**A preliminary consideration of**

**A 1.5 TeV Injector Accelerator for the LHC**

(Draft version #8)

Henryk Piekarz, Gijs de Rijk and Lucio Rossi

CERN - FERMILAB

March 26, 2006

1.  **Motivation**

A primary goal for the LER (Low Energy Ring) Injector Accelerator for
the LHC is to be able to inject 1.5 TeV proton beams, instead of the
current 0.45 TeV beams from the SPS. At this new energy the field
harmonics \[1\] of the LHC magnets are satisfactory enough to prevent
the luminosity losses expected to appear with the transfer of the lower
energy SPS beams. In a long term, the LER injector accelerator would
greatly facilitate the implementation of the doubling of the LHC energy
(LHC2). We assume that this proposal is primarily aimed at advancing the
goals and extending the frontiers of the high-energy elementary particle
physics.

2.  **Elected boundaries for the LHCI design and construction**

As presented in some detail in Chapter 13, it is expected that design
and construction of the LER will take about 5-6 years. In order to
minimize potential impact of the LER implementation process on the
ongoing LHC physics program the following LER design and construction
criteria have been adopted:

\- The LER accelerator will be installed in the LHC tunnel during
regular

LHC shutdowns,

\- No new tunnels digging will be required,

-   The current SPS-LHC beam injection scheme will remain intact and
    will be used as is to inject beams into the LER ring. At any time a
    reversal to the standard SPS-LHC injection and the LHC operations
    will be possible,

-   The LER accelerator components will be designed and fabricated using
    as much as possible the known technologies, so only the component
    design followed by prototyping to verify the performance, and to
    facilitate the procurement for the mass production, will be used.

3.  **Outline of the new injection scheme for the LHC accelerator
    complex**

We propose to install the LER accelerator inside the LHC tunnel. This
accelerator would accept 0.45 TeV proton beams from the SPS through the
TI2 and TI8 transfer lines, and then accelerate these beams to 1.5 TeV,
so as to match best the beam momentum acceptance of the LHC magnets. The
LER accelerator would be based on super-ferric, combined function
magnets which were originally proposed for the VLHC Stage 1, a p-p
collider in the US \[2\], as they require only minimal space in the
accelerator tunnel. This magnet and its supporting systems (conductors,
power supply, current leads, etc.) were recently successfully tested at
Fermilab \[3-7\].

In the new LHC beam injection scheme the proton bunch stacking and the
formation of the full intensity beam is performed in the LER ring with
the beam passing through the LHC accelerator beam pipe in most of LHC
straight sections. This means that in some straight sections the LER and
the LHC accelerators share the same beam pipe.

This scheme is being proposed to eliminate costly digging of new bypass
tunnels around each detector.

Once the stacking of the clock-wise and the counter-clock 0.45 TeV beams
in LER is complete, the beams are accelerated to 1.5 TeV and then passed
into the entire LHC ring using a single transfer mode operation in which
only one set of the LER transfer line magnets needs to be ramped down in
a time period determined by the time interval between the tail and the
head of the beam train. This idea of LER to LHC beam transfer is
illustrated in figure 1.

![](media/image1.jpeg){width="6.025in" height="3.39375in"}

Figure 1. The principle of the LER - LHC proposed beam transfer method.
D stands

for dipole magnet and PM for fast pulsing dipole magnet

The time slot for beam transfer is 3 microseconds, while the beam
circulation time in the LHC ring is \~ 89 microseconds. After the beam
transfer into the LHC ring is complete, and the beam circulates only in
the LHC ring, all the remaining LER magnets (transfer lines and main
arc) may be ramped down, and remain on standby for the duration of the
store (\~10 h). This may help to reduce potential effects of the LER
magnets fringe field on the operation of the LHC magnets at 7 + 7 TeV,
and also it will save some refrigeration power used for the operation of
the LER magnets.

The minimum allowable vertical separation between the LER and LHC rings
is about 135 cm. In the IR regions, where the detectors reside, the
total length of the straight sections is about 528 m. The available
space at the LHC ring level, however, that could be used for the
insertion the LER-LHC transfer-line magnets totals only to about 80 m on
each side of the detector. This situation poses a great challenge for
the transfer of the 1.5 TeV beam between these two rings. A possible
conceptual LER-LHC transfer line design and arrangement of the transfer
line magnets in the IR1 and IR5 regions are discussed in Chapters 8 and
9.

The proposed conceptual LER-LHC injection scheme together with the LER
ring arrangement is shown in figure 2.

![](media/image2.jpeg){width="5.997222222222222in"
height="4.727083333333334in"}

Figure 2. A conceptual arrangement of the LER-LHC injection scheme

At present the SPS beam is transferred to the LHC rings by using the TI2
(clockwise circulation) and the TI8 (counter-clock circulation) beam
lines. A set of fast kicker magnets placed in the front straight
sections of the Point 2 (ALICE detector) and Point 8 (LHCb detector)
facilitates beam transfer into the LHC ring. These kicker magnets use
about half of the available space on one side of these straight
sections. Consequently, if the LER beams are required to pass through
the LHC beam pipe at the Points 2 and 8 (and so to facilitate the ALICE
and the LHCb operations with LER), the TI2 and TI8 lines must inject
beams into the LER rings at a shorter distance than presently to LHC.
This will free some space for the transfer of the LER beams to the LHC
ring in the front section of the Points 2 and 8, but it will
considerably complicate the TI2 and TI8 beam lines. The need for the
operations of the LHCb and Alice detectors with the LER is physics
driven, and if they are desired for the LHC operations with the upgraded
luminosity (and energy) then the modifications to the TI2 and TI8 beam
lines must be considered. For now we propose the LER-LHC injection
scheme that does not assume the ALICE and the LHCb detectors operating
with the upgraded LHC luminosity (or energy) resulting from the LER
implementation. Our scheme, however, allows run these detectors with a
standard LHC operation mode any time even after the LER installation and
operation.

