# Presentation: 471313

## NuMI Target Hall Performance/Plans

- Jim Hylen
- DOE Tevatron Operations Review
- March 27, 2007

## Outline

**Overview of target hall**
**	****	****	****and target/horn experience**
**Summary of problems causing 1 day or more downtime, and corrective actions underway**
**(back-up slides describing individual problems)**
**Spares status**
**Plans for target with evolving beam conditions**

## How NuMI  beam is produced

- Design for 0.4 MW proton beam

## Target for Low Energy Neutrino Spectrum

- Graphite Fin Core
- 6.4 mm wide

- Water cooling tube

- Backing target out of horn produces neutrinos at higher energies

- Fits within the horn.

## Experience with the NuMI Target

|  | Max.
Proton/spill | Max.
Beam Power | Integrated
Protons on Target |
| --- | --- | --- | --- |
| Target Design
 specification | 40e12 p.p.p. | 400 kW | 370 e18 p.o.t.
lifetime |
| 1st target
Before leak | 25e12 p.p.p.
11e12 day before leak |  69 kW |  0.7 e18 p.o.t. |
| 1st target
After leak | 30e12 p.p.p. | 270 kW |  158 e18 p.o.t. |
| 2nd target | 40e12 p.p.p. | 320 kW |  105 e18 p.o.t. |

- 1st Target took beam for over a year, 820 MWhr integrated beam power.  Two problems:
-   water leak soon after turn-on; back-pressure with Helium to keep water out
-   target motion drive shaft froze up after year of operation – stuck in H.E. focus
- 2nd Target is running (no leak)

## Magnetic Horns focused by toroidal field between conductors

- _Magnetic Horns_ focused by toroidal field between conductors

- 3 Tesla peak field
- 200 kA peak current
- To be focused,  must penetrate inner conductor
- Low mass (2 mm thick nickel-coated aluminum)
- Parabolic shape produces “Lens” field (Pt kick  Radius)
- Water spray cooling on inner and outer conductors
- Inner conductor dominated by joule heating
- Outer conductor dominated by beam heating
- 3 m long focusing region
- Achieved ~ 0.1 mm radial tolerance after weld

- Outer Conductor

- Inner Conductor

- Stripline

- Drain

- Insulating Ring

- Water Spray Nozzle

- 

- 

- 

## Horn Inner conductors

- Parabolic inner conductors:
-    3 Tesla max. magnetic field
-    3 m active length each horn

- Inner conductors welded
-  together at FNAL by
-  lead engineer Kris Anderson

## NuMI Horns Experience

- Horns in target hall
-   June 2004
- 1st run with beam
-   Jan. 2005
- Accumulated:
-   15 Million pulses
-    1,350 MWhr
-      integrated beam power
- Still running with first set of horns

## Target Hall during construction

- 1/2 of the
- 8000 tons
-  of shielding
-  is installed

##  Work cell    Target module in beam-line	    1st target being removed

-  Work cell    Target module in beam-line	    1st target being removed

## NuMI work cell for radio-activated components

- Shown during test-assembly
-  above ground
- Lead-glass windows (not
-  shown)
- Remote controlled door
- Remotely installable
-  top shielding

## All NuMI target hall beam components and innermost shield layers are installed /removed remotely with crane and cameras

- Crane includes remote hook rotation.                       Steel shielding block being moved.

## Big Picture of Maintenance

- NuMI target hall is a difficult system
- High radiation forces remote handling
-  repairs take a long time
- Target hall is nasty environment
- E.g. humidity has PH of 2.6, very corrosive
- Limited list of materials are rad-hard enough
- Interventions are time-consuming
- Access to components requires 1 shift just to put electronics back on target hall crane
- Must un-stack, then re-seal shielding each access
- Components are an order of magnitude larger than Pbar’s
*Achieving high up-time requires design of robust components*
- Biggest current concern:
- Producing an adequate supply of spare horns
- Usually replacement takes less time than repair

- If you have no spare
-    - you must repair !

## NuMI Performance – POT/week

**Horn 2 ground fault**

**Tritium Mitigation**

- Accelerator
- Shut Down

**Horn 1 cooling**
** ****spray clog**

**Horn 1 water **
**line repair**
**and target **
**replacement**

**Beam-line magnet **
**replacement**

**Target pile chiller**
** ****replacement**

- Accelerator
-  down

## Up (513) and down (83) days 5/1/05 – 3/22/07  86% / 74% efficiency excluding / including sched. shutdown

| Days | Description     (**non-recurring) |  | Long term corrective action |
| --- | --- | --- | --- |
| 513 | Up for beam |  |  |
| 95 | Accelerator scheduled down |  |  |
| 25 | Horn cooling spray clog ** |  | Check valves, filters on skids |
| 14 | Horn water line repair |  | Eliminate braze on spares |
| 14 | Target motion frozen |  | Graphalloy bushing on spare |
| 10 | Horn ground fault |  | Pin feet, float modules |
| 8 | Tritium mitigation ** |  | Condensate sys./dehumidifiers |
| 6 | Replace NuMI beam-line magnet |  |  |
| 4 | Replace accelerator magnet |  |  |
| 2 | Replace pile chiller compressor |  | New hot spare chiller unit |

