# Presentation: 793058

## Rotatable Collimators as a Possible US Contribution to the LHC Luminosity Upgrade Project

**Rotatable Collimators ****as a Possible US Contribution ****to the LHC Luminosity Upgrade Project**

- 20 June 2008
- LARP DOE Review
- Tom Markiewicz/SLAC

*BNL - FNAL- LBNL - SLAC*

_**US LHC Accelerator Research Program**_

## Note With Pride

## System Design

**Momentum**
**Collimation**

**Betatron**
**Collimation**

*C. Bracco*

**Behind each of 30 C-C 1m secondary collimators (“Phase I, TCSG”) is an empty slot for an “improved” (Phase II) collimator**

## LHC Phase II Base Concept

- physical constraints
- current jaw design

** ****beam spacing: geometrical constraint**
** ****Length available 1.47 m flange - flange**
** ****Jaw translation mechanism and collimator support base: LHC Phase I**
** ****>10 kW per jaw Steady State heat dissipation (material dependent)**

**Cu coolant supply tubes twist  to allow jaw rotation**

**Hub area**

**Glidcop     Cu     Mo**

**Cantilever Mo shaft @ both ends**

**Helical cooling channels**
**25mm below surface**

**20 facets**

## Cu Jaw-Cu Hub-Mo Shaft Design

**Cu Jaw-Cu Hub-Mo Shaft Design**

**2mm shaft-jaw gap gives x5 improvement in thermal deformation over solid shaft-jaw design**
**1260 um ******** 236 um (60kW/jaw, ********12min)**
**  ****426 um ********   84 um (12kW/jaw, ********=60min)**
**Rather than Cu, Moly shaft improves**
**Gravity sag x3: **
**     ****200 um ******** 67 um**
**Thermal bulge 30%: **
**     ****339 um ******** 236 um**

## Status of RC Program

- Jaw support & rotation mechanism **COMPLETE** (June 2007)
- First full single jaw-hub-shaft unit **COMPLETE**
- Preliminary tests indicate **performance in accord with FEA** to ~10%
- Work to complete RC1:
- Finalize RF design
- Test a few new concepts to simplify machining & brazing process
- Full length graphite choke when brazing coil to mandrel
- Keystone reduction
- Use 360° 1⁄4-length jaws with braze wire rings cut on ID rather than 90° jaws
- Anything to reduce number mating surface prep requirements for brazes
- Order parts for 2-3 new jaws: copper mandrels, Mo shafts, Glidcop® jaws
- Fab & braze 2-jaws, 4-supports, RF features in new vacuum tank
- Metrology & vacuum tests
- Mechanical motion tests on existing CERN system
- Ship to CERN

## Final Jaw Braze 22 April 2008

## 9kW External Heater Thermal Test Setup

**9kW External Heater Thermal Test Setup**

- Heater cable

- Water flow control

- Jaw in support stand

- Heaters strapped on jaw

- Water flow tube

- Extra heater

## Comparison of Sagitta & Temperature with ANSYS as a function of angle wit respect to heater

- •Jaw with two 5 kW heaters modeled
- •Includes accurate representation of
- •Water flow/temp change
- •Material properties
- •Thermal expansion
- •Heat flow / thermal conductivity
- Data ~10% larger than ANSYS

## Performance Risks

- Will thermal-mechanical testing of the first jaw validate the shaft-hub-jaw design that should limit maximum jaw deflection into the beam area to 230 microns for 10 second bursts of 60kW beam absorption
- Will the mechanical accuracy of the device be adequate (40 um)
- Will the basic jaw-adjustment and jaw-rotation work as planned
- Will the effective impedance and RF characteristics of the jaw and the transition to the vacuum tank aperture be adequate
- Will the device vacuum be sufficiently low
- When damaged by an aborted beam, will the extent of damage be sufficiently localized to allow rotation to a clean surface, as planned