The beam from TI2 transfer line enters the LHC ring at the short
straight section just in front of the Pt2. It travels through the Pt2,
and is then transferred to the LER ring. It passes the Pt3 area, and it
is transferred into the LHC beam pipe only at the Pt4 where it will use
the RF system of the LHC. After Pt4 the LER beam goes back to its ring
until it reaches Pt5 where it shares the LHC beam pipe while passing
through the CMS detector. It is again bumped into the LER ring until it
reaches Pt6 where it is bumped into the LHC beam pipe to use the beam
dump facility. After Pt6 it enters the LER ring again, passes Pt7 and
Pt8, and re-enters the LHC beam pipe at Pt1 (ATLAS). Immediately after
Pt1 it is bumped back into the LER ring, and will stay there until
reaching Pt4. The beam from the TI8 has the same path in LHC/LER as the
TI2 one, except that it enters the LER ring right after Pt8 and it
travels in a counter-clock direction. We assume that the LER will have
its own momentum and betatron clearing systems at Pt3 and Pt7,
respectively.

4.  **The VLHC Stage 1 magnet and its main characteristics**

A conceptual design of the VLHC Stage 1 main arc dipole magnet is shown
in figure 3. The magnet features 2 pole gaps between the top and the
bottom half-cores. The magnetic field is induced by up to a 100 kA
current from a single, transmission line conductor located in the center
of the half-core assembly. The field in the pole gap is entirely shaped
by the iron, facilitating magnetic design. The VLHC Stage 1 magnet is a
combined function gradient dipole with 2 half-cell versions, focusing
and de-focusing, placed interchangeably along the accelerator ring. The
magnet pole gap is 20 mm high, and the beam pipe is elliptical with an
effective vacuum space of 18 mm (v) and 28 mm (h). In the tests, the
magnetic field was measured using a 69 cm long, 15.2 mm diameter
tangential coil, and with a Hall probe array of 102 sensors. The
characteristic measured dipole strength versus current is shown in
figure 4, and in figures 5,6 we show the measured quadrupole strength
and the sextupole harmonic versus the dipole field (data analysis from
\[7\]). The quadrupole strength reflects the design gradient of 4%. The
sextupole and other normal and skew field harmonics (in units at 10 mm)
up to the order of 10 were found relatively small, not exceeding 2-3
units (or 0.02-0.03 %). The accuracy of the measurements is especially
poor at low fields (the tangential coil design was optimized for the
high fields).

> ![](media/image3.jpeg){width="3.751388888888889in"
> height="3.1333333333333333in"}
>
> Figure 3. The VLHC Stage 1 magnet conceptual design
>
> ![](media/image4.jpeg){width="4.622916666666667in"
> height="2.9166666666666665in"}
>
> Figure 4. The measured dipole field versus current
>
> The circle represents the maximum current for the collider operation.
>
> ![](media/image5.jpeg){width="4.500694444444444in"
> height="3.311111111111111in"}

Figure 5. The measured quadrupole strength as a function of the dipole
field

The maximum dipole field for collider operations is 1.966 Tesla.

![](media/image6.png){width="5.083333333333333in"
height="3.3520833333333333in"}

Figure 6. The measured sextupole strength as a function of the dipole
field

5.  **Adaptation of the VLHC Stage 1 magnet to the LER**

    1.  Dipole field and gradient of the LER arc magnet

> A preliminary design of the LER optics \[8\] used the VLHC combined
> function magnets with a goal to replicate the LHC optics and match the
> LHC footprint. The LER and LHC optics are shown in figures 7 and 8,
> respectively. The dispersion suppressers were modeled on the ones of
> the Main Injector at Fermilab -- 2/3 the bend and ¾ the length of arc
> cells. A list of arc and dispersion suppression cells for LER that
> allows exactly reproduce the LHC lattice is shown in Table 1.
>
> Table 1

+---------+----------+-----------+-------------+-------+-----+------+
| Cell    | Cell     | Magnet    | Magnet      | N     | B   | B'   |
| Type    | Length   | Type      | Length      | umber |     |      |
|         |          |           |             |       | \(  | (    |
|         | \(m\)    |           | \(m\)       | per   | T\) | T/m) |
|         |          |           |             | Cell  |     |      |
+---------+----------+-----------+-------------+-------+-----+------+
| Arc     | 107      | GF/GD     | 12          | 8     | 1.  | 4    |
|         |          |           |             |       | 595 | .858 |
+---------+----------+-----------+-------------+-------+-----+------+
| Sup     | 80       | GSF/GSD   | 8           | 8     | 1.  | 10   |
| pressor |          |           |             |       | 595 | .112 |
+---------+----------+-----------+-------------+-------+-----+------+

> At 1.595 T field the required magnet current is only 55 kA thus
> considerably lower than that of the VLHC (89 kA for 1.966 T of the
> nominal operation field). The required LER gradient corresponds to +/-
> 3%, as oppose to +/- 4% of the VLHC. The lower field and the gradient
> improve further the quality of the main arc magnets as the operations
> are further away from the saturation region that becomes very strong
> above 1.9 T. A preliminary list of the LER quadrupole parameters at
> IR1 and IR5 is shown in Table 2.
>
> Table 2

