3 MeV H - Chopper Beam Dump Pre-design study

3 MeV H- chopper beam dump Presentation by L.Bruno 1

3 MeV H- Chopper Beam Dump

Pre-design studyBy L.Bruno AB/ATB

M.Magistris AB/OPM.Silari TIS/RP


The Pre-design study

OUTLINE

1. Introduction 2. Engineering baseline proposal

3. Radiation studies 4. Engineering studies

5. Issues & future work

6. Summary


Driving Parameters

… continuously intercept a 3 MeV H- beam pulsed at

50 Hz with 2.8 ms long pulses. The maximum average

beam current to be absorbed is 1.1 mA, with a mean

power of 3.3 kW. The beam is circular and has a

uniform profile of 6 mm radius, which results in a

surface heat flux of ~30 MW m-2 .

The chopper beam dump has to …


Beam time-structure

20 ms

2.8 ms

Coarse structure

Fine structure

5 bunches to the end-of-

line3 bunches

to the dump

Because of inertia, the fine bunch time-structure does not affect the mechanical behaviour of the dump.


Lay-out of the chopper line

135 mm flange-to-flange only !

End-of-line

dump

Chopperdump

The dump placed after the chopper would be able to absorb also the beam at the end of the 3 MeV test facility.


Engineering baseline

The dump core is shrink-fit into an actively-cooled metal jacket. The cooling tubes are bonded by plastic deformation to the jacket

Front view Side view

= 10 degreesJacket Cooling

tubes

Dump core

Chopped beam

Water

Un-chopped beamVacuu

m

Air

~ 100 mm

Water

Water

Vacuum flange


Materials

Jacket: •Aluminium

•Dispersion strengthened copper - Cu Al2O3

Core: •Graphite / C-C composite

•Hexagonal boron nitride

•Aluminium nitride

•Molybdenum alloy (TZM)

•Copper

Tubes:

•Stainless steel 316 LN

•Duplex st. steel (1.4462)


Elastic scattering of protons It depends on the composition of the dump core

Inelastic interactionsScored with an energy threshold of 1 keV

IonizationProduction of X-rays, estimated with an energy threshold of 1 keV

Transport of photons and electronsSimulation of the whole electromagnetic cascade; energy threshold for particle transport = 1 keV

The baseline was studied to investigate:

Radiation studyby the Monte Carlo code FLUKA


Energy distributionPer primary 3 MeV proton

A

B

Energy deposited in the dump core:A = 0.525 keV +/- 0.17% B = 2.9801 MeV +/- 0.004% (99.3%)

Energy escaping from the dump:X-Rays, e- : 0.1029keV +/- 0.4%p, X-rays, e- : 14.60 keV +/- 0.5%( = 0.029% of the beam energy)

Energy deposition occurs at the inner surface of the dump core.

Beam spot


Induced radioactivity

There is no (p,n) reaction !!!

Element

Coulomb barrier [MeV]

(p,n) Threshold [MeV]

11B 1.69 3.57 ( 11C )12C 1.97 20.2 (12N )14N 2.05 6.89 ( 14O)16O 2.41 17.7 (16Fe)

Al 3.37 The Coulomb barrier prevents the 3 MeV protons from

reactingCu 5.83

Cross-check: No inelastic interactions were scored with FLUKA

on C, Cu, AlN, BN and TZM.


C Al N

Cu

TZM

Downstream of the dump, there is a flux of scattered protons.

The colour plots give the fraction of the primary protons scattered per square centimeter at 6 cm distance downstream of the dump.

The maximum of this flux ranges from 0.1 per mil (carbon) to 3 per mil (TZM) of the incoming protons (6.85 1016 p+s-1)

Scattered proton fluxPer primary 3 MeV proton


Scattered proton spectrumat 20 cm downstream of the dump

The spectrum of scattered protons 20 cm downstream of the dump at 0°, 15° and 30° with respect to the beam axis peaks at 1.5 MeV.

1.5 MeV


Electron flux [cm-2 proton-1]

5 cm downstream of the dump, a maximum energy of ~6 keV was scored for the electrons emitted from copper. The corresponding x-ray flux (1-4 keV, 1 keV being the FLUKA lower threshold) is about 3 10-6 cm-2 per proton.

TZMC

Top view


Finite Element Analysis

2D Steady-state thermal fieldfor a 10-fold geometric dilution of the heat flux

2D Steady-state stress fieldcooling tubes are checked against the ASME rules (American Society of Mech. Engineers)

Material choiceresults are shown for the most promising Copper-based configuration

Opportunities to optimizewater cooling parameters and structural behavior

The baseline was studied to investigate:


Finite Element Models

2D STEADY-STATE THERMAL ANALYSIS

Boundary Conditions: Subcooled flow boiling at 20 °C, 40 bars, 12 ms-1 with turbulence promoter. Minimum heat transfer coeff. is 54 kWm-2.Load: Heat flux of 3 MWm-2 . (geometrical dilution factor of 10).

2D STEADY-STATE MECH. ANALYSIS

Boundary Conditions: simple support (x-symmetry plus fixed point), GPS (Generalized Plane Strain) without bending.Load: Thermal field plus 40 bar water pressure.

Cu Al2O3

3 MWm-

2

Duplex St.Steel

Fixed point

6

Water cooling

R21

Ø8.4/8

4

12


Temperature [°C]

Tmax= 90°C

Subcooled flow-boiling is effective in limiting the maximum temperature of the dump core (Tmax=90°C).

The maximum heat flux at the inner surface of the cooling tubes is1.13 MWm-2,which is far below the critical heat flux (>100 MWm-2) for the given cooling parameters.


Von Mises Stress [Pa]

VM,max=134 MPa in Cu Al2O3VM,max=142 MPa in St. Steel

The maximum Von Mises stresses are below 2/3 of the yield stress at the working temperature in the dump core (177 MPa for CuAl2O3) and below the ASME allowable Sm value in the cooling tubes (207 MPa for the duplex stainless steel).


Issues and further work

Dump system Cooling systemAlignment

Temperature / Thermal gradientDynamic effects / Mech. strengthRadiation damage

Dump core

Handling

Dump assembly

Heat removal principle

Geometrical accuracyBackgroundVacuum / Outgassing

None expected To be validatedUnknown

Problems? ...


Status in April 2003

1. A proposal for the engineering baseline of the chopper beam dump is available;

2. The pre-design study of its physical and mechanical behavior was performed;

3. The most promising materials have been identified;

4. The interfaces for handling, cooling, instrumentation and control are being defined.

5. A detailed technical study is to be performed next.

Summary


Design guidelines

The dump should be…

• a reliable, permanent component;

• easily installed, serviced and dismantled;

• compact, robust with possibly in-situ spares;

• “Cost-effective”: the same design should be re-usable within an SPL-like machine.

3 MeV H - Chopper Beam Dump Pre-design study

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