# . R&D Programs and Engineering Studies

The purposes of Research and Development and engineering studies are to
reduce technical risk and cost, and to improve performance. The
following sections discuss briefly what we see now as the most important
R&D that should be vigorously pusued for both Stage 1 and Stage 2. There
is a distinct difference in the nature of the R&D between Stage-1 and
Stage-2; the work on the low-energy collider emphasizes systems issues,
engineering and cost reduction, while the R&D for the high-energy
machine is strongly slanted toward the development of components. This
difference is appropriate, because the components of the Stage-1
collider are relatively straightforward, whereas the Stage-2 machine
requires cutting-edge devices, particularly magnets.

## 10.1 R&D for the Stage-1 VLHC {#rd-for-the-stage-1-vlhc .unnumbered}

Because of the simplicity of the magnet and accelerator systems of the
Stage-1 collider, there are only a few risk-associated R&D studies
needed. Most of the R&D effort is devoted to reducing costs.

### 10.1.1 Tunneling R&D and Engineering {#tunneling-rd-and-engineering .unnumbered}

The major cost driver in the Stage-1 collider is tunneling and other
underground construction. Large investments in underground construction
R&D and engineering studies are easily justified because even small
improvements in efficiency will save considerable cost and avoid
significant financial risks. Furthermore, the results of this R&D that
would be useful to a broad range of business and government far beyond
high-energy physics. It might be possible to find funding from sources
outside of HEP to support this R&D. The R&D is of two types:
improvements in the current tunnel boring machine and conveyor belt muck
removal systems, and trying new and innovative methods that might, if
susccessful, reduce cost and improve safety.

Typically, forty percent or more of tunneling costs are in labor. Hence,
development of automated or semi-automated procedures looks very
promising. Such procedures could also result in improved safety, since
fewer workers would be underground and at risk of injury. This is not
fancy technology that will be difficult to develop and sell to the
conservative tunneling industry, but relatively straightforward
application of existing techniques that are widely used in other
industries.

From a study carried out for Fermilab \[1\] cost drivers in conventional
tunneling in Fermilab region geology are well understood. Improvement in
TBM utilization can be achieved by fully instrumenting the TBM and
trailing gear with pressure sensors, flow meters in the hydraulic and
water systems, vibration sensors placed on all critical devices, and TV
cameras positioned to watch all moving components. The TBM can be
remotely operated from any place on the construction site. This
dramatically reduces labor costs and improves job safety. Maintenance
can be done as scheduled. Breakdowns aren\'t as costly, because you
don\'t have large crews standing around waiting for a repair to be
completed. The cost per meter of tunnel can be significantly reduced
\[2\]. A Fermilab group has formed an informal collaboration with the
Kenny Construction Company to instrument a TBM in a TARP Tunnel under
construction.\[3\] and gather such data.

There are also many possibilities for the development of better tools
and machinery to make tunneling faster, safer and cheaper. In a
systematic R&D program aimed at reducing tunnel costs, new approaches to
tunneling can be explored. A visionary goal is to have no people
underground except during maintenance. The mining industry is moving
toward totally robotic systems but this technological evolution has not
yet reached the construction industry. A modified TBM with corner
cutters \[4\] \[5\] will produce a flat floor and allow use of a battery
operated (no diesel fumes), rubber tired autonomous muck removal and
transportation system.

Close collaboration between accelerator designers and tunnel engineers
can also cut costs. The many additions, side caverns and adits that an
accelerator seems to require drive up the cost of underground
construction. Careful engineering of the accelerator in conjunction with
the tunnel may be able to eliminate some of these and significantly
reduce costs. This study will involve a multi-disciplinary team of
accelerator scientists, engineers and underground construction experts.

