**PRELIMINARY DRAFT 7**

**Fermilab-TM-2149**

**May 18, 2001**

*Report by the collaborators of*

*The VLHC Design Study Group:*

**Brookhaven National Laboratory**

**Fermi National Accelerator Laboratory**

**Laboratory of Nuclear Studies, Cornell University**

**Lawrence Berkeley National Laboratory**

![](media/image1.wmf){width="6.486805555555556in"
height="4.414583333333334in"}

Design Study for a Very Large Hadron Collider

The VLHC Design Study Group:

Giorgio Ambrosio[^1], Terry AndersonError: Reference source not found,
Nikolai AndreevError: Reference source not found, Emanuela BarziError:
Reference source not found, Bob Bauer[^2], Pierre BauerError: Reference
source not found, Sergey Belomestnykh[^3], Robert BernsteinError:
Reference source not found, Mike Blaskiewicz[^4], Rodger BossertError:
Reference source not found, John CarsonError: Reference source not
found, Deepak ChichiliError: Reference source not found, Pete
Conroy[^5], Don CossairtError: Reference source not found, Christine
DarveError: Reference source not found, Dmitri DenisovError: Reference
source not found, Angelika DreesError: Reference source not found,
Alexander DrozhdinError: Reference source not found, Luciano
ElementiError: Reference source not found, David FinleyError: Reference
source not found, Wolfram FischerError: Reference source not found,
Bill FosterError: Reference source not found, Peter GarbinciusError:
Reference source not found, Norman GelfandError: Reference source not
found, Henry GlassError: Reference source not found, Steve Gourlay[^6],
Ramesh GuptaError: Reference source not found, Mike HarrisonError:
Reference source not found, Steve HaysError: Reference source not found,
Yuenian HuangError: Reference source not found, Linda ImbasciatiError:
Reference source not found, Alan JacksonError: Reference source not
found, John JohnstoneError: Reference source not found, Vadim
KashikhinError: Reference source not found, Vladimir KashikhinError:
Reference source not found, Kurt KennedyError: Reference source not
found, Jim KerbyError: Reference source not found,
Arkadiy KlebanerError: Reference source not found, Glen LambertsonError:
Reference source not found, Mike LammError: Reference source not found,
Chris LaughtonError: Reference source not found, Valery LebedevError:
Reference source not found, Peter LimonError: Reference source not
found, Alexander MakarovError: Reference source not found, Ernest
MalamudError: Reference source not found, John MarrinerError: Reference
source not found, Phil MartinError: Reference source not found, Mike
MayError: Reference source not found, Nikolai MokhovError: Reference
source not found, Chuck Nelson[^7], King Yuen NgError: Reference source
not found, Tom NicolError: Reference source not found,
Barry NorrisError: Reference source not found, Igor NovitskiError:
Reference source not found, Andy OleckError: Reference source not found,
Tom PageError: Reference source not found, Steve PeggsError: Reference
source not found, Lee PetersenError: Reference source not found,
Tommy PetersonError: Reference source not found, Henryk PiekarzError:
Reference source not found, Fulvia PilatError: Reference source not
found, Mauro PiviError: Reference source not found, Duane PlantError:
Reference source not found, Vadim PtitsynError: Reference source not
found, Roger RabehlError: Reference source not found, Gianluca
SabbiError: Reference source not found, Phil SchlabachError: Reference
source not found, Tanaji SenError: Reference source not found,
Vladimir ShiltsevError: Reference source not found, Jeff SimsError:
Reference source not found, Jim StraitError: Reference source not found,
Mike SyphersError: Reference source not found, Gianni TassottoError:
Reference source not found, Steve TepikianError: Reference source not
found, Iouri TerechkineError: Reference source not found, Jay
TheilackerError: Reference source not found, John TompkinsError:
Reference source not found, Dejan TrbojevicError: Reference source not
found, Vladimir TsvetkovError: Reference source not found, William
TurnerError: Reference source not found, Jim VolkError: Reference source
not found, Masayoshi Wake[^8], Bruce WagenerError: Reference source not
found, Ron WalkerError: Reference source not found, George WojcikError:
Reference source not found, Meiqin XiaoError: Reference source not
found, Ryuji YamadaError: Reference source not found, Victor YarbaError:
Reference source not found, S.Y. ZhangError: Reference source not found,
Alexander ZlobinError: Reference source not found

**Editors:**

H. Glass, P. Limon, E. Malamud, G.W. Foster,

P. Garbincius, S. Peggs, J. Strait, M. Syphers, J. Tompkins, A. Zlobin

**Acknowledgments**

The authors thank Michael Witherell, Director of Fermilab, and the U.S.
Department of Energy for their support of this study. They also thank
Joe Lach (Fermilab) for his contributions in understanding tunneling and
geology, and Ping Wang (Fermilab)for creating the web site for
maintaining this document.