+----------------+-----------------+-----------------+-----------------+
| Quad           | L (mag)         | B' (left)       | B' (right)      |
|                |                 |                 |                 |
|                | \(m\)           | (T/m)           | (T/m)           |
+----------------+-----------------+-----------------+-----------------+
| Q4             | 4.0             | \- 62.92        | 62.92           |
+----------------+-----------------+-----------------+-----------------+
| Q5             | 4.0             | 68.98           | -68.98          |
+----------------+-----------------+-----------------+-----------------+
| Q6             | 4.0             | \- 97.83        | 97.83           |
+----------------+-----------------+-----------------+-----------------+
| Q7             | 4.0             | 80.88           | -80.88          |
+----------------+-----------------+-----------------+-----------------+
| Q8             | 4.0             | \- 91.25        | 91.25           |
+----------------+-----------------+-----------------+-----------------+
| Q9             | 4.0             | 56.46           | \- 56.46        |
+----------------+-----------------+-----------------+-----------------+
|                |                 |                 |                 |
+----------------+-----------------+-----------------+-----------------+
| Q10            | 3.0             | -81.27          | 80.62           |
+----------------+-----------------+-----------------+-----------------+
| Q11            | 3.0             | 68.45           | \- 68.45        |
+----------------+-----------------+-----------------+-----------------+
| Q12            | 3.0             | \- 58.38        | 56.39           |
+----------------+-----------------+-----------------+-----------------+
| Q13            | 1.5             | 48.02           | \- 39.53        |
+----------------+-----------------+-----------------+-----------------+

> ![](media/image7.jpeg){width="5.748611111111111in"
> height="3.6791666666666667in"}
>
> Figure 7. The LER (LHC-I) optics at IR1, designed based on VLHC LF
> magnets
>
> ![](media/image8.jpeg){width="5.627083333333333in"
> height="3.6131944444444444in"}
>
> Figure 8. The LHC optics at IR1

2.  Beam separation in the LER magnet

The VLHC magnet was designed (and tested) for a beam separation of 150
mm. The LHC beam separation is 194 mm. With a single beam transfer mode
there is no need to equalize the beam separation for the two
accelerators. Both the LER and LHC circulating beams use their own set
of horizontally bending magnets to pass the beam pipe in the straight
sections. The minimizing the size of the magnet cores is important for
the magnet cost reduction as the cost of the iron yokes dominates the
cost of the magnet.

3\. Beam gap in the LER magnet

The VLHC magnet gap is 20 mm. The preliminary LER lattice design \[8\]
suggests that a 20 mm gap may be sufficient, but more detailed lattice
simulations are needed to reach a more binding conclusion. As the
nominal operating current for the LER magnet is 55 kA widening of the
gap by (20-30)% is certainly feasible as the B-field response to the
current is nearly linear below 1.6 T, and the conductor can operate up
to 100 kA. In that case, however, a new magnetic design with an enlarged
iron yoke would be needed. A larger magnet yoke will also incur
increased magnet cost.

4.  Return conductor for the LER magnet ring

The LER main-arc dipole magnets will be powered with a single
transmission line conductor using a single power supply and a single set
of current leads. The arrangement of the transmission line conductor as
proposed for the VLHC (235 km circumference) is shown in figure 9. A
possible arrangement of quench detection and

![](media/image9.jpeg){width="4.745833333333334in" height="3.64375in"}

Figure 9. A conceptual arrangement of the VLHC transmission line
conductor

protection circuits is also indicated. The drive conductor loops through
half of the accelerator circle, turns 180 degree back, runs as a return
conductor the full circle, turns again 180 degree and then excites the
remaining half of the accelerator magnets. This makes the continuing
length of conductor to be \~ 470 km (this will be \~52 km for the LER).
As the current in the overlapping conductors runs in the opposite
directions the magnetic fringe field is strongly suppressed at far
distances. This is important for the protection especially of low flying
civil aviation aircrafts. The magnetic fringe field due to the return
conductor sections inside the magnet is small, but in the areas between
the magnets it is strong (1 Tesla conductor self-field). The alternative
is to use a drive conductor only, and to install heavy magnetic
shielding (e.g. 4 cm thick steel plates) covering all the open sections
of the conductor. This may be very inconvenient at the magnet joints but
especially at the cryogenic ones where the access is needed for
servicing. From the aviation safety point of view there would never be
100% guarantee that the fringe fields are suppressed using "removable"
shielding. The issue of the return conductor may be revisited again for
the LER case as the accelerator circumference is 10 times smaller, and
likewise the cost of the installation of the iron shielding.

Both the drive and the return conductors must bypass the detector areas.
In case of a single conductor a heavy magnetic shield would have to be
installed to protect the detectors (and people). The drive and the
return conductors are separated vertically by 28 cm, and the cryostat
pipe enclosing both of them is only 36 cm in diameter. This indicates
how much space is needed in the area behind the detectors for the
installation of a bypassing conductor lines.

5.  LER ring location in the LHC tunnel

> The inspection of the LHC accelerator tunnel leaves only one
> possibility for the location of the LER magnet, and that is in the
> space above the LHC magnet as shown
>
> ![](media/image10.jpeg){width="3.0006944444444446in" height="2.75in"}
>
> Figure 10. A possible arrangement of the main arc LER magnet in the
> LHC tunnel
>
> in figure 10. In order to minimize the vertical distance between the
> LHC and LER rings the return conductor of the super-ferric magnet will
> be placed in the space above this magnet, rather then below as in the
> VLHC case. This new arrangement is shown in figure 10. There is a 4 cm
> thick steel shield placed on the top of the magnet to suppress any
> effect of a fringe field from the return conductor on the field in the
> LER magnet gap. There is also probably a need for a protection of the
> LHC magnet from the fringe field propagating below the LER magnet.
> Fringe field simulations are needed to determine the location and
> thickness of the magnetic shielding for the LHC magnet.