### 10.1.2 Vacuum System {#vacuum-system .unnumbered}

The vacuum system for the Stage-1 collider is a surprising cost driver.
Development and studies of different methods to reduce its cost is are
worthwhile. These could include simpler and less costly ion pumps and
improved beam-tube materials and fabrication techniques. There are a
number of possibilities. There may be practical non-evaporable getter
material (NEG) that will pump semi-inert gasses such as methane. It
would also be worthwhile to investigate the possibility that NEG strips
exposed to synchrotron radiation and/or secondary electrons can pump
methane. If so, this would eliminate the need for ion pumps. Another
fruitful area of investigation is thin film NEG coatings which are under
development at CERN. At a minimum these could be useful in special
regions of the machine where conventional pumping solutions are
difficult or not possible. The possibility that these coatings could
replace the NEG strips, and possibly eliminate the need for ion pumps
when exposed to synchrotron radiation, should also be investigated.
Photodesorption coefficients of thin film NEG coated beam tubes and the
pumping speed of these coatings in the presence of synchrotron radiation
need to be documented.

The possibility of using the already present cryogenics of the magnet
transmission line for a beam tube cryopump was recognized at the
beginning of the study but it was felt that the cost of the cold to warm
transitions and thermal shields would exceed the cost of the system that
was analyzed. Perhaps this question should be reexamined. Unless the
cryopump temperature is equal to or less than \~3K cryosorber will need
to be added to pump hydrogen beyond one monolayer.

### 10.1.3 Beam Stability {#beam-stability .unnumbered}

There are a number of potential beam stability issues in the Stage-1
collider. As discussed in Chapter 3, these have been solved in the
design study by rebunching the beam in the Tevatron before injection
into the collider, and by using an audio frequency tune-modulation
quadrupole in the Stage-1 collider. Neither of these steps seems
difficult or expensive, but they do need to be studied both on paper and
by experiments on existing machines. In addition, there are some other
promising possibilities, particularly feedback systems, that are even
less costly and also deserve study.

Studies at Fermilab that might lead to reduced transverse beam emittance
would allow lower current in the Stage-1 collider and have many good
effects, including reducing the possibility of beam instabilities.

### 10.1.4 Magnetic field quality {#magnetic-field-quality .unnumbered}

Superferric magnets are unlikely to have many field-quality problems
except near saturation. Nevertheless, we have not yet made a
field-quality magnet with the correct cross section for the design-study
lattice. There is a contract with ??? in Russia to make a six-meter-long
magnet with accurate laminations. It might be useful at the same time to
build and test cross sections with some fast-turnaround fabrication
method, such as wire EDM machining. A study of the sensitivity of the
magnetic field to steel chemistry and production tolerances would also
be informative and might lead to cost-savings. Many of these
measurements can be carried out on the magnet test bench shown in Fig.
10-1. In this apparatuse, 10 turns of water-cooled conductor are used to
emulate the 100 kA single-turn conductor in the Transmission Line
magnet. It is a simple matter to make yokes of any desired pole shape
and size, clamp them around the conductor, and make accurate
measurements.

![](media/image1.jpeg){width="5.30625in" height="4.229861111111111in"}

Fig. 10-1 Apparatus for magnetic field quality maesurements

###  {#section .unnumbered}

### 10.1.5 High-field quadrupoles {#high-field-quadrupoles .unnumbered}

The interaction regions of the VLHC require high-gradient quadrupoles
that seem feasible but are beyond the present state-of-the-art. These
magnets need to be developed, and since such developments have
traditionally taken many years, the R&D should start now. The target
gradient for these magnets, 300 T/m, requires Nb~3~Sn of improved
performance, and, hence, a parallel superconducting materials R&D
program is also required. The U.S. LHC collaboration has proposed
developing quadrupoles of similar performance for a luminosity upgrade
of the LHC. If that effort is funded, it may accomplish the necessary
R&D for the VLHC, as well.

![](media/image2.png){width="4.43125in" height="4.073611111111111in"}
Fermilab is particularly well-positioned to lead the high-gradient
quadrupole R&D effort. In recent years, they have built the
infrastructure necessary to do this work---reaction ovens, a
strand-testing facility, a compact cable-making machine, winding and
curing tooling for model and full-sized magnets, and a vertical dewar
test facility that will soon have 30 kA capability, shown in Fig. 10-2.
In addition, if wide cables are required LBNL is the world leader in
cable-making R&D, and has a facility to make cables containing up to 60
strands. This infrastructure at the two labs allows the flexibility of
design and fast turn-around necessary for a successful R&D program
involving such challenging magnets.

