![](media/image1.wmf)

MTA Line Critical Device Justification

Area Information

+------------------------+---------------------------------------------+
| # Area/s o             | MTA Hall and beamline stub (all areas       |
| r Enclosures Protected | downstream of shield wall)                  |
+------------------------+---------------------------------------------+
| **Beam Type and        | Proton Beam from Linac                      |
| Source**               |                                             |
+------------------------+---------------------------------------------+
| **Beam Energy**        | 400 MeV                                     |
+------------------------+---------------------------------------------+
| **Beam Intensity**     | 1.6E13 Protons/pulse, a maximum of 3.5E17   |
|                        | protons/hr                                  |
+------------------------+---------------------------------------------+

Critical Device 1

+------------------------+---------------------------------------------+
| # Device Name          | E:UHB03                                     |
+------------------------+---------------------------------------------+
| **Device Type**        | 4-magnet horizontal dipole string           |
+------------------------+---------------------------------------------+
| **Device Location**    | Magnets Located in MTA beamline -- upstream |
|                        | of shield wall                              |
+------------------------+---------------------------------------------+
| **Critical Device      | L:MUCDC                                     |
| Controller**           |                                             |
+------------------------+---------------------------------------------+
| **CDC Location**       | Booster West Gallery                        |
+------------------------+---------------------------------------------+
| **Method of            | Contactor Opened                            |
| Operation**            |                                             |
+------------------------+---------------------------------------------+

Critical Device 2

+------------------------+---------------------------------------------+
| # Device Name          | E:UBS01                                     |
+------------------------+---------------------------------------------+
| **Device Type**        | Beam Stop                                   |
+------------------------+---------------------------------------------+
| **Device Location**    | In a partial cave upstream section of the   |
|                        | shield wall                                 |
+------------------------+---------------------------------------------+
| **Critical Device      | L:MUCDC                                     |
| Controller**           |                                             |
+------------------------+---------------------------------------------+
| **CDC Location**       | Booster West Gallery                        |
+------------------------+---------------------------------------------+
| **Method of            | Air Solenoid/gravity closed                 |
| Operation**            |                                             |
+------------------------+---------------------------------------------+

Failure Mode Backup

+------------------------+---------------------------------------------+
| # Backup System        | Linac beam stops                            |
+------------------------+---------------------------------------------+
| **Backup Device        | 750 KeV Beamstop #1, 750 KeV Beamstop #2    |
| Names**                |                                             |
+------------------------+---------------------------------------------+
| **Location**           | 750 KeV Line                                |
+------------------------+---------------------------------------------+

**Failure Analysis**

+------------------------+---------------------------------------------+
| **Is there an unsafe   | None Identified At This Time                |
| failure mode?**        |                                             |
|                        |                                             |
| (If yes please         |                                             |
| explain)               |                                             |
+------------------------+---------------------------------------------+
| Is there a common      | None Identified At This Time                |
| failure mode between   |                                             |
| Device 1 and 2?        |                                             |
|                        |                                             |
| (If yes, please        |                                             |
| explain)               |                                             |
+------------------------+---------------------------------------------+

Prepared By: C. Johnstone Date: November 13, 2023

Department: External Beams

Reviewed By:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Date:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

> AD Interlock Engineer

Reviewed By:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Date:
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

> AD RSO

**Description and Explanation:**

Civil construction and installation of a beamline have been completed to
support an experimental facility designed which uses the primary,
400-MeV H^-^ beam extracted directly from the Fermilab Linac. The
facility located just southwest of the Linac will be capable of
accepting the full Linac beam intensity (1.6 x 10^13^ protons \@15 Hz)
up to the radiological limits permitted by the shielding and
radiological controls --- making it one of the few such facilities in
the world where a primary beam is available for high-intensity
experiments. This area will be used initially for tests of prototype
muon cooling apparatus (conclusive tests require full Linac beam). A 12'
shield wall separates the MuCool (Muon Cooling) Test Area or MTA hall
from the linac enclosure, preventing personnel access and limiting
exposure to radiation from full linac operation. ." The layout of the
beamline is given in Figure 1.

A low-loss beamline with specialized insertions for linac beam
diagnostics has been simultaneously incorporated into the design of this
beamline. This alternative mode of operation, designed to provide
measurements of linac beam properties, greatly enhances the
functionality of this line, making a valuable contribution to
accelerator operation. In the so-called emittance-measurement mode of
operation beam is transported to a beam stop just short of the MTA hall
at the end of the enclosure "stub.