In figure 11 and figure 12 the preliminary LER magnet locations and
supports are shown for a typical LHC ring location, and for the location
with the cryogenic feeds, etc., respectively. The magnet will be
supported from two crossing I-beams fastened to the top and side of the
concrete wall of the tunnel. The spacing is to be determined by an
engineering analysis of the strength required to support the magnet
weight of 500 kg/m. There are, however, some obstacles for the LER
magnets, typically located at the Points 1 through 8. The main obstacles
are: (1) the LHC magnet power cables on the distribution boxes which are
fed to the magnet top (\~10 m long space at each Point is used), (2)
helium feeds from the top or from the sides at all Points (\~ 15 m
space), and the power cables for the accelerating cavities at Point 4
(\~ 50 m). Although the re-arrangement or bypassing of these obstacles
may not be easy it does not appear to be an un-surmountable task. These
areas could also be used as a beam drift space, so no magnetic elements
would then be needed.

![](media/image11.jpeg){width="4.504166666666666in"
height="3.165277777777778in"}

Figure 11. Mounting of the LER magnet in a typical location in the LHC
ring

> ![](media/image12.jpeg){width="4.495833333333334in"
> height="3.0493055555555557in"}
>
> Figure 12. Mounting of the LER magnet in a location with LHC magnet
> cryo-feed
>
> **6. Cryogenic support**

Transmission line magnets use supercritical helium at 4.5 K, 4 bar
pressure and 60 G/s flow rate, with a total liquid inventory of about
50,000 L. The LHC QRL system at CERN can deliver 1700 G/s of
supercritical helium, thus the 60 G/s flow required for the LER magnets
is in the margin of the projected LHC operational needs. Therefore, it's
conceivable that no new cryogenic plant needs to be built to support the
LER operation. The LER magnets could tap into the QRL line at any
convenient distance, e.g. each 1000 m.

> **7. Main arc magnet assembly work and its installation in the
> tunnel**

The half-cores and the transmission line conductors will be fabricated
in an outside factory. The magnet assembly work, which is basically the
laser welding of the half-cores into a magnet, can be done in an outside
facility, or in an assembly hall at CERN. The assembled magnets would
then be lowered down into the LHC tunnel, and placed on the prepared
I-beam supports. The conductor splicing, the closing of the helium flow
connections, beam pipe installation, instrumentation connections, etc.,
would all be done in the tunnel. The tunnel work can proceed during any
operation break of the LHC accelerator.

8.  **LER to LHC beam transfer design at 1.5 TeV**

Beam transfer from the LER ring into the LHC ring is the most
challenging task of the LER proposal that needs to be very seriously
dealt with. The injection scheme with one accelerator residing on the
top of the other has been done before (e.g. Recycler and the Main
Injector at Fermilab) but at considerably lower energies.

The vertical separation of the LER and LHC rings can be made to be about
135 cm. This means that the 1.5 TeV beam needs to be bent down (or up)
off the LER (or LHC) ring, transported, and then bent into the LHC (or
LER) ring over a vertical distance of 135cm. About half of this
distance, 67.5 cm, is needed to clear any LHC magnets. Once the LER beam
cleared these magnets it will not be difficult to transfer the beam into
the LER ring. The operation of clearing the LHC magnets must take place
necessarily within the available free space in the straight section so
the transfer line magnets can reside at the LHC ring level. Although the
total length of the LHC straight section is about 528 m, such a free
beam path is no longer than 100 m on each side of the detector. As
pointed out earlier we assumed no re-arrangement of the LHC magnets in
the IR regions, so the completion and operation of the LHC accelerator
proceeds as originally planned.

A preliminary LER lattice design \[8\] was made to produce the footprint
as close as possible to that of the LHC to preserve the best possible
beam quality in the LER ring and in the LER-LHC beam transfer operation.
Consequently, the LER-LHC transfer line magnets must use only the magnet
free sections between D1 and Q5. The proposed design assumes that the
beam transfer is made using 4 bends (Fig. 13), each with 84 T-m bending
power. Two bends lift the LER beam to the level of 0.675 m to allow the
transfer line magnets to pass over the D2 magnet of LHC. The next two
bends put the beam at 1.35 m above the LHC ring. The 1.35 m level
becomes the nominal level of the LER ring. In the horizontal plane the
LER beams separation of

![](media/image13.jpeg){width="5.622916666666667in"
height="2.884027777777778in"}

Figure 13. A conceptual arrangement of the LHC-LER transfer line

150 mm will be achieved by rotating a bit the vertically bending magnets
in a plane that is perpendicular to the beam direction.

9.  **Conceptual design of the LER-LHC transfer line magnets**

In the horizontal plane the clock-wise and counter-clock LHC beams have
no separation at D1, but they are separated by 194 mm at D2. The first
magnet pair of the 1^st^ vertical bend section must be placed at a
location that the clock and counter-clock beams are separated enough to
allow for operations of these magnets with good quality of magnetic
fields. We assume that \~100 mm beam separation may be sufficient to
design a good quality first magnet pair. Such a beam separation is near
the middle of the D1--D2 distance of 86.6 m, and puts severe strain on
accomplishing there the two first bends. The path for the first two
bends may be slightly expanded, however, by placing additional,
horizontally bending dipole next to the exit of the D1. As the beams
travel in the opposite directions, and at the D1 they are inclined with
the opposite sign angles, a single dipole magnet will carry the task of
bending both the LER beams off their central LHC paths. The bending
power of this magnet must be strong enough to increase the LER beams
separation at the first vertical bend to \~100 mm, but the LER beam must
stay well within the 40 mm diameter of the LHC beam pipe. A set of two,
short, 1 T-m magnets will allow to kick each beam by \~5 mm sideways at
the location of the first vertical bend (\~ 20 m from the face of D1)
thus providing the required minimum 100 mm LER beams separation for the
magnet pair of the 1^st^ vertical bend.

