# Presentation: 485313

## MARS15 energy deposition studies for LARP quadrupoles

***April 27, 2006***
- Igor Rakhno
**Fermi National Accelerator Laboratory**

- Model updates and restrictions
- Magnetic field scaling
- εmax for quads with **StSt** liner and Ø 90, 100, 110 mm
- εmax *vs* liner thickness
- Alternative material for liner is **W-25 Re**
- Comparison between **StSt** and **W-25 Re** liners
- Spacers
- Dynamic heat load

## MARS15 code and IP5 model upgrade(from N. Mokhov)

- The MARS15 model of the IP5 inner triplet was substantially upgraded.
- LHC lattice v6.5.
- Recent changes in the CMS detector inner region and in the machine-detector interface have also been implemented into the model.
- MARS15 physics and transport models have been further improved.

_***Starting point for the updates***_
- “Second generation high gradient quadrupoles for the LHC interaction regions”
*                **T. Sen, J. Strait, and A. V. Zlobin** - ***PAC 2001**
- “Beam physics issues for a possible 2nd generation LHC IR”
*T. Sen, V. Kashikhin, P. Limon, N. Mokhov, I. Rakhno, J. Strait,*
*M. Syphers**, **M. Xiao**, **A. Zlobin** – ***EPAC 2002**
- “Protecting LHC IP1/IP5 components against radiation resulting from
- colliding beam interactions”
**LHC Project Report 633, 2003**

## Key points to the model update

_***Key points to the model update***_

- All the thicknesses ΔR for all the components, **except for the liner**, are kept constant.
- Radial distances are varied.
**Baseline liner thickness:               ****cold bore**
- in Q1 – **6.2****+****1.5 mm;**
- in Q2A, Q2B, Q3 – **1.5 mm.**

## Aperture restrictions from T.Sen, J.Strait, A.Zlobin (PAC 2001)

##                              LHC IP5 LBQ                 90-mm Nb3Sn quads  

##                              LHC IP5 LBQ                  90-mm Nb3Sn quads

## Cross section of a 90-mm Nb3Sn quad

## Normalization and spare space

- All results are normalized to the luminosity of **10****35** cm-2s-1.
- The design for the 90-mm Nb3Sn quads does **not** provide extra space for a liner in the region of Q2AB-Q3, just baseline.
-      In the region of Q1 there are spare **3 mm**.
- For the 100-mm Nb3Sn quads there are spare **5 mm** for
-      Q2AB-Q3 and **8 mm** for Q1.

## Magnetic field scaling

- The magnetic field map from Vadim Kashikhin
- was used and the following scaling procedure was
- applied to keep the same gradient of 200 T/m:
- (Bx, By)
- (X90, Y90)            X90 →  X = X90 (D(mm)/90)
-                             Y90 →  Y = Y90 (D(mm)/90)
-                             B90 →   B = B90 (D(mm)/90)

## Quench limit and the design goal(from N. Mokhov and A. Zlobin)

- Current **NbTi** quads:                **1.6 mW/g**  and  **0.5 mW/g**
**Nb****3****Sn** quads for the upgrade:  **5.0 mW/g**  and  **1.7 mW/g**

-        Baseline StSt liner thickness

- Design goal

-        Baseline StSt liner thickness

- Design goal

-        Baseline StSt liner thickness

- Design goal

## Peak power density vs inner coil diameter

## Peak power density vs extra liner thickness

- Peak power density *vs* extra liner thickness

- Design goal

## Do we really need that thick liner?

- Energy deposition in the quads is mostly due to electromagnetic showers (e± and γ).
- Electron and gamma spectra in the inner Q2B coil
-      (in the hottest spot) reveal that about **50%** of all gammas
-      are in the region of **200 - 400 keV**.
- We can use high-Z material and take the advantage of increased photoabsorption at the same weight.

## Electron and gamma spectra in the hottest spot in Q2B                       γ                                             e±

## Photon interaction cross sections in iron and tungsten

**Tungsten Rhenium alloy (W-25 Re):**
- 75 wt. % W
- 25 wt. % Re
- ρ = 19.7 g/cc
**www.matweb.com**

- _StSt__ liner __*vs*__ __W25 Re__ liner_*Peak energy deposition in ****inner**** coil*

- Design goal

## Spacers

- Remove the SC cable from the hottest spots and fill in the empty space with a low-Z material - spacer.
- Two materials are considered – aluminum and graphite.

## Spacers

- The spacers seems do not provide substantial local relief.
- A lot of computer time is required if this option is still of interest.

##      Comparison between StSt and W-25 Re liners 

##      Comparison between StSt and W-25 Re liners(TAS between Q1 and Q2A as well as liner cooling at LN2 could help)  

## Numerical data on dynamic heat load (W/m) in IP5 inner tripletwith the  StSt and W-25 Re liners of baseline thickness. Inner coil diameter = 100 mm 

|   |   StSt liner
   Liner        SC coil       Total | W-25 Re liner
   Liner         SC coil       Total |
| --- | --- | --- |
|  
           Q1
           Q2A
           Q2B
           Q3
Correctors, TASB

         Total
  |             
       81           109         268 
       22           132         259
       50           134         256
       60           155         305
       85           117         259

     298           647       1347  |      
     165            56           278
       26            91           191
       59          105           224
       68          117           257
     146            78           271

     464          447         1221 |
|  |  |  |

## Conclusions

- Calculated data on **ε****max** and **dynamic heat load** for the LHC inner triplet with Nb3Sn quadrupoles of various diameters are provided.
- Several liner thicknesses are considered.
**StSt** and **W-25 Re** liners are considered.
**StSt** liner of increased thickness (baseline+5mm) does not provide an adequate protection for the 100-mm coils (**ε****max** **>1.7 mW/g**).
- An alternative way to reduce εmax in superconducting coils – **spacers** (aluminum and graphite) – does not look very promising.
**W-25 Re** liner of increased thickness (baseline + 2 mm) provides an adequate protection for the 100-mm coils (**ε****max** **≈** **1.2 mW/g) . **

## Conclusions cont’d

- Dynamic heat loads scale with the luminosity, *i.e.* exceed
-     1 kW for the upgrade.  Possible modifications of the quads
-      can not give rise to a significant variation of the heat loads
-      (it is true, at least, for the total heat load).
- The heat loads remain to be the outstanding issue putting constraints on the cooling system capability and the cryoplant capability and cost.  This will be studied in great details in FY07, revisiting the idea of the inner absorber cooled at liquid nitrogen temperatures.
- Dipole-first scheme will be revisited in Q3 and Q4 of FY06.