## RF Design

**RF Design**

- Low resistance RF contact

- Slot for Spiral RF Spring

- Short RF Test Jaw with End Socket mounted

**Bearing Race**

**SiN4 balls**

**UNDER STUDY**
- Contact Resistance Measurements
- Stretched Wire Impedance Measurements
- Trapped mode study using Omega3P

## Braze Test #3: Vacuum tests: No improvement

- 3rd Jaw Braze Test Assembly has been vacuum baked at 300°C for 32 hours. Results in slightly lower pressure.
- Inclusion of longitudinal grooves in the inner length of jaws for better outgasing
- Test Chamber setup similar to previous test.

|  | 2nd 20cm Prototype | 3rd 20cm Prototype |
| --- | --- | --- |
| Baseline | 3.2E-9 Torr | 2.4E-9 Torr?? |
| w/ jaw assy. | 3.7E-9 Torr | 3.4E-9 Torr |
| Presumed  jaw assy. pressure | 4.5E-10 Torr | 10E-10 Torr?? |
| LHC requirement | 7.5E-10 Torr | 7.5E-10 Torr |

- Under Investigation...

## Exact Nature & Extent of Damaged Region

- Thin Cu sample in FFTB electron beam at SLACHole = Beam Size

- 2000um 500 kW 20 GeV e- beam hitting a 30cm Cu block a few mm from edge for 1.3 sec  (0.65 MJ)

- FNAL Collimator with .5 MJ

## Accident Case: Permanent deformation AND Molten copper

**Case:** beam abort system fires asynchronously, **8 full intensity bunches into jaw**
**Model:**   - increased resolution 3-D ANSYS & FLUKA models
-               - Thermal heating/cooling analysis followed by quasi-static stress analysis
-               - Jaw ends constrained in z during 200 ns, released for 60 sec cool-down
-               - 0.27 MJ deposited in 200 ns
-               -  Molten material removed from model after 200 ns
**Result: **- 57e3 peak temperature (ultra fine model)
-               - **54 ********m permanent deformation** (concave)

## RC Ready for “Production” in FY2010

- RC Design essentially complete and first jaw constructed and tests according to calculation.
- In principle all procedures, methods, parts finalized and need only “push the button” to fabricate first full prototype.
- Beam tests in 2009-10 will hopefully remove remaining technical risk factors.
- Destructive testing of the by-design damageable Copper may be prove extensive enough to remove RC from consideration
- Procedures, tooling, Q/C facilities for “large” production run could be developed in parallel with production of the first full prototype in FY2009, if desired.

## Point With Alarm

## The Problem

- Suggesting that the US manufactures 36 of these devices for the 30 reserved Phase II secondary collimator lattice slots (plus 6 spares)
- Ignores the CERN collimation “White Paper” plan calling for construction and mechanical, vacuum & beam testing of three “complementary” designs (SLAC RC, CERN High Z, CERN Low Z with coating) that can bring LHC luminosity from 1034 to 1035 before a production decision is made
- The Cu secondary RCs do not give x10 improvement in luminosity
- When originally proposed LARP RC was to help get from <1E34 to 1E34 proton **L**
- Improved “local” collimation efficiency calculations point to
- Beam intensity limited by protons that MISS all secondary collimators & quench SC magnets in “dispersion suppressor” down-beam of IR7 collimation
- Local protection of these magnets by new “Cryogenic collimators” in the SC part of LHC
- More efficient PRIMARY collimators (Crystals, Electron lens, ...for example)
- “Final” opportunity to solve all remaining collimation issues:
- set up time (install beam pickups into collimator jaws)
- ion collimation
- correct any remaining mechanical issues from phase I (rack & pinion + motor redesign)
- Impedance limitations through means other than low resistivity metal
- Beam-based feedback & Landau damping
- Increased triplet apertures, cryo-collimators may allow fewer or larger gap collimators
- Does not address adequately the quality control issues seen in CERN’s Phase I collimator production nor has there yet been any talk or agreement with CERN on interface, installation, or engineering support issues.