A preliminary LER-LHC transfer line magnet arrangement is shown in Fig.
14.

![](media/image14.jpeg){width="5.989583333333333in"
height="3.7847222222222223in"}

Figure 14. A preliminary arrangement of the LER-LHC transfer line
magnets

The 1^st^ vertical bend is arranged using three sets of magnets. The
first set consists of fast pulsing pairs of single bore magnets that
when turned off allow the clock-wise beam to pass into the LHC ring. A
beam drift space after the first set of magnets is created to allow for
the LER and LHC beam pipe separation. The second set consists of pairs
of normal-conducting magnets that can be placed just above the LHC beam
pipe. The third set consists of the two-bore, high-field superconducting
magnets to complete the 1^st^ bend. The 2^nd^, 3^rd^ and 4^th^ bends
consists of two-bore, high-field superconducting magnets.

In order to understand the choice and arrangement of the magnets in the
1^st^ bend we must look at the timing sequence of the SPS-LER-LHC beam
transfer scheme. This is schematically indicated in figure 15. When the
SPS is ready for beam transfer all LER magnets, including those in the
transfer lines, are ramped to the fields proper for the 0.45 TeV beam.
The ramping time of 100 sec is characteristic of the main arc LER
magnets. The stacking of the 1^st^ SPS beam begins and it lasts for
about 3'. Then the stacking of the 2^nd^ SPS beam begins and lasts for
about 3' as well. As soon as the stacking of the 2^nd^ beam is complete
the LER magnets ramp to 1.5 TeV, again in the 100 s time. The 1.5 TeV
beams may circulate for 10 ms, or so to stabilize, and then the fast
pulsing LER-LHC transfer line magnets are turned off forcing the beams
to circulate from now on in the LHC rings only. At this point all
remaining LER magnets are ramped down.

![](media/image15.jpeg){width="5.621527777777778in"
height="3.3131944444444446in"}

Figure 15. Timing sequence for the LER-LHC beam injection

> The LER-LHC beam transfer procedure described above requires fast
> pulsing magnets to be ON during SPS to LER transfer and the subsequent
> ramping to 1.5 TeV of all magnets in both LER rings. Then they are
> turned off in a very short period of time (\~3 microseconds) to force
> beams circulation in the LHC rings only. This is an unusual
> application of a fast pulsing magnet. In the accelerators, these
> magnets (known as "kickers") are mostly used to remove the beam from
> the circulation, e.g.
>
> for beam dumping. It means that they are ramped-up in a very short
> time period, stay ON until the beam is out, and then slowly ramp-down
> to a stand-by mode. The beam transfer from one accelerator to another
> is typically done using a tandem of a kicker and Lambertson magnets.
> The kicker magnet is used to move the beam in (or out) of the
> field-free zone in Lambertson. In the LER application Lambertson
> magnet would have to stay ON during the LER beam stacking, and then
> facilitate the subsequent beam energy increase. Then the kicker magnet
> paired with Lambertson would force the LER beam into a field-free
> zone, and thus allow the beam passage into the LHC ring. The kicker
> would have to have the rise time of 3 microseconds, stay ON for 87
> microseconds, and then decay in 3 microseconds so its field would not
> interfere with the circulating LHC beam. This shows that the kicker
> design with the application of the Lambertson magnet in the LER-LHC
> beam transfer may be difficult. In addition, the Lambertson magnets
> are very difficult to design as well. They heavily rely on the
> application of iron cores thus being limited to rather low magnetic
> fields. With the required beam bending in the vertical plane, the
> spatial closeness of the clock-wise and counter-clock circulating
> beams, and a very limited free space between the D1 and D2 LHC dipoles
> the application of the Lambertson magnets for the LER-LHC beam
> transfer seems rather unlikely.

The fast pulsing vertical dipole set of \~10 T-m total bending power
must lift the LER beam by \~ 70 mm above the LHC nominal beam line using
the overall beam path of \~17 m. The magnet aperture gap must
accommodate the space needed for the LHC beam pipe (40 mm), and the
magnet aperture width must accommodate the vertical deflection of the
LER beam (up to 40 mm). With the exception of the magnet set next to the
dipole D1, the fast pulsing magnets have horizontal B-field orientation
to facilitate beam bending in the vertical direction.

The proposed fast pulsing magnets must be powered with a single
conductor in order to minimize the inductance. Typically such magnets
can be designed with inductance \~ 1 micro-Henry for the length of about
1 m. The lower the inductance the lower is the voltage generated when
the magnet current supply is turned off. In fact, the choice of the
magnet size, and its B-field are driven by the parameters of the
availability of the power supply. Based on our experience with the power
supply for the VLHC low field magnet, we concluded that we could use a
90 kA dc power supply for the fast pulsing magnet operations. With a 1
micro-Henry magnet inductance the expected voltage drop at 3
microseconds turn-off is \~ 30 kV, plausibly manageable as well. We
select the individual magnet length to be (0.8 - 0.9) m, and we add the
beam drift spacing for the magnet connections as well as a longer drift
space for the separation of the LHC and LER beam pipes. With a selected
90 kA current source the magnet B-field decreases as the magnet aperture
increases while accommodating increased vertical separation of the LER
beam. In order to estimate the available B-fields with the 90 kA
currents we assumed magnet conductor geometry that is based on the
"crossing ellipses" \[9\] as shown in Fig. 16. Using a formula from
\[9\] (3.22, page 31) we derived B-fields for 90 kA current but with
vertical beam separation of 10, 20, 30 and 40 mm and the magnet gap of
40 mm. The deduced B-fields are: 1.55 T, 1.40 T,

![](media/image16.jpeg){width="4.5in" height="3.1034722222222224in"}

Figure 16. Dipole magnet model approximation

1.28 T and 1.17 T for the 10, 20, 30 and 40 mm LER-LHC beam separation,
respectively. With these magnet B-fields we arranged the first section
of the 1^st^ bend of the transfer line magnets as presented in Table 3.