Fig. 10-2 The vertical magnet test facilitywith a model LHC IR

quadrupoleready to be inserted for testing.

### 10.1.6 Magnet production, handling and operation {#magnet-production-handling-and-operation .unnumbered}

The very long magnets discussed in the design study raise a number of
issues that are certainly soluble but need both detailed engineering and
some R&D. These include the welding of the half-cores from the inside to
permit an open-gap magnet; design of the cryogenic pipes and support
system for large thermal contractions; beam pipes and transmission lines
with short or non-existent bellows; the use of thicker laminations,
extruded steel yokes, and less costly low-carbon steel to reduce the
cost of the steel yokes; handling, transportation and installation needs
to be engineered and prototyped. The R&D plan must contain the
fabrication andoperation of long magnets in a "string test" that will
prototype all of the issues involving the production, handling,
installation and operation of the transmission-line magnets.

### 10.1.7 Cryogenic system {#cryogenic-system .unnumbered}

![](media/image3.wmf){width="4.0in" height="2.8944444444444444in"}The
Transmission-Line magnet can, in principle, have a very small heat load,
which leads to a small cryogenic plants spaced far apart, and low
operating costs. With the plants spaced 40 km apart, there is the
possibility of flow instabilities if there are regions of high relative
heat load due to assembly errors or bad vacuum. These issues can only be
understood and resolved by the combined use of computer simulation,
bench-top laboratory experiments and large-scale demonstrations, using
components fabricated in a realistic production environment. The results
of these efforts will be fed back into the production and quality
assurance methods, and will influence the designs of the instrumentation
and controls systems, including software for stable control and recovery
during upset conditions. The first test string at the MS-6 location at
Fermilab, shown in Fig. 10-3, will answer many of these questions. It
will have magnets and transmission line mock-ups connected to a
well-instrumented refrigerator close by. It is expected to be
fullyoperational in mid-2002, although earlier tests will be done using
helium from dewars.

Fig. 10-3 A test apparatus for transmission-line loop. The green magnet
is used as the primary of a transformer to induce 100 kA in the
single-turn superconducting transmission line.

Using turbo compressors could increase the efficiency of the cryogenic
plant. In order to use turbo compressors, helium must be mixed with high
molecular-weight gasses at the inlet of the machine and effectively
separated at the outlet. It is necessary to developed reliable
separation/purification system to keep contamination of the Helium below
required level.

As mentioned above, one of the issues of operating with supercritical
helium is control of instabilities. One way to avoid those problems is
to operate at higher temperature, in gaseous helium. It seems possible
to add superconductor to the transmission line, which will have a small
cost impact, permitting the transmission line at to operate at a higher
temperature. This would make control easier and the refrigerator more
efficient, and may lead to a net cost reduction.

### 10.1.8 Public Acceptance and Outreach {#public-acceptance-and-outreach .unnumbered}

One of the major hurdles that must be overcome before any big machine
can be built is convincing the public that building and operating the
collider under their homes and neighborhoods is both safe and
environmentally sound. As a community, we have not been very adept at
this activity in the past, but we will need to be in the future. A
program of understanding the attitudes and real concerns of our
neighbors and interacting with them in constructive ways must be
started. In addition, understanding what other labs, such as CERN and
DESY have done to permit them to construct off their sites would be
useful. Studies and simulations of beam accidents and their effect on
the environment are absolutely necessary, as are studies of the
environmental impacts of the actual construction of the underground and
surface facilities.

Even though we believe the VLHC to be the least expensive way to get to
the energy frontier, it is not cheap. Getting the public and political
support necessary to be funded will be a very challenging task. It must
begin by educating and informing American citizens and their leaders of
the importance of this research to their culture, civilization and
well-being. As a community, we need to lead in this effort and not leave
it up to the funding agencies. Again, understanding what our citizens
and leaders view as important, and how we might fit in among those
perceptions is the first step.

