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The proposed Next Linear Collider (NLC) will require over 1400 adjustable quadrupoles between the main linacs' accelerator structures. These 12.7 mm bore quadrupoles will have a range of integrated strength from 0.6 to 138 Tesla, with a maximum gradient of 141 Tesla per meter, an adjustment range of +0 to -20% and effective lengths from 324 mm to 972 mm. The magnetic center must remain stable to within 1 micron during the 20% adjustment. In an effort to reduce costs and increase reliability, several designs using hybrid permanent magnets have been developed. Four different prototypes have been built. All magnets have iron poles and use Samarium Cobalt to provide the magnetic fields. Two use rotating permanent magnetic material to vary the gradient, one uses a sliding shunt to vary the gradient and the fourth uses counter rotating magnets. Preliminary data on gradient strength, temperature stability, and magnetic center position stability are presented. These data are compared to an equivalent electromagnetic prototype. NLC DESIGNThe Next Linear Collider 1 (NLC) is future electron/positron collider that is based on copper accelerator structures powered with 11.4GHz X-band RF. It is designed to begin operations with a center-of-mass energy of 500GeV or less, depending on the physics interest, and to be adiabatically upgraded to 1 TeV cms with a luminosity of 2~3 x 10 34 cm -2 s -1 . The facility is roughly 30 km in length and supports two independent interaction regions. For the main linac there will be over 1400 quadrupoles between the accelerator structures. To reduce costs and increase reliability adjustable permanent magnets are considered for these structures. Based on Fermilab's experience with permanent magnets used in their Recycler, a collaboration between SLAC and Fermilab is exploring designs and prototypes. . To achieve the required pole tip field rare earth permanent magnets are required. Samarium Cobalt (Sm 2 Co 17 ) was chosen for its high residual B field (Br) and small temperature variation of the field. The center stability requirement of ±0.001 mm is driven by the Beam Based Alignment (BBA) process for these quads. When a beam position monitor detects movement of the beam the position of the related quadrupole will be adjusted to bring the beam back on the correct trajectory. The BPM to quadrupole center calibration process requires that the quad strength be lowered by 20% over several seconds during which change the magnetic center must not shift by more than 1 micron. This calibration will be done monthly. MAGNET REQUIREMENTSFour different styles of quadrupole were designed and built. These are called the corner tuner, wedge tuner, sliding shunt, and the rotating quad. This paper briefly describes each style and the results of testing the magnetic center stability of each one's prototype using a stretched wire measurement system. The magnets were modeled using PANDIRA and TOSCA.

New low-impedance vacuum chambers were installed in the SLC damping rings for the 1994 run after finding a single bunch instability with the old chamber. Although the threshold is lower with the new vacuum chamber, the instability is less severe, and we are now routinely operating at intensities of 4.5× 10 10 particles per bunch (ppb) compared to 3× 10 10 ppb in 1993. The vacuum chamber upgrade is described, and measurements of the bunch length, energy spread, and frequency and time domain signatures of the instability are presented.