The cross-section area of the conductors in all magnets is 236 mm2. With
such a small conductor cross-section the power dissipation even at 30 kA
makes it impossible to operate for a time period of 10 minutes, or so,
as needed for the LER-LHC beam transfer. The solution to this problem is
to make the conductors out of the OFHC copper (e.g. 99.999% pure), and
operate magnet at the temperatures below 20 K. The resistance of a 1 m
long magnet conductor is then in the range of 2x10\^{-8} ohms.
Preliminary analysis \[10\] using a described below mechanical design of
the magnet suggests that a very small flow rate of supercritical liquid
helium (less than 3 G/s) is needed to sustain magnet operations
"indefinitely" at 30 kA, and comfortably long time for the operations at
90 kA. A conceptual design of a fast pulsing magnet pair is shown in
figure 16. The elliptically shaped magnet conductors are housed inside
the cryo-pipe (austenitic steel, 0.65 mm) and outside the elliptical
vacuum beam pipe. The elliptically shaped conductors will be assembled
from multiple layers of thin copper plates to minimize possible effect
of Eddy currents at high frequency application. In our application the
fast pulsing magnets are ramped-up at slow pace so only at the magnet
power turn-off the Eddy currents may appear. This should be of less
concern, though, for the beam transfer operation.

Table 3

![](media/image17.jpeg){width="5.995833333333334in"
height="3.602777777777778in"}

> ![](media/image18.jpeg){width="5.99375in" height="3.625in"}

Figure 17. A conceptual design of a fast pulsing magnet pair

> The isolation of the cryo-pipe from the conductors is provided by a 2
> mm thick Nomex. Nomex is a material frequently used for the electrical
> insulation in both warm and cold environment. A 2 mm thick Nomex
> withstands a pulsed voltage of more than 60 kV. This material is very
> hard, and no measurable compression is observed in tests with 10
> Ton/m2 pressure. Its mechanical strength increases at cryogenic
> temperatures. The magnetic force between the conductors will push them
> apart. In order to minimize this distractive effect the tops of the
> conductors should be flattened and properly matched to the insulating
> Nomex, to the cryo-pipe wall behind and finally to the G11 support
> rings (subject of simulations). The beam pipe is made of 0.65 mm thick
> austenitic steel as well to eliminate beam pipe magnetization. The
> electrical insulation (60 kV) is provided by 10 layers of 25 um Kapton
> tape. The liquid helium flows in the space between the cryo-pipe and
> the Nomex insulation, covering nearly all area of the conductor. The
> Nomex insulator is a very well machine-able material thus allowing for
> punching frequent perforations to facilitate efficient cooling in
> spite of a small cross-section area of the liquid helium flow.
>
> Although the magnetic field in the gap is entirely generated by the
> conductor the trespassing fields from the neighboring magnet will
> affect its quality. In order to minimize this effect each magnet is
> embedded inside the pair of C-type cores. All cores are insulated from
> each other with G11 sheets. The cores are wounded using a 50 um Fe3%Si
> tape. Magnetic cores made of such tapes were recently successfully
> used in the production of fast (3 microsecond rise time) kicker
> magnets \[11\]. We crudely estimated that 20 mm thick core is
> sufficient to minimize the trespassing fields to a manageable level.
> As the beams in the transfer line part away the thickness of the core
> can be increased, if needed.
>
> The magnet cryo-pipe will be covered with MLI for the heat absorption,
> and the whole magnet assembly will be placed inside the cryostat. This
> allows minimization of the current leads due to low resistance of the
> OFHC copper in a cold state. This also considerably minimizes the size
> of the power supply itself as it is largely determined by the size of
> the copper bars carrying the current in each of the rectifiers, and
> subsequently to the magnet. Portion of the rectifiers may need,
> however, to be kept above 100 K to insure proper operation of the
> diodes. A design of a 90 kA power supply with partial components
> working at cold temperatures is now considered \[12\].
>
> Turning-off the fast pulsing magnets in a time span of 3 microseconds
> is the most challenging part of the LER transfer line magnets
> proposal. As the resistance of the magnet conductors is a small
> fraction of micro-ohms, the turning off the power supply will result
> in a long decay time of the magnet current. A short current decay time
> constant must be then enforced on the system. Typically the IGCT
> (Integrated Gate Commutating Thyristors) device installed in-line with
> the magnet leads is used for such applications. The IGCT's, however,
> are bulky, expensive and it would be difficult to use them in a cold
> environment of the magnet. A new idea of enforcing fast magnet current
> decay that takes advantage of the cold environment around the magnet
> is proposed. A conceptual design \[12\] of such a system is shown in
> Fig. 17. In this design the power connections to the magnet as well as
> the portion of the power supply itself are placed in a cryogenic
> environment made of 3 zones. The15 K zone contains magnet conductors
> as described earlier. The 40 K zone is primarily to support working of
> the HTS leads to the magnets. We anticipate that it may be possible to
> place the switcher cells inside the 100 K zone if diodes designed to
> operate at such temperatures are available. On one of the current
> leads to the magnet there are 3 logically distinctive systems: HTS,
> PT - power transformer and SD - superconducting dump. In order to stop
> magnet current the PT accepts reversed, 30 kV, 100 kA and 3
> microseconds long power signal. The superconductor heats-up, the HTS
> leads stop conducting and the current returns to the power supply
> through SS substrate of the HTS and the shunt resistors. The key to
> success to this idea is the feasibility to use the SS substrate of the
> HTS as a dump resistor. The switcher cells have no connection to the
> ground. Consequently, the unloading of the current must take place
> within the conductors in the power supply system, and the simulations
> \[12\] indicate that a minimum resistance of SD should be \~ 0.2 Ohm
> with SR at \~ 0.075 Ohm. The HTS super-conductors use the SS tape as a
> substrate but they also have substantial amount of the stabilizing
> silver that makes their resistance in a non-superconducting state very
> low \[13\]. The CuNi:NbTi conductor soldered to the SS bar offers much
> higher resistance in a non-superconducting state \[14\] but it
> requires operations at 4.5 K. In that case both the magnet and the
> accompanying superconducting dump resistor would have to probably
> operate at 4.5 K. The advantage of using the CuNi:NbTi conductor is
> that it would minimize the size of the dump resistor. As the
> supercritical helium is readily available in the tunnel, this should
> not be the problem.
>
> ![](media/image19.jpeg){width="5.497916666666667in"
> height="3.5590277777777777in"}
>
> Figure 18. A conceptual arrangement of a power supply with cryogenic
> environment