### 10.1.9 Other Engineering Studies {#other-engineering-studies .unnumbered}

There are numerous issues for the construction and operation of the VLHC
that can be solved by engineering studies that will not involve much
R&D. In many cases, these are as important and challenging as the R&D
itself. Among them are studies of the integration of construction and
installation to reduce the total construction period. This is a complex
organizational problem tht could be studied through computer simulation.
Other computer simulation studies might include construction and
operational safety, which could inform us about the number of necessary
egress points, the design of tunnel vehicles, and even safety and
administrative practices.

The cost analysis presented in this study is very preliminary. It must
be improved by continued iteration and deeper detail. In addition, there
are other staging options and designs beside the one chosen for this
study. It is important that some effort be invested early in the program
to understand what the VLHC might look like and cost if those other
designs were used. Exercises of this type must go hand-in-hand with
discussions of high-energy physics goals and the politics of
international collaboration and planning.

## 10.2 R&D for the Stage 2 VLHC {#rd-for-the-stage-2-vlhc .unnumbered}

### 10.2.1 High Field Magnet R&D {#high-field-magnet-rd .unnumbered}

The VLHC-2 magnet system configuration with vertical bore arrangement
adopted in this study dictated the configuration of the SC magnets
described in Section 6.1. Arc dipole magnets are based on the common
coil design and react-and-wind fabrication technique. This approach is
regarded at this time as most innovative and cost effective although it
requires significant efforts to prove it experimentally. Extensive R&D
works in this direction are carried out at Fermilab, LBNL and BNL. There
are also other magnet design approaches based on the traditional
cos-theta (shell-type) coil geometry which allows both horizontal and
vertical bore arrangement as it is shown in Figures 10-4 and 10-5. All
those magnets were developed at Fermilab for VLHC and meet the VLHC-2
requirements including the operation field range, field quality,
critical current and critical temperature margin, quench protection,
etc. \[1\]. The designs and parameters of arc quadrupole magnets that
match these dipole magnets are described in \[2,3\]. Due to small
bending radii in the cos-theta type coils they are forced to use the
wind-and-react technique in order to avoid a large degradation of the
cable critical current during coil winding. The cos-theta coil
configurations allow reducing the coil cross section area by \~20% with
respect to the block type coil with the same coil bore diameter. These
coils can be placed much closer to each other, especially in case of the
horizontal bore arrangement, reducing the iron yoke (and magnet as a
whole) size, weight and cost. It is most straightforward for the warm
yoke design \[4\] shown in Figure 10-5.

![](media/image4.png)

*Fig. 10-4. Cos-theta cold-warm yoke dipole with vertical bore
arrangement. The yoke cold part is shown on the picture, the 15 mm thick
yoke warm part with ID=680mm is not shown.*

![](media/image5.png)

*Fig. 10-5. Cos-theta warm yoke dipole with minimized size and weight.*

Model magnet R&D programs carried out in several U.S. national Labs and
universities have to address the main question: which design approach
and fabrication techniques are the best for the VLHC-2. The VLHC-2
Magnet R&D program will consist of three traditional stages: stage 1 -
short model R&D, stage 2 - full-scale prototype fabrication and tests,
stage 3 - magnet string (hale-cell) test. It would require funding on
the level of 5-10 M\$ per year during 5-10 years to study different
magnet designs and technologies, to select the best arc magnet design,
to fabricate and test a series of full-scale prototypes, to build and
test magnet system half-cell to demonstrate the feasibility of VLHC-2
magnet system. Based on the results of this program the input (base) for
the cost estimate and schedule of VLHC-2 will be provided.

### 10.2.2 Strand and cable R&D {#strand-and-cable-rd .unnumbered}

To build the high field SC magnets with a required for VLHC-2 nominal
field/field gradient and reliable operation margins, the superconducting
strands must provide certain parameters discussed in Section 6.1 and
summarized in Table 10.1 \[5\].

