PEP II Transverse Feedback System

Ron Akre

Anatoly Krasnykh

Uli Wienands

MAC April 15, 2004

PEP II Transverse Feedback System

PEP II TFB Receiver

Phase shifters were added to phase dX, dY and SUM channels separately

Orbit offset correction is now done by changing beam orbit to minimize dX and dY

Spare Receiver Chassis has been tested and is ready to go

PEP II TFB ReceiverWalter Berry of LBL showed us a problem with the way phased the receiver chassis, small differences in timing between BPM cables can cause a sine like term and in worst case cause us to phase up 90 degrees off in the mixers. We now phase with only 1 BPM cable connected. Procedures for setup are in progress.

RED = BPM Gaussian Pulse : BLUE = 10pS time Shifted Gaussisn : GREEN = 1428MHz Reference

1.0 Unit Peak

0.05 Units Peak

RED = Difference of 2 Gaussian Pulses 10pS time shifted

BLUE = Difference of 2 Gaussian Pulses with 5% Amplitude difference

PEP II TFB Digital DelaysTemperature Related Trips and Spurious signals due to low clock levels are related to setup

Temperature Trip Levels need to be Calibrated

The digital delays require higher clock power levels: currently 10dBm, needs 13dBm

Current System has Obsolete Parts – 8 Bits at 476MHz - New Fiber Optic and Digital Delays are being looked into. Digital systems are favored due to the diagnostic capability.

Off the shelf parts for a 12 to 14 bit system at 238MHz are available. Design at 238MHz is much easier than at 476MHz.

Similar system could be used as diagnostics – measure growth rates

Commercial ADC PCI Scope cards – 8 Bit at 500MHz also available

PEP II TFB Power Amplifiers and FiltersPower Amplifiers

The single largest reliability concern this run. Each of the 8 amplifiers has 8 power transistors. During this run we have lost about 30 power transistors, almost half.

Installation of new tune tracker electronics required higher bandwidth of power amplifiers. Many of the existing amplifiers required tuning to increase rise times and reduce overshoot, the cost is 0.5dB of peak power out.

Filters

Previous failures have been due to faulty connectors. New 7/16 DIN connectors have been installed in LER Y- and there has been no failures. The by-2 pattern helps greatly in reducing the beam power reaching the amplifier.

 

PEP II TFB Kickers

Uli Wienands, Anatoly Krasnykh, Artem Kulikov, Jay Langton, Many Others

Blackening of the electrodes was done by baking them in an oven.

The Moly electrodes will be mounted in the spare kicker this month.

The spare kicker will be installed into LER this summer.

PEP II TFB KickersBeam Induced Signals from the TFB Kicker Electrodes

Magnitude of HOM power is practically the same in both cannels

There is not good directivity for the high frequency range

PEP II TFB Kickers

Z0Zk, tk

Zp, tp

Zp, tp

Z0

1. Sigma_beam < dR

2. dt_b < 2tp + tk

3. Reflection on the (Z0, Zp, Zk) nodes

dt_b

When the known kicker theories do not work and why?

Beam induced power is in both feeders !!!

HOM power to the kicker load

HOM power to the amplifier

PEP II TFB System Bandwidth

Bandwidth of feedback is being evaluated.

Will a 238MHz Digital Delay be sufficient?

Can we drop the bandwidth below 119MHz?

How can we eliminate slope due to Gap Phase Transient?

1 10 7 1.5 10 7 2 10 70.15

0.1

0.05

0

0.05

0.1

0.15

Seconds

Volts

LER TFB Y- ASP OUT NO FILTER

1 10 7 1.5 10 7 2 10 70.15

0.1

0.05

0

0.05

Seconds

Volts

LER TFB Y- ASP OUT 117MHz Bessel Filter

PEP II TFB Concerns for Higher Current Running

Feedback Gain and Output Power – We do not have a factor of 2 margin.

LER has run for several weeks with only 1 power amplifier in vertical. LER was often lost when HER beam goes away.

Plan to do growth rate measurements in LER using LFB electronics.

If larger power amplifiers are required, more rack space is required

Filters are currently working well – no failures with new connector

Only 1 filter has 7/16DIN connector – the rest use N connectors

Kickers

New Moly electrodes will handle much higher temperatures

7/16DIN Feed-through connectors will replace SC, and eliminate SC to N adapters.

PEP II TFB Summary

New Kicker Electrodes and larger, 7/16 DIN, connectors will allow higher current running.

The knowledge gained of the system components this run will allow faster and better setup of the TFB with fewer problems.

More diagnostics are being looked at for the future to allow a better understanding of how the system is operating and to what levels the beam can be stabilized.