Physics and Technology of Linear Collider Facilities

 

“A roller-coaster ride through the subject of linear colliders – the Next BIG Thing!”

 

“I hear the roar of the Big Machine

Two worlds and in-between…”

The Sisters of Mercy

 

Course Material (as presented at Santa Barbara, June 2003)

Unit 1

introduction and overview

Nick Walker

lecture (printed two-up)

PDF

538 KB

lecture

PPT

1,016 KB

notes

PDF

404 KB

worked examples

PDF

49 KB

Unit 2

linac technology

Peter Tenenbaum

lecture (printed two-up)

PDF

290 KB

lecture

PPT

787 KB

notes (units 2+3)

PDF

506 KB

worked examples

PDF

15 KB

Unit 3

linac technology cont.

Peter Tenenbaum

lecture (printed two-up)

PDF

578 KB

lecture

PPT

775 KB

notes on power sources

PDF

136 KB

worked examples

PDF

18 KB

Unit 4

damping rings

Andrzej Wolski

lecture (printed two-up)

PDF

1,037 KB

lecture

PPT

1,067 KB

notes

PDF

394 KB

worked examples

PDF

45 KB

Unit 5

bunch compressors

Andrzej Wolski

lecture (printed two-up)

PDF

175 KB

lecture

PPT

238 KB

notes

PDF

216 KB

worked examples

PDF

34 KB

Unit 6

beam delivery systems

Andrei Seryi     

lecture (printed two-up)

PDF

3,440 KB

lecture

PPT

9,164 KB

Unit 7

beam-beam effects

Nick Walker

lecture (printed two-up)

PDF

812 KB

lecture

PPT

1,272 KB

Unit 8

stability issues and feedback

Andrei Seryi     

lecture (printed two-up)

PDF

4,206 KB

lecture

PPT

12,791 KB

Unit 9

a)   beam-based alignment

b)   SLC and the alternatives

c)   course review

Nick Walker

lecture (printed two-up)

PDF

811 KB

lecture

PPT

1,250 KB

final exam with worked answers

PDF

33 KB

 

Additional material (simulations, lab. activities, animations etc) for units 6, 7 and 8 can be found here.

 

NEW: Nick Walker’s lecture emittance preservation in electron linacs given at the CAS school in Triest (2005):

Nick Walker’s lectures on S.C. electron linacs given at the CAS school in Zeuthen (2003):


June 2003 Syllabus

What’s in Store

The lecture series is divided into nine units designed to cover in various levels of detail all the major issues facing the design and realization of a high-energy electron-positron linear collider:

  1. A Linear Collider Overview
  2. Accelerating Structures and Linac Beam Dynamics
  3. Production of High Powered Microwaves
  4. Damping Rings
  5. Bunch Compression
  6. Beam Delivery System
  7. Beam-Beam and other Interaction Region Effects
  8. Stability Issues and Beam-Based Feedback Systems
  9. The SLC and the Alternatives

 

We first introduce the reasons behind the various sub-systems of a linear collider via the important parameter of luminosity (lecture 1). Lecture 2 discusses the luminosity issue further in the framework of the important beam-beam interaction. Lectures 3-8 then cover each of the machine sub-systems in detail, with an emphasis on both the fundamental concepts (accelerator physics and engineering), and the particular challenges facing that sub-system. Finally, lecture 9 summarizes all that we have learnt by reviewing both the only existing linear collider (the SLC), and the various proposals for the next generation machines. Every single sub-system of a Linear Collider pushes accelerator physics and engineering beyond the current state-of-the-art! In other words, we are boldly going where no man has gone before.

Course Structure

Each unit will take the form of an informal lecture session, ranging from two to three hours (with a break for much needed coffee), and an associated tutorial session. The tutorial sessions will consist of  worked examples and/or  computer simulations. We also intend to schedule additional work-group sessions as the need arises to discuss further topics of interest. It is our hope that the course will be dynamic in the sense that we will react to the needs of the participants. To that end we encourage the participants to ask  questions and contribute to ‘round-table’ discussions on the topics presented.

