# Presentation: 618091

## Linear Collider R&D in the U.S.

- Steve Holmes
- Chicago Linear Collider Workshop
- January 9, 2002

## Outline

- Goals
- R&D Program Elements
- NLC Activities in the U.S.
- TESLA Activities in the U.S.
- Site Studies in the U.S.
- Remaining Technology Challenges

## Goals of the U.S. Program

- Context
- The directors of the U.S. laboratories have publicly stated their support for construction of a linear collider as an international endeavor based on the optimum technology. This vision has been further supported by the HEPAP Subpanel and its European and Asian counterparts.
- Goals
- The goal of the U.S. Linear Collider R&D program is to develop the technology that would support construction of a linear collider, operating at an initial energy of 500 GeV and luminosity of at least 1034 cm-2 sec-1, and upgradable to an energy in excess of 1 TeV.
- Bulk of the U.S. effort is currently being directed into x-band (11 GHz) based implementation.
- Aiming for technology demonstration/decision on the timescale of 2003-04. (As is superconducting effort.)

## Goals of the U.S. ProgramPerformance Parameters

|  | NLC/JLC | JLC(C) | TESLA |  |
| --- | --- | --- | --- | --- |
| Energy (CM) | 500 | 500 | 500 | GeV |
| Repetition Rate  | 120 | 100 | 5 | Hz  |
| Bunches/pulse  | 190 | 72 | 2820  |  |
| Bunch separation  | 1.4 | 2.8 | 337  | nsec |
| Particles/bunch | 7.5109 | 1.11010 | 21010  |   |
| Beam sigma at IP (H)  | 245 | 318 | 553 | nm  |
| Beam sigma at IP (V)  | 2.7 | 4.3 | 5.0 | nm  |
| B | 4.7 | 3.4 | 3.2 | %  |
| Luminosity Enhancement  | 1.4 | 1.7 | 2.1  |  |
| Luminosity  | 201033 | 8.61033 | 341033 | cm-2sec-2   |
| Beam power  | 13 | 6 | 23 | MW |

## LC R&D Program Elements

- Energy Performance
- RF Structures
- An accelerating structure must be developed that can support the desired gradient in an operational setting and there must be a cost effective means to fabricate this structure.
- RF power generation and delivery
- The rf generation and distribution system must be capable of delivering the power required to sustain the design gradient.
- 	Demonstration projects: NLC 8-pack test, TTF-II
- Luminosity Performance
- The specified beam densities must be produced within the injector system, preserved through the linac, and maintained in collision at the interaction region.
- Damping ring performance
- Vibration specification and site characterizations.
- Wakefield suppression/compensation and IR feedback schemes.
-  R&D Facilities: ATF, ASSET, NLCTA, TTF, and LINX(?)

## LC R&D Program Elements

- Energy Upgrades
- There need to be plausible visions of how to upgrade the energy (to and beyond 1 TeV) somewhere down the road.
-  Gradient R&D to establish the limits of x-band and SC structures.
- Site(s)
- At least one viable site has to be identified and understood. This includes both technical feasibility and public acceptance/support.
-  Site studies
- Cost
- The cost of facility construction and operation has to be understood.

## LC R&D Program ElementsNLC(/JLC) Program

- 		_**SLAC**__**	**__**FNAL**__**	**__**LBNL**__**	**__**LLNL**__**	**__**KEK**_
**Structures**
- 	Gradient R&D	  ✓			  ✓	 ✓
- 	Industialization		   ✓
**Power Source/Distribution**
- 	Klystron Development	  ✓				 ✓
- 	Modulator Development	  ✓			  ✓	 ✓
**System Integration**
- 8-pack test	  ✓ 	    ✓** ****	****   **✓	 ✓
**Civil/Siting****	**** **✓	   ✓			 ✓
**Injector**
- 	Source/linacs	  ✓	   ✓
- 	Damping Rings			   ✓		 ✓
**Beam Delivery****	**** **✓			  ✓

## The NLC R&D ProgramStructures/Gradient R&D

- An aggressive R&D Program has been triggered by observation of cavity deterioration following 1000+ hours of operation a little over a year ago.
_**Test Structure**__**	**__**L (m)**__**	**__**V**_**g **_**(% c)**__**	**__**     Maximum Gradient **__**a**__**    Stable Operation **__**b**_
**DDS3****	****	****1.8****	****     12****	****	****  50****	****	****    40**
**T105VG5****	****	****1.0****	****      5****	****	****  70****	****	****    60**
**T53VG5****	****	****0.5****	****      5****	****	****  85****	****	****    65**
**T53VG3****	****	****0.5****	****      3****	****	****  90****	****	****    70 (NLC Spec)**
- Unloaded gradient (MV/m) used during processing.
- Unloaded gradient (MV/m) at which operation is stable.
-  5000 hours of high-power operation of the NLCTA.

