# Presentation: 091386

## 
Beam Instrumentation

W. C. Turner
LBNL

Presented at the LAPAC Review of the US LARP
FNAL
17-18 Jun 2002

- Beam Instrumentation
- W. C. Turner
- LBNL
- Presented at the LAPAC Review of the US LARP
- FNAL
- 17-18 Jun 2002

***brookhaven - fermilab - berkeley***

_**US LHC ACCELERATOR RESEARCH PROGRAM**__**                               **_

## Outline

- 						Lead	Needed for 	 _Instrument_ 				_Lab_ 	_commissioning?_
- Luminosity instrumentation		LBNL	      yes
- Longitudinal density monitor	LBNL	      yes
- Phase locked loops			BNL	      desirable
- Electron lens			FNAL	       no
- Bunch by bunch closed orbit	LBNL	       no
- 	feedback correction system
- “Advanced” feedback systems	FNAL	       no

## 1. Luminosity instrumentation

- Propose to instrument the high luminosity IR absorbers TAN and TAS. These absorbers are being provided by LBNL as part of US LHC Accelerator Project
- The instrumentation will provide a crucial storage ring operations tool for bringing beams into collision and optimization of luminosity
- The lumi instrumentation concept as it now exists was not part of the US LHC Accelerator Project baseline, however early development was funded by re-allocation of resources within the US LHC AP
- It is proposed to fund this work to completion under the US LHC Accelerator Research Program

## Contributors to luminosity instrumentation

- LBNL
- 	Jean Francois Beche
- 	Philip Datte
- 	Franco Manfredi
- 	Jacques Millaud
- 	Vincent Riot
- 	William Turner

- Univ. of Pavia/INFN
- 	Lodovico Ratti
- 	Gian Luca Traversi
- CERN
- 	Maurice Haguenauer
- 	Massimo Placidi
- 	Hermann Schmickler

## Brief history of the luminosity monitor

- Ion collection mode ionization chamber 		Jan 1997
- proposed, measure average L
- Electron collection mode proposed, 40MHz 	Nov 1998
- Lumi mini workshop at CERN, endorsed ionization	Apr 1999
- 	chamber development
- CDR organized by US LHC Accel Project		Sep 1999
- First SPS H4 beam test				Jul 2000
- Second SPS H4 beam test			Sep 2001
- Second Lumi mini workshop at LBNL		Nov 2001

## TAN and TAS absorbers in IPs 1 and 5

-  The TAS absorbs ~200W of forward collision products that have
-    escaped the beam tube in front of Q1 (mostly charged pions and photons)
-  The TAN absorbs ~ 200W of forward neutral collision products (mostly
-    neutrons and photons) and is placed in front of the outer beam separation
-    dipole D2
-  Instrument the TAN and TAS to measure and optimize the luminosity of
-   colliding bunch pairs with 40MHz resolution

## Neutral Absorber (TAN) exploded view

- Iron shielding

- Copper/steel absorber

- IP

- Arcs

- Removable copper bars,
- Luminosity instrumentation

- Marble shielding

- Beam tubes

## TAS exploded view

- Vacuum bakeout
- strip heater

- Telemanipulator
- support

- Luminosity instrumentation
- slot

- IP

## Detectors in the TAN

- We have been contacted by several groups that have expressed interest in installing detectors in the TAN
- Y. Muraki, Univ of Nagoya, photon detector
- S.White, BNL, ATLAS ZDC for heavy ion calorimetry
- M. Murray, Texas A&M, CMS ZDC for heavy ion calorimetry
- M. Rijssenbeek, Stonybrook, ATLAS forward physics
- In general these are not yet approved or funded efforts. We make our drawings freely available with the caveat that plans should be compatible with the luminosity instrumentation we are designing and they keep H. Schmickler, CERN BI Group Ldr, informed of their work
- Eventually if these and our own plans are approved and funded there will need to be integration of these efforts