The course will also include problem sets to be solved in the afternoon/evening (during the tutorial and/or after dinner), and a final exam on the last day of class.  Grades, for those who take the class for credit, will be based on the final exam score (60%) and the cumulative score on problem sets (40%). 

Books and Course Material

As with any subject “on the cutting edge”, there is a lack of single source text books covering the subjects. Instead, the relevant information is  distributed across a legion of conference and workshop publications, review articles and – in a few exceptional cases – some text books. We will, however, produce a concise bibliography of those source materials that we feel cover the relevant topics (i.e. the ones we used ourselves). In addition, there will be written course notes provided for each lecture unit.

Your Lecturers

We are (in alphabetical order)

 

Between us, we represent something like 50 man-years of active R&D on linear collider design. We are all relatively young and dynamic, and all of us are extremely excited about the concept of building such a challenging machine (if not just a little crazy). You can be assured that we are putting a lot of work into trying to infect you with the same excitement and enthusiasm!

If you have any questions, comments or even suggestions, please don’t hesitate to contact one or all of us.

We look forwarded to seeing you in Santa Barbara.

 


Course Unit Summaries

Unit 1: A Linear Collider Overview

This introductory lecture will set the stage for the following more detailed lectures. The overall main parameters and their constraints will be introduced via the important issue of the achievable luminosity (the luminosity scaling laws). Once these primary parameters have been introduced, the basic methods of achieving them will be discussed using an overview of the various sub-systems of a linear collider. In addition to the specific LC material, the lecture will also contain a review of the necessary basic accelerator physics and terminology that will be required for the remainder of the course, including: concept of transverse phase space; transverse emittance; emittance preservation; effect of acceleration on transverse emittance; the b function and betatron oscillations; longitudinal emittance.

Summary:

  • Why an LC and not super-LEP (cost optimization)
  • The LC Luminosity Issue:
    • luminosity scaling with center-of-mass energy
    • collider luminosity expression
    • derivation of scaling laws for LC luminosity
    • identification of primary free parameters –  total RF power; vertical emittance; bunch length; beamstrahlung etc.
    • constraints on free parameters and realistic parameter sets
  • Overview of LC sub-systems (the ‘Generic’ LC)
    • sources (e+ and e-)
    • damping rings
    • bunch compression
    • main linac
    • final focus

 

 

Unit 2: Beam-Beam and other Interaction Region (IR) effects

The intense beam-beam interaction in a linear collider constrains the available luminosity through energy loss (beamstrahlung) and associated beam-beam induced backgrounds. This lecture will focus quantitatively on the particle dynamics of the beam-beam interaction (the ‘classical’ effects), while dealing somewhat more qualitatively with the subject of beamstrahlung and pair production (the quantum effects).

Summary:

  • electric field from a very flat beam
  • equation of motion of an electron in the field of the opposing beam
    • the linear solution and the Disruption Parameter Dx,y
    • oscillation number
  • the beam-beam kick and its importance for collision control (feedback)
  • beam-beam instabilities
    • single-bunch instability
    • multi-bunch kink instability, crossing-angles and crab-crossing
  • quantum effects
    • beamstrahlung and the ¡ parameter
    • pair production and backgrounds

 

Unit 3 & 4: The  Main Linac

The main linacs and their associated technology are at the heart of the linear collider. The following two lectures will specialize on the challenging problems of peak RF power generation  and the design of the accelerator structures and the beam dynamics of acceleration.

Unit 3:  Accelerating Structures and Linac Beam Dynamics

The linacs are constructed from many thousands of accelerating structures. An accelerating structure is a cavity or wave guide used to accelerate the beam. Apart from the primary goal of producing longitudinal acceleration, the structures are required to reduce other non-desirable effects such as wakefields and so-called higher-order modes (HOMs). Efficiency of energy transfer from RF to beam is also a primary concern and forms the principle design criterion for optimization.  The beam dynamics of the particles bunches within the structures is of pivotal concern in maintaining the required small emittance of the beam (both transverse and longitudinal).

