Overview of Low Energy RHIC e-Cooler (LEReC) project and needed RHIC upgrades Vladimir N. Litvinenko Department of Physics and Astronomy, Stony Brook University Collider-Accelerator Department, Brookhaven National Laboratory Center for Accelerator Science and Education August 13,

Content: my talk is an introduction to the detailed description of the LEReC 11:00 Expected luminosity performance with cooling – A. Fedotov 11:30 Layout, infrastructure and engineering - J. Tuozzolo 13:30 Electron cooling specifications and parameters – A. Fedotov 14:00 SRF accelerator – S. Belomestnykh 14:30 Laser and photocathode – B. Sheehy 15:30 Electron beam transport and dynamics – D. Kayran 16:00 Beam stability and requirements on technical components – I. Pinayev 16:20 RHIC and AGS aspects for low-energy operation – M. Blaskiewicz 16:40 Effects on hadron beam from electron bunches – G. Wang 2

LEReC Goals Enable RHIC low-energy collisions of heavy ions (from about 3.8 GeV/n to 10 GeV/n with about ten-fold higher luminosity Reduce, if possible, beam-losses and associated back- ground Build a compact, in-tunnel system Fit within a single AIP budget Re-use as much as possible of existing/or planned infrastructure 3

4 © A. Fedotov What is possible?

How to cool ? 5

What was considered? Moving FNAL’s Pelletron Using ERL SRF Gun (704 MHz) Using existing RHIC RF system Various locations in RHIC: IP4, IP2, IP12 Magnetized e-beam Finished with –a stand-alone 2-cell 5 MeV SRF Gun/Linac –operating at low frequency ~ 100 MHz –using 500 MHz NC RF cavity for flat-top acceleration –cooling two beams with a single accelerator –located at IP2 –re-using a lot of hard-ware presently built for CeC Proof-of-Principle experiment 6

Fundamentals The main limitations for the RHIC luminosity at low energies are coming from: –Space-charge dominated beam-dynamics –Shrinking dynamic aperture –Shrinking RF bucket –IBS Additional limitation: –Limited tunability of existing RHIC RF allows to collide beams only at a very limited number of energies below 10 GeV/u (3 to 4) 7

RF 8 Three main scaling –the energy acceptance is proportional to 3/2 power of beam energy: –the voltage required to keep constant acceptance is proportional to cube of the harmonic number (i.e. doubling RF frequency requires 8-fold increase in voltage!) –increasing the bunch-length (e.g. space-charge effects mitigation) require low voltage and/or low harmonic number

Acceptances of Existing RHIC RF Systems (in eV*sec) MHz RF Systems

4.5MHz Cavity C&F –A concept and feasibility study has been started to propose a 4.5MHz cavity design for the new low energy gold program. –Two design typologies are being considered for this effort. Ferrite Loaded Cavity A ferrite loaded cavity design has been fabricated and initial performance testing has been performed. Alumina Disk Reentrant Cavity Preliminary simulations of an alumina disk reentrant cavity design have been completed and plans to build a scaled down version currently underway. © A. Zaltsman

4.5MHz Cavity C&F Ferrite Loaded Cavity –Center Frequency = 4.7MHz –Q = 22 –Drive Power = 2KW –Max Voltage = 4KV (Without Bias) © A. Zaltsman

4.5MHz Cavity C&F Alumina Disk Reentrant Cavity –Center Frequency = 4.55MHz –Estimated Q = 4000 –Estimated Drive Power = 5KW –Max Voltage = 40KV © A. Zaltsman

Choosing 4.5 MHZ RF system Low frequency RF has serious advantages –Long bunches to increase bunch intensities and provide room for cooling – Large longitudinal acceptance Without low frequency RF the luminosity can not be increases at low energies (below 7 GeV/u) very the increase of the luminosity is the most critical It is also broadly tunable to cover all necessary energies for LE RHIC scan –γ=4.1 require 3% tunability –γ=2.55 will require 8% tunability The number of RF bucket will be constant (60) independent of the beam energy Collisions occurring in both RHIC detectors –Tunable 9 MHz tunable RF cavities would provide for a slightly higher luminosity (because of 2x bunches) but would require 8 times higher voltage, and would be significantly more expensive. 13

Timing: Need to tunable RF Cooling beams in two ring simultaneously requires that length of the e-beam loop (measured from the IP) will be an integer number of the distance between ion bunches If number of the bunches (as in a current operations) is changing, then the loop’s length has to be adjusted Tuning RF frequency and keeping distance between buncher of 1/60 th of RHIC circumference fixes the geometry of the cooler 14

Timing is important! Using ~24 th harmonic of 4.5 MHz (e.g. ~108 MHz) SRF electron accelerator for LEReC Since SRF frequency is not widely tunable, in general we are operating with electron bunches sliding through the hadron beam Estimation for a worst case (1 kick, 9 free passes, full mix in 10 turns) modulation of the focusing scenario could cause emittance growth time of ~ seconds for 4.5 MHz case and 12.5 sec for 28 MHz case Solution is to keep fixed e-beam pattern over-lapping the hadron bunch

Patterns at s=0 Electron beam has following pattern: Hadron sees on Nth turn Pattern repeats itself if

Fixed pattern condition In our case let’s select energy of 10 GeV/u: Lets introduce fixed pattern conditions RHICCircumference m Central energy10GeV   fo E+04Hz ho1440

Fixed pattern condition m  E, GeV/n ……………………………

There are 100 points satisfying this condition between 2.65 GeV/u and 10 GeV/u This is sufficient for a detailed energy scan

CeC Proof-of-Principle Experiment 40 GeV/u Au ions cooled by 22 MeV electrons Under contraction Commissioning/test should start in 2015

Using CeC PoP experience and infrastructure

22 Details Top Level Conclusion Based on the physics of the process (and some considerations of the costs) we made choices for main components of the electron cooler In combination with tunable 4.5 MHz RF system this system promises to deliver 10-fold boost in RHIC luminosity at energies below 10 GeV/u The beam dynamics, IBS and cooling simulation indicate that the required cooling speed as well as ion beam parameters Our predictions are based on the space charge and the beam-beam parameters demonstrated in RHIC energy scan I We did not find any show-stoppers for current design There is synergy with CeC PoP experiment Engineering of the system will start after this review