Tevatron Sextupole Circuit Modification

Final load drawing for sextupoles in new configuration.  PDF

Load drawing by sector (C-sector initially installed with chromaticity polarity not shown here).  PDF

Final installation steps. Word Doc

Overview

In the Low Beta optics, the Tevatron has a large second order chromaticity.  This is easily seen by looking at the chromaticity measurement made on July 19, 2005 (shown below).  The chromaticity at one end of the bunch can be drastically different than the chromaticity at the other end of the bunch.  This put limitations on the chromaticity settings where the Tevatron can run stably.   

In order to linearize the tune vs momentum curves in the chromaticity diagram, the Tevatron Sextupoles circuits will be modified.  In the final version of the modification, 44 sextupoles will be removed from the SF and SD loops and put on smaller circuits.  To power these new elements, new power supplies will be installed in service buildings A2, C2, and E2.  These will be Main Injector style supplies.  The Bulk Power supplies will be named T:A2SEX, T:C2SEX, and T:E2SEX.  The regulator names will be of the form T:SFHHU where the SF indicates the circuit powers sextupoles at focusing locations (SD is the other option for these fields), HH indicates the service building that the power supply is in, and U indicates that the sextupoles are upstream of the power supply (D is the other option for this field).

The modifications of these circuits will take place in two steps.

Step I.

Only the C-sector sextupoles will be used.  They will be connected in the positive polarity and run at the same currents as SF and SD.  The only difference in current that these sextupoles should experience is that they will not be part of the B2 drift compensation and the snapback.  The purpose of this step is to commission the power supplies with as little difference to operation as possible.  This allows us to separate hardware problems from beam physics issues.

Step II.

All of the new power supplies (3 bulks powering 4 regulators each) will be commissioned.  In this configuration, there will be an equal number of the re-wired sextupoles running in the negative polarity as in the positive polarity.  The new circuits will therefore not effect the chromaticity.  The remaining elements on SF and SD will need to run harder to leave the chromaticity unchanged.   This is a much more substantial change to the way the Tevatron operates.

Hardware:

In each of the service buildings there is a complete rack devoted to these circuits.  The reference comes from a 465 in a nearby crate, and these cards also provide status and control for the regulators.  The bulk supply is controlled by a 218 card.  Below are photos of the regulators, QPMs, and Control power chassis.  The bulk supply is in the bottom of the rack, but not shown here.

REGULATORS

QPMs

CONTROL POWER CHASSIS

Spares are similar but not interchangeable with MI parts.  The slew rate is much slower for the Tevatron regulators.  I am still trying to find out where the spares are stored, what is the protocol for changing components, etc.

There are still some issues we are solving concerning the on/off and reset of the individual regulators.  One problem with the present hardware is that it is difficult to have a Tevatron Quench turn the regulators off.

The new circuits will be loaded by page C49, and will be part of the chromaticity group.  The new power supplies should appear on the lockout list as they are placed into service.  The new supplies will initially be placed in the Tevatron abort loop.  We may determine at a later date that this is not desired, but they will be part of the abort initially.