***Table 10.1.*** Strand target parameters for the VLHC-2 high field
magnets.

  ---------------------------------------------- ------------------------
  **Parameter**                                  **Value**

  Strand diameter                                0.300-1.000 mm

  Critical current density J~c~(4.2K,12T)        \>3000 A/mm^2^

  Effective filament diameter d~eff~             \<40 μm

  Cu stabilizer                                  \>50%

  Residual resistivity ratio (RRR)               \>100
  ---------------------------------------------- ------------------------

Nb~3~Sn is currently the material foreseen for the development of VLHC-2
high field SC magnets thanks to its properties and commercial
availability. At this time there are three technologies that may reach
the above technical goals: Internal Tin (IT), Modified Jelly Roll, and
Powder-in-Tube (PIT). In the second half of 2000, a Superconductor R&D
National Program for HEP applications was started by DOE \[6\]. This
program was oriented on reaching the conductor target parameters
presented in Table 10.1 and optimization the Nb~3~Sn strand cost. This
program has proved remarkably successful. In only a few months of R&D,
U.S. companies IGC and OST improved the critical current density of
Nb~3~Sn strands by 30%. Figure 10-3 shows the progress in time of
Nb~3~Sn strand critical current density since 1984. A trendline
extrapolation suggests an achievement of the 3000 A/mm^2^ goal within
year 2004-2005.

![](media/image6.wmf)

*Fig. 10-6. Improvement in J~c~ (4.2 K, 12 T) of Nb~3~Sn since 1984 up
to date.*

The critical current density of Nb~3~Sn strands is controlled by a few
parameters, such as the volumetric fraction of Nb~3~Sn phase that can be
packed in the non-Cu part of a strand, strand heat treatment procedure,
flux pinning mechanisms. All these parameters are now under
investigation and optimization \[7-9\] in order to reach the required
Jc.

Another critical parameter responsible for the persistent current effect
in magnets and strand stability is the strand magnetization determined
by Jc⋅d~eff~, where d~eff~ is an effective filament diameter. For the
Nb~3~Sn strands produced using the most cost effective technologies such
as IT or MJR d~eff~ is quite large \~100-120 μm, and only PIT provides
it on the level of 50 μm resulting in a significant increase of the
strand cost \[10\]. An optimization of the strand design and technology
aming on the reduction of d~eff~ in the high Jc Nb~3~Sn strands is an
important next step of the Conductor R&D program.

In magnet design, it is also necessary to reduce the critical current
degradation of the original virgin strands as well as to control the
interstrand resistance, responsible for the thermal and electromagnetic
coupling between the strands, during magnet fabrication and operation.
In case of the wind-and-react technique, both strand plastic deformation
during cabling (before reaction), and cable compression in the coil
during magnet fabrication and operation (after reaction, due to coil
pre-compression and Lorenz force) contribute to I~c~ degradation and
interstrand resistive coupling. In case of the react-and-wind method,
there is also to take into account the I~c~ degradation due to the
bending strain introduced during winding. The cable R&D program goals
are summarized in Table 10.2. Cable studies performed at Fermilab and
LBNL show significant progress in developing of SC cable for accelerator
magnets during last 1-2 years. The results obtained prove that cable R&D
goals will be certainly achieved \[11-14\].

*Table 10.2.* Cable R&D goals.

  ----------------------------------------- -----------------------------
  **Parmeter**                              **Value**

  Number of strands                         28-60

  Packing factor                            87-90%

  Cabling degradation                       \< 10 %

  Bending degradation                       \< 10 %

  Compression degradation                   \< 10 %

  Strand crossover resistance               \>10 mcOhm
  ----------------------------------------- -----------------------------

As was shown in section 6.1.8, the cost of Nb~3~Sn strands is one of the
major cost drivers of the VLHC-2 magnet system. NbTi strands for
accelerator magnets, thanks to previous HEP projects and the MRI magnet
business, can be purchased in large quantities for about \$100/kg. The
small quantity price (e.g., 2 tons purchased for the U.S. LHC program)
is considerably higher -- about \$150/kg. It is apparently the lowest
prices for this conductor since most of the cost savings and property
improvements available for NbTi have been realized at this point. The
status of Nb~3~Sn presents a stark contrast to NbTi. The quantities
being purchased are small at present (annually approximately 0.5 ton for
accelerator magnets, 2 tons for NMR magnets, and 2 tons for fusion
energy magnets). This factor of 100 lower volume means that the
economies of scale available for NbTi do not exist. Consequently, at
this time, Nb~3~Sn conductor costs about \$750/kg.