## Incident particle fluxes per pp interaction calculated with MARS code (Mokhov, FNAL)

- 				(a) TAN			   (b) TAS

- An example: TAN neutrons
-  L   = 1034 cm-2s-1, inel = 80mb 	=>  8x108 pp int/s
- <n> = 0.33 neutrons/pp int	=>  2.6x108 n/s
- f   = 40 MHz bunch xing	    	=>  6.6 n/bunch xing

## The right-left asymmetry ratio is a sensitive function of the crossing angle

-  - TAN 142 m from IP, xing angle = 150 mrad

-  Measurement of the asymmetry ratios at the positions of the TAS
-    and TAN on both sides of an IP may allow determination of IP pos.
-    and xing angle

## Concept for optimization of luminosity

** ******  = error offset amplitude
-  d = intentional sweep amplitude

- Define the detector current

- Integrate to obtain the luminosity and error offset, 0 < *t* < *T*,

## Integration times are sufficiently short to be practical even for the lowest luminosity envisioned (TOTEM) 

-  Bunch by bunch measurements increase the integration times by the
-    number of bunches (x2835 for L = 1034, x36 for TOTEM)
-  The practical sweep frequency needed for beam-beam separation
-    measurements will determine the integration time at the
-    highest luminosity

## Bringing the beams into initial collision

- One approach - start with a coarse grid map with successively finer mesh followed by application of the beam sweeping method with successively smaller radii
- An extreme example - TOTEM, L = 1028cm-2s-1
- Total integration time allowing for two iterations of each beam sweep =
- 	approximately 45 min

## The ionization chamber approach for the detector (must withstand 100-200MGy/oper yr)

-  60 gaps, 10 parallel x 6 series
-  segmented into quadrants
-  0.5 mm gap spacing
-  copper, ceramic construction
-  Radiation hard gas Ar+2%N2, e-
-   drift velocity 3.2cm/sec
-  3m rad hard cable to electronics

## An analog board has been fabricated and shown to meet the bandwidth and noise requirements

-  Delta function noise
-    charge
-  ENC = 1824 e-
-  Triangular pulse noise
-    charge (20ns)
-  ENC = 5107 e-
-  Ballistic deficit
-   = 3.0±0.5
-  S = 2.6x104e- for 1pp
-  interaction
- 	=> S/N > 5
-  Transfer function =
- 	0.45x10-3 mV/e-

## Use the MARS code to

- Understand the energy flow in hadronic/em showers
- Understand the energy deposition by hadronic/em showers
- Estimate the ionization chamber signal from the flux of ionizing radiation for LHC and for SPS H4 test beams

## Flux and mean energy of particles near the shower maxima of 300 and 450 GeV primary protons

- (a) 300 GeV proton

- (b) 450 GeV proton

-  A similar calculation for the TAN absorber on LHC predicts on
-   average 268 mips per pp interaction => use SPS beams to
-   simulate LHC conditions

## Predicted signal at shower maximum in 300 GeV proton beam

- 6 atmos Ar+2% N2 => 6x97 = 582 electron-ion pairs/cm-mip
- Ten 0.5mm gaps => 0.5x582 = 291 electrons/mip
- 231 mips/p at shower max => 6.7x104 electrons/p
- Transfer function 0.45V/e
- Ballistic deficit ~ 3±0.5
- Cable attenuation = 20%
- Expected signal
- => 0.5x6.7x104x.45x10-6x0.8 /3 = 4.0±0.8 mV

## Photo of the setup in SPS H4 300 GeV proton beam, Sep 2001

- Two quadrants of the detector

- Absorber and detector in
- The 300GeV SPS H4 beam

## Waveform averaging improves proton shower S/N ratio

-  Pulse height 4.2mV in good agreement with MARS
-   prediction 4.0±0.8 mV

## N1/2 scaling of rms noise

- ENC = 1.28/0.45x10-3
-         = 2,840 e

## Pulse height spectrum for proton triggers

- Spectrum of the
- interacting proton showers

- Noise spectrum due to non
- interacting proton fraction

## A typical proton shower waveform delayed 25 ns and added to itself 10 times

-  Peaking time = 16ns < 25ns
-  Pile up saturates in 3 pulses
-  Trailing pulses do not interfere
-   with the peak of the leading
-   pulse

