Accelerator R&D towards eRHIC

Yue Hao, C-AD For the eRHIC Team

eRHIC, linac-ring EIC • Linac=ERL, or the luminosity is negligible • The first proposed linac-ring collider

– 250GeV (p) *15.9 (e) @1.5e33 cm-2 s-1 • Why linac-ring

– Luminosity, remove the limitation of b-b parameter of e-beam

– High spin polarization (e-beam) – Easy to upgrade – Easier synchronization with various ion energy.

I. Ben-Zvi, J. Kewisch, J. Murphy and S. Peggs, Accelerator Physics Issues in eRHIC, NIM A463, 94 (2001), C-A/AP/14 (2000).

eRHIC Layout

Luminosity Defined by PSR = 12 MW Defined by ξp = 0.015

Defined by ∆Qsp = 0.035

Beam Synchronization, Detail

• Ion at sub-TeV energies is not ultra-relativistic, Change in energy velocity frequency

• Linac-ring scheme enable a trick to adjust the frequency of RF to sychronize electron and ion at discrete ion energies

• Reduces the need of path lengthening. • Ring-ring scheme can not take the trick.

eRHIC R&D efforts • IR design, crab cavity and dynamic aperture • Beam cooling – major R&D efforts, high priority R&D • Polarization and Polarimetry (including electron

polarimetry) • Polarized 3He production and acceleration • Polarized electron source • Superconducting RF system • Multipass ERL and related beam dynamics • FFAG energy recovery pass • Linac-ring beam-beam interaction • ......

NS-FFAG Layout of the eRHIC

Arc #2 #1 7.944 GeV #2 9.266 GeV #3 10.588 GeV #4 11.910 GeV #5 13.232 GeV #6 14.554 GeV #7 15.876 GeV #8 17.198 GeV #9 18.520 GeV #10 19.842 GeV #11 21.164 GeV

Arc #1 #1 1.334 GeV #2 2.565 GeV #3 3.978 GeV #4 5.300 GeV #5 6.622 GeV

7.944 – 15.876 GeV

* 21GeV Design, Jan'14

Trajectory in FFAG 2.5819 m

0.90805 m Half of 1.09855 m

21.164 GeV 19.824 GeV 18.520 GeV 17.198 GeV 15.876 GeV 14.554 GeV 13.232 GeV 11.910 GeV 10.588 GeV 9.266 GeV 7.944 GeV

θD=3.057567mrad

BD=0.1932 T, Gd=-49.515 T/m

ρD=296.985 m

x(mm)

θF=3.699017 mrad ρF=296.984m

Bf= 0.1932 T, Gf=49.515 T/m

5.02

-7.5

Bmax[-0.178, 0.442 T] Bmax[-0.013, 0.4215 T]

Other half of QF magnet

28.

764

cm -4.61

4.17

28.

764

cm

Half of 1.09855 m

QF BD

Magnet for FFAG arcs

Two alternative magnets

Permanent Magnet

Iron (steel)

Bunch-by-Bunch BPM With fewer BPMs than magnets, the space between some FFAG magnets could be used entirely by a BPM; this design produces “stretched” output pulses (from 13 ps rms bunches) intrinsically in the BPM in-vacuum hardware

1.0 ns

1.18 ns = ½ 422 MHz rf wavelength = minimum FFAG bunch spacing

long sampling platforms

signal processing: use pair of 2 GSPS ADCs triggered ~ 200 ps apart

Multi-pass FFAG Prototype

• There is on-going plan to build a multi-pass FFAG Energy Recovery Linac prototype to prove the principle and the method of detecting and correcting the beam. – Energy of linac ~100MeV – # of passes: ~4

IR design

Crab-cavities

p

e

Forward detector components

SC magnets

IR and DA

• 10 mrad crossing angle and crab-crossing • 90 degree lattice and beta-beat in adjacent arcs

(ATS) to reach beta* of 5 cm • Combined function triplet with large aperture for

forward collision products and with field-free passage for electron beam

• Only soft bends of electron beam within 60 m upstream of IP

Beam cooling, CEC PoP

o Traditional stochastic cooling does not have enough bandwidth to cool intense proton beams (~ 3×1011/nsec). Efficiency of traditional electron cooling falls as a high power of hadron’s energy. Coherent Electron Cooling has a potential for high intensity beams including heavy ions.

o Research Goals: •Develop complete package of computer simulation tools for the coherent electron cooling •Demonstrate cooling of the ion beam •Validate developed model •Develop experimental experience with CeC system

Gun

Beam Dump

FEL Section Helical Wigglers

Low Power Beam Dump

Flag

ICT

ICT

Flag

Flag

Flag

Linac

Bunching Cavities

Pepper Pot

Modulator Section

Kicker Section

Parameter Units Value

Electron Energy MeV 21.9

R.M.S. normalized emittance mm mrad 5

Peak current in FEL A 60-100

R.M.S. momentum spread 1.0×10-3

Charge per bunch nC 1-5

Parameter Units Value

Ion’s Energy GeV/u 40

R.M.S. normalized emittance

mm mrad 2

R.M.S bunch length ns 1.5

R.M.S. momentum spread 3.5×10-4

Repetition rate kHz 78.3

CEC PoP, cont’d

CEC PoP, anticipated results

Ion bunch – 2 nsec

Electron bunch – 10 psec

After 60 sec After 250 sec After 650 sec

r.m.s. length of the cooled part 80-120 ps. The cooling effects can be observed with oscilloscope 2 GHz or more bandwidth or spectrum analyzer with similar upper frequency

Modeling of cooling is performed with betacool by A. Fedotov

CEC timeline

• CEC PoP RHIC ramp is developed • Injection system (112 MHz gun, 500 MHz

buncher) were installed. • Main cavity (704MHz) is fabricated. • Commission injector system in July 2014 • Experiment starts 2015

Polarized e-source • We are aiming at a high-current (50 mA), high-

polarization electron gun for eRHIC. • The principle we are aiming to prove is funneling

multiple independent beams from 20 cathodes. • External review was carried out in 2012. • Next week, first HV conditioning and possibly first

beam!

• eRHIC will utilize five-cell 422 MHz cavities, scaled versions of the BNL3 704 MHz cavity developed for high current linac applications.

• Stability considerations require cavities with highly damped HOMs. • The HOM power is estimated at 12 kW per cavity at a beam current

of 50 mA and 12 ERL passes. • Apply funding to build prototype.

5-cell SRF cavity

HOM ports

FPC port

HOM high-pass filter

Crab Cavity • Development of a highly compact

Double Quarter Wave Crab Cavity at 400 MHz.

• Prototype to be tested in the CERN SPS in 2016- 2017.

Helium vessel Cavity

FPC

Input power waveguides

Tuning system

Cryo jumper

Thermal shielding (80K – nitrogen)

Magnetic shielding

ERL test facility • The BNL ERL objectives 20 MeV at >100 mA (500 mA

capability). • Experiment in progress, will see first photo-emission soon. • Loop in Oct, 2014, project completes in 2016.

All hardware in house, most installed

Electron beam disruption Ion Beam

e

Summary

• There are many on-going simulation and experiment aiming on the challenge port of eRHIC.

• The design now is based on extensive simulations.

• R&D experiments are on-going, need few years to finish.

THANK YOU FOR YOUR ATTENTION!