## Other long term actions

- Corrosion protection
- Improve dehumidification of target pile
- Planned installation summer 2007
- Selection of materials
- E.g. stainless sheathing instead of nickel coating of shielding on remote electrical clamp for spares
- Accelerate production of spares
- Batch process horns
- Doing several at once is much more efficient
- Engineer hired specifically for spare horn welding
- Tech. assigned specifically to track parts

## Horn spray flowmeter

-    with beads

- Horn nozzle for inner conductor
-   is eliptical ~40 mils short direction
-     (48 total)
-     outer conductor nozzles round,
-        25 mils diameter (19 total)
-           plus two side-spray nozzles

- June 30, 2006, resin beads from deionization
-  bottle clogged the water spray lines on Horn 1

- New, uncontaminated beads
-   Beads are ~ 20 mils diameter

## The gravity un-assisted check valve

- When water skid was turned off for maintenance,
-       beads floated backwards
-           through improperly mounted check valve

## Fan push,  water-in-barrel filter,   vacuum suck

- Out
- Resin Beads

- Fan push,  water-in-barrel filter,   vacuum suck

## Two horn water system leaks:Horn 2 in February 2006, Horn 1 in August 2006

- Have brazed ceramic electrical insulators on horn water lines
- They are strain-relieved with invar+ceramic clam-shells
- On horn 1, developed a 7gal/day
-  water leak on line to spray header
- On horn 2, leak on suction line
-   drew air in, reducing amount
-   of water ejector pump could
-    remove from horn collection tank
- Both ceramic sections were
-   successfully replaced
- Speculate braze corrodes...
-  planning to switch from brazed
-  to a shrink-fit ceramic/steel
-  connection for spare horns

- Two horn water system leaks:Horn 2 in February 2006, Horn 1 in August 2006

## High dose rates made Horn 1 ceramic replacement challenging

- 75 r/hr ( 0.75 Sv/hr) on contact
- 35 r/hr ( 0.35 Sv/hr) at 1 foot

-              Repair people got weekly dose limit in a few seconds

## Shielding for Horn 1 ceramic repair job

-  of the work-cell
-  with window
-  for work

- ( Horn is in
-   work-cell,
-   behind the door )

## Mock-up and practice for repair

- Plan, time, and practice,
-  practice, practice repair
- Needed to undo two
-   Swagelok fittings,
-   remove old section,
-   insert new section,
-   and tighten two fittings.
- Time est: 2 min. of
-   actual work in slot
- Dose for this “2 min.” job
-   was 371 mr, (3.7 mSv)
-   divided over ~10 people.
- The rest of job is in much
-   lower radiation field,
-   but dose can be non-negligible
-   due to time involved.

## Frozen drive shaft on target motion system

- On 2nd carrier  -
-  Light lube
-  of nuclear grade
-  anti-seize compound

- Old jammed pillow-block

- After month-long test in High Energy position
-   drive shaft will not rotate to move target
-     into Low Energy position
- On target carrier #3, change to
-   Graphalloy bushing

## Horn 2 ground fault -- loose foot on horn

- Owl shift Thurs. Sept. 29, 2005 intermittent horn trips.
- Owl shift Sat. Oct. 1, hard ground fault of 1 ohm.
-     *-removing stripline fingers Horn 2 + stripline block*
-     -*when Horn 2 moved to work cell ground fault cleared*
*    **-foot left behind in chase, nut had vibrated off*
*    **-scorch marks seen under foot*
- Moved old foot, installed new foot

- Horn 2 before beam
-      *1.5 inch clearance foot to floor*

## Horn 1, after a year of beam

- Horn is corroding – eventually will have to replace it

## Spares Status – Horns and target 

## Plan for target for evolving beam condition

- Existing target was designed for 4.0e13 p/pulse, 400kW
- After summer shutdown, slip-stacking may provide up to
- 		4.5e13- 4.8e13 p/pulse, 400 kW (when pbar source not running)
- By increasing beam spot size to 1.2 mm RMS for 4.5e13,
- 	will have same stress as current 1.0 mm RMS for 4.0e13 on target
- Have tested larger spot size, baffle scraping by beam still fine
- Preliminary Monte Carlo indicates negligible impact
- 		on neutrino spectrum

## Plan for target for evolving beam condition

- For NOVA experiment (2011),
-   target no longer needs to fit in horn  M.E. target design
- With ANU sub-project, beam specification is
- 		4.9e13 p/pulse, 700 kW
- By increasing beam spot size to 1.3 mm RMS,
- 	will have same stress as current 1.0 mm RMS for 4.0e13 on target
- Moving water cooling further from beam-spot reduces water-hammer
- Still work to do on window and outer casing cooling,
- 		but does not appear to be any show-stoppers

## Medium Energy Target for NOVA running

- IHEP Design

- 120 cm

## Plan for target for evolving beam condition

- A possible next stage for beam after ANU is to re-use Accumulator Ring
- Plan to use essentially same NOVA M.E. target design
- With Accumulator, beam specification could be
- 		8.3e13 p/pulse, 1200 kW
- By increasing beam spot size to 1.5 mm RMS,
- 	would have calculated stress safety factor of x1.4 on graphite
- Still work to do on window and outer casing cooling,
- 		but appears doable