## Synchronous overlay of ten 2.4k event waveforms and the 24k mean waveform

## Ten pulse summation, pulses successively delayed by 25ns

## Successively fit and subtract the leading pulse

## Unzipped and raw peak heights track one another within statistical error => supports 40MHz capability

## Fe absorber thickness scan agrees with MARS calculation

## Left-right/(left+right) asymmetry defines the shower axis (crossing angle in LHC)

## Radiation hardness test 

- On LHC the hadron energy incident on the TAN
-     is ~ 1 GJ/yr; neutrons, <E> = 2 TeV
- Simulate hadron showers with equivalent energy flux of SPS 450 GeV protons
- Compress 1 yr radiation exposure on LHC to ~ 1 wk on SPS extracted beam
- Assume one slow 5.8 spill every 15.8s
-     => ~5x1011 p/spill, reasonable
- Periodically insert a collimator to reduce intensity to ~ 106p/spill to verify single proton shower operation
- Investigating possibilities in ENH1 area (p0 and M2)

## Outline of R&D program for luminosity instrumentation

- 2003	40MHz bunched beam test
- 2004     High radiation beam test
- 2005     MARS simulations of LHC performance
- 		Bench tests of electronics and parasitic impedances
- 		Design optimization
- 2006     Fab and install TAN luminosity instrumentation
- 		Software development
- 2007    Design optimization
- 		Fab and install TAS luminosity instrumentation
- 		Software development
- 		Integration into LHC operating system
- Cont’d

## Outline of R&D program for luminosity instrumentation – cont’d

- 2007	Commissioning
- 		Single beam LHC backgrounds
- 		Observe first LHC collisions
- 		First LHC luminosity optimization
- 		Cross calibration with ATLAS, CMS and TOTEM
- 2008	Software development
- 		Integration into LHC operating system
- 		Studies of lumi optimization, bunch to bunch variation of 	luminosity, machine development studies
- 		Remote operation from LBNL under LHC operating conditions

## Luminosity monitor summary

- There is convincing evidence the ionization chamber approach to luminosity optimization of LHC can operate at the 40MHz bunch frequency and over the full range of luminosity
- The behavior of the ionization chamber is reasonably well understood and in agreement with MARS calculations
- 40MHz bunched beam and high radiation tests in SPS are highly desirable
- Since SPS will not run in 2005 these experiments need to be done in 2003, 2004 when funding for US LARP is very tight
- Bringing the instrument into full operation on LHC could provide an excellent opportunity for training graduate students and post docs

## 2. Longitudinal density monitor

- Applications
- Debunched beam at injection
- Population in abort gap
- Ghost bunches
- Beam centroid and shape
- Functional Requirements
- (ref. C. Fischer, LHC-BSRL-ES-0001.00 rev 0.1 draft, 11 Nov 01)

## LHC bunch pattern

## Several methods are being investigated

- All utilize radiation from a 2-period undulator and D3 in IR4
- The time resolution required generally rules out em pickups
- 1. Non-linear mixing of “synchrotron-undulator” radiation with a cw laser oscillator
- 2. A photodiode array with TDCs
- 3. Gated PMT or APD for abort gap

## Extraction mirror and photon flux

- Beam

- Photons

- Mirror, 10mm x 50mm

- 5mm

- 30mm = 15V

- 10m

- D3

- Undulator

- V

- 1.48mrad

- Ref. Laurette Ponce
- PhD thesis in prep.