The goal of the HEP Conductor Development Program is to demonstrate that
Nb~3~Sn costs can be reduced to the \$150/kg range when the production
processes are scaled-up to those used for NbTi. In order to demonstrate
this, the key is to scale up the unit process quantities, i.e. billet
sizes, to the NbTi equivalent, and also to procure the raw materials in
quantities that will show economies of scale. The necessary
technological steps and the costs to do this as well as the overall
process costs are discussed in \[15\]. These scale-up efforts will
require about 1 M\$/year for three years for each process that is
selected for scale-up. However, the cost savings projected for a
LHC-size project will return this investment many times over, and may be
the critical factor determining the feasibility of such a project.

### 10.2.3 IR magnets for flat beam optics {#ir-magnets-for-flat-beam-optics .unnumbered}

The parameters of various IR magnets required for the flat beam optics
are given in Table 6-6. The layout is shown in Fig.3-25. The following
are the major design considerations of these IR magnets:

-   Small aperture (specially in quadrupoles for generating high
    gradients)

-   Brittle superconductors that must be used for generating high
    field/gradient

-   Large Lorentz forces (associated with high fields)

-   Small separation between the two apertures (associated with the
    doublet optics)

Given the importance of these few magnets, the state of the art
superconductors are used in the design. The ends of conventional cosine
theta designs put a practical limit on the minimum aperture,
particularly in quadrupole magnets made with brittle material. To
overcome this and other limitations VLHC-2 IR doublets are based on
non-traditional magnet designs with racetrack coils. These are conductor
friendly designs with large bend radii and are suitable for containing
large Lorentz forces.

The minimum separation between the two apertures in Q1A determines the
layout of the entire IR region and the maximum beam size for the given
optics. In addition, it also establishes the maximum pole tip field of
this and other magnets. In conventional 2-in-1 designs, the minimum
separation is determined by the conductor width required for generating
field gradient and the support structure required for containing large
Lorentz forces. In the proposed design the amount of conductor between
the two apertures is much smaller than on any other side and no support
structure is required between the two apertures. This brings a large
reduction in spacing (by about a factor of five) between the two
apertures. The cross section of the proposed design is shown in
Fig.10-7. In order to facilitate large bend radii, returned path of all
turns is further away from the aperture. Field contours and field lines
in the aperture of this magnet are also shown in Fig.10-7. The design is
based on react-and-wind Nb~3~Sn superconductor with a current density in
the coil of 2500 A/mm^2^ at 12 T. The magnets based on these design
principles use much larger amount of conductor than that in a
conventional design. However, the cost of conductor is not a major issue
in designing a few critical high performance magnets.

![](media/image7.jpeg){width="2.4944444444444445in"
height="2.040277777777778in"}
![](media/image8.jpeg){width="1.5013888888888889in"
height="2.0618055555555554in"}

Fig.10-7: A conceptual design of 2-in-1 Q1A (left) and flux distribution
in the coil region of the magnet (right). The design minimizes the
spacing between two apertures.

This design also introduces a strong coupling and a cross talk between
the two apertures. The superimposition of a dipole field on the
quadrupole coils increases the peak field on the conductor and reduces
the maximum achievable gradient. The maximum gradient in Q1A (minimum
separation) is, therefore, 400 T/m as compared to 600 T/m in Q1B, Q2A
and Q2B where this effect is much smaller. The goal is to minimize the
cross talk induced harmonics with the exception of the dipole field. By
symmetry, the normal even harmonics and skew odd harmonics are
theoretically zero. The target field harmonics are given in Table 3-34.
These values will be obtained either by design or by correction. Table
3-34 includes harmonics from both design and construction errors,
however, the harmonic errors are dominated by the design. These
harmonics are expected to come down as the design evolves. All four
quadrupoles will have a different cross section.

