# Presentation: 492513

##  The NLC Design

**Linear Collider Workshop 2000 **
**FNAL**
**October 24****th****, 2000**

## NLC Design Changes

- Focused on cost reduction over last year – expect 30% reduction
- Many RF system improvements
- Facility length reduced by 20%
- Hi/Lo energy IR scheme and BDS redesign to optimize L and open future expansion possibilities
- Investigating 180 Hz operation
- Technology based on results from test facilities: FFTB, NLCTA, ASSET, KEK ATF and knowledge gained from SLC operation

- 26 km

## NLC Project Scope

- Injector Systems
- Main Linac
- Housing with all internal services
- Half filled for initial 500 GeV cms
- Upgrade by adding rf, water, power to the 2nd half of the tunnels
- Beam Delivery (high energy IR)
- Two BDS tunnels and IR halls with services
- some magnet strengths must be increased to get from 1 TeV to 1.5 TeV

- 1.5 TeV
- 0.5 - 1.0 TeV
- (1.5 TeV withincreased gradientor length)
- 1.5 TeV(length will support a 5 TeV FFS)

## NLC Energy Evolution

- Stage 1:	Initial operation
- 			500 GeV cms
- 			L = 5x1033  20x1033    500 fb1
- Stage 2:	Add additional X-band rf components
- 			1 TeV cms
- 			L = 20x1033  30x1033    1000 fb1
- Higher Energy Upgrades:
- 1.5 TeV with upgrade of linac rf system or length increase
- injector and beam delivery built for 1.5 TeV
- 3 TeV+ with advanced rf system and upgraded injector
- see CLIC parameters: “*A 3-TeV e+e- Linear Collider Based on CLIC Technology*,” CERN-2000-008
- beam delivery sized for 3 to 5 TeV collisions

## NLC Progress

- Established collaborations with KEK, LBNL, LLNL, and FNAL
- KEK focused on rf development
- Berkeley concentrating on magnet design and damping ring issues
- Livermore focusing on solid-state modulators and - IR
- Fermilab taking responsibility for main linac beamline:
- Performed bottoms-up cost estimate for Lehman review
- Successful Lehman review  8B$ project cost
- Have demonstrated most *necessary* rf hardware (NLC Test Accelerator) **however** the cost optimized hardware is still in development **and **rf power handling is still a question
- More aggressive rf design for lower cost and better efficiency
- Working on cost reduction throughout design: expect 30%

## NLC RF System

- RF system consists of 4 primary components:
- Modulators: line ac  pulsed dc for klystrons (500 kV, 250 A)
- Klystrons: dc pulse  75MW at 11.424 GHz
- RF Pulse Compression (DLDS): compresses rf pulse temporally, increasing the peak power, and delivers the power to the structures
- Accelerator Structures (DDS & RDDS): designed to transfer power to the beam while preventing dipole mode driven instabilities
- Each linac has 100 modules consisting of 1 modulator, 8 klystrons, 1 DLDS system, and 24 accelerator structures
- Need good efficiency, reliability, and low cost!

## Solid-State Modulator

- Conventional modulators are expensive and inefficientwith short pulses: ~ 60%
- Program at LLNL todevelop ‘Induction Modulator’based on solid-state IGBTs: efficiency ~ 80%
- IGBTs developed for e-trains   with 2 to 3 kV and 3kA
- Drive 8 klystrons at once
- Full modulator finished thiswinter

- 10 Core Test Stack

## Solid State Modulator 8-pac

## PPM Klystrons

## XP-1 75 MW Klystron

- XP-1 based on very successful 50 MW Periodic-Permanent Magnet (PPM) klystron but included many ‘simplifications’
- XP-1 testing results:3us pulse lengthlimited by modulatoraverage power 72 MW and peak power >80 MW
- Designing a second 75 MW tube with better field profile and features to improve manufacturing—to be tested this fall

## DLDS Pulse Compression

- 4 Delay Lines, 2 Modes/Line
- Effective Compression Ratio=8
- Klystron Pulse Width=3.05 s  Accelerator Pulse Width=0.381 s
- Total Waveguide Length=174 km (for a 500 GeV Collider)

- Klystron 8-Pack

- Combiner/Launcher System

- Delay Lines
- 120.65 mm diameter waveguide

- Extractor
- Extracts the TE12 mode and passes the TE01mode

- 56.3 m

- Beam direction

## DLDS Pulse Compression Test

- All components have been designed
- Multi-mode transmission properties have been verified
- High power testswill start in 2001
- Full system test in2003

- NLCTA Setup

## Accelerator Structures

## DDS3 Structure BPM Test

## RDDS1 Structure Construction

- RDDS1 cells were designed at SLAC and machined at KEK – final machining performed on diamond-turning lathe
- Attained excellent results:frequency errors less than 1 MHz, i.e. <1m errors
- Tolerances for dipole modefrequencies are 5 times looser!
- Bonding process still needsto be understood!