The application of the cryogenic environment to the fast pulsing magnet
power supply facilitates also their assembly and installation in the
tunnel. Between 3 to 4 fast pulsing dipoles of the LER-LHC transfer line
would be housed in a common cryostat, with 2 Power Supply assemblies
mounted on its top. Possible vertical and horizontal arrangements of the
normal-conducting, cold magnets is shown in Fig. 19 and Fig. 20,
respectively.

![](media/image20.jpeg){width="2.7493055555555554in"
height="2.4444444444444446in"}

> Figure 19. A vertical view of the fast pulsing dipole arrangement in
> the tunnel
>
> ![](media/image21.jpeg){width="5.501388888888889in" height="3.25in"}
>
> Figure 20. A side view of the vertical pulse magnet set in the tunnel.
> Note, the
>
> horizontal and vertical scales are not the same.

**10. The LER-LHC transfer line design with re-arrangement of the LHC D1
magnet**

> As presented above the fast pulsing magnet and its power supply
> although seem feasible to fabricate may be difficult for routinely
> frequent operations. Therefore one should try to simplify them and
> minimize their quantity. One way to do that is to allow for the LER
> and LHC beams to separate before the LHC dipole D1. This gives
> advantage of not only additional distance to generate LHC and LER beam
> separation but more importantly it minimizes strongly the length and
> the number of required fast pulsing magnets. While the proper design
> of the transfer line that allows for some re-positioning of D1 is in
> progress \[8\], we schematically present the principle of this idea in
> figure 21. A short, horizontally bending magnet, H0, is placed in
> front of D1.

![](media/image22.jpeg){width="5.989583333333333in"
height="3.814583333333333in"}

> Figure 21. A conceptual arrangement of the LER-LHC transfer line
> magnets with

re-positioned D1 dipole

> At this location the clock-wise and the counter-clock beams are not
> separated. So, a single bore dipole working in tandem with D1 will
> deflect both LER beams. The idea is to deflect the LER beams enough
> away from LHC beam path so the LHC beams will miss the first LER
> vertical dipole on the outside of the magnetic core. Consequently, the
> H0 dipole is the only required fast pulsing magnet in the LER-LHC
> transfer line. We estimate that \~3 m long, 2.5 T, H0 dipole will
> provide \~70 mm separation between LHC and LER beams in the location
> of the first vertical dipole. This allows operation of all vertical
> dipoles as continually powered magnets. The H0 magnet gap is
> sufficient to be only 40 mm wide so with a 90 kA current a 2.5 T field
> can be achieved. All other transfer line magnets are basically the
> same as in the original scheme described in Chapter 9.
>
> In the above scheme the D1 must be moved away from the IP by about 3 m
> to make a space for the new H0 magnet. This will require slight
> increase (about 10% or so) of the D1 operational field. In addition,
> the D1 horizontal aperture must allow for the acceptance of the LER
> beams, probably separated by some (100-120) mm at the exit of D1.

**11. Detector safety with the LHCI-LHC transfer lines**

If the LER accelerator ring would bypass the IR regions than potential
detector damage related to the magnets failure during the LER-LHC beam
transfer would be eliminated. For the LER beams to bypass the detectors
in the straight section area would require a minimum bending angle of \~
180 mrad. It would be difficult to design successful transfer line beam
optics for such a large bend angle, and than match the LER footprint to
the LHC one. Probably the beam would have to be kicked off the LER ring
at a much further distance than 260 m (1/2 of straight section) thus
increasing tunnel construction cost, now estimated at \$M (20-25) per
600 m of length.

In order to minimize potential damage to the detectors one can install
additional steel collimators of at least 10 m length between the first
fast pulsing magnet set at the D1 LHC dipole and the first vertical fast
pulsing magnet further downstream. The CMS studies \[15\] indicate that
with a total loss of a 7 TeV beam at radius of 15 mm the instantaneous
fluence in the tracking detector is equivalent to 5-10% of the annual
LHC operation dose. The maximum energy of the LHCI beam is 1.5 TeV
reducing considerably the expected above radiation dose, and so with the
additional collimators the radiation dose due to the LER transfer line
magnets failure should be viewed as minor by comparison to possible
failures of the standard LHC operations.

