# Presentation: 014190

## AC Dipole Report

- M. Bai,1 R. Calaga,1 W. Fischer,1 A. Jansson,2
- S. Kopp,3† R. Miyamoto,3§ P. Oddo,1 M. Syphers2
- 1*Brookhaven National Laboratory*
- 2*Fermi National Accelerator Laboratory*
- 3*University of Texas at Austin*
- 	§PhD student
- 	†Caution:  particle physicist!

## Simple View of AC Dipole:Near-resonant excitation

- unstable if m=z

- Simple View of AC Dipole:Near-resonant excitation

- Long lasting large coherent oscillation with  preserved

**AC Dipole**

*Data from AGS*

**IP2**

**IP1**

**IP3**

**IP4**

## More Complicated View:Driven Oscillation  Free Oscillation!!  

***ν*****d ****- *****ν***

***ν*****d ****- *****ν***

***β*****d**** [m]**

_**Measured **__***β***__** from Fits**_

**True *****β***

_**Phase Space @ an **__**IP**_

_**true **__***β***_

_***δ***__*** = -0.01***_

_***δ***__*** = -0.02***_

**R. Miyamoto *****et al*****, **
**Submitted to PRST-AB (also**
**arXiv:0709.4192)**

## Two Driving Terms of an AC Dipole

***ν***

**1−*****ν*****ac dipole**

***ν***

**1−*****ν***

***ν*****ac dipole**

**Amplitude of the Driven Motion vs. Machine Tune**
**(For the AC Dipole)**

**Amplitude of the Driven Motion vs. Machine Tune**
**(For the Beam)**

***ν*****ac dipole**

**R. Miyamoto *****et al*****, Submitted to PRST-AB (arXiv:0709.4192)**

## Analytic Expression of the Driven Motion 

***ν***** = .58 (Tevatron)**

***ν***** = .30 (RHIC,**** ****LHC)**

*S. Kopp (U.Texas) – LARP Collaboration 10/17/07*

- (AC Dipole introduces something that looks like a “quad error”)

## Amplitude vs. Driving Tune

**Measured tune from fits**

**driving tune**

**driving tune**

**driving tune**

## Launching Activities at CERN

- Mei Bai visited CERN and worked with Rogelio Tomas, Rama Calaga and Frank Schmidt on the AC dipole applications
- She has developed a new fitting code which incorporates Ryoichi’s ‘two mode’ analysis.
- Glenn from CERN is developing a JAVA application for LHC optics correction.
- In a meeting with Rogelio, Frank, Rama, Yiton Yan from SLAC, Akio Morita from KEK they discussed wanting to see this tested in RHIC during the coming run.

## High lights from CERN visit (Mei)

- Rogelio organized an meeting with us, Rama, Frank Schmidt, Javier, Yiton from SLAC, Akio Morita from KEK and a few others to discuss the applications of LHC ac dipoles
- Linear optics measurement and gradient correction
- Dynamic aperture measurement
- Non-linear resonance driving term measurement
- Meeting Summary: Rogelio
- A collection of techniques and software applications are being prepared to measure and correct the LHC optics on-line.
- Experiments are being performed in RHIC and SPS to assess these techniques
- Realistic simulations of LHC optics measurement and correction are also being performed with satisfactory results, so far. The AC dipole could play a key role in the measurement.
- Two points have to be clarified concerning the AC dipole: the discrepancy that Mei is observing between model and experiment and the safety issues for the LHC AC dipole.
- Yiton Yan offered his collaboration in the implementation of the MIA analysis for the LHC, with the advantage of obtaining a virtual machine that would reprocuce the observations. A perfect communication between the optics measurement on-line application and the on-line model application is being established.

## High lights from the CERN visit

- discussed with Yiton Yan on what we need to do to modify his MIA for the ac dipole optics measurements.
- Analyze the dedicated ac dipole optics data with artificial quadrupole error during the RHIC 2007 Au run. Both Mei’s and Rama’s code can identify the artifical gradient error correctly. Rama also compared this with his optics measurements with one-turn kicker.
- Ed comment from Sacha:  it seems to be well-established that we can properly observe a quad error that has been artificially inserted.  But this is not a “blind analysis”.  What evidence can we provide that the AC Dipole would really diagnose (and lead to correction) an effect on-line?

