Preliminary

Spallation Neutron Source

Beam Collimators and

Beam Dump Thermocouples

Interface Control Document

Rev. 1

May, 2002

Brian Oerter

John Smith

Hans Ludwig

Nickolas Simos

John Brodowski

Collimators

Collimators for removing halo particles are installed in the SNS
transfer lines and the ring. These units have aspects, which are common
to all of them; however, they all differ in significant ways. The
aspects that they have in common are they all have a large absorbing
structure to capture the primary halo particles, and most of the
secondary particles. The absorbing structure is contained in a primary
shield box, which in turn is surrounded by a secondary shield. The bulk
of the absorber consists of a stainless steel structure, cooled by light
water, and the shielding is manufactured of iron plates. Finally, each
absorber has a double walled collimation tube, through which the
operating beam passes. The gap between the two tube walls is filled with
helium, thus ensuring that the inner tube has an inert outer layer
(reducing corrosion concerns), and in the case of a tube failure the
helium will be detected in the vacuum chamber prior to a more
catastrophic event.

Briefly the collimators in the HEBT, Ring, and RTBT consist of the
following:

1)  In the HEBT line the collimators are all integrated with charge
    exchange foils, and a magnet. Two collimators are used to clean the
    beam in the X and Y directions respectively, and one is used to
    collimate the off-momentum particles. The first two collimators are
    integrated with quadrupole magnets, and the third collimator is
    integrated with a di-pole magnet. There are four charge exchange
    foils each for the X -- and Y -- directions respectively, and two
    for momentum collimation, thus implying a total of ten foil drives
    and associated controls.

2\) There are two types of collimators in the ring. The primary
collimator consists of four (metal to be determined) scrapers surrounded
by an absorbing structure, which in turn is embedded in shielding. The
secondary and tertiary collimators are fixed aperture absorbers
surrounded by shielding. In all cases the collimator tubes in the ring
are coated with titanium nitride. The placement of these collimators is
critical to their efficient operation.

3)  In the RTBT the collimators act as a final protection of the target
    in case there is a problem in the beam extraction system. They are
    essentially identical, and need to be placed between quadru-pole
    magnets in the line.

The following instrumentation and control will be required to determine
the proper operation of the collimators:

Scrapers:

There are four X-Y scrapers in the HEBT line. Two in the X plane, and
two in the Y plane. Each plane has two stripper blocks, one on each side
of the beam. The motion of each block is individually controllable with
a stepper motor. There will be two limit switches on each of the eight
collimator blocks, to limit the range of motion. There is also a home
switch on each axis to provide a reference position from which motion is
initiated. An LVDT or potentiometer will provide an analog 0V -- 10 V
signal to indicate the position of each axis.

Summary:

Location of Controls chassis: HEBT building

Number of axis: 8

Number of limit switches: 16

Number of analog readbacks: 8

Number of home switches: 8

Date to start prototype tests mm/yy

ORNL installation date mm/yy

Momentum Collimator:

The momentum collimator is similar to the X-Y collimator in the HEBT
line, except there are only two axis of motion.

Summary:

Location of Controls chassis: HEBT building

Number of axis: 2

Number of limit switches: 4

Number of analog position readbacks: 2

Number of home switches: 2

Date to start prototype tests mm/yy

ORNL installation date mm/yy

Thin Foil Stripper:

The thin foil stripper is a carousel containing twelve foils. The system
has two axis of motion. The first axis moves the foils in a circular
motion on a chain permitting one foil at a time to be inserted into the
beam. Motion is controlled by a stepper motor. Twelve position switches
are provided to indicate which foil is in the beam.

The second axis is an in-out motion of the foil assembly allowing
movement of the foils into or out of the beam. Two limit switches are
provided for this axis.

Summary:

Location of controls chassis: Ring building

Date controls are required ASAP

Number of axis: 8

Number of limit switches: 16

Number of analog position readbacks: 8

Number of home switches: 8

Date to start prototype tests mm/yy

ORNL installation date mm/yy

Thick Foil Stripper:

The thick foil stripper is a long carbon foil. This stripper has a
single axis of motion. The carbon stripper has four positions as
indicated by five micro switches. Two of these switches serve as limit
switches and the other three indicate the three intermediate positions.

Summary:

Location of controls chassis Ring building

Number of axis: 1

Number of limit switches: 2

Number of analog position readbacks: 0

Number of position switches: 3

Date to start prototype tests mm/yy

ORNL installation date mm/yy

Primary collimator:

The primary collimator consists of four scrapers located in the ring in
the straight section after the injection straight section. The maximum
travel of each scraper is 2 inches. The accuracy of this system is not
known at this time, but microstepping may be required to get the
necessary accuracy. The scraper will be water cooled.

Summary:

Location of controls Ring building

Number of axis: 4

Number of limit switches: 8

Number of analog position readbacks: 4

Number of home switches: 4

Number of water temperature readbacks 4

Number of water flow readbacks 4

Date to start prototype tests mm/yy

ORNL installation date mm/yy

Absorbers/collimators

There are eight of these devices in the HEBT,ring and RTBT. These are
fixed aperture devices. There are one pressure, flow and temperature
sensor per absorber.

Summary:

Location of controls 2 in HEBT

3 in the ring

3 in RTBT

Date required fy04

Number of axis: 0

Number of limit switches: 0

Number of analog position readbacks: 0

Number of home switches: 0

Number of water temperature readbacks 16\*

Number of water flow readbacks 8

Number of pressure readbacks 8

Date to start prototype tests mm/yy

ORNL installation date mm/yy

\* temp in and out for each

Note: Need to know what transducers will be used for flow and pressure
readbacks

![](media/image1.png){width="2.325in" height="5.7340277777777775in"}

# HEBT Scraper, one axis 

![](media/image2.png){width="3.5194444444444444in"
height="5.874305555555556in"}

# 

# 

# 

# 

# Thick foil stripper

![](media/image3.wmf)

# Thin Foil Stripper

![](media/image4.png){width="6.028472222222222in" height="8.0in"}

# Primary Collimator 

Beam Stop Thermocouples

There are two beam stops. One beam stop is located at the end of the
LINAC and a second in the transfer line between the ring and the target.
The temperature of the beam stops must be monitored. A programmable
temperature threshold shall be provided. The output of the monitoring
circuit shall provide a positive "true" signal to the Machine Protection
System (MPS) if the dump temperature is below the programmed limit. An
unspecified number of thermocouples will be selected for connection to
the MPS.

The beam stops in the passive dumps will operate at about 600 F.
Thermocouples are welded to the beam stop near where it thins so they
will operate at a slightly lower temperature. Each beam stop will have
28 "K" type thermocouples. 24 will be in an array on the beam stop, and
four more shall be mounted directly behind the stops. Individual
shielded twisted pair cable will be run directly from each thermocouple
to the controls interface electronics. The thermocouple wire gauge shall
be specified so that the loop resistance from the thermocouple to the
controller electronics is less than 100 ohms. The estimated run length
of the thermocouple wire between the thermocouple and the controls
interface is 380'.

The controls interface for the LINAC dump thermocouples will be in the
HEBT service building in controls cabinet HEBT_CTL_CAB02. The controls
interface for the RTBT dump thermocouples will be in the RTBT service
building in controls cabinet RTBT_CTL_CAB02. Communication with the
thermocouple controllers is expected to be Ethernet through which all
settings and temperature readings are made. The individual alarms for
each thermocouple will allow flexible configuration of the thermocouple
array connection to the MPS system.