Two critical devices will be implemented for MTA beamline operation to
insure beam will not reach the MTA experimental hall or the upstream
enclosure stub in the event of a personnel access. The only access to
these areas is via a long hall or stairwell from the pit or from the
upper level of the service buildings. Figure 2 is a drawing of the upper
service buildings, the pit and the MTA experimental hall (upper right
corner). In the \~2 sec time span to fully recognize and trip critical
devices, it would be impossible for personnel to reach the beam
enclosure. (However, note that the present ability to run the Linac and
simultaneously allow personnel access in the MTA experimental hall and
the enclosure stub -all areas downstream of the shield blocks- will be
retained.) Personnel safety with respect to radiation exposure will
therefore be insured by these two critical devices in the MTA beamline,
and, in the event of an accident condition or unauthorized access, will
fully prevent beam from reaching the MTA hall and stub (both critical
devices will prevent beam being transported via the 3.25" beampipe which
extends through the 12' of concrete blocks separating the enclosures).

[MTA beamline description]{.underline}

The MTA beam is derived directly from the Linac and extracted via two
pulsed C magnets (see Figure 1) located upstream and downstream of the
400-MeV transfer line chopper. The two magnets collectively kick the
beam through a 10.5 degree bend away from the transfer line. Once
extracted, the beam is steered through an additional 40 degrees by a
string of 4 westward-bending cooling ring dipoles (UHB03A-D), powered
from a single DC supply. A final reversed bend of 5 degrees straightens
the beam relative to the MTA enclosure walls (before it traverses the
shield wall) and provides the horizontal dispersion suppression
necessary for the beam diagnostic measurements.

The original civil construction employed an \~1.5 degree
vertically-inclined ramp to access the linac enclosure. This ramp is
leveled underneath the shield wall at the elevation shown in Figure 1.
Three vertical bends (UB01-2) provide the necessary upward vertical beam
trajectory to follow the ramp. The vertical bend magnet, UVB03 then
levels the beam to the MTA enclosure stub and simultaneously provides
vertical dispersion suppression. The final vertical bender, UVB04 is
reserved for targeting beam in the experimental hall.

As mentioned above, the beamline incorporates a specialized,
dispersion-suppressed straight for highly-accurate transverse emittance
measurements. The 10 meter-long, dispersion-suppressed insertion for
transverse emittance measurements takes advantage of the 12' of shield
wall to establish a tomography diagnostic section with profile monitors
and capability to change phase advances between monitors (thereby
measuring phase space slices). The 12'-long, 3.25" beampipe which
transports beam through the shield wall is shadowed by a 6"-diameter
beam stop (UBS01) partially inserted in a cave at the upstream end of
the shield wall. Beam cannot entered this section of the line when
beamstop #1 (UBS01) is deactivated.

The C magnets are pulsed devices and therefore do not qualify as a
critical device. Only two devices in the MTA line qualify as critical
devices: string of 4 westward-bending cooling ring dipoles (UHB03A-D),
and a beam stop (UBS01 located at the upstream end of the shield wall.
Both devices are capable of completely stopping beam within the Linac
enclosure upstream of the shield wall with no residual beam transmitted.
(Although the C magnets cannot serve as critical devices, a beam-permit
based state of the two critical devices will be a condition for
energizing.) The following describes the justification for the two
designated critical devices. Also included in this document is a
discussion of accident conditions in the proximate 400-MeV Transfer Line
and its radiation implications for the experimental hall and stub**.**

![](media/image2.wmf)

![](media/image3.wmf){width="5.378472222222222in"
height="4.738194444444445in"}

![](media/image4.wmf){width="5.65625in" height="3.9375in"}

Figure 1. The entire layout of the MTA bamline top and two cropped
versions showing the critical devices, the UBS01 beamstop and the UHB03
dipole string in larger detail.

![](media/image5.wmf){width="5.9944444444444445in"
height="4.814583333333333in"}

Figure 2. A drawing of the MTA civil construction showing the service
buildings, lower left, the pit and the MTA experimental hall (upper
right).

**MTA Beamline Critical Devices and Accident Modes**

The following are technical and functional descriptions of the two
devices designated as critical devices. These two devices, the 4-dipole
string, UHB03, and the beam stop, UBS01, prevent beam from reaching the
MTA hall and stub. They also fully protect the MTA hall against two
classes of accidents: not only from a beam accident in the MTA beamline,
but also from a beam accident in the proximate 400-MeV line. The worst
case accident cases are described in a following section. Any failure of
either of the two critical devices will deactivate the Linac Critical
Devices and Linac beam is stopped.