- _Side View_

## Non linear mixing of “synchrotron-undulator” radiation with a pulsed laser (M. Zolotorev)

## Avalanche photodiode array

- Single photon counting used to get 104 dynamic range

- 5,400 photons/rev
- 0.5 < < 1.0

-  Arrays of APDs are just becoming available, Radiation Monitoring
-   Devices Model A6404, 64 pixels, $8k

## Comparison of estimated integration times

-  APD has advantage of faster integration time, Laser
-   Mixing (LM) has advantage of better time resolution

## Longitudinal density R&D

- The laser mixing (LM) approach is an outgrowth of techniques used at the LBNL ALS for production of femtosecond pulses
- An FY 02 LDRD is supporting development of this and the APD techniques for longitudinal density measurement
- A continuation of support has been requested for FY03
- By the end of FY03 we should have documented experience of the relative merits of these two approaches
- Time resolution
- Integration time
- Cost
- Complexity
- ...

##  Schematic ALS bunch map

## Data acquisition board for developed for ALS longitudinal density (P. Datte et al)

## Outline of R&D program for longitudinal monitor(funding limited)

- 2003	Preliminary analysis for LHC
-     Analysis and preliminary LHC design
-  	Design
-  	Final design, begin procurements
-  	Fabrication
- 		Commission simple and robust abort gap system
- 2008 	Software development
- 		Install and commission complete longitudinal density system
- 		Measurement of longitudinal density during injection, ramp 	and flattop, colliding beam operation
- 		Characterize debunched beam at injection, bunch profile, 	ghost bunches, longitudinal tails

## 3. Phased locked loops (PLL)ref. P. Cameron et al, RHIC

- The goal is to control the tune during the acceleration ramp to avoid resonance crossing and beam loss
- The PLL method is to shake the beam and observe the resonant beam transfer function when the shaking frequency is at the fractional betatron tune
- Once the fractional tune is measured with the PLL it is used in a feedback system to regulate the quadrupole current and tune
- RHIC 2000 – preliminary PLL tune measurements using resonant BPM
- 50W, 4m stripline kicker, track tune with precision 10-4
- No emittance blowup observed
- RHIC 2001 – incorporate PLL tune measurement into feedback loop
- RHIC Future Plans – combine with measurement and feedback control of chromaticity

## RHIC PLL measurement of beam transfer function; betatron sidebands

- 238.195MHz(harmonic 3060)

- 5kHz

## RHIC 2000 PLL tune measurement

- Quad current

- Tune

- 10sec

- Ref; P. Cameron et al, PAC2001

## Loss of PLL tune regulation without control of chromaticity

- RHIC experience closing PLL tune feedback loop during a ramp indicates chromaticity must be controlled as well as tune

- Blk horiz tune
- Red PLL amplitude
- Blu PLL phase

- Quad correction
- strength

- Loss of
- PLL lock

## Chromaticity measurement

- Methods considered
- Head tail phase shift
- Schottky signals
- Tune modulation caused by small radial (energy) oscillations – preferred method

- ~.00001 tune modulation
- induced by 2Hz 100micron
- radial oscillation of the beam

## PLL summary

- PLL loops for controlling tune and chromaticity are an attractive proposal for optimizing overall integrated luminosity of RHIC and LHC by improving ramp efficiency
- In practice they are difficult to make work owing to tune coupling, beam-beam tune shift, chromaticity and S/N
- From now through commissioning BNL proposes to devote ~1/3 FTE plus travel expenses to collaborate with CERN on PLL applications
- As RHIC operation matures and LHC is commissioned it is imagined that this collaboration would generate new proposals

## 4. Electron lens(ref. V. Shiltsev et al, Tevatron)

- A electron lens is being developed for compensation of the beam-beam tune shift of the pbar beam at FNAL (_T_evatron _E_lectron _L_ens or TEL)
- Focusing for protons, defocusing for pbars
- Predicted Q ~ 0.01 for Je = 3A, Le = 2.5m, Ue = 7.6keV (e = 0.13), x ~ 110m, 980 GeV pbar

## Tevatron pbar footprints in tune plane

- No beam-beam compensation
- 1 electron lens (TEL)
- 2 TELs
- 2 TELs, shaped beams