Design Study for a Very Large Hadron Collider

# . Introduction

Particle physics makes its greatest advances with experiments at the
highest energy. The only sure way to advance to a higher-energy regime
is through hadron colliders --- the Tevatron, the LHC, and then, beyond
that, a Very Large Hadron Collider. At Snowmass-1996 \[1\],
investigators explored the best way to build a VLHC, which they defined
as a 100 TeV collider. The goals in this study are different. The
current study seeks to identify the best and cheapest way to arrive at
frontier-energy physics, while simultaneously starting down a path that
will eventually lead to the highest-energy collisions technologically
possible in any accelerator using presently conceivable technology. This
study takes the first steps toward understanding the accelerator physics
issues, the technological possibilities and the approximate cost of a
particular model of the VLHC. It describes a staged approach that offers
exciting physics at each stage for the least cost, and finally reaches
an energy one-hundred times the highest energy currently achievable.

## 1.1 The Goals of this Study {#the-goals-of-this-study .unnumbered}

In November, 2000, the Fermilab director commissioned a study for the
purpose of beginning to understand the consequences of a staged approach
to the VLHC \[2\]. The major goals of the study are:

-   To determine the basic parameters of a proton-proton collider of
    E~cm~ greater than 30 TeV and luminosity of at least 10^34^
    cm^-2^s^-1^, while preserving the option of eventual operation of a
    collider with E~cm~ greater than 150 TeV in the same tunnel.

-   To identify the major technology and construction challenges, the
    important accelerator physics issues, and any unusual operational,
    environmental, safety and health requirements.

-   To estimate the current-day construction costs of the major cost
    drivers for the initial collider configuration, assuming it is built
    using Fermilab as the injector.

-   To identify areas requiring significant R&D to establish the
    technical basis for the facility.

This study is not a conceptual design report, nor is it a complete cost
estimate. To accomplish either of those goals would have taken more than
the available time and resources. Instead, it is a broad-brush study,
intended to describe the major issues. It provides information about the
resources needed to construct such a facility and highlights any serious
technical problems, allowing concentration of future effort. Since
strategic planning requires accurate conclusions about feasibility and
costs of facilities, this study is likely to be the first of a series of
increasingly focused studies of the VLHC.

## 1.2 A Staged Approach to the VLHC {#a-staged-approach-to-the-vlhc .unnumbered}

The staged approach to the VLHC the construction and operation of a
collider made from simple and inexpensive components, followed at a
later time by a higher-energy collider in the same tunnel. The plan has
the following guidelines:

-   Each stage must hold the promise of new and exciting particle
    physics.

-   The first stage should lead to and assist in the realization of the
    next stage.

-   Each stage should be a reasonably low-cost step across energy
    frontier.

The VLHC satisfies all of these guidelines. The cost of tunneling is in
general significantly less than the cost of a collider's technical
components. Thus, it is cost-effective to increase tunnel circumference
if doing so lowers the cost of the expensive technical components enough
to reduce the overall cost of the collider. Hence, Stage 1 of this
design uses low-field superferric magnets that are themselves
inexpensive, and also require simple and less costly support systems,
such as cryogenics and power supplies. However, the use of a low-field
magnet requires a large tunnel to reach the energy frontier. In this
design, we have settled on 40 TeV collision energy with two detectors,
requiring a ring circumference of 233 km. In a further attempt to reduce
costs, we have sited the collider at Fermilab, permitting the use of the
existing Fermilab injector chain and physical plant, valued at well over
\$1 billion. It also takes advantage of Fermilab's irreplaceable
organizational infrastructure and expertise, further reducing design and
startup costs.

The large circumference of the collider ring would also have advantages
for Stage 2. Above 30 TeV beam energy, synchrotron radiation becomes an
important factor in high-energy proton colliders. In a cryogenic
environment, it is one of the properties that limits the ultimate energy
and luminosity of such machines. The design operating energy of the
high-energy collider is 175 TeV, but the 35 km radius of curvature of
the VLHC would permit it to reach 200 TeV collision energy with
reasonable luminosity and power consumption. Since the first collider
serves as the injector into the second collider, the common
circumference permits a straightforward and fast filling scheme for the
second machine, eliminating potentially troublesome issues connected
with field quality in high-field magnets.

There are disadvantages to a staging scenario. It requires patience and
the willingness to start down a multi-decade path toward the highest
collision energy. The need to anticipate the approximate design of both
stages at the time civil construction begins, may dictate certain
conservative allowances in the design that a single-step plan would not
require. The inside diameter of the tunnel or additional surface service
areas are obvious examples. Both colliders are in the same tunnel,
requiring a period of six years or more for the conversion from the
initial configuration to the higher-energy one. During this time there
would be no physics program. A staging scenario using a very large
tunnel suffers from potential additional cost not only because the
tunnel is longer, but also because it traverses more disparate geology,
potentially incurring higher costs per unit length. Whether this is true
depends on the geology of the various possible Fermilab sites. This
study addresses the topic. Finally, although staging the colliders may
be a low-cost approach, a non-staged approach might be an even
lower-cost way to build a collider of a specific energy.