## RHIC ac dipole optics data – 2007(Mei’s analysis)

## Parameters of RHIC, TeV, and LHC

| machine(GeV) | RHIC(250) | Tev (150) | Tev (980) | LHC(7000) |
| --- | --- | --- | --- | --- |
| frev [kHz] | 78 | 47.7 | 47.7 | 11 |
| ν, 1-ν | 0.71 | 0.58, 0.42 | 0.58, 0.42 | 0.3, 0.7 |
| fm [kHz] | 55 | 20 | 20 | 3, 8,14,19 |
| (Bρ) [Tm] | 833.9 | 500 | 3,300 | 23,000 |
| δ | ≥ 0.01 | ≥ 0.01 | ≥ 0.01 | ≥ 0.01 |
| β (βm) [m] | 45(11) | 80 (47) | 80 (47) | 180** |
| σ [mm] | 0.75 | 1.3 | 0.5 | 0.3 |
| BmL [Gm] (4σ)  | 142 | 50 | 140 | 190 |
| IFNAL [A] | 284 | 100 | 450 | 610 |

*** Serano’s talk @ LTC gives ****m**=258m at location of MKQ kicker*

## “Musical Dipoles”

- Desired excitation *f *in audio band
- Use commercially-available, cheap amplifiers
- Parallel resonant circuit
- Match impedance of the amplifer
- Maximizes current in the magnet
- Use pinger magnet
- Iron core  good field
- Large *R**magnet*  low *Q*

*A. Jansson*

## Current Status of Work at CERN

- Testing started using new 2 Lab.Gruppen FP13000 amps and 4:1 transformers
- 1500Apk magnet current achieved
- 2128Apk should be possible at resonance                                 with an adequate AC-supply
- The 7σ (1800Apk) goal seems in reach
- Peter Oddo has been working with Javier Serrano to implement CERN system (great to have CERN presence!)

- As I reported last year, CERN has decided to adopt the FNAL solution of audio amps driving a pinger
- Spec: 1800 A in MKQ for 7 @ 7 TeV.
- 4 pingers (MKQs)
- Lab-Gruppen Class-H amp

## Goal:  Tunability of Resonant Circuit

- Peter Oddo (BNL) is developing continuous tuning technique using single switched capacitor with MOSFT at BNL
- Tunes resonant frequency by varying parallel capacitor
- C changes because of variable duty cycle of the switch
- Simulations suggest *f ~ *400 Hz

## 7.33-9.04kHz (±10%) range
Basic Topology, 0.56W,  Q=15-19
Coil current fairly constant ~2.2Apk
3rd harmonic –33dBc
Consistent with simulation

- Basic Topology, 0.56W,  Q=15-19
- Coil current fairly constant ~2.2Apk
- 3rd harmonic –33dBc
- Consistent with simulation

- Low-power Switched-capacitor Results

- Always on

- Always off

- Switching

- 7.33kHz

- 9.04kHz

- 8.67kHz

- Coil current

- Coil voltage

- Drive current

- Switch voltage

## Initial Conclusions on Switched Cap’s

- Maximum Q limited by existing MOSFET technology
- MOSFETs evaluated have a dissipation factor of 0.45-1% (or Q 100-220)
- The need for many paralleled MOSFETs favor using a binary weighted capacitor-bank and modulating the LSB
- Modulating a smaller capacitance will also reduce distortion
- Modulation is not necessary for the LHC (low-Q)

## Intermediate Solution for Selective Tunability of LHC AC-Dipole

- Bit1

- 5-bit binary-weighted capacitor-bank
- 0.255-0.345 (±15%) tune range
- 2.867-3.880kHz
- 0.002-0.005 tune steps
- 22-54 Hz
- Static MOSFET switching
- Can be replaced with mechanical switches or straps
- Conservative design
- Can withstand CW operation
- Peter and Mei have been working with Javier Serrano this Fall to implement this solution

- Bit0

- Bit2

- Bit3

- Bit4

-  GND Plate

-  MOSFET Module

- Capacitor

-  Coil/Drive Plate

## In the Coming FY08 Year

- Can already point to this as a LARP success?
- $80k allocated to this task for FY07
- We promised a conceptual plan by Dec. 2007
- Largely, this done for PAC07 (_[arXiv:0709.2753](http://xxx.lanl.gov/abs/0709.2753)__)_
- We’ve asked for similar $80k this year
- There are still issues for consideration
- Demonstrate 1800 Amp magnet current for 7** at 7TeV
- Completion of continuous tuning capacitor circuit
- Completion of “in-out” selective capacitor switching
- On-line diagnostic tools, analysis (if not the software, at least the demonstrated analysis)
- Great to have a presence at CERN!
- Study issues of machine protection, possible interferences with damper (other?) systems (not clear this is a LARP task, however).
- I view this task as being completed after FY08 (move to commissioning work, doesn’t need separate task).