# Presentation: 143753

## HEBT, Ring, and RTBT BPM SystemBeam-based Alignment

- Peter Cameron
- July 23, 2002

## Outline

- Techniques and Principles
- Measurement Time and Accuracy
- Trim Quad Switching
- Differences between Ring and HEBT/RTBT
- A Challenge to AP?
- Conclusions/Action Items

- BNL Diagnostics Review

## A Variety of Techniques

- Ballistic Alignment - CLIC
- Dispersion Free Steering - some processing
- Two-Beam Alignment
- SLC Injector Consecutive Quad Pairs
- NLC Main Linac - individual quad modulation
- Fast K modulation
- Slow K modulation

- BNL Diagnostics Review

## Principle of BBA

- Beam off-center thru quad imparts kick, which can be measured by all BPMS of proper phase
- Use dipole corrector to sweep beam across quad, record all BPMs
- Increment quad trim and repeat

- BNL Diagnostics Review

## Basic Method

- Icorr= -10

- ya

-   0                    20        0                    20        0                     20
-            Iquad                                    Iquad                            Iquad

- Icorr= 0

- Icorr= +10

- ya/ Iquad

- y0

- -10        0        10

- offset

- BNL Diagnostics Review

## Measurement Time

- Characteristic time of solid core quads is a few seconds (measurement in progress), settling time ~ 10 seconds
- Characteristic time of solid core correction dipoles is a few tenths of a second (measurement planned), settling time ~ 1 second
- If a measurement consists of 5 quad settings for each corrector setting, and 5 corrector settings, then measurement time per quad plane ~ 5 minutes, or an 8 hour shift to do the ring
- The order in which you take the data doesn’t matter!
- If a measurement consists of 5 corrector setting for each quad setting, and 5 quad settings, then measurement time per quad plane < 1 minute, or an hour to do the ring

- BNL Diagnostics Review

## Kick Amplitude

- Beam offset in quad gets kicked. Magnitude of kick is
- 	 = k . L . y
- Where
- 	k = quad strength  = .2998 g/p ~ 0.3/m2
- 	g = quad gradient ~ 10 T/m
- 	p = beam momentum ~ 1 GeV/c
- 	L = quad length ~ 0.4 m
- 	y = beam offset ~ 10 mm
- So that  ~ 1.2 milliradians and kickerpickupm
-  ~ 180 mm
- With a quad modulation of k ~ 2*10-2, the position modulation is
-  ~ 3.6 mm

- BNL Diagnostics Review

## Processing Simulation Comparison – 15ma Beam 1mm displacement 210mm diam BPM

- BNL Diagnostics Review

## Alignment Accuracy

- Position modulation due to quad modulation is of the order of a few mm, can be measured at all available pickups.
- For HEBT electronics, resolution is ~ 100 microns for a single minipulse
- For Ring, we might expect to do BBA with 10 times the 15mA minimum current shown on the previous transparency shown on previous transparency, expected resolutions will also be in the 100 micron range
- Can average over many pulses/turns, and over many BPMs
- Reasonable expectation is that accuracy will be considerably greater than the 1mm AP spec.

- BNL Diagnostics Review

## Trim Quad Switching

- For the Ring, a total of 52 trim windings are powered by 16 power supplies (typically 4 trims/supply) max 40A at 75V
- Supplies are two 20 modules in parallel, spares may be available for BBA supply
- Trim windings come back to an intermediate junction location, where switching will be done
- Make-before-Break and Sequence carefully to equalize coil energy before disconnecting
- Consider coil inductance and resistance to assure ‘clean switching transient’

- BNL Diagnostics Review

## Trim Quad Switching Diagram

- Close switch A to shunt one trim winding - “a little ripple”
- Use switch B to connect the BBA power supply, and ‘modulate’
- Bring BBA power supply current to zero, close switch C, switch B
- Either:
- Ramp trim power supply to zero (preferred choice) or
- Have transient absorbers across each magnet
- Open switch A, adjust trim current as required

- BNL Diagnostics Review

## Required Hardware

- ~150 switches, 40A 75V
- 20 power supply (spare may be available)
- Transient absorbers (if required)
- Controller
- Rack space

- BNL Diagnostics Review

## HEBT and RTBT

- Trim windings are present on all quads in HEBT and RTBT, but there are no trim power supplies. Trims are available for Diagnostics as single user.
- Only half of RTBT quads have BPMs
- Half of HEBT and RTBT quads have their own individual power supplies. The balance are in six strings of four, two strings of three, and one string of two.

- BNL Diagnostics Review

## Complications

- Absence of downstream BPMs at end of HEBT
- Use Ring 400MHz system?
- Effect of stripper?
- Absence of quad trims on 36cm quads at end of RTBT - but only one quad per power supply
- Absence of downstream BPMs at end of RTBT – will position measurement be available on target?

- BNL Diagnostics Review

## A Challenge to AP?

- Those guys get to have all the fun!
- Do we need independent BBA quad trim modulation?
- For a string of four quads modulated, with full complement of ring BPMs and corrections dipoles, is it not possible to extract relative offsets of the BPMs on those four quads using matrix methods?

- BNL Diagnostics Review

## Conclusions/Action Items

- Refine details of switching scheme, improve cost estimate
- Refine accuracy calculation
- Examine techniques beyond simple ‘sweep the dipole, change the quad, sweep the dipole...’
- Explore BBA in the background of machine operations - continuous BPM calibration

- BNL Diagnostics Review