## Efficiency StudiesChiara Bracco (CERN)

- Performance (Efficiency) of collimation system depends on # particles getting into the cold aperture (>10) per unit length as a function of location around the LHC given the optics model AND an aperture model
- 500E6 Halo protons tracked over 200 turns in 10cm steps by Bracco et al to get loss maps for each magnet
- Beam intensity limitations are due to losses in the dispersion suppressor above the quench limit.

- Phase I to II Global Improvement

- Phase I Beam Intensity Limit

## Intensity Limit at “Dispersion Suppressor” with Phase II at Nominal Collimation SettingsChiara Bracco (CERN)

- Losses due to particles that hit primaries but that do not see the secondaries

- While philosophy is every bit helps (take the x3.6) “ultimate” luminosity may require different collimation settings or completely different collimators (crystals as primaries?)

## Cryogenic Collimators in Beam1 Dispersion Suppressor

- Copper secondaries set to nominal 7 settings
- Carbon secondaries set to relaxed opening (26.5)
- Cryogenic collimators (material copper, length 1m) placed at 300m and 387m from IR7 at 15.
**Peak reduced by a factor > 30.**

- T. Weiler/CERN

## Graphite -> Copper

- Switching to copper will decrease the imaginary part of the impedance but increase the real part
- This is either good or bad depending on how you want to damp beam instabilities (Landau Damping versus Feedback)
- So, impedance still dominated by copper collimators

## References for CERN Planning

**Executive Summary**
***Second Phase LHC Collimators***
- R. Assmann
- 2007-04
***Description Phase 2 Collimator Project***
- R. Assmann
- 2007-07-02
**Collimation Issues for the Two LHC+ Scenarios and Future Plans**
- R. Assmann
- Beam’07
- 2007-10-01

## White Paper Plan

- The R&D and prototyping of at least three different concepts for advanced collimation designs, each addressing different possible limitations to LHC luminosity.
- Operational experience of the LHC with the Phase I collimation system to understand the nature of any luminosity limit and the best ways to ameliorate deleterious effects with already installed systems.
- Testing of prototypes at CERN to their technological limits before any installation in the LHC
- Installation and testing of qualified Phase II prototypes in the LHC during the second full year of LHC operation with a decision on phase II design and production, which may require more than one technology, at the end of the year.
- Production of the collimators during years 3-4 of LHC operation, installation during regularly scheduled shutdowns and use beginning with year 5 of LHC operation.

## White Paper Schedule

- Technology Decision  Fall 2010

- Construction 2011-12

- Installation

- 2013 Run

## CERN Phase II R&D Budget

## CERN Pre-Production Manpower vs. Time

## Production Estimated at 8M CHF

## My Opinion

- LARP, through SLAC, is participating fully in the Phase II Collimation project as outlined in the CERN “White Paper” plan and any action on LARP’s part that looks, as this does, like it is circumventing the agreed to schedule damages our relationship with our colleagues and is doomed to failure.
- If, after the R&D process concludes in October 2010, a decision is made to produce some number of rotatable copper collimators, SLAC is ready to participate.
- This exercise should only be taken at the “CD-0” level: mission need and ballpark cost estimate, and is hopefully, laying the bureaucratic groundwork for eventual US participation in construction of collimators

## Ask for Money

## Unscrubbed Unit Cost Based on work done to date: $250k

## Project Cost “x2 Estimate”

- Unit Cost for Tank, 2 jaws, rotation & support, RF	$250k
- Unit Cost for Rack & pinion, motors, LVDTs		$50k
- These below are probably underestimates:
- Assembly, test & qualification at SLAC			4 FTEs
- 	36 units over 2 years					$200k
- EDI&A							6 FTE
- Lab overhead						42%
- LAUC Proposal specifies 4+1 RCs
- Saturate the LAUC $ request to maximum allowed
- We don’t know how many if any RCs will be part of the final plan

## Project Schedule

- Dominated by braze operations and braze oven cycles
- 72 jaws with 3 braze cycles per jaw
- 2 years for production is aggressive but possible
- 1 year construction seems impossible