Summary:

  • Overview:  The main linac as a repetitive array of acceleration and focusing elements
  • Making a usable accelerating wave (introduction to modes & wave guides)
    • electromagnetic waves in free space and why they are useless for acceleration

o       EM waves in regular cylindrical wave guide and why they are equally useless for acceleration

o       Single-cell accelerating cavities (in which we develop the basic formalism and “rules of the road” for…

    • multi-celled accelerating cavities (aka disc-loaded wave guides)
  • Travelling- and Standing-Wave Accelerator Structures

 

Unit 4a:  Accelerating Structures and Linac Beam Dynamics (2)

Summary:

  • Limits to Acceleration Devices
    • multibunch beam loading and compensation
    • single-bunch (very transient) beam loading
    • self-loading
    • multibunch transverse wakefields and BBU, and cures for same
    • single-bunch transverse wakefields, and cures for same
    • Limits to Accelerating Gradient
  • Special Issues in Superconducting Linacs
  • Optimization Issues

 

Unit 4b:  Production of High-Powered Microwaves

The generation of short bursts of high-powered  microwaves required to accelerate the beam  is a major challenge to the designs of the linear collider. Much R&D is currently being invested in the production of the necessary components (modulators, klystrons, high-power wave guides). Of particular importance are ‘pulse compression’ techniques, which can be used to generate the required short-pulse high peak-power from a longer, lower peak-power one.

Summary:

  • qualitative description of a modulator
  • semi-quantitative description of a klystron
    • How (qualitatively)  a klystron works
    • Explain perveance quantitatively
    • Frequency/power limitations in high-powered klystrons
  • transportation and compression of microwaves
    • wave guides and modes
    • wave guide losses and their mitigation, over-moded guides
    • manipulation:  hybrids, combiners, splitters
    • pulse compression concepts:
      (a) SLED
      (b) SLED-II
      (c) Binary Pulse Compression
      (d) DLDS
  • two-beam acceleration as a substitute for klystrons at high frequencies

 

Unit 5: Damping Rings

Generation of extremely small vertical emittance beams using a damping ring  is of fundamental importance to achieving the required high luminosity. Damping rings are storage rings, and have a great deal in common with other electron storage rings (such as modern light sources). However, damping rings differ significantly from their contemporary counterparts in the need for very much smaller emittances, faster damping, and high injection efficiency. The extreme requirements push the present day storage ring technology well beyond what has been achieved. This lecture will deal with the fundamental design issues of a damping ring with special emphasis on the challenges these important sub-systems present.

Summary:

  • principles of radiation damping
    • synchrotron and betatron oscillations in a storage ring
    • classical radiation: longitudinal and transverse damping
    • quantum excitation and equilibrium emittance
    • lattice design for low emittance storage rings
    • adjusting damping times using  wigglers
    • choice of design parameters
  • acceptance issues
    • chromaticity and chromatic correction
    • dynamic aperture
    • RF acceptance
  • alignment and stability
    • betatron coupling
    • vertical dispersion
    • closed orbit distortion
    • sensitivity indicators
    • alignment, correction and tuning techniques
  • introduction to collective effects
    • impedance effects
    • Touschek effect and intra-beam scattering
    • space-charge
    • electron cloud
    • ion effects

 

Unit 6: Bunch Compression

Bunch compression is required to reduce the long bunch coming from the damping ring (~millimeters) to the bunch lengths compatible with the linac RF wavelength and the beam-beam interaction (luminosity). This lecture will review the standard method of bunch compression using RF cavities to introduce a longitudinal energy correlation along the bunch, followed by a non-isochronous magnetic system. These systems general require careful balancing of non-linear terms arising from the non-linearity of both the RF and the magnetic fields. As well as classical effects, quantum effects (both incoherent and coherent synchrotron radiation) must also  be considered.