## High Power Damage

- Have had difficulty processing 1.8m long structures to 70 MV/m (NLC design gradient)
- Single cells can operate at 150  200 MV/m without damage
- A 26 cm structure has been run to 140 MV/m (some damage)
- A 75 cm structure has been run at 90 MV/m (some damage)
- Observed significant damage in 1.8 m structures at 50 MV/m
- Recent workshop on rf breakdown phenomena
- Theoretical model predicts the *damage* is related to the group velocity of the rf power in the structure
- Building 12 structures with KEK to study length and group velocity dependence – will be tested in 2001
- Studying cleaning and improved manufacturing techniques

## NLC RF System Highlights

- Developing solid-state modulator with LLNL
- Much less expensive, more reliable, smaller package
- Demonstrated (periodic permanent magnet) PPM 75 MW klystron operation for NLC with 3s rf pulse (2x expected!)
- Half as many klystron/modulator systems required!
- Tested mode propagation needed for multi-moded DLDS
- Less expensive rf pulse compression system
- Built DDS3 structure and RDDS1 structure with KEK
- DDS3 exceeded alignment requirements and demonstrated rf BPM
- RDDS will shorten linac length by 6%—sub-micron errors in cell fabrication
- Starting intensive gradient studies with CERN and KEK
- High power component tests finished in 2001 and full system test in 2003

## NLC Cost Reduction Strategy

- Costs distributed throughout system  attack all
- Primary changes:
- Solid state modulator (powers 8 klystrons for 40% of the cost)
- Longer linac rf pulses (half as many klystrons/modulators)
- Permanent magnets (eliminate cable plant/PS, improved reliability)
- Cut & cover tunnels (lower cost but may need terrain following)
- Moving electronics to tunnel (eliminate cable plant)
- Redesign bunch compressors (lower final energy, shorter system)
- Redesign collimation system (reduce length of by factor of two)
- New final focus (reduce length and components in BDS)
- Expect reduction in cost by 30% with another 10% possible from scope reduction **if** **desired**
- Additional gains from further R&D and layout changes

## FNAL Prototype PM Quad

**FNAL Prototype PM Quad**

- Mechanical Adjuster Concerns
- Calibration
- 1 m Magnetic Axis Stability
- Response Time
- Reliability

- Rotatable PM (Nd-Fe-B) Block
- to Adjust Field  (+/ 10%)

- Steel Pole Pieces (Flux
- Return Steel Not Shown)

- PM (Strontium
- Ferrite) Section

## Post-Linac Collimation System

- Tighter

- Looser

- Optics Tolerances

- Never

- Seldom

**Single Pulse Collimator Damage**

**ZDR**

-  ‘Consumable’ collimators     damaged 1000x per year

- ‘Renewable’ collimators   damaged each pulse

- Conventional collimators        not damaged

-  High power beams will   damage collimators unless   beam sizes are increased
-  Studying ‘consumable’   and ‘renewable’    collimator systems

- Always

- Consumable Collimators

- Beam damage

-  Experimental study of    collimator wakefields

## Post Linac Collimation

- Most main linac faults will be energy errors  design for passive energy collimation
- Infrequent betatron errors  ‘consumable’ betatron collimation
- Reduce collimator system length from 2.5 km to roughly 1.2 km—still working on optimal design

## Collimator Muon Production

## Final Focus and Interaction Region

- Old final focus was a scaled up model of the SLAC Final Focus Test Beam (FFTB) beamline
- Modular design with orthogonal control using symmetry
- Chromatic correction is performed with pairs of sextupoles at large dispersion points separated by  to cancel geometric aberrations—requires lots of bending to generate 
- Length of system: was roughly 1.8 km—driven by synchrotron radiation at 1.5 TeV
- New design: chromatic correction is performed at final doublet so synchrotron radiation has little effect
- Length is roughly 700m and will operate at 5 TeV!