VLHC IR region uses three types of dipole magnets. The design of all
insertion region dipoles is also based on racetrack coils. D1A, D1B (one
each on each side) are single aperture dipoles and D2 (two on each side)
is a 2-in-1 dipole. The operating field in the smaller aperture (25 mm)
dipole D1A is 16 T (quench field \~18 T) and it uses High Temperature
Superconductor (BSCCO-2212) in a hybrid design. The operating field in
the larger aperture (50 mm) dipole D1B is reduced to 12 T to reduce the
Lorentz forces in larger aperture. This field can be entirely obtained
by Nb~3~Sn superconductor.

### 10.2.4 Cryogenic-related R&D for a high field VLHC.  {#cryogenic-related-rd-for-a-high-field-vlhc. .unnumbered}

The large total cryogenic system power, the magnet string lengths, total
cold mass, and total helium inventory for a VLHC-2 cryogenic system go
well beyond that of previous systems. Scaling up standard cryogenic
methods and systems to the size of a VLHC results in some new problems
which call for R&D. The following is a list of some possible areas for
R&D in cryogenics for a high field VLHC.

1.  It would be very desirable to reduce the installed cryogenic system
    power to significantly less than the presently estimated 105 MW. The
    heat load with the biggest potential for reduction by some
    innovative method is probably the synchrotron radiation. Developing
    methods for removing some significant fraction of the synchrotron
    radiation at room temperature could permit a dramatic reduction in
    cryogenic system size (both power and inventory) for a high field
    VLHC.

2.  Static heat load (thermal radiation and conduction) reduction might
    be possible. One should investigate the possible utilization of
    techniques developed for MRI or by NASA (e.g., trace cooling of
    supports and/or trace cooling of an inner shield). It could also be
    beneficial to fund a development effort toward better multilayer
    insulation (MLI) and MLI installation.

3.  Improve cryogenic plant efficiency. Although there is no
    thermodynamic advantage in a heavier gas as a working fluid in a
    cycle, there might be some advantage of a higher molecular weight
    refrigerant (nitrogen or neon) in permitting the use of very
    large-scale air separation compressors and expanders. Hans Quack
    (cryogenics professor at University of Dresden, Germany) states: "At
    a paper, which I am going to present at the CEC in Madison, I am
    going to propose a new system with a mixture of helium and neon as
    refrigerant. Such a refrigerant is nearly as efficient as helium, it
    allows power recovery of the turbines and a turbo compressor as main
    compressor and one can go down to 27 K."

4.  Improve helium screw compressor efficiency. This R&D item was listed
    at the Bloomington workshop in 1994 and the Jefferson Lab workshop
    in 1999. Quoting from the 1999 report: "Screw compressor efficiency
    (FY94 recommendation): This one component accounts for more than
    half of total inefficiency of a refrigeration system. We use screw
    compressors rather than the more efficient reciprocating compressors
    because of their very high reliability. The root problem is that the
    He market is so small compared to Freon that it is difficult to get
    the vendor's R&D attention."

5.  Another R&D item from the 1999 Jefferson Lab workshop which is again
    worth listing is a study of flow instabilities in long systems.
    Density wave instabilities could cause serious trouble for a VLHC,
    and a thorough understanding of this phenomenon would be required to
    ensure good design.

###  {#section-1 .unnumbered}

### 10.2.5 Synchrotron Radiation and Vacuum {#synchrotron-radiation-and-vacuum .unnumbered}

Almost twenty years ago, when people started studying very high energy
colliders like the SSC, the LHC and the Eloisotron, it was immediately
recognized that the effect of synchrotron radiation on the beam tube
vacuum and the cryogenic system would be a major issue and R&D
challenge. Numerous experiments and calculations have been done since
that time (REFS), and they still remain major issues for the design and
operation of high energy hadron colliders.