## Illustration of TEL1 and parameters

- 3.65m

## TEL1 summary

- Maximum proton beam tune shift Q = +.009, reasonable agreement with theory, good beam lifetime > 12hrs
- One shift with antiprotons, maximum tune shift Q = -.007, behavior similar to protons
- Continue development work with proton beams – ebeam pulser flattop, wider ebeam, beam alignment, 120Hz ripple, etc
- Currently TEL1 used as “soft collimator” for cleaning abort gap and avoiding quenches due to beam loss
- Viewpoint on application of electron lens to LHC
- Initial LHC operation will be at low beam intensity and not require beam-beam compensation
- Meanwhile FNAL will continue to develop the TEL
- Evaluate proposal for LHC after initial commissioning depending on progress at FNAL and the LHC need as beam current and luminosity are increased

## 5. Bunch by bunch closed orbit correction system 

- As bunches approach the IP they experience ~15 long range collisions on each side of the IP, “pacman” bunches at the head and tail experience different numbers of kicks than the center bunches leading to orbit distortion
- The kicks are nearly anti-symmetric about the IP so the offset is negligible at that IP but depending on parameters there can be orbit distortion around the machine, in particular at the other IPs
- The orbit distortion is a slowly varying function of position within a ~ 80 bunch train, as a consequence the needed bandwidth for orbit correction is reduced from 40 to ~ 40/15 ~ 2.5MHz

## Schematic of orbit distortion and corrective kicks around at IP (Corlett and Lambertson, CERN LHC Proj Note 147)

-  Idea is to measure the closed orbit deviation outside the IP
-   and apply a corrective kick that compensates for different
-   positions along a bunch train

## Schematic of pickups and kickers located between D2 and Q4

-  For maximum normalized beam-beam kick ~10-5 m 1/2, ~ 200m,
-   V ~ 1 MV for 10m stripline kicker, P ~ 40kW per kicker

## Bunch by bunch closed orbit correction summary

- Present calculations (W. Herr) predict the effect is neglible when the hi luminosity IPs are on opposite sides of the ring and have orthogonal crossing planes (IPs 1 and 5)
- A bunch by bunch orbit correction system is therefore not envisioned unless operational experience dictates that it is needed, a fractional FTE is proposed during commissioning for this evaluation

## 6. Advanced feedback systems

- FNAL has proposed evaluating the possible need for advanced feedback systems after initial beam operation – for example for correction of ground motion at the IPs
- The evaluation should occur during commissioning and working up the luminosity toward the design goal of 1034 cm-2s-1 and can be expected to result in new proposals in the 2007-10 time frame

## Global Accelerator Network (GAN)

- Concept grew out of an ICFA study on remote operation of future accelerators which concluded that
- most accelerator operations are already performed remotely
- there appears to be no technical obstacle to control room operation of an accelerator from a remote site, even from another continent
- the major challenge lies in solving management, sociological and communication problems
- Our near term interest is
- monitoring luminosity and longitudinal density instrumentation during LHC operations
- participating in machine development studies from US labs
- The experience gained in these initial relatively modest activities will give some indication of the real difficulty of the sociological challenges

## Collaborative computing tools will be used to facilitate GAN activities

- Immersive video (Access Grid Node)
- Shared notebooks
- Remote control and monitoring
- Workflow management
- Infrastructure
- Security
- Low-latency networking

## Proposed instrumentation plan summary

- Deliver 8ea ionization chamber luminosity systems and level of effort support of integration software, commissioning (2007)
- 	and machine development studies
- Deliver 2 ea simple, robust APD or PMT systems (abort gap) for initial commissioning, 2ea laser mixing or APD array systems for measurement of complete longitudinal density profile as soon as funding allows (2008?)
- Provide level of effort support of PLL development for LHC commissioning and operation
- Provide evaluation of need for advanced systems during LHC commissioning – electron lens, bunch by bunch closed orbit correction system, advanced feedback systems

## Post docs and grad students

- Development and commissioning of the luminosity monitor and longitudinal density monitor provide a valuable opportunity for training young accelerator physicists

## Preliminary Instrumentation Budget, FY02k$