## The NLC R&D ProgramStructures/Gradient R&D

- Hours of Operation at 60 Hz

- 1700 hrs

- 1500 hrs

- 500 hrs

- 1200 hrs

- 0.5 m
- Vg = 3 %

- 1.8 m
- Vg = 12 %

- 0.5 m
- Vg = 5 %

- 1.0 m
- Vg = 5 %

## The NLC R&D ProgramStructures/Gradient R&D

- Distribution of Breakdowns
- (70 MV/m, 400 ns, 10 hr run)

- T53VG3
- (vg  from 3.3% to 1.6% c)

-  It appears likely that the next iteration NLC design will be based on low group velocity, modest length accelerating structures.

- Structure (T53VG3RA) with adaptive input coupler now being tested.

## The NLC R&D ProgramStructures/Industrialization

- The NLC requires ~11,000, 0.9 meter, accelerating structures to reach 500 GeV. Fermilab has undertaken the task of developing an industrialization process for x-band structures fabrication
- Short term Goals
- Driven by desire to initiate 8-pack test at SLAC in late 2003/early 2004
- Structures fabrication facility
- Assembly of eighteen 0.9 (or twenty four 0.6) meter structures
- Includes twelve (or 18) destined for 8-pack test at SLAC
- Capability of >1 structure/month by December 2002
- Tolerances/acceptance criteria
- Develop complete understanding of tolerances and develop QC criteria and specifications
- Girders
- Develop girder design and prototype
- Delivery of two complete girders to SLAC for 8-pack test

## The NLC R&D ProgramStructures/Industrialization

- Status
- IB-4 conversion to structures fabrication facility nearly complete (w/NICADD support)
- First 20 cell Fermilab structure, FXA-001, complete
- FXA-002 nearing completion

- “Small” furnace and the structures fabrication facility at Fermilab

## The NLC R&D Program Structures/Industrialization

- Goals for FY02
- Complete fabrication facility
- Fabricate and test FXA-002,003
- Fabricate and test FXB-001-003
- Achieve production rate of one structure/month (December 2002)
- Complete structures QC and acceptance criteria
- Identify vendors and production techniques for FXC-001-006
- Prototype of support girders

- FXA-001 undergoing bead pull measurement at Fermilab

## The NLC R&D ProgramRF Power Sources/Klystrons

- The NLC requires ~2000 klystrons, each capable of delivering
- 75 MW
- 3 sec
- 120 Hz
- Status
- 75XP1 constructed and operated at 75 MW x 3 sec (@10 Hz)
- Three more tubes, one built jointly with CPI, are being fabricated to be ready for test in first half of 2002
- Eight tubes required by end of 2003 for 8-pack test.

- 75XP1 tube at SLAC

## The NLC R&D ProgramRF Power Sources/Modulators

- The NLC requires ~250 modulators each capable of delivering
- 500 KV
- 3 sec
- 120 Hz
- Status
- Development based on solid state high power switching technology, led by LLNL
- 500 KV x 3 sec achieved in “4-Dog”

- “4-Dog” Solid-State Modulator at SLAC

## The NLC R&D Program8-pack Test

- “8-pack” test:  Proof of principle demonstration of the NLC rf generation and distribution system
- Goals:
- “Single feed” demonstration in 2002
- Deliver rf power suitable to support 70 MV/m (unloaded) for one girder (5.4 m) of structures.
- Test facility for rf power system to run independently of the high-gradient structure testing.
- Complete 8-pack in late 2003
- Demonstrate full power source with one DLDS arm.
- Demonstrate full power operation of two girders (10.4 m) worth of accelerating structures, including at least one of the final RDDS design.

## The NLC R&D Program8-pack Test

- Full “8-Pack”
- NLCTA Fall 2003

- NLC “Single Feed”
- (5.4 m of Accelerator)

## The NLC R&D ProgramOther Areas

- Electron polarization with thin strained-lattice (SLAC/Wisconsin/Nagoya)
- Polarization of 78% measured at NLC-spec beam density with no sign of charge saturation.
- Damping ring studies at the ATF (KEK/SLAC/LBNL).
- Intra-beam scattering.
- Multi-bunch dynamics.
- Permanent magnet R&D (FNAL/LBNL)
- Very close to achieving required 1 m center stability under adjustement
- Final focus and beam collimation (SLAC/DESY)
- Optics designs and collimator wakefield studies at ASSET
- Linx proposal?
- Photon-photon collider (LLNL).
- IR design and Mercury laser prototype.

