Workshop on Optical Stochastic Cooling

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Workshop on Optical Stochastic Cooling

    OSC Workshop Summary

    W. Franklin ( 2-15-2006)

    An Optical Stochastic Cooling (OSC) workshop was held at MIT-Bates on February 2,

    2006, in order to explore the technical issues that would need to be addressed for

    successfully mounting the experiment and to understand the benefit that would ensue for

    the RHIC program. This synopsis will present the important points from the workshop

    discussion and the next steps that need to be taken to move forward.


    1) Calculations suggest OSC has the potential to yield significant improvements in

    performance for RHIC and eRHIC through improvements in beam lifetime and

    background reduction if technical challenges can be met. Benefits would be

    greatest for protons and light ions, particularly if the cooling rate could be large

    enough to match the growth in beam emittance from beam-beam interactions

    which reduce the luminosity.

    2) Optical stochastic cooling is largely complementary to electron cooling. OSC

    would produce strongest cooling of the beam halo, while electron cooling is more

    efficient in cooling at short distances, i.e. the core of the beam. Reduction of the

    halo is of essential interest to both the STAR and PHENIX collaborations that are

    developing silicon vertex tracking upgrades using sensors located very close to

    the vertex to measure displaced vertices from decays of short-lived particles.

    3) OSC may allow smaller emittance electron beams in storage rings. This could

    have great potential for higher brightness light sources using electron storage

    rings. This would be directly testable at Bates.

    4) A demonstration experiment of OSC performed at Bates would further

    development of the technique for use at higher-energy proton and ion machines.

    As the operating cost for machines such as RHIC is high, the parallel

    development of OSC at the available Bates accelerator is highly cost effective. In

    particular, OSC at Bates would explore much of the beam physics but would have

    far less stringent amplifier requirements and far lower cost. Such an experiment

    would be tailored to study questions of interest to RHIC.

    5) Much of the discussion pertained to necessary steps to mount an OSC

    demonstration experiment at Bates on the shortest possible time scale. Steps

    include a preliminary experimental feasibility study using the Bates South Hall

    Ring and a parallel design study on development of the optical amplifier system.

    6) Possibilities to both minimize the cost and reduce implementation time were

    explored. These include reuse of existing components and designing an

    operational schedule for the machine with other proposed accelerator physics

    studies to minimize running time.

    7) There is enormous synergy between the Bates THz and OSC proposals. This

    includes many of the diagnostics and controls and studies of the orbit response.

    Work Plan

    1) The optimal energy to do the experiment needs to be determined. The effect of

    Touschek (intrabeam) scattering which reduces the storage lifetime at lower

    energy in the South Hall Ring (SHR) must be balanced vs. the benefit of lowering

    the energy to yield a longer synchrotron radiation damping time to observe OSC.

    These topics are being investigated by the Bates Accelerator Physics Group.

    2) Several issues regarding configuration of the Bates accelerator complex to meet

    the specific conditions for an OSC test must be explored experimentally during a

    SHR feasibility study.

    i. Control of the bunch filling pattern for SHR operation (underway)

    ii. Performance of SHR diagnostics for fast profile monitoring

    iii. Low current, few bunch operation of the SHR

    iv. Beam profile optimization for OSC demo (transverse and longitudinal)

    A test run as soon as possible is required to investigate these topics.

    3) Reuse of existing undulators would produce significant cost savings for the

    experiment. The properties of the undulators are somewhat flexible, but it is

    important to have two which are identical. Furthermore, their properties will drive

    the design of the rest of the components. All workshop participants agreed to

    look for viable options, such as prototype or spare undulators from light sources.

    4) Development of the optical amplifier is a tractable problem for the Bates

    experiment. Required power levels and gain are somewhat lower than the original

    estimates in the proposal and will simplify the design. Development of the

    amplifier at the MIT Research Laboratory for Electronics (RLE) can proceed

    independently of accelerator development. A rough estimate of 6 months to order

    and assemble the amplifier was given.

    5) The design and implementation of the bypass chicane is the greatest challenge of

    the project. This requires only modest capital funds provided that many existing

    magnets and power supplies from the decommissioned Bates Extraction Line are

    utilized. The primary challenge is the realization of a highly isochronous design

    which eliminates particle mixing in the bypass. The LBNL group has carried out

    preliminary calculations for such a bypass. The system must be built to allow the

    OSC system to be tuned with a small number of adjustable parameters.

    Significant mapping of the bypass response using SHR kickers will be required.

    6) Diagnostics and fast feedback present another significant challenge for the

    experiment and an opportunity to significantly advance the field. Phase stability must be achieved between the delayed electron bunch and its amplified undulator radiation at the sub-micron level. Workshop participants with significant experience in microwave stochastic cooling emphasized the importance of a clean signal to indicate proper tuning of the OSC system. Interferometric techniques will be expensive and there was significant discussion on development of a direct diagnostic based on undulator or dipole edge radiation.

    7) Simulation for the South Hall Ring could play an important role in development and analysis of the OSC experiment. A scientific computing collaboration between BNL and Bates has recently been forged for a SciDAC proposal.

    Workshop on Optical Stochastic Cooling

    February 2, 2006

    MIT-Bates Accelerator Center

9:00 - Opening Remarks (R. Milner)

    9:10 - Transit-Time Optical Stochastic Cooling (A. Zholents)

    9:45 The Optical Stochastic Cooling Program at BNL (V. Yakimenko)

10:45 Coffee Break

    11:00 Optical Stochastic Cooling Proposal at MIT-Bates (W. Franklin)

11:45 Optical Amplifier Development at MIT (F. Kaertner)

12:15 Lunch served

13:00 Visit to MIT-Bates South Hall Ring

13:30 Discussion

15:15 Coffee Break

15:30 Working plan formation

16:30 - Adjourn

Participants in the Optical Stochastic Cooling workshop at MIT/Bates on 02/02/2006

Name Affilation email address

    Taylan Akdogan MIT Marcus Babzien BNL Mike Blaskiewicz BNL Mike Brennan BNL

    Dan Cheever MIT Karen Dow MIT

    Manouchehr Farkhondeh MIT Wolfram Fischer BNL Bill Franklin MIT Franz Kaertner MIT Jan van der Laan MIT Richard Milner MIT

    Thomas Roser BNL

    Aleem Siddiqui MIT Stephen Steadman MIT Chris Tschalaer MIT Genya Tsentalovich MIT Bill Turchinetz MIT Defa Wang MIT

    Dong Wang MIT Fuhua Wang MIT

    Vitaly Yakimenko BNL Alexander Zholents LBL Max Zolstorev LBL

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