# Presentation: 469937

## Beam Loss at Slow Extraction of J-PARC MR 

**Masahito Tomizawa****  KEK ACC. Lab.**

**Introduction of J-PARC MR Slow Extraction **
**Beam Hit Rate on ESS Wires**
**Behavior of Protons Mutiple-Scattered on ESS Wires****     **

**FNAL****2005/03/8**

## Slow Extraction of J-PARC Main Ring

**Slow Extraction of J-PARC Main Ring**

**3.3x10****14**** protons per pulse(****15********A****)**** full beam power : ****750kW**** @50GeV**
**beam loss: as possible as small ****	****	****<1% (7.5kW)**** level****        radiation safety problem**** **
**coasting beam extraction**** **
**third integer resonance**** separatrix : linear       ****easy to tune separatrix angle and                                             step size by adjusting resonant sextupoles**

## psext4_007.dat

- mad332.madenv4.com

## Septa Parameters

**	****	****        ****thickness****	****  length  magnetic field    kick angle****	****	****            (mm)            (m)           (T)****	****	****   (mrad)**
**SM11**** ****	****          ****	****	****1.5              1.5          0.113 ********1.0****SM12**** ****	****           ****	****	****  ****3               1.5          0.226 ********2.0**
**SM21-24 (4 units)               7            0.8375       0.524              ********2.584**
**SM30,31 (2 units)****           ****30             1.14         1.432               ********9.61**
**SM32,33 (2 units)****           ****64             1.14         1.652 ********22.17**

**Septa Parameters**

**Parameters of Electrostatic septa (reference design)**
**	****	****              ****thickness        voltage(kV)         L****	****         kick angle****  ****	****	****	****  (********m)              /gap(mm)         (m)****	****            (mrad)**
**ESS1:W/Re(3%) wires    80+20                170/25             1.5   ********-0.2**
**ESS2:W/Re(3%) wires    80+20********         170/25             1.5  ********-0.2**

## Beam Loss Mechanism of  Slow Extraction

**○****Primary Beam hits ESS wires**
** **** ****---> reduce hit rate**
**    ****(1)Real Loss at ESS wires (make radiation)**
** ****(2)Protons go out of wires by multiple scattering **
**	****(a)to extracted side:****	****one path**
**	****	**** • ****hit on downstream components, SM,,,, **** ****	****	**** • extracted from the ring**
**	****(b)to circulating side:    circulating in the ring**
**	****	**** • ****hit on other components, SM,,,, **** ****	****	**** • extracted from the ring**

**wires**

**electrode**

**circulating side**

**extracted side**

** **

## 50GeV primary beam hit rate on ESS wires

**50GeV primary beam hit rate on ESS wires**

**Circulating Beam Parameters**
**ε****x****=6.1π mm********mrad ****ε****y****=6.1π mm********mrad********p/p=±0.25% **

**Qv=20.775**

-  **min. hit rate  0.8%  @100********m**** min. hit rate  0.5%  @50********m**

**beam hit rate on ESS wires**

- tri0103_095

- tri0103_090
- (sca0122_2_044)

**before 3turns **

**extraction**

- w=100m, L=1.5m

## MARS Simulation of scattering in the ESS wires

**Head-on Hit**
**H: 80********m, ± 0.1mrad****V: 20mm, ±1mrad**
**Uniformly distributed beam**

**MARS Simulation of scattering in the ESS wires**
**	****	****               ****by T.Yokoi**

**Low Density Bulk Model**

## Protons scattered on the ESS wires (MARS)

**“****real loss rate”  = [N(hit)-N(scatt.)]/N(hit)**
**    ****real loss**** ****750kW x0.01 x 0.077=0.58kW**

**Protons scattered on the ESS wires (MARS)**

**40cm downstream from ESS1 exit**

- Scattered to circulating side

- Scattered to extracted side

- sadin_foilsct_case1.dat
- r12_case1.com

- sadin_foilsct_case1.dat
- r12_case1.com

**(Reference ESS design)**

## Behavior of protons mutiple-scattered at ESS wires 

** ****	****	**** **
**Tracking: **
**○ ****initial beam condition by MARS**
**○ ****check losses at ESS, SM and vacuum chambers with real shape**
**○****particles scattered to extracted side and circulating side**
**○****tracked up to ring exit**
**○ ****two x-y collimators (downstream from ESS)**
**	****	****scrape halo of scattered particles**
**	****	****do not scrape primary extracted beam  **