Summary:

  • the basic approach (linear optics)
    • longitudinal phase space transformations
    • choice of RF and magnet parameters
  • T566 compensation (non-linear optics)
    • phase space distortion from non-linear effects
    • use of RF nonlinearities to compensate magnet nonlinearities
  • design constraints
    • emittance growth from synchrotron radiation
    • effects of coherent synchrotron radiation
  • twostage systems
    • why use a two-stage bunch compressor?
    • telescopes in longitudinal phase space

 

Unit 7: Beam Delivery Systems

The Beam Delivery System (BDS) is the term used for the high-energy transport system from the exit of the linac to the interaction point (IP). It serves several functions, the most important of which is the strong demagnification of the beam at the IP. The magnetic optics design requires special attention to high-order aberrations arising from the required correction of the strong chromaticity of such systems. Synchrotron radiation effects must also be considered, and ultimately set the limits on the achievable beam sizes at the IP. The BDS systems also contain the halo collimation systems which are necessary to shield the physics detector from the beam ‘halo’. The design and constraints on the BDS are some of the most challenging in the linear collider.

Summary:

  • Fundamental issues affecting BDS design
    • Beam phase volume
    • Chromaticity (estimate FD chromaticity)
    • Synchrotron radiation
  • Methods to compensate chromaticity (estimate geometric terms and introduce pairs of sextupoles)
  • Example of FFTB (also discuss IP beam size instrumentation)
  • SR in bends (estimate SR in bends and needed length)
  • Local chromaticity correction in FD (estimate 2nd order dispersion term)
  • Comparison of New/Old FF performance in illustrations
  • Methods of design
  • Errors in FF and their influence (estimate tolerances for some examples)
  • Tuning FF with knobs
  • Beam halo and IR background
  • Collimators and design constraints (wakes, survivability)
  • Nonlinear collimation        

Unit 8: Stability Issues in Linear Colliders

Colliding nanometer beams at the IP places unprecedented requirements on the stability of the accelerator components. Many man-years have been invested in the study and modeling of ground motion effects (‘fast’ vibration and long-term drift) on the performance of a linear collider. The extremely tight tolerances on alignment (ranging from hundreds of microns to a few nanometers) mean that continuous correction algorithms (feedback) are mandatory.   In the following lecture, the issues of ground motion and beam-based  feedback correction  will be introduced.

Summary:

  • Tolerances—example of FD
  • Disturbing effects—ground motion
    • Scale of the phenomena
    • Methods of description—power spectrum
    • Importance of correlation in space and time
    • Two dimensional spectrum
    • Fast and slow motion and IP feedback
    • Waves, ATL, systematic motion
  • Methods of evaluation of ground motion effects
    • Example of simple beamline and uncorrelated motion 
    • Spectral response function
  • Technical noises—illustration
  • IP feedbacks
    • Beam-beam and deflection curve
    • Beam-beam feedback gain function
    • train-to-train and intratrain cases
  • Illustration—integrated simulations of LC stability

Unit 9: The SLC and the Alternatives

The SLAC Linear Collider (SLC) operated between 1988 and 1998, and is often quoted as a proof of principle of a linear collider. The SLC differed in many respects from a ‘true’ LC, not least in the fact that it used the same  linac to accelerate both electrons and positrons (with looped ‘arcs’ at the end to bend the beams in collision). To conclude this series of lectures, we will review the original design specifications of the SLC in the light of what we have learnt. We will then discuss both the final achieved SLC parameters, and the various proposals for the next linear collider. This lecture will differ somewhat from the previous ones, in that it will form a more open ‘workshop’  discussion session of the various issues.

Summary:

  • The original SLC parameter set
  • The ‘final’ SLC parameter set
  • The current LC proposals:
    • NLC/JLC         X-band (11.4 GHz) warm RF machine
    • TESLA            L-band (1.3 GHz) superconducting machine
    • CLIC               X-band (30 GHz) two-beam accelerator

 

 

Tutorials and Simulations sessions

These sessions are intended to provide real and useful practical experience on both design of  a linear collider subsystem and operating the collider (at least in a simulated world). You will feel and enjoy how you can improve (or otherwise?) the luminosity by adjusting klystron phases to optimize BNS damping, applying beam-based correction (even invented or improved by you), or by tuning the final focus. You will play with the same tools that linear collider designers use (and maybe you will suggest how these tools can be improved!).

Tutorial Session Summaries

To be completed – stay tuned!