The cryogenic issues fall into two categories: removal of heat from the
beam-tube liner, and the total heat load. These are complexbut well
understood cryogenic issues involving cryogen flow, thermal
conductivity, pressure drop, and other parameters. So many parameters,
in fact, that the solutions must be experimentally verified in addition
to being simulated on computers. In spite of the complexity of the
system, it is expected that modeling will accurately predict the proper
design.

The vacuum system is more difficult to understand, and must be
experimentally verified. The usual solution proposed, but which will be
testedfirst in the LHC approximately six years from now, is to have a
beam-tube liner, shown in Fig.10-8, which intercepts the sychrotron
radiation at elevated temperature (to take advantage of improved Carnot
efficiency), and which has small perforations that permit gas to escape
and be trapped, cryopumped and shadowed between the liner and the beam
tube. This system must be tested at sychrotron light sources, although a
lot will be learned during the early operation of the LHC. Among the
issues are pumping speed, desorption coefficients and clean-up time.

![](media/image9.png)

Fig.10-8 A model of the VLHC beam-tube liner

![](media/image10.png){width="2.7284722222222224in"
height="2.7944444444444443in"} A photon-stop has been proposed as a
possibility to intercept the intense synchrotron radiation in the Stage
2 VLHC. \[1\] The photon-stop, shown in Fig.10-9, is a piece of metal or
semiconductor that protrudes into the beam pipe between magnets, and
intercepts all ormost of the sychrotron radiation before it hits the
beam-tube liner. The advantage of the photon stop is that it may be able
to be operated at temperatures close to 300 K, thus saving significant
amounts of cryogenic power, possibly more than 30 percent. A first pass
engineering design of such a device has been completed. \[2\] The
results of numerical impedance calculations \[3\] give additional
support to the viability of the approach.

Fig.10-9 A model of a proposed VLHC photon stop, to be placed between
magnets to absorb synchrotron radiation at 300 K.

An Argonne National Laboratory-Fermilab collaboration proposes a
multi-step R&D plan towards the realization of such a device. \[4\] In
the first step a photon stop prototype would undergo tests in the
Advanced Photon Source (APS) photon-beam in a device that could be
operated wholly at room temperature. Simultaneously, cryogenic tests of
prototypes could take place at Fermilab. A photon beam is not required
for such tests. A full-blown cryogenic and vacuum test series of the
photon-stop in a VLHC-like setting is proposed as the final stage. An
important part of the R&D is to understand the effect of the photon
stops on the beam stability. This can be accomplished with a combination
of sophisticated calculations and bench or beam measurements.

\[1\] I. Terechkine, "*Synchrotron Radiation in the VLHC*", Fermilab,
Technical Division Note, unpublished, 01/01.

\[2\] P. Bauer et al., "*A Photon-Stop for VLHC-2 -- Engineering Design
-- Part 1*", Fermilab, Technical Division Note TD-01-023, 04/01.

\[3\] N. Solyak et al., "*A Photon-Stop for VLHC-2 -- Impedance
Calculations*", Fermilab, Technical Division Note TD-01-014, 04/01.

\[4\] Fermilab Technical Division Note TD-01-30

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

\[1\] J. Lach, R. Bauer, P. Conroy, C. Laughton, E. Malamud, \"Cost
Model

for a 3 TeV VLHC Booster Tunnel,\" Fermilab TM-2048, April 11, 1998.

\[2\] The Robbins Company, \"Tunnel Cost Reduction Study,\" July 16,
1999.

\[3\] Joseph Lach, \"Instrumentation of a 17ft Diameter Tunnel Boring

Machine in the Chicago Dolomite.\"

\[4\] G.W. Foster, \"An Unmanned, Battery-Operated TBM Tunneling

Scenario,\" October 6, 1998. (VLHCPub-85)

\[5\] G.W. Foster, M.P. May, \"Generic Accelerator tunneling R&D at

Fermilab,\" August 1999.

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