0 18.7 1.1 2.2 1.0

Impact on Electron Injector Fanglei Lin, Jiquan Guo The electron injection from the CEBAF to the collider ring should have no problem. The injection time for the energy above 7 GeV is within a few minutes in the current design. At 12 GeV, it is only ~40 s as we estimated. The injection time is approximately proportional to the stored electron current in the colllider ring. So the injection time is still acceptable if we increase the beam current, say by 30%. Note that, the polarization lifetime is very short at high energies, ~6 minutes at 12 GeV. We better have the injection time short at this energy. The equilibrium polarization with a top-off injection can be maintained if we keep the same ration of I_ring/I_inj. That means we have to increase the averaged injection current while we increase the stored electron beam current in order to keep the equilibrium polarization unchanged. Otherwise, the equilibrium polarization is reduced. But we think we have enough room to do this. Overall, initial injection and top-off injection should be ok while increase the stored beam current at high energies.

Impact on Electron Collective Effects Rui Li I looked at the behavior of collective effects assuming the electron current increases by factor of 2 for E>= 10GeV, it looks like we are safe for the instabilities (here I assume the higher average electron current is achieved by increasing the single bunch charge). (1) The longitudinal microwave instability For I=3A, this instability causes most concerns for the electron energy E=3GeV, for which we still need to explore mitigation scheme. Yet it’s not a worry for E=10GeV. Even when the bunch current increases by a factor of 2 at E>=10 GeV, there is still a large safety margin for this instability. (2) The transverse mode coupling instability For I=3A, this instability is not a concern for the whole electron energy range. When the bunch current increases by a factor of 2 at E=10 GeV, there is still a large safety margin for this instability. (3) Longitudinal and transverse coupled bunch instability For I=3A, the growth time of these instabilities at E=10 GeV are many times longer than that for E=3 GeV. So with the increase of beam current by 2, and with the increase of the number of cavities (as Bob mentioned), the growth time is about the same (for the longitudinal case) or longer (for the transverse case) as that at E=3 GeV. This should be suppressed by the much stronger synchrotron radiation damping at 10GeV (and if necessary, bunch-by-bunch feedback system can help). (4) Fast Ion Instability The growth rate of this instability at 10 GeV is more than 2 orders of magnitude smaller than that at 3 GeV. With the increase of current by a factor of 2, the growth rate of this instability is about the same as that in the PEPII HER, and should be manageable. So in general, we should be fine with the higher current at the higher energy regime.

Impact on RF System Bob Rimmer if I understand it the simplest thing is to say that the bunched beam cooling will work at full ion current at top energy so the luminosity will be higher. if we have to raise the electron current we can add more power. Worst case this is about $10M/MW so an additional $50M plus about 10 more cavities. Hopefully we can get this number down to more like $1M/MW so it’s not such a big deal. More cavities gives more impedance but at high energy the damping is strong so probably this is OK. Using an ante-chamber design should allow higher current and higher kW/m Injection should be OK, I think. I guess polarization lifetime will be a bit shorter at 12 GeV. SR at IP will be harder if no changes are made to the layout, especially mask heating. All other resistive and resonant heating effects go up as I^2, but get easier if we relax the bunch length a bit. if we have extra power we can run full current to higher energy as well, fattening the luminosity in the mid range. We can run higher than 3A at low energy if other limits allow. All this gets easier if we can make the ring bigger.

Revisiting Detector Space 7 m Focus length f equals detector space for thin lens approximation f2=β*βmax σ*=(εβ*)1/2 σmax=(εβmax)1/2 Reducing detector space  lowering beta-star (keeping same beam size/aperture)  decreasing beam spot size at IP  increasing luminosity

Luminosity Performance vs. Detector Space βy=5mm 100 GeV p x 5 GeV e βy=6mm βy=10mm βy=1.2mm

eRHIC Ring-Ring Luminosity V. Ptitsym, 1st EIC Joint Accelerator Collaboration Meeting, 10/12/2017 Baseline curve relies on hadron cooling just strong enough to reach 1034 cm-2s-1 (IBS growth times > 2h) Very low pt run curves are for collecting data with very forward proton scattering (pt ~200 MeV)