[Critical Device UHB03]{.underline}

As described above, UBH03 is a westward-bending string of 4 Cooling Ring
Dipole (CRD) elements (with refurbished coils) which steer the extracted
linac beam through a total bend angle of 40 degrees. A cross section of
the magnet is provided in Figure 3. A 2" x 4"(HxV) beampipe is installed
in each of these magnets. These are powered by a single, DC, LAMDA power
supply which can be de-energized on the timescale of a second since
power is not stored in the supply itself.

[Critical Device UBS01]{.underline}

The internal configuration of the beam stop is as follows.  The beam
stop is a cylinder 26\" in length and consists of two parts: 18 inches
of carbon steel on the upstream end followed by 8 inches of polyethylene
on the downstream.  The outer diameter of the steel is 6" and that of
the polyethylene , 5.75".  Both ends are flanged to 3.25" beampipe and
these dimensions were designed to completely shadow the 3.25' beam tube
installed in the shield wall. Figure 4 is the mechanical drawing for
both beamstops installed in the MTA beamline; one at the upstream end of
the shield wall and the second as the final element before entering the
MTA hall itself.

![](media/image6.wmf){width="4.645833333333333in"
height="2.6979166666666665in"}

Figure 2. A cross section of a Cooling Ring Dipole (CRD). A 2"x4"
beampipe is inserted into the 4" vertical aperture of this magnet for
the MTA beamline.

![](media/image7.wmf){width="5.9944444444444445in"
height="2.5076388888888888in"}

Figure 3. Drawing of the beamstops used in the MTA beamline.

[Accident Modes]{.underline}

1)  [Beam Accidents in the 400 MeV Line]{.underline}

Linac beam cannot be mis-steered to the extent that primary beam enters
the section of Linac enclosure that houses the MTA beamline which
ultimately leads to the experimental hall. Beam accidents, or spills,
however can occur where beam is fully steered into an element in the
400-Mev line and scattered beam does enters this part of the enclosure.
For the MTA, the worst case scenario is when full beam is deposited on
either the chopper (vertical displacement only) or on Q74 or Q2. These
elements represent an accident condition closest to a direct line of
sight with the beampipe through the shield wall. There are two accident
scenarios for this condition.

a.  the shield wall, beamstop, and narrow beampipe penetration through
    the shield wall is sufficient to prevent beam or any significant
    radiation from penetrating downstream of the shield wall. The
    beamstop has a 6" diameter and shadows the 4" diameter, 12' length
    of beampipe. If the C magnets are accidentally powered overriding
    the beam permit requirement, then even with both magnets on at full
    strength, beam cannot be deflected down the part of MTA beamline
    enclosure continuous with the Linac enclosure (upstream of the
    shield wall). At full C-magnet power, beam strikes the 2^nd^
    quadrupole in the MTA line and at partial power beam could
    potentially strike either the first quadrupole in the MTA line or
    the enclosure divide wall between the transfer line and MTA line
    enclosures. These are the worst-case scenarios and the beam stop
    fully protects against scattered radiation.

b.  [Beam Accidents in the MTA Beamline]{.underline}

If the UHB03 dipole string and C magnets are both activated, then beam
is stopped fully by the beamstop in the shield cave at the start of the
shield block wall. This has been confirmed by modeling the shielding and
beamstop in MARS. The geometry model of the region is shown in Figs. 4
and 5. The following color scheme is employed to denote materials used
in the model: green, grey, blue, violet, and red correspond to soil,
concrete, air, steel, and polyethylene, respectively. The model
corresponds to the 'as built' shielding configuration.

![](media/image8.wmf){width="2.3854166666666665in"
height="2.1881944444444446in"}![](media/image9.wmf){width="2.3715277777777777in"
height="2.265972222222222in"}

![](media/image10.wmf){width="2.7041666666666666in"
height="2.4770833333333333in"}![](media/image11.wmf){width="2.397222222222222in"
height="2.2055555555555557in"}

Figure 4: Geometry model of the shield wall and internal beam stop
UBS01, profile(top left), plan view (top right), upstream (bottom left),
downstream (bottom right).

![](media/image12.wmf){width="4.925in" height="4.925in"}

Figure 5. Dose distribution for full beam impinging on beam stop

[Safety System Interlocks and Critical Device Circuit]{.underline}

The following diagram outlines the critical device circuit. If the
interlocks are dropped by a personnel access or accident condition, the
power to UHB03 is switched off and the beamstop is closed. Failure mode
of either critical device is the Linac Critical Devices.

![](media/image13.jpeg){width="5.919444444444444in"
height="2.7597222222222224in"}

[Radiation Safety Issues]{.underline}