##    Loss of scattered particles for 750kW beam

**Reference ESS design     ****	****Tungsten 80********m, effective thickness100********m, **
**     ****	****1.25mm spacing, L=1.5m**
**○****Slow extraction long straight section    **
**	****	****	****     ****real loss**
**	****ESS1****	****         ****0.64kW**
**	****quadrupole****	****     0.044kW**
**	****duct****	****                    0.03kW**
**	****ESS2****	****	****     0.12kW **
**	****Slow collimator  1   0.11kW**
**	****Slow collimator  2   0.28kW**
**	****SM11****           ****0.33kW**
**	****SM12****	****	****     0.053kW**
**○****Other LSS****、****arc. section**** ****<0.5W/m**
**・****Total loss in the whole ring is ****1.88kW**** **
**・****Loss is ****localized**** at slow extraction  LSS****  ****   ****	**

## Loss Map of Scattered Protons

**Loss Map of Scattered Protons**

**straight section**

**dipole**

**quadrupole**

**quadrupole**

**straight section**

**Loss of protons scattered to circulating side**

**Loss of protons scattered to extracted side**

**(Reference ESS design)**

## Protons Extracted from the Ring

- Sca0122_3_044

**       ****Survived protons ****(scattered to circulated side)**
- Sca0123_1_090

**       ****Survived protons ****(scattered to extracted side)**
- sca0122_2_044

**Protons Extracted from the Ring**

**99%**

**0.41%**

**0.34%**

**Extraction efficiency 99.75%**

**(Reference design)**

## Ribbon foils (AGS type)

** ****ESS1: W, 30********m+20********m, 1mm, 4mm spacing, L=1.5m, 0.2mrad**
** ****ESS2 :W, 30********m+20********m, 1mm, 4mm spacing, L=1.5m, 0.2mrad**

**ESS2**

**ESS1**

**Thinner:  reduce hit rate**
**Mechanically stronger: reliable**
**Smaller deviation due to electric filed  **
** **

## Slide 14

## Scatterer+ribbon ESS

** ****Scatterer: 30********m+20********m, 1mm, 40mm spacing, L=0.5m, 0mrad**
** ****ESS1: W, 30********m+20********m, 1mm, 4mm spacing, L=1.0m, 0.133mrad**
** ****ESS2: W, 30********m+20********m, 1mm, 4mm spacing, L=2.0m, 0.267mrad**

**ESS2**

**ESS1**

**scatterer**

**Scatterer: low average mass density, no electric field**
**Beam hits scatterer**
**Multiple scattering is dominant process****--> radiation is reduced**
**Beam hit rate on downstream ESS foils is small**
**   **
**Needs more space to get same kick angle **
** **

## Summary (50GeV 750kW beam)

**	****	****	****   ****real loss ****	****	****            extraction****	****	****          in the whole ring****	****	****efficiency**
**80+20********m wires****	****    ****1.88kW****	****	****	****99.75%**** ****	****     ****	****	**
**30+20********m ribbons****	****    ****1.05kW****	****	****	****99.86%****scatterer+ribbons****	****    ****0.71kW****	****	****	****99.91%**** **

**•****Predicted real loss is comparable with ****  that of existing machine (AGS..), probably acceptable**
**• ****Ribbons or scatterer+ribbons is effective **
**• ****Predicted extraction efficiency is very high**
**• ****Scatterer+ribbons reduces “tail” **

**•****Validity of low density bulk model**
**•****Other code (GEANT...) **

- sca0122_10_044

##  •Production of Slow Extraction Devices

**  ****will start from spring 2006.**
** •****We have one more year to fix ESS scheme!**
**•****Scattering simulations **
**•****R&D Ribbon ESS (alignment and high voltage test)**