Other concepts for a VLHC, such as a big tunnel and moderate-field
magnets, or a much smaller tunnel with much stronger magnets and a new
purpose-built injector, might reach higher energy sooner but would cost
more than Stage 1 of this design. Each of these concepts deserves
exploration. This study will offer a baseline for comparison. The staged
approach has the singular merit that the relatively inexpensive Stage 1
would address the issues of siting, tunneling, injector performance and
survival of a frontier U.S. physics program, allowing the field to
address the technical and fiscal challenges of Stage 2 with a healthy
program in place.

## 1.3 The Technical Description and Challenges {#the-technical-description-and-challenges .unnumbered}

Table 1.1 shows the high-level parameters of both stages of the VLHC. To
arrive at these parameters required addressing a number of challenging
accelerator physics issues. At this early stage there appear to be few
technical problems in reaching the listed performance of Stage 1. Making
the arc magnets inexpensively and very long as well as learning how to
transport and install them in a tunnel, will take R&D investment over
the next few years. The small beam pipe and large circumference dictate
the need to study and understand beam instabilities at injection.
Preliminary evidence indicates that feedback and RF manipulations within
the current state-of-the-art will control these instabilities. If
further study points to a problem, the beam pipe size could be increased
with tolerable effects on the total project cost. The dynamic aperture
is more than adequate and closed orbit distortions are benign and easily
corrected when simulated using expected magnet and alignment errors.
Strong, large-aperture quadrupoles for the interaction insertions will
require considerable R&D in the next few years. It is particularly
interesting to note the low average power consumption, comparable to
that of Fermilab's 800 GeV fixed-target program. Power is mostly
concentrated at the cryogenic service buildings, of which there are five
off the existing Fermilab site. These double in number and grow larger
for Stage 2 .

Table 1.1. The high-level parameters of both stages of the VLHC.

  -------------------------------------------- -------- ------------- -------- ------------ --
                                                        **Stage 1**            **Stage 2**  

  Total Circumference (km)                              233                    233          

  Center-of-Mass Energy (TeV)                  40                     175                   

  Number of interaction regions                2                      2                     

  Peak luminosity (cm^-2^s^-1^)                1 x                    2.0 x                 
                                               10^34^                 10^34^                

  Luminosity lifetime (hrs)                    24                     8                     

  Injection energy (TeV)                       0.9                    10.0                  

  Dipole field at collision energy (T)         2                      9.8                   

  Average arc bend radius (km)                 35.0                   35.0                  

  Initial Number of Protons per Bunch          2.6 x                  7.5 x                 
                                               10^10^                 10^9^                 

  Bunch Spacing (ns)                           18.8                   18.8                  

  β\* at collision (m)                         0.3                    0.71                  

  Free space in the interaction region (m)     ± 20                   ± 30                  

  Inelastic cross section (mb)                 100                    133                   

  Interactions per bunch crossing at L~peak~   21                     58                    

  Synchrotron radiation power per meter        0.03                   4.7                   
  (W/m/beam)                                                                                

  Average power use (MW) for collider ring     20                     100                   

  Total installed power (MW) for collider ring 30                     250                   
  -------------------------------------------- -------- ------------- -------- ------------ --

Stage 2 presents more technical challenges. First, discovering how to
build cost-effective high-field superconducting magnets will require a
significant investment over the next 10 years or more, although with a
large-circumference ring means the magnets are not extraordinarily
strong. Perhaps the most difficult problem is one that this report
barely addresses: how to deal with the large number of interactions at
each bunch crossing. Because of the high beam energy, this equals about
50 kW per beam, most of which goes forward into the insertion region
collimators and magnets. It will require a major R&D effort for the
detector and magnet designers to deal with this issue. The next most
important issue for Stage 2 is synchrotron radiation power. It appears
that five watts per meter, or even 10, can be removed from the magnets,
and that synchrotron radiation will not cause a vacuum problem at those
power levels. The power does show up in the cryogenic system, however,
and must be dealt with.

Figure 1.1 shows an artist's conception of the physical layout of the
injectors and the collision halls. The VLHC ring is tangent to the
Tevatron, but much deeper. The injection lines bend very gradually,
because they also serve as ramps to install the very long (65 m) Stage 1
magnets. The collider is deep in order to permit tunneling mostly in the
extensive layer of excellent Galena-Platteville Dolomite. The collision
halls are large and typical of those at LHC.