> **12. Crossover magnets and beam dump**

The beam crossover magnets that utilize the transmission line conductor
were discussed in the VLHC Design Study \[1\], and the same proposal
could be applied to the LER accelerator as well. The LER accelerator
will utilize the RF and the beam dump systems of the LHC accelerator.

13. **Major component cost estimate**

The cost in 2001 \$ includes 20% contingency, and it was estimated by
scaling down by a factor of 10 from the VLHC proposal \[1\]. The cost of
the power supply systems, cooling water, etc. is included in the cost of
the components.

> \[\$M\]
>
> 1\. Main arc magnets 80

2.  Correctors and special magnets 12

3\. Transfer line magnets 12

3.  Installation (120 people @ 100K\$/y) 24

4.  Beam pipe vacuum system 15

5.  Main arc magnet cryogenic support 7

Grand Total \$M 150

> The cost of the magnet support fixtures in the tunnel, and the cost of
> some other necessary modifications (e.g. possible need for enlargement
> of the tunnel height/depth at the transfer line magnet locations) is
> not included in the above estimate.

14. **Schedule of magnets fabrication and installation in the tunnel**

> A task flow-chart is shown in figure 22, and the very tentative
> schedule is a speculation
>
> ![](media/image23.jpeg){width="5.989583333333333in"
> height="4.304861111111111in"}

Figure 22. A task flow-chart for the LER accelerator design and
construction

> based in part on VLHC Stage1 construction schedule proposal \[1\].
>
> Time Lapsed time
>
> \[Y\] \[Y\]
>
> 1\. LER accelerator design, including transfer lines 1 1

2.  Prototyping and testing transfer line magnets

> (and main arc dipole magnet, if needed) 2 2

3.  Preparation of main arc magnet industrial production 1 2

> 4\. Magnet production 3 5
>
> 5\. Magnet installation in the tunnel 2 5
>
> 6\. LER commissioning 1 6

Items 1--3 and the items 4-5 can proceed simultaneously, but item 4 must
follow items 1-2, so the magnet production cannot start sooner than 2
years from the time "zero". As soon as some main arc magnets are
produced and tested, the installation in the LHC tunnel may begin. The
overall lapsed time for the LER completion work will be determined,
however, by the number of months per year allowed for the LER
installation, and the number of crews working simultaneously on the
installation in the tunnel. We assumed that 20 crews of 6 people should
be able to install 40 magnets per week, or 1200 magnets in 30 weeks (\~8
month). Hence with one 4-months break of the LHC operation in a year,
the LER installation in the tunnel may be completed in a period of two
years. In summary, the LHC operation with the LER as injector could be
ready in 6 years from the time "zero".

15. **Conclusions**

We made a very preliminary and first look at the feasibility of
installing an injector accelerator ring (LER) in the LHC tunnel using
the VLHC Stage 1 super-ferric magnets. We believe that there are no
obstacles in principle for such an undertaking. The transfer of the beam
from the LER ring to the LHC one is challenging, but it seems to be
feasible and cost effective. A considerable simplification of the
LER-LHC transfer line can be achieved with a minor re-arrangement of the
D1 LHC dipole. Finally, any further considerations of the LER
accelerator sub-systems, the designing of the transfer line magnets,
re-designing (if needed) of the main arc magnet, designing of the
corrector and other special magnets can only proceed after a study of
the LER accelerator lattice, LER to LHC injection scheme, and the
interaction between the LER and the LHC accelerators is completed.

# Acknowledgements

> We greatly profited from several illuminating discussions with
> Gianluigi Arduini,
>
> Jean-Pierre Koutchouk, Yvon Muttoni, John Osborne, Germana Riddone of
> CERN,
>
> with Giorgio Ambrosio, William Foster, Steven Hays, John Johnstone,
> Vladimir Kashikhin, Michael Lamm and Tanaji Sen of Fermilab, and with
> Masayoshi Wake of KEK.
>
> We are also greatly indebted to Steve Holmes, Robert Kephart and Peter
> Limon for inspiration and support.

**References**

1.  LHC Design Report Vol 1, O. Brunning et al., CERN-2004-003, Section
    4.7 Dynamic aperture

2.  Design Study for a Staged VLHC, Fermilab-TM-2149, 2001

3.  H.Piekarz, Test of 2 Tesla Superconducting Transmission Line Magnet
    System, MT19, Genoa, 2005

4.  S.Hays, The 100 kA DC Power Supply for a Staged Hadron Collider
    Superferric Magnet, MT19, Genoa, 2005

5.  Y.Huang, The 100 kA Current Leads for Superconducting Transmission
    Line Magnet, MT19, Genoa, 2005

6.  Vl. Kashikhin, Test Results of a 2 Tesla Transmission Line Magnet
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7.  G.Velev, Field Quality Measurements of a 2 Tesla Transmission Line
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8.  J. Johnstone, Preliminary design of the LHCI lattice and the
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> transfer line, work in progress, 2006

9.  Martin N. Wilson, Superconducting Magnets, ISBN 0 19 854810 9 (Pbk)

10. Y. Huang, Cryogenic Analysis of the LER Fast Pulsing Magnet, work in
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11. M. Mayer, D. Fox, F. Castronuovo and U. Jansson, IEEE Transactions
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13. L. Masur and J. Kellers, Development of Long Length HTS wire for

> Electrical Power Applications, American Superconductor Corporation,
>
> Two Technology Drive, Westborough, MA 01581, USA

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> Fermilab-TM-2149, 2001

15\. CMS Technical Proposal, CERN/LHCC 94-38