## The NLC R&D ProgramLINX Proposal

- Goals:
- Test stabilization techniques proposed for future linear colliders and demonstrate nanometer stability of colliding beams
- Investigate new optical techniques for control of beam background
- Provide a facility where ultra-small and ultra-short beams can be used for a variety of other experiments
- Eventually gamma-gamma facility

- What is it?:  A facility to provide e+e- collisions with 30 GeV, ~50nm beams

## TESLA R&D in the U.S.

- The U.S. is in a unique position as the only region in the world in which the technology choice for a linear collider does not appear to be “locked in”. However the character of the U.S. effort on TESLA is fundamentally different from the NLC program because leadership comes from abroad (DESY).
- US members of the TESLA collaboration
- Argonne National Laboratory
- Cornell
- Fermilab
- Jefferson Lab
- UCLA
- Elements of the U.S. Program
- Collaboration on construction and operation of the TESLA Test Facility (TTF)
- Collaboration on preparation of the TESLA proposal
- Superconducting materails/processing/fabrication R&D
- Injector development and R&D
- Engineering/cost study of the TESLA proposal (w/SLAC participation)
- SCRF operational experience at Cornell and JLab

## TESLA R&D in the U.S.Highlights

- Superconducting structure R&D
- Fundamental investigations into breakdown phenomona, surface conditions and processing at Cornell
- Flat beam studies at Fermilab/NICADD Photoinjector Laboratory (FNPL)
- Goal
- Generate a flat beam with an emittance ratio tailored to future linear collider requirements (****H/V  100)
- Typical emittance ratio achieved thus far is ~40 (@17 MeV and 1 nC)
- Next step is to increase emittance ratio by decreasing space charge.

## TESLA R&D in the U.S.Highlights

- Engineering/Cost Study
- Develop an understanding of:
- Scope included in the TESLA estimate
- Basis and estimating methodology
- Supporting studies (industrialization, schedules, etc.)
- Implicit (or explicit) implementation choices
- Mapping onto a U.S. style estimate
- Report should be available by mid-to-late February
- Opportunities
- Activities centered at FNPL (many also applicable to NLC):
- Flat beam experiments
- Remote operations demonstration
- 3.9 GHz (3rd harmonic) cavity to support longer bunches
- Polarized rf guns?
- Layout/proposal for Photoinjector III
- Engineering study of TESLA in a deep site
- Pursue other opportunities with U.S. collaborators

## LC Site InvestigationsU.S. Sites

- 127

## Outstanding Technology Challenges(SDH Perspective) 

- Energy Performance
- RF Structures
- It is safe to assume that both NLC and TESLA will demonstrate structures capable of supporting their design accelerating gradients (50 and 24 MV/m respectively) over the next year or so.
- The critical issue that is going to take longer is to develop/demonstrate the manufacturing methodology that could allow construction of the linac in a finite time, for a finite cost (especially in the case of NLC/JLC).
- RF power generation and delivery
- The NLC/JLC rf distribution system has yet to be demonstrated. It is clever, but may not work. The fall back is a system similar to that described in the 1996 ZDR. Alternative implementations deserve continued consideration.
- Both NLC and TESLA have to develop/demonstrate an industrial capability for delivering klystrons and modulators.
- Multibeam klystron average tube lifetime needs demonstration

## Outstanding Technology Challenges (SDH Perspective) 

- Luminosity Performance: There are so many challenges (and opportunities) here it is impossible to list them all. A sampling:
- Sources
- Polarization (e- appears OK, what about e+?)
- Flat beams
- Damping Rings
- Damping ring performance specs still await demonstration at ATF
- The TESLA damping ring seems somewhat problematic due to issues (like space-charge) related to its large circumference.
- Emittance preservation
- Tolerances, alignment mechanisms, feedback algorithms all have to be defined in greater detail for both NLC and TESLA.
- IR Feedback
- Seems to be a viable concept for TESLA, can NLC scheme be validated?
- Is LINX necessary or desirable testbed?
- Reliability
- We need a serious assessment/reliability model for these machines.

## Outstanding Technology Challenges (SDH Perspective)

- Energy Upgrades
- 800-1000 GeV
- NLC has a relatively clean vision of achieving 1 TeV based on doubling the length of the linac.
- TESLA has a vision of 800 GeV based on an rf power upgrade with a fixed length linac. This assumes a performance of 35 MV/m in the accelerating structures. This has yet been demonstrated, and is unlikely before TTF-II (2003/04)
- Beyond 1 TeV?
- Possible paths for NLC and TESLA have not been shown. Do they exist?
- Site(s)
- Criteria definition
- Site investigation and characterization
- Public/community Relations
- (DESY is clearly ahead in this area)
- Cost
- This has to be iron-clad

## Summary

- Linear Collider R&D is being pursued in the U.S. and abroad with a goal of establishing underlying technologies in late 2003/early 2004 timeframe.
- Both NLC and TESLA are currently on paths that are expected to lead to credible technology demonstrations on this timescale.
- Current support levels in the U.S. (and perhaps also abroad) could imperil this timescale.
- We need more resources (=_people_ +$) on this.
- The experimental community can help by getting directly involved in the machine R&D and technology discussion.
- If we are successful on the R&D (_and_ establishing public support _and_ forming an international collaboration) the world could construct such a facility over the ~2006-2012 time period

- 9th International Workshop on Linear Colliders
- February 4-8, 2002 at SLAC
**http://www-conf.slac.stanford.edu/lc02/**