![](media/image2.wmf){width="6.486805555555556in"
height="4.520833333333333in"}

Figure 1.1. A cartoon diagram of the VLHC showing Fermilab's existing
accelerator complex, the new injection tunnels and the approximate
locations of the detector halls.

The significant synchrotron radiation power present in Stage 2 VLHC
allows a trade-off of energy for luminosity. This study chooses 175 TeV
as the design energy and 2x10^34^ as the design peak luminosity for
Stage 2. At slightly lower luminosity, and higher, but still achievable
magnetic field strength, this design could reach 200 TeV collision
energy, as shown in Table 1.2. At lower energy, higher luminosity is
possible. Even better luminosity performance can be achieved by
"leveling" the luminosity to limit the inelastic collision debris power
at the interaction point.

Table 1.2. Properties of the Stage 2 VLHC at various energies. The
luminosity is limited by synchrotron radiation power and damping time,
power at the interaction point due to inelastic collisions,\
and the beam-beam tune shift.

  ------------------ --------------- ---------------- --------------------
  *Collision Energy  *Magnetic Field *Leveled         *Optimum Storage
  (TeV)*             (T)*            Luminosity       Time (hrs)*
                                     (cm^-2^s^-1^)*   

  Stage 1 40         2               1.0 x 10^34^     20

  Stage 2 125        7.1             5.1 x 10^34^     13

  Stage 2 150        8.6             3.6 x 10^34^     11

  **Stage 2 175**    **10**          **2.7 x 10^34^** **8**

  Stage 2 200        11.4            2.1 x 10^34^     7
  ------------------ --------------- ---------------- --------------------

## 1.4 Gaining Public Support for a Very Large Hadron Collider {#gaining-public-support-for-a-very-large-hadron-collider .unnumbered}

Construction of a new frontier accelerator at Fermilab will require not
only the support of the national and international scientific community
and U.S. and foreign governments, but also the support of Fermilab's
neighbors, the people who live in surrounding communities. Just as
important as technology development, infrastructure and site geology in
determining whether Fermilab will be able to build a new accelerator is
sociology. It is all too easy to imagine a scenario in which local
opposition to an offsite accelerator makes it impossible for Fermilab to
build such a machine. While community support will be necessary to some
degree no matter what future accelerator Fermilab ultimately builds, it
is a particularly important issue in the consideration of accelerators
that would extend beyond the Fermilab site. And since, of all the
proposed future Fermilab accelerators, the Very Large Hadron Collider
would extend the farthest beyond Fermilab's borders, issues of public
support are likely to have the greatest impact.

Although we cannot predict exactly what will most concern community
members, the proposal to construct an accelerator beyond the Fermilab
site is likely to raise many issues including: risks to environment,
safety and health; effects on property values; esthetics; perceptions of
the degree of community control in the decision-making process;
neighborhood disruption during construction; and appropriate use of
government funds.

How can Fermilab address such issues and build local public support for
future accelerators? Clearly, the traditional "decide, announce, defend"
model is a formula for failure. Fermilab needs to begin now to build the
level of community dialogue, trust, understanding and support that
building a VLHC---or any future accelerator---will require.

Some steps that Fermilab is now taking or has planned include: a
comprehensive community opinion survey that will provide invaluable
baseline information on the current perception of Fermilab, including
questions about attitudes toward possible laboratory expansion beyond
the current site; creating a long-term community outreach plan that
includes future accelerators at Fermilab; forming a laboratory-community
organization to serve as a public advisory group; consulting with other
laboratories that have successfully dealt with similar community
outreach issues; and the use of various Fermilab resources, e.g.,
Science Education programs, Saturday Morning Physics, open houses, and
the Office of Public Affairs, to build support for future facilities.

Building a new frontier accelerator at Fermilab will not only have a
profound effect on the future of our own laboratory and of U.S.
high-energy physics but on the future of our local community. We believe
that most of its effects would be positive, in the form of the economic,
cultural and environmental benefits that it will bring to the region.
However, it will be up to Fermilab to communicate both the benefits AND
the costs of such a project. Involving the community from the beginning
in planning for a future accelerator will be challenging, time-consuming
and costly; but ultimately it is likely to be the only way to create the
level of community trust and support that such a project will require.

#### References  {#references .Reference-heading .unnumbered}

\[1\] D.G. Cassel, ed., et al., *New Directions for High-Energy Physics,
Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics*,
Vol. 1, p. 251.

\[2\] Charge to the VLHC Study from the Fermilab Director.

[^1]: Fermilab

[^2]: Illinois State Geological Survey, Champaign, IL

[^3]: Laboratory of Nuclear Studies, Cornell University

[^4]: Brookhaven National Laboratory

[^5]: consultant, Elmhurst, IL

[^6]: Lawrence Berkeley National Laboratory

[^7]: CNA Consulting Engineers, Minneapolis, MN

[^8]: KEK, Japan