## New Final Focus

- One third the length - many fewer components!
- Can operate with 2.5 TeV beams (for 3  5 TeV cms)
- 4.3 meter L* (twice 1999 design without tighter tolerances)
- Optical functions are not separated and dispersion in the FD

- 1999 Design

- 2000 Design

## Hi/Lo IR Layout

- Final focus aperture is set by low energy beams 1/ but highest energy operation is limited by magnet strength, synchrotron radiation and system length
- Final focus has limited energy range without rebuilding magnets  and vacuum system
- Simplify design by dedicating one IR to ‘low’ energy operation and one to ‘high’ energy operation
- ‘Low’ energy range of  90–350? GeV (build arcs for 500 GeV)
- ‘High’ energy range of 250–1000 GeV (with upgrade to 1.5 TeV)
- High energy beamline would have *minimal bending* to allow for upgrades to very high collision energies
- ‘High’ energy BDS could be upgraded to multi-TeV operation!

## Hi/Lo IR Layout

- High energy IP0.25-5.0 TeVupgraded in stages

- Low energy IP92-350 (500??) GeV

- Low energy (50 -
- 175 GeV) beamlines

- Multiple beams line mightshare main linac tunnel

- Centralized injector systempossibly for TBA drive beamgeneration also

**e+**

**e-**

- Site roughly 26 km in lengthwith two 10 km linacs

- Possible staged commissioning

## Luminosity Scaling  with Energy

- Assuming same injector, the luminosity scales as:

-   Luminosity in high     energy FF scales linearly    with energy between 250    and 1 TeV
-   Low energy FF scales    similarly but at lower    energy!

## Design versus Intrinsic Luminosity

- Intrinsic luminosity:
- this is the luminosity the machine could deliver limited by physical effects
- Design luminosity:
- this includes operational limitations and is the luminosity for which the collider is *designed*
- includes use of tuning techniques developed during SLC operation

- Example: at 500 GeV cmsx / y [10-8 m-rad]

## Luminosity Evolution

- Previously NLC was aimed at *L* goal of 11034 at 1 TeV
- NLC was based on large ‘operating plane’ with 50% spot size and charge variation **plus** built-in margins including 50% charge overhead and 300% 
- Components were spec. to tightest tolerances over range
- NLC damping rings spec. to produce y = 0.02 mm-mrad although only 0.03 mm-mrad is required initially
- SLC used ‘emittance bumps’ to reduce emittance dilution from 1000% to 100%—technique not included in initial emittance budget
- NLC is a 2nd generation LC - many tools and techniques were developed for SLC and used at FFTB and more recently PEP-II
- Design luminosity is 4x higher than ‘operating plane’ values
- Actually, present prototypes and R&D results are even better!
- y < 25% in linac if production components are similar to prototypes

## Design Parameters 

-   Trade luminosity versus beamstrahlung:    increase x  B decreases faster than *L*

## Beam Loading

- CMS energy changes with beam current due to beam loading
- Luminosity also scales with beam current

## 180 Hz Operation Possibility

- 180 Hz operation is decoupled from low/high energy IR
- two options: 180 Hz at 500 GeV or 120-60 Hz at 500 GeV and 60-120 Hz at lower (250 GeV) energy
- Choice depends on AC power
- Primary issues are:
- power consumption, average heating and radiation
- machine protection (60 Hz minimum operation for any low  beam)
- emittance generation / damping rings must be redesigned
- duplicate BDS beam lines for dual energy operation
- Might start low energy IR before before completion of high energy IR and full facility

## Outstanding Issues (a few of many!)

- Sources
- Current limit in e- source and target limits in e+ source
- Damping rings
- Require excellent stability
- In addition to conventional instabilities, new effects may be important
- RF breakdown
- Difficulty processing up to 70 MV/m and damage at 5060 MV/m
- 450 Joules in DLDS rf pulse compression system
- Collimation and IR
- Have to collimate ‘all’ particles outside 8x and 40 y without destroying collimators or beam emittance
- Need high field magnets in IR with nm-level stability
- Reliability

## Summary

- Lots of progress on NLC design in last year!
- Lehman review positive but cost was too high!!
- Continual improvement in rf components  cost reductions
- More aggressive approach to design  cost reductions
- New concepts  cost reductions
- Lots of ideas for further improvements
- Expect 30% cost reduction with further reduction possible from additional R&D and/or scope reduction
- NLC is designed for high luminosity (similar to TESLA) ***however*** neither design has much margin at these parameters
- NLC facility